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Biomolecules

(5) Water : Liquid of life, major constituent of cell (about 60-90%) and exists in intracellular, intercellular and
in vacuoles. In cells it occurs in free state or bound state (KOH, CaOH etc.).

(i) Properties of water : It is colourless, transparent, tastless and odourless, neutral (pH-7) liquid. It is
universal solvent, as it can dissolve both polar and non-polar solutes. High boiling point due to hydrogen bonding.
Shows high degree of cohesion and adhesion. It can undergo three states of matter i.e. solid liquid gas. It is
dense and heaviest at 4C and solid below it.

(6) Carbohydrates : e.g. sugars, glycogen (animal starch), plant starch and cellulose.

(i) Source of carbohydrate : Mainly photosynthesis. It exists only in 1% but constitutes 80% of the dry
weight of plants.

(ii) Composition : It consists of carbon, hydrogen and oxygen in the ratio Cn H 2nOn . It is also called
saccharide and sugars are their basic components. Classification of carbohydrates can be summarised as :–

Carbohydrates

Monosaccharides and Oligosaccharides (number of Polysaccharides (number of
their derivatives monosaccharides from 2 to 10, di, monosaccharides over 10)
tri, tetrasaccharides etc.)

Monosaccharides e.g. Derivatives of Homopolysaccharides Heteropolysaccharides
Triose - 3C, Tetrose - 4C monosaccharides (starch, amylopectin, (glycoproteins, starch,
Pentose - 5C, Hexose - 6C glycogen, cellulose etc.) proteins)
Heptose - 7C, Octoses - 8C

Nanoses-9C, Decoses - 10C

Uric acid e.g. Aroic acids e.g. Aminosaccharides e.g. Phosphosaccharides e.g. Glycosides e.g.
glycouronic acid, glucaroic acid, glucosamine, glucose-6- phosphate, nucleotides, nucleosides,
galactouronic acid galactaroic acid galactosamine fructose 1,6 biphosphate etc. Coenzymes etc.

Monosaccharides : These are single sugar units which can not be hydrolysed furthur into smaller
carbohydrates. General formula is Cn H 2nOn , e.g. Triose-3C, glyceraldehyde, dihydroxyacetone, etc., tetrose,
pentose, hexose, etc. About 70 monosaccharides are known, out of which only 20 are present in plants and
animals.

(i) Important Hexoses

(a) Glucose : C6 H12O6 . Grape sugar is dextrose. Grape is sour due to presence of tartaric acid. Fructose is
called fruit sugar (sweetest among natural sugars) and glucose is called " sugar of body". Normal level of blood
glucose is 80-120mg/100ml. If it exceeds then condition is called "glucosuria".

(b) Fructose : Occurs naturally in fruit juices and honey. Hydrolysis of cane sugar in body also yields
fructose.

(c) Galactose : It is called as brain sugar. It's an important constituent of glycolipids and glycoproteins.

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(d) Mannose : It is obtained on hydrolysis of plant mannans and gums. It is constituent of albumins, globulins
and mucoproteins.

(ii) Structure of monosaccharides

(iii) Properties of monosaccharide HO H
|
(a) Monosaccharides are colourless, sweet C H–C–H
tasting, solids. 1| 1|
H – C – OH H – C = OH
(b) Due to asymmetric carbon, they exist in | |
different isomeric forms. They can rotate HO – C – H
polarized light hence they are dextrorotatory and | HO – C – H
leavorotatory. H – C – OH |

(c) D-glucose after reduction gives rise to a | H – C – OH
mixture of polyhydroxy alcohol, sorbitol or H – C – OH |
mannitol.
| H – C – OH
(d) The sugars with a free aldehyde or H – C – OH |
ketone group reduce Cu++ to Cu+ (cupric to
cuprous) 6| H – C – OH
H
(e) Sugars show oxidation, esterification and 6|
fermentation. H

(f) The aldehyde or ketone group of a 6 CH 2OH
simple sugar can join an alcoholic group of
another organic compound bond C-O-C the | O
process involves loss of water and is called
condensation (H-O-H) or H+OH → H2O . H C H 6 CH2OH O
|5
| H ||

C 4 C1 C5 H
| | | |
HO OH C1
H HO HO OH H |
|4
| 3 2 | C 3| CH 2OH
C C |
H C
|| | 2
H OH
OH
Glucose
(Pyranose Form) Fructose
(Pyranose Form)

Fig : Open chain and ring forms of three hexoses

(iv) Functions of monosaccharides

(a) Glucose is the ultimate source of ATP in the cell respiration.

(b) It is used in formation of vitamin C.

(c) The intermediate compounds for the formation of glucose in photosynthesis are triose, tetrose, pentose and
heptose, etc.

(d) Galactose is a constituent of agar-agar.

(e) Glucose is a blood sugar and xylose is a non nutritive sweetner.

(f) Polymerisation of these molecules forms macromolecules.

(g) Ribose and deoxyribose are constituent of nucleic acids and nucleotides

(h) Glyceraldehyde and dihydroxyacetone are trioses.

(i) Sugars have free aldehyde or ketone group which can reduce Cu++ to Cu+ and are called reducing sugars.
Benedicts or fehling's test are used to confirm the presence of reducing sugars.

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Oligosaccharides : Formed due to condensation of 2-10 monosaccharide units, the Oxygen bridge is
known as "glycoside linkage" and water molecule is eliminated. The bond may be α and β.

CO C CH HC

HC CH HC CH

CH HC CO C

OH OH OH OH

α-glycosidic linkage β-glycosidic linkage

(i) Disaccharides : Composed of two molecules of same or different monosaccharide units. Also called
"double sugars". Molecular formula is C12 H 22O11 .

(a) Maltose : Also called "malt sugar" stored in germinating seeds of barley, oat, etc. It is formed by enzymatic
(enzyme amylase) action on starch. It is a reducing sugar.

(b) Sucrose : "Cane sugar" or " table-sugar". Obtained from sugarcane and beet root and on hydrolysis splits
into glucose and fructose.

(c) Lactose : Milk sugar or 5% in mammalian milk. On hydrolysis yields glucose and galactose. Streptococus
lacti converts lactose in to lactic acid and causes souring of milk.

(ii) Trisaccharides : Composed of three molecules of sugars. Molecular formula is C18 H32O16 .

(a) Raffinose : Found in sugar beet, cotton and in some fungi. It is made up of glucose, fructose and
galactose.

(b) Gentianose : Found in rhizomes of gentian species, made up of glucose and fructose.

(iii) Tetrasaccharides : Composed of four molecules of same or different sugars. Stachyose is found in
Stachys tubefera. It is made up of two unit of galactose, one unit of glucose and one unit of fructose.

(iv) Polysaccharides : General formula is (C6 H10O5 )n formed by condensation of several molecules (300-
1000) of monosaccharides, (Described under " Macromolecules").

(v) Reducing and Non-reducing carbohydrates : Those which reduce Tollen's reagent or fehling solution
are called reducing sugars and those do not reduce are called non-reducing sugars. All monosaccharides and
disaccharides except sucrose are reducing. While all polysaccharides are non-reducing sugars.

(7) Lipids : Term lipid was coined by Bloor. These are esters of fatty acids and alcohol. They are
hydrophobic insoluble in water but soluble in benzene, ether and chloroform. Lipids are classified into three
groups:–

(i) Simple lipids : These are the esters of fatty acids and glycerol. Again they are typed as :–

(a) Fats and Oils : (Natural lipids or true fats). These triglycerides of fatty acid and glycerol. Fats which are
liquid at room temperature are called oils. Oils with polyunsaturated fatty acids are called polyunsaturated e.g.
sunflower oil, lower blood cholesterol.

(b) Fatty acids : Obtained by hydrolysis of fats. Formic acid is simplest fatty acid (HCOOH). These are of 2
types :–

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Saturated fatty acids : The fatty acids which do not have double bond in between carbon atoms.e.g.
butyric acid, palmitic acid,hexanoic acid, etc. They have high melting points, solid at room temperature and
increase blood cholesterol.

Unsaturated fatty acids : The fatty acids which have double bonds in carbon atoms. e.g. 8 hexadecanoic
acid, 9 octadecanoic acid etc. They have lower melting points mostly found in plant fats, liquid at room temperature
and lower the blood cholesterol.

(c) Waxes : These are simple lipids composed of one molecule of long chain fatty acid and long chain
monohydric alcohol. Waxes have high melting point, insoluble in water, resistant to atmospheric oxidation,
chemically inert and not digested by enzymes. They reduce rate of transpiration by making plant tissue water proof
and work as excellent lubricant.

Types of waxes

 Plant wax : Forms coating.

 Bee's wax : It is secretion of abdominal glands of worker honeybee. It consist of palmitic acid and myricyl
alcohol.

 Lanolin or Wool fat : It is secreted by cutaneous glands, also obtained from wool of sheeps. It consists
of palmitic acid, oleic or stearic acid and cholesterol.

 Sebum : It is secretion of sebaceous gland of skin.

 Paraffin wax : Obtained from petrolium.

(ii) Compound lipids : They contain some additional or element. Group with fatty acid and alcohol on the
basis of group they may be of following types:

(a) Phospholipids : These contain phosphoric acid. It helps in transport, metabolism, blood clotting and
permeability of cell membrane. It is a bipolar molecule i.e. phosphate containing end is hydrophilic whereas fatty
acid molecules represent hydrophobic (non-polar tail). Phospholipids again comprises.

Lecithin : These are yellowish grey solids, soluble in ether and alcohol but insoluble in acetone. On
hydrolysis they yield glycerol, fatty acid, phosphoric acid and choline. Lecithins are broken down by enzyme
lecithinase to lysolecithin. The enzyme is found in venom of bee and cobra.

Cephalins : Found in animal tissue and soyabean oil. Cephalin contains choline or serine sometimes and
stearic acid, oleic acid, linoelic and arachidonic acid.

(b) Glycolipids : These contain nitrogen and carbohydrate beside fatty acids. Generally found in white
matter of nervous system. e.g. sesocine frenocin.

(c) Chromolipids : It includes pigmented lipids e.g. carotene.

(d) Aminolipids : Also known as sulpholipids. It contains sulphur and amino acids with fatty acid and
glycerol. Cutin and suberin are also compound lipids resistant to water and also provide mechanical support in
plants.

(iii) Derived lipids : These are obtained by hydrolysis of simple and compound lipids. Derived lipids include
following components :–

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(a) Sterols : Lipids without straight chains are called sterols. They are composed of fused hydrocarbon rings
and a long hydrocarbon side chain. Best known sterol is cholesterol, present in high concentration in nervous tissue
and in bile. Cholesterol is also the precursor of hormones like progesterone, testosterone, estradiol and cortisol and
vitamin D. Diosgenin is obtained from yam plant (Dioscorea) used in making anti- infertility pills.

(b) Digitalin : It is prepared from leaves of Foxglove (Digitalis lantana) is a heart stimulant.

(c) Ergosterol : Present in food, found in ergot and yeast. It is precursor of another form of vitamin D,
ergocalciferol ( D2 ).

(d) Coprosterol : It is found in faeces. It is formed as a result of the reduction by bacteria in intestine from
the double bond of cholesterol between C5 and C6.

(e) Tarpens : It is essential oil and present mostly in oils of camphor, eucalyptus, lemon and mint. Phytol is a
terpenoid alcohol present in Vitamin A, K, E and in pigments like chlorophyll carotenoid. Other forms are licopene,
gibberellins and natural rubber.

(f) Prostaglandin : It is hormone like compound derived from arachidonic acid. Mostly present in secretion
of seminal vesicles in males and menstrual cycle fluid in females.

(g) Blubber : A very thick layer of subcutaneous fat in whale.

(iv) Functions of lipids

(a) Oxidation of lipids yields comparatively more energy in the cell than protein and carbohydrates. 1gm of
lipids account for 39.1 KJ.

(b) The oil seeds such as groundnut, mustard, coconut store fats to provide nourishment to embryo during
germination.

(c) They function as structural constituent i.e. all the membrane system of the cell are made up of lipoproteins.

(d) Amphipathic lipids are emulsifier.

(e) It works as heat insulator.

(f) Used in synthesis of hormones.

(g) Fats provide solubility to vitamins A, D, E, and K.

(8) Amino acids : Amino acids are normal components of cell proteins (called amino acid). They are 20 in
number specified in genetic code and universal in viruses, prokaryotes and eukaryotes. Otherwise amino acids may
be termed rare amino acids, which take part in protein synthesis e.g. hydroxyproline and non- protein amino acids
do not take part in protein synthesis e.g. Ornithin, citrullin, gama-aminobutyric acid (GABA) a neurotransmitter, etc.

(i) Structure and Composition : Amino acids are basic units of protein and made up of C, H, O, N and

sometimes S. Amino acids are organic acids with a carboxyl group (–COOH) and one H
amino group (−NH 2 ) on the α -carbon atom. Carboxyl group attributes acidic |
properties and amino group gives basic ones. In solution, they serve as buffers and help NH 2 C− COOH
to maintain pH. General formula is R − CHNH 2 .COOH . − |

R

Amino acids are amphoteric or bipolar ions or Zueitter ions. Amino acids link with each other by peptide bond
and long chains are called polypeptide chains.

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Biomolecules

(ii) Classification

Based on R-group of amino acids.

(a) Simple amino acids : These have no functional group in the side chain. e.g. glycine, alanine , leucine,
valine etc.

(b) Hydroxy amino acids : They have alcohol group in side chain. e.g. threonine, serine, etc.

(c) Sulphur containing amino acids : They have sulphur atom in side chain. e.g. methionine, cystenine.

(d) Basic amino acids : They have basic group (−NH 2 ) in side chain. e.g. lysine, arginine.

(e) Acidic amino acids : They have carboxyl group in side chain. e.g. aspartic acid, glutamic acid.

(f) Acid amide amino acids : These are the derivatives of acidic amino acids. In this group, one of the
carboxyl group has been converted to amide (−CO.NH 2 ) . e.g. asparagine, glutamine.

(g) Heterocyclic amino acids : These are the amino acids in which the side chain includes a ring involving
at least one atom other than carbon. e.g. tryptophan, histidine.

(h) Aromatic amino acids : They have aromatic group (benzene ring) in the side chain. e.g. phenylalanine,
tyrosine, etc.

On the basis of requirements : On the basis of the synthesis amino acids in body and their requirement,
they are categorized as :–

(a) Essential amino acids : These are not synthesized in body hence to be provided in diet e.g. valine,
leucine, isoleucine, theronine ,lysine, etc.

(b) Semi-essential amino acids : Synthesized partially in the body but not at the rate to meet the
requirement of individual. e.g., arginine and histidine.

(c) Non-essential amino acids : These amino acids are derived from carbon skeleton of lipids and
carbohydrate metabolism. In humans there are 12 non- essential amino acids e.g. alanine, aspartic acid, cysteine,
glutamic acid etc. Proline and hydroxyproline have, NH (imino group) instead of NH 2 hence are called imino
acids. Tyrosine can be converted into hormone thyroxine and adrenaline and skin pigment melanin. Glycine is
necessory for production of heme. Tryptophan is the precursor of vitamin nicotinamide and auxins. If amino group
is removed from amino acid it can form glucose and if COOH group is removed, it forms amines e.g. histamine.

(iii) Functions of amino acids

(a) Amino acids are building blocks of proteins and enzymes.

(b) By glycogenolysis, they form glucose.

(c) Hormones like adrenaline and thyroxine are formed with the help of tyrosine.

(d) Antibiotics often contain non-protein amino acids.

(e) They are precursour of many substances.

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(9) Nucleotides : Structurally a nucleotide can be regarded as a phosphoester of a nucleoside. A
combination of nitrogens base and a sugar is called nucleoside and combination of a base, a sugar and phosphate
group is known as nucleotide.

Types of nitrogen base Nucleoside Nucleotide
Adenine Adenosine Adenylic acid
Guanine Guanosine Guanylic acid
Cytosine Cytidine Cytidilic acid
Thymine Thymidine Thymidylic acid
Uracil Uridine Uridylic acid

There are two types of pentose sugars, ribose found in RNA and deoxyribose found in DNA. Nucleotides form
2% of the cell component.

N2 base + Pentose sugar → ‘Nucleoside’
Nucleoside + Phosphoric acid → ‘Nucleotide’ + H 2O .

There are two types of bases which occur in the nucleic acids.

(i) Purines : Purines are 9 membered double ringed nitrogenous bases which possess nitrogen at 1' ,3' ,7' and
9' positions. They are adenine (A) and guanine (G).

(ii) Pyrimidines : They are smaller molecule than purines. These are 6 membered single ringed nitrogenous
bases that contain nitrogen at 1' and 3' positions like cytosine (C), thymine (T) and uracil (U). In DNA adenine pairs
with thymine by two H 2 bond and cytosine pairs with guanine by three H 2 bond.

A nucleotide may have one, two or three phosphates, as one in AMP (adenosine monophosphate), two in
ADP (adenosine diphosphate). The phosphate bond is called high energy bond and it release about 8 K cal. ATP
was discovered by Karl Lohmann (1929). Formation of ATP is endergonic reaciton.

(iii) Functions of nucleotides : Following are the major functions of nucleotides.

(a) Formation of nucleic acids : Different nucleotides Adenine Ribose P PP
polymerize together to form DNA and RNA.
A. A (TriphTosPphate)
(b) Formation of energy carrier : They help in formation (Adenosine) NCC N
of ATP,AMP, ADP, GDP, GTP, TDP,TTP, UDP, etc. which on
breaking release energy. Adenine C–H

(c) Formation of Coenzymes : Coenzymes like NAD, O O OH CC N
NADP, FMN, FAD, CoA, etc are formed. Coenzymes are non-
proteinaceous substance necessory for the activity of the || || || N
enzymes.
B. HPOh–oOPs|Hp~hOat~eOP|rHa~dPiOcua~rOlis|nPHe–O–OCC||HH2OHC||H O H C Ribose
| |
C H
|
OH

(iv) Some important Coenzymes Fig : Structure of ATP molecule
(a) NAD+ (Nicotinamide adenine dinucleotide) or Code A-Diagrammatic, B-Molecular

hydrogenase-I is involved in many hydrogen transferring reaction. It is Coenzyme I (Vit B5).

Chapter 5 62

Biomolecules

(b) Coenzyme II or Code hydrogenase II or NADP+ ; TPN (triphopyridine) etc. it is similar in functioning to
Coenzyme-I.

(c) Coenzyme A : It is a complex thiol derivative unlike Co-I and Co-II, Co-A is not a oxidising- reducing
Coenzyme but is acylating i.e. Co-A accepts acetyl groups from one metabolite and denotes them to another in the
presence of specific enzymes. Most important Co-A compound is acetyl Co-A (activated acetate). Beside acylation
Coenzyme-A can also undergo phosphorylation.

(d) Flavonucleotides : FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide) take part in
oxidation reaction and also function as dehydrogenase. FMN is vitamin B2 or riboflavin.

(v) Important points

(a) On the basis of presence of aldehyde or ketone groups glyceraldehyde may be termed as an aldotriose and
dihydroxyacetone is then called ketotriose.

(b) General formula of oligosaccharide is Cn (H 2O)n−1 .

(c) Isomaltose has α-1-6 linkage.
(d) Musein is a polysaccharide.

(e) Cobalt is constituent of vit.B12 and required for synthesis of phytochromes and auxins.
(f) Copper is a constituent of plastocyanine and co-factor of respiratory enzymes.

(g) Boron is necessory for plants in sugar translocation.

(h) Galactose is a constituent of 'gum arabic'.
(i) Sweetest protein is monellin.

(j) Lipidosis in born or acquired characteristic syndrome due to lipid metabolism.

(k) Cellulose nitrite is used in propellant explosis.

(l) Nickle is required for activity of urease.
Macromolecules .

Macromolecules are polymerisation product of micromolecuels, have high molecular weight and low solubility.
They include mainly polysaccharide, protein and nucleic acids.

Polysaccharide : They are branched or unbranched polymers of monosaccharides jointed by glycosidic
bond. Their general formula is (C6 H10O5 )n. They are also called glycans polysaccharides are amorphous, tasteless
and insoluble or only slightly soluble in water and can be easily hydrolysed to monosaccharide units.

(1) Types of polysaccharides

On the basis of structure

(i) Homopolysaccharides : These are made by polymerisation of single kind of monosaccharides. e.g.
starch, cellulose, glycogen, etc.

(ii) Heteropolysaccharide : These are made by condensation of two or more kinds of monosaccharides.
e.g. chitin, pectin, etc.

On the basis of functions

(i) Food storage polysaccharides : They serve as reserve food. e.g. starch and glycogen.

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Biomolecules

(ii) Structural polysaccharides : These take part in structural framework of cell wall e.g. chitin and
cellulose.

(2) Description of some polysaccharides

(i) Glycogen : It is a branched polymer of glucose and contain 30,000 glucose units. It is also called animal

starch. Their general formula is (C6 H10O5 )n . It is also found as storage product in blue green algae, slime moulds,

fungi and bacteria. It is a non-reducing sugar and gives red colour with iodine. In glycogen, glucose molecule are

linked by 1 – 4 glycosidic linkage in straight part and 1 – 6 linkage in the branching part glycogen has branch points

about every 8-10 glucose units.

CH 2OH CH 2OH CH 2OH CH 2OH CH 2OH

OO O O
α − 1 − 4 linkage

(ii) Starch : Starch is formed in photosynthesis and function as energy storing substance. Generally found in
the form of grains, which contain 20% water. It is found abundantly in rice, wheat, legumes, potato (oval and
ecentric shaped), banana, etc. Starch is of two types. Straight chain polysaccharides known as amylose and
branched chain as amylopectin. Both composed of D – glucose units jointed by α − 1 − 4 linkage and α − 1 − 6
linkage. It is insoluble in water and gives blue colour when treated with iodine. Amylose consists of 200 – 500
glucose units. It is stored inside chloroplast or spherical leucoplast and known as amyloplasts.

(iii) Inulin : Also called “dahlia starch”(found in roots). It has unbranched chain of 30 – 35 fructose units
linked by β − 2 – 1 glycosidic linkage between 1 and 2 of carbon atom of D – fructose unit.

(iv) Cellulose : An important constituent of cell wall (20 – 40%), made up of unbranched chain of 6000 β–D
glucose units linked by 1 – 4 glycosidic linkage. It is fibrous, rigid and insoluble in water. Wood (20 – 50%) and
cotton (90%) contain large amount of it. Rayon (artificial fibre) cellulose, nitrate (used as explosive) and carboxyl
methyl cellulose (used as cosmetics and ice cream) are obtained by activity of “cellulase” enzyme. It doesn’t give
any colour when treated with iodine.

(v) Chitin : It is a polyglycol consisting of N-acetyl–D–glucosamine units connected with β − 1, 4 glycosidic
linkage. Mostly it is found in hard exoskeleton of insects and crustaceans and some times in fungal cell wall. Second
most abundant carbohydrate.

(vi) Agar-Agar : It is a galactan, consisting of both D and L galactose and it is used to prepare bacterial
cultures. It is also used as luxative and obtained from cell wall of red algae e.g. Gracilaria, Gelidium, etc.

(vii) Pectin : It is a cell wall material in collenchyma tissue may also be found in fruit pulps, rind of citrus fruits
etc. It is water soluble and can undergo sol gel transformation. It contain arabinose, galactose and galacturonic
acid.

(viii) Neutral sugars : It is found associated with cellulose in cell wall. The common sugars in hemicellulose
are D-xylose, L–arabinose, D-galactose, D-mannose and D-glucusonic acid. e.g. hemicellulose.

(ix) Gum : It secreted by higher plants after injury or pathogenic attacks. It is viscous and seals the wound. It
involves sugars like L-arabinose, D-galactose, D-glucusonic acid. e.g. gum arabic.

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Biomolecules

(x) Mucopolysaccharides : These are gelatinous substance, containing amino sugars, uronic acid, etc. All
slimy substances of plant are mucopolysaccharide. e.g. hyaluronic acid, vitreous humour, chondridine sulphate,
heparin, husk of isabgul and mucilage of also.

(xi) Glycoproteins : They include some plasmaprotein and blood group substances. They doesn’t contain
uronic acid.

(xii) Murein : It is a peptidoglycan, linked to short chains of peptides. It is constituent of cell wall of bacteria
and blue green algae.

(3) Properties of polysaccharides

(i) They are tasteless and colourless solids.

(ii) Insoluble in water, soluble in alcohol and more soluble in ether.

(iii) Can be easily hydrolyzed into their monosaccharide.

(iv) Their molecular weight is high.

(v) They do not diffuse through plasma membrane.

(4) Functions

(i) Cellulose pectin and chitin are constituents in cell wall of higher plants but peptidoglycan in the cell wall of
prokaryotes.

(ii) They are reserve food material.

(iii) They form protective covering.

(iv) They can be used as culture medium.

(v) Being insoluble they do no exert osmotic or chemical influence in the cell.

(vi) Fibres are obtained used in making cloth and rope.

(vii) Nitrocellulose and trinitrate cellulose (gun-cotton) used as explosive.

Protein : The word protein was coined by Berzelius in 1838 and was used by G. J. O
Mulder first time 1840. 15% of protoplasm is made up of protein. Average proteins contain
16% nitrogen, 50–55% carbon, oxygen 20–24%, hydrogen 7% and sulphur 0.3 – 0.5%. Iron, ||
phosphorous, copper, calcium, and iodine are also present in small quantity.
− NH − C−
Peptide linkage.

(1) Structure of proteins : It is due to different rearrangement of amino acids. When carboxyl group
(−COOH) of one amino acid binded with amino group (– NH2) of another amino acid the bond is called peptide
bond. A peptide may be dipeptide, tripeptide and polypeptide. The simplest protein is Insulin. According to Sanger
(1953) insulin consists 51 amino acids. A protein can have up to four level of conformation.

(i) Primary structure : The primary structure is the covalent connections of a protein. It refers to linear
sequence, number and nature of amino acids bonded together with peptide bonds only. e.g. ribonuclease, insulin,
haemoglobin, etc.

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Biomolecules

(ii) Secondary structure : The folding of a linear polypeptide chain into specific coiled structure (α − helix) is
called secondary structure and if it is with intermolecular hydrogen bonds the structure is known as β − pleated
sheet. α − helical structure is found in protein of fur, keratin of hair claws, and feathers. β − pleated structure is
found in silk fibres.

(iii) Tertiary structure : The arrangement and interconnection of proteins into specific loops and bends is
called tertiary structure of proteins. It is stabilized by hydrogen bond, ionic bond, hydrophobic bond and disulphide
bonds. It is found in myoglobin (globular proteins).

(iv) Quaternary structure : It is shown by protein containing more than one peptide chain. The protein
consists of identical units. It is known as homologous quaternary structure e.g. lactic dehydrogenase. If the units are
dissimilar, it is called as heterogeneous quaternary structure e.g. hemoglobin which consists of two α − chains and
two β − chains.

(2) Classification of proteins : Proteins are classified on the basis of their shape, constitution and function.

On the basis of shape

(i) Fibrous protein/Scleroprotein : Insoluble in water. Animal protein resistant to proteolytic enzyme is
spirally coiled thread like structure form fibres. e.g. collagen (in connective tissue), actin and myosin, keratin in hairs,
claws, feathers, etc.

(ii) Globular proteins : Soluble in water. Polypeptides coiled about themselves to form oval or spherical
molecules e.g. albumin insulin hormones like ACTH, oxytosin, etc.

On the basis of constituents

(i) Simple proteins : The proteins which are made up of amino acids only. e.g. albumins, globulins,
prolamins, glutelins, histones, etc.

(ii) Conjugated proteins : These are complex proteins combined with characterstic non–amino acid
substance called as prosthetic group. These are of following types :–

(a) Nucleoproteins : Combination of protein and nucleic acids, found in chromosomes and ribosomes. e.g.
deoxyribonucleoproteins, ribonucleoproteins, etc.

(b) Mucoproteins : These are combined with large amount (more than 4%) of carbohydrates e.g. mucin.

(c) Glycoproteins : In this, carbohydrate content is less (about 2 – 3%) e.g. immunoglobulins or antibiotics.

(d) Chromoproteins : These are compounds of protein and coloured pigments. e.g. haemoglobin,
cytochrome, etc.

(e) Lipoproteins : These are water soluble proteins and contain lipids. e.g. cholesterol and serum
lipoproteins.

(f) Metalloprotein : These are metal binding proteins, AB1–globin known as transferring is capable of
combining with iron, zinc and copper e.g. chlorophyll.

(g) Phosphoprotein : They composed of protein and phosphate e.g. casein (milk) and vitellin (egg).

(iii) Derived proteins : When proteins are hydrolysed by acids, alkalies or enzymes, the degredation
products obtained from them are called derived proteins. On the basis of progressive cleavage, derived proteins are
classified as primary proteoses, secondary proteoses, peptones, polypeptides, amino acids, etc.

Chapter 5 66

Biomolecules

On the basis of nature of molecules
(i) Acidic proteins : They exist as anion and include acidic amino acids. e.g. blood groups.
(ii) Basic proteins : They exist as cations and rich in basic amino acids e.g. lysine, arginine etc.
(3) Function of Proteins
(i) Proteins occur as food reserves as glutelin, globulin casein in milk.
(ii) Proteins are coagulated in solutions, alkaline to the isoelectric pH by positive ions such as
Zn2+ , Cd 2+ , Hg 2+ etc. Casein – pH 4.6, cyt. C – 9.8, resum globulin 5.4, pepsin 2.7, lysozyme 11.0 etc.

(iii) Proteins are the most diverse molecule on the earth.
(iv) Proteins work as hormone as insulin and glucagon.
(v) Antibiotics as gramicidin, tyrocidin and penicillin are peptides.
(vi) They are structural component of cell.
(vii) They are biological buffers.
(viii) Monellin is the sweetest substance obtained from African berry (2000 time sweeter than sucrose).
(ix) Proteins helps in defence, movement activity of muscles, visual pigments receptor molecules, etc.
(x) Natural silk is a polyamide and artificial silk is a polysaccharide. Nitrogen is the basic constituent.

Nucleic acid .

(1) Definition : Nucleic acids are the polymers of nucleotide made up of carbon, hydrogen, oxygen, nitrogen
and phosphorus and which controls the basic functions of the cell. These were first reported by Friedrich Miescher
(1871) from the nucleus of pus cell. Altmann called it first time as nucleic acid. They are found in nucleus. They
help in transfer of genetic information.

(2) Types of nucleic acids : On the basis of nucleotides i.e. sugars, phosphates and nitrogenous bases,
nucleic acids are of two types which are further subdivided. These are DNA (Deoxyribonucleic acid) and RNA
(Ribonucleic acid).

DNA (Deoxyribonucleic acids)
(i) Types of DNA : It may be linear or circular in eukaryotes and prokaryotes respectively.
(a) Palindromic DNA : The DNA helical bears nucleotide in a serial arrangement but opposite in two strands.

− T − T − A − A − C − G − T − T − A − A.......
− A − A − T − T − G − C − A − A − T − T......
(b) Repetitive DNA : This type of arrangement is found near centromere of chromosome and is inert in RNA
synthesis. The sequence of nitrogenous bases is repeated several times.
(c) Satellite DNA : It may have base pairs up to 11 – 60bp and are repetitive in nature. They are used in
DNA matching or finger printing (Jefferey). In eukaryotes, DNA is deutrorotatory and sugars have pyranose
configuration.
(ii) Chargaff’s rule : Quantitatively the ratio of adenine (A) to thymine (T) and guanine (G) to cytosine (C) is
equal. i.e. “Purines are always equal to pyrimidine”.

Chapter 5 67

Biomolecules

(iii) C value : It is the total amount of DNA in a genome or haploid set of chromosomes.

(iv) Sense and Antisense strand : Out of two DNA strand one which carries genetic information in its
cistrons is called sense strand while the other strand does not carry genetic information, therefore, doesn’t produce
mRNA. The non-functional DNA strand is called antisense strand.

(v) Heteroduplex DNA : Hybrid DNA formed as a result of recombination is called heteroduplex DNA. It
contains mismatched base pair of heterologous base sequence.

(a) X-Ray crystallography study of DNA : It was done by Wilkins. It shows that the two polynucleotide
chains of DNA show helical configuration.

(b) Single stranded DNA (ssDNA) : It is single helixed circular. And isolated from bacteriophage φ × 174
by Sinsheimer (1959). It does not follow chargaff’s rule. The replicative form (RF) has plus – minus DNA helix. e.g.
parvovirus.

(c) Double helical model of DNA : It is also known as Watson and Crick model.

RNA or Ribonucleic acid : RNA is second type of nucleic acid which is found in nucleus as well as in
cytoplasm i.e. mitochondria, plastids, ribosomes etc. They carry the genetic information in some viruses. They are
widely distributed in the cell.
Important Tips

• ds DNA : All eukaryotes, bacteria, polyoma virus and small pox virus.

• ss DNA : Bacteriophage φ ×174 and parvovirus.

• ds RNA : Reogroup of viruses, wound tumour virus.
• ss RNA : TMV, TNV Poliomyelitis.
• Single genome : virus, bacteria, F2 and R17.
• Segmented genome : Orthomyxovirus (influenza virus).
• Natural silk is a polyamide and have nitrogen in high amount.
• Cairns noticed process of replication of DNA in bacteria and said to be “theta mode”.
• S. Ochoa (1967) synthesized RNA in vitro.
• Actinomycin D prevents transcription.
• Genomic RNA was discovered by Franklin and Conrat (1957).
• DNA end with no unpaired base is called blunt end.
• Portion of DNA that codes for the final mRNA is exon.
• Pribnow box : The sequence of boxes that orient RNA polymerase so that synthesis proceeds left to right.
• Hogness box : (TATA box). The hypothesized eukaryotic RNA polymerase II promoter. Analogous to the pribnow box.
• Nick – A single strand scission of the DNA.
• Bacteriophage T2 infects E. coli (bacteria).
• Width of DNA helix is 2nm (20 Å).
• DNA polymerase-III makes mistake about every 1 in 104 bases and joins an incorrect deoxyribonucleotide to growing chain.
• The two dimensional structure of tRNA is clover leaf like, but three dimensional form is L-shaped.
• Initiation of polypeptide chain is done by methionine.
• Term DNA was given by Zacharis.
• The mitochondria DNA differs from nuclear DNA because of lacking binding histones.

Chapter 5 68

Cell Cycle and Cell Division

Cell division/Cell reproduction/Cell cycle.
(1) Introduction : It is the process by which a mature cell divides and forms two nearly equal daughter cells

which resemble the parental cell in a number of characters.

"Continuity of life" is an important intrinsic characteristic of living organisms and is achieved through the
process of reproduction. The reproduction may be asexual or sexual. Both of these involve the division and
replication of cells. Even the growth and development of every living organism depends on the growth and
multiplication of its cells.

In unicellular organisms, cell division is the means of reproduction by which the mother cell produces two or
more new cells. In multicellular organism also, new individual develop from a single cell. The zygote, by the cell
division. Cell division is central to life of all cell and is essential for the perpetuation of the species.

(2) Discovery : Prevost and Dumas (1824) first to study cell division during the cleavage of zygote of frog.

Nagelli (1846) first to propose that new cells are formed by the division of pre-existing cells.

Rudolf virchow (1859) proposed “omnis cellula e cellula” and “cell lineage theory”.

A cell divides when it has grown to a certain maximum size which disturb the karyoplasmic index
(KI)/Nucleoplasmic ratio (NP)/Kernplasm connection. Two processes take place during cell reproduction.

(a) Cell growth : (Period of synthesis and duplication of various components of cell).

(b) Cell division : (Mature cell divides into two cells).

(3) Cell cycle : Howard and Pelc (1953) first time described it. The sequence of events which occur during
cell growth and cell division are collectively called cell cycle. Cell cycle completes in two steps:

(i) Interphase

(ii) M-phase/Dividing phase

(i) Interphase : It is the period between the end of one cell division to the beginning of next cell division. It is
also called resting phase or not dividing phase. But, it is actually highly metabolic active phase, in which cell
prepares itself for next cell division. In case of human beings it will take approx 25 hours. Interphase is completed in
to three successive stages.

G1 phase/Post mitotic/Pre-DNA synthetic phase/Gap Ist : In which following events take place.
(a) Intensive cellular synthesis.

(b) Synthesis of rRNA, mRNA ribosomes and proteins.

(c) Metabolic rate is high.

(d) Cells become differentiated.

(e) Synthesis of enzymes and ATP storage.

(f) Cell size increases.

(g) Decision for a division in a cell occurs.

(h) Substances of G stimulates the onset of next S – phase.

(i) Synthesis of NHC protein, carbohydrates, proteins, lipids.

Chapter 6 69

Cell Cycle and Cell Division

(j) Longest and most variable phase.

(k) Synthesis of enzyme, amino acids, nucleotides etc. but there is no change in DNA amount.

S-phase/Synthetic phase

(a) DNA replicates and its amount becomes double (2C - 4C).

(b) Synthesis of histone proteins.

(c) Euchromatin replicates earlier than heterochromatin.

(d) Synthesis of NHC (non-histone chromosomal proteins).

(e) Each chromosome has 2 chromatids.

G2-phase/Pre mitotic/Post synthetic phase/gap-IInd
(a) Intensive cellular synthesis.

(b) Increase in energy store.

(c) Mitotic spindle protein (tubulin) synthesis begins.

(d) Chromosome condensation factor appears.

(e) Synthesis of 3 types of RNA and
NHC proteins.

(f) Synthesis of ATP molecule and
storage.

(g) Duplication of mitochondria, Growth
plastids and other cellular macromolecular 10–20%
complements.
G2 5 –10%
(h) Damaged DNA repair occur. S M

(ii) M-phase/Dividing phase/Mitotic DNA replication
phase 30–50%

(a) Nuclear division i.e. karyokinesis G1
occurs in 4 phases – prophase, metaphase,
anaphase and telophase. It takes 5-10% Active protein and
(shortest phase) time of whole division. RNA synthesis
30–40%

(b) Cytokinesis : Division of Fig : Different stages of cell cycle (Mitotic cycle).
cytoplasm into 2 equal parts. In animal cell, it
takes place by cell furrow method and in
plant cells by cell plate method.

(4) Duration of cell cycle : It depends on the type of cell and external factors such as temperature, food
and oxygen. Time period for G1 , S, G2 and M-phase is species specific under specific environmental conditions.
e.g. 20 minutes for bacterial cell, 8-10 hours for intestional epithelial cell, and onion root tip cells may take 20
hours.

Chapter 6 70

Cell Cycle and Cell Division

(5) Regulation of cell cycle : Stage of regulation of cell cycle is G1 phase during which a cell may follow
one of the three options.

(i) It may start a new cycle, enter the S-phase and finally divide.

(ii) It may be arrested at a specific point of G1 phase.

(iii) It may stop division and enter G0 quiscent stage. But when conditions change, cell in G0 phase can
resume the growth and reenter the G1 phase.

Types of cell division : It is of three types, Amitosis, Mitosis and Meiosis.

Important tips

• G0 – phase : The cells, which are not to divide further, do not proceed beyond the G1 phase and start undergoing differentiation into
specific type. such cells are said to be in G0 phase.

• Generation time : Period between 2 successive generation (range 8 hr – 100 days).
• Mitogens : Chemicals which enhance or stimulate cell division e.g. lymphokinase (in man)
• Cell cycle duration : 20 minutes in bacteria , 20 hrs in root tip of onion, 2-3 hrs in yeast, 24 hrs in man.
• G0 phase : Cell only starts dividing when the period is favorable otherwise, it remain viable for months or years as such in G0

phase.
• During the mitosis of He-La cells, the longest period is gap I phase or G1.
• DNA replication occurs in S-phase.
• In a cell cycle the condensation of chromosome with visible centromere occurs during M-phase.
• Sequence in cell cycle is G1, S, G2, M .
• M-phase is of shortest duration of cell cycle.
• In G2 , the damaged DNA is repaired.
• Histone protein and RNA synthesis occurs in S-phase.
• Duplication of chromosome occurs at S- phase.

Amitosis : (Gk amitos = without thread, osis = state) It is also called as direct cell division. It was discovered

by Remak (1855) in RBC of chick embryo. In this division there is no Nucleus
differentiation of chromosomes and spindle. The nuclear envelope does not

degenerate.The nucleus elongates and constricts in the middle to form two

daughter nuclei. This is followed by a centripetal constriction of the

cytoplasm to form two daughter cells. It is primitive type of division occuring

in prokaryotes, protozoans, yeasts, foetal membrane of mammals, cartilage Plasma Daughter
of mammals, degenerating cells of the diseased tissues and in the old tissues. membrane Cells

Mitosis : (Gk. Mitos = thread; osis = state) Fig : Amitosis

(1) Definition : It is also called indirect cell division or somadtic cell division or equational division. In this,
mature somatic cell divides in such a way that chromosomes number is kept constant in daughter cells equal to
those in parent cell, so the daughter cells are quantitatively as well as qualitatively similar to the parental cell. So it is
called equational division.

(2) Discovery : Mitosis was first observed by Strasburger (1875) and in animal cell by W.fleming (1879) term
mitosis was given by Fleming (1882).

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Cell Cycle and Cell Division

(3) Occurrence : Mitosis is the common method of cell division. It takes place in the somatic cells in the
animals. Hence, it is also known as the somatic division. It occurs in the gonads also for the multiplication of
undifferentiated germ cells. In plants mitosis occurs in the meristematic cells e.g. root apex and shoot apex.

(4) Duration : It ranges from 30 minutes to 3 hours time is species-specific but also depends upon type of
tissues, temperature.

(5) Process of mitosis : Mitosis is completed in two steps

Karyokinesis : (Gk. karyon = nucleus; kinesis = movement) Division of nucleus. Term given by Schneider
(1887).

Cytokinesis : (Gk –kitos = cell; kinesis = movement) Division of cytoplasm, Term given by Whitemann
(1887).

Karyokinesis : It comprises four phases i.e. Prophase, Metaphase, Anaphase, Telophase.

(i) Prophase : It is largest phase of karyokinesis.

(a) Chromatin fibres thicken and shorter to form chromosomes which may overlap each other and appears
like a ball of wool. i.e. Spireme stage.

(b) Each chromosome divides longitudinally into 2 chromatids which remain No Interphase
attached to centromere.
Centrosome
(c) Nuclear membrane starts disintegrating except in dinoflagellates. Nucleus
(d) Nucleolus starts disintegrating.
(e) Cells become viscous, refractive and oval in outline. Nucleolus
Nuclear

membrane
Plasma
membrane
Cell wall

(f) Spindle formation begins. Chromo
(g) Cell cytoskeleton, golgi complex, ER, etc. disappear. somes

(h) In animal cells, centrioles move towards opposite sides. Prophase
(i) Lampbrush chromosomes can be studied well.
Spindle
fibres

(j) Small globular structure (beaded) on the chromosome are called Equator of
chromomeres. spindle

Metaphase

(ii) Metaphase Equatorial
(a) Chromosomes become maximally distinct i.e. size can be measured. Plate

(b) A colourless, fibrous, bipolar spindle appears. Cell plate Metaphase

(c) Spindle is formed from centriole (in animal cells) or MTOC (microtubule Cell wall
organising centre) in plant cells successively called astral and anastral spindle.

(d) Spindle has 3 types of fibres. New cell wall Telophas

 Continuous fibre (run from pole to pole). New plasma
 Discontinuous fibre (run between pole to centromeres). membrane
 Interzonal fibre (run between 2 centromere).
(e) Spindle fibre are made up of 97% tubulin protein and 3% RNA. Divided cell
Fig : Various stages of mitosis

Chapter 6 72

Cell Cycle and Cell Division

(f) Chromosomes move towards equatorial plane of spindles called congression and become arranged with
their arms directed towards pole and centromere towards equator.

(g) Spindle fibres attach to kinetochores.

(h) Metaphase is the best stage for studying chromosome morphology.

(iii) Anaphase

(a) Centromere splits from the middle and two chromatids gets separated.

(b) Both the chromatids move towards opposite poles due to repulsive force called anaphasic movement.

(c) Anaphasic movement is brought about by the repolymerisation of continuous fibres and depolymerisation
of chromosomal fibres.

(d) Different shape of chromosomes become evident during chromosome movement viz. metacentric
acrocentric etc.

(e) Chromosomes takes V, J, I or L shapes.

(f) The centromere faces towards equator.

(g) The chromatids are moved towards the pole at a speed of 1 µm/minute. About 30 ATP molecules are used
to move one chromosome from equator to pole.

(iv) Telophase

(a) Chromosomes reached on poles by the spindle fibers and form two groups.

(b) Chromosomes begin to uncoil and form chromatin net.

(c) The nuclear membrane and nucleolus reappear.

(d) Two daughter nuclei are formed.

(e) Golgi complex and ER etc., reform. Furrow Cell
Mid body plate
Cytokinesis : It involves division of cytoplasm in animal cells, the
cell membrane develops a constitution which deepens centripetally and is Fig : Furrowing Cell plate formation
called cell furrow method.
(In animals) (In plants)
In plant cells, cytokinesis occurs by cell plate formation.

(6) Significance of mitosis

(i) It keeps the chromosome number constant and genetic stability in daughter cells, so the linear heredity of
an organism is maintained. All the cells are with similar genetic constituents.

(ii) It helps in growth and development of zygote into adult through embryo formation.

(iii) It provides new cells for repair and regeneration of lost parts and healing of the wounds.

(iv) It helps in asexual reproduction by fragmentation, budding, stem cutting, etc.

(v) It also restores the nucleo-plasmic ratio.

(vi) Somatic variations when maintained by vegetative propagation can play important role in speciation.

Chapter 6 73

Cell Cycle and Cell Division

(7) Types of Mitosis

(i) Anastral mitosis : It is found in plants in which spindle has no aster.

(ii) Amphiastral mitosis : It is found in animals in which spindle has two asters, one at each pole of the
spindle. Spindle is barrel-like.

(iii) Intranuclear or Promitosis : In this nuclear membrane is not lost and spindle is formed inside the
nuclear membrane e.g. Protozoans (Amoeba) and yeast. It is so as centriole is present within the nucleus.

(iv) Extranuclear or Eumitosis : In this nuclear membrane is lost and spindle is formed outside nuclear
membrane e.g. in plants and animals.

(v) Endomitosis : Chromosomes and their DNA duplicate but fail to separate which lead to polyploidy e.g.
in liver of man, both diploid (2N) and polyploid cells (4N) have been reported. It is also called endoduplication and
endopolyploidy.

(vi) Dinomitosis : In which nuclear envelope persists and microtubular spindle is not formed. During
movement the chromosomes are attached with nuclear membrane.

Important tips

• Pericentriolar cloud : A clear cytoplasmic area with no cell organelle between the centriole pair and astral rays.
• Root tips of onion are best material for studying mitosis.
• Kinetochore : A discoidal area on each chromatid and is the site of attachment of spindle fibres.
• In mitosis, plectonemic coiling takes place, in which sister chromatids are tightly coiled upon each other and are not easily separable.

Paranemic coiling found in meiosis.

• Chromosomal fibres are also called tractile fibres, while continuous fibres are also called interpolar fibres.
• Mitogens : The agents which stimulate cell division e.g., cytokinins, auxins, gibberllins, insulin, temperature, steroids.
• Mitotic poision : The agents which inhibit cell division.

(a) Azides and Cyanides : Inhibit prophase.
(b) Colchicine : Inhibits spindle formation at metaphase.
(c) Mustard gas : Agglutinates the chromosomes.
(d) Chalones : These were first reported by Laurence and Bullough (1960). They are peptides and glycoproteins secreated by
extracellular fluid of healthy cells and inhibit cellular division.
• Karyochoriosis : A type of mitosis in fungi in which is intranuclear nucleus divides by furrow formation.
• C-mitosis : Colchicine induced mitosis.
• After undergoing certain divisions, cells die. This is called as “ Hayflick limit”.
• Actinomycin D and tetracyclin inhibit cell division.
• 7 mitotic divisions occur to form embryosac in angiosperms.
• Mitosis index is the ratio of dividing and non-dividing cells.

Meiosis : (Gk. meioum = to reduce, osis = state)

(1) Definition : It is a special type of division in which the chromosomes duplicate only once, but cell divides
twice. So one parental cell produces 4 daughter cells; each having half the chromosome number and DNA amount
than normal parental cell. So meiosis is also called reductional division.

Chapter 6 74

Cell Cycle and Cell Division

(2) Discovery : It was first demonstrated by Van Benden (1883) but was described by Winiwarter (1900).
Term “meiosis” was given by Farmer and Moore (1905).

(3) Occurrence : It is found in special types and at specific period. It is reported in diploid germ cells of sex
organs (e.g. primary spermatocytes of testes to form male gametes called spermotozoa and primary oocytes to form
female gametes called ova in animals) and in pollen mother cells (microsporocytes) of anther and megasporocyte of
ovule of ovary of flowers in plant to form the haploid spores. The study of meiosis in plants can be done in young
flower buds.

(4) Process of meiosis : Meiosis is completed in two steps, meiosis I and meiosis II

Meiosis I : In which the actual chromosome number is reduced to half. Therefore, meiosis I is also known as
reductional division or heterotypic division. It results in the formation of two haploid cells from one diploid cell. It is
divided into two parts, karyokinesis I and cytokinesis I.

Karyokinesis I : It involves division of nucleus. It is divided into four phases i.e. prophase, metaphase,
anaphase, telophase.

Prophase I : It is of longest phase of karyokinesis of meiosis. It is again divisible into five subphases i.e.
leptotene, zygotene, pachytene, diplotene and diakinesis.

(i) Leptotene/Leptonema

(a) Chromosomes are long thread like with chromomeres on it.

(b) Volume of nucleus increases.

(c) Chromatin network has half chromosomes from male and half from female parent.

(d) Chromosome with similar structure are known as homologous chromosomes.

(e) Leptonemal chromosomes have a definite polarization and forms loops whose ends are attached to the
nuclear envelope at points near the centrioles, contained within an aster. Such peculiar arrangement is termed as
bouquet stage (in animals) and syndet knot (in plants).

(f) E.M. (electron microscope) reveals that chromosomes are composed of paired chromatids, a dense
proteinaceous filament or axial core lies within the groove between the sister chromatids of each chromosome.

(g) Lampbrush chromosome found in oocyte of amphibians is seen in leptotene.

(ii) Zygotene/Zygonema

(a) Pairing or “synapsis” of homologous chromosomes takes place in this stage.

(b) Synapsis may be of following types.

 Procentric : Starting at the centromere.

 Proterminal : Starting at the end.

 Localised random : Starting at various points.

(c) Paired chromosomes are called bivalents, which by furthur molecular packing and spiralization becomes
shorter and thicker.

(d) Pairing of homologous chromosomes in a zipper-fashion. Number of bivalents (paired homologous
chromosomes) is half to total number of chromosomes in a diploid cell. Each bivalent is formed of one paternal and
one maternal chromosome (i.e. one chromosome derived from each parent).

Chapter 6 75

Cell Cycle and Cell Division

(e) Under EM, a filamentous ladder like nucleoproteinous complex, called synaptinemal. Complex between
the homologous chromosomes which is discovered by “Moses” (1953).

(iii) Pachytene/Pachynema

(a) In the tetrad, two similar chromatids of the same chromosome are called sister chromatids and those of two
homologous chromosomes are termed non-sister chromatids.

(b) Crossing over i.e. exchange of segments between non-sister chromatids of homologous chromosome
occurs at this stage.

It takes place by breakage and reunion of chromatis segments. Breakage called nicking, is assisted by an
enzyme endonuclease and reunion termed annealing is added by an enzyme ligase. Breakage and reunion
hypothesis proposed by Darlington (1937).

(c) Chromatids of pachytene chromosome are attached with centromere.

(d) A tetrad consists of two sets of homologous chromosomes each with two chromatids. Each tetrad has four
kinetochore (two sister and two homologous).

(e) A number of electron dense bodies about 100 nm in diameter are seen at irregular intervals within the
centre of the synaptonemal complex, known as recombination nodules.

(f) DNA polymerase is responsible for the repair synthesis.

(iv) Diplotene/Diplonema

(a) At this stage the paired chromosomes begin to separate (desynapsis).

(b) Cross is formed at the place of crossing over between non-sister chromatids.

(c) Homologous chromosomes move apart they remain attached to one another at specific points called
chiasmata.

(d) At least one chiasma is formed in each bivalent.

(e) Chromosomes are attached only at the place of chiasmata. Chromatid Centromere

(f) Chromatin bridges are formed in place of synaptonemal complex
on chiasmata.

(g) This stage remains as such for long time. Chiasma
(v) Diakinesis

(a) Chiasmata moves towards the ends of chromosomes. This is
called terminalization.

(b) Chromatids remain attached at the place of chiasma only.

(c) Nuclear membrane and nucleolus degenerates.

(d) Chromosome recondense and tetrad moves to the metaphase plate.

(e) Formation of spindle.

Chapter 6 Fig : Showing crossing over during meiosis

76

Cell Cycle and Cell Division

(f) Bivalents are irregularly and freely scattered in the nucleocytoplasmic matrix.
When the diakinesis of prophase-I is completed than cell enters into the metaphase-I.

Nuclear Nuclear
membrane membrane
Nuclcolus
Nuclcolus
Chromosome
network Chromosome
network
Cytoplasm showing

chromomeres

Cytoplasm

Cell wall Cell membrane

Cell membrane Cell wall
A B

Cell wall Cell wall

Cell membrane Cell membrane
Nuclear membrane
Nuclcolus Nuclcolus
Nuclear membrane

Pair of Pair of sister
homologous chromatids
chromosomes
showing synspsis Non- soster
chromatids of
C homologous
chromosomes
showing
crossing over
D

Cell wall Cell wall
Cell membrane Cell membrane

Nuclcolus Disappearing
nucleolus and
Nuclear membrane nuclear membrane
disspearing

Homologous Homologous
chromosomes chromosomes
showing chlasma separating from
one another
EF
Fig : A-F Meiosis : Prophase I. A. Cell before entering leptotene, B. Leptotene, terminalleation

C. Zygotene, D. Pachytene, E. Diplotene, F. Diakinesis.

Metaphase I : It involves;
(i) Chromosome come on the equator.
(ii) Due to repulsive force the chromosome segment get exchanged at the chiasmata.

Chapter 6 77

Cell Cycle and Cell Division

(iii) Bivalents arrange themselves in two parallel equatorial or metaphase plates. Each equatorial plate has one
genome.

(iv) Centromeres of homologous chromosomes lie equisdistant from equator and are directed towards the
poles while arms generally lie horizontally on the equator.

(v) Each homologous chromosome has two kinetochores and both the kinetochores of a chromosome are
joined to the chromosomal or tractile fibre of same side.

Anaphase-I

(i) It involves separartion of homologous chromosomes which start moving opposite poles so each tetrad is
divided into two daughter dyads. So anaphase-I involves the reduction of chromosome number, this is called
disjunction.

(ii) The shape of separating chromosomes may be rod or J or V-shape depending upon the position of
centromere.

(iii) Segregation of mendalian factors or independent asortment of chromosomes take place. In which the
paternal and maternal chromosomes of each homologous pair segregate during anaphase-I which introduces
genetic variability.

Telophase-I

(i) Two daughter nuclei are formed but the chromosome number is half than the chromosome number of
mother cell.

(ii) Nuclear membrane reappears.

(iii) After telophase I cytokinesis may or may not occur.

(iv) At the end of Meiosis I either two daughter cells will be formed or a cell may have two daughter nuclei.

(v) Meiosis I is also termed as reduction division.

(vi) After meiosis I, the cells in animals are reformed as secondary spermatocytes or secondary oocytes; with
haploid number of chromosomes but diploid amount of DNA.

(vi) Chromosomes undergo decondensation by hydration and despiralization and change into long and thread
like chromation fibres.

Interphase : Generally there is no interphase between meiosis-I and meiosis-II. A brief interphase called
interkinesis, or intermeiotic interphase. There is no replication chromosomes, during this interphase.

Cytokinesis-I : It may or may not be present. When present, it occurs by cell-furrow formation in animal cells
and cell plate formation in plant cells.

Significance of meiosis-I :

(i) It separates the homologous chromosomes to reduce the chromosome number to the haploid state, a
necessity for sexual reproduction.

(ii) It introduces variation by forming new gene combinations through crossing over and randon assortment of
paternal and maternal chromosomes.

Chapter 6 78

Cell Cycle and Cell Division

(iii) It may at times cause chromosomal mutation by abnormal disjunction.
(iv) It induces the cells to produce gametes for sexual reproduction or spores for asexual reproduction.
Meiosis-II : It is also called equational or homotypical division because the number of chromosomes remains
same as after meiosis-I. It is of shorter duration than even typical mitotic division. It is also divisible into two parts,
Karyokinesis-II and Cytokinesis-II.

Karyokinesis-II : It involves the separation of two chromatids of each chromosome and their movement to
separate cells. It is divided in four phases i.e., Prophase-II, Metaphase-II. Anaphase-II and Telophase-II.

Almost all the changes of Karyokinesis-II resembles to mitosis which involves.

(i) It starts just after end of telophase I.

(ii) Each daughter cell (nucleus) undergoes mitotic division.

(iii) It is exactly similar to mitosis.

(iv) At the end of process, cytokinesis takes place.

(v) Four daughter cells are formed after completion.

(vi) The sister kinetochores of one chromosome are separated.

(vii) The four daughter cells receive one chromatid each of the tetravalent.

(viii) Centromere divide at anaphase II.

(ix) Spindle fibres contract at prophase II.

Cytokinesis-II : It is always present and occurs by cell furrow formation in animal cell and cell plate
formation in plant cell.

So by meiosis, a diploid parental cell divides twice forming four haploid gametes or sex cells, each having half
the DNA amount than that of the parental cell and one-fourth of DNA present in the cell at the time of beginning of
meiosis.

(5) Significance of meiosis

(i) Constancy of chromosome number in successive generation is brought by process.

(ii) Chromosome number becomes half during meiosis.

(iii) It helps in introducing variations and mutation.

(iv) It brings about gamete formation.

(v) It maintains the amount of genetic informative material.

(vi) Sexual reproduction includes one meiosis and fusion.

(vii) The four daughter cells will have different types of chromatids.

(6) Why the necessity of meiosis-II : The basic aim of meiosis is to reduce the number of chromosomes to
half. The chromosomes that separate in the anaphase of meiosis-I are still double. Each consist of two chromatids
and has 2n amount of DNA. Thus reduction of DNA content does not occur in meiosis-I. Truely haploid nuclei in

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terms of DNA contents as well as chromosome number are formed in meiosis-II. When the chromatids of each
chromosome are separated into different nuclei. Thus meiosis-II is necessary.

Difference between Mitosis and Meiosis

S.No. Characters Mitosis Meiosis

I. General Somatic cells and during the multiplicative Reproductive germ cells of gonads.
phase of gametogenesis in germ cells.
(1) Site of occurrence Throughout life. During sexual reproduction.
Haploid or diploid. Always diploid.
(2) Period of occurrence Parental cell divides once. Parent cell divides twice.
(3) Nature of cells Two. Four.
(4) Number of divisions Genetically similar to parental cell. Amount Genetically different from parental cell.
(5) Number of daughter cells of DNA and chromosome number is same Amount of DNA and chromosome number is
(6) Nature of daughter cells as in parental cell. half to that of parent cell.

II. Prophase Shorter (of a few hours) and simple. Prophase-I is very long (may be in days or
(7) Duration months or years) and complex.
Formed of 3 subphases : early-prophase, Prophase-I is formed of 5 subphases:
(8) Subphases mid-prophase and late-prophase. leptotene, zygotene, pachytene, diplotene
and diakinesis.
(9) Bouquet stage Absent. Present in leptotene stage.
(10) Synapsis Absent. Pairing of homologous chromosomes in
zygotene stage.
(11) Chiasma formation and Absent. Occurs during pachytene stage of prophase-I.
crossing over.
Comparatively in earlier part. Comparatively in later part of prophase-I.
(12) Disappearance of nucleolus
and nuclear membrane Plectonemic. Paranemic.

(13) Nature of coiling Only one equatorial plate Two plates in metaphase-I but one plate in
III. Metaphase metaphase-II.
Lie at the equator. Arms are generally Lie equidistant from equator and towards
(14) Metaphase plates directed towards the poles. poles in metaphase-I while lie at the equator
in metaphase-II.
(15) Position of centromeres Two chromosomal fibre join at Single in metaphase-I while two in
centromere. metaphase-II.
(16) Number of chromosomal
fibres

IV. Anaphase

(17) Nature of separating Daughter chromosomes (chromatids with Homologous chromosomes separete in

chromosomes independent centromeres) separate. anaphase-I while chromatids separate in

anaphase in anaphase-II.

(18) Splitting of centromeres and Occurs in anaphase. No splitting of centromeres. Inter-zonal fibres
development of inter-zonal are developed in metaphase-I.
fibres

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Cell Cycle and Cell Division

V. Telophase Always occurs Telophase-I may be absent but telophase-II is
(19) Occurrence always present.

VI. Cytokinesis Always occurs Cytokinesis-I may be absent but cytokinesis-II
(20) Occurrence is always present.
(21) Nature of daughter cells 2N amount of DNA than 4N amount of
(22) Fate of daughter cells DNA in parental cell. 1 N amount of DNA than 4 N amount of
Divide again after interphase. DNA in parental cell.
VII. Significance
(23) Functions Do not divide and act as gametes.

(24) Variations Helps in growth, healing, repair and Produces gametes which help in sexual
multiplication of somatic cells. reproduction.
(25) In evolution Occurs in both asexually and sexually
reproducing organisms. Produces variations due to crossing over and
Variations are not produced as it keeps chance arrangement of bivalents at
quality and quantity of genes same. metaphase-I.
It plays an important role in speciation and
No role in evolution. evolution.

(7) Types of meiosis : On the basis of time and place, meiosis is of three types

(i) Gametic/Terminal meiosis : In many protozoans, all animals and some lower plants, meiosis takes place
before fertilization during the formation of gametes. Such a meiosis is described as gametic or terminal.

This type of life cycle with diploid adult and gametic meiosis is known as the diplontic cycle.

(ii) Zygotic or Initial Meiosis : In fungi, certain protozoan groups, and some algae fertilization is
immediately followed by meiosis in the zygote, and the resulting adult organisms are haploid. Such a meiosis is said
to be zygotic or initial. This type of life cycle with haploid adult and zygotic meiosis is termed the haplontic cycle.

(iii) Sporogenetic Meiosis

(a) Diploid sporocytes or spore mother cells of sporophytic plant, undergo meiosis to form the haploid spores
in the sporangia.

(b) Haploid spore germinates to form haploid gametophyte which produces the haploid gametes by mitosis.

(c) Haploid gametes fuse to form diploid zygote which develops into diploid sporophyte by mitotic divisions.
e.g. In higher plants like pteridophytes, gymnosperms and angiosperms.

Chapter 6 81Fig : Three types of Meiosis

Cell Cycle and Cell Division

Important tips

• Brachymeiosis : Failure of meiosis-II. It is characteristic feature of fungi.
• Meiosis-II is not mitosis as it occurs haploid number of chromosomes and chromatids formed may not be similar to each other.
• Restitution nucleus : A colchicine treated cell has the nucleus with double sets of chromosomes.
• In cyperus, one meiosis produce only one pollen instead of four so that meiotic division required to produce fruits will be = number of

fruits × 2.
• Chiasmata first observed by Janseens (1909).
• When sister chromatids are loosely arranged and are easily separate. It is found in meiotic chromosomes.
• Mitosis ends in 1- 2 hours while meiosis may take 24 hrs to few years.
• Neuron cells are always in interphase.
• When the chromosome duplicates but karyokinesis does not take place the number of chromosome per cell will increases, it is called

endomitosis or endoduplication.
• Process of inducing mitosis into a cell – mitogenesis.
• To study mitosis root tips are fixed in 1: 3 acetic acid and methanol.
• Colchicine inhibits spindle formation and enhance duplication in number of chromosomes.
• At the time of cell division electrostatic force is responsible for terminalization.
• Mitotic crossing over takes place in parasexual cycle.

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Introduction.

There are millions of organisms – plants, animals, bacteria and viruses. Each one is different from the other in
one way or the other. About more than one million of species of animals and more than half a million species of
plants have been studied, described and provided names for identification. Thousands are still unknown and are yet
to be identified and described. It is practically impossible to study each and every individual. Also, it is difficult to
remember their names, characters and uses. However, biologists have devised techniques for identification, naming
and grouping of various organisms.

The art of identifying distinctions among organisms and placing them into groups that reflect their most
significant features and relationship is called biological classification. Scientists who study and contribute to the
classification of organisms are known as systematists or taxonomists, and their subject is called systematics (Gk.
Systema = order of sequence) or taxonomy (Gk. Taxis = arrangement; nomos = law).

History of classification : References of classification of organisms are available in Upanishads and
Vedas. Our Vedic literature recorded about 740 plants and 250 animals. Few other significant contributions in the
field of classification are :

(1) Chandyogya upanishad : In this, an attempt has been made to classify the animals.

(2) Susruta samhita : It classifies all 'substances' into sthavara (imbobile) e.g. plants and jangama (mobile)
e.g. animals .

(3) Parasara : Here, angiosperms were classified into dvimatruka (dicotyledons) and ekamatruka
(monocotyledons). He was even able to find that dicotyledons bear jalika parana (reticulate veined leaves and
monocotyledons bear maun laparna parallel veined leaves).

(4) Hippocrates, and Aristotle : They classified animals into four major groups like insects, birds, fishes and
whales.

Types of system of classification.

Different systems of classification proposed from time to time have been divided into three basic categories
viz., artificial systems, natural systems and phylogenetic system (However, Redford, (1986), included mechanical
systems as a fourth category).

(1) Artificial system of classifications : These systems are more or less arbitrary as the plants are classified
merely on the basis of gross morophology, habit and their importance to man. The main advocates of artificial
system of classifications were :

(i) Theophrastus : Father of botany. Theophrastus was a disciple of Plato and later Aristotle. In his book De
Historia plantarum, he classified about 500 kinds of plants into four major group; trees, shrubs, subshrubs and
herbs.

(ii) Caius Plinius Secundus : He described the biological, medicinal and agricultural aspects of plants in 37
volumes of Natural History. He used the term 'Stamen' for the first time.

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(iii) Pedanios Dioscorides : He described about 600 plants of medicinal importance in his Materia Medica.

(iv) Charaka : Indian Scholar. He classified plants of medicinal importance in his Charaka Samhita.

(v) Andrea Caesalpino : He described 1520 species in 16 volumes of De Plantis libri grouped as herbs and
trees. He further classified plants based on fruit and seed characters.

(vi) John Ray : He was a British botanist who published three volumes of his work Historia Generalish
Plantarum consisting of improved classification originally proposed by him in Methodus Plantarum Noven. He was
the first to divided the groups herbs, shrubs and trees into Dicots and Monocots on the basis of the presence of two
or one cotyledons respecitvely. He coined the term species.

(vii) Carolus Linnaeus : Father of taxonomy. A swedish botanist, who published an artificial system of
classification based exclusively on floral characters. Linnaeus published several manuscripts including Hortus
cliffortianus and Genera plantarum (1737). In his Genera plantarum he listed all the plant genera known to him. He
published his best known Species plantarum in 1753. In this book he listed and described all species of plants
known to him. He established binomial nomenclature.

(2) Natural System of Classifications : These systems of classification are based not only on the characters
of reproductive organs and structural morphology but used as many taxonomic characters or traits as possible to
classify the plants. The advocates of natural systems of classification are listed below :

(i) Michel Adanson : A French botanist, who classified plants and animals using as many characters as
possible and proposed a natural system of classification.

(ii) A.L. de Jussieu : Classified plants based on natural characters. In his system of classification he grouped
the plants resembling each other in a set of characters.

(iii) A.P. de Candolle : He grouped all alike plants together and published a new classification of plants in
his book Theorie elementaire de la botanique (1813).

(iv) George Bentham and Joseph Dalton Hooker : These two English botanists classified plants based on
original studies of specimens. They published their well known scheme of classification in Genera plantarum (1862–
83). This system of classification is still regarded as the best classification, especially from the practical point of view.

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Bentham and Hooker's classification (Broad outline)

Plant Kingdom

Cryptogams Phanerogams
(Non-flowering plants) (Seed bearing plants)

Class Monocotyledonae
(Seed having one cotyledons)
Dicotyledonae Gymnospermae
(Seed having two cotyledons) Monochlamydeae
(Petals absent)
Sub-Class
Bicarpellatae
Polypetalae Gamopetalae (Ovary superior, Bicarpellary)
(Petals free) (Petals fused)
e.g., Solanaceae, Labiatae
Series

Inferae Heteromerae
(Ovary inferior)
e.g., Compositae

Thalamiflorae Disciflorae Calyciflorae
(Petals and stamens hypogynous) (Petals and stamens (Petals and stamens
e.g., Ranunculaceae hypogynous, a nectariferous perigynous/epigynous)
Brassicaceae, Malvaceae disc at the base of the ovary) e.g., Leguminosae, Cucurbitaceae
e.g., Rutaceae

Series

Microspermae Epigynae Coronarieae Calycinae Nudiflorae Apocarpae Glumaceae
(Ovary Perianth petaloid, ovary (Free (Perianth small,
inferior) superior e.g., Liliaceae scale-lke or chaffy
carpels) e.g., Gramineae)

Merits and Demerits of Bentham and Hooker's system of classification
Merits
This system is regarded as most convenient and suitable for practical utility and is followed by most of the
herbaria due to following reasons :
(a) Every genus and species was studied from actual specimens available in British and continental
herbaria.
(b) It is the first great natural system of classification. This is very useful for practical purposes.
(c) Gymnosperms have been considered as third taxon and kept between dicots and monocots.
(d) In monocots, stress has been given to relative position of ovary and perianth characteristics.

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(e) Great emphasis has been given to free or fused conditions of petals distinguishing dicots into three sub-
classes Polypetalae, Gamopetalae and Monochlamydeae.

Demerits : There are some demerits in the classification of Bentham and Hooker. Some of them are :

(a) The greatest demerit of this system is the retention in the group monochlamydeae, a number of orders
which represent affinities with those in which biseriate perianth is the rule.

(b) Placing gymnosperms between dicots and monocots.

(c) Here monochlamydeae is considered as most highly evolved and polypetalae as primitive among dicots.

(d) Cucurbitaceae family with fused petals is placed in Polypetalae.

(e) Liliaceae is separated from Iridaceae and Amaryllidaceae merely on the character of ovary, without
keeping in mind other similarities.

Differences between Natural and Artificial classification

No. Characters Natural classification Artificial classification
1. Number of characters Only few characters are considered.
Almost all the characters are
2. Hereditary considered. Members of different groups are
constitution usually not similar in hereditary
Members are mostly alike in pattern.
3. Flexible hereditary pattern of different
groups. Stable classification.
4. Phylogeny
5. Information May change with advancement in Not related phylogenetically.
knowledge. Provides only limited information.
6. Recent advances
Closely related phylogenetically. Cannot incorporate new work.
7. Convenience
8. Little known plants Provides plenty of useful Difficult. position and
information.
Not certain about
Recent useful research can be easily identification.
incorporated.

Identification of plants easy.

Got the place at definite place.

(3) Phylogenetic system of classifications : These systems of classifications are mainly the
rearrangements of natural systems using as many taxonomic characters as possible in addition to the phylogenetic
(evolutionary) informations. Some important phylogenetic systems of classifications were proposed by –

(i) A.W. Eichler : A German botanist who proposed phylogenetic system of classification and published in
the third edition of Syllabus der vorlesungen (1883).

(ii) Adolph Engler and Karl Prantl : These two german botanists classified plant kingdom on the basis of
their evolutionary sequences. They started with simplest flowering plants and ended with plants of complex floral
structures.

(iii) C.E. Bessey : He classified flowering plants on the basis of their evolutionary relationships.

(iv) John Hutchinson : A British botanist published his phylogenetic system of classification in 'The Families
of Flowering Plants'.

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(v) Armen Takhtajan : A Russian botanist who published his system of classification in Botanical Review.

(vi) Arthur Cronquist : Published his classification in 'An Integrated System of Classification of Flowering
Plants'.

Differences between Natural and Phylogenetic classification

No. Characters Natural classification Phylogenetic classification
1. Number of characters
Based on several constant Along with several constant characters,
2. Evolutionary characters. evolutionary sequences are also
sequences considered.
Not considered. Classification based
3. Practical utility basically on common characters. Evolutionary sequence, natural
affinities and relationship taken into
Used adequately as an aid for easy account.
identification.
Phylogenetic and adopted by many
countries.

Plant nomenclature.

Plant nomenclature may be defined as the system of naming plant. Almost all plants (and animals too) are
known by different common names in different parts of the world. Even within the same country people of different
states and regions use different common names. Iphomoea batatas, for example, is called sweet potato in English,
Shakarkandi in Hindi, Meetha alu in Assamies and Bengali, Kundmul in Telagu, Ratalu in Marathi and
Jenasu in Kannad. The common names are thus quite confusion. This necessiated the need of giving scientific
names so that scientists of different parts of the world could understand each other work. The earliest scientific
names were polynomial, i.e., they were composed of many words (which gave the characteristics of plants), e.g.,
Sida acuta (a member of Malvaceae) was named as Chrysophylum foliis, ovalis superne glabris parallel striatis
subtus, tomentosonitidis. Such long names were difficult to remember. Hence, to make it easier binomial system of
nomenclature was introduced.

(1) Binomial system of nomenclature : The credit of giving binomial system of nomenclature goes to
Swedish naturalist, Carolus Linnaeus. He employed this system in his book Species Plantarum, published in
1753. According to this system the name of a plant or animal is composed of two Latin (or Latinised) words, e.g.,
potato is Solanum tuberosum. The first word (i.e., Solanum) indicates the name of the genus (called generic
name) and the second word (i.e., tuberosum) denotes the name of the species (called specific name). The
generic name always begins with a capital letter and the specific name with a small letter and printed in italics.

The generic and specific names always have some meaning. They are based on some special characters of the
plant, on the name of any scientist or on some legend.

All plants having general similarity and relations are given a common generic name, e.g., potato, brinjal, black
nightshade (makoi) have been placed in the genus Solanum. However, their specific names distinguish them from
each other – potato is Solanum tuberosum, brinjal is S. melongena and black nightshade is S. nigrum.

Usually the name of the author, who names a plant, is also written in full or in abbreviated form after the
specific name. Thus, in case of Mangifera indica L., the L. stands for Linnaeus and in Lychnis alba Mill., the Mill.
stands for Miller.

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Sometimes a single species is described under different names by different authors. These name are called
synonyms. In such cases, the name under which the species is first described, is considered to be valid.

(2) Trinomial nomenclature : Certain species are divisible into smaller units, called varieties, on the basis of
finer differences. The name of the variety is written after the specific name. Thus, the name may become trinomial
or three word name. e.g., Homo sapiens europeus is the name of the man of European race. Trinomial
nomenclature is simply an extension of the Linnaean system.

(3) Code of biological nomenclature : Anyone can study, describe, identify and give a name to an
organism provided certain universal rules are followed. These rules are framed and standardised by International
Code of Botanical Nomenclature (ICBN) and International Code of Zoological Nomenclature (ICZN). The codes
help in avoiding errors, duplication, confusion and ambiguity in scientific names. The codes are established and
improved upon at International Botanical and Zoological Congress held from time to time. The names of bacteria
and viruses are decided by International Code of Bacteriological Nomenclature (ICBN) and International Code of
Viral Nomenclature (ICVN). Similarly, there is a separate International Code of Nomenclature for Cultivated Plants
(ICNCP).

Explanation of terminology (Units).

(1) Taxon : The term taxon is used to represent any unit of classification. The unit (i.e., taxon) many be large
(e.g., Plant Kingdom) or small (e.g., Algae, Fungi, or a single species).

(2) Category : Various sub-divisions of plants kingdom such as division, class, order, family, etc., are referred
to as categories. In the hierarchy of categories kingdom is the highest and species is the lowest category. The
following is hierarchial series :

(i) Kingdom : It is the highest category in biological classification. All plants are include in plant kingdom.

(ii) Division : It is a major group in the Linnean hierarchy used in the classification of plants (equivalent to
phylum in animal classification). It is a taxonomic category between kingdom and class. The subcategory of division
is subdivision. The suffix of division is – ophyta.

(iii) Class : A division is divided into classes. It is a taxonomic category between the division and order. Its
suffix is – ae. The subcategories of class are subclass and series. In the class contain organism least similar to one
another.

(iv) Order : A class includes one or more orders. It is a taxonomic category between the class and family. Its
suffix is – ales. The subcategory of order is suborder.

(v) Family : An order is divided into one or more families. It is the taxonomic category between the order and
the genus. Its suffix is – aceae. The subcategories of family are subfamily, tribe and subtribe.

(vi) Genus : The plural of genus is genera. A family includes one or more genera. The generic name is
important and printed in Italics (If hand written, it is underlined). The subcategories of genus are subgenus,
section and subsection.

(vii) Species : It is the smallest rank of taxonomic classification. The first letter of the species is denoted with
small letter. The species is printed in Italics (It is underlined if hand written). A genus may include one or more
species. The subcategories of species are subspecies, varieties, subvarieties, form and subform.

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(3) New systematics or Biosystematics : The term new systematics was proposed by Sir Julian Huxley in
1940. In the new systematics, the species are considered related to one another, mutable and the work of gradual
modification. This is in confirmity with the facts of evolution.

Forms of new systematics : There are several forms of new systematics –

(i) Morphotaxonomy : It is based on the structural features of the organisms.

(ii) Cytotaxonomy : It is based on the somatic chromosomes of organisms.

(iii) Biochemical taxonomy or Chemotaxonomy : It is based on the protein and serum analyses and on
the chemical constituents of the organisms.

(iv) Numerical taxonomy : It involves quantitative assessment of similarities and differences in order to
make objective assessments. Characters of organisms are given equal weight and the relationships of the organisms
are numerically determined, usually with the aid of a computer.

(v) Experimental taxonomy : It is based on the genetic relationship determined with the help of
experiments.

Important Tips

• The arrangement of organism in to groups termed as classification.
• Forming the rules for classification known as Taxonomy.
• De candolle : Coind the term taxomy in 1913.
• Floral characters are used as basis of classification and for identifying new species because floral characters are conservative when

compared with vegetative characters.
• In Bentham and Hooker's classification Dicotyledons have been kept before Monocotyledons. Seeds plants have been divided into

Dicots, Gymnospermae and Monocots.
• Among the vegetative characters, venation in leaf in one of highly acceptable characters for classification of angiosperms.
• In Engler and Prantl's system Monocotyledons have been kept before Dicotyledons.
• In Bentham and Hooker's classification 202 families have been identified.
• Bentham and Hooker's classification is a natural system of classification and very helpful for practical purposes.
• For declaration of new species, floral characters of new species should be used.
• In Bentham and Hooker's system of classification, evolutionary criteria have not been followed hence not phylogenetic.
• Hooker complied first complete flora of India and wrote the book 'Flora of British India'.
• Bentham and Hooker : Gave the first natural classification of plants.
• Engler and Prantl : Gave the first phylogenetic classification of plants.
• Engler and Prantl's and Hutchinson's system of classification are phylogenetic.
• 411 families have been recognised in Hutchinson's system of classification and 280 families have been identify in Engler and Prantl's

system of classification.
• Father of Botany : Theophrastus, a Greek philosopher, produced the first book on botany, Historia Plantarum, student of Aristotle.
• After the work of Linnaeus, another significant publication was that of Augustin de Candolle in theory elementaire de la botanique.
• The correct sequence of taxa in Linnaean hierarchy is species → genus → family → order→ class.
• A system for naming the organisms called nomenclature.
• Bauhin (1623) proposed the binary system of nomenclature which was elaborated by Linnaeus (1753) in to binomial system.

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• An international code of Botanical nomenclature (IBCN) come into existence in 1930.
• International code for nomenclature is divided into three parts i.e. (i) Principles (ii) Rules and recommendations (iii) Provisions.
• Priority : Nomenclature of taxonomic groups is based upon priority of publication.
• Monotypic Genus : A genus having only one species, e.g., Home.
• Polytypic Genus : A genus containing more than one species, e.g., Panthera, Solanum.
• John Ray : An English naturalist, 1627–1705, introduced the term species. It is a basic unit of classification.
• J.K. Maheswari described the plants of India in 'Flora of Delhi'.
• Phylogeny was introduced by Homock but concept was introduced by Heackel.
• Phylogenetic classification reflect the evolutionary relationships of organisms.
• Type Specimen : Original specimen is called holotype; duplicate of holotype is termed isotype; additional one is known as paratype;

and a new one when the original is lost is referred to as neotype.

Modern system of classification.
(1) Two kingdom system of classification : This system of classification is the oldest it was suggested by

Carolus Linnaeus in 1758. He divided the living word (organism) in to two kingdoms, Plantae (for all plants like
tree, shrubs, climbers, creepers, moss and floating green algae) and Animalia (For animals).

(2) Three kingdom system of classification : Ernst Haeckel, a German biologist and philosopher,
suggested a third kingdom protista in 1866 for –

(a) Unicellular organisms such as bacteria, protozoans and acellular algae.
(b) Multicellular organisms without tissue such as algae and fungi.
(3) Four kingdom system of classification : It was proposed by Copeland in 1956. The two additional
kingdoms were Monera for the bacteria and blue green algae and Protista for protozoans, algae and fungi.
(4) Five kingdom system of classification : R.H. Whittaker, an American ecologist. He proposed five
kingdom system of classification in 1969.
This system replaced the old, two-kingdom grouping of living organisms. As already discussed, a division of
living world merely into plant and animal kingdoms is too simple. It does not take into account the gradual
evolution of distinct plant and animal groups and it allows no place for those primitive organisms that even now are
neither plants nor animals nor that are both. In this classification eukaryotes were assingned to only four of the five
kingdom.
Five-kingdom classification is based on the following four criteria :
(i) Complexity of cell structure.
(ii) Complexity of organism's body.
(iii) Mode of obtaining nutrition.
(iv) Phylogenetic relationship.
The five kingdom are : Monera, Protista, Fungi, Plantae and Animalia.

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Kingdom Monera (The prokaryotes).
Monera (Monos – single) includes prokaryotes and shows the following characters :
(1) They are typically unicellular organisms (but one group is mycelial).
(2) They lack nuclear membranes.
(3) Ribosomes and simple chromatophores are the only subcellular organelles in the cytoplasm. The

ribosomes are 70 S. Mitochondria, plastids, Golgi apparateus, lysosomes, endoplasmic reticulum, centrosome, etc.,
are lacking.

(4) The predominant mode of nutrition is absorptive but some groups are photosynthetic or chemosynthetic.
(5) Reproduction is primarily asexual by fission or budding.
(6) Protosexual phenomenon also occurs.
(7) The organisms are non-motile or move by beating of simple flagella or by gliding.
(8) Flagella, if present, are composed of many intertwined chains of a protein flagellin. They are not enclosed
by any membrane and grow at the tip.
(9) Moneran cells are microscopic (1 to few microns in length).
(10) Most organisms bear a rigid cell wall.
(11) The kingdom Monera includes true bacteria, mycoplasmas, rickettsias, actinomycetes (ray fungi) etc.
Microbiologists also include blue green algae (i.e., Cyanobacteria) under the group bacteria because of the presence
of prokaryotic cell structure. Studies have established that the members of archaebacteria group are most primitive
and have separated from eubacteria group very early in the process of evolution. Furthermore, these studies have
also concluded that the archaebacteria and eubacteria possibly originated from a more ancient form of life called
Progenote.
(12) Nutrition : They show both autotrophic and heterotrophic modes of nutrition.
(i) Autotrophs : These are able to form their own food by one of the following methods.
(a) Photoautotrophs : They prepare their own food by reducing CO2 using light energy.
(b) Chemoautotrophs : They form their food by energy derived from chemical reaction.
(ii) Heterotrophs : A few live in symbiosis while others form association of commensalism. Saprophytes
also called 'saprobes' cause decay, fermentation or putrefaction of dead organic matter. Some bacteria are
facultative sasprophyte (= facultative parasites). In the process of fermentation there is anaerobic break-down of
carbohydrates into CO2, alcohol and some energy. Putrefaction or decay is anaerobic break-down of proteins
accompanied by foul smell due to evil smelling gases produced in the process.
The saprobes produce enzymes which convert non-diffusible food substrates (carbohydrate fats, proteins, etc.)
into simpler diffusible form which diffuses into the cytoplasm and is assimilated, i.e., converted into body cytoplasm
or stored as reserve food.

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Still others live on other living organisms (animals, plants or man) in the form of parasites directly absorb their
food from the body of host. Some of the parasites are non-pathogenic i.e., cause no ill-effect or disease in the
host, while some are pathogenic causing diseases in the host.

(d) Major Producer Decomposer Consumer
ecological role
Autotrophy Heterotrophy Heterotrophy
(c) Mode of photosynthesis absorption ingestion
nutrition
Kingdom
fungi

Kingdom Kingdom
Plantae Animalia

(b) Complexity (Multicellular) Kingdom Direction of evolution
of organism Simple protista

(uncellular)

(a) Complexity Eukaryotes Kingdom
of cell monera
Prokaryotes
Autotrophy
chemosynthesis

Fig : Probable phylogenetic relationships among the kingdoms

(13) Reproduction : It is primarily asexual by binary fission or budding. Mitotic apparatus is not formed
during cell division. Distribution of replicated DNA into daughter cells is assisted by cell membrane. Exchange of
genetic material between two bacterial cells is known to occur but no gametes are formed. Sterols, the precursor
molecules of sex hormones, have been reported from certain prokaryotes. Many bacteria form resistant spores.

Kingdom Protista (Unicellular eukaryotes).
Protista (Protistos = Primary) includes unicelluar eukaryotes and show the following characters :
(1) Protists include solitary unicellular or colonial unicellular eukaryotic organisms which not form tissues.
(2) Simple multinucleate organisms or stages of life cycles occur in a number of groups.
(3) The organisms possess nuclear membranes and mitochondria.
(4) In many forms, plastids, (9+2 strand) flagella and other organelles are present.
(5) The nutritive modes of these organisms include photosynthesis, absorption, ingestion and combination of these.
(6) Some protists possess contractile vacuole for regulation of their water content.
(7) Their reproductive cycles typically include both asexual divisions of haploid forms and true sexual

processes with karyogamy and meiosis.
(8) The organisms move by flagella or by other means or are non-motile.

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(9) Nutrition : It is may be photosynthetic, holotrophic, saprotrophic and parasitic. Some have mixotrophic
nutrition (holotrophic + saprobic). Chemosynthetic nutrition is lacking. Certain protozoans decompose organic
matter, such as cellulose, in the gut of termites and woodroaches. They live as symbionts. The photosynthetic,
floating protists are collectively called phytoplankton. They usually have a cell wall. The free-floating, holozoic
protozoans are collectively termed zooplankton. They lack cell wall to allow ingestion of particulate food.

(10) Reproduction : It is occurs by both asexual and sexual methods :

(i) Asexual reproduction : It is the most common method of reproduction in protists in which the genetic
constitutions of young ones remains the same as that of the parent. Under favourable environmental conditions,
they reproduce asexually several times a day resulting in population explosions. The major types of asexual
reproductions are as follows :

(a) Binary fission : The parent cell divides into two approximately equal daughter cells either transversely
(e.g., Paramecium), longitudinally (e.g., Euglena) or axially (e.g., Amoeba) by mitosis.

(b) Multiple fission : Division of parent cell into a number of daughter cells is called multiple fission. It
occurs in Amoeba.

(c) Plasmotomy : Fission of multinucleate protist into two or more multinucleate offsprings by the division of
cytoplasm without nuclear division is called plasmotomy. It occurs in Opalina.

(d) Budding : In this type of asexual reproduction, a small bud is formed from the parent body which
separates and develops into new individual. e.g., Paracineta, Arcella, etc.

(e) Spore formation : Sessile or stalked sporangia containing spores are formed in slime moulds. They
liberate the spores which can withstand a prolonged period of desiccation. On germination, each spore gives rise to
new individual. e.g., Slime moulds.

(ii) Sexual reproduction : Sexual reproduction is believed to have originated in primitive protists. It involve
meiosis (reduction division) and syngamy. It occurs following types.

(a) Isogamy : The two fusing gametes are structurally and functionally similar, e.g., Monocystis.

(b) Anisogamy : The two fusing gametes are similar but differ only in their size and/or motility, e.g.,
Ceratium.

(c) Oogamy : Large non-motile gametes are fertilized by smaller motile gametes, e.g., Plasmodium.

(11) Major group of protists : Unicellular protists have been broadly divided is to three major grous

(i) Photosynthetic protists : Protistan algae e.g. Dinoflagellates (i.e. Ceratium, Glenodinium,
Gymnodinium, Gonyaulax, Noctiluca and Peridinium), Diatoms (Navicula, Nitzchia, Melosira, Cymbella,
Amphipleura, Pinnularia) and Euglenoids or Euglena like flagellates (Euglena, Eutreptia, Phacus, Peranema).

(ii) Consumer protists : Slime moulds or Myxomycetes, e.g., Physarum, Physarella.

(iii) Protozoan protists : It is include four phyla – Zooflagellata (e.g., Trypanosoma, Giardia,
Trichonympha, Trichomonas, Leishmania etc.), Sarcodina (e.g., Amoeba, Entamoeba, Pelomyxa, Mestigamoeba
etc.), Sporozoa (e.g., Plasmodium, Monocystis, Eimeria etc. all are endoparasites) and Ciliata (e.g., Paramecium,
Vorticella, Opalina, Podophyra etc.).

Dinoflagellates (Division-Pyrrophyta)

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(1) Habit and Habitat : This is well defined group of unicellular, golden-brown photosynthetic organisms.
Majority of them are motile and flagellated but a few are non-motile and non-flagellated. Flagellated forms exhibit
peculiar spinning movement. Hence, they are called whorling whips. The group includes about 1000 species.
Most of them are marine but some occur in fresh water. Majority of the forms are planktonic and cover the surface
of water body imparting them the characteristic colours.

(2) Structure

(i) Cell wall : The cell wall of dinoflagellates, if present, is composed of a number of plates made up of
cellulose. It is called theca or lorica. The theca contains two grooves-longitudinal sulcus and transverse girdle or
annulus. The cell surface usually bears sculpturing and hexagonal platelets.

(ii) Flagella : Usually the cells possess two flagella which are of different types (heterokont). One flagellum is

transverse which arises from an anterior point in the transverse girdle. It is Epivalve Transverse
helical in form and ribbon-furrow and trails behind the cell. It is narrow, flagellum

smooth and acronematic type. Both the flagella arise through pores in

lorica.

(iii) Nucleus : Cells possess a relatively large and prominent nucleus Hypovalve
known as mesokaryon. The interphase nucleus has condensed
chromosomes which lack histones. Longitudinal
flagellum

(a) (b)

(iv) Plastids : There are numerous discoid chloroplasts without
pyrenoids. They are yellow-brown to dark-brown in colour due to
presence of characteristic pigments – Chlorophyll a, c, α - carotene and
xanthophylls (including dinoxanthin and peridinin).

(v) Reserve food : The reserve food material is starch or oil. (c) (d)

(vi) Pusule : The cells possess an osmoregulatory organelle called Fig : Some dinoflagellates (a) Glenodinium
pusule which superficially looks like contractile vacuole. (b) Peridinium (c) Gynnodium
(d) Gonyaulax
The cells posses mitochondria, ribosomes and Golgi bodies. They
also possess mucilage bodies or vesicles below the cell membrane.

(3) Nutrition : In dinoflagellates it is mainly holophytic or photosynthetic. However, some forms are saprobic,
parasitic, symbiotic or holozoic. For example, an colourless Blastodinium is parasite on animals.

(4) Reproduction

(i) Asexual reproduction : Dinoflagellates reproduce asexually through cell division or by the formation of
zoospores and cysts.

The cell division starts from posterior end. During cell division, centromeres and spindle are not seen. The
spindle is replaced by cytoplasmic microtubules. During mitosis, the chromosomes break up into pairs of romatids.
The nuclear envelops and nucleolus persists during divison.

(ii) Sexual reproduction : If it is occurs, is isogamous or anisogamous. Two cells conjugate by a conjugation
canal where the two amoeboid gametes fuse to form a diploid zygote. Life cycle involves zygotic meiosis (e.g.,
Ceratium, Gymnodinium etc.) or gametic meiosis (e.g. Noctiluca).

Diatoms (Division-Bacillariophyta)

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(1) Habit and Habitat : Most of the diatoms occur as phytoplanktons both in fresh and marine waters. A
few forms occur as benthos the bottom of water reservoirs. Some are terrestrial and grow on moist soil. Diatoms
constitute a major part of phytoplankton of the oceans. It is estimated that a 60 ton blue whale may have
approximately 2 tons of plankton (mostly diatoms) in its gut.

(2) Structure

(i) Shape : The cells of diamots are called frustules or shell. They are microscopic, unicellular, photosynthetic
organisms of various colours and diverse forms. They may be circular, rectangular, triangular, elongated, spindle-
shaped, half-moon shaped, boat-shaped or filamentous.

(ii) Symmetry : They exhibit mainly two types of symmetry-radial symmetry as in centrales (e.g. Cyclotella)
and isobilateral symmetry as in Pennales (e.g. Pinnularia).

(iii) Cell wall : The cells of diatoms are called frustules. The cell wall is chiefly composed of cellulose
impregnated with glass-like silica. It shows sculpturings and ornamentations. It is composed of two overlapping
halves (or theca) that fit togather like two parts of a soap box. The upper half (lid) is called epitheca and the lower
half (case) is called hypotheca.

(iv) Flagella : Diatoms do not possess flagella except in the reproductive stage. They show gliding type of
movement with the help of mucilage secretion. They float freely on the water surface due to presence of light weight
lipids.

(v) Nucleus : Each cell has a large central vacuole in which a prominent nucleus is suspended by means of
cytoplasimc strands. The cells are diploid (2 N). In case of centrales, the nucleus lies in the peripheral region.

(vi) Plastids : The cells possess plate-like or discoid chromatophores (or chloroplasts). They contain
Chlorophyll a, Chlorophyll c, carotenes, diatoxanthin, diadinoxanthin and fucoxanthin (chlorophyll b is absent).

(vii) Reserve food : The reserve food material is oil and a polysaccharide – chrysolamisarin (or
leucosin).

(3) Reproduction

(i) Asexual reproduction : The most common method of multiplication is binary fission (cell division) that
occurs at night. In this process, each daughter individual retains one half of the parent cell and the other half is
synthesized i.e. epitheca is retained and the hypotheca is synthesized. As a result, one of the two daughter
individual is slightly smaller than the parent cell and there is gradual reduction in the frustule over the generations.
However, the normal size is maintained by – formation of rejuvenescent cells (auxospores), growth of protoplast
secreted from the frustule and secretion of new frustule of larger size.

(ii) Sexual reproduction : Reproduction takes place by the fusion of gametes. Meiosis is gametic i.e. takes
place during the formation of gametes. The diploid nucleus of parent cell divides by meiosis into 2 or 4 daughter
cells. Out of 4 haploid daughter nuclei only one or two survive and rest degenerate. Thus they produce only one or
two gametes. The gametes may come out by an amoeboid movement and fuse externally in pairs within a
mucilaginous sheath to produce zygote. The diploid zygote then a transformed into auxospore.

Important Tips

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• The term prokaryotes and eukaryotes were coined by Fott.
• In five kingdom system of classification, the main basis of classification is structure of nucleus.
• Gold Fuss give the term 'Protozoa'.
• Ernst Haeckel proposed the term 'Protista'.
• Photosynthetic protists fix about 80% of CO2 in the biosphere.
• Protistology : Study of protists.
• Monerology : Study of monerans.
• Slime moulds possess animal like as well as fungi like character.
• Euglenoids possess plant like as well as animal like characters.
• De Bary (1887) classified slime moulds as a animal and called them 'Mycetozoa'.
• Macbrid coind the term 'Myxomycetes' (Slime moulds).
• Dinoflagellates, due to spinning caused by activity of transverse flagellum (in cingulum/annulus) and longitudinal flagellum (in sulcus),

represent whorling whips.
• Dinoflagellates with bioluminescence/phosphorescence due to light producing protein luciferin are called fire algae. e.g. Noctiluca,

Pyrocystis, Pyrodinium etc.
• Leeuwenhock (1674, 1675, 1681) was first to observe and sketch protozoan protists including Vorticella and Giardia.
• Acellular organisms do not contain cellular structure e.g., viruses or not considered as cells but as complete organisms e.g., protists.
• Wall-less multicellular protoplasm of acellular slime moulds having branched veins and with process of cyclosis are called

phaneroplasmodium.
• Dinoflagellates symbionts in other protists and invertebrates are called zooxanthellae.
• Some dinoflagellates produce blooms or red tides. e.g. Gonyaulax, Gymnodinium etc.
• Silicon is present in the frustule of diatoms.
• Auxospones are formed by diatoms.
• Noctiluca dinoflagellate is called 'night light'.
• Diatoms are emploid as a source of water glass or sodium silicate.
• Ganobacteria term was coined by IBCN (1978).

Kingdom fungi.

(1) Introduction : The science dealing with the study of fungi is called as mycology. The knowledge of fungi
to mankind dates back to prehistoric times. Clausius, 1601 may be regarded as one of the earliest writers to describe
fungi. Bauhin (1623) also included the account of known fungal forms in his book Pinax Theatric Botanica. The
fast systematic account of fungi came from Pier Antonio Micheli (1729) who wrote 'Nova Plantarum Genera'. He
is described by some workers as founder or mycology. Linnaeus (1753) also included fungi included fungi in his
'Species Plantarum'. Elias Fries (1821-31) gave a more detailed account of fungi in his 'Silloge Fungorum' in
25 volumes describing some 80,000 species of fungi. This work remains unparalleld even today.

(2) Thallus organization : The plant body of true fungi (Eumycota), the plant body is a thallus. It may be
non-mycelial or mycelial. The non-mycelial forms are unicellular, however, they may form a
pseudomycelium by budding. In mycelial forms, the plant body is made up of thread like structures called hyphae
(sing. hypha). The mycelium may be aseptate (non-septate) or septate. When non-septate and multinucleate, the
mycelium is described as coenocytic. In lower fungi the mycelium is non-septate e.g., Phycomycetae. In higher

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forms it is septate e.g., Ascomycotina, Basidiomycotina and Deuteromycotina. In some forms the plant body is
unicelled at one stage and mycelial at the other. Their organization is sometimes described as dimorphic.

Holocarpic and Eucarpic : When the entire mycelium is converted into reproductive structure, the thallus is
described as holocarpic. However, if only a part of it becomes reproductive, the thallus is called as eucarpic. The
eucarpic forms may be monocentric (having a single sporangium) or polycentric (having many sporangia).

(3) Specialised formation : In higher forms the mycelium gets organised into loosely or compactly woven
structure which looks like a tissue called plectenchyma. It is of two types :

(i) Prosenchyma : It comprises loosely woven hyphae lying almost parallel to each other.

(ii) Pseudoparenchyma : If the hyphae are closely interwoven, looking like parenchyma in a cross-section, it
is called as pseudoparenchyma.

In addition to above, the fungal mycelium may form some specialized structures as under :

(a) Rhizomorphs : Its a 'root-like' or 'string-like' elongated structure of closely packed and interwoven
hyphae. The rhizomorphs may have a compact growing point.

(b) Sclerotia : Here the hyphae gets interwoven forming pseudoparenchyma with external hyphae becoming
thickened to save the inner ones from desiccation. They persist for several years.

(c) Stroma : It is thick mattress of compact hyphae associated with the fruiting bodies.

(4) Cell organization : The cell wall of fungi is mainly made up of chitin and cellulose. While chitin is a
polymer of N-acetyl glucosamine, the celulose is polymer of d-glucose. Precisely, the cell wall may be made up of
cellulose-glucan (Oomycetes), chitin chitosan (Zygomycetes) mannan-glucan (Ascomycotina), chitin-mannan
(Basidiomycotina) or chitin-glucan (some Ascomycotina, Basidiomycotina and Deuteromycotina). Besides, the cell
wall may be made up of cellulose-glycogen, cellulose-chitin or polygalactosamine-galactan.

In higher fungi, where the mycelium is septate, the septa are of several types :

(i) Solid septum : It has no perforations.

(ii) Perforated septum : It has several perforations.

(iii) Acomycetean septum : It has a single large pore in the centre of the septum.

(iv) Bordered pit type septum : It has a perforation in the septum resembling the bordered pit of tracheary
elements.

(v) Dolipore septum : It has a single barrel shaped Plasma Vacuole Endoplasmic
pore in the septum due to thickened rim. The pore has a cap membrane reticulum
of ER called parenthosome.

The cell wall is closely associated with the inner layer, the Hyphal wall Mitochondria Ribosome Nucleus Microbodies
plasma membrane. In fungi, specialized structure called Fig : Diagrammatic electronmicrograph of a
lomasomes are also found associated to the plasma fungal cell
membrane. They appear to be as infoldings or invagination of
the membrane. Almost similar structures called
plasmalemmasomes are also found associated to the
membrane. The cell contains one or more well defined

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eukaryotic nuclei. In fungi the nuclei show intranuclear mitosis which is sometimes referred to as karyochorisis.
They also contains mitochondria, E.R., ribosomes, microbodies, lysosomes, vacuoles and crystals of reserve food
particles (glycogen, lipid etc.). The cells lack golgi and chloroplast and therefore, chlorophyll and starch grains are
also absent. However, a reddish pigment, neocercosporin has been isolated from the fungus Cercospora kikuchii.
The vacuoles are bound by tonoplast. The genetic material is DNA.

(5) Nutrition : The fungi are achlorophyllous organisms and hence they can not prepare their food. They live
as heterotrophs i.e., as parasites and saprophytes. Some forms live symbiotically with other green forms.

(i) Parasites : They obtain their food from a living Host cells
host. A parasite may be obligate or facultative. The
obligate parasites thrive on a living host throughout their (a) Haustoria Intercellular hyphae
life. The facultative parasites are infact saprophytes which Intracellular hyphae Haustorium (b)
have secondarily become parasitic. While the above Ectoparasitic hypha
classification is based on the mode of nutrition, however, on
the basis of their place of occurrence on the host, the Epidermal
parasites can be classified as ectoparasite, endoparasite cells
and hemiendoparasite (or hemiectoparasite). The
ectoparasites occur on the surface of the host tissue whereas (c)
the endoparasites are found within the host tissue. The
forms belonging to the third category are partly ecto- and Fig : Parasitic hyphae and haustorial
partly endoparasites. In parasitic forms. The mycelium may appendages : (a) Interacellular hyphae
occur within the host cells (intracellular) or in between the
host cells (intercellular). (b) and(c) Intercellular hyphae with
haustoria

Some forms produce rhizoids for absorbing food. The parasitic fungi produce appressoria for adhering to
the host. For absorbing food, the obligate parasites produce haustoria. As a result, the plasma membrane of the
host cell becomes convoluted but it does'nt break. The fungal cell wall also remains intact. The haustoria may be
finger-like, knob-like or branched. Each haustorium is distinguishable into a base, stem and body.

(ii) Saprophytes : They derive their food from dead and decaying organic matter. The saprophytes may be
obligate or facultative. An obligate saprophyte remains saprophytic throughout it's life. On the other hand, a
facultative saprophyte is infact a parasite which has secondarily become saprophytic.

(iii) Symbionts : Some fungal forms grow in symbiotic association with the green or blue-green algae and
constitute the lichen. Here the algal component is photosynthetic and the fungal is reproductive. A few fungal
forms grow in association with the roots of higher plants. This association is called as mycorrhiza. They are two
types – Ectotrophic mycorrhiza and Endotrophic mycorrhiza e.g., (VAM).

(6) Reproduction : The fungi may reproduce vegetatively, asexually as well as sexually :

(i) Vegetative reproduction

(a) Fragmentation : Some forms belonging to Ascomycotina and Basidiomycotina multiply by breakage of
the mycelium.

(b) Budding : Some unicelled forms multiply by budding. A bud arises as a papilla on the parent cell and
then after its enlargement separates into a completely independent entity.

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(c) Fission : A few unicelled forms like yeasts and slime molds multiply by this process.
(d) Oidia : In some mycelial forms the thallus breaks into its component cells. Each cell then rounds up into
a structure called oidium (pl. oidia). They may germinate immediately to form the new mycelium.
(e) Chlamydospores : Some fungi produce chlamydospores which are thick walled cells. They are
intercalary in position. They are capable of forming a new plant on approach of favourable conditions.

(ii) Asexual reproduction

(a) Sporangiospores : These are thin-walled, non-motile spores formed in a sporangium. They may be uni-
or multinucleate. On account of their structure, they are also called as aplanospores.

(b) Zoospores : They are thin-walled, motile spores formed in a zoosporangium. The zoospores are of several types :

 Uniflagellate with whiplash type flagellum e.g., Allomyces.

 Uniflagellate with tinsel type flagellum e.g., Rhizidiomyces.

 Biflagellate with a tinsel type and a whiplash type flagella e.g., Saprolegnia.

 Biflagellate with two whiplash type flagella e.g., Plasmodiophora.

(c) Conidia : In some fungi the spores are not formed inside a sporangium. They are born freely on the tips
of special branches called conidiophores. The spores thus formed are called as conidia. On the basis of
development, two types of conidia are recognised namely thallospores and blastospores or true conidia.

Thallospores : In some forms the thallus itself forms spore like bodies called thallospores. The thallospore
are of two types namely arthrospores and chlamydospores.

 Arthrospores : They are thinwalled spores formed in basipetal order e.g., Endomyces.

 Chlamydospores : Some of the hyphal cells are converted into thick walled chlamydospores. They may
be terminal or intercalary e.g., Ustilago, Saprolegnia.

Blastospores : They develop on conidiophores in acropetal or basipetal succession. They are of two types –

 Porospores : When the blastospores develop by the balooning of the inner wall of conidiophore, it is
called as porospore e.g., Alternaria.

 Phialospore : On the other hand, when the first conidium carries the broken parent wall of conidiophore
and subsequent conidia possess a new wall, such basipetally formed conidia are called as phialospore e.g.,
Aspergillus.

Bi-celled conidia are formed in Trichothecium. In Fusarium it is possible to differentiate smaller microconidia
from larger macroconidia. Sometimes the conidiophores form specialised structures as under :

Synnema or Coremium : Here the conidiophores get arranged in closely placed parallel plates.

Acervulus : It is a cushion-shaped mass of hyphae having closely packed conidiophores.

Sporodochium : It is also a cushion-shaped acervulus like structure having loosely arranged conidiophores.

Pycnidium : It is pitcher-shaped, embedded body which opens to exterior by a pore called ostiole. It is lined
by conidiogenous hyphae. The conidia developing in pycnidia are often described as pycniospores.

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(iii) Sexual reproduction : With the exception of Deuteromycotina (Fungi imperfecti), the sexual
reproduction is found in all groups of fungi. During sexual reproduction the compatible nuclei show a specific
behaviour which is responsible for the onset of three distinct mycelial phases. The three phases of nuclear behaviour
are as under :

Plasmogamy : Fusion of two protoplasts.

Karyogamy : Fusion of two nuclei.

Meiosis : The reduction division.

These three events are responsible for the arrival of the following three mycelial phases :

Haplophase : As a result of meiosis the haploid (n) or haplophase mycelium is formed.

Dikaryotic phase : The plasmogamy results in the formation of dikaryotic mycelium (n + n).

Diplophase : As a result of karyogamy the diplophase mycelium (2n) is formed.

In some fungi plasmogamy, karyogamy and meiosis do occur in a regular sequence but not at specified time
or points in life cycle. Such a cycle is described as parasexual cycle and phenomena celled parasexuality recorded
by Pontecorvo and Roper.

The fungi reproduce sexually by the following methods :

 Isogamy : It involves fusion of two morphologically similar flagellate gametes.

 Anisogamy : Here the two gametes are motile but morphologically dissimilar. The larger gamete may be
called as female and the smaller one as male.

 Heterogamy : It involves fusion of a non-motile female gamete (egg) with the motile male gamete
(antherozoid). While the male gamete is formed inside the antheridium, the female is produced inside
the oogonium. Both the sex organs are unicelled structure.

 Gametangial contact : It involves fusion of two gametangia. In lower forms the female gametangium is
called as oogonium. The male gametangium is termed as antheridium. A contact develops in between
the two gametangia and then the male nucleus is transferred into the female directly or through a tube.

 Gametangial copulation : In this case the fusion occurs in between the two gametangia. When it occurs
in some holocarpic forms where the entire thallus acts as gametangium, the phenomenon is called as
hologamy. In others, dissolution of cell wall in between the two gametagial brings about gametangial
copulation.

 Spermatization : Here the uninucleate male gametes called spermatia are formed in special structures
called spermogonia or pycnidia. The female gametangium is called as ascogonium which has a long
neck called trichogyne. The spermatium attaches itself with the trichogyne and transfers the male nucleus,
thus bringing about dikaryotisation.

 Somatogamy : In higher fungi there is reduction of sexuality to the maximum level. Here two hyphae of
opposite strains are involved in fusion thus
bringing about dikaryotization.

(7) Clamp connection : In Basidiomycotina,
the dikaryotic cells divide by clamp connections.
They were first observed by Hoffman, (1856) who

Chapter 7 100Dikaryotic Pouch Conjugate Septation Dissolution of
cell formation division lateral septum

Fig : Various stages in the formation of clamp connections

Biological Classification Part 1

named it as 'Schnallenzellen' (buckle-joints). A lateral pouch like outgrowth arises which projects downward like a
hook. This pouch or clamp becomes almost parallel to the parent cell. The two nuclei now undergo conjugate
division in such a way that one spindle lies parallel to the long axis of the cell and the other somewhat obliquely. As
a result, one daughter nucleus enters into the clamp. Now, septae appear separating the clamp and the lower
hyphal cell. The upper cell has both the nuclei. The clamp with a nucleus now fuses with the lower cell. The septum
between the pouch and the lower cell is dissolved and thus the lower cell now contains both the nuclei of opposite
strains. The entire process takes some 23-45 minutes.

(8) Heterothallism : Blakeslee, (1904) while working with Mucor sp. observed that in some species sexual
union was possible between two hyphae of the same mycelium, in others it occured between two hyphae derived
from 'different' spores. He called the former phenomenon as homothallism and the latter as heterothallism.
Thus, the homothallic species are self-fertile whereas the heterothallic are self sterile. In heterothallic species the two
'thalli' are sexually incompatible. They are said to belong to opposite strains. Blakeslee designated them as + and –
i.e., belonging to opposite strains or mating types. Whitehouse, (1949) differentiated the phenomenon into two
categories as under :

(i) Morphological heterothallism : When male and female sex organs are located on different 'thalli' the
heterothallism is said to be morphological. Such species are generally described as dioecious.

(ii) Physiological heterothallism : In bisexual forms the two sex organs may be located on the same
'thallus' or on different 'thalli'. In some forms the two sexes even when present on the same 'thallus' are unable to
mate, the heterothallism is said to be physiological. Such forms are self-sterile as they need genetically different
nuclei. Such nuclei are absent when the same 'thallus' forms the two sex organs. Heterothallic fungi may be bipolar
or tetrapolar.

(9) Classification of fungi : It is based largely on the characteristics of the life cycle involved like.

Nature of somatic phase, kinds of asexual spores, kinds of sporangia, nature of the life cycle and presence or
absence of perfect or sexual stage.

Kingdom Fungi

Sub-kingdom

Gymnomycota Oomycota Eumycota
(Myxomycota) Mycelium Mycelium
Slime Moulds now aseptate septate
excluded from fungi and
placed under protista

Phycomycetes Zygomycetes Mycophycophyta
(Oomycetes (Conjugation fungi) (Dual organisms)
Algal fungi) e.g. Rhizopus, Mucor
Phytophthora, Lichens, e.g.,
Albugo, Pythium Usnea, Parmelia

Chapter 7 Deuteromycota Ascomycota Basidiomycota
(Fungi imperfecti) (Sac fungi) (Club fungi)
Sexual reproduction absent, Aspergillus, Puccinina,
e.g., Alternaria, Cercospora, Penicillium, Ustilago,
Microsporum, Trichophyton. Agaricus
Neurospora
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Biological Classification Part 2

(10) Salient features of classes

(i) Phycomycetes (Oomycetes/Egg fungi) : It is also called lower fungi, mycelium is coenocytic. Hyphal
wall may contain chitin or cellulose (e.g., Phytophthora). Asexual reproduction occurs with the help of conidio-
sporangia. Under wet conditions they produce zoospores. Under dry conditions, the sporangia directly function as
conidia. Zoospores have heterokont flagellation (one smooth, other tinsel). Sexual reproduction is oogamous. It
occurs by gametangial contact where male nucleus enters the oogonium through a conjugation tube. The fertilized
oogonium forms oospore. e.g., Sapolegnia, Albugo (Cystopus), Phytophthora, Phythium, Sclerospora.

(ii) Zygomycetes (Conjugation fungi) : Mycelium is coenocytic. Hyphal wall contains chitin or fungal
cellulose. Motile stage is absent. Spores (Sporangiospores/aplanospores) are born inside sporangia. Sexual
reproduction involve fusion of coenogametes through conjugation (Gametangial copulation). It produces a resting
diploid Zygospore. On germination, each zygospore forms a germ sporangium at the tip of a hypha called
promycelium e.g., Mucor, Rhizopus.

(iii) Ascomycetes (Ascus : sac, mycete : fungus) : These are unicellular as well as multicellular fungi. In the
latter, mycelium is septate. The asexual spores formed in chains are called conidia. The spores are formed
exogenously, i.e. outside sporangium. They detach from the parent and form new mycelia. Sexual reproduction is
through ascospores, which are formed endogenously (within the mycelium) in a sac like structure called ascus (pl.
asci). The gametes involved in sexual reproduction are nonmotile compatible and are generally represented as +
and –. The fusion of gametes is followed by reductional division that produces haploid ascospores. The fruiting
body called ascocarp.

The ascocarp are of four types :

(a) Cleistothecium : It is an ovoid or spherical fruiting body which remains completely closed e.g.,
Aspergillus.

(b) Perithecium : It is a flask shaped fruiting body which opens by a single pore called ostiole. It is lined by
sterile hyphae called paraphyses. The asci are also mixed with paraphysis e.g., Cleviceps.

(c) Apothecium : It is a saucer-shaped fruiting body. The asci constitute the fertile zone called hymenium
e.g., Peziza.

(d) Ascostroma : It is not a distinct fruiting body. It lacks its own well defined wall. The asci arise directly with
a cavity (locule) of stroma. It is also called as pseudothecium e.g., Mycosphaerella.

(iv) Basidiomycetes : They are the most advanced fungi and best decomposers of wood. These are called
club fungi because of a club shaped end of mycelium known as basidium. They have septate multinucleated
mycelium. Septa possess central dolipores and Lateral clamp connections. The sexual spores called basidiospores
are generally four in number. They are produced outside the body (exogenuous) unlike ascomycetes where they are
endogenous. Two compatible nuclei fuse to form zygote, which undergoes meiosis and forms four basidiospores.
The fruiting body containing basidia is a multicelular structure called basidiocarp. The common members are
edible mushrooms (Agaricus). Smut and Rust.

(v) Deuteromycetes (Fungi inperfecti) : The group include all those fungi in which sexual or perfect stage
is not known. Mycelium is made of septate hyphae. Asexual reproduction commonly occur by means of conidia.

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Biological Classification Part 2

(11) Economic importance

(i) Harmful aspects

(a) Crop diseases : Several important crop plants are destroyed due to fungi diseases. Some important ones
are listed here under :

Some plant disease caused by fungi

Disease Crop Causal organism

White rust of crucifers Family Cruciferae Albugo candida or Cystopus

Early blight of potato Potato Alternaria solani

Tikka disease of groundnut Groundnut Cercospora personata or C. arachidicola

Ergot disease of rye Rye Claviceps purpurea

Red rot of sugarcane Sugarcane Colletotrichum falcatum

Powdery mildew Wheat Erysiphe polygoni

Powdery mildew Peas Erysiphe graminis

Wilt of gram Gram Fusarium orthaceras

Bankanese disease and food rot of rice Rice Gibberella fujikuri

Leaf spot of oats Oats Helminthosporium avenae

Brown leaf spot of rice Rice Helminthosporium oryzae

Flag smut of wheat Wheat Urocystis tritici

Flag smut of oat Oats Ustilago avenae

Covered smut of barley Barley Ustilago hordei

Covered smut of oat Oats Ustilago kolleri

Smut of sugarcane Sugarcane Ustilago scitaminea

Loose smut of wheat Wheat Ustilago tritici

Late blight of potato Potato Phytophthora infestans

Club rot of crucifers Cabbage Plasmodiophora brassicae

Downy mildew of grapes Grapes Plasmopara viticola

Black rust of wheat Wheat Puccinia graminis-tritici

Brown rust of wheat Wheat Puccinia recondita

Yellow rust of wheat Whet Puccinia striiformis

Damping off of seedlings Various seedlings Pythium sp.

Blast of rice Rice Pyricularia oryzae

Grain smut of jowar Jowar Sphacelotheca sorghi

Wart disease of potato Potato Synchytrium endobioticum

Leaf curl of peach Peach Taphrina deformans

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(b) Diseases in human beings : Several diseases in human beings are found to be caused by fungi infecting
different parts of the body. Some of them are given hereunder as :

Disease Causal organism Place of infection
Athletes foot
Ring worm Epidermophyton floccosum Foot

Moniliasis Trichophyton sp., Microsporum sp., Epidermophyton sp., Skin
Aspergillosis Myxotrichum sp.
Torulosis
Candida albicans Nails

Aspergillus niger, A. flavus, A. terrus Lungs

Cryptococcus neofomans Lungs, CNS

(c) Spoilage of food : Some forms like Rhizopus, Mucor, Aspergillus, Cladosporium grow on food articles
and spoil them. Cladosporium grows even at a temperature of – 6°C.

(d) Mycotoxins : Some fungi produce toxic metabolites which cause diseases in human beings. They usually
contaiminate cereals and oil seed crops. Four types of mycotoxins are generally identified :

 Aflotoxins : e.g., Aflotoxin B1, B2, M1, M2, G1, G2; They are produced mainly by Aspergillus flavus and A.
parasiticus. They are well know for their carcinogenic effect.

 Zearalenone : It is produced by Fusarium sp.

 Ochratoxins : They are produced by Aspergillus and Pennicillium sp.

 Trichothecenes : They are produced by fungi like Cephalosporium, Fusarium etc.

(e) Poisonous fungi : Some fungi are extremely poisonous e.g., Amanita phalloides ('death cup'). A. verna,
Boletus satanus. Forms like Coprinus, Psilocybe are less poisonous. The fungus Amanita phalloides produces toxins
like α-amanitin, phalloidin etc. which are very poisonous.

(f) Ergotism :The fungus causing 'ergot' disease of rye (Secale) is Cleviceps purpurea. It contains many
poisonous alkaloids in their sclerotia. It causes poisoning in human beings. It's acute condition is called as 'St.
Anthony's fire'.

(g) Hallucinogenic drugs : The hallucinogenic drug LSD (Lysergic acid Diethylamide) is extracted from
Cleviceps purpurea as also from Inocybe. Besides, the mushroom Amanita muscaria is also hellucinogenic.

(h) Rotting of wood : Rotting of wood is caused due to degradation of lignin and cellulose. It is brought
about fungi like Polyporus sp., Fomes sp. and Ganoderma sp., Forms like Fusarium, Penicillium leave stains on the
wood.

(i) Allergies : Spores of Mucor, Aspergillus, Penicillium, Puccinia etc., present in the atmosphere cause
allergies.

(j) Deterioration of articles : Forms like Aspergillus, Cladosporium, Rhizopus, Chaetomium, Alternaria
deteriorate cork, rubber, leather, textile and even plastics.

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Biological Classification Part 2

(ii) Useful aspects

(a) Food : Forms like Agaricus bisporus, Morchella esculenta, Lentinus edodes, Clavatia gigantia, Volvariella
volvacea are edible. The yeast Saccharomyces cerevisiae is used for making 'yeast cake'. When mixed with cereal
flour, the yeasts produce a preparation called incaparina. The Single Cell Protein (SCP) obtained from yeasts,
Penicillium, Fusarium etc. are used as substitute of protein food, Rhizopus oligosporus, when processed with
soybeans yield a food preparation called 'tempeh'. It has high protein contents.

(b) Flavoring of food : Penicillium roquefortii and P. camemberti are employed for flavoring cheese.

(c) Brewing and baking : Yeasts are generally used in bakeries and breweries. The sugars are fermented by
yeasts into alcohol and CO2. While the former in main product of breweries CO2 is mainly useful in bakeries.

(d) Organic acids : Several organic acids are commercially produced by fungi, some of which are given
hereunder :

Organic acids Source
Citric acid Aspergillus niger
Gallic acid Penicillium glaucum
Gluconic acid Aspergillus niger, Penicillum purpurogenum
Fumaric acid Rhizopus stolonifer, Mucor sp.
Lactic acid Rhizopus nodosus
Kojic acid Aspergillus flavus
Oxalic acid Aspergillus niger
Acetic acid Candida sp.

(e) Antibiotics : The antibiotics are chemicals produced by living organisms that kill other living organisms.
The first known antibiotic is penicillin that was extracted from Penicillium notatum by A. Fleming, (1944). Raper
(1952) also extracted the same antibiotic from P. chrysogenum. Besides, several other antibiotics have been
extracted since then.

Antibiotics Source

Griseoflavin Penicillium griseofulvum

Citrinin P. citrinum

Cephalosporin Acremonium sp.

Ramycin Mucor ramannianus

Proliferin A. proliferans

Jawaharin A. niger

Patulin Aspergillus clavatus

Fumigatin Aspergillus fumigatus

Viridin Gliocladium virens

Penicillin Penicillium chrysogenum, Penicillium notatum

Trichothecin Trichothecium roseum

Campestrin Agaricus campestris

Frequentin Aspergillus cyclopium

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