General Properties of Bases
Physical Properties
a. They are soapy to touch.
b. They have bitter taste.
c. They turn red litmus to blue.
d. They turn methyl orange yellow and phenolphthalein pink.
e. They turn turmeric paper brown.
Chemical Properties
a) They produce hydroxyl ions (OH-) in aqueous solution.
b) They neutralizes acids to form salt and water.
KOH + HCl → KCl + H2O
Water
Potassium Hydrochloric Potassium
hydroxide acid chloride
2NaOH + H2SO4 → Na2SO4 + 2H2O
Sodium Sulphuric Sodium Water
hydroxide acid sulphate
c) Bases react with carbon dioxide to form carbonate.
K2O + CO2 → K2CO3
d) They react with metals like zinc and aluminium and produce hydrogen.
Zn + 2NaOH → NaZnO2 + H2
Sodium zincate
2Al + 2NaOH + 2H2O → 2NaAlO2 + 2H2
Sodium aluminate
e) When a base is heated with an ammonium salt, ammonia gas is given off. It can
be recognized by its extremely pungent smell.
NaOH + NH4Cl → NaCl + H2O + NH3
Sodium
Sodium Ammonium Water Ammonia
hydroxide chloride chloride
Ca(OH)2 + (NH4)2CO3 → CaCO3 + 2H2O + 2NH3
Calcium Ammonium Calcium Water Ammonia
hydroxide carbonate carbonate
Blooming Science & Environment Book 8 173
Some bases which are commonly used in daily life:
Bases Uses
1. Sodium hydroxide 1. In the manufacture of soap.
2. Potassium hydroxide 2. Fire wood ash- filtered wood ash is used for washing
clothes in rural area.
3. Aluminium hydroxide
3. As medicine (antacid) for gastric patients.
Salt
A salt is a compound formed by the partial or complete neutralization of an acid by
the base. A salt is a neutral substance. It does not have acidic and basic properties.
Some salts are salty while most of the salts taste bitter. Sodium chloride, potassium
chloride, calcium chloride, calcium sulphate etc. are examples of salts.
NaOH + H2SO4 → NaHSO4 + H2O
Water
Sodium hydroxide Sulphuic Acid Sodium Bisulphate
2NaOH + H2SO4 → Na2SO4 + 2H2O
Water
Sodium Sulphate
Types of Salt
There are three types of salt.
1. Normal salt: Normal salt is produced by the complte displacement of
hydrogen atom of an acid by a metal, e.g., NaCl, K2SO4, KNO3, NH4Cl, KCl,
etc.
2. Acidic salt: Acid salt is produced by the partial displacement of replaceable
hydrogen atom present in the acid molecule by a metal or electropositive radical.
It is acidic in nature e.g., NaHSO4 (sodium hydrogen sulphate), Na2HPO4
(sodium hydrogen phosphate), KHSO4 (potassium hydrogen sulphate), etc.
3. Basic salt: Basic salt is produced by the partial replacement of hydroxyl group
of the base by the acid radical. It is alkaline in nature, e.g., 2PbCO3. Pb (OH)2
(white lead), CH3COONa (sodium acetate), [K2SO4Al2(SO4)312H2O] (potash
alum) etc.
Properties of Salts
1. Some salts are salty in taste but most of the salts are bitter in taste.
2. Salts do not cause any change in the colour of indicators like litmus paper,
methyl orange and phenolphthalein.
3. Some salts are white while some salts are coloured.
4. Most of the salts are soluble in water.
174 Blooming Science & Environment Book 8
Some salts and their uses are given below:
Salts Uses
1. Sodium chloride As edible salts (table salt, rock salt)
2. Copper sulphate As an insecticide
3. Magnesium sulphate Used in constipation
4. Calcium sulphate Plastering fractured bones, in the manufacture of chalk
Indicator
An indicator is a substance which changes colour in the presence of acids or alkalis.
In the laboratory, we use three indicators. These are litmus, phenolphthalein and
methyl orange.
Indicator Acid Base
Red litmus No change in colour Blue colour
Blue litmus Red in colour No change in colour
Phenolphthalein Colourless Rose colour
Methyl orange Red in colour Yellow in colour
Apart from this, many other naturally occurring coloured substances can be used as
indicators. Turmeric powder mixed in water is a bright orange-yellow which turns a
brick red in the presence of alkalis. Many red or blue colored flowers contain natural
dyes which can be used as indicators. If you crush the petals and boil them in hot
water, you may be able to prepare the liquid as an indicator. Another such indicator
can be prepared by boiling, mashing and straining a finely chopped beetroot.
Universal Indicator Scan for practical experiment
A universal indicator is a mixture of several indicators and is
used to find the strengths of acidic and alkaline solution. An
indicator prepared by several ordinary indicators of different
colours is called universal indicator. It shows different
characteristic colours for each pH value of the solution. The visit: csp.codes/c08e17
red and dark or deep red colour shows acidity whereas blue
and dark or deep blue colour shows basicity. It shows green colour in neutral solution.
The colour changes from yellow to orange and then to red as the pH of the solutions
decreases from 7 to 1. The colour changes from blue to violet when pH increases
from 7 to 14.
Acidic Neutral Basic
pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
UI red pink orange yellow green greenish blue bluish violet
violet
pH Scale: Change of colour in the universal indicator (U.I) at different pH values
Blooming Science & Environment Book 8 175
The acidic and basic strength of solutions are compared with a number scale called
pH scale. It is a scale whose number ranges from 1 to 14. The value assigned to each
substance is called pH scale number. The number 7 (or pH value of 7) indicates
neutral substance. Distilled water has pH = 7 so it is neutral substance. The number
lower than 7 shows acidic substance and the number higher than 7 shows basic
substance. The lower the pH, the more acidic is the substance. The acidic strength of
solution increases gradually. HCl, a strong acid has pH-1, boric acid (a weak acid)
has pH 5.2. As the value increases towards 14 the basic strength of the solution also
increases. A strong base, sodium hydroxide solution has a pH-13 while ammonium
hydroxide, a weak base, has a pH-10.
pH meter
The pH of a substance can also
be measured by pH meter. The
pH of a solution is numbered in
pH meter, and hence it can be
read directly.
A pH paper is also used as
universal indicator. The pH Fig: pH meter
paper is dipped in the solution whose pH is to be measured. The colour of the pH
paper changes and this change in colour is compared with the coloured chart paper to
find the pH of the solution. The colour chart paper is a printed paper which contains
different pH numbers corresponding to different colours.
Main Points to Remember
1. Acids have a sour taste and turn blue litmus red. They react with metals to give
hydrogen, with carbonates to give carbon dioxide and with metallic oxides to
give a salt and water.
2. Bases are hydroxides of metals. They have a bitter taste and turn red litmus blue.
3. Bases which are soluble in water are called alkalis.
4. Acids give hydrogen ions (H+) and bases give hydroxyl ions (OH-) when
dissolved in water.
5. Bases react with acidic oxides to give salt and water and with ammonium salts
to give ammonia.
6. The reaction of an acid with a base to form a salt and water is called neutralization.
7. Common properties of acids are the properties of hydrogen ions, H+.
8. Phenolphthalein turns solution of any base to red in colour. There is no action
of acids on phenolphthalein.
176 Blooming Science & Environment Book 8
9. Some acids, bases and salts find use in daily life.
10. Salts can be prepared by the neutralization reaction between an acid and a base.
They can also be prepared by displacing the hydrogen of an acid by metal or by
the reaction between a metal oxide or another salt with an acid.
11. An indicator is a substance which changes its colour in acid and bases (alkalis).
PRO J ECTWORK
Make an indicator by extracting red cabbage juice. Use it to test various acids,
bases and salt and make a table to show the colour change.
Exercise
1. Answer the following questions.
a. What is an acid?
b. What is a base? What is an alkali?
c. Mention any two physical properties of a base.
d. Mention three indicators used in the laboratory.
e. Name any two salts that are used in our daily life.
f. What is the difference between base and alkali?
g. Name three acidic substances which are used in daily life.
h. What is universal indicator? Make a chart to show the effect of acid and
base on various indicators.
i. Name the acid found in milk, pickle, lemon and bhogate. Mention any
two bases that are used in our daily life.
j. How can you differentiate between acids and bases?
Red Blue
k. Water, sodium hydroxide and sulphuric acid B
are placed in the diagram below. If they show
change on litmus as shown in the diagram,
which beaker has acid and which has base? A C
l. Define organic and inorganic acids with
examples.
m. What is pH-scale? Define pH meter.
n. What change of colour would you except when the acid, base and salt are
placed in the various indicators. Show in the tabular form.
Blooming Science & Environment Book 8 177
2. Define the following.
a. Indicator b. Salt c. Alkali
d. Acid e. Base f. Basic salt
3. Give reasons.
a. All alkalies are bases but all bases are not alkalies.
b. Orange is sour in taste.
4. Name the following.
a. An acid b. A base c. An acidic salt
d. A basic salt e. Colourless indicator
f. Strong acid g. Strong base
Glossary
Acid : a substance that gives hydrogen ion (H+) in a aqueous solution
Base : metallic oxides and hydroxide in aqueous solution
Salt : a neutral substance formed by acid & base
Alkali : a soluble base
Indicator : a substance used to detect acid, base or salt by changing of its colour.
178 Blooming Science & Environment Book 8
Chapter
15 Some Useful Chemicals
Learning Outcomes Estimated Periods: 5+1
On the completion of this unit, the students will be able to:
describe properties of water.
define and differentiate hard and soft water.
tell different types of hardness of water.
describe and demonstrate process of removal of harness of water(By boiling
and using washing soda)
to tell the uses of some chemicals like sodium carbonate, sodium bicarbonate
and glycerol.
Water
Natural Water
Water is the commonest substance on the earth without water life on the earth is
impossible. Water plays vital role for the existence of plants and animals on the earth.
The natural sources of water are:
1. rain, 2. river and lakes, 3. springs,
4. wells are rarely found in pure state, 5. sea
Rainwater is considered
one of the purest form
of naturally occurring
water. Rain is produced Rain
by the condensation of
the water vapour present Cloud
in the air. As rainfall
takes place or after snow
melts on high peaks Vapour
in the Himalayas, the
water flows along the Water
surface of the earth and
brings different kinds of Fig: Water cycle
impurities. Some of the mineral and organic matters like clay, sand, straw, bacteria,
etc., remain suspended in it and make it muddy and unsafe to drink. Besides gases,
Blooming Science & Environment Book 8 179
the nature of the dissolved matter depends upon the type of the beds over which river
water passes.
Nearly one-third of the rainwater seeps into the ground through soft and loose strata
of sand, gravel and chalk. Soon it reaches some impermeable stratum of clay and
slate. It remains in the form of the water table. In some cases it remains trapped in
this layer and tries to escape out from the small cracks of rocks which we call spring.
The water in the well is one example of trapped water below the ground. Water from
wells has been used from time immemorial for drinking and irrigation purposes.
Rivers flow into the seas. The water becomes impure due to the accumulation of
varieties of impurities that have been dissolved.
Hard and Soft Water
Scan for practical experiment
Water is the best solvent and it is also known as universal
solvent. Because of its capacity to dissolve, many substances
are mixed with it. Some of the dissolved substances are useful
for plants and animals whereas some are very harmful. In most
of the cases, the salts of various metals are mixed in water.
These soluble salts of metals cause hardness in water. Soft visit: csp.codes/c08e18
water is the one which can produce lather with soap easily.
But hard water cannot produce lather as easily as soft water. These impurities form
a thick coat inside boilers.
Hardness of water is due to the presence of soluble salts of magnesium and calcium.
The salts of magnesium such as magnesium bicarbonate, magnesium chloride,
magnesium sulphate or the salts of calcium such as calcium bicarbonate, calcium
chloride, calcium sulphate dissolved in water bring hardness in water.
Hardness of water may be temporary or permanent. Temporary hardness is due
to the presence of salts such as calcium bicarbonate (Ca(HCO3)2) or magnesium
bicarbonate (Mg(HCO3)2). Temporary hardness can be removed easily.
Permanent hardness is due to the presence of salts such as magnesium chloride
(MgCl2), magnesium sulphate (MgSO4), calcium chloride (CaCl2) and calcium
sulphate (CaSO4) dissolved in water.
Removal of Temporary Hardness
This hardness present in water can be removed by using the following methods.
1. By Heating: Salts like calcium bicarbonate and magnesium bicarbonate
dissolved in water cause temporary hardness. While heating, soluble salts
of calcium and magnesium (bicarbonates) change into insoluble salts. The
chemical equations are given below.
180 Blooming Science & Environment Book 8
Calcium Bicarbonate Heat Calcium carbonate + Carbon dioxide + Water
Ca(HCO3)2 CaCO3 + CO2 + H2O
Magnesium Bicarbonate ∆ Magnesium Carbonate + Carbon dioxide + Water
Mg(HCO3)2 MgCO3 + CO2 + H2O
2. Treating with Lime Water: Temporary hardness of water can be removed by
treating it with lime water. The chemical equations are given below.
Calcium Bicarbonate + Calcium Hydroxide → Calcium Carbonate + Water
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O
Magnesium Bicarbonate + Calcium Hydroxide → Calcium Carbonate + Magnesium Carbonate + Water
Mg (HCO3)2 + Ca(OH)2 → CaCO3 + MgCO3 + 2H2O
Removal of Permanent Hardness
Permanent hardness of water cannot be removed by heating only. We know that
permanent hardness is caused by the presence of chlorides and sulphates of calcium
and magnesium. Soluble salts of calcium and magnesium are in turned to insoluble
salts by the following methods.
1. Treatment with Washing Soda
Soluble salts of calcium and magnesium change into insoluble salts due to the
treatment with sodium carbonate (washing soda).
Calcium Chloride + Sodium Carbonate → Calcium Carbonate + Sodium Chloride
CaCl2 + Na2CO3 → CaCO3 + 2NaCl
Calcium Sulphate + Sodium Carbonate→ Calcium carbonate + Sodium Sulphate
CaSO4 + Na2CO3 → CaCO3 + Na2SO4
Magnesium Chloride + Sodium Carbonate → Magnesium Carbonate + Sodium Chloride
MgCl2 + Na2CO3 → MgCO3 + 2NaCl
Magnesium Sulphate + Sodium Carbonate→ M agnesium Carbonate + Sodium Chloride
MgSO4 + Na2CO3 → MgCO3 + 2Na2SO4
2. Permutit Process
Permutit is the trade name for an artificially prepared sodium zeolite or sodium
aluminium orthosilicate obtained by fusing together sodium carbonate, silica
and alumina. Its composition resembles Na2Al2SiO8 or Na2Z, where, Z stands
for Zeolite = Al2SiO8. It possesses higher quantity of reactive with calcium and
magnesium ions forming insoluble calcium or magnesium zeolites.
Calcium salts + Sodium zeolite → Calcium zeolite + sodium salts
Ca++ + 2Na2Z → CaZ2 + 4Na
Magnesium salts + sodium zeolite magnesium zeolite + sodium salts
Mg++ + 2Na2Z → MgZ2 + 4Na
Blooming Science & Environment Book 8 181
Thus, by passing hard water through a cylinder packed with permutit, all the ions
of soluble salts of calcium and magnesium responsible for the hardness of water
are retained and replaced by sodium ions. In due course, however, the permutit is
exhausted or loses its capacity of reacting with these salts by having given up all
its sodium ions. This can be regenerated by soaking in a 10% solution of common
salt when the reverse change takes place and calcium and magnesium ions pass into
solution and sodium zeolite is formed again.
CaZ2 + 2NaCl → Na2Z + CaCl2
MgZ2 + 2NaCl → Na2Z + MgCl2
The resulting calcium and magnesium chlorides are washed out and the regenerated
permutit is used over again.
Advantages and Disadvantages of Hard Water
Advantages
1. Hard water contains calcium salt dissolved in it which helps to strengthen the
bones and teeth.
2. Water is somewhat tasty due to dissolved salts of calcium and magnesium.
3. Hard water is used in beer industries. Hard water Sodium
chloride
Disadvantages solution
1. Hard water leads to consumption of more soap Soft water
while washing clothes.
Permutit
2. A bright white cloth becomes dull due to the salts Coarse sand
dissolved in water.
Waste
3. In industries, due to hard water, the life of boilers Permutit Process
decrease. This is due to the calcium salt deposited during boiling.
Drinking Water
Water is used for many purposes. The water that contains micro-organism should not
be used for drinking. The water containing micro-organisms is known as contaminated
water. Contaminated water carries many diseases such as cholera, typhoid, and many
more. Many other diseases are transmitted through water. To keep healthy, we must
drink safe and clean water. The drinking water must be boiled. During boiling, the
micro-organisms are killed. It is advised that everyone should drink boiled water to
stay away from diseases that transmit through water.
182 Blooming Science & Environment Book 8
Sodium Carbonate
Sodium carbonate is a very useful chemical compound. It is also called as ‘Washing
soda’ . It is a compound of sodium metal with molecular formula Na2CO3. It is basic
in nature and available in the form of white powder.
Uses
1. Sodium carbonate is used in making soap.
2. It is used in manufacture of different glasses.
3. It is used in paper industries.
4. It is used to remove hardness of water.
5. It is used in the preparation of caustic soda.
Sodium bicarbonate
Sodium bicarbonate is a very useful chemical. It is also called ‘Edible soda’or’Baking
soda.’ Its molecular formula is NaHCO3. It is found in the form of white powder
and soluble in water. Baking powder is prepared by mixing it with potassium
hydrogen tartarate. Mainly sodium bicarbonate is used in the form of Baking powder
in baking industries to increase the volume of cakes, biscuits, breads, etc.
Uses
1. Sodium bicarbonate is mainly used to make baking powder.
2. It is used to neutralize the acidity in stomach.
3. It is used to manufacture various soft drinks.
4. It is used in fire extinguisher.
Glycerol
Glycerol is an important chemical substance used in our daily life. It is commonly
called as ‘Glycerin’. It is prepared from an organic compound called propane. It is a
colourless viscous liquid with sweet taster and soluble in water. Its molecular formula
is C3H5 (OH)3 which is also written as CH2OH-CHOH-CH2OH. It is a compound of
alcohol group which is one of the trihydric alcohols.
Uses
1. Glycerol is used to prevent from skin crack.
2. It is used to manufacture medicines, printing ink and stamp pad ink.
3. It is used to manufacture cosmetics, body lotion and high quality soaps.
4. It is used as sweetening agent in confectioneries.
5. It is used to prevent tobacco from drying.
6. It is also used to prevent fruits and foodstuffs from drying
Blooming Science & Environment Book 8 183
Main Points to Remember
1. The natural sources of water are: rain, river, lakes, springs, wells and sea.
2. Rainwater is the purest form of naturally occurring water.
3. As the sea water gets heated due to the sun, it evaporates and water vapour is
taken to long distance by wind and it becomes cloud due to condensation. The
cloud collides with the Himalayas which act as blocks of ice and falls as rain.
The rain water may pass through springs and rivers and they reach the ocean
again. The water completes a cycle.
4. Soft water gives lather with soap easily. Hard water consumes large amount of
soap to give lather.
5. Hardness of water is due to the presence of soluble salts of magnesium and
calcium, e.g. calcium sulphate, calcium bicarbonate, magnesium bicarbonate,
magnesium sulphate, etc.
6. There are two kinds of hardness present in water.
(a) Permanent hardness and (b) Temporary hardness
7. Temporary hardness of water is due to the presence of soluble salts of magnesium
and calcium such as Calcium bicarbonate and Magnesium bicarbonate.
8. Permanent hardness of water is due to the presence of soluble salts of
magnesium and calcium such as magnesium sulphate, magnesium chloride,
calcium sulphate, calcium chloride.
9. Temporary hardness of water can be removed by:
(a) Boiling hard water
(b) By treating it with lime water
10. Permanent hardness of water can be removed by:
(a) Treating with washing soda
(b) By using permutit process.
11. Advantages of hard water are:
(a) Hard water contains calcium salt dissolved in it which helps to strengthen
the bones and teeth.
(b) Water is somewhat tasty due to dissolved salts of calcium and magnesium.
(c) Hard water is used in beer industries.
12. Disadvantages of hard water are:
(a) Hard water leads to consumption of more soap while washing clothes.
(b) Bright white clothe becomes dull due to the salts dissolved in water.
(c) In industries, due to hard water, the life of boilers decrease. This is due
to the calcium salt deposited during boiling.
184 Blooming Science & Environment Book 8
PRO J ECTWORK
Take some water in a bucket. Mix some calcium bicarbonate it. Divide water in
two halves and boil one sample. Now wash a small piece of clothes by using both
water. Observe the difference and draw your conclusion.
Exercise
1. Fill in the blanks.
(a) Hardness of water is caused by the presence of salts of __________ and
__________.
(b) Presence of bicarbonate of calcium and magnesium result ___________
hardness of water.
(c) Presenc ___________ and ____________ result ______________
hardness of water.
(d) Soluble salts turn into ______________ salts due to heating.
(e) Permanent hardness can be removed by using _______ or __________.
(f) Sodium zeolite has composition ______________.
(h) The molecular formula of washing soda ______________.
2. Answer the following questions.
a. What is the importance of water in human life?
b. What is meant by hard and soft water?
c. How do you remove the temporary hardness of water? Give chemical
equations also.
d. How do you remove permanent hardness of water? Give chemical
equations also.
e. What are the advantages and disadvantages of hard water?
f. Write an essay on “Importance of water in life”.
g. What is called permutit? Why is it used?
h. Write down the important uses of
(a) Washing soda (b) Edible soda (c) Glycerol
Blooming Science & Environment Book 8 185
3. Write with balanced chemical equations, What happens when;
(a) The water containing calcium bicarbonate is heated?
(b) The water containing magnesium bicarbonate is heated?
(c) The water possessing permanent hardness is treated with washing soda?
(d) The water possessing temporary hardness is treated with lime water?
Glossary
sewage : waste matters from homes
dissolve : disappear in liquid
dumping : disposing waste matters
lather : foam
shipping : transport or distribution
treat : react with
186 Blooming Science & Environment Book 8
Chapter Biology
16 Living Organisms
Learning Outcomes Estimated Periods: 12+2
On the completion of this unit, the students will be able to:
introduce micro-organisms like bacteria, fungi, virus.
describe structure and function of modification of plants’ parts(root, stem
and leaf)
describe germination and dispersal of seed with different methods.
describe and demonstrate life cycle of a flowering plant.
Introduction
Biology is the science that deals with study of living organisms. The term biology is
derived from the combination of two Greek word-‘bios’ that means life and ‘logos’
that means knowledge.
First scientific study of living organisms was undertaken by a Greek naturalists,
Aristotle. So he is considered as Father of Biology. After that many other scientists
and naturalists had major contribution in development of modern biology.
The science of plants is called Botany and the science of animals is called Zoology.
Nowadays the term biology is replaced by the term ‘Life Sciences’ due to its
multidisciplinary approach.. It is thought that living organisms were evolved from
chemosynthesis.
A. Introduction of Micro-organisms
Bacteria
Bacteria are a large domain of prokaryotic micro-organisms. Typically, they are a
few micrometer in length and wide range of shapes, ranging from spheres to rods
and spirals. Bacteria are present on most habitats on earth, growing in soil, acidic
hot springs, radioactive waste, water and deep in earth’s crust as well as in organic
matter and live bodies of plants and animals, providing outstanding examples of
mutualism in the digestive tracts of humans, termites and cockroaches. The vast
majority of bacteria are rendered harmless by the protective effects of the immune
system and a few are beneficial. However, a few species of bacteria are pathogenic
Blooming Science & Environment Book 8 187
and causes infectious diseases including cholera, syphilis, anthrax, leprosy and
bubonic plague. The most common fatal bacterial diseases are respiratory infections,
with tuberculosis alone killing about 2 million people a year.
Bacteria are the smallest free living organisms. The size of smallest bacterial cell
is 0.15 to 0.3 mm and the size of largest bacterial cell is about 500 mm in length.
Majority of bacteria range from 0.5 - 1 mm in width and 2-5 mm in length.
Streptococci
( Streptococcus
pyogenes)
Diplococci Chain of bacili Vibrio
( Streptococcus ( Bacillus anthracis) (vibrio cholerae)
pneumoniae)
Tetrad
Flagelate rods Spirilla
( Salmonela typhi) (Helicobacter pylori)
Staphylococci Sarcina Spore-former Spirochaetes
( Staphylococcus ( Sarcina (Clostridium (Treponema pallidum)
ventriculi) botulinum)
aureus )
Fig. Different shapes in Bacteria
Capsule
Cell wall
Plasma membrance
Cytoplasm
Ribosomes
Plasmid
Pill
Bacterial Flagellum
Nucleoid (circular DNA)
Fig. A bacterial Cell
Antibiotics are used to treat bacterial infections. The bacteria called gram positive
bacteria are susceptible to antibiotics but gram negative bacteria are more resistant
to antibiotics.
According to mode of nutrition bacteria are of following types:
188 Blooming Science & Environment Book 8
Autotrophic Bacteria:
These bacteria can synthesize their food from inorganic substances like higher plants.
According to source of energy they are of two types:
(i) Photoautotropic
(ii) Chemoautotropic
Heterotrophic Bacteria:
They cannot synthesize their own food. They obtain their food from other organisms.
They are of following types:
(i) Saprophytic Bacteria: They get food from organic remains. e.g. animal
excreta, fallen leaves, meats, jams etc. They breakdown complex organic
substance into simple compounds either anaerobically or aerobically by
fermentation, putrefaction or decay. These bacteria dispose off the dead bodies
and organic wastes and also release raw materials for reutilization. So, they are
called nature’s scavangers. e.g. Pseudomonas.
(ii) Symbiotic Bacteria: These bacteria live in mutual beneficial association with
other organisms and share the benefits. e.g. Rhizobium lives in root nodules of
legumes, from which it obtains food and shelter. In return, it helps plants by
fixing nitrogen.
(iii) Parasitic Bacteria: They live in contact with other organisms to get organic
compounds for their growth and breakdown the host’s connective tissues,
cellulose etc. some parasitic bacteria cause disease to the organisms called
pathogenic bacteria.
Beneficial Effects of Bacteria:
Role in Agriculture:
(i) Nature’s Scavenger: They decompose and decay dead plants and animals and
clean the environment.
(ii) Nitrification: Bacteria change ammonium compounds to nitrates which are
useful for leguminous plants.
(iii) Symbiotic Nitrogen Fixation: Some bacteria live symbiotically in the roots of
some plants, fix atmospheric nitrogen and make it available for the plants.
(iv) Manure: Saprophytic bacteria convert farm refuse, dung and other organic
waste into manure.
(v) Gobar gas plant: Bacteria convert animal dung and other organic wastes into
manure along with production of fuel gas.
(vi) Sewage disposal: Organic content of sewage are broken down by bacterial.
Blooming Science & Environment Book 8 189
Role in Industry:
(i) Dairy Industry: Milk is converted into curd, yoghurt, cheese etc. by bacterial.
(ii) Vitamins: Different kinds of vitamins are produced from bacteria. e.g.
Vitamin B12 is made from Bacillus megatherium
Negative Effects of Bacteria
a. Spoilage of Food: Saprophytic bacteria cause rotting of vegetables, fruits,
meats, etc.
b. Diseases: Over 90% of animal disease and 10% of plant diseases are caused by
bacteria.
c. Denitrification: Some bacteria like thiobacillus and micrococcus convert
nitrate into gaseous nitrogen.
Fungi Scan for practical experiment
A fungus (plural fungi) is a member of large group of
eukyarotic organisms that includes micro-organism such as
yeasts and moulds as well as the more familiar mushrooms.
These organisms are classified as a kingdom-mycota or fungai.
It is a large kingdom over 1,00,000 species. This kingdom
is separated from plants, animals and bacteria. One major visit: csp.codes/c08e19
difference is that fungal cells have cell wall which contain
chitin, whereas plants cell walls contain cellulose. Real fungus belong to division
Eumycota, whereas other fungus (molds) belong to division Maxomycotina.
The branch of biology devoted to the study of fungi is called mycology.
Genetic studies have shown that fungi are more closely related to animals than to
plants.
General Characters of Fungi
1) They are eukaryotic organisms.
2) The vegetative body is made of numerous filaments called hyphae. The hyphae
form a tangled mass called mycelium. But some fungi are unicellular eg. yeast.
3) They lack chlorophyll and obtain their food from dead organic matter. They are
either saprophytes or parasites. They hare heterotrophic.
4) Cell wall is made of chitin.
5) Reserve food material in the form of glycogen and oil. Starch is absent.
6) They reproduce by vegetative, asexual and sexual methods.
190 Blooming Science & Environment Book 8
Structure of Fungal Body
The fungal body is made of a number of Sporangium Spore
elongated, tubular filaments called hyphae,
except yeast and a few unicellular fungi. The
hyphae are tangled and form mycelium.
A mycellium develops from single spore. Food source
Spore germinates and gives rise to a hypha. Hyphae
The hyphae branches near the tip so that
hyphae are developed in all direction and form cottony or wooly mass called
mycellium
Structure of Fungal Cell
Fungal cell has eukaryotic structure. Vacuole
Cell wall contains chitin and other Cell wall Dictyosome
Lipid
polysaccharides, protein, lipid, Hyphal wall
Glaycocen particle
Endoplasmic reticulum, mitochondria, Ribosome Endoplasmic
vacuoles, ribosome etc. are of typical
type but Golgi bodies contain only Nucleus reticulum
cisterna. Nucleus are small as compared Cytoplasm
to other eukaryotes.
Plasma
membrane
Reproduction in Fungi Fig: Fungal cell
1) Vegetative Reproduction
It includes fragmentation, budding, fission, sclerotica, rhizomorphs.
2) Sexual Reproduction
In this process they produce gamete cells which fuse together to reproduce
new fungus. This occurs by copulation, contact, fusion of two hyphae etc.
Made of Nutrition in Fungi
Fungi lack chlorophyll so they cannot synthesize their food by themselves. They get
their food from the dead and decayed remains of plants and animals or from other
fungus. According to this they have three modes of heterotrophic nutrition.
i) Saprophytic Fungi
They absorb food from dead or decaying organic matter. Some of them are found
only in decaying substances not in the body of living organisms.
They are called obligate saprophytes. Some are found in both decaying substances
and in the body of living organisms. They are called facultative saprophytes or
facultative parasites.
Blooming Science & Environment Book 8 191
ii) Parasitic Fungi
They obtain their nourishment from the protoplasm of the living plants or animals
(hosts). The parasites which only grow in living cells are called obligate parasites.
They cause several diseases to their hosts.
iii) Symbiotic Fungi
Some fungi form partnership with other group of plants by which both the plants and
fungi are benefited. This type of association is called symbiosis. And such fungi are
called symbiotic fungi
Importances and Uses of Fungi
1) Fungi perform an essential role in the decomposition of organic matter and
have fundamental role in nutrient cycling and exchange.
2) Fungi are used as biological pesticides to control weeds, plant diseases and
insect pests.
3) Industrially fungus are being used to produce various enzymes, antibiotics, etc.
and in leavening and fermentation of various food products.
4) Fungus like different types of mushrooms are used as direct source of foods.
Virus
The word ‘Virus’ is defined from Latin word ‘venom’ which means poisonous
fluid. A virus is an extremely small, infectious and potentially pathogenic micro-
organism which can multiply within living cells only. Study of virus is a branch of
biology called virology. Virus was first discovered by Ivan Iwanowski in 1892 AD as
extremely small micro-organism.
Nature
Viruses are fully dependent on the other living organisms, so called obligatory
parasites. They cannot grow and persist outside living cells. They show both living
and non-living characteristics, so called borderline of living and non-living things.
S.N. Non-living characteristics S.N. Living Characteristics
1. They do not show the activities like 1. They can infect and attack the
nutrition, growth, reproduction other organisms.
outside the living cells.
2. They can be crystallized like a 2. They possess DNA and RNA.
non-living things. They are able to devide and
reproduce inside host cell.
Virus causes many types of diseases like yellow fever, common cold, measles. etc
in man and tobacco mosaic in tobacco, curling of leaves in papaya and yellowing
192 Blooming Science & Environment Book 8
of leaves in ladyfinger in plants. The size of virus varies from 25 to 250 nanometer
(one nanometer is one million of a millimeter). Virus may be of different shapes like
spherical, rod-shaped and hexagonal.
Head Fiber Knob domain Core Protein
Collar HBc
Core Hexon Penton base
Helical sheath Core protein Linear DNA
genomic
Tail pins DNA DNA
Hexagonal Terminal protein polymerase
base plate
Surface
Rod shaped virus Protein HBc
Hexagonal virus Spherical virus
Virus are very minute and acellular (without any cells) forms of life and are much
smaller than bacteria. Some viruses do not contain nucleus while others have no
cytoplasm. Some contain DNA and others contain RNA. Depending upon the types
of nucleus acid contained , viruses are placed into two sub-phyla dexovira (DNA
viruses) and ribovira (RNA viruses). Viruses causing cough contain DNA and viruses
causing AIDS, polio, common cold contain RNA.
Based on the host cells, viruses are divided into types. They are;
1. Plant virus: virus which infects plants.
2. Animal virus: virus which infects animals.
3. Bacterio phase virus: virus which infects bacteria
Structure
All viruses have basically the same composition. They Head
do not contain a nucleus, cytoplasm or cell membrane.
Virus consists of an outer protein coat called head Collar
which is made up of hexagonal protein core called Core
capsid. Inside the capsid, it has either DNA or RNA Helical sheath
as the hereditary materials.
The tail is attached to the head by collar. The another Tail pins
end of tail has a basal plate that bears six long tail
fibres. The tail consists of a central hollow core Hexagonal base
surrounded by a contractile sheath. plate
Fig: Bacteriophage
The capsid is made up of a number of identical sub-site called capsomeres. Some viruses
are rod shaped e.g. TMV and influenza viruses. Some viruses have complex shape. The
bacteriophage is a tadpole-shaped virus with a 20 sided head and a long tail.
Blooming Science & Environment Book 8 193
Charateristics of Virus
a. Virus reproduce in large number.
b. Viruses have enzymes. Smallpox virus contains vitamins like riboflavin and
biotin.
c. Viruses contain genetic characters and transfer parental characters to the
offspring.
Specific Characteristics of Virus
Particular virus attacks particular host and particular cell. Different viruses attack
different types of living cells. For eg, common cold virus attacks nasal and throat
cells. Polop virus attacks nerves of spinal cord etc. Viruses are host specific.
B. Modification of Different Parts of Plant
There are different types of plants in our surrounding. The plants are different in size
and nature. The plants are found in different habitat. Mainly there are some basic
parts in plants which are root, stem and leaf. These parts have their definite functions.
These parts are also modified into different forms according to the location, structure,
habitat and functions to form. This is called as modification of plants parts.
Modification of Roots.
Roots are the underground parts of a plant. Basically roots absorb water and mineral
salts for the plant and fix the plant firmly in the soil. There are two types of roots; Top
root system and Fibrous root system.
In many plants the normal types of root is modified variously Scan for practical experiment
and performs several functions for the survival of plant in
surrounding environment. This is called the modification of visit: csp.codes/c08e20
root. The roots are modified for following three functions;
1. For storage of food
2. For mechanical support
3. For vital functions
1. For storage of food
Some tap roots are modified to store the food material. It changes its shape and size
due to accumulation of food materials. According to their shape, they are of following
types;
a) Spindle shaped root with middle part swollen and gradually
tapering towards the both ends. For example. Radish.
Radish
194 Blooming Science & Environment Book 8
b) The upper part of the root becomes almost globular due to
maximum swelling and tapers sharply towards the lower end.
e.g. Turnip
Turnip
c) Broad at the base and gradually taper towards the apex
like a cone. For example: Carrot
Carrot
Similarly some fibrous roots are also modified for storing the food materials. Some
examples of such roots are sweet potato, Dahlia, Asparagus, Indian spinach, etc.
2. For mechanical support
In some plants, roots arise from the main stem, branches or lower nodes above the
ground and grow vertically towards the soil to give mechanical support to the plants.
According to their origin they are of following types;
a) Prop root : These are the roots arising from the main stem Banayan tree
and branches of a tree . These roots grow vertically downwards
to the soil to provide support to the plant body. These roots
often look like pillars and allow the tree to grow in a large
area. For example: banayan tree (Bar).
b) Stilt root: These are the roots arise from lower nodes above the ground level and
give rise to a ring of stout and slender roots. They grow down wards into the soil and
give support to the stem. For example: Maize, Sugarcane etc.
Maize and Sugarcane plants
with stilt roots
c) Climbing roots : These roots develop from the nodes and Peper betel
internodes of the many tropical climbers like long pepper. They
attach themselves to any support and help in climbing.
Blooming Science & Environment Book 8 195
3. For vital functions
In some plants roots are modified for doing different functions according to the
structure of plants. These are of following types;
a) In some parasitic plants like Australian christmass tree roots are developed to
absorb nutrients from other plants by sucking.
b) In some plants like orchid, a special kind of aerial roots are developed which
absorb moisture from the air.
c) The roots of plant growing on marshy place come out of the ground to help in
respiration. eg. Rhizophora
d) In some plants like trapa, long slender hanging roots develop from the branches
which contain chlorophyll and carry out photosynthesis.
e) Some of roots of aquatic plants are spongy in nature and help the plants to float.
eg. water hycianth, pistia, etc.
Orchid plant Rizophora Water hycianth
Modification of Stem
Stem is the part of a plant that lies above the ground. It gives rise to leaves, buds,
branches, flowers and fruits. Stem is erect and has some distinct regions called nodes.
Leaves arise from the nodes. The stem provides mechanical support to the plant and
transports prepared foods, water and minerals to the required parts. In some plants
stem is modified into different forms according to its surrounding for the growth and
development of plants. There are different types of modification in stem.
1. Underground modification
2. Sub - aerial modification
3. Aerial modification
1. Underground modification of stem
In some plants the underground stem is thick and fleshy by the deposition of food.
The stem develop under the soil first and gives off aerial shoots annually under
196 Blooming Science & Environment Book 8
favourable conditions. Some of such stems are Rhizome of ginger and fern; Tuber of
yam and potato; Onion bulb etc.
Onion plant Ginger plant Potato plant
2. Sub-aerial modification of stem
Sub- aerial stems are found in plants with weak stems in which branches lie
horizontally on the ground. A part of the stem grows below the soil and a part above
the soil. These stems mainly take part in vegetative propagation. For example; such
stems are found in plants like mint, grasses, black jasmine, chrysanthemum, water
hyacinth etc.
Sub-aerial modification of stem
3. Aerial modification of stem
Aerial stem is modified into different shape in different plants.
In Some xerophytes plants, stem is like a leaf and stores food. In these plants leaves
are modified into thorns. So the stem carries out photosynthesis process for For
example: Cactus, Opuntia etc.
In some plants stem is modified into tendril. It is a thin, leafless, thread-like, spirally
curled branch. It helps a weak plant to climb.
Grape vine Cactus Bougainvillea
In some plants stem is modified into a hard, often straight, pointed and woody
structure called thorn. For example Bougainvillea, castus , lemon, etc.
Blooming Science & Environment Book 8 197
Modification of leaf
A leaf is the flat green lateral outgrowth of the stem.Leaves is arranged in such a
way that they do not overlap each other. So all of them get sufficient sunlight for
preparing food. The leaves are mainly responsible for photosynthesis process as they
are green in colour due to the presence of chlorophyll. In some plants the leaves are
modified into various forms to perform various special functions according to their
habitat and nature.
In some plants leaves are modified into tendrils. These are thin, slender, wire - like
coiled structures developed to support the climbers. For example: Pea.
In carnivorous plants, the leaf is modified into thorns mainly in xerophytes plants.
It reduces the loss of water by reducing transpiration and also protects the plant. Eg.
Cactus, Opuntia, etc.
Leaves of some plants are thin, dry, papery, stockless, brownish structures that reduce
transpiration.eg.Pinus, Asparagus. In onion such leaves are thick and fleshy to store
the food.
In carnivorous plants, the leaf is modified into bladder which helps in catching and
digesting the small aquatic animalcules. In some other carnivorous plants (pitcher
plants) the lamina or leaf blade is modified into pitcher which captures and digests
the insects.
Pea plant Cactus Pinus plant Pitcher Carnivivous plant
C. Seed
A seed is a fertilized ovule. Flowering plants produce seeds. Seeds of different plants
vary in shapes and sizes. Some seeds are small and some are large. Orchid seeds
are small and seeds of Mango, coconut, pumpkin, jackfruit, pineapple, etc are large
in size. Though seeds vary in shapes and sizes, they have the same basic structural
details.
Parts of a Seed
Every seed has many parts. They are seed coat, endosperm, plumule, radicle,
cotyledons and embryo. Seed coat
Seed Coat Endosperm
The seed coat is the outer most layer of Embryonic
leaves
the seed. It consists of two layers. Outer Embryo
layer is testa and inner is tegmen. Testa Cotyledon
protects the seed from fungi, bacteria and Primary root
insects.
198 Blooming Science & Environment Book 8
Embryo
While carefully separting two cotyledons of a seed, a small embryo can be seen
attached to one of the cotyledons. It has two parts: the plumule (future shoot) and
radicle (future root).
The plumule is the upper flat part and radicle is the lower pointed end. The major
portion of seed is occupied by endosperm. It supplies food for the growing embryo.
The major portion of seeds of maize, wheat and rice is occupied by endosperm. So
they are called endospermic seeds.
The seeds of pea, gram, mango have no well developed endosperm. Such seeds are
called non-endospermic seeds.
Hilum
It is a clear scar left by the stalk of a seed. It represents the Scan for practical experiment
point by which the seed is attached to the fruit.
Micropyle
Micropyle is a small hole near or above the hilum. It allows visit: csp.codes/c08e21
water to enter embryo. When the seeds like peas or gram are
soaked in water, they swell due to the absorption of water
through the micropyle.
Cotyledons
They remain attached to the embryonic axis. They store food for the embryo.
Types of Seeds
On the basis of the number of cotyledons, seeds are of two types. They are
monocotyledonous and dicotyledonous seeds. The gram, pea, bean, mustard,
mango, orange, etc. are dicotyledonous plants. The seeds of these plants contain two
cotyledons. The rice, wheat, maize, barley, etc. are monocotyledonous plants. Seeds
of these plants have only one cotyledon.
Structure of a Dicotyledonous Seed: Pea
The basic structure of pea and other plants seeds is same. The pea seeds are larger
and round in shape. A pea seed has three parts. They are seed coat, an embryo and
cotyledons. Seed coat
1. Seed Coat: It is the outermost covering of the Plumula
seed. It is made up of two layers: outer testa
and inner tegmen. It protects the inner part Hypocotyl
of the seeds from injury, high temperature, Radicula
microbes and insects. Storage Embryonic
Cotyledons axis
Blooming Science & Environment Book 8 199
A large scar left by the stalk of the seed is hilum. It is also the point of attachment
to the fruit.
There is a tiny pore at one end of the seed coat, called micropyle. When the
seeds are soaked in the water, the water enters through the micropyle. This
results the swelling of the seeds and helps to germinate.
2. Cotyledons: On either side of the embryo, two cotyledons are present. They
may store the food for the growing embryo.
In some seeds like dicotyledonous seeds of castor, endosperm is present on
one side of the embryo or surrounding the embryo on all sides. Such seeds are
called endospermic seeds. Endosperm is fleshy in which food is stored for the
growing embryo.
In most of the seeds like bean, pea, mango, gram, etc. endosperm is absent.
Such seeds are called non-endospermic seeds. In these seeds the food is stored
in cotyledons during the maturation of seeds.
3. Embryo: An embryo is called baby plant. It is present with one of the cotyledons.
It contains distinct lower part, the radicle and upper part the plumule. During
the germination of the seed, the radicle grows into the root while the plumule
grows into the shoot of the plant.
Structure of Monocotyledonous Seed: Maize
Maize is one seeded fruit or grain. It is Seed coat
more or less flattened and triangle on Endosperm
one side. Each maize grain is made up of Embryonic
the following parts. leaves
Embryo Cotyledon
Seed Coat: It is the outermost covering Primary root
of the grain. In this, the seed coat and
fruit wall are fused together to form a
protective layer.
Embryo: On one side of the grain, there is a light white coloured small egg-shaped
area. This area contains the embryo. An embryo contains a single lateral cotyledon
and embryo axis with plumule and radicle are at its two ends. The radicle is present
at the pointed part of the seed while the plumule is found in the flat part.
The major portion of the grain is occupied by endosperm. It is yellow or white
coloured food materials in the form of proteins and starch. Thus, the maize is called
endospermic seed. Beside maize, the other monocotyledonous seeds like rice, wheat,
etc. are also endospermic seeds.
200 Blooming Science & Environment Book 8
Differences between Monocotyledonous Seeds and Dicotyledonous Seeds.
S.N. Monocotyledonous Seeds S.N. Dicotyledonous Seeds
1. The seeds have only one 1. The seeds have two cotyledons.
cotyledon.
2. Generally seeds are endospermic. 2. Generally seeds are non-
endospermic.
3. Hilum and micropyle are very 3. Hilum and micropyle are distinct.
much small.
4. It is a single seeded fruit. 4. The seeds are formed inside the
fruit.
5. Embryo or baby plant is very 5. Embryo or baby plant is large.
small.
6. There is one seed coat. 6. There are two seed coats called
testa and tegmen.
7. Plumule is very small. 7. Plumule is large.
Example : Maize, wheat, etc. Example: Pea, gram, etc.
Functions of Seeds
1. A seed develops into a new plant after getting suitable conditions. Therefore, it
helps in reproduction.
2. The cotyledons of seeds store the food material which is used during the
germination of seed while germinating. A seed cannot manufacture food itself.
3. The seed coat of the seeds protects the inner part of the seeds from injury,
microbes and insects.
Seed Dormancy and Germination
Generally a fresh seed of a plant does not germinate eventhough it gets required conditions.
This is because a seed has to pass dormant period once before its maturation.
Dormancy of a seed is defined as the total time period after its maturation in which
a seed does not germinate even when provided with all the required conditions for
germination.
The conditions required for the seed germination are water, oxygen and optimum
temperature.
The process by which embryo of a seed grows into a new plant under suitable
conditions is called germination.
Germination of Seed
The process of development of an embryo of a seed into a new plant under a suitable
condition is called germination. The embryo of seeds remains inactive but alive till
the environment is not suitable for germination for short or long duration of time
Blooming Science & Environment Book 8 201
after maturation. It means that, the seeds of some plants grow into new plants as soon
as the seeds get suitable condition like soil, water, light, air and suitable temperature.
Some seeds like seeds of cereals remain inactive and do not terminate immediately
after maturation. Such seeds are called dormant seeds. After the completion of
dormancy period and onset of suitable conditions, the seed begins to germinate.
Activity
To prove that the air, water and suitable temperature are essential for the
germination of seed.
Material required: a beaker, a ruler, three bean seeds, thread, etc.
Procedure
1. Take three bean seeds and tie them with thread at three
position of a ruler as shown in the figure.
2. Take a beaker and put the ruler with the seeds into the
beaker.
3. Pour water into the beaker in such a way that the
lowest seed is under the water, the middle one is partly
immersed in the water and the uppermost seed is in the
air.
4. Let the beaker remain in warm place for a few days. After that, what will you
observe?
Observation
You will see that the lowermost seed does not germinate and gets decay due to
water. The uppermost seed remains as such and has no sign of germination. But
the middle one germinates to form a small new plant.
Conclusion
The middle seed germinates into a new plant because it gets all the conditions. From
this activity, we have concluded that the seed requires air, suitable temperature and
water to germinate.
Fruit
Fruit is defined as a matured ovary containing seeds. It develops from the ripened
ovary after pollination and fertilization. There are varieties of fruits. The fruits are of
various coloured. They are found in different shapes and sizes according to the plant,
e.g. mango, apple, orange, banana, pomegranate, guava, berry-berry (kafaal), leechi,
coconut, etc.
202 Blooming Science & Environment Book 8
The fruit consists of three parts they are epicarp, mesocarp and endocarp.
1. Epicarp: It is the outermost covering of the fruit. It Exocarp
acts as the skin layer of the fruit. Its function is to (epicarp)
protect the inner part of the fruit. Mesocarp
2. Mesocarp: It is the middle part of the fruit which Endocarp
is usually fleshy type. It forms the edible part of the
fruit.
3. Endocarp: The endocarp is the innermost hard
stony part of the fruit that encloses the seed. Its main function is to give
protection to the seeds.
Functions of Fruit Scan for practical experiment
The main functions of a fruit are a given below: visit: csp.codes/c08e22
1. The fruits protect the seeds from unfavorable
environmental conditions and animals.
2. In most of the cases, fruits help in dispersal of seeds.
3. Fruits also provide nutrition to the developing embryo.
4. The fruit stores food materials which are used by animals
as a source of food energy.
Dispersal of Seeds
We know that the plants are fixed at one place. They cannot change their place in
order to fulfill their basic needs. So, it is essential to disperse seeds in distant places
from the parent plant to obtain basic needs and large space. The dispersal of seeds
may be defined as the scattering of seed to distant places from their parent plants.
The dispersal carries the seeds to the area germinate into new plants which grow and
reproduce their own kind to keep continuity of their races into nature.
There are various ways of dispersal of seeds. Some of them are as given below:
1. By wind 2. By water
3. By the plants itself and 4. By man and other animals
1. By Wind
The wind dispersal plants usually produce seeds in
those seasons when winds and storms frequently
occur. The wind dispersed seeds are very small, light
and provided with silky fibres, pappus or wings to
fly. Such seeds can be carried by wind to over 1000
km.
Blooming Science & Environment Book 8 203
Some examples of wind dispersed seeds are cotton, poppy, maple, tukiphul,
simal, grass, etc.
2. By Water
The dispersal of seeds by water is not common in
various plants because seeds may decay in water.
However, the seeds of coconut, walnut, lotus, etc. are
dispersed by water. These seeds can float on the water
without decaying by their fibrous outer coat. They
also have hard seed coat that protects from water. These seeds germinate into
new plants when they get suitable environment near the edge of stream, pond,
river, sea shore, etc.
3. By the Plants Itself
In this type of dispersal, fruits of some plants dry up
on maturity and break with a great force. This results
seeds of that fruits in dispersal of a distance of few
metres. Seeds of pea, balsam, beans, lady’s finger, etc.
are dispersed in this way.
4. By Man and Other Animals
Man and all other types of animals take part in the
dispersal of seeds.
Man is an agent in the dispersal of seed because he
has taken seeds of many plants during harvesting the
crops and for his fancy and economic value. For example, Nepal received a
number of important plants like tobacco, potato, maize, cabbage, cauliflower,
etc. brought by the Portuguese and Britishers respectively.
Some seeds have special sticky glands, hooks or spines, etc. These structures help
the seed to attach to the clothes and the fur of animals. In this way the seeds are
carried by man and animals to a distance and some of the stuck seeds falls in the soil
and germinate into new plants.
Seeds of tomato, mulberry, guava, cucumber, etc. are very small so they are eaten
along with fruit by human and other animals. Seeds of such fruits have seed coats
that come out with the stools wihout any harm from the alimentary canal of animals.
As animals move from place, seeds are also dispersed.
204 Blooming Science & Environment Book 8
D. Life cycle of a Flowering Plants
Introduction
We see different kinds of plants around us. Most of the food substance we obtain
from plants. People destroy many plants for different uses. But some plants die
themselves. Still their number do not decrease. What is the secret of this? You
might have noticed different plants around you. Some have flowers and some have
no flowers. The plants with flowers are called flowering plants and plants without
flowers are called non-flowering plants. Flowering plants are produced from seeds. A
flowering plant has two types of organs - vegetative organs and reproductive organs.
Vegetative organs: Root, stem, branches and leaves are vegetative organs.
Reproductive organs: Flowers are the reproductive organs.
Flower
A complete flower has
four parts. These parts are Androecium
arranged in four whorls.
These are arranged on Gynoecium Corolla
Calyx
thalamus.
Fig: Parts of a flower
The small stalk by which
the flower is attached
to the branch is called
pedicel. The swollen
part of the pedicel is the
thalamus.
Calyx
The first and the outside whorl is the calyx. This is made of sepals. Usually this is
green in colour. But sometimes it has other colour also For example brinjal. The
important function of the calyx is to protect the flower in the bud stage because it
is green in colour it may help in photosynthesis also. In some flowers the sepals
are separate. Such flowers are called polysepalous flowers; e.g. Pumpkin. In some
other the sepals join together to form a cup like structure. Such flowers are called
gamosepalous flowers. e.g. Hibiscus.
Corolla
This is the second whorl of the flower. It is colourful and it is formed of petals.
Some flowers have nectar and smell. In some flowers the petals remain separate.
Such flowers are called polypetalous flowers e.g. mustard. In some others they join
Blooming Science & Environment Book 8 205
together, form a tube like structure e.g. pumpkin.. Because of the colour, nectar and
smell, insects and other animals are attracted and they help in pollination. Also,
flowers give beauty to the plants.
Androecium
This is the third whorl and it is the male reproductive organ. Anther
This is made up of one or more stamens. A stamen has two
parts. A long slender stalk called filament and a swollen Filament
part on the top called anther. The two lobes of the anther
is connected in between with a connective. Each lobe has
two sac like structures filled with pollen grains. After the
maturation of the anther, inside the pollen grains, the male Fig: Androecium
gametes are formed.
Gynoecium Stigma
Style
This is the innermost whorl and it is female reproductive organ.
This is made up of one or more carpels. The lower swollen part is Ovary
called ovary and the elongated thread like part is called style. The
tip of the style is the stigma. In the matured ovary, oval shaped
ovules are found. Each ovule has ovum inside which is the female
gamete. The flowers with all the four whorls are called complete
flowers.
Pollination Fig: Gynoecium
Pollination is defined as the process of transferring pollen grains from anther to the
stigma of the same flower or different flower.
When the butterflies and other insects visit the flowers to take the nectar, they help in
pollination and thus help to complete the life cycle of a plant. There are two different
types of pollination.
1. Self pollination 2. Cross pollination
Self Pollination
Transfer of pollen grains from one flower to the stigma of the
same flower or another flower of the same plant is called self
pollination or autogamy. This usually takes place in bisexual
flowers: e.g. Peas.
Cross Pollination Fig: Self Pollination
Transfer of pollen grains from the anther of a flower to stigma of a flower in another
plant is called cross pollination (allogamy). This takes place in unisexual flower e.g.
Pumpkin.
206 Blooming Science & Environment Book 8
Fig: Cross Pollination
Differences between Self Pollination and Cross Pollination.
Self Pollination Cross Pollination
1. It is the transfer of the pollen grains 1. It is the transfer of pollen grains from
from another to stigma of the same or anther of flower to stigma of same
another flower of same plant. special.
2. It occurs in bisexual flowers. 2. It occurs in both bisexual and
unisexual flower.
3. Pea plant, balsam flowers, etc. 3. Mustard flower, cucurbits, etc.
Fertilization
This is the process by which the male and the female gamete fuse together to form
the zygote. After pollination the pollen grains grow on the stigma and produce pollen
tube. This tube grows towards the ovary. At the tip of the pollen tube remains two
male gametes. Similarly in the ovule also female gametes are produced.
The fusion of male and female gametes to Pollen grains
form a zygote is called fertilization.
Style
The tip of the pollen tube breaks near the Pollen tube
ovule and male gamete fuses with the female Stigma
gamete and the zygote is formed. This is called
fertilization. Changes take place in the zygote
and it becomes the embryo.
After fertilization, petals, sepals, androecium Fertilized ovum
and gynoeciun dry out. The embryo becomes Ovary
the further plant, ovule becomes the seed and
the ovary becomes the fruit.
The seeds germinate when they get enough
heat, light, water and air and form plants. In
Fig: Fertilization 207
Blooming Science & Environment Book 8
this way, life of plant starts from seed and after the formation of plant it produces
flowers. The flowers produce fruits and seeds. Like this, the life cycle of plant is
completed.
Flowering
plant
Seedling Flowers
Fruit with
Pistil Stamen
seeds
Ovule Anther
Embryo
Female Male
gamete gamete
Zygote
Mustard Plant
Classification
Kingdom : Plantae Flower
Sub-Kingdom : Phanerogams Fruit
Division : Angiosperm Stem
Sub division : Dicotyledonous Leaf
Mustards are several plant species in the genera Node
Brassica and Sinapis, whose small mustard seeds Internode
are used as a spice and condiment. The seeds are
also pressed to make mustard oil. The green leaves Bud
of mustard are edible and are eaten as vegetable.
Here, we will discuss in detail about the species Primary root
brassica campestris which is locally known as Secondary root
Tori.
Fig: Mustard plant
The word mustard comes from the middle English mustard, meaning condiment, which
in turn comes from old French motarde. There are about 40 species of mustard plants.
Mustard is an annual herb and is a cool season plant. Its body consists of two parts: one
underground part called root system and the aerial part called shoot system.
208 Blooming Science & Environment Book 8
Root:
It is the underground part of the plant. The root of mustard is tap root as it bears
secondary and tertiary roots. The root absorbs water and mineral required for the
plant, from the soil. The root also keeps the plant upright, by anchoring in the soil.
The tap root arises from the radicle of embryo
Shoot:
The aerial part or the part of the plant above the ground which consists of stem, leaf
and floral parts is called the shoot system.
Stem :
The stem bears leaves, branches and flowers.
The stem has following functions:
i) It supports leaves, flowers and fruits.
ii) Stem conducts water and mineral from root to the leaves.
iii) It also helps to transport the synthesized food from green leaves to roots, fruits
and organs of storage.
Leaf: Axillary
bud
The leaf is thin flattened lateral outgrowth
of the stem. It develops from the node from Stem
its superficial tissue. It is green in colour,
because of the presence of chlorophyll and Apex
it synthesizes organic food from inorganic Petiole Veins Midrib
matter like carbon oxide and water. So, Leaf base Lamina
green leaves are called the kitchen of the
Fig: A mustard Leaf
plants. Leaf base, petiole and lamina are the main parts of the leaf.
Leaf base is the part of the leaf attached to the stem.
Petiole is the stalk of the leaf. It lifts the lamina above the stem and provides it
maximum exposure to light. The leaf with petiole is termed as petiolate and the leaf
without petiole is termed as sessile.
Lamina or leaf blade is the terminal, thin flattened structure that forms the most
conspicuous part of leaf.
Leaf apex is the tip of the leaf.
Leaf margin is the border or outline of the lamina. Mid rib is the extension of the
Blooming Science & Environment Book 8 209
petiole, running through the middle portion of the lamina. That forms a rigid, linear
structure. Mid-rib gives rise to branches called veins and veinlets. The arrangement
of veins and veinlets in the leaf lamina is called venation. Mustard plant leaf has
reticulate venation.
All the parts discussed above are vegetative parts. The flower is the reproductive part
of the plant.
Life Cycle of Mustard Plant
A mature mustard plant (Tori) produces yellow flowers. Each flower consist of
calyx, corolla, androecuim and gynoecium. Out of these four whorls gynoecium and
androecium produce female and male gametes respectively whilst calyx and corolla
have supportive role in reproduction.
The adroecium of mustard plant consists of six stamens, which have two parts
filament; a slender tube like structure and a bilobed anther. The anther bears four
pollen sacs. Each sac is filled with yellow coloured powder, called pollen grains,
when develop as male gamete.
The gynoecium consists of two carpels. Carpel or pistil consists of three parts stigma
,style and ovary. A mature ovary develops the female gamete called ovum. When
male and female gametes are mature, the pollen grains (male gametes) from anther
are transferred to stigma of pistil, by means of wind, insects, birds or other animals.
This process of transference of pollen grains from anther of stamen to stigma of pistil
is called the pollination. The pollination is either self or cross whether as transference
of pollen grains take place within or two different flowers of same or different plants.
The pollen grains on the stigma produce pollen tube. The pollen tube grows towards
the ovary through the style and finally reaches the ovary consisting of ovule.
Here the male gamete fuses with the female gamete forming the zygote. The process
of fusion of male and female gametes is called fertilization. Actually in angiosperm
fusion of two male gametes occurs: one with egg and another with definitive nucleus,
so, it is called double fertilization. After fertilization, the other parts of the flower
wither but the ovary develops into fruit and the zygote develops into seeds. A seed
consists an embryo or baby plant. An embryo has main three parts: radicle, plumule
and cotyledon. The radicle develops into root, plumule develops into shoot and
cotyledon provides nutrients required for new plant during germination until the
root fully develops and starts working. The development of sprouts from seed needs
suitable condition of water, temperature, light and soil. Seeds are enclosed within the
fruits. The fruits dry up and burst and seeds are scattered tetting seeds go to soil and
germinate. The sprout develops into mature plant and produces flower repeating the
same stages of life cycle.
210 Blooming Science & Environment Book 8
A complete flower
Stigma
Pollen grains
Mustard plant Pollination
Seedling Ovary
Filament
Stamen Pistil
Male gamete Female gamete
Fertilization
Zygote
Seed Fruit Embryo
Fig: Life cycle of mustard
Main Points to Remember
1. Bacteria, virus and fungi are micro-organisms.
2. Roots, stem and leaves are vegetative parts.
3. There are two types of seeds. They are monocotyledonous and dicotyledonous.
4. Air, water, light and temperature are conditions for germination.
5. The process of development of embryo of a seed into a new plant is called
germination.
6. The process of transferring of pollen grains from anther to stigma is called
pollination.
7. The process of fusion of male and female gamete is called fertilization.
8. A complete flower has four whorls arranged in circles.
9. Some flowers are bisexual and some other are unisexual.
10. Oil is extracted from the seeds of mustard.
Blooming Science & Environment Book 8 211
11. The flower of mustard is a complete flower as it has all whorls.
12. Mustard has tap root system.
13. The mustard flowers are yellow in colour.
14. In a mustard fruit there are many small seeds.
15. The four whorls of a flower are calyx, corolla, androecium and gynoecium.
PRO J ECTWORK
Collect some mustard flowers and study their sepals, petals, androecium and
gynoecium with the help of a magnifying lens or a dissecting microscope and
write the result of your observation.
Exercise
1. Fill in the blanks.
A. The study of virus is called ____________.
b. Fusion of male gamete and female gamete is called ____________.
c. The main root below the soil is called _______________.
d. All the organs of a plant above the soil is called _______________.
e. The organs of a flower are arranged in ________________
2. Write notes on.
A. Germination b. Fertilization
c. Gynoecium d. Androecium
e. Pollination f. Virus
3. Answer the following questions.
A. What are micro-organisms?
b. Write types of bacteria.
c. Fungi is called saprophyte, why?
d. What are parts of a seed?
e. Write functions of roots and leaves.
f. What is germination? Write conditions necessary for germination.
g. What is pollination?
h. What are two groups of organs in a plant?
212 Blooming Science & Environment Book 8
i. What are the four whorls of a flower?
j. Draw a neat diagram of a flower and label its parts.
k. What is a complete flower?
l. Draw a neat labeled diagram of a mustard plant.
m. Draw a labeled diagram showing the life cycle of a mustard plant.
n. Name the disease caused by virus.
4. Distinguish between. b. Self and cross pollination
A. Monocot and Dicot d. Male and female gamate
c. Bacteria and Fungi
e. Pollination and fertilization
5. Give reasons.
a. Bacteria are both useful and harmful.
b. Virus is called obligatory parasite.
c. Mustard is a complete flower.
d. Maize is a monocot plant.
e. Pea is a dicot plant.
f. Fungi is called saprophyte.
Glossary
vary : differ
absorption : taking of liquid into the substance
store : put something safely to use in future
maturation : process of becoming mature
adverse : unfavourable, undesirable, harmful
swell : increase in size
endosperm : the tissue that surrounds the embryo in a seed
microbes : microscopic organisms
Pseudopodia : false feet of amoeba
cytoplasm : the jelly like fluid present in between nucleus and nuclear member
cell : the structural and functional unit of life
mitochondria : power house of cell
Blooming Science & Environment Book 8 213
Chapter Cell and Tissue
17
Learning Outcomes Estimated Periods: 6+3
On the completion of this unit, the students will be able to:
describe structure of plants and animal cells in brief.
classify plants and animals tissue.
describe animal tissue (epithelial tissue) and plant tissue( meristematic
tissue) in short.
study the relation between cells, tissue and organs.
Introduction
The cell is a basic unit of life. The structural and functional unit of living body is
called a cell. It is also defined as the smallest organized unit of living body which is
independent and self-reproducing under favourable condition. The number of cells
present in the living organism varies from one to many. Unicellular organisms are
singled-celled animals. Most of the plants and animals are multicellular in structure.
Fully grown up plants and animals contain billion and billion of cells. The number of
the cell is never fixed for any multicellular organism because they are continuously
deflected by cell multiplication and cell replacement.
Even a single cell performs all the functions of a living being such as growth, nutrition,
digestion, respiration, excretion, respond to external stimuli etc. For example:
amoeba, paramecium and other unicellular animals. Living beings are made of cells.
There is no life, if there is no cell. The cell has a very important role in the living
beings.
The cell is so small that it cannot be visible to the naked eyes. One needs a microscope
to look at the cell. The shape of the cells are extremely variable. Typically the animal
cell is spherical in shape. But there are many different shapes of cell are found such
as, elongated, oval, rounded, triangular, cuboidal, polygonal, irregular etc. The size
of the cell are also vary. There are microscopic (0.25 mm) to the biggest cell (170mm
× 135mm).
214 Blooming Science & Environment Book 8
amoeba Plant cell Yeast
Basically all the plant and animal cell consists of the cell wall or cell membrane,
cytoplasm and nucleus.
Plant Cell
Cell wall
The plant cell has cell wall. It is made of cellulose which is non-living things. The
cell-wall gives the cell a definite shape. The cell-wall consists of a semi-permeable
membrane. Cell-wall provides protection and support to the cell.
Cytoplasm
It is a substance in which protein, Golgi body
Fig: Plant Cell
minerals, fats, water, etc. found.
There are various organelles in the Cell wall
cytoplasm such as mitochondria, Membrance Chloroplast
golgi bodies. Mitochondria is Ribosomes Mitochondrion
necessary for respiration of the Nucleus Endoplasmic
cell. It acts as power house of the reticulum
body because they produce energy. Necleolus Cytoplasm
Cytoplasm takes active part in all
cellular activities such as growth, Vacuole
nutrition, respiration, reproduction
etc.
Vacuoles
Plant cells have large and many vacuoles. They contain water, minerals, glucose and
other substances needed for the cell. It is also known as aqueous solution cell-sap.
Vacuoles acts as the storehouse for excess water, waste products etc. It also keeps the
cell in shape. It regulates the amount of glucose in the cell.
Nucleus
It is the controlling centre of the cell. It is generally round in shape. It is located at
the centre of the cell. It consists of nuclear membrane, nucleoplasm and nucleolus.
Blooming Science & Environment Book 8 215
Nucleus consists of sugar, minerals, protein etc. It consists of thread like elongated
structure called chromosomes. Chromosomes contain genetic codes and transmit
from generation to generation. They appear only during cell-division. Nucleus acts
as a life-centre for the cell. Nuclear membrane provides partition between nucleus
and cytoplasm. Nucleolus synthesizes ribonucleic acid and protein. Nucleus plays
active role during reproduction of the cell.
Plastids
In the cytoplasm of the plant cell, there are various types of plastids, such as
chloroplasts, chromoplasts, leucoplast etc. Chloroplasts make plant green and help in
photosynthesis. Chromoplasts make flower and some other parts colourful. It helps
to attract insects for pollination. Colourful flowers are attractive, ornamental and
economically useful.
Leucoplasts generally found in roots and other parts of the plant where light do not
reach. It helps for storing food materials such as carbohydrates, protein etc.
Animal Cell
Cell Membrane
The animal cell is bounded Nuclear envelop Cell membrance
by cell-membrane. It is made Nucleus Mitochondria
of protein and lipids. It is
porous, thin and invisible. It Nucleolus Ribosomes
is very delicate. It holds the Chromatin
cell together and plays an Endoplasmic
reticulum
important part in controlling Lysosome Golgi bodies
what passes into and out of Vacuole
it. Cell membrane protects
the internal structures of the Cytoplasm
cell and different organelles Fig: Animal Cell
of the cytoplasm. It maintains
the shape of the cell. It acts as selective permeable membrane and transports the
substances like sugar, sodium etc.
Cytoplasm
The substance which surrounds the nucleus is called cytoplasm. It is bounded
peripherally by the cell membrane. It has similar structures and functions as in the
plant cell. The cytoplasm produces energy, makes things and stores food. Many
chemical reactions take place inside it.
216 Blooming Science & Environment Book 8
Vacuoles
Unlike the plants cells, animal cells have small vacuoles. These occur in the form of
globular structures inside cytoplasm. Each vacuole is surrounded by a cytoplasmic
membrane. The vacuole contains a sugary liquid called cell-sap. Some animal cells do
not contain vacuoles. There are different types of vacuoles. They are food vacuoles,
water vacuoles, contractile vacuoles etc.
Nucleus
Nucleus of the cell is centrally located. It consists of a fluid cell nucleoplasm inside
it. There are chromosomes. The chromosomes carry the genetic materials through
genes. The size of the nucleus is different in different cells. The shape of nucleus
vary as well. It may be circular, oval, elongated etc. Nucleus is the main organ
which controls all the functions besides transmission of heredity information and
reproduction. The other structures and functions are almost similar to the nucleus of
the plant cell.
Centrosome
This is the characteristics feature of animal cell. It consists of centrioles and
centrospheres. It helps in cell division.
Differences between Plant and Animal Cell:
S.N. Plant Cell S.N. Animal Cell
1. It has cell wall made up of 1. The cell wall is absent. The cell is
cellulose surrounding plasma enclosed by a plasma membrane.
membrane.
2. A mature plant cell has a large, 2. Vacuoles are either temporary,
permanent central vacuole. small or absent altogether.
3. Centriole and centrosome are 3. Centriole and centrosome are
absent. present except in invertebrates.
4. Its nucleus is pushed to one side 4. Its nucleus is usually central.
by vacuole.
5. Mitochondria are usually fewer. 5. Mitochondria are usually
numerous.
6. Have plastids in them. 6. Usually plastids are absent in
them.
7. Golgi bodies are smaller and 7. Golgi bodies are bigger and found
scattered in cytoplasm. near nucleus in the form of a
block.
8. Usually plant cells are bigger and 8. Usually animal cells are smaller
of regular shape. and have irregular shape.
Blooming Science & Environment Book 8 217
Tissue
Cells combine together inside the body to form a tissue, each of which has a
specialized function e.g. blood, muscles, bone etc. Blood is a kind of tissue which
helps in inter transportation. Muscle is another kind of tissue which also consists
of many cells and provides flesh inside our bodies and helps in movement. Thus, a
tissue may be defined as a group or layer of similarly specialized cells which together
performs certain special functions. Each kind of tissue consists of cells which are
usually alike in size, shape and arrangement.
Types of Tissue
On the basis of the types of cells found in tissues, they are classified into animals and
plant tissues:
A. Plant Tissue
In the simplest plants, the whole plant body is made up of either a single cell or a
colony of cells. Since plants of this kind are usually found in water, each cell is in
direct contact with water and minerals. In advanced vascular plants, a division of
labour occurs among different kinds of cells. Cells of plants exhibit great variation
in size and structure. A group of plant cells performing essentially the same function
and common to similar structure is called a plant tissue.
Plants are able to produce new tissues throughout their life. Plant tissues can be
classified on the basis of characters like nature of cells, origin and method of
development, position in plant body etc. On the basis of the stages of development,
plant tissues are divided into two types:
a. Meristematic tissue b. Permanent tissue
Meristematic Tissue
The group of young cells which have the capacity of active Scan for practical experiment
cell division is called meristem. The cells of this tissue are
of different shapes with big nucleus, thin cell wall and dense visit: csp.codes/c08e23
cytoplasm. It does not have intercellular space. The vacuoles
are few and small in size. The major function of this tissue is
to help in growth.
On the basis of origin, the meristems are classified as: Primary
meristems and Secondary meristems.
a. Primary Meristems: Those meristems, which are derived directly from the
meristems of embryo and persist throughout the life of the plant, are called
primary meristems. They are responsible for the primary growth and lie mainly
on the apices of stems and roots.
218 Blooming Science & Environment Book 8
b. Secondary Meristems: Those meristems, which are formed as new meristems
in permanent cells by re-differentiation, are called secondary meristems.
Secondary meristems are usually lateral in position and are responsible for
increasing the diameter of plant organ.
On the basis of location in the plant body, the meristems are divided in three
types. They are apical, lateral and intercalary Apical meristem
meristems.
i. Apical Meristems: These meristems are Intercalary
primary meristems, present in the growing meristem
points i.e. apices of root and shoot. Their
activity mainly helps in the increase in length.
ii. Lateral Meristems: These meristems are Lateral
embedded in the permanent tissues and meristem
are laterally located. e.g. cork cambium of Fig: Meristematic tissue
roots and stems. Their activity helps in the
increase in girth or diameter of the plant.
iii. Intercalary Meristems: These meristems are located between regions of
permanent tissues beneath the apical meristem. It is also known as the
part of apical meristem. It is found at the base of leaves above the nodes.
The activity of intercalary meristems is to increase the length of axis in
which they are restricted.
Permanent Tissue
It contains living or dead cells without the power of division and not undergoing
furthur change. It is called primary permanent tissue if it is developed from apical
meristem and is called seconday permanent tissue if it is developed from lateral
meristem.
The permanent tissues are of three types- Simple (made up of similar cells which
form uniform mass), complex (different types of cells working together as a unit)
and secretary or special tissues (for the purpose of secretion).
Relation between Cell, Tissue, Organ and System in Plants
A flowering plant consists of root system and shoot system. These two systems of a
plant are made of different type of organs. The root system is made of root cap, root
tip, lateral roots, main root etc. like organs and shoot system is made of different type
of organs like leaves, stem, flower, fruits, buds, etc.
These different types of plant organs are made of different type of plant tissues like
parenchyma, (epidermis, cortex, endodermis and pith), schlerenchyma (pericycle)
xylem and phloem (vascular tissues) etc.
Blooming Science & Environment Book 8 219
B. Animal Tissue
The body of multicellular animals is made up of many cells. These cells show a
wide range of structural and functional specializations. A group of animal cells with
similar size, shape and specific functions are called animal tissues. They are divided
into four major types on the basis of their size, shape and functions of the cells. They
are:
1. Epithelial tissue 2. Muscular tissue
3. Connective tissue and 4. Nervous tissue
Epithelial Tissue Scan for practical experiment
The tissue which covers the body surface, organs, visit: csp.codes/c08e24
ducts, blood vessels etc., is called epithelial tissue. It
is composed of single or many layers of cells. Cells
of this tissue are compactly arranged and there is no
intercellular space in them. The epithelial tissue rests on
a non-cellular basement membrane. They may contain
special type of glands but blood vessels are absent. The
main functions of epithelial tissue are as follows:
1. They form a protective covering on the external surface of the body and
protect the internal tissue from mechanical injuries and entry of germs.
2. They help in the exchange of materials from the surrounding environment.
3. They help in secretion of hormones and other required juices.
4. They help in the absorption of digested food and water in the alimentary
canal.
On the basis of form and structure, epithelial tissues are grouped into the
following types:
a. Squamous/Pavement epithelium b. Cubical epithelium
c. Columnar epithelium d. Glandular epithelium
e. Ciliated epithelium f. Stratified epithelium
a. Squamous/Pavement Epithelium:
Squamous epithelium consists of single layer of
cells. The cells of the epithelium are thin, broad Nucleus
and flat which are arranged like the mosaic tiles
on a floor. Due to it they are also called pavement Basement
membrane
epithelium. All the cells of this tissue are arranged Fig: Pavement epithelium
edge to edge and form delicate lining or covering. It is found in the skin epidermis,
lining of the mouth, body cavities, esophagus and blood vessels. It helps in protection,
exchange of gases and ultra-filtration.
220 Blooming Science & Environment Book 8
b. Cubical Epithelium: It is also a single layered
epithelial tissue. It consists of cuboidal cells; having
equal height and width. It has spherical nucleus placed
more or less in the centre. The cells are closely fitted Nucleus
together and lie on a basement membrane. It is found in Basement
the duct of sweat gland, thyroid gland, liver, uriniferous membrane
tubule, uterus etc. It is actively involved in the
Fig: Cubical epithelium
conduction of secretary materials. It also helps in absorption and excretion.
c. Columnar Epithelium: Columnar epithelium is made up
of a single layer of cells. The cells of this epithelium are
elongated and also lie on a basement membrane. The nucleus
is usually located at the base of the cell. The height of the cell Nucleus
exceeds its width. It is found in lining of the stomach, Basement
membrane
intestine, reproductive organs, urinogenital organs, gall-
bladder, salivary gland etc. It main functions are absorption Fig: Columnar epithelium
and secretion.
d. Glandular Epithelium: Glandular epithelium is a single Nucleus
layered tissue. It is also modified form of columnar
epithelium. The cells of this epithelium are specialized for
the secretion of chemical substances needed for different
activities of life. Liver, pancreas, mammary glands, sweat
glands and mucous glands are the examples of such tissues. Fig: Glandular epithelium
These cells secrete hormone, enzymes, saliva, mucus, etc.
e. Ciliated Epithelium: Ciliated epithelium is a single Cilia
layered tissue. It is modified form of columnar or cubical
epithelium. It has fine, hair like processes called cilia at Nucleus
free margin. It is found in lining of the uterine tubes,
nasal passage and respiratory tract. In the uterine tubes,
the cilia propel ova towards the uterus, and in the Basement
respiratory tract, it propels mucus towards the throat. membrane
Fig: Ciliated epithelium
f. Stratified Epithelium: Stratified epithelium is
formed of many layers (usually 5 to 8) of cells. In Nucleus
the deepest layers, the cells are mainly columnar
and, as they grow towards the surface they become
flattened. The lowest layer is called germinal layer Basement
which, produces new cells and the formed cells are membrane
pushed upwards. They are also of different types and
are mainly found in the nails, hair, and conjunctiva Fig: Stratified epithelium
of eyes and larynx. It prevents loss of water and protects from mechanical injury.
Blooming Science & Environment Book 8 221
Relationship between Cell, Tissue, Organ and System
Unicellular organisms carry out all the vital life activities such as growth, respiration,
food assimilation, excretion and reproduction within a cell. Such animals shown
cellular organization. A tissue is defined as the collection of similar cells having the
same structure adapted to the performance of the same function or set of functions.
When cells are organized to form tissue, it is called tissue level of organization.
Animal tissues are muscle, blood, bone, liver, epithelium etc.
Tissues in a group constitute an organ. Some organs perform only one particular function
heart-blood circulation whereas other perform more than one function [kidney-removal
of nitrogenous wastes as well as regulates water balance in body]. Animal organs are
lungs, kidneys, liver etc.
Different organs work in combined and coordinated way. Thus forming a system.
For example digestive, circulatory, excretory etc. Digestive system includes mouth,
pharynx, oesophagus, gizzard, stomach and intestine. Its main function is digestion
of food materials and absorption of nutrients.
The circulatory system supplies food and oxygen to the body cells. Blood removes
the metabolic wastes from the tissue to the excretory organs from where they are
expelled.
System in Human body, their organs and Functions
S.n System Organs Important Function
1. Skeletal system Bones & cartilages To give frame work of
body, to hold body upright
2. Muscular system Muscles & skin & to protect vital organs.
3. Digestive system To move body & to
Mouth, alimentary cover it.
4. Respiratory canal, liver To digest food and
System and pancreas absorb digested foods.
Nose, trachea and
5. Circulatory lungs To exchange oxygen
system & carbondioxide and
Heart, blood and to release energy by
blood vessels burning food.
To circulate blood &
transport various things in
body.
222 Blooming Science & Environment Book 8
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