Biology

Do you know ? the flowering behaviour in plants - Soyabean
Bioassays for : and Meryland mamoth variety of tobacco.
Auxins - Avena curvature test. They found that soyabean plant flowers during
Gibberellins - Alpha amylase bioassay. late summer and tobacco variety during winter,
Cytokinins - Chlorophyll retention test. irrespective of their germination and growing
Ethylene - Tripple pea test. season. They studied effects of different
ABA - Inhibition of alpha amylase test. temperatures, nutrition, soil moisture, etc. in
respect of flowering. None of these were found
Internet my friend to regulate flowering. However, experimentally
they found that the exposure to specific duration
Collect information of synthetic plant of light (i.e. photoperiod) had profound
hormones. influence on flowering. They examined the
effect of day length on flowering by using
Can you tell? artificial illumination. They concluded that
the relative length of the day was most crucial
1. Why is auxin called a growth regulator? in the growth and development of flowers to
2. Effect of Gibberellin application on apple. which they coined the term photoperiodism.
3. How can we overcome apical dominance? Based on the photoperiodic response, plants
4. Which is standard bioassay method for were classified in three categories viz, Short
Day Plants (SDP), Long Day Plants (LDP)
auxins? and Day Neutral Plants (DNP).
5. ABA is called as stress hormone. Why?

7.10 Photoperiodism : Do you know ?
Higher plants reproduce sexually by
Organs for reception of photoperiodic
producing special structures called flowers. stimulus - Leaf is the chief organ for receiving
Plants exhibit transition from vegetative the photoperiodic stimulus as demonstrated by
growth to reproductive growth during which Knoff (1934). Defoliated plants will not flower
flowers are produced. Like vegetative growth, even if the plants are exposed to proper duration
reproductive growth is also influenced by of light.
several environmental and nutritional factors. Photoperiodic stimulus - It is a chemical
Among the environmental factors - light stimulus transported through phloem and is
and temperature exert profound influence on called florigen which is hormonal in nature.
flowering. The influence of light is known as
Photoperiodism and that of temperature, is Photochemical receptors in the leaves
Vernalization. are the biloproteins (pigments) located in the cell
membrane. These are called Phytochromes.
Light as an environmental factor influences
germination of seed, vegetative growth, Blue wavelengths of light influences
photosynthesis, etc. Light as a factor as three flowering.
aspects viz, Quality, Intensity and Duration
of light. It is the duration of light that has a. Short Day Plants (SDP) :
profound effect on flowering in higher plants. These plants usually flower during winter

The term photoperiodism was used by and late summer when day length is shorter than
Garner and Allard (1920). They were studying the critical photoperiod (critical photoperiod
is that length of photoperiod above or below
which flowering occurs). These are called

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long night plants because they require long Phytochrome :
uninterrupted dark period/ night for flowering. Hendricks and Borthwick (1952) observed
If dark period is interrupted even by a flash
of light, SDP will not flower. Some of the that flowering in SD plants is inhibited, if dark
short day plants are Dahlia, Aster, Tobacco, period is interrupted even by a flash of red
Chrysanthemum, Soybean (Glycine max), light of 660 nm. If it is immidiately followed
Cocklebur (Xanthium), etc. by far red light (730 nm), then SD plants will
flower. This observation led them to conclude
b. Long Day Plants (LDP) : that some pigment system in plant receives the
Plants that flower during summer are photoperiodic stimulus. These pigment proteins
are called phytochromes.
called long day plants. They require longer
duration of light than the critical photoperiod, The leaves produce light-receiving
for flowering. They are called short night proteinaceous pigment called phytochrome
plants as they require short dark period. When that induces flowering. It exists in two
long dark period is interrupted by a brief flash interconvertible forms viz, red (Pr) and far
of light, LD plants can flower e.g. pea, radish, red (Pfr). When Pfr absorbs far red light, it
sugar beat, cabbage, spinach, wheat, poppy, is converted into Pr and vice versa. These
etc. are located in the cell membrane of green
cells.
Light Flash Darkness a. Requires
of light a relatively 660nm (red)
Critical Pr Pfr
dark period long of
uninterrupted 730nm (far red)

darkness. Darkness

b. Requires a During day time, Pfr accumulates in
relatively small the plants. It inhibits flowering in SDP but
initiates flowering in LDP. During dark period
duration of Pfr changes into Pr, it stimulates/ promotes
darkness/ no flowering in SDP and inhibits flowering in
darkness at all. LDP.

Flash of light Always Remember

Control of morphogenesis by light and
phytochrome, is called photomorphogenesis.

Fig. 7.9 : Photoperiodism Internet my friend

c. Day Neutral Plants (DNP) : Melchers proposed that chilling treatment
These plants flower throughout the may induce formation of hypothetical floral
hormone, vernalin.
year round, independent of duration of light
(photoperiod). They do not require specific 7.11 Vernalization (Yarovization) :
photoperiod to flower. Therefore, they are Temperature as environmental factor
called Day neutral plants e.g. Cucumber,
tomato, cotton, sunflower, maize, balsam, etc. influences several physiological processes
including reproduction. Temperature as a
factor has three cardinal points viz, minimum,

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optimum and maximum temperature. It is Advantages of vernalization :
a low temperature (chilling) treatment that • Crops can be produced earlier.
induces early flowering in plants as was • Crops can be cultivated in regions where
evidenced by Klippart (1918). Chouard (1960)
defines vernalization as accelaration of the they do not grow naturally.
ability to flower by chilling treatment. The
term vernalization was coined by T.D Lysenko 7.12 Mineral nutrition :
(1928) for the effect of low temperature on Plant absorbs water, gases, mineral,
flowering in plants.
nutrients, etc. from surroundings. Green plants
It is an influence of temperature on for the synthesis of their organic food need
development and flowering. Many plants inorganic substances (elements) which are
such as cereals, crucifers require a period of obtained from soil in the form of minerals.
cold treatment for flowering. It is the method Minerals constitute most commonly occuring
of inducing early flowering in the plants by solid, inorganic materials obtained from the
pretreatment to their seeds/ seedlings at low earth’s crust.
temperature (1-60C for one to one and half
months’ duration). The site of vernalization is Chemical analysis of plant ash clearly
believed to be shoot apical meristem. Generally, indicates that plant absorbs mineral elements
vernalization is effective at seed stage in from surroundings (soil, air and water) for
annual plants. Vernalization stimulus is also a its use. About 36 to 40 different elements of
chemical stimulus named as vernalin. This can periodic table are used as minerals by the
be transferred through grafting (Melcher 1939). plants. These are absorbed in ionic (dissolved)
form as PO4 , CO3 , SO4 , etc.,usually through
Know the Scientist : roots (regions of elongation and growth).

The low temperature induces early Sources of minerals :
flowering which was first noticed by Plants derive necessary elements from the
Klippart (1957) while working on two
varieties of wheat- ‘winter wheat’and ‘spring atmosphere, soil and water. Carbon enters the
wheat’. The winter wheat sown in winter, plant as atmospheric carbon-dioxide.
produces flowers in the following summer.
The spring wheat sown in the spring and Source of hydrogen is water and oxygen
produces flowers during summer. However, comes from air and water. Carbon, Hydrogen
if winnter variety is sown in spring does not and oxygen are not minerals in origin.
produce flowers during summer but does so
in the next year’s summer. He observed that Source of nitrogen is the soil. Plant derives
if germinated seeds of ‘winter wheat’ are nitrogen from both mineral and non-mineral
treated with low temperature, it can behave origin.
as spring wheat. He concluded that winter
wheat requires low - temperature exposure Classificaion of minerals :
before the onset of flowering. Earlier, on the basis of their requirement

The reversion of vernalization by high minerals were classified as essential and
temperaturetreatmentiscalleddevernalization. non-essential. Essential minerals are those
that are indispensible without which plants
can not complete their life cycle e.g. C, H, O,
N, P, etc. These elements play structural and
physiological roles. Their absence can produce/
cause major deficiency symptoms. The non-
essential elements are not indispensable and
they do not produce/ cause any deficiency
symptoms. This classification is absolete now.

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Basedonthequantityrequirement, minerals Symptoms of Mineral deficiency in plants :

are classified as minor or microelements and Any visible deviation from the normal

major or macroelements. Microelements are structure and function of the plant, is called

required in traces because they function in symptom or hunger sign. The concentration

the catalytic role e.g. Zn, Cu, Al, Si, etc. as of the essential elements below which plant
co-factors. Macroelements are required in growth is retarded, is termed as critical
large quantity. They mainly play the nutritive concentration.
and structural roles e.g. C, H, O, P, Mg, N, K,
S, etc. C, H, O are non mineral major elements. The element is said to be deficient when
This classification is not accepted now. present below the critical concentration. Certain
morphological changes are indicative of the
deficiency of particular element. Deficiency

Know the Scientist : symptoms also depend on the mobility of
the elements in the plants. The deficiency

Criteria for Essentiality of elements symptoms appear first in young tissues when
proposed by Arnon and Stout (1939) : The elements are relatively immobile e.g. sulphur,
elements must be absolutely necessary for calcium.
supporting normal growth and reproduction.
These elements must be having specific When the elements are actively mobilized
functions and should not be replaceable by within the plants and exported to young
another element. The element must be directly developing tissues, the deficiency symptoms
involved in the nutrition of the plant. If an are visible first in the older tissues (senescent
element satisfies all above three criteria, it is leaves). e.g. nitrogen, magnesium, potassium.
considered to be an essential element.
Some important deficiency symptoms seen
in plants are:
• Stunting : The growth is retarded. The stem

appears condensed and short.

Do you know ? • Chlorosis : It is the loss or non-development
of chlorophyll resulting in the yellowing of
Liebig showed the Essentiality of leaves
mineral nutrients and put forth the ‘Law of
minimum’. According to this law, the yield of • Necrosis : It is the localized death of tissue
crop plant is determined by the amount of of leaves.
essential element that is present (available) in
the minimum quantity. • Mottling : Appearance of green and non-
green patches on the leaves.

• Abscission : Premature fall of flowers,

Now a days minerals are classified on the fruits and leaves.

basis of their biochemical functions.

Table : 7.10 Roles of Mineral Elements in Plants

Element Region of plant in Functions Deficiency
which required symptom

Nitrogen Everywhere Constituent of proteins, nucleic acids, Stunted
NO-2 or NO-3 particularly in vitamins, hormones, coenzymes, ATP, growth,
or NH+4 meristematic tissues chlorophyll. chlorosis.

Phosporus Younger tissues, Constituent of cell membrane, certain Poor growth,
H2PO-4 or obtains from older, proteins, all nucleic acids and nucleotides leaves dull
HPO2-4 metabolically less required for all phosphorylation reactions. green.
active cells

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Helps in determining anion- cation balance

in cells involved in protein synthesis, Yellow edges

Potassium Meristematic tissues, involved in formation of cell memberane to leaves,
K+
buds, leaves, root tips and in opening and closing of stomta; premature
Calcium
Ca2+ increases hardness; activates enzymes and death.

Magnesium helps in maintenance of turgidity of cells.
Mg2+
Meristematic and Involved in selective permeability of cell stunted
Sulphur differentiating membranes, activates certain enzymes growth.
SO42- tissues, accumulates required for development of stem and root
in older leaves apex and as calcium pectate in the middle
Iron lamella of the cell wall.
Fe3+
Manganese Leaves, withdrawn Activates enzymes in phosphate Chlorosis
(trace) from ageing leaves metabolism, constituent of chlorophyll,
Mn2+ and exported to maintains ribosome structure.
Molybdenum developing seeds
(Trace)
MoO22+ Stem and root Constitutent of certain proteins, vitamins Chlorosis
tips; young leaves (thaimine, biotin CoA) and Ferredoxin.
remobilised during
senescence Constituents of ferredoxin and cytochrome,
activates catalase required for synthesis of Chlorosis
Everywhere carries chlorophyll.
along leaf veins.
Chlorosis,
Leaves and seeds Activates certain enzymes (carboxylases) grey spots on

Everywhere, MO3+ leaves.
particularly in roots
Activates certain enzymes in the nitrogen Slight
metabolism. retardation of
growth.

Boron (trace) Leaves and seeds Required for uptake and utilisation of Ca2+, Brown heart
BO3-3 or B4O72- pollen germination and cell differentiation, disease.
carbohydrate translocation.

Copper (trace) Everywhere Activates certain enzymes. Die-back of
Cu2+ shoots.
Activates various enzymes especially
Zinc (trace) Everywhere carboxylases, part of carbonic anhydrase Malfomred
Zn2+ and various dehydrogenases needed for leaves
auxin synthesis

Chlorine Everywhere With Na+ and K+ helps to determine solute Poor growth
Cl- concentration and anion-cation balance of the plant
in cells, essential for oxygen evolution in
photosynthesis.

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Do you know ? Minerals salt absorption :
Most minerals in the soil are charged
• Constituents of protoplasm and cell
walls : C,H,O,N,P,S are important and particles hence, they can not pass across cell
permanent constituents of the protoplasm membrane. Hence most of the minerals are
and the cell wall. absorbed actively with the expenditure energy.
Minerals can also be absorbed passively
• Osmotic potential : The osmotic pressure without expenditure of energy. Mineral ion
of cell is the result of mineral salts and absorption is independent of water absorption.
organic compounds dissolved in the cell
sap. Mineral ion absorption can occur in two
ways :
• Catalytic functions : Many elements a. Passive Absorption : Movement of
like Fe, Cu, Zn, Mg, Mn, Cl, etc. act as mineral ions into the root occurs by diffusion.
catalysts in various enzyme reaction of Molecules or ions diffuse from a region of
plant metabolism. their higher concentration to a region of their
lower concentration. The movement of mineral
• Permeability of cytoplasmic membrane: ions into root cells as a result of diffusion is
Permeability of membrane is influenced without expenditure of energy is called passive
by the presence of the various ‘cations’ absorption. Passive absorption can take place
and ‘anions’ of the mineral elements in the by direct ion-exchange, in direct ion-exchange
external medium like ca+, k+. mass flow and Donnan equilibrium.

• Components of energy related chemical b. Donnan equilibrium : It is based on the
compounds : Phosphorus in ATP and Mg assumption that certain negatively charged
in chlorophyll. ions, after their entry into the cell, become
fixed on the inner side of the cell membrane
Do you know ? and can not diffuse outside through the cell
membrane. Therefore, additional mobile
The atmospheric CO2 is virtually cations are required to balance these fixed
the only source of carbon, which is the basic anions. Obviously concentration of cations
constituent of all the organic compounds. become more due to accumulation. This kind
of passive absorption of anions/ cations from
Internet my friend cell exterior against their own concentration
gradient in order to neutralize the effect of
• Collect information about hydroponics cations/ anions, is called Donnan equilibrium.
and find its use in kitchen garden.
Active Absorption: Uptake of mineral ions
• Collect information on Aeroponics. against concentration gradient, is called
active absorption, such movement requires an
Toxicity of Micronutrients : expenditure of energy by the absorbing cell.
Mineral ion concentration which reduces This energy is derived from respiration and
is supplied through ATP. When the roots are
the dry weight of tissues by 10%, is considered deprived of oxygen, they show a sudden drop
as toxic. Toxicity of one element may inhibit in active absorption of minerals. The mineral
the uptake of the other e.g. Mn competes with ions accumulated in the root hair pass into the
Fe, Mg for uptake, but inhibits Ca translocation cortex and finally reach the xylem.
to shoot apex. Thus, Mn toxicity develops
deficiency symptoms of Ca, Mg and Fe.

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The minerals in the xylem are then carried Nitrogen is a limiting nutrient in the
along with water to other parts of the plant along agricultural ecosystems. It exists as nitrogen
the transpiration stream and are subsequently atoms with a strong triple covalent bond
assimilated into organic molecules and then (N ≡ N). A regular supply of nitrogen to the
redistributed to other parts of the plant through plants is maintained through biological and
the phloem. physical process.

Do you know ? Nitrogen fixation :
Atmosphere is the source of nitrogen. It
To explain active absorption of minerals
Hoagland and Davis (1923) put forth Carrier can not be used directly. It combines with C,
hypothesis. Specific proteins in the membrane H, N and O to form compounds before being
of root cells actively pump ions into the used. Conversion of free nitrogen (N2) of the
cytoplasm of epidermal cells of root. These atmosphere into nitrogenous salts to make
proteins are called carriers that pump both it available for the plants, is called nitrogen
cations and anions from the soil. According to fixation. It is of two types : Physical and
Bennet and Clarke (1956) protein conjugated
with lecithin acts as carrier. Biological fixation.

7.13 Nitrogen cycle: Physical Nitrogen fixation: It occurs in
It is series of natural processes by which several steps and starts with combination of
atmospheric nitrogen with oxygen under the
Nitrogen enters successively from air to influence of electric discharge and thunder
organisms through soil and back to environment. storm produce nitric oxide.
Plants use photosynthetic product, the sugars to
make proteins. To do this, they need nitrogen. N2 + O2 Electric discharge 2 NO
Unfortunately, it is very innert (nonreactive).
Plants need nitrogen in a reactive form usually Nitrogen oxygen Thunder storm Nitric oxide
as nitrate ions.
The nitric oxide is then oxidized to nitrogen
peroxide in the presence of oxygen.

2NO + O2 Oxidation
Nitrogen2pNeOro2xide
Atm. N2
During rains, the nitrogen peroxide combines
Non biological with rain water to form nitrous acid and nitric
nitrogen fixation acid which come to ground along with rains.

Biological nitrogen
fixation
Dentrifying Nitrates in the soil Commercial 2NO2 + Rain water NitrousHANcOid2 N+itriHc NAOci3d
bacteria in soil fertilisers in
soil

NH3 in plants On ground, the alkali radicals of soil react
with nitric acid to produce nitrites and
Nitrates, nitrites Amino acids nitrates.(absorbable form)
in the soil in plants

Nitrifying bacteria HNO3 + Ca or K salts Ca or K nitrates
in the soil
Industrial nitrogen fixation. It occurs by Haber-
Plant proteins
NH3 in soil Death Food Bosch nitrate process at high temperature and

Ammonifying Animals pressure. 4500c
bacteria in the soil
Excreta Death N2 + 3H2 A2mNHm3onia

Combustion Nitrogenous organic 200 atm
matter in soil

Ammonia is then converted to urea as it is

Fig. 7.11 Nitrogen cycle less toxic.

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Internet my friend Symbiotic N2 fixation :
The best known nitrogen fixing symbiotic
Enlist names of symbiotic and free living
nitrogen fixing bacteria. bacterium is Rhizobium. This soil living/
dwelling bacterium forms root nodules in plants
belonging to family Fabaceae e.g. beans, gram,
groundnut etc.

Always Remember Ammonification :

Today nearly 80% of nitrogen found After the death of plants and animals,
in human tissues originate from the Haber-
Bosch process. various fungi, actinomycetes and some

ammonifying bacteria decompose the tissues

Biological Nitrogen fixation : It is carried out and convert organic nitrogen into amino
by prokaryotes called as ‘Nitrogen fixers’ or
Diazotrophs’. It accounts nearly 70% of natural acid and then to ammonia and back into the
nitrogen fixation. Nitrogen fixers are either
symbiotic or free living. The cyanobacteria fix ecosystem. Ammonia (NH4+) is now available
significant amount of nitrogen in specialized for uptake by plants and other micro-organisms
cells called heterocysts.
for growth.
Nitrogen fixation is high energy requiring
process and nitrogen fixers use 16 molecules of Proteins Microbial amino acids
ATP to fix each molecule of nitrogen to form decomposition
ammonia.
Amino acids AmmNoHn3ia + ROH
organic acid

Nitrogen assimilation :

In soil, nitrogen is present as nitrates,

N2 + 8H+ +8e- + 16ATP 2NH3 +H2 + nitrites and ammonia (NH4+). It is obsorbed by
16ADP + 16Pi the green plants and converted to nitrogenous

organic compounds like amino acids, DNA,

Ammonia is then converted into amino acids. etc. This is known as nitrogen assimilation.

Nitrification : From plants, nitrogen as biomolecules like

Most of the soil bacteria participate in amino acids, enters food chain and moves to

converting ammonia into nitrate, the form animals and then to decomposers through the

of nitrogen which can be used by plants and death of animals.

animals. This involves two steps performed by Nitrates are first converted to ammonia

two different types of bacteria. but it is highly toxic and immediately used

First a soil bacteria convert ammonia into for conversion into amino acids, which are

nitrogen-di-oxide (nitrite) eg. Nitrosomonas, then transported to other parts of the plants for

Nitrosococcus, etc. synthesis of proteins.

2NH3 + 3O2 Nitrosomonas 2HNO2 + 2 H2O NO3- + 2e- + 2H+ NO2- + H2O
Nitrosococcus NO2- +8e- + 8H+ NH4+ + 2H2O

Then another type of soil bacterium called Amino Acid synthesis :
Amino acids are building blocks of proteins.
Nitrobacter adds a third oxygen atoms to create
The amino acids are synthesized through :
nitrate. Reductive amination : Ammonia reacts with
2HNO2 + O2 Nitrobacter 2HNO3 alpha ketoglutaric acid to form glutamic acid
(glutamate).
These bacteria are chemoautotrophs. By

metabolizing nitrogen along with oxygen, they

obtain energy to power their own life processes.

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α Ketoglutaric acid + NH4 + NADPH2 Amides like asparagine and glutamine
Glutamate dehydrogenase Glutamate + are formed from glutamic acid and aspartic
acid respectively by addition of another amino
H2O+ NADP group to each. Amides are transported to other
Transamination : Amino group of one amino parts of plants via xylem vessels.
acid (-CHNH2) is transfered to keto position
(-CO) of other carboxylic acid. Denitrification :
It is the process in which anaerobic bacteria
Glutamic acid + oxaloacetic acid
can convert soil nitrates back into nitrogen gas.
Glutamate aspertate α - Ketoglutaric acid + Denitrifying bacteria removes fixed nitrogen
Aminotransferase Aspartic acid i.e. nitrates from the ecosystem and return it to
the atmosphere in inert form.
Amides :
Denitrifying bacteria includes Bacillus
Ammonia may be absorbed by amino spp., Paracoccus spp. and Pseudomonas
denitrificans. They transform nitrates to nitrous
acid to produce amides. The process is called and nitric oxides and ultimately to gaseous
nitrogen.
amidation. The amides are the amino acids

having two amino groups. Extra amino group is

attached to acidic group (-COOH) in presence

of ATP. 2NO3 2NO2 2NO N2

Glutamic acid + NH4++ ATP alpha Sedimentation : Nitrates of the soil are washed

glutamine + ADP away to the sea or leached deep into the earth

Aspartic acid + NH4++ ATP Aspargine along with percolating water.
+ ADP

Do you know ?

1. Soil nitrogen is replenished by excretion of animals, (as ammonia, urea and uric acid)
ammonification and nitrification.

2. Plastids contain nitrite reductase which reduces it to ammonia.

Activity :
Label the following diagrams and identify the types of germination.

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Exercise

Q. 1 Multiple choice questions. 8. Essential macroelements are ............
1. Which of the hormones can replace a. manufactured during photosynthesis
vernalization? b. produced by enzymes
a. Auxin c. absorbed from soil
b. Cytokinin d. produced by growth hormones
c. Gibberellins
d. Ethylene 9. Function of Zinc is ................
a. closing of stomata
2. The principle pathway of water b. biosynthesis of 3-IAA
translocation in angiosperms is .......... c. synthesis of chlorophyll
a. Sieve cells d. oxidation of carbohydrates
b. Sieve tube elements
c. Xylem 10. Necrosis means ...............
d. Xylem and phloem a. yellow spots on the leaves
b. death of tissue
3. Abscisic acid controls .................. c. darkening of green colour in leaves
a. cell division d. wilting of leaves
b. leaf fall and dormancy
c. shoot elongation 11. Conversion of nitrates to nitrogen is
d. cell elongation and wall formation called .....................
a. ammonification
4. Which is employed for artificial b. nitrification
c. nitrogen fixation
ripening of banana fruits? d. denitrification

a. Auxin b. Ethylene

c. Cytokinin d. Gibberellin 12.How many molecules of ATP are

5. Which of the following is required for required to fix one molecule of nitrogen?
stimulation of flowering in the plants?
a. Adequate oxygen a. 12 b. 20
b. Definite photoperiod
c. Adequate water c. 6 d. 16
d. Water and minerals
Q. 2 Very Short Answer Questions :
6. For short day plants, the critical period 1. Enlist the phases of growth in plants?
2. Give the full form of IAA?
is ................. 3. What does it mean by ‘open growth’?
4. Which is the plant stress hormone?
a. light b. dark/ night 5. What is denitrification?
6. Name the bacteria responsible for
c. uv rays d. both a and c conversion of nitrite to nitrate.
7. What is role of gibberellin in rosette
7. Which of the following is day neutral plants?
plant? 8. Define vernalization.
a. Tomato 9. Define photoperiodism.
b. Cotton 10. What is grand period of growth?
c. Sunflower
d. Soybean

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Q. 3 Short Answer Questions : Q. 4 Long Answer Questions :
1. Write a short note on : 1. Explain sigmoid growth curve with the
a. Differentiation b. Redifferentiation help of diagram.
2. Differentiate between Arithmetic and 2. Describe the types of plants on the basis
Geometric growth. of photoperiod required, with the help of
3. Enlist the role and deficiency symptoms suitable examples.
of : 3. Explain biological nitrogen fixation
a. Nitrogen b. Phosphorus c. Potassium with example.
4. What is short day plant? Give any two
examples.
5. What is vernalization? Give its
significance.

Project :
1. Grow seed in the deep tray on soil medium and study different stages of germination. Prepare

powerpoint presentation with the help of pictures/photographs of the same.
2. Prepare chart differentiating the epigeal and hypogeal germination.
3. Collect the information about the viviparous germination in plants growing along seashore.
4. Identify and label the deficiency symptoms in the given diagram.

152

8 Respiration and Circulation

Can you recall? the cells of stem, leaf and root. These air
spaces are continuous. Oxygen diffuses into
1. Definition of respiration. the air space through stomata (the pores on
2. The types of cellular respiration. leaves and young stems), carbon dioxide and
3. Why should we respire all the time? water vapour diffuse out. In the aerated soil,
the oxygen dissolves in the film of moisture or
All living organisms require energy to water around the root tissue and enters it by
carry out various life processes. The energy diffusion.
that is stored in the body in the form of complex
organic compounds (potential energy) is Woody flowering plants (trees and shrubs)
however not usable by the organisms unless it have an external impervious bark. Here,
is converted into usable form. This conversion gaseous exchange occurs through small pores
is achieved through the process of respiration. in the stem surface, called lenticels.

Respiration : It is a biochemical process of Stomatal pore
oxidation of organic compounds in an orderly
manner for the liberation of chemical energy in Lenticels
the form of ATP.
Bark
C6H12O6 + 6O2 6 CO2 + 6H2O + 38 ATP
Leaf Stoma
For this, the process of gaseous exchange
Fig. 8.1 : Organs of gaseous exchange in
takes place between the organism and the plants

environment. The site of gaseous exchange is Curiosity Box :

called the respiratory surface. 1. What are the main features of respiratory
surface?
Use your brain power
2. Which are the parts of plant help in the
What would happen if respiration take process of gaseous exchange?
place in one single step?
Respiration in Animals :
8.1 Organs of Respiratory Exchange : As compared to plants, animals show wide
Respiratory exchange is a simple physical
variety of respiratory surfaces or organs. The
process. For efficient gaseous exchange, the respiratory surfaces differ in various animals.
respiratory surface should have the following In animals, depending upon the complexity
features : of organization and the surrounding medium,
certain parts of the body have become
a. It should have a large surface area. specialized into different types of respiratory
b. It should be thin, highly vascular and organs. In the higher animals, these respiratory
organs are also associated with a transport
permeable to allow exchange of gases. system.
c. It should be moist.

Gaseous exchange in plants :
The shape and structure of plants facilitate

gaseous exchange by diffusion. A terrestrial
flowering plant has many air spaces between

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Organism Habitat Respiratory Nasal cavity Pharynx
Aquatic surface/ Nostril
Protists, Sponges organ Mouth Left
and Coelenterates Larynx lung
Plasma Trachea
membrane Right main Ribs
bronchus
Flatworms like Aquatic or Plasma Right lung Diaphragm
membrane, Air sac with blood
Planaria, Annelids semiquatic general body Alveolous capillaries
surface (moist
(earthworm, nereis, skin)
Tracheal
leech), amphibians tubes and
spiracles
(frog) Book lungs

Insects Terrestrial Book gills

Arachnids like Terrestrial External gills

spiders and Internal gills
scorpions

Limulus Aquatic
(Arthropod)

Amphibian tadpoles Aquatic
of frog,
salamanders and
newts

Fish Aquatic Fig. 8.3 : Human Respiratory system

Reptiles, Birds and Terrestrial Lungs Nose :
The nose has a pair of slit like openings
Mammals
called external nares or nostrils for entry of
Turtles Underwater cloaca air into the nasal cavity. The nasal cavity is
divisible into right and left nasal chambers by
Table 8.2 : Respiratory surface/ organ in a mesethmoid cartilage. Each nasal chamber
organisms is further divided into three regions.
i. Vestibule : It is the proximal part about
Use your brain power
the nostrils. Its skin has hair for filtering
Why large animals can not carry out the air and traping the dust and suspended
respiration without the help of circulatory particles in the inhaled air.
system? ii. Respiratory part (conditioner) : The
middle thin walled highly vascular part for
8.2 Human Respiratory system: warming and moistening the inhaled air.
The respiratory system brings about iii. Olfactory or sensory chamber : The
uppermost part is lined by olfactory
inspiration, expiration and exchange of gases epithelium for detection of smell.
in the lungs. These are then transported by
blood from the lungs to the different tissues Pharynx :
and parts of the body. The respiratory system It is divisible into three parts. The
and be divided into an upper respiratory system
having external nares, nasal cavities, internal nasopharynx is the uppermost part from
nares, nasopharynx, nose, throat and associated the nasal chamber it leads into oropharynx
structures. The lower respiratory system refers (common passage for food and air). This
to the larynx, trachea, bronchi, bronchioles and
lungs.

154

continues below as the laryngopharynx. Find out
Between the nasopharynx and oropharynx
is the palate bone. The pharynx has a set of • Kavya underwent a surgical procedure
lymphoid organs called tonsils. called Rhinoplasty. What could have been
the reason for such a surgery? On which
Larynx : part of the body is it carried out?

It is called voice box. It is the part of the • What is the role of tonsils in our body?
respiratory tract which contains vocal cords How many pairs of tonsils do we have?
for producing sound. The larynx extends from
the laryngopharynx and the hyoid bone to the Do you know ?
trachea. It is a hollow, tubular structure. Its
wall is made up of cartilage plates held by • Shreyas choked while eating dinner. How
membranes and muscles. Internally, it is lined can you help him? What is the immediate
by a pair of folds of elastic vocal cords (true help that can be given to him?
vocal cords). Voice is produced by passage of
air between the vocal cords and modulations • What is a role of epiglottis?
created by tongue, teeth, lips and nasal cavity.
The larynx opens into the layngopharynx Bronchi :
through a slit like opening called glottis. This The trachea divides into right and left
opening of the trachea or wind pipe is guarded
by a leaf like flap called epiglottis. It prevents primary bronchi as it reaches the middle of
the entry of food into trachea. the thoracic cavity. The bronchi are supported
internally by ‘C’ shaped incomplete rings of
Hyoid Epiglottis cartilage. The primary bronchi divide to form
bone secondary and tertiary bronchi which lead into
Thyrohyoid terminal bronchioles ending into alveoli.
membrane
Lungs :
Thyroid Laryngeal These are the main respiratory organs of
cartilage prominence
(Adam’s Apple) humans. One pair of spongy and elastic lungs
are present in the thoracic cavity. Each lung
Tracheal cartilage is enclosed and protected by a double pleural
membrane, outer parietal and inner visceral
Fig. 8.4 : Larynx membrane. Between the two pleura is a pleural
cavity filled with a lubricating fluid called
Trachea (wind pipe) : pleural fluid. It is secreted by the membranes.
It is a long tube 10 to 12 cm in length. It runs The right lung is larger and divided into 3 lobes,
while the left lung is smaller and divided into
through the neck in front of the oesophagus and 2 lobes. Each lobe of the lung has the terminal
extends into and upto the middle of thoracic bronchioles ending in a bunch of air sacs, each
cavity. It is supported by ‘C’ shaped 16 to 20 with 10 to 12 alveoli.
rings of cartilage which prevent the collapse
of trachea. It is lined internally with ciliated, Alveoli :
pseudostratified epithelium and mucous glands These are thin walled lobulated structures,
that trap the unwanted particles preventing
their entry into the lungs. like a bunch of grapes. Each alveolus is
surrounded by a network of capillaries of
pulmonary artries and veins. These have
highly elastic wall made up of a single layer

155

of squamous epithelium resting on a basement A. Breathing :
membrane of connective tissue. There are It is a physical process by which gaseous
about 700 million alveoli in the lungs and
they provide the surface area for exchange of exchange takes place between the atmosphere
gases. and the lungs. It involves inspiration and
expiration (see fig. 8.5). Both these steps
Internet my friend involved parts of the thoracic cage, the ribs,
sternum and the intercostal muscles and
1. What is the importance of pleural fluid? muscles of the diaphragm.
2. Find the total surface covered by the
Inspiration : During inspiration, the
alveoli. atmospheric air is taken in to the lungs. It
occurs due to the pressure gradient formed
Diaphragm : It is a muscular septum that between the lungs and the atmosphere. It is
separates the thoracic and abdominal cavity. It an active process in which the diaphragm
is dome shaped and on contraction it becomes becomes flat and goes downward, the external
flattened. intercostal muscles contract so the ribs and
sternum move upward and outward. This leads
8.3 Mechanism of respiration : to an increase in the thoracic volume and a
Respiration is a biological process decrease in pressure of thorax and the lungs.
To equalize the low pressure inside the lungs,
involving exchange of gases between the air from the atmosphere rushes into lungs. This
atmosphere and the lungs and it results in the is inspiration.
formation of ATP. It includes the following
processes: Expiration : During expiration, the thorax
A. Breathing contracts causing air to be exhaled. The
B. External respiration diaphragm relaxes and is pushed upwards. It
C. Internal respiration becomes dome shaped. The intercostal muscles
D. Cellular respiration also relax pulling the rib cage inward and
downward. This causes a decrease in thoracic
Try This volume and leads to increase in pressure in
the thorax and the lungs as compared to the
Count the number of breaths you take atmospheric pressure. So air from the lungs
in the following situations (a). After a good rushes out. This is expiration.
night’s sleep (b). During a vigorous activity
(running, climbing stairs etc) (c). After the One inspiration and one expiration is one
vigorous activity. Do you find any difference breath.
in the count?
Air b. Expiration
a. Inspiration Air (Breathing out)
(Breathing in)
Rib cage
Rib cage moves moves down
up and forward and inward

Pressure in lungs

decreases and air

comes rushing in.

Diaphragm contracts and moves down Diaphragm relaxes and moves up

Fig. 8.5 : Breathing

156

B. External respiration/ Exchange of gases at Pulmonary volumes and capacities
(Normal values)
the alveolar level :
Lung Volumes :
An alveolus consists of a layer of simple Tidal volume (T.V.) : It is the volume of air
inspired or expired during normal breathing.
squamous epithelium resting on a basement It is 500 ml.
Inspiratory reserve volume (IRV) : The
membrane. It is intimately associated with a maximum volume of air, or the extra volume
of air, that is inspired during forced breathing
dense network of capillaries. The capillary wall in addition to T.V. Its value is 2000 to 3000ml.
Expiratory reserve volume (ERV) : The
is also made up of simple squamous epithelium maximum volume of air that is expired during
forced breathing after normal expiration. Its
resting on a thin basement membrane. Both value is 1000 to 1100ml.
Dead space (DS) : The volume of air that is
the layers have similar structure and are thin present in the respiratory tract (from nose to
the terminal bronchioles), but not involved in
walled. Together they make up the respiratory gaseous exchange. It is 150 ml.
Residual volume (RV) : The volume of air
membrane through which gaseous exchange that remains in the lungs and the dead space
even after maximum expiration. It is 1100 to
occurs i.e. between the alveolar air and the 1200ml.
Lung capacities :
blood. Total Lung capacity : The maximum amount
of air that the lungs can hold after a maximum
Diffusion of gases will take place from forcefull inspiration (5200 to 5800ml).
Vital capacity (VC) : The maximum amount
an area of higher partial pressure to an area of of air that can be breathed out after a
maximum inspiration. It is the some total of
lower partial pressure until the partial pressure TV, IRV and ERV and is 4100 to 4600ml.

in the two regions reaches equilibrium.

The partial pressure of carbon-dioxide of

blood entering the pulmonary capillaries is

45 mmHg while partial pressure of carbon-

dioxide in alveolar air is 40 mmHg. Due to this

difference, carbon dioxide diffuses from the

capillaries into the alveolus.

Similarly, partial pressure of oxygen of

blood in pulmonary capillaries is 40 mmHg

while in alveolar blood it is 104 mmHg. Due to

this difference oxygen diffuses from alveoli to

the capillaries.

blood from blood goes
pulmonary to pulmonary

artery vein
Alveolus

Capillary (Air) CO2 Use your brain power
Alveolar O2
membrane Why does gas exchange in the alveolar
Respiratory region very rapid?
membrane
C. Internal respiration :
Surface The two main components of blood
fluid
involved in transport of the respiratory gases-
Oxygen diffuses into Carbon dioxide diffuses CO2 and O2, are the RBCs and the plasma.
red blood cells into alveolus i. Transport of oxygen :

Fig. 8.6 : Exchange of gases between Of the total oxygen transported only
3% is transported in a dissolved state by the
alveolus and capillary plasma. The remaining 97% is bound to
the haemoglobin (Hb) present in the RBCs.

157

Haemoglobin acts as the respiratory carrier. It

has a high affinity for O2 and combines with
it to form oxyhaemoglobin. Theoretically, one

molecule of Hb has 4 Fe++, each of which can

pick up a molecule of oxygen (O2).
Hb + 4O2 Hb (4O2)
Oxyhaemoglobin is transported from lungs

to the tissues where it readily dissociates to

release O2.

Hb (4O2) Hb + 4O2
However, the degree of saturation of Hb

with O2 depends upon the O2 tension i.e. ppO2. Oxygen ppO2 (mm Hg)
• 100% saturation is rare.
Graph 8.7 : Oxyhaemoglobin dissociation
• Maximum saturation of 95 to 97% is at curve (pp = partial pressure)

ppO2 in alveoli (100 mmHg). Carbon monoxide poisoning :
• Degree of saturation decreases with the Affinity of haemoglobin for carbon

drop in ppO2. This begins the dissociation monoxide is about 250 times more, than for
of HbO2. oxygen. In the presence of carbon monoxide,
• At 30 mmHg of ppO2, only 50% saturation haemoglobin readily combines to form a
can be maintained. stable compound carboxyhaemoglobin.
The haemoglobin is blocked by carbon
• The relationship between HbO2 saturation monoxide, preventing oxygen from binding
and oxygen tension (ppO2) is called with haemoglobin. Thus, less haemoglobin
oxygen dissociation curve. This oxygen - is available for oxygen transport depriving
haemoglobin dissociation curve is a sigmoid the cells of oxygen. This is carbon monoxide
curve and it shifts towards the right due to poisoning.
- increase in H+ concentration, increase in
ppCO2 and rise in tempreature and rise in Use your brain power
DPG (2, 3 diphosphoglycerate), formed in
the RBCs during glycolysis. It lowers the While working with the car engine in
affinity of haemoglobin for oxygen. a closed garage, John suddenly felt dizzy and
fainted. What is the possible reason?
Bohr effect : It is the shift of oxyhaemoglobin
dissociation curve due to change in partial ii. Transport of CO2 :
pressure of CO2 in blood. Carbon dioxide is readily soluble in water

Haldane effect : Oxyhaemoglobin functions and is transported by RBCs and plasma in three
as an acid. It decreases pH of blood. Due to different forms.
increase in the number of H+ ions, HCO-3
changes into H2O and CO2. a. By plasma in solution form (7%) : Only

In the alveoli where ppO2 is high and ppCO2 7% of CO2 is transported in a dissolved form as
is low, oxygen binds with haemoglobin, but in carbonic acid (which can breakdown into CO2
the tissues, where ppO2 is lower and ppCO2 is and H2O).
high, haemoglobin does not hold as much O2.
It releases O2 for diffusion into the tissue cells. CO2 + H2O H2CO3

158

b. By bicarbonate ions (70%) : Nearly 70% the RBCs. To maintain the ionic balance
of carbondioxide released by the tissue cells
diffuses into the plasma and then into the RBCs. between the RBCs and the plasma, Cl-
• In the RBCs, CO2 combines with water in
diffuses into the RBCs. This movement of
the presence of a Zn containing enzyme,
carbonic anhydrase to form carbonic acid. chloride ions is known as chloride shift or
• Carbonic anhydrase enzyme is found in the
RBCs and not in the plasma. Hamburger’s phenomenon.
• The rate of formation of carbonic acid
inside the RBC is very high as compared to • HCO3- that comes into the plasma joins
its formation in the plasma. to Na+ / K+ forming NaHCO3 / KHCO3 (to
maintain pH of blood).
• Carbonic acid being unstable almost
immidiately dissociates into HCO-3 HCO-3 + Na+ NaHCO3
and H+ in the presence of the enzyme Sodium bicarbonate
carbonic anhydrase (CA) leading to large
accumulation of HCO-3 inside the RBCs. • H+ is taken up by protein (haemoglobin).
Hb + H+ HHb
CO2 + H2O CA H2CO3 CA H+ + HCO-3
(Reduced Hb)
• It thus moves out of the RBCs. This would
bring about inbalance of the charge inside These H+ ions might be expected to lower

blood pH, but they are buffered by haemoglobin

by the formation of deoxyhaemoglobin

(reduced haemoglobin).

• At the level of the lungs in response to

the low partial pressure of carbon dioxide

(ppCO2) of the alveolar air, hydrogen ion

Tissue cell CO2 Binds to plasms
proteins
CO2 CO2 CO2+H2O slow H2CO3 HCO3- + H+
Interstitial HCO3-
Cl- Chloride shift
fluid fast Cl- (In) via
CO2 CO2+H2O Carbonic H2CO3 HCO3- + H+
CO2 transport
CO2
anhydrase HHb protein

CO2+ Hb HbCO2 (Carbaminohaemoglobin)

Red blood cell HbO3 O2 + Hb

CO2 O2
O2
O2 (dissolved in plasma) Blood plasma

Fig. 8.8 : Oxygen pickup and carbon dioxide pickup at the tissue

Alveolus Fused basement membranes HCO3- + H+ HCO3- Chloride shift
CO2 CO2 (dissolved in plasma) Cl- (Out) via
CO2 transport
CO2+ H2O slow H2CO3 protein
CO2
CO2+H2O fast H2CO3 HCO3- + H+ Cl-
CO2 Carbonic
anhydrase (Carbamino-
CO2+ Hb HbCO2 haemoglobin)

Red blood cell O2+ HHb HbO2 + H+

OO22 O2 (dissolved in plasma) Blood plasma

Fig. 8.9 : Oxygen pickup and carbon dioxide release in the lungs

159

and bicarbonate ions recombine to form neurons in the medulla (inspiratory center),
carbonic acid and under the influence of ventro lateral group of neurons in medulla
carbonic anhydrase yields carbon dioxide (inspiratory and expiratory center) and
and water. pneumotaxic center located in pons (primarily
H+ + HCO-3 CA H2CO3 CA CO2 + H2O limits inspiration, slow wave sleep and rapid
eye movement sleep). Apneustic center in the
c. By red blood cells (23%) : Carbon dioxide medulla is antagonistic to the neumotaxic
binds with the amino group of the haemoglobin center. It controls non rapid eye movement
and form a loosely bound compound sleep and wakefullness.
carbaminohaemoglobin. This molecule readily
decomposes in region where the partial pressure Brain
of carbon dioxide (ppCO2) is low (alveolar
region), releasing the carbon dioxide. Breathing
control centers

Hb + CO2 HbCO2 Pons Breathing
control centers
Use your brain power Medulla stimulated by :

1. What is the role of haemoglobin in the Nerve impulses a. CO2 increase in
transport of oxygen in the blood? trigger blood (acts directly)

2. Write a note on chloride shift. contraction of b. Nerve impulse
muscles from O2 sensor
D. Cellular Respiration : indicating O2
It is the last step taking place inside the cell Intercostal
nerves decrease
where food is oxidized and ATP is generated. It
can be shown by two steps: Phrenic
nerves
a. Oxidation : Breaking down of complex
organic molecules into simple inorganic
molecules with release of heat energy.

C6H12O6 + 6O2 6CO2 + 6H2O + 686 Kcal

b. Phosphorylation : It involves trapping the Diaphragm O2 sensors
heat energy in the form of high energy bond of Intercostal muscles in artery
ATP molecule. ATP is used to carry out vital life (aortic arch)
processes and so is called as energy currency of
the cell. Fig. 8.10 : Regulation of Breathing

ADP + iP + 7.3 Kcal ATP During inspiration when the lungs expand
to a critical point, the stretch receptors are
8.4 Regulation of Breathing : stimulated and impulses are sent along the
Respiration is under dual control : nervous vagus nerves to the expiratory centre. It then
sends out inhibitory impulses to the inspiratory
and chemical. Human adults breathe about 12 center.
times/minute while a new born about 44 times/
minute. Normal breathing is an involuntary The inspiratory muscles relax and
process. Steady rate of respiration is controlled expiration follows. As air leaves the lungs
by neurons located in the pons and medulla during expiration, the lungs are deflated and
and are known as the respiratory centres. It the stretch receptors are no longer stimulated.
regulates the rate and depth of breathing. It Thus, the inspiratory centre is no longer
is divided into three groups : dorsal group of inhibited and a new respiration begins. These

160

events are called the Hering-Breuer reflex. movements some may be reflexes, but others
The Hering-Breuer reflex controls the depth can be initiated voluntarily e.g. coughing and
and rhythm of respiration. It also prevents the yawning.
lungs from inflating to the point of bursting.
Internet my friend
The respiratory centre has connections
with the cerebral cortex which means we can 1. Find out information about the various
voluntarily change our pattern of breathing. modified respiratory movements and
Voluntary control is protective because it write it in a tabular form.
enables us to prevent water or irritating gases
from entering the lungs. But the ability to stop 2. What is the significance of such
breathing is also limited by the build up of movements?
carbon dioxide in the blood.
8.5 Modified Respiratory Movements : 8.6 Common disorders of respiratory system:
The given table shows a list of some
Some respiratory movements are different
from the normal movements and help express common respiratory disorders, their symptoms,
emotion or clear the air passage. Of these cause and treatment.

Table 8.11 : Common disorders of respiratory system

Disorder Symptoms Cause Treatment
Emphysema Breakdown of alveoli, Smoking, air Quit smoking, avoid polluted
shortness of breath air, administer oxygen to
pollution relieve symptoms
Quit smoking, avoid polluted
Chronic Coughing, shortness of breath Smoking, air air, if possible move to
bronchitis pollution warmer, drier climate

Acute Inflammation of bronchi, Viruses and If bacterial, take antibiotics,
bronchitis shortness of breath, yellow bacteria cough medicine, use vaporizer
mucous coughed up.

Sinusitis Inflammation of the sinuses, Viruses and If bacterial, take antibiotics
mucous discharge bacteria and decongestants, use
vaporizer

Laryngitis Inflammation of larynx, vocal If bacterial, take antibiotics,
cords, sore throat, hoarseness Viruses and cough medicines, voice rest,
of voice, mucous build up and bacteria avoid irritants like smoke
cough

Pneumonia Inflammation of lungs ranging Consult physician
from mild to severe, cough immediately, antibiotics,
and fever, shortness of breath, Bacteria, viruses cough medicines, stay warm
chills, sweating, chest pain,
blood in mucous

Constriction of bronchioles, Allergy to pollen,
mucus build up in bronchioles, some foods, food Use of inhalants to open
Asthma periodic wheezing, difficulty in additives, pet hair, passage ways, avoid irritants

breathing. etc.

Occupational Long term
Respiratory exposure to dust
Disorders- Inflammation fibrosis, lung particles silica and Protective mask and gear
silicosis, damage. asbestos, particles during work.
asbestosis
during occupation

161

Think about it The wastes generated within are given out into
the surrounding.
Why is it difficult to hold one’s breath
beyond a limit? Transportation in organisms and
animals occurs by diffusion and by active
Artificial ventilation : transport between the cells. This mechanism is
It is also called artificial respiration. It is the suitable where the surface area of body is large
and the distance between parts of the body in
method of inducing breathing in a person when the organism is extremely small. Cyclosis is the
natural respiration has ceased or is faltering. If streaming movement of the cytoplasm shown by
used properly and quickly, it can prevent death almost all living organisms e.g. Paramoecium,
due to drowning, choking, suffocation, electric Amoeba, root hair cells of many plants and
shock, etc. The process involves two main steps WBCs in animals. It is for transportation
: establishing and maintaining an open air within the cell or intracellular transport. In
passage from the upper respiratory tract to the sponges and coelenterates the surrounding
lungs and force inspiration and expiration as in water is circulated through the body cavities.
mouth to mouth respiration or by mechanical In flat worms there is parenchymal circulation.
means like ventilator. In round worms there are no blood vessels and
the body fluid is moved around the viscera by
Ventilator : contraction of body wall and muscles. This is
A ventilator is a machine that supports
extracellular transport.
breathing and is used during surgery, treatment
for serious lung diseases or other conditions Observe and Discuss
when normal breathing fails. It is mainly used
in hospitals as part of life support system. Observe the diagram and discuss the pro-
Ventilators do the following, cess with your friends.
1. Get oxygen into the lungs.
2. Remove carbon dioxide from the lungs. Mouth Food CO2 O2
3. Help the patient breathe. ↑
↑↑
8.7 Transportation in living organisms :
All living organisms, whether Blood

unicellular or multicellular show an important Digestive ↑ Respiratory
property of exchange of material with their system ↑ system
surrounding as well as between various parts
of the their cell or body. Heart Intestitial
fluid
Can you recall? ↑↑
↑↑
Which type of circulation is present in Nutrients↑ Circulatory ↑
cockroach? How is it different from that of system
humans? Body
↑ ↑↑ cells

Urinary
system

Intestine

↑ ↑
Anus

Unabsorbed Metabolic waste
matter (feces) products (urine)

Internet my friend

Organisms take up oxygen and nutrients 1. Which is type of circulation present in
from the surrounding, these are circulated amphibians and reptiles?
within the body for various metabolic activities.
2. Enlist organisms without a proper
transport system.

162

Use your brain power 2. Closed circulation : In all the vertebrates,
higher molluscs and annelids, blood is
What is the co-relationship between circulated all over the body through a
activeness of organism and complexity of network of blood vessels. In this type of
transport system? circulation, blood flows within the blood
vessels and does not come in direct contact
8.8 Circulation in animals : with cells and body tissues. Exchange of
In higher animals the circulation is material between blood and body tissues is
through an intermediate fluid called lymph.
carried out by special fluids blood and lymph. Blood flows with high pressure and contains
Blood vascular system : respiratory pigments like haemoglobin for
transportation of respiratory gases.
Higher animals from Annelida to The closed circulation can be divided into
chordata have a special circulating fluid, the
blood which is pumped to the tissues by the two main types : single and double circulation.
heart through the blood vessels.
Single circulation : In single circulation, the
Types of blood vascular system : blood passes through heart only once during
1. Open circulation : In animals having each cycle as in fishes. Deoxygenated blood
is pumped from heart towards gills, where
an open circulation, blood is circulated it undergoes oxygenation. This oxygenated
through the body cavities (haemocoels). blood moves towards various body parts, gets
The visceral organs lie in the blood filled deoxygenated and returns back to heart for
body cavity. Exchange of material takes next cycle.
place directly between blood and cells or
tissues of the body. The blood flows with Gill capillaries
low pressure and usually does not contain
any respiratory pigment like haemoglobin, Artery Gill
so it does not transport respiratory gases. circulation
e.g. Arthropods (cockroach, studied in 11th Heart Ventricle
std.) and Molluscs. Atrium Systemic
circulation
Observe and Discuss

Observe the diagram and give
appropriate labels.

Vein

Systemic capillaries

Fig. 8.12 : Single circulation

163

Since, the heart of fish carries only Blood Composition and Coagulation : Study
deoxygenated blood, it also called ‘venous of blood is called haematology. An average
heart’. adult has about 4 to 6 liters of blood. It is a red
coloured fluid connective tissue derived from
Double circulation : In double circulation, embryonic mesoderm. It is slightly alkaline
blood passes through heart twice during each (pH 7.4), salty and viscous fluid. It is heaviere
cycle; it occurs in birds and mammals. In these then water. It has two main components- the
animals, heart pumps deoxygenated blood to fluid plasma (55%) and the formed elements
lungs for oxygenation and it returns to heart i.e. blood cells (44%). These can be separated
as oxygenated blood. This is ‘pulmonary by centrifugation.
circulation’. The oxygenated blood is pumped
from the heart towards various body parts Plasma : It constitutes 55% of the blood. It is a
(except lungs) and returns back to the heart straw-coloured, slightly alkaline, viscous fluid
as deoxygenated blood. This is ‘systemic and consists of following:
circulation’. Human heart shows double
circulation. Table 8.14 : Composition of plasma

Pulmonary Heart Superior and Contents Percentage
veins inferior vena
1. Water 90 %
Right Left cava 2. Proteins (albumen, globulin, 7 to 8 %

atrium atrium properdin, prothrombin, fibrinogen) 1%
3. Inorganic salts (Na, K, Mg, Ca, Fe,
Lungs Right Left Body 1 to 2 %
ventricle ventricle organs Mn and Cl-, HCO-3 and PO3-4)
4. Others :
Pulmonary Dorsal a. Food (glucose, amino acids, fatty
artery aorta
acids, triglycerides)
Pulmonary circulation Systemic circulation b. Wastes (urea, uric acid and

Fig. 8.13 : Double circulation creatinine)
(Diagrammatic) c. Regulators (hormones, enzymes,

Internet my friend vitamins)
d. Anticoagulants (heparin)
e. Cholesterol and antibodies
f. Dissolved gases (O2, CO2, N2)

1. Find out the difference between coelom Internet my friend
and haemocoel?
1. Find out the percentage and functions of
2. Name respiratory pigments present in different blood proteins.
the blood of different animals.
2. What is the clinical importance of
8.9 Circulatory System in Human : haematokrit value?
The human circulatory system is composed
3. Differentiate between plasma and serum.
of blood vascular and lymphatic system.
Formed elements :
Blood vascular system : The blood cells that are produced in the
In human beings it consists of blood, heart
body are collectively called formed elements.
and blood vessels. It is responsible for various Human blood contains three types of formed
functions like transport, homeostasis and elements as red blood corpuscles (RBCs), white
protection. blood corpuscles (WBCs) and platelets.

164

8.10 Red blood corpuscles / Erythrocytes : Do you know ?

Erythrocytes are the most abundant cells in Each erythrocyte approximately contains
the human body. They are circular, biconcave 270 million molecules of haemoglobin.
and enucleated (in camel and llama they are Normal content of haemoglobin in blood of
nucleated). men is about 14 – 17 gm% and in women
it is about 13 – 15 gm%. Condition with
The red colour or RBCs is due to an oxygen less number of RBCs or less amount of
carrying pigment, the haemoglobin, in their haemoglobin or both is called as anaemia.
cytoplasm. In males, their average number
is about 5.1-5.8 million/mm3 (per µL) and in Each molecule of haemoglobin is a
females about 4.3-5.2 million/mm3. This is protein-iron complex. It consists of four
called total RBC count. The average life span polypeptide (globin) chains 2 alpha and 2
of RBCs is 120 days. The process of formation beta chains. An iron – porphyrin (haem)
of RBCs is called erythropoiesis. group is attached to each chain and all
four chains are bound together. Each haem
RBCs are produced from haemocytoblasts group can carry one O2 molecule and thus
/ reticulocytes. The erythropoeitic organ of the one haemoglobin molecule can carry four
foetus is the liver and spleen and in the adult, O2 forming oxyhaemoglobin. CO2 interacts
it is mainly the red bone marrow. Vitamin with amino acid residues of globin chains
B12, folic acid and heme protein are required and forms carbaminohaemoglobin. After
for production of RBCs The old and worn out haemolysis, haemoglobin is broken down.
RBCs are destroyed in the liver and spleen Its globin part is broken to recycle the amino
(graveyard of RBCs). Condition with increase acids. Iron of heme group is stored as ferritin
in the number of RBCs is called polycythemia in the liver and porphyrin group of heme is
and with decrease in number of RBCs is converted into green pigment biliverdin and
called as erythrocytopenia. The hormone then into red-orange coloured bilirubin. These
erythropoietin produced by the kideny cells pigments (mainly bilirubin) are added to bile
stimulates the bone marrow for production of and finally removed out of body along with
RBCs. faeces.

Mature erythrocyte is devoid of nucleus, Internet my friend
mitochondria or other membrane bound cell
organelles. Its cytoplasm (stroma) is rich in 1. Compare between myoglobin and
haemoglobin and O2 carrying proteinaceous haemoglobin.
pigment that gives red colour to the RBCs and
blood. It also contains an enzyme, carbonic 2. In the erythrocytes, nucleus and
anhydrase. mitochondria are absent. Explain?

Erythrocytes are responsible for the 8.11 White blood corpuscles / Leucocytes:
transport of respiratory gases O2 and CO2, Leucocytes are colourless, nucleated and
maintaining pH and viscosity of blood. They
also contribute in the process of blood clotting. amoeboid cells larger than RBCs.Due to their
The hematocrit is ratio of the volume of RBCs amoeboid movement they can move out of the
to total blood volume of blood. It is different capillary walls by a process called diapedesis.
for men and women. A normal adult has on an average, 5000-11000
WBCs per mm3 of blood. Decrease in number of

165

WBCs (<4000) is called leucopenia (common a. Neutrophils : Granules are very fine, large
in HIV, AIDS and TB patients or those exposed in number, evenly distributed and stained
to radiations, shock, etc). Temporary increase in with neutral stains (dyes). Neutrophils are
number of WBCs is called as leucocytosis. It is about 70% of total WBCs. These cells are
due to infection. It also occurs during pregnancy spherical and nucleus is several lobed (2-
and in newborn babies. Uncontrolled increase 7). These are able to perform amoeboid
in number of WBCs is a type of blood cancer movements and phagocytosis. They are
called leukemia. WBCs are mainly concerned responsible for destroying pathogens by the
with defense mechanism i.e. protection. process of phagocytosis. ‘Pus’ is mixture of
dead neutrophils, damaged tissues and dead
Types of WBCs : microbes.

These are colourless, irregular nucleated Think about it
cells and show polymorphism (exist in variable
forms). They can be classified into two main Why and when do the leucocytes perform
types such as granulocytes and agranulocytes. diapedesis?

A. Granulocytes : b. Basophils / Cyanophils : These cells have
very few granules of large size, and stain with
These are WBCs with a granular basic stains like methylene blue. Basophils
cytoplasm, also called Polymorpho nuclear are non-phagocytic, small, spherical cells and
leucocyte (PMN) cells. They have lobulated are about 0.5-1% of total WBCs.. Nucleus
nuclei in different shapes. Granulocytes are is twisted. They are present in infected and
formed from myeloid stem cells and once allergic conditions only. Basophils secrete
formed, do not divide. Granulocytes constitute heparin, histamine and serotonin.
about 72% of total WBCs. Granules are
actually secretory vesicles which contain c. Eosinophils / Acidophills : Acidophills
various secretions, enzymes, etc. Depending contain lysosomal granules that are stained
upon staining property of the granules, these to red colour with acidic stains like eosin.
granulocytes are classified into three types as Eosinophils are about 1 – 3 % of total WBCs.
neutrophils, basophils and acidophills. Nucleus is bilobed. They destroy antigen-
antibody complex by phagocytosis. Their
Think about it number increases in allergic condition and they
show antihistaminic property. They are also
What are the granules in granulocytes? responsible for detoxification as they produce
antitoxins.

Granules

Nucleus

a. Neutrophil Nucleus c. Eosinophil d. Lymphocyte e. Monocytes

b. Basophil

Fig. 8.15 : Granulocytes and Agranulocytes

166

B. Agranulocytes : 8.12 Thrombocytes / Platelets:
Agranulocytes are about 28% of total Thrombocytes are cellular fragments

WBCs. Cytoplasm of these leucocytes is formed from the large cells called
without granules. They are formed from megakaryocytes. These are produced in bone
lymphoid stem cells and can divide by mitosis. marrow. They are very small, oval shaped cell
Nuclei of agranulocytes are large in size but fragments without nucleus. Normal count of
are not lobulated like the granulocytes. There thrombocytes in human blood is about 2.5 – 4.5
are two types of agranulocytes - Lymphocytes lakh / mm3 of blood. If number of thrombocytes
and Monocytes. decreases than normal, condition is called as
thrombocytopenia. This condition causes
a. Lymphocytes : Lymphocytes are the internal bleeding (haemorrhage). Platelets
smallest of all WBCs and have a large spherical secrete platelet factors which are essential
nucleus. They constitute about 25-30% of total in blood clotting. They also seal the ruptured
WBCs. Depending upon function, two types blood vessels by formation of platelet plug/
of lymphocytes are present as B-lymphocytes thrombus. They secrete serotonin a local
and T-lymphocytes. B-lymphocytes mature vasoconstrictor.
in bone marrow and are responsible for
antibody production/humoral immunity. It is RBC WBC
a highly specific antigen, antibody immunity
T-lymphocytes mature in thymus and are Platelets
responsible for cell-mediated immunity. Helper
T-cells, killer T-cell, memory T-cells and
suppressor T-cells are four main subtypes of
T-lymphocytes.

b. Monocytes : Monocytes are the largest of Fig. 8.16 : Blood smear
all the WBCs. Its nucleus is large and bean
or kidney shaped. They form 3-5% of WBCs. Blood Clotting/ Coagulation of blood :
Monocytes are actively motile and give rise Clotting or coagulation is the process of
to macrophages. They are mainly phagocytic
and destroy the bacteria and dead or damaged converting the liquid blood into a solid form.
tissue by phagocytosis. This process may be initiated by contact
of blood with any foreign surface (intrinsic
Internet my friend process) or with damaged tissue (extrinsic
process). Intrinsic and extrinsic processes
1. What are the reasons for changes involve interaction of various substances called
in number of neutrophils and the clotting factors by a step wise or cascade
importance of complete blood count mechanism. There are in all twelve clotting
(CBC)? factors numbered as I to XIII (factor VI is not
in active use). Interaction of these factors in
2. Why and when are heparin, histamine a cascade manner leads to formation of the
and serotonin secreted? Are these enzyme thrombin. Thromboplastin, helps in
biomolecules secreted by any other cell/ the formation of enzyme prothrombinase. This
organ in our body? enzyme inactivates heparin and it also converts
inactive prothrombin into its active thrombin.

167

Thrombin converts soluble blood protein- (base) and conical at lower end (apex). Conical
fibrinogen into insoluble fibrin. Fibrin forms a end is slightly tilted to left side and rests above
mesh in which platelets and other blood cells the diaphragm.
are trapped to form the clot. Blood clotting
occurs as shown in the following flowchart. Heart is enclosed in a membranous sac
called pericardium. Pericardium is formed
Observe and Discuss of two main layers - outer fibrous and inner
serous pericardium.
Observe the flow chart and discuss the
process with your friends. Pericardium Heart wall

Extrinsic Pahway Intrinsic Pahway Trabeculae
carneae
Damage to tissue Inactive Damage to the Fibrous
outside the vessel factor X blood vessel pericardium Myocardium
(Cardiac
Tissue Cascade of Parietal layer muscles)
Thromboplastin clotting factors of serous
Endocardium
pericardium
Activated
factor X Pericardial
space
Prothrombin Thrombin
Visceral layer
Fibrinogen Fibrin Blood Clot of serous

pericardium
(Epicardium)

Curiosity Fig. 8.17 : Heart wall and Pericardium

1. What is blood clotting? How and when Serous pericardium is soft, moist and
does it occur? elastic. It is formed of squamous epithelium and
is further divisible into two layers as parietal
2. What is immunity? Name its types. and visceral layer. Parietal and visceral
3. Why does the platelet count decrease in layers of serous pericardium are separated by
a pericardial space. This space is filled with
dengue patient? pericardial fluid (about 50ml) which acts as
4. Why does our immune system fail a shock absorber and protects the heart from
mechanical injuries. It also keeps the heart
against pathogens like Trypanosoma and moist and acts as lubricant.
Plasmodium?
5. What is the relation between immunity Heart wall :
and organ transplantation? The heart is mesodermal in origin. Its wall
6. How do monocytes perform amoeboid
movement and phagocytosis? is formed of three layers, outer epicardium,
7. How do monocytes modify into middle myocardium and inner endocardium.
macrophages? Epicardium is thin and formed of a single
layer of flat squamous epithelium resting
8.13 Heart : on basement membrane. Myocardium is the
Heart is the main pumping organ of the middle thick layer formed of cardiac muscles.
Endocardium is a single thin layer formed of
circulatory system. It is reddish brown in colour, squamous epithelium. The epicardium and
hollow, muscular organ, roughly the size of endocardium are protective in function whereas
one’s fist. Its average weight is about 300gm myocardium is responsible for contraction and
in males and 250gm in females. It is conical in relaxation of heart.
shape and lies in mediastenum- i.e. the space
between two lungs. It is broader at upper end

168

External structure of heart : pulmonary trunk bifurcates into right and left
The human heart is four chambered. pulmonary arteries. Aorta (systemic aorta) is
divisible into three regions as ascending aorta,
The two superior chambers are called systemic arch /aortic arch and descending
atria (auricles) and inferior two are called aorta. The Ligamentum arteriosum joins
ventricles. Externally, the atria are separated pulmonary trunk and aortic arch. It is the
from ventricles by a transverse groove called remnant of an embryonic duct called ductus
coronary sulcus or atrioventricular groove. arteriosus. The aortic arch gives out three
The two ventricles are externally separated arteries viz. brachiocephalic (innominate)
from each other by two grooves, the anterior artery, left common carotid and left sub-
and posterior inter-ventricular sulci. Coronary clavian. The right atrium recieves superior and
arteries and coronary veins run through inferior vena cava along its dorsal surface.
these sulci. Pulmonary trunk arising from Pulmonary veins open into left atrium along
right ventricle and aorta from left ventricle the dorsal surface of heart.
are present on anterior surface of heart. The
left subclavian artery
Left common carotid artery
Brachiocephalic artery Superior vena cava

Aorta Right pulmonary artery
Right pulmonary veins
Left pulmonary artery
Left pulmonary vein Inferior vena cava
Right Ventricle
Left Atrium
Coronary sinus

Left Ventricle

Apex of heart

Fig. 8.18 : Posterior (dorsal) view : External structure of human heart

Superior vena cava Left subclavian artery
Right pulmonary artery Aorta
Right pulmonary veins Ligamentum arteriosum
Left pulmonary artery

Pulmonary trunk
Left pulmonary veins

Right coronary atery Left Atrium

Right atrium Branch of left coronary
Coronary Sulcus artery

Right Ventricle Left Ventricle
Inferior vena cava

Fig. 8.19 : Anterior (ventral) view : External structure of human heart

169

Superior vena cava Left common carotid artery
Pulmonary trunk
Right pulmonary artery Left pulmonary artery
Pulmonary semilunar valve
Left pulmonary veins
Opening of superior
vena cava Left atrium
Bicuspid (Mitral) Valve
Right pulmonary veins
Chordae tendinae
Right atrium Papillary muscles
Tricuspid valve
Left Ventricle
Right ventricle Interventricular septum

Inferior vena cava
Columnae carnae

Fig. 8.20 : Internal structure of human heart

Internal structure of heart: shows several ridges called columnae carnae
Atria : These are the thin-walled receiving or trabeculae carnae which divide the lumen
chambers of heart. They are separated from of ventricle into small pockets or fissures. The
each other by inter-auricular septum. Inter- lumen of ventricles also shows inelastic fibers
auricular septum has an oval depression called called chordae tendinae. These attach the
fossa ovalis. It is a remnant of the embryonic bicuspid and tricuspid valves to the ventricular
aperture called foramen ovalis.

Superior vena cava (precaval), inferior wall (papillary muscles) and regulate their
vena cava (postcaval) and coronary sinus opening and closing.
open into the right atrium. Opening of the
postcaval is guarded by a Eustachian valve The right ventricle opens into the
while the Thebesian valve guards the opening pulmonary aorta and left ventricle opens into
of coronary sinus into right atrium. Four the aorta. These openings are guarded by three
pulmonary veins open into the left atrium. semilunar valves each. These valves prevent
These openings are without valves. the backward flow of blood into the ventricles.

Both the atria open into the ventricles Pumping action of heart :
of their respective sides by atrioventricular
apertures. These openings are guarded by The heart acts as the main pumping organ
cuspid valves. The tricuspid valve is present of the circulatory system. The pumping action
in the right AV aperture and bicuspid valve is brought about by a rhythmic contraction
(mitral valve) is present in the left AV aperture. and relaxation of the cardiac muscles or heart
All these heart valves help in maintaining a muscles. Contraction of heart muscles is systole
unidirectional flow of blood. They also avoid and relaxation of heart muscles is diastole.
back flow of blood.
A single systole followed by diastole
Ventricles : These are inferior, thick-walled makes one heart beat. The heart beats 70 to
pumping chambers of the heart. The right 72 times per minute. This is called heart rate.
and left ventricles are separated by an inter- During each heart beat ventricles pump about
ventricular septum. Wall of the left ventricle is 70 ml of blood this is called stroke volume.
more muscular and about 3-times thicker than It means heart pumps about 72 (heart rate) x
the right ventricle. Inner surface of the ventricles 70 ml (stroke volume) = 5040 ml ≈ 5 liters of
blood per minute this is called cardiac output.

170

Right atrium Left atrium

Sinoatrial (SA) Node Left ventricle
Atrioventricular (AV) Node Purkinje fibers

Atrioventricular (AV)
Bundle (Bundle of his)

Right and Left
Bundle Branches

Right ventricle

Fig. 8.21 : Conducting system of human heart

Conducting tissue of heart: These branches form network in ventricular
The human heart is myogenic i.e. the heart walls and these are called Purkinje fibers.
Bundle of His and Purkinje fibers spread
is capable of generating a cardiac contraction impulses in ventricles. As a result both the
independent of nervous input. It also shows ventricles contract simultaneously.
auto rhythmicity i.e. it can generate its own
rhythm by specialized muscles. A specialized Do you know ?
cardiac musculature called the nodal tissue is
distributed in the heart. A part of this nodal Sometimes, valves are defective. Due to
tisse is present in the upper right corner of the this, abnormal or adventitious sound is heard,
right atrium. It is called SA Node or Sino- called ‘heart murmuring’ or ‘hissing.’
atrial node. It lies at the base of opening of
superior vena cava. Another mass of nodal 8.14 Working mechanism of human heart :
tissue, the modified muscular fibers also called Cardiac Cycle :
autorhythmic fibers (conducting tissue) control
the beating rate of heart. Conducting (nodal) Human heart alternately contracts and
tissue consists of SA node, AV node, bundle of relaxes. Contraction is called systole and
His and Purkinje fibers. relaxation is called diastole. Atria and
ventricles contract alternately. Consecutive
Conducting system of the heart : systole and diastole constitutes a single
SA node (sinu-atrial node) is present in heartbeat or cardiac cycle. It is completed in
0.8 sec. On an average, 72 beats are completed
the right atrium. It acts as pacemaker of heart in one minute in an adult, at rest.
because it has the power of generating a new
wave of contraction and making the pace of a. Atrial systole (AS):
contraction. SA node passes the contraction Right atrium receives deoxygenated
to the left ventricle and also to the AV node.
AV node (atrio-ventricular node) is present in blood and left atrium receives oxygenated
the right atrial wall near the base of interatrial blood. When both the atria are completely
septum. It acts as pace setter of heart. filled with blood, pressure is exerted on the
wall. In response to this pressure, SA node
Bundle of His/ Tawara branches start gets excited and generates cardiac impulse.
from AV node and pass through interventricular Due to this, cardiac muscles in the atrial wall
septum. Bundle of His forms two branches, the contract causing atrial systole. During atrial
right and left bundles, one for each ventricle. systole, blood is pumped into ventricles. Blood

171

is prevented from going back to the veins and Right side of heart contains deoxygenated
coronary sinus by Eustachian and Thebesian and left contains oxygenated blood. Total
valve respectively. After completing systole the volume of blood pumped during one ventricular
atria go into diastole. systole is called stroke volume (SV) and it is it
approximately 70 ml.
In normal conditions, atrial systole is for
0.1 sec. and atrial diastole (AD) is for 0.7 sec. Cardiac output (CO):
It is the volume of blood pumped out per
b. Ventricular systole (VS):
The impulse which started from SA node min. For a normal adult human being it is
calculated as follows :
now reaches the AV node and it gets excited. AV
node sends impulses to bundle of His and from (CO) = SV × HR
bundle of His to Purkinje fibers. Purkinje fibers = 70 × 72 = 5040 ml/min
spread impulses all over the wall of ventricles.
Due to this, ventricular wall contracts causing Regulation of cardiac activity :
ventricular systole. During ventricular Though human heart is myogenic,
systole, right ventricle pumps deoxygenated
blood into pulmonary trunk and left ventricle it is also under dual control, the nervous
pumps oxygenated blood into aorta. During as well as hormonal. The nervous control
ventricular systole the cuspid valves close both includes the part of autonomic nervous
the atrioventricular apertures preventing blood system. Sympathetic system (with hormone
flow into atria (lubb sound is heard). epinephrine as neurotransmitter) increase
the rate of heartbeat during emergency.
In normal conditions, ventricular systole Parasympathetic system (with acetylcholine
lasts for 0.3 sec. and ventricular diastole (VD) as neurotransmitter) reduces rate of
lasts for 0.5 sec. During ventricular diastole, heartbeat.
semilunar valves are closed, preventing
backflow of blood from pulmonary trunk and Nervous control includes the part
systemic aorta into ventricles (dub sound is of the autonomous nervous system- its
heard). cardiovascular center lies in the medulla
oblongata. It controls rate of heart beat in
For about 0.4 second, both atria and response to inputs from various receptors like
ventricles are in diastole. When all the proprio-receptors (which monitor the position
chambers of heart are in diastole, this condition of limbs and muscles), chemoreceptors
is called joint diastole or complete diastole. (monitoring chemical changes in blood) and
Thus, duration of one cardiac cycle is 0.8 sec. baroreceptors (monitoring the stretching of
main arteries and veins).
AS
Chemical control of the heart rate
VS VD includes the conditions like hypoxia,
acidosis, alkalosis causing decreased
Joint diastole cardiac activity, hormones like epinephrine
AS AD and norepinephrine enhance the cardiac
activity. Besides, concentration of cations
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 like K+, Ca++ and Na+ have major effect on
cardiac activity. Cardiac activity decreases
Time in sec with the elevated blood level of K+ and Na+

Fig. 8.22 : Diagramatic representation of
cardiac cycle

172

8.15 Blood vessels : Veins :
There are three main types of blood vessels Veins are thin walled, mostly superficial

in the human circulatory system viz, arteries, vessels which carry blood from the organs
veins and capillaries. towards the heart. The capillaries around the
various organs join to form the veins. Except
Arteries : for the pulmonary veins or other veins of the
body carry deoxygenated blood towards the
These blood vessels carry blood from heart heart.
to various parts/organs of the body, there they Portal vein : A portal vein e.g. hepatic portal
branch into arterioles and further into fine vein, differs from the other normal veins in
capillaries. They normally carry oxygenated that its starts as capillaries from one organ and
blood to all parts of the body (except the capillarises in some intermediate organ e.g.
pulmonary artery which carries deoxygenated liver, before taking the blood towards the heart.
blood). They are usually situated deep in the Histologically, the veins also show the three
body except a few like the radial, brachial, layers like in the arteries. The tunica externa,
femoral, etc. which are superficially located. tunica media and tunica interna. However, the
In a T. S. of artery, its wall shows three layers. tunica media is comparitively thiner and their
lumen is wide and narrow. Internal valves at
1. Tunica externa or tunica adventitia regular intervals can be seen. Blood flows with
2. Tunica media flow pressure and the valves prevent backflow
3. Tunica interna or intima of blood.

The outermost tunica externa is a thick, Capillary :
tough layer of collagen fibers. The tunica These are a network of minute blood
media is made up of smooth muscles and
elastic fibres. This thick muscular and elastic vessels. They are thin walled having a single
layer makes the arterial wall pulsatile. The layer of flat squamous epithelium resting
innermost tunica interna is a single layer of on a single basement membrane. They are
flat compact endothelial cells surrounding the mainly involved in exchange of materials.
lumen. The angular margin around the lumen Wall of capillaries is formed of single layer
shows tesselations. Arterial lumen is devoid of of squamous epithelium and it is stretchable.
valves and blood flows through it rapidly and Blood flows through the capillaries under
with high pressure. high pressure. Wall of capillaries bear small
endothelial pores or fenestrae through which
Tunica externa blood cells (WBCs) can escape by the process
called as diapedesis.
Lumen Lumen
Pulse : It is a series of pressure waves that
Artery Tunica media Vein travel through the arteries due to ventricular
Tunica interna systole. It is the strongest in arteries closer
to the heart and gradually becomes weak in
Lumen arteries away from heart. It can be felt easily in
Capillary the superficial arteries like radial artery in the
wrist and carotid artery in the neck. The pulse
Fig. 8.23 : T. S. of Artery, Vein and Capillary can be felt at particular points on the body. All
locations where the pulse can be felt are shown
in the figure 8.27.

173

Facial Temporal (arteriosclerosis), deposition of fats like
Carotid cholesterol in the arteries (atherosclerosis),
renal diseases and emotion induced hormonal
Brachial changes, obesity, etc. Blood pressure lower
than normal i.e. below 90/60 mmHg is called
Dorsalis Radial hypotension and blood pressure higher than
pedis Femoral normal i.e. above 140/90 mmHg is hypertension.

Popliteal Various factors that affect the blood pressure
Posterior are cardiac output, peripheral resistance, blood
tibial volume, length and diameter of blood vessels,
viscosity of blood, age, gender, venous return,
Fig. 8.24 : Pulse points sleep, emotions, exercise, anxiety, etc.

Pulse rate is equal to heart rate. Pulse rate Think about it
higher than normal (above 100 beats/min)
is called tachycardia and slower pulse rate Why do obese persons are prone to
(below 60 beats/min) than normal is called hypertension?
bradycardia.
Normal cardiac output is 5 lit/min.
Use your brain power Increase in cardiac output increases systolic
pressure. Peripheral resistance depends upon
Why do the veins have valves? the diameter of blood vessels. Decrease in
diameter of arterioles and capillaries under the
8.16 Blood pressure (B. P.): effect of vasoconstrictors like vasopressin or
The pressure exerted by blood on the wall ADH cause increase in peripheral resistance
and thereby increase in blood pressure. Blood
of the blood vessels is called blood pressure. loss in accidents decreases blood volume and
It is measured by the sphygmomanometer. It is thus the blood pressure. Blood pressure is
usually measured from the arteries. directly proportional to Viscosity of blood.

Arterial Blood Pressure: Blood pressure increases with age due to
Pressure exerted by blood on the wall of increase in inelasticity of blood vessels.Amount
of blood brought to the heart via the veins per
artery is arterial blood pressure. Pressure on unit time is called the venous return and it is
arterial wall during ventricular contraction directly proportional to blood pressure. Blood
(systole) is systolic pressure (SP). For a normal pressure is also directly proportional to the total
healthy adult the average value is 120 mmHg. length of the blood vessel. Blood pressure can
also be affected by vaso constriction or vaso
Pressure on arterial wall during relaxation dilation. Females have slightly lower BP than
of ventricles is diastolic pressure (DP). For a males her age before menopause. However, the
normal healthy adult it is 80 mmHg. risk of high B. P. increases in the females after
menopause sets in.
B P = SP / DP
= 120/80 mmHg Internet my friend

Blood pressure is normally written as 120/80 Surf the internet for video-clips of
mmHg. Difference between systolic and angiography, angioplasty and by-pass
diastolic pressure is called pulse pressure. surgery. Gather more information about
Normally, it is 40 mmHg. these medical procedures.

Deviations from normal blood pressure
value indicate malfunctioning of heart. It
may be due to high or low blood volume,
arterial inelasticity or hardening of arteries

174

1. Think about it called as Korotkoff sounds. Pressure in the
1. Why the heart-recipient has to rely upon cuff is further lowered till any pulsatile sound
cannot be heard due to smooth blood flow. At
life-time supply of immunosupressants? this moment, pressure indicated in manometer
2. Why the transplanted heart beats at higher is diastolic pressure. An optimal blood presure
(normal) level reads 120/80 mmHg.
rate than normal?
Measurement of blood pressure: Hypertension :
Persistently raised blood pressure higher
Blood pressure is measured with the help
of an instrument called sphygmomanometer. than the normal is called hypertension. 140/90
This instrument consists of inflatable rubber bag mmHg is called as threshold of hypertension
cuff covered by a cotton cloth. It is connected and the 180/120 mmHg and higher readings
with the help of tubes to a mercury manometer are dangerous to the health. It may damage the
on one side and a rubber bulb on the other heart, brain and kidneys.
side. During measurement, the person is asked
to lie in a sleeping position. The instrument Under the condition of hypertension,
is placed at the level of heart and the cuff is heart uses more energy for pumping which
tightly wrapped around upper arm. The cuff is causes angina pectoris- the chest pains due
inflated till the brachial artery is blocked due to lowered blood supply to cardiac muscles
to external pressure. Then pressure in the cuff and may lead to myocardial infarction. There
is slowly lowered till the first pulsatile sound are more chances of brain hemorrhage due
is heard. to hypertension as arteries in brain are less
protected by surrounding tissues as compared
At this moment, pressure indicated in to other organs. In kidney, hypertension may
manometer is systolic pressure. Sounds heard cause kidney failure.
during measurement of blood pressure are
Coronary Artery Disease (CAD) :- It is also
Fig. 8.25 : Sphygmomanometer known as atherosclerosis. In this, calcium, fat
cholesterol and fibrous tissues gets deposited
in blood vessels suppling blood to the heart
muscles making the lumen narrow.

Angina Pectoris :
It is the pain in the chest resulting

from a reduction in the blood supply to the
cardiac muscles because of atherosclerosis or
arteriosclerosis. It is charactarized by severe
pain and heaviness in the chest. The pain may
spread to the neck, lower jaw, left arm and
left shoulder. The pain usually results from
exertion, when there is more demand of oxygen
by the heart, but the supply does not meet the
requirement.

Angiography :
X-ray imaging of the cardiac blood

vessels to locate the position of blockages

175

is called angiography. Depending upon the 8.17 Electrocardiogram:
degree of blockage, remedial procedures like Graphical recording of electrical variations
angioplasty or by-pass surgery are performed.
In angioplasty, a stent is inserted at the site detected at the surface of body during their
of blockage to restore the blood supply while propagation through the wall of heart is
in by-pass surgery, the atherosclerotic region electrocardiogram (ECG). This recording
is by-passed with part of vein or artery taken may be in the form of printout or onscreen
from any other suitable part of the body, like display. The instrument used for this recording
hands or legs. is the ECG machine or electrocardiograph.
This instrument detects and amplifies the
Heart Transplant : signals.
Replacement of severely damaged heart
Various electrodes are used for recording
by normal heart from brain-dead or recently of signals. Four electrodes are positioned on
dead donor is called heart transplant. Heart limbs; two on arms and two on legs. These are
transplant is necessary in case of patients with limb electrodes. Six electrodes are positioned
end-stage heart failure and severe coronary on chest. These are chest electrodes.
arterial disease.
In a normal record, three different waves
Silent Heart Attack : are recognized as P-wave, QRS complex and
Silent heart attack, also known as silent T-wave. P-wave is a small upward deflection
from baseline of graph. It represents the atrial
myocardial infarction is a type of heart attack depolarization. The QRS complex starts as
that lacks the general symptoms of classic heart a slight downward deflection from baseline,
attack like extreme chest pain, hypertension, continues as sharp and large upright wave
shortness of breath, sweating and dizziness. and ends as a downward wave. QRS complex
Symptoms of silent heart attack are so mild represents the ventricular depolarization.
that a person often confuses it for regular T-wave is small, wide and upwardly
discomfort and thereby ignores it. It has been elevated wave. It represents the ventricular
studied that men are more affected by silent repolarization.
heart attack than women.
Millivolts Atria Ventricles S-T
Know the Scientist : +2 segment

Akash Manoj, a teenager from Chennai RR interval
invented the non-invasive technique to
predict the possibility of a silent heart attack. +1 R
Interestingly, he invented this technique
when he was in class-X. P T
0
For his innovation, he had been invited
to the Rashtrapati Bhavan as a guest of P-R interval Q-T interval
the President of India under the Innovation -1 = 0.16 sec
Scholars In-Residence Programme. 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

His innovative kit analyses the level of Time (sec)
FABP3 (Fatty Acid Binding Protein-3) with
the help of UV light. It is the smallest protein Fig. 8.26 : Normal ECG
in the blood.
ECG helps to diagnose the abnormality
Find out more information about..... in conducting pathway, enlargement of heart
chambers, damages to cardiac muscles,
reduced blood supply to cardiac muscles and

176

causes of chest pain. A physicial can find out Curiosity
the defect in the heart by examining the wave
pattern and the time interval betwen them. 1. What is depolarization and repolarization?
2. What is the correlation between
8.18 Lymphatic System :
Lymphatic system consists of lymph, depolarization and repolarization as ell as
contraction and relaxation of the heart?
lymphatic vessels, some organs and tissues. 3. How are the signals detected and amplified
The word ‘lymph’ means ‘clear water’ and it by electrocardiograph?
is a fluid connective tissue with almost similar 4. Who discovered ECG?
composition to the blood except RBCs, platelets
and some proteins. Fluid from intercellular Internet my friend
spaces of the body tissue enters into the
lymphatic vessels, from here it is discharged Location of lymph nodes in human body.
into the blood vessels (veins) through the
thoracic duct and the right lymphatic duct.

Tonsil

Subclavian vein Cervical lymph nodes
Thymus gland Red bone marrow
Axillary lymph nodes Spleen

Thoracic duct Inguinal lymph nodes
Appendix

Popliteal lymph nodes

Fig. 8.27 : Lymphatic System
177

Do you know ?

Tonsils are small lymphatic nodules in pharyngeal region. Normally there are five tonsils
strategically positioned to fight against inhaled and ingested foreign substances. Inflammation
of tonsils is called as tonsillitis. It is caused due to viral or bacterial infection. Symptoms
include sore throat, fever, swollen lymph nodes, nasal congestion, difficulty in swallowing,
headache, etc. Viral tonsillitis cures naturally but bacterial tonsillitis needs antibiotic treatment.
Tonsillectomy is performed in some patients who do not respond to the treatment.

Systematic circulation Lymph node Pulmonary circulation
Veins Lymphatic capillaries
Lymphatic duct
Subclavian vein Heart Pulmonary blood capillaries
Arteries
Lymphatic Systemic blood capillaries
vessel

Valve

Lymph node

Lymphatic capillaries

Blood capillary Arteriole Lymph
Blood
Venule Endothlium
Tissue cell of lymphatic
capillary
Blood Tissue cell
Lymph
Intestitial fluid Intestitial fluid
Lymphatic capillaries
Anchoring
a. Relationship of lymphatic capillaries to tissue cells filament
and blood capillaries Opening

b. Details of lymphatic capillary

Fig. 8.28 : Circulation and Lymphatic System

178

Activity :
1. Prepare chart for different types of heart muscles and their functions.

2. Differentiate between the functioning of heart in frog and human.

Human Heart Frog Heart

179

Exercise

Q. 1 Choose the correct alternatives from those 11. Cockroach shows which kind of
given below and complete the statements. circulatory system?
a. Open b. Closed
1. The muscular structure that separates the c. Lymphatic d. Double
thoracic and abdominal cavity is _______.

a. pleura b. diaphragm 12. Diapedesis can be seen in _________
c. trachea d. epithelium
cell.

2. What is the minimum number of plasma a. RBC b. WBC
membrane that oxygen has to diffuse
across to pass from air in the alveolus to c. Platelet d. neuron
haemoglobin inside a R.B.C.?
13. Opening of inferior vena cava is guarded
a. Two b. Three c. Four d. Five by __________.
a. bicuspid valve
3. ________ is a sound producing organ, b. tricuspid valve
c. Eustachian valve
a. Larynx b. Pharynx d. Thebesian valve
c. Tonsils d. Trachea
14. ___________ wave in ECG represent
4. The maximum volume of gas that is inhale atrial depolarization.
during breathing in addition to T.V is _____. a. P b. QRS complex
c. Q d. T
a. residual volume b. I.R.V.
c. G.R.V. d. vital capacity

5. ________ muscles contract when the 15. The fluid seen in the intercellular spaces
external intercostal muscles contract
a. Internal abdominal in Human is _________
b. Jaw
c. Muscles in bronchial walls a. blood b. lymph
d. Diaphragm
c. interstitial fluid d. water

Q. 2 Match the Respiratory surface to the
organism in which it is found.

6. Movement of cytoplasm in unicellular Respiratory surface Organism
Plasma membrane Insect
organisms is called __________. Lungs Salamander
External gills Bird
a. diffusion b. cyclosis Internal Gills Amoeba
Trachea Fish
c. circulation. d. thrombosis.

7. Which of the following animals do not

have closed circulation?

a. Earthworm. b. Rabbit Q. 3 Very short answer questions.
1. Why does trachea have ‘C’ shaped rings
c. Butterfly d. Shark of cartilage?
2. Why is respiration in insect called direct
8. Diapedesis is performed by _________. respiration?
3. Why is gas exchange very rapid at
a. erythrocytes b. thrombocytes alveolar level.
4. Name the organ which prevents the
c. adipocytes d. leucocytes following the entry of food into the
trachea while eating.
9. Pacemaker of heart is _________.

a. SA node b. AV node

c. His bundle d. Purkinje fibers

10. Which of the following is without nucleus?

a. Red blood corpuscle b. Neutrophill

c. Basophill d. Lymphocyte

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Q 4. Short answer questions. 5. Intrinsic and extrinsic process of
1. Why is it advantageous to breathe clotting.
through the nose than through the
mouth? Q. 7 Long answer questions.
2. Identify the incorrect statement and 1. Smita was working in a garage with
correct it, the doors closed and automobiles
a. A respiratory surface area should engine running. After some time she felt
have a large surface area. breathless and fainted. What would be
b. A respiratory surface area should be the reason? How can she be treated?
kept dry. 2. Shreyas went to a garden on a wintry
c. A respiratory surface area should be morning. When he came back, he
thin, may be 1mm or less. found it difficult to breath and started
3. Given below are the characteristics of wheezing. What could be the possible
some modified respiratory movement. condition and how can he be treated?
Identify them. 3. Why can you feel a pulse when you
a. Spasmodic contraction of muscles of keep a finger on the wrist or neck but
expiration and forceful expulsion of not when you keep them on a vein?
air through nose and mouth. 4. A man’s pulse rate is 68 and cardiac
b. An inspiration followed by many output is 5500 cm3.Find the stroke
short convulsive expiration volume.
accompanied by facial expression. 5. Which blood vessel of the heart will
have the maximum content of Oxygen
4. Write a note on blood plasma. and why?
5. Explain blood clotting in short. 6. If the duration of the atrial systole is
6. Describe pericardium. 0.1 sec and that of complete diastole
7. Describe valves of human heart. is 0.4 sec, then how does one cardiac
8. What is role of papillary muscles and cycle complete in 0.8 sec?
7. How is blood kept moving in the large
chordae tendinae in human heart? veins of the legs?
9. Explain in brief the factors affecting 8. Describe histological structure of
artery, vein and capillary.
blood pressure. 9. What is blood pressure? How is it
measured? Explain factors affecting
Q. 5 Give scientific reason. blood pressure.
1. Closed circulation is more efficient than 10. Describe human blood and give its
open circulation. functions.
2. Human heart is called as myogenic and
autorhythmic. Project :
3. Person who has undergone heart • Visit pathological laboratory to study
transplant needs lifetime supply of
immunosupressants. various blood tests like Hb detection,
4. Arteries are thicker than veins. CBC, blood groups.
5. Left ventricle is thick than all other
chambers of heart. • Visit hospital to study how to take ECG,
stress test, measurement of BP, etc.
Q. 6 Distinguish between :
1. Open and closed circulation. • Evaluation of ECG on broad basis.
2. Artery and vein.
3. Blood and lymph. • Use of stethescope.
4. Blood capillary and lymph capillary.
• Differential count of WBCs.

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9 Control and Coordination

Can you recall? cells form tissues, organs and systems which
must work in coordination with each other for
1. What is the need for the control and co- smooth internal functioning of the body. Also
ordination in multicellular animals ? the organism must be able to respond and
coordinate with respect to various stimuli or
2. How do plants carry out control and changes in the external environment.
coordination ?
In the lower animals like Hydra and
Unicellular organisms have a simple Planaria the nervous system achieves this
organisation of their life processes. However function, while in higher more complex
a multicellular organisation of the body animals, it is done by two coordinating systems
organs and organ systems required both, a - the nervous (elctrical) system and endocrine
control over their life processes as well as a (chemical) control system. These two systems
coordination between the various systems in will be studied separately though they work in
order to maintain homeostasis of the organism. coordination with each other.
Plants and animals both show a control and
coordination mechanism. In plants this done NERVOUS COORDINATION
by sending chemical signals and brining about 9.1 Nervous System in Hydra :
various types of movements (e.g. phototropic,
chemotactic, thingmotactic, etc). Animals, Hydra, a cnidarian shows the diffused
specially the higher vertebrates show a gradual nervous system, which is the most primitive
increase in the complexity of their control and nervous system. The cnidarians are thus the
coordination by giving both electrical and first animal group showing true simple nervous
chemical singles. In this chapter now you will system. It consists of the sensory cells and the
study about development of nervous system nerve cells or neurons along with their fibres.
in different animal groups and details of the The nerve cells are scattered or distributed
system in humans. throughout the body and inter connected to
each other by synapses between their fibres to
The porifera (sponges) are the most form the nerve net. There are two nerve nets
primitive of the animal phyla. both in the mesoglea, one connected towards
the epidermis and second towards the gastro-
Can you recall? dermis. There are sensory cells scattered in the

1. Do sponges have tissues and organs ? Tentacles
2. Can sponges coordinate their various
Nerve net
functions ?
Fig. 9.1 : Nerve net in Hydra
Even though there are different types of
cells in sponges for carrying out different
functions, a proper nervous system is lacking.
However to bring about efficient working of
the body these multicellular animals show
division of labour among the cells. This leads to
specialization of cells for the various activities
like digestion, respiration, excretion and others.
Later in the higher animals, phyla the different

182

body wall and tentacles, but sense organs are include sensory cells arranged in lateral cords
lacking. Neurons have fibres but there are no in the body. A pair of photosensory structure,
sensory and motor nerves. The nerve impulse the eyes are located on dorsal side of the brain.
shows no polarity or direction. Thus in Hydra, Also there are single sensory cells scattered in
activation of sensory cells can happen at any the body.
point, and from this point impulse can be carried
through out the body in any direction, thus In the above examples of Hydra, Planaria
bringing movements of the body or tentacles and the earlier studied examples of cockroach
eg. catching of prey during feeding. and humans, we have seen the gradual
evolution or changes of the neural system.
The diffused types of nervous system is the There is a high level of specialization in the
first important landmark in the nervous system. formation of neurons as electrically signalling
It is seen in the ctenophora as well as in the cells and also in the entire system, gradually
enteric system or gut wall of higher animals from a diffuse neural system to a centralized
including man. nervous system. The expansion into a properly
9.2 Nervous System in Planaria (flatworm) : organized system involving the brain, its
gradual expansion in size and functions.
Planaria is a flatworm belonging to the This has lead to centralization of various
phylum platyhelminthes. It is the most primitive sense organs assisting in coordinating the
animal with a central nervous system (CNS) internal environment with that of the external
located on the ventral side of body. It consists environment. Also there evolution of a complex
of a mass of cerebral or cephalic ganglion networking system which efficiently transmits
appearing like an inverted U shaped brain. signals between one part or organ of the body
These lie in the anterior or head region and from and another.
each ganglion arise nine branches towards the
outer side. Ventrally from below the ganglia Activity :
arise a pair of Ventral Nerve Cords (VNC) or
long nerve cords. These are inter connected Note the changes taking place in the
to eachother by transfer nerve or commissure internal environment of the body, when a
in a ladder like manner. The peripheral nerve person goes from resting state into a state of
plexus arising laterally from VNC. The PNS physical activity.

Eyespot 9.3 Neural tissue
The neural tissue consists primarily of two
Brain
types of cells viz the neurons and the neuroglia
Nerve cords or glial cells. While a nerve is bundle of axons,
the word ‘nerve’ is used for a bundle of axons
Transverse nerve outside the CNS while inside the CNS for the
same, word ‘tract’ is used. The nerves may be
Fig 9.2 Ladder type nervous system in sensory or motor or mix type i.e. having both
Flatworms e.g. Planaria the types - sensory and motor fibres.

All these along with nervous organs make
up the nervous system of the higher animal and
bring about coordination and control of various
activities of the body. This is done through
the receptors which bring in sensory inputs
towards the central nervous system. Processing
is carried out in the CNS and then through the

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Ependymal cell Oligodendrocytes Satellite cells

Astrocytes Microglia Schwann cells

Fig. 9.3 : Types of Neuroglial cells

motor commands, the response is sent out. The and neuroplasm. A clear film of cytoplasm
nerves arising from the cytons of the CNS, surrounds the nucleus around which there are
travel throughout the body transmitting the nurofibrils, Nissl’s granules and other cell
nerves impulses to or from the CNS. organelles Nissl’s granules are riboprotein
components. They play an important role
Curiosity Box: in the synthesis of the enzyme required for
Find out about the nervous system in formation of the neurotransmitter. Neurofibrils
play an important role in transmission of nerve
Earthworm. impulse. Dendrons are many small conical
processes arising from the cyton. These are
Internet my friend highly branched into fine dendrites. Nissl’s
granules and neurofibrils both can be seen
1. How many neurons are present in the at the base of the dendrons. They transmit
human body and specifically in the brain? message towards the cyton. Axon is a single
long, usually unbranched process arising
2. Normally what percentage of cranial from the cyton at the axon hillock. It consists
capacity is used by an average human ? of a bundle of neurofibrils. Nissl’s granules
are absent. Terminally, the axon gives out
3. What is the ratio between neurons and branches called telodendrons. The axons carry
neuroglia ? the messages away from the cytons. The axons
may give out lateral branches called collaterals.
Neurons/Nerve cells : These are the The terminal branches attach to a muscle,
structural and functional units of the nervous gland, skin or telodendrites of another neuron.
system. (You may recall the structure of The interconnection between two neurons or
a neuron studied in earlier classes). Each neuron with motor organ is called synapse. It is
multipolar neuron has three parts - cyton or
cell body, dendron and axon. The cyton has
a distinct central nucleus with a nucleolus

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Table 9.4 : Types of Neuroglial cells and their functions

Location Cell type Functions

CNS (Central Oligodendrocytes These cells have few branches and mainly form the
Nervous System) myelin sheath around the central axons, which form
the white matter of CNS. Myelin an isulating sheath
is made up of protein and fatty substances. It allows
quick transmission of electrical impulses.

Microglia or brain Small sized cells with few branches. These are derived
macrophages from monocytes and act as macrophages. They go to
the site of injury, dead neurons and cell debris in the

CNS. They mediate immune response in the CNS.

Astrocytes Star shaped cells and the most abundant glial cells of
CNS. They have varied roles in the brain, secretion

and absorption of neural transmitter and maintence of

blood-brain barrier BBB. Regulate the transmission of

electrical impulses with the brain.

Ependymal cells Form single layer of squamous or columnar, often
ciliated epithelial cells lining the ventricles or brain

cavities and central canal of spinal cord. Mainly

responsible for production and probably also for

circulation of CSF in brain ventricles and central

canal.

PNS (Peripheral Schwann Cells These are the most abundant glial cells of PNS. They
Nervous System) produce myelin sheath around medullated nerves of
PNS.
Satellite cells They support the functions of neurons.

usually axo-dendronic or may be axo-axonic, endonurium are surrounded by connective
axo-somatic or dendro-dendronic. tissue, called perineurium and a still large
bundle of nerves is covered on the outer side by
The cytons are generally found inside the epineurium. Blood is supplied to all the nerves
brain, spinal cord (CNS) and in the ganglia. to provide oxygen and nutrients.
Small groups of cell bodies inside the white Neuroglial cells :
matter of brain are called basal nuclei. A
bundle of axons called nerve may be covered The neuroglial cells are far greater in
only by neurilemma in the non-medullated number than the neurons. Most of the supporting
nerves while in the medullated nerves it is cells of the nervous system are derived from the
covered both by medullary sheath and on the same embryonic tissue layer (ectoderm) that
outside by neurilemma. Conduction of impulse produces neurons. The term neuroglia refers
by the medullated nerves is 50 times faster than to the supporting cells of the Central Nervous
in the non-medullated nerves. The connective System (CNS) and Peripheral Nervous System
tissue covering around the nerve fascicule is (PNS).
called endoneurium. Few nerve fasciculi with

185

9.4 Synapse : they may produce an impulse due to addition
It is a junction between two nerve cells or summation of stimuli.
e. All or none law - The nerve will either
with a minute gap (synaptic cleft) in between conduct the impulse along its entire length or
them which allows transmission of impulse by will not at all conduct the impulse, as in case
a neurotransmitter bridge. of subliminal or weak stimulus.
1. Properties of nerve fibres : f. Refractory period - It is the time interval
a. Excitability/Irritability - The nerve fibres, on (about millisecond) during which a nerve fails
account of presence of a polarised membrane, to respond to a second stimulus however strong
have the ability to perceive stimulus and enter it is.
into a state of activity. g. Synaptic delay - The impulse requires about
b. Conductivity - It is ability to transmit the 0.3 to 0.5 milliseconds to cross a synapse. This
excitation. time is required for release of neurotransmitter
c. Stimulus - It is any detectable, physical, from the axon terminal and excitation in the
chemical, electrical change in the external dendron of the next neuron.
or internal environment which brings about h. Synaptic fatigue - The transmission of nerve
excitation in a nerve/muscle/organ/organism. impulse across the synapse halts temporarily
In order to be effective, the stimulus must have a due to exhaustion of its neurotransmitter.
minimum intensity called threshold stimulus. i. Velocity - The rate of transmission of impulse
Subliminal (weak) stimulus will have no is higher in long and thick nerves. It is higher
effect while supraliminal (strong) stimulus in homeotherms than in poikilotherms. The
will produce the same degree of impulse as the velocity of transmission is higher in voluntary
threshold stimulus. fibres (100 - 120 m/second in man) as opposed
d. Summation effect -A single subliminal to autonomic or involuntary nerves (10-20 m/
stimulus will have no effect but if many such second). Similarly it is faster in medullated
weak stimuli are given in quick succession,

Presynaptic neuron 1 Nerve
impulse

Ca2+
2 Ca2+

Ca2+ Ca2+
Synaptic end bulb Voltage-gated Ca2+
channel
Synaptic cleft Cytoplasm

3 Synaptic
vesicles

Ca2+ Na+
Neurotransmitter

Neurotransmitter 4 K+
receptor 5 Ligand-gated
channel open
Ligand-gated
channel closed Postsynaptic neuron Postsynaptic 7 Nerve impulse
6 potential

Fig. 9.5 : Synaptic transmission

186

nerve, as the impulse has to jump from one node gland cell/ muscle) and 3. The post synaptic
of Ranvier to the next. At the synapse where the neuron.
neurons communicate with one another. The
neuron carrying an impulse to the synapse is The impulse travels along the axon of the
the pre-synaptic neuron. The neuron receiving pre-synaptic neuron to the axon terminal. Most
input at the synapse is the post synaptic neuron presynaptic neurons or axons have several
or generator region (gland or muscle). A synaptic knobs at their ends or terminals. These
synaptic cleft or a small intercellular space lies knobs have arrays of membranous sacs, called
in between two cells having a width about 20- synaptic vesicles, that contain neurotransmitter
30 nm between them. . molecules.

The process by which the impulse from When an impulse reaches a synaptic
the pre-synaptic neuron is conducted to the knob, voltage sensitive Ca++ channels open
post-synaptic neuron or cell is called synaptic and calcium (Ca++) diffuses inward from the
transmission. It is a one way process carried extracellular fluid.
out by neurotransmission.
2. Types of synapses The increased calcium concentration inside
a. Electrical synapse : In this type of synapse the cells, initiates a series of events that fuse
gap between the neighbouring neurons is the synaptic vesicles with the cell membrane
very narrow. The synapse between such of presynaptic neuron, where they release their
closed neurons is mechanical. The electrical neurotransmitters by exocytosis. Once the
conductive link is formed between the pre and neurotransmitters bind to the receptors of the
post synaptic neurons. At the gap junction, the post-synaptic cell, the action is either excitatory
two cells are within almost 3.8 nm distance (turning a process on) or inhibitory (turning a
of each other. Transmission across the gap is process off). This is dependent on the nature of
faster but depends on the connection located the neurotransmitter involved.
at the gap junctions between the two neurons.
Electrical synapses are found in those places Once the impulse has been transferred across
of the body requiring fastest response as in the the synapse, the enzyme like cholinesterase
defence reflexes. also they are bidirectional, destroys the neurotransmitter and the synapse
allowing transmission in either direction or is ready to receive a new impulse.
may be unidirectional.
b. Chemical synapse : These are specialized 9.5 Transmission of nerve impulse :
junctions through which cells of the neural The neurons are cells with some specials
system send chemical signal to the other
neurons and to non-neuronal cells, such as features. The cells can be excited. The
gland and muscle. Synaptic gap is larger than nerve impulse is a wave of bioelectrical or
that in electrical synapse and it is 20-40 nm. electrochemical disturbances passing along a
neuron. The transmission of the nerve impulse
Achemical synapse between a motor neuron along the long nerve fibre/axon tube is a
and a muscle cell is called a neuromuscular result of electrical charges across the neuronal
junction. There are three components of a membrane during conduction of an excitation.
typical chemical synapse. 1. The presynaptic Each neuron has a charged cellular membrane
terminal (mostly axonic terminal), 2. The with a voltage which is different on the outer
synaptic membrane of the post synaptic cell and inner side of the membrane. The plasma
(usually on the dendrite of the next neuron/ membrane separates the outer and inner
solutions of different chemical compounds but
having approximately the same total number
of ions. The external tissue fluid has both Na+

187

and K+ but there is predominance of Na+ and Generation of nerve impulse :
Cl-, while K+ is predominant within the fibre
or in the intracellular fluid. This condition of 1. Depolarization : The origin and maintenance
a resting nerve is also called a polarised state of resting potential depends on the original
and it is established by maintaining an excess perfect state. Any change or disturbance to
of Na+ on the outerside. On the inside there is the membrane will cause Na+ to enter into the
an excess of K+ along with large negatively membrane and lower the potential difference
charged protein molecules and nucleic acid. (lesser than -70 millivolts). This makes the
Some amount of Na+ and K+ is always leaks membrane more permeable to Na+, so there will
across the membrane. The Na+/K+ pump in the be rapid influx of Na+. This property is peculiar
membrane actively restores the ions to their to a nerve membrane.
appropriate side. Against the concentration and
electrochemical gradient, Na+ is being forced The voltage gated Na+/K+ channels
out and K+ is being forced inside the membrane. are special in 2 ways : They can change the
This process is called sodium pump or Na-K potential difference of the membrane as per the
exchange pump. This active process requires stimulus received and also the gates operate
ATP energy. The difference in distribuiton of separately and are self closing.
Na+ and K+ on the two sides of the membrane
produces a potential difference of -50 to -100 During resting potential, both gates are
millivolts (average is -70 millivolts). closed and resting potential is maintained.
However during depolarization the Na+
This potential difference seen in a resting gates open but not the K+ gates. This causes
nerve is thus called resting potential. (-70 Na+ to rush into the axon and bring about a
millivolts) and it is mainly due to differential depolarisation (opposite of polarity). Extra
permeability of the resting membrane which cellular fluid (ECF) becomes electronegative
is much more permeable to K+ than to Na+. with respect to the inner membrane which
This results in slightly more K+ diffusing out becomes electropositive. The value of action
than Na+ moving inside and causing slight potential is +30 millivolts to +60 millivolts.
difference in polarity. Also ions like negatively This triggers depolarisation in the next part
charged proteins and nucleic acids inside the while it itself starts going to repolarisation.
cell make the overall charge negative on the
inside and positive charge on the outside. Na+ K+ K+ Na+ Na+- K+
K+ Pump
The nerve membrane not only has leakage High Na+
channels but also has many gated channels for Resting
Na+/K+. These are also called voltage gated High K+ Axon
channels. These channels enable the neuron Negative organic ions
to change it membrane potential to active
potential in response to a stimuli. The Na+/K+ Polarized K+ Na+ Stimulus
gated channels are separate so transport of membrane Depolarised applied
both these ions is separately done. However
during resting potential, both these gates are Polarised Excited
closed and the membrane resting potential is Axon
maintained.
K+ Na+ K+ Na+
Na+ K+

Polarised Depolarised Re-polarised Excited
Axon

K+ Na+ Na+ K+

Fig. 9.6 : Polarisation and Depolarisation
along a nerve

188

2. Re-polarization : Change in the polarity Chart 9.7 : Steps in generation and conduction
from depolarized, back to the original state is of nerve impulse
done by the process of repolarization. It occurs
after a short interval called refractory period. Application of stimulus on a resting nerve
The large number of Na+ on the inside causes a
drop in the permeability of membrane to Na+ Permeability of membrane changes and it
and at the same time making it more permeable becomes more permeable to Na+
to K+ ions by opening the K+ voltage gates
and slowly closing the Na+ gates. This action Na+ ions diffuse into the neuron from the ECF
is a localized activity. K+ ions passes out very
rapidly as compared to slow entry of Na+. Number of positive ions inside axon increases

In this period, Na+ gates are closed, K+ Membrane potential changes from -70 mV to
gates are open and Na+ - K+ pumps becomes about +30 mV and this change in the membrane
operational. This process of producing a wave
of stimulation → causing depolarization → potential is called action potential
repolarization is repeated continuously upto the
end of axon terminal. It is a self propagating Since the polarity has been reversed from
process. negative on outside and positive inside it is also

In medullated nerves, the insulating fatty called depolarization (compared to ECF)
myelin sheath prevents flow of ions between
the axoplasm and ECF. The transport pump and Repolarisation : At the peak of action potential
gated channels can operate only in the region (+30 mv), the Na+ channels close. K+ gates open.
of nodes of Ranvier, where myelin sheath is The membrane becomes more permeable to K+
absent.
K+ ions diffuse out of the axon
The action potential cannot travel as a
wave of membrane depolarization it has to The inside of the membrane (becomes less and
jump from node to node. This process called less positive) becomes negative once again
saltatory conduction, is at the rate of 120
m/second. It is faster than the continuous Axoplasm inside becomes negatively charged
conduction in non-medulated fibre (50 :1). and ECF becomes positively charged respectively

Do you know ? 9.6 Human Nervous System :
The nervous system in humans is well
Na-K pump operates actively and by use
of carrier (for every 3 Na+ pumped out 2K+ developed and complex. It is broadly classified
are pumped in). It is electrogenic. into three parts. viz, CNS, PNS and ANS.

Always Remember 1. Central nervous system (CNS) : The brain
and spinal cord are the parts of CNS which lie
The resting potential of axon is -70 along the mid dorsal axis. Brain is enclosed
mV. Na+- K+ Pump pumps out 3 Na+ ions for within the brain box/cranium of the skull,
every 2 K+ ions they pump into the cell. whereas the spinal cord occupies the vertebral
canal of the vertebral column. Inner to these
Can you tell? bony coverings, are three protective membranes
called meninges. That protect the brain and
1. Explain how is impulse transmitted spinal cord.
through a synapse?
a. Dura mater : It is the outermost tough,
2. Describe the conduction of a nerve non vascular, thick and fibrous meninx and is
impulse in the neuron. attached to the inner side of the cranium. It is
separated from the underlying arachnoid mater
by the subdural space, filled with a serous fluid.
b. Arachnoid mater : It is the middle, thin and
non vascular layer of connective tissue having
web like appearance. It is separated from the

189

Can you recall? oxygen to the brain. It protects the brain from
desiccation.
Nervous system
CSF is slightly alkaline fluid with a specific
Central nervous Peripheral Autonomic gravity of 1.005. A total of 100 -120 cc of CSF
system (CNS) nervous system nervous system is present in and around the CNS.

(PNS) (ANS) Curiosity Box:
CSF is released by the pia mater. Inside
Brain Spinal Cranial Spinal
cord nerves nerves the ventricles/cavities of the brain, there is
release of CSF by the choroid plexuses and
Sympathetic Parasympathetic the ependymal cells.
nervous nervous system
system Does this CSF remain enclosed inside the
ventricles ?
Brain
What can be the outcome of such a
Forebrain Midbrain Hindbrain situation ?

Cerebrum Diencephalon

Optic Optic Do you know ?
lobes Chiasma

Cerebellum Pons Medulla Blood brain barrier (BBB) -
varolii oblongata Keeps a check on passage of ions and large
molecules from the blood to the brain tissue.
pia mater below by a narrow subarachnoid Endothelial cells lining the blood capillaries
space filled with cerebro spinal fluid - CSF. help in this process along with the astrocytes.
c. Pia mater : It is the innermost delicate,
highly vascular membrane lies in close contact Always Remember
with the CNS.
CSF is continuously generated by the
CSF (cerebrospinal fluid) : It is lymph like ependymal cells lining the ventricles and
extra cellular fluid secreted by choroid plexuses central canal and simultaneoulsy drained
of pia mater present inner to subarachnoid out of the brain into the blood stream.
space in the ventricles of the brain within CSF maintains a constant pressure inside
the central canal of spinal cord. The CSF is the cranium. The nervous tissue is without
secreted by the pia mater, the choroid plexuses lympatic vessels.
and the ependymal cells lining the ventricles of
the brain and central canal of spinal cord. The Think about it
three openings in the roof of medulla oblogata
help in draining out the CSF from brain to the During extraction of a tooth, the dentist
outside. The meninges and CSF act as a shock gives an injection of Anaesthesia to the
absorber and protect the brain and spinal cord patient before extraction. Is the action
from mechanical injuries. It also maintains potential generated ? How does the local
constant pressure inside cranium. It helps in anaesthesia work? What is the effect of pain
exchange of nutrients and wastes between killer on the nervous system.
blood and brain tissue. It helps in the supply of

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band of nerve fibres called corpus callosum.

Can you recall? The outer surface of cerebrum is called
cerebral cortex while the deep inner part is
Label the various parts of the digram cerebral medulla. The cerebral cortex has
and recall their functions. outer thin region composed of grey matter and
inner medulla composed of white matter.

The surface of each cerebral hemisphere

is greatly folded by many convolutions or
gyri and grooves called sulci. These greately
increase total surface area for accomodation of
the vast number of nerve cells.

Each cerebral hemisphere is further divided

into four main lobes by three deep sulci. These

A. The Human brain : are -
The study of all aspects of the brain is Centre sulcus which demarcates frontal lobe
from the parietal lobe.
called encephalology. The brain can be divided Parieto-occipital sulcus separates the parietal
into three main parts - forebrain, midbrain and from occipital lobe.
hindbrain. The lateral or sylvian sulcus demarcates the
a. Forebrain : Forebrain consists of olfactory temporal lobe from the frontal and parietal
lobes, cerebrum and diencephalon. lobes
i. Olfactory lobes :
Since these three sulci are not complete,
These are highly reduced in human brain the lobes are not clearly demarcated from each
and covered by cerebrum from all sides except other. A fifth median lobe called insula or
ventral. Each lobe consists of a olfactory insular cortex is folded deep within the lateral
peduncle and olfactory bulb. sulcus.
ii. Cerebrum :
The grey matter of cerebral cortex
It is a largest part of the brain, making up mainly consists of cell bodies of billions of
about 85 % of total brain. It is divided into right neurons along with non-medulated fibres and
and left cerebral hemisphere by means of a dendrons. The white matter mainly has axons
deep median, long fissure. The two hemispheres
internally connected to each other by a thick of myelinated nerves.

Chart 9.8 Parts of Brain

Brain

Forebrain Midbrain Hindbrain
Prosencephalon Mesencephalon Rhombencephalon

Cerebral Corpora quadrigemina Metencephalon Myelencephalon
peduncles or
crura cerebri

Cerebellum Pons varolii Medulla
Diencephalon Hypothalamus oblongata

Rhinencephalon Telencephalon Epithalamus Thalamus
reduced olfactory cerebrum divided
incompletely into
lobes (2) two cerebral
hemispheres

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