Download CLASS-X BIOLOGY EPISODE –1 STATE S

CLASS-X
BIOLOGY EPISODE – 1
STATE SYLLABUS
Control and Co-ordination
Cricket is very popular in India. In a game of cricket you have batsmen, bowlers
& fielders. A team that is fielding has all its team members on the field. They
have a task to perform. They have to dismiss 10 batsmen of the opposing side. If
a bowlers does not bowl properly the team looses. If the bowler is good but the
fielders are not good the team looses. If the captain does not plan properly does
not change bowlers according to the conditions of pitch, does a bad field
placement, is unable to assert, the team looses. The game involves a high
degree of Co-ordination among the team mates, a high degree of control as per
the situations. Then the team is successful. If the batsmen do not bat well their
team looses.
In the same manner a human body also acts. The body responds to the stimulus.
The body would show different responses to different environmental conditions.
In hot climate we sweat profusely but in cold climates there is little sweating. The
pupil becomes narrow in bright light but opens wide in dim light. This is response
to stimulus. Response to changing environment is IRRITABILITY.
Sweating
Shivering
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All living organisms exhibit irritability. On germination, a seed develops roots first,
then the stem, then flowers and lastly the fruit. The growth and development
occurs in a sequence at specific times of life cycle.
Multi cellular organisms have a number of organs performing different functions.
These organs have to work as a team. If each organ functions independent of the
other, then the organism may not live longer.
When you are crossing a street there should be co-ordination between eye, ear
and muscles of leg. Based on what the eye sees and what the ear hears the legs
function. For functioning of legs the muscles need glucose and oxygen.
People crossing a road
The role of digestive system and respiratory system come into picture. All these
organs will function to the required limits. The limits are set by the nervous
system which analyses the situation and acts.
Thus, for a perfect and healthy functioning of an organism there should be
control and coordination. In living organisms there is a finely tuned coordination
to respond to the environmental changes and to carry out specific functions at
specific time in the life cycle. The harmony of functions is maintained by a control
system.
Chemical Co-ordination in Plants
Let us now examine how coordination is brought about in plants.
What are the structures or substances that bring about coordination between the
activities of different part of the Plant?
Plants do not have a nervous system or endocrine glands.
In plants chemicals play a major role in coordination. Like hormones in animals
the chemical substances in plants work at minute concentrations.
What are these chemical substances?
The chemical substances which coordinate the growth process in plants are
known as “PL ANT GROWTH SUBSTANCES”
These substances can increase or decrease growth.
How many types of substances are there in plants?
There are five major growth substances in plants. They are
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a)
b)
c)
d)
e)
Auxins
Gibberellins
Cytokinins
Abscisic acid and
Ethylene
These substances have different functions. The first three substances i.e.,
auxins, gibberellins and cytokinins promote growth while abscisic acid and
ethylene inhibit growth.
Let us examine each substance in more detail.
Auxins:- What is the chemical name of auxins?
Auxin refers to a chemical compound called INDOLE ACETIC ACID (IAA).
From where does a plant get these auxins? Are they synthesized in the Plant?
Auxins are synthesized in the meristematic and enlarging tissues.
What are the functions of axuins?
1) Auxins promote growth and elongation of stems, roots.
2) Promote enlargement of fruits
3) Loosen cellulose frame work of cell wall which helps in cell enlargement.
4) Promote cell division in vascular cambium.
5) Promote root initiation.
6) Responsible for “a pical dominance”.
What is apical dominance?
As the stem is growing it develops lateral buds and the growing region is the
apex from apical bud.
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Animate fig 2.1.4
1. show a plant.
2. remove the apical bud.
3. show growth of lateral buds into branches
4. apply auxins with a brush on tip.
5. show growth from apex and dorman lateral buds.
Images of plants
If the apical bud is removed, the lateral bud starts growing into branches. If we
apply auxins to the tip in the region where the apical bud has been removed, we
observe later that the lateral buds stop growing and the apical buds begin to
grow again.
This proves that auxins which are produced in the apical bud region promote
growth and are responsible for apical dominance.
The shedding of leaves by plants in some seasons is due to non
production of auxins. However in the presence of Auxins the shedding of leaves
is inhibited n the those seasons.
Plants bend towards light due to auxins. This is known as Phototropism.
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Auxins also are responsible for geotropism. Root grow downwards i.e., positively
geotropic while the stem grows against gravity in the upward direction, hence
negatively geotropic.
Image
Some of the auxins produced or synthesized by artificial methods in laboratories
are
1). 2, 4 dichloro phynoxy acetic acid.
2).Naphthalene Acetic acid and
3). Indole Butyric Acid.
A spray of auxins can prevent early fruit drop.
Gibberellins:Gibberellins were first isolated from a fungus Gibberella fujikuori. A rice plant
infected with the fungus grew a long stem with long internodes. The substance
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that caused this condition was isolated in the fungus and named as Gibberellic
acid.
The Gibberellins
1).Bring about elongation of stem.
2).Increase the leaf blade area.
3).Increase the size of fruits.
All these conditions are due to stimulation of cell division by gibberellin both in
leaves and stem.
A spray of gibberellins can result in seed less fruits.
Gibberellins are useful in inducing enzymes. These enzymes are used in
mobilization of stored nutrients.
From where does the plant procure gibberellins?
They are synthesized in roots, shoots, buds, young leaves, embryos etc.
Gibberellins are produced synthetically by artificial means from fungal cultures.
How are the Gibberellins useful to the plant?
1.They are used in fruit settling as in grapes and for growing seedless fruits.
2,They are also used in brewing industry to stimulate amylase activity in barely
seeds.
3.They enhance the malting of barely grains.
See this animation. Here a cabbage plant has been administered gibberellinys.
See how the stem elongates, the leaf blade branches.
Image
Cytokinins:- Not only gibberellins but another substance called Cytokinin has
the function of stimulating cell division and cell elongation. However cytokinins
can function only in the presence of
auxins.
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Cytokinins are produced in actively growing tissues of roots, embryos and
developing fruits.
Cytokinins are useful in
1).Stimulating cell division and cell elongation in the presence of auxins.
2).Delay the process of aging in leaves
3) Prolonging life of fresh leaf crops like cabbage, spinach, coriander etc.
4).Breaking the dormancy of seeds to germinate.
Abscisic Acid:A plant can not go on growing. At a stage there will be inhibition of growth. The
inhibition of growth is brought about by Abscisic acid (ABA).
It is natural in a plant to shed leaves occasionally and shed flowers and fruits.
This is because of the action of abscisic acid.
Application of abscisic acid to buds leads to dropping off of buds.
Abscisic acid is useful in closing stomata during drought conditions preventing
the loss of water.
Ethylene(Ethene):When an injured or a ripe fruit is placed with other fruits, it quickens ripening of
other fruits.
Why does this happen?
The ripe or injured fruit releases a gaseous substance known as ethylene. A high
concentration of auxins induce ethylene formation.
While gibberellins bring about elongation of stem, ethylene inhibits elongation.
However, it stimulates transverse expansion of the stem.
Ethylene also accelerates abscission of leaves, flowers and fruits.
If you see the table that follows, you will observe that the plant growth factors, by
stimulating or inducing or inhibiting actions, bring about a normal growth of plants
parts liKe stem, leaves, buds, flowers, fruits etc.
The plant growth factors are not transported from the region of their synthesis.
Hence they are different from hormones. Hormones work at a distant organ from
where they are produced.
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