Chapter 7 : Coordination in Plants, Plant and animal hormones
1. Explain the coordination in plants.
Plants lack nervous and muscular system. They respond to stimuli by showing 2 types of
movements – growth independent and growth dependent.
Growth independent movements are usually quicker than growth dependent ones, and
involve the use of electrochemical signals by the plant. To achieve this movement, the plant
cells change shape by altering their water content. Eg. drooping of leaves of a touch-me-not
plant when it is touched.
Growth dependent movements happen due to the action of phytohormones. Eg. Growth of
the shoot towards light.
2. What happens when the leaves of a touch-me-not plant are touched?
When the leaves of a touch-me-not plant are touched, the plant uses electrical-chemical
means to convey this information from cell to cell. Plant cells at the leaf base change their shape
by changing the amount of water in them. This results in folding and drooping of leaves.
3. How does control and coordination take place in plants?
In plants the control system is not specialized. The control and coordination in plants is
performed by chemical substances known as plant hormones or phytohormones.
Phytohormones are different types namely Auxins, Gibberellins, Cytokinins, Abscisic Acid
and Ethylene
4. What are the plant growth regulators?
The chemical substances (phytohormones) produced by the plants are plant growth
regulators. Eg. Auxins, gibberellins, cytokinins.
5. Which part of the plant body produce growth regulators?
Growing tips (such as shoot tip).
6. Name the phytohormone that inhibits growth in plants.
Abscisic Acid inhibits growth in plants. Its effects include wilting of leaves.
7. What is tropism?
The movement of a plant in the direction of a stimulus is called tropism.
8. What are the different types of tropism seen in plants?
Phototropism, Geotropism, Chemotropism, hydrotropism are the different types of
tropism seen in plants.
1
9. What is nastic movement?
It is an immediate response that is neither towards nor away from the stimulus. The
direction of response is not dependent on the direction of the stimulus.
Eg. Bending or drooping of leaves or touching the “touch me not” plant.
10. Phytohormones control responses in the plant body. Other than this what are the
other ways by which plants respond to stimuli?
(i) Plants use electrical-chemical means to convey information from cell to cell.
(ii) Plants cells change shape by changing the amount of water in them, resulting in swelling
or shrinking which ultimately brings about movement.
11.What are the different types of movement shown in plants?
There are two types of movement seen in the plants:
i) one dependent on growth
ii) the other independent of growth.
12. Name the multicellular organism in which coordination is achieved only by means
of chemicals.
Plants achieve their coordination by means of chemicals called hormones.
13. What are plant hormones?
They are special chemical compounds released by different parts of the plant.
regulate growth, development and responses to the environment.
They help to
14. How is the movement of leaves of the sensitive plant different from the movement
of a shoot towards light?
i) Movement of leaves of the sensitive plant is not directional to the stimulus of touch
(nastic movement) . But the movement of shoot is directional to the light (phototropism).
ii) Movement of leaves (drooping down) of the sensitive plant is due to change in the
amount of water present in them. The movement of the shoot towards light is due to
growth controlled by growth hormone called auxin.
15. Give an example of the plant hormone that is a growth promoter and inhibitor
respectively.
Auxin promotes growth in plants. Abscisic acid is a growth inhibitor.
16. How do auxins promote the growth of a tendril around a support?
Tendrils are sensitive to touch. When a part of a tendril comes in contact of a support,
the growth hormone auxin diffuses to the other side. This causes growth in the part of the
tendril away from the support. This makes the tendril to circle around the support.
2
17. Differentiate between Tropic movements and Nastic movements.
Tropic Movements
1. It is the movement of the plant in the
direction of stimulus.
Eg : Movement of the plant towards light
(phototropism).
Nastic Movements
1. When the movement is neither towards nor
away from the stimulus.
Eg: Bending and drooping of touch me not
leaves on touching.
18. What is Growth dependent or tropic movement?
Growth dependent movements or tropic movements are slow, occurring either towards or
away from the stimulus. The movement of plants in the direction of stimulus is known as
'tropism'. Tropic movements are shown in response to environmental factors such as light,
gravity, water and chemicals.
Eg. Plant roots are positively geotropic and negatively phototropic whereas plant shoots are
usually negatively geotropic and positively phototropic. Pollen tubes show chemotropism by
growing towards the ovules.
19. Explain the conduction of information in plants and animals.
In Plants
No specialised tissue for conduction of
information
Cells change their shape by changing the
amount of water in them.
In Animals
Specialised tissue for conduction of
information
Cells change their shape due to the
presence of specialized proteins.
20. Explain the movements due to growth on plants.
i) Thigmotropism: When a tendril comes in contact with a support, then the part of the
tendril away from the support grows more rapidly than the part of the tendril that is in
contact with the object, thus the tendril circles around the object and appears to cling to it.
ii) Phototropism: Directional movement of a plant/plant part in response to light, for
example: shoots show positive phototropism.
iii) Geotropism: Directional movement of a plant/plant part in response to gravity, for
example: roots show positive geotropism.
iv) Chemotropism: Directional movement of a plant/plant part in response to chemicals,
for example- growth of the pollen tube towards the ovule.
v) Hydrotropism: Movement of a part of a plant in response to water, for example: root
3
21. Explain the role of phytohormones.
Plant hormones or phytohormones : These are chemical substances produced naturally by
plants; they are capable of being translocated and regulate one or more physiological processes
when present in low concentrations.
Hormone
Auxins
Gibberellins
Cytokinins
Abscisic Acid
Ethylene
Function
They are released in response to light,
promote cell elongation, also promote the
development of seedless fruits.
Growth of stem, seed germination,
flowering.
Cell division (in fruits and seeds) ,
breaking of seed dormancy.
Inhibits growth, promotes wilting of
leaves.
Promotes fruit ripening processes.
22. How is the movement of the leaves of the sensitive plant different from the movement of a shoot
towards light?
i. Leaves of the sensitive plant move quickly in response to touch. There is no growth
involved in this movement. The directional movement of shoot towards light is slow and
is caused by growth. If it is prevented from growth, it will not show the movement.
ii. In the movement of the leaves of sensitive plant, the stimulus is touch. In
phototropism, the stimulus is light.
iii. Also, in sensitive plant, the movement is caused by the sudden loss of water from the
swellings at the base of leaves. In phototropism the bending is caused by unequal growth
on two sides of the shoot.
23. Explain the importance of animal hormones .
 The hormones in animals are produced by the endocrine glands, and they play an
important role in control and coordination. Hormones are chemical substances that
control and coordinate activities of living organisms and also their growth.
 Animal hormones do not bring about directional growth depending on environmental
cues, but promote controlled growth in various areas to maintain the body design.
 The various endocrine glands in humans are hypothalamus, pineal gland, pituitary
gland, thyroid gland, parathyroid glands, thymus, pancreas, adrenal glands, ovary (in
female) and testis (in males).
4
24. Explain the important characteristics and functions of hormones.
i. They are secreted by the endocrine glands and are called ‘chemical messengers’.
ii. They are poured directly into blood stream as endocrine glands have no ducts of their own
(ductless glands).
iii. They usually have their effect at sites different from the sites where they are made. They
act on specific areas called target organs.
iv. Hormones coordinate body activities and growth
v. They are released in minute quantities.
Hormone
Growth
Hormone
Thyroxin
Endocrine Gland
Pituitary
Adrenaline
Adrenal gland
Insulin
Testosterone
Pancreas
Testis
Oestrogen
Ovary
Thyroid Gland
Function
Regulates growth and
development of body
Controls carbohydrate,
protein and fat metabolism
Prepares the body to deal
with emergency situations
Regulates blood sugar levels
Causes development of
sexual organs and secondary
sexual characteristics in
males
Ovary Causes development
of sexual organs and
secondary sexual
characteristics in females
Deficiency disease
Dwarfism
Goitre
---Diabetes
-----
-----
25. How does our body respond to emergency situations ?
In case of flight or fight reaction to an emergency situation, Adrenal glands release
adrenaline into blood. Its target organ is the heart.
i. The heart begins to beat faster resulting in supply of more oxygen to the muscles.
ii. The blood to the digestive system and skin is reduced due to the contraction of muscles
around small arteries in these organs. This diverts the blood to our skeletal muscles.
iii. The breathing rate increases because of the contraction of the diaphragm and the rib
muscles.
iv. All these responses together enable the body to be ready to deal with the situation.
26. Why are some patients of diabetes treated by giving injections of insulin?
5
Insulin produced by the pancreas regulates the level of blood sugar glucose in the blood.
When a person’s pancreas does not produce enough insulin, blood sugar level rises, a disease
called diabetes. Such diabetic patients are given injections of insulin so that the sugar level in
the blood can be controlled.
27. Why is the use of iodized salt advisable?
Iodine is important for the thyroid gland to make thyroxin hormone. Thyroxin regulates
carbohydrates, proteins and fat metabolism in the body so as to provide the best balance for
growth. If iodine is deficient in the diet, thyroxin cannot be produced and the thyroid gland at
the neck swells, a condition called goiter. Use of iodized table-salt can provide the required
amount of iodine in the diet.
28. Explain the Difference between nervous and endocrine system.
Nervous system
Endocrine system
Electrical impulses
Chemical compounds
Mode of communication
Speed of communication
Very quick
Slow
Can reach
Only cells connected by
nervous system
All cells of the body
Continuity
Cannot continuously
transmit impulses
Can act steadily and
persistently
6