CHAPTER 7

CONTROL AND COORDINATION

 STIMULI & COORDINATION
✔ The changes in the environment to which the organisms respond and
react are called stimuli.
✔ The response of organisms to a stimulus is usually in the form of some
movement of their body part.
✔ The animals can react to stimuli in many different ways because they
have a nervous system and an endocrine system involving hormones.
✔ The plants react to stimuli in a very limited way.
✔ The working together of the various organs of an organism in a
systematic manner so as to produce a proper response to stimulus, is
called coordination.
LEARNING OBJECTIVES
✔ Control & coordination in Plants
□ Plant hormones
□ Tropic Movement
□ Nastic movement
✔ Coordination in Animals
□ Human nervous system
• Peripheral nervous system
• Central nervous system
□ Endocrine system
 COORDINATION IN PLANTS
✔ In plants control and coordination is done by chemical substances called plant hormones
or phytohormones.
✔ There are five main types of plant hormones. They are :- Auxins,
Gibberillins, Cytokinins, Abscisic acid and Ethylene.
1. Auxins :- cell enlargement, cell differentiation, promote fruit growth.

2. Gibberillins :- cell enlargement, cell differentiation in presence of auxins. Helps in

breaking the dormancy in seeds & fruits, promote growth in fruits

3. Cytokinins:- promotes in cell division, Helps in breaking the dormancy in seeds & buds,
delay ageing in leaves, promotes opening of stomata, promote fruit growth.

4. Abscisic acid :- promotes dormancy in seeds and buds, promotes closing of stomata,
promotes wilting and falling of leaves.

5. Ethylene :- helps in flowering and ripening of fruits.

 PLANT MOVEMENTS
✔ Movements of the plant are usually caused by an unequal growth in
its two regions by the action of plant hormones, under the influence of
the stimulus.
✔ If one side of a stem has more auxin than the other side, then the side of
stem having more auxin hormone will grow faster than the other side
having less auxin hormone. This will cause the stem to bend.
✔ Movement in any part of the plant is usually a growth movement.
✔ The plant movements made in response to external stimuli fall into two
main categories: tropisms and nasties.
 TROPISMS (Tropic Movement)
 A growth movement of a plant part in response to an external stimulus in
which
the direction of stimulus determines the direction of response is called tropism.
 Directional movement.
 TYPES OF TROPISMS
GEOTROPISM PHOTOTROPISM
TYPES OF TROPISMS
CHEMOTROPISM Usefulness of
Tropic Movements:
The various types of tropic
movements help the plants to
survive. These tropic movements
help the plant to obtain water and
nutrients from soil and light from
the sun, which are necessary for
growth and survival.
 NASTIES (NASTIC MOVEMENT)
✔ The movement of a plant part in response to an external stimulus in which the
direction of response is not determined by the direction of stimulus is called
nastic movement.
✔ Non-directional
✔Thigmonasty- The stimulus is touch.
The folding up of leaves of a sensitive plant (Mimosa pudica) on touching. Here
✔Photonasty – The stimulus is light.
The opening of the petals of dandelion flowers in morning bright light and
closing in the evening when the light fades. The closing of the petals of
moonflower in the morning in bright light and opening at dark when the light
fades.
 Functions of Phytohormones
1. Germination of seeds (Breaking the dormancy of seeds)
2. Growth of root, stem and leaves
3. Movement of stomata
4. Flowering in plants
5. Ripening of fruits
6. Tropic movements
7. Nastic movements
 Coordination in Animals
 A system made up of nerve cells is called nervous system. The coordination
in simple multi-cellular animals takes place through nervous system only.
(Eg. Hydra)
 In animals control and co ordination is done by the nervous system and
endocrine system. The nervous system consists of the brain, spinal cord and
nerves.
 Five sense organs which contain receptors
 Receptors :- cell/group of cells which is/are sensitive to a particular type of
stimulus
 Type of receptors:
• Photoreceptors in the eyes to detect light.
• Phonoreceptors in the ears to detect sound.
• Olfactory receptors in the nose to detect smell.
• Gustatory receptors in the tongue to detect taste.
• Tangoreceptors in the skin to detect touch.
 Coordination in Animals
 Sensory nerves :- are nerves
which carry information from the
receptors (sense organs) to the
brain and spinal cord.

 Motor nerves :- are nerves which

carry information from the brain
and spinal cord to the effectors
(muscles and glands).

 Effectors :- are the muscles and

glands which respond to the
information from the brain and
spinal cord through the motor
nerves.
 Coordination in Animals
 There are two systems of coordination of activities in humans. These are:
 Human nervous system
Parts of the nervous system

The human nervous system consists of the Central

Nervous System and Peripheral Nervous System.

- The central nervous system - consists of the

brain, and spinal cord.

- The peripheral nervous system - consists of

cranial nerves arising from the brain and spinal
nerves arising from the spinal cord.
 Nerve cell (Neuron)
Neuron is the structural and functional unit of the nervous system.
It has a cell body called cyton containing a nucleus and
cytoplasm. It has several branched structures called dendrites. It
has a long nerve fibre called axon which is covered by a
protective covering called Myelin sheath. The junction between
two neurons is called synapse. Messages pass through the nerve
cell in the form of chemical and electrical signals called nerve
impulse. The dendrites receive the information and starts a
chemical reaction which produce electrical impulse which passes
through the axon.
Transmission of messages through neurons
 BRAIN
The brain is the main coordinating centre in the human body. It is protected by the cranium. It is covered
by three membranes called meninges filled with a fluid called cerebrospinal fluid which protects the
brain from shocks. The brain has three main parts.

1. Fore brain :- consists of the cerebrum and olfactory lobes. It is the thinking part of the brain and
controls voluntary actions. It controls touch, smell, hearing, taste, sight, mental activities like
thinking, learning, memory, emotions etc.

2. Mid brain :- controls involuntary actions and reflex movements of head, neck, eyes etc.

3. Hind brain :- consists of cerebellum, pons and medulla.

a) Cerebellum :- controls body movements, balance and posture.

b) Pons :- controls respiration.

c) Medulla :- controls heart beat, blood pressure, swallowing, coughing, sneezing, vomitting.
Diagram of Brain
 SPINAL CORD
The spinal cord starts from the
brain and extends through the
vertebral column. It has 31 pairs of
spinal nerves. It carries messages
to and from the brain. It also
controls reflex actions.
 REFLEX ACTION
Reflex action is a sudden, unconscious and
involuntary response of the effectors to a stimulus.
Eg :- We suddenly withdraw our hand if we
suddenly touch a hot object. In this reflex action,
the nerves in the skin (receptor) detects the heat
and passes the message through the sensory
nerves to the spinal cord. Then the information
passes through the motor nerves to the muscles
(effector) of the hand and we withdraw our hand.
 REFLEX ARC
The pathway of a reflex action is called
reflex arc. In a reflex arc the stimulus is
received by the receptors (sense organs)
and it passes through the sensory nerves
to the spinal cord. From the spinal cord
the information passes through the
motor nerves to the effectors
(muscles/glands) for the response.
 Endocrine glands in human beings
The endocrine glands also help in control
and coordination. The endocrine glands
produce chemical substances which help to
control and coordinate various activities in
the body.

The endocrine glands in our body are :-

pineal, hypothalamus, pituitary, thyroid,
parathyroid, thymus, adrenal, pancreas,
testes and ovary.
 Examples of coordination by endocrine glands
• When we are frightened or angry, the adrenal glands produce more adrenalin hormone which is sent
through the blood to the heart, rib muscles and diaphragm. This increases breathing rate to supply
more oxygen to the muscles to prepare the body to either run away or fight with the enemy.
• Iodine is needed by the thyroid gland to produce the hormone thyroxin. Thyroxin controls the
metabolism of carbohydrates, fats and proteins and helps in proper growth. If the diet is deficient in
iodine it causes goitre.
• The pituitary gland produce growth hormones. Deficiency of this hormone in childhood causes
dwarfism. Excess of this hormone causes tall growth.
• The pancreas produces the hormone insulin which controls the blood sugar level. Increase in blood
sugar level causes diabetes. A diabetic patient has to take insulin injections to control his blood sugar
level.
• The testes in males produces the hormone testosterone which controls the production of sperms and
changes during puberty.
• The ovary in females produces the hormone oestrogen which controls the production of eggs and
changes during puberty.
THANK YOU