Control and Coordination

IMPORTANT NOTES

1. Stimulus is defined as any change in the external or internal environment of an organism which brings about a response from it.

2. The working together of the various organs in a systematic manner is called coordination.

3. Chemical coordination in both plants and animals is responsible for growth and development.

4. The plant movement which is dependent on growth, is called tropic movement or tropism.

5. The type of movement which is independent of growth is called nastic movement.

6. The plants use electro-chemical means to convey the information from cell to cell.

7. In plants, there is no specialised tissue for the conduction of information, unlike animals.

8. Movement of a plant or its parts due to light is called phototropism.

9. Movement of a plant or its parts due to water is called hydrotropism.

10. Movement of a plant or its parts due to gravity is called geotropism.

11. Certain chemical substances in plants necessary for growth are plant hormones also called phytohormones.

12. Some of the hormones stimulate plant growth while others act as growth inhibitors. For this reason, plant hormones are often referred to as growth regulators.

13. Five main groups of growth regulators are auxin, gibberellin, cytokinin, ethylene and abscisic acid. 
— auxin stimulates cell elongation and growth.
— gibberellin stimulates growth and flowering.
— cytokinin stimulates cell division and chlorophyll retention.
— abscisic acid is a growth inhibitor and brings about fall in leaves and fruits.

14. The coordinated activity of an organism depends on the continuous input of information for the internal and external environment.

15. Animals possess a number of sense organs to perceive different sensations.

16. The functional junction between nerves is called synapse.

17. In animal, the nervous system controls and coordinates various functions in the body.

18. NERVES 
— Sensory Nerves (carry messages from the sense organs to the brain)
— Motor nerves (carry messages from the brain to the effector organs like muscles/ glands)
— Mixed Nerves (function as both sensory and motor nerves)

19. Brain is the ultimate coordinator of the body. The three parts of the brain are:
(a) Fore-brain mainly consists of cerebrum, the largest and the specialised portion of the brain. It is further divided into four parts:
(i) frontal lobe controlling muscular activities.
(ii) parietal lobe controlling touch, smell, etc.
(iii) temporal lobe controlling hearing.
(iv) occipital lobe controlling vision.
(b) Mid-brain controls a few motor activities.
(c) The hind-brain is in turn made of
(i) cerebellum, deals with coordination of postures.
(ii) pons varolii, controlling respiration and its regulation.
(iii) medulla oblongata regulates reflexes like swallowing, coughing, etc.

20. The brain being an extremely delicate organ is well protected by the cranium or the brain box, three coverings called ‘meninges’ and a fluid in between the meninges called the cerebrospinal fluid.

21. The functional unit of the nervous system is the neuron, whose structure can be detailed as follows :

22. Reflex actions are unconscious or involuntary responses of the effector organs to a stimulus, which is monitored through the spinal cord. The route thus taken by the impulse (i.e., from the receptor organs to the spinal cord) and the response thereof (i.e., from the spinal cord to the effector organs) is known as the reflex arc. Sneezing, coughing, withdrawal of the hand upon touching a hot object are examples of reflex action.

23. Hormones are chemical substances secreted in trace amounts by endocrine glands and are the means of information transmission.

24. The hormones in animals show following characteristic features: 
(i) They are synthesised by endocrine glands.
(ii) They are produced at a place other than the site of action. They travel through blood to other parts where they cause changes.
(iii) They are secreted directly into the blood stream.
(iv) They act on specific tissues or organs. The tissues or organs that respond to the hormones are called as target organs. For example, the target organs for the hormone adrenaline includes the heart.
(v) They are secreted in response to changes in the external or the internal environment of the body and are also called chemical messengers.
(vi) They may stimulate or inhibit the activity of the target organ, thus regulating its activity.
(vii) They are effective in minute quantities, often in trace amounts which are difficult to detect at times.
(viii) Excess or deficiency of a hormone may lead to serious consequences.

25. The chemical messengers of our body are the hormones produced by the endocrine system. Hormones are carried by the blood to their target organs where they bring about appropriate actions.

26. The master endocrine gland of the body is the pituitary gland also known as the hypophysis. Hypophysis is in turn under the control of hypothalamus—a part of the brain located at the base of cerebrum.