CONTROL AND COORDINATION-REV. QUESTIONS BIO. CLASS X

1. What is reflex action? Explain with an example along with the diagram of the stated example. Define reflex arc.
A. It is an accurate, unconscious, involuntary and instantaneous response to a stimulus.
e.g.: Hand is withdrawn on being picked.
The pathway taken by a stimulus to travel from receptor organ to effector organ is known as reflex arc.
Schematic pathway:
STIMULUS------->RECEPTOR ORGAN-----(sensory neuron)----->SPINAL CORD---(motor neuron)----->EFFECTOR ORGAN------->RESPONSE
See text book for diagram.
2. Distinguish between nastic and tropic movement?
-----------NASIC--------------------------TROPIC-----------
1. Growth is not involved.--------1. Growth is involved.
2. Movement is not directional.-2. Movement is directional.
3. Stimulus is diffused.------------3. Stimulus is unilateral.
3. How is hormone secretion is regulated by feedback means?
A. Feedback system is a regulatory mechanism in which presence of certain level of substance promotes or inhibits its further formation.
e.g.: Regulation of thyroxine production by its concentration in blood.
Concentration is detected by hypothalamus of brain. If its low the information from hypothalamus moves o pituitary. The pituitary sends information to the thyroid through blood. Then thyroid gland secretes more thyroxine.

If thyroxine in blood is excess hypothalamus stops producing information to pituitary and pituitary stops producing information to thyroid gland to secrete thyroxine.
4. What is the role of brain in reflex action?
A. the reflex action in which spinal cord is involved, brain acts as the information collecting centre. But in some other reflexes such as salivation at the site or smell of food, closing of eyes in bright light the brain acts as the relay centre transferring impulse from sensory to motor neuron.
5. What’s the role of control and coordination in an organism?
A. Multicellular organisms consists of a number of components i.e. organs or tissues, each specialised to perform a particular function.
Most activities need simultaneous and sequential functioning of number of organs e.g. feeding- 1. Eyes locate food. 2. Nose smells it. 3. Hands pick up food 4. Mouth opens to receive food 5. Teeth and muscle masticates food. 6. Saliva moistens the food. 7. Tongue perceives taste and pushes crushed food. All these work is possible through a system of control and coordination.