Control and coordination NCERT intext questions
1. What are the differences between a reflex action and walking?
Reflex actionWalking1. Reflex action is the immediate response of the spinal cord to a sudden impulse.1. Walking is a voluntary action which is controlled.2. It is conducted by the spinal cord.2. It is controlled by hind-brain (by cerebellum).3. It occurs in a fraction of seconds.3. It takes longer time.
2. What happens at the synapse between two neurons?
The neurons lie end-to-end in a chain to transmit the impulses in an animal body. There occurs a very minute gap between terminal portion of axon of one neuron and dendron of the other neuron. This gap is called synapse. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap (synapse), and start a similar electrical impulse in the dendrite of the next neuron.
Synapses actually act like one way valves. This is because the chemical substance is present at only one side of the gap. In this way synapses ensure that nerve impulse travels only in one direction.
3. Which part of the brain maintains posture and equilibrium of the body?
Cerebellum in the hind-brain maintains posture and equilibrium of the body.
4. How do we detect the smell of an agarbatti (incense stick)?
The olfactory receptors in our nose detect the smell of agarbatti. The information in the form of nerve impulse is transmitted to olfactory lobes of fore brain. The message is interpreted there.
5. What is the role of the brain in reflex action?
The reflexes which involve only the spinal cord are called spinal reflexes. The spinal reflexes are produced in the spinal cord but the message of reflex action taken also goes on to reach the brain where the thinking process occurs. Some reflex arcs involve the brain, rather than the spinal cord only. They are called cerebral reflexes. Closing of eyes when exposed to flash of light and salivation at the sight of tempting food are the examples of cerebral reflexes.
6. What are plant hormones?
In plants, certain chemical substances are necessary for proper growth and development. These chemical substances are called plant hormones or phytohormones. Different plant hormones help to coordinate growth, development and responses to the environment. For example, auxins, gibberellins, cytokinins, ethylene and abscisic acid are plant hormones.
7. How is the movement of leaves of a sensitive plant different from the movement of a shoot towards light?
Movement in the leaves of a sensitive plant (Mimosa pudica) occurs due to turgor changes in the cells which causes drooping of leaves/leaflets. Movement of a shoot towards light is a phototropic movement which is caused due to differential growth that occurs due to more concentration of auxins in one side.
8. Give an example of a plant hormone that promotes growth.
Auxin is the plant hormone that helps in cell elongation and growth.
9. How do auxins promote the growth of a tendril around a support?
The movement of tendril around the support is caused by the hormone auxin. Less auxin occurs on the side of contact as compared to the free side. Auxin promotes the growth on the free side. As a result of growth on the free side, the tendril coils around the support.
10. Design an experiment to demonstrate hydrotropism.
Experiment to demonstrate hydrotropism:
(I) Take a wire mesh and cover it with moist saw dust.
(II) Place some germinated seedling (pea or gram) on the moist saw dust.
(III) Keep the saw dust moist by sprinkling water at regular intervals. Observe after 2-3 days.
(IV) As the radicals come out of the seeds, they are seen to move towards the perforation. After some growth they bend back and enter the perforations to reach the moist saw dust in complete disregard of gravity (positive hydrotropism).
Conclusion: Bending of radicals back into moist saw dust is a hydrotrophic movement. It occurs despite being against the force of gravity.
11. How does chemical coordination take place in animals? [NCERT Exemplar]
In animals, chemical coordination is achieved through the agency of hormones which function as chemical messengers or informational molecules. Hormones are secreted in a very small amount by specialised tissues in the body called endocrine glands. These glands are ductless and pour their secretions directly into blood. Blood transports them to the target tissues/organs. Hormones coordinate the activities of living organisms and also their growth. For example, pancreas secretes two hormones—insulin and glucagon.
12. Why is the use of iodised salt advisable?
Iodine is necessary for the thyroid gland to make the hormone thyroxine. Thyroxin regulates carbohydrate, protein and fat metabolism in the body to provide balance for growth. Deficiency of iodine can lead to goitre.
13. How does our body respond when adrenaline is secreted into the blood?
Adrenaline hormone is secreted in small amounts all the time but in large amounts it is secreted when a person is frightened. It then prepares our body for action. It increases the rate of heartbeat and breathing, raises blood pressure and allows more glucose to go into the blood to give us a lot of energy so as to quickly fight or run away from the frightening situation. Adrenaline is termed as ‘hormone of emergency’.
14. Why are some diabetes patients treated by giving insulin injections?
The insulin hormone controls the metabolism of sugar. When pancreas does not produce or secrete sufficient amount of insulin into blood, then the sugar level in the blood rises. Therefore, the patient excretes sugar (glucose) in urine, feels excessive thirst and also urinates excessively. The people having severe diabetes are treated by giving injections of insulin.
