Control and Coordination — Class 10 Science
Science · Chapter 6
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Chapter summary
Key ideas & terms
- Neuron
- A nerve cell that conducts electrical impulses.
- Reflex arc
- The nerve pathway followed in an automatic reflex action.
- Hormone
- A chemical messenger secreted by an endocrine gland into the blood.
- Tropism
- Directional growth of a plant in response to a stimulus.
Extra questions & answers
What is the difference between a reflex action and walking?
A reflex action is an automatic, rapid response not under conscious control, whereas walking is a voluntary action controlled by the brain.
Why is the use of iodised salt advisable?
Iodine is needed by the thyroid to make thyroxine; iodised salt prevents deficiency disorders such as goitre.
What is a neuron, and what are its main parts?
A neuron is a nerve cell that carries information as electrical impulses; its main parts are the dendrites, cell body (cyton), axon and nerve endings.
What is a reflex action? Give an example.
A rapid, automatic response to a stimulus that is not under conscious control, such as quickly pulling the hand away from a hot object.
What is a reflex arc?
The pathway through which a reflex action takes place: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle), allowing a quick response (refer to the reflex-arc diagram in your NCERT textbook).
Name the three major parts of the human brain and one function of each.
The cerebrum (thinking and voluntary actions), the cerebellum (balance and coordination of movement) and the medulla (involuntary actions like heartbeat and breathing).
What are hormones? Name two and their functions.
Chemical messengers secreted by endocrine glands into the blood; for example, insulin (from the pancreas) controls blood sugar and adrenaline (from the adrenal glands) prepares the body for emergencies.
Why is the use of iodised salt advisable?
Iodine is needed by the thyroid gland to make the hormone thyroxine; iodised salt prevents iodine deficiency disorders such as goitre.
What are tropic movements in plants? Give two types.
Directional growth movements of plants in response to a stimulus, e.g. phototropism (towards light) and geotropism (roots growing towards gravity).
How do plant hormones help in coordination?
Plant hormones such as auxins, gibberellins, cytokinins and abscisic acid regulate growth, cell division, ripening and responses like the closing of leaves and growth towards light.
Activity 6.1
Put some sugar in your mouth. How does it taste?
The sugar tastes sweet because gustatory receptors on the tongue detect its sweetness.
Block your nose by pressing it between your thumb and index finger. Now eat sugar again. Is there any difference in its taste?
The sugar still tastes sweet, although its overall flavour may seem weaker because blocking the nose prevents smell from contributing fully to the sensation of taste.
While eating lunch, block your nose in the same way and notice if you can fully appreciate the taste of the food you are eating.
The food does not taste as flavourful when the nose is blocked because much of what we experience as flavour depends on signals from olfactory receptors in the nose.
Is there a difference in how sugar and food taste if your nose is blocked? If so, why might this be happening? Read and talk about possible explanations for these kinds of differences. Do you come across a similar situation when you have a cold?
Yes. Sugar can still be recognised as sweet by receptors on the tongue, but the detailed flavour of food becomes difficult to appreciate when the nose is blocked. This happens because taste and smell work together to produce the full sensation of flavour. A similar effect occurs during a cold, when a blocked nose reduces the ability to smell and food seems less tasty.
QUESTIONS
1. What is the difference between a reflex action and walking?
A reflex action is a rapid, automatic and involuntary response to a stimulus, usually carried out through a reflex arc without waiting for conscious thought. Walking is a voluntary action that is initiated and controlled by the brain, although balance and precision are coordinated by the cerebellum.
2. What happens at the synapse between two neurons?
When an electrical impulse reaches the end of the axon of one neuron, it causes the release of chemical substances. These chemicals cross the synaptic gap and stimulate the dendrite of the next neuron, where a new electrical impulse is generated.
3. Which part of the brain maintains posture and equilibrium of the body?
The cerebellum maintains the posture and equilibrium of the body and also helps make voluntary movements precise.
4. How do we detect the smell of an agarbatti (incense stick)?
Olfactory receptors in the nose detect the chemicals released by the burning agarbatti. These receptors generate electrical impulses that travel through sensory nerves to the fore-brain, where the smell is interpreted.
5. What is the role of the brain in reflex action?
The spinal cord produces the immediate response in a reflex action so that the body can react quickly. At the same time, information about the stimulus is also sent to the brain, which becomes aware of the event and may guide further voluntary action.
Activity 6.2
Fill a conical flask with water.
A conical flask is filled with enough water to supply moisture to the germinating seeds.
Cover the neck of the flask with a wire mesh.
The neck is covered with a wire mesh so that the seeds can be supported above the water while their roots can grow towards it.
Keep two or three freshly germinated bean seeds on the wire mesh.
Two or three freshly germinated bean seeds are placed on the wire mesh with space for their roots and shoots to grow.
Take a cardboard box which is open from one side.
A cardboard box open on one side is prepared so that light can reach the seedlings mainly from one direction.
Keep the flask in the box in such a manner that the open side of the box faces light coming from a window (Fig. 6.5).
The flask is placed so that light from the window enters through the open side of the box and falls on the seedlings from one direction.
After two or three days, you will notice that the shoots bend towards light and roots away from light.
The observation shows that shoots are positively phototropic because they grow towards light, whereas roots are negatively phototropic because they grow away from light.
Now turn the flask so that the shoots are away from light and the roots towards light. Leave it undisturbed in this condition for a few days.
After the flask is turned and left undisturbed, the newly growing regions gradually adjust their directions in response to the changed direction of light.
Have the old parts of the shoot and root changed direction?
The older parts generally do not change their direction noticeably because their growth has slowed or stopped. Bending mainly occurs in the actively growing regions.
Are there differences in the direction of the new growth?
Yes. The new shoot growth bends towards the new source of light, while the new root growth bends away from it.
What can we conclude from this activity?
The activity demonstrates phototropism. Actively growing shoots respond positively to light by bending towards it, while roots respond negatively by growing away from it. The response occurs mainly in the growing regions.
QUESTIONS
1. What are plant hormones?
Plant hormones are chemical substances produced in plants that coordinate their growth, development and responses to environmental stimuli. They are formed in one region and move to other regions where they produce specific effects.
2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
The leaves of a sensitive plant move rapidly in response to touch without involving growth. Their cells change shape because of changes in water content. A shoot bends towards light slowly through unequal growth: cells on the shaded side grow longer than those on the illuminated side.
3. Give an example of a plant hormone that promotes growth.
Auxin is a plant hormone that promotes growth by stimulating cells, especially in shoots, to grow longer.
4. How do auxins promote the growth of a tendril around a support?
When a tendril touches a support, auxin becomes distributed unevenly. The side away from the support grows faster than the side in contact with it. This unequal growth makes the tendril bend and coil around the support.
5. Design an experiment to demonstrate hydrotropism.
Place moist soil in a container and put a porous pot filled with water near one side. Plant a few germinating seeds in the soil at some distance from the porous pot. Keep the rest of the soil comparatively dry and leave the setup undisturbed for several days. On carefully removing the soil, the roots will be seen bending towards the porous pot, where more water is available. This demonstrates positive hydrotropism in roots.
Activity 6.3
Look at Fig. 6.7.
The figure shows the positions of the principal endocrine glands in male and female human bodies.
Identify the endocrine glands mentioned in the figure.
The glands shown are the pineal gland, pituitary gland, thyroid gland, parathyroid glands, thymus, pancreas, adrenal glands, testes in males and ovaries in females. The hypothalamus is also labelled and helps control the release of several hormones.
Some of these glands have been listed in Table 6.1 and discussed in the text. Consult books in the library and discuss with your teachers to find out about other glands.
Other endocrine glands and hormone-producing tissues include the pineal gland, which secretes melatonin; the parathyroid glands, which help regulate calcium levels; and the thymus, which supports the development of the immune system. Their secretions act on particular target tissues and contribute to coordination in the body.
Activity 6.4
Hormones are secreted by endocrine glands and have specific functions. Complete Table 6.1 based on the hormone, the endocrine gland or the functions provided.
The completed entries are: Growth hormone — Pituitary gland — Stimulates growth in all organs; Thyroxin — Thyroid gland — Regulates metabolism for body growth; Insulin — Pancreas — Regulates blood sugar level; Testosterone — Testes — Development of male sex organs and male secondary sexual characteristics; Oestrogen — Ovaries — Development of female sex organs and regulation of the menstrual cycle; Adrenaline — Adrenal gland — Prepares the body for emergency situations by increasing heart rate, breathing rate and blood supply to skeletal muscles; Releasing hormones — Hypothalamus — Stimulate the pituitary gland to release hormones.
QUESTIONS
1. How does chemical coordination take place in animals?
Chemical coordination in animals is carried out by hormones secreted by endocrine glands. The hormones are released directly into the blood, transported throughout the body and recognised by specific target organs or tissues, where they produce coordinated responses.
2. Why is the use of iodised salt advisable?
Iodised salt supplies iodine, which the thyroid gland needs to produce thyroxin. Thyroxin regulates the metabolism of carbohydrates, proteins and fats and supports proper growth. A deficiency of iodine can reduce thyroxin production and cause goitre.
3. How does our body respond when adrenaline is secreted into the blood?
Adrenaline prepares the body to face an emergency. It makes the heart beat faster, increases the breathing rate and redirects more blood towards the skeletal muscles. Blood supply to the digestive system and skin is reduced, allowing more oxygen and energy to reach the muscles for rapid action.
4. Why are some patients of diabetes treated by giving injections of insulin?
Insulin is produced by the pancreas and helps regulate the level of sugar in the blood. In some patients with diabetes, the pancreas does not produce enough effective insulin, so blood sugar rises. Insulin injections provide the required hormone and help bring blood sugar under control.
EXERCISES
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.
(d) Cytokinin. Cytokinin is a plant hormone that promotes cell division, particularly in regions of active growth such as fruits and seeds.
2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
(b) synapse. It is the small gap across which chemical substances carry a signal from one neuron to the next.
3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
(d) all of the above. The fore-brain is involved in thinking, the medulla helps regulate heartbeat and the cerebellum maintains balance.
4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Receptors detect changes or stimuli inside and outside the body, such as light, sound, temperature, pressure, taste and smell. They convert this information into nerve impulses that are sent to the nervous system. If receptors do not work properly, the body may fail to detect danger or respond correctly. For example, defective pain or heat receptors could prevent a person from withdrawing from a hot object, damaged photoreceptors could impair vision and malfunctioning auditory receptors could cause hearing loss.
5. Draw the structure of a neuron and explain its function.
A neuron should be drawn with branched dendrites connected to a cell body containing a nucleus, a long axon and nerve endings at the far end. Dendrites receive information and generate an electrical impulse. The impulse passes through the cell body and travels along the axon. At the nerve endings, it causes chemicals to be released across a synapse, transmitting the signal to another neuron, muscle cell or gland.
6. How does phototropism occur in plants?
Phototropism occurs because light causes an unequal distribution of auxin in a growing shoot. When light falls from one side, auxin moves towards the shaded side. Cells on that side grow longer than cells on the illuminated side, causing the shoot to bend towards the light. Roots generally show the opposite response and grow away from light.
7. Which signals will get disrupted in case of a spinal cord injury?
A spinal cord injury may disrupt sensory signals travelling from body parts to the brain and motor signals travelling from the brain to muscles and glands below the injured region. Reflex arcs passing through the damaged part may also be affected, causing loss of sensation, movement or reflex responses.
8. How does chemical coordination occur in plants?
Chemical coordination in plants occurs through plant hormones. These substances are produced in one part of the plant and diffuse or are transported to another part, where they regulate growth, cell division and responses to stimuli. Auxins, gibberellins and cytokinins promote growth, while abscisic acid inhibits growth.
9. What is the need for a system of control and coordination in an organism?
An organism contains many organs and tissues that must work together. A system of control and coordination detects changes in the environment, processes information and produces suitable responses. It also coordinates internal activities such as movement, growth, metabolism and development, helping the organism survive and function as an integrated whole.
10. How are involuntary actions and reflex actions different from each other?
Involuntary actions are routine activities that occur without conscious control, such as heartbeat, digestion and salivation. They are mainly regulated by the mid-brain, hind-brain and autonomic nervous system. Reflex actions are immediate, automatic responses to particular stimuli, such as withdrawing a hand from a hot object. They usually follow a short reflex arc through the spinal cord to produce a rapid protective response.
11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Nervous coordination uses electrical impulses carried through neurons. It is very fast, reaches only cells connected by nervous tissue and generally produces brief, precise responses. Hormonal coordination uses chemical messengers released by endocrine glands into the blood. It is slower, can reach widely separated target organs and often produces longer-lasting effects. Both systems transmit information, act on specific target cells and work together to coordinate body functions.
12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
In a sensitive plant, movement occurs when plant cells change their water content and consequently their shape. The plant has no muscles or specialised nervous tissue, and the movement is not caused by growth. Movement of our legs is produced when nerve impulses reach muscle fibres and cause special proteins within them to change their arrangement. The muscles then contract and shorten, moving the bones of the legs.