NCERT CLASS 10 SCIENCE CHAPTER 6 CONTROL AND COORDINATION
NCERT CLASS 10 SCIENCE
CHAPTER 6 – CONTROL AND COORDINATION
IN-TEXT QUESTIONS AND ANSWERS
1. What is the difference between a reflex action and walking?
A reflex action is a quick, automatic and involuntary response to a stimulus. It usually takes place without conscious thinking.
Walking is a voluntary action controlled by the brain. It involves conscious coordination of muscles and body movements.
2. What happens at the synapse between two neurons?
When an electrical impulse reaches the end of a neuron, it causes the release of chemicals. These chemicals cross the synaptic gap and generate a new electrical impulse in the next neuron.
3. Which part of the brain maintains posture and balance of the body?
The cerebellum, a part of the hindbrain, maintains posture, balance and coordination of voluntary movements.
4. How do we detect the smell of an agarbatti?
Receptors present in the nose detect the smell of an agarbatti. They generate electrical signals that are transmitted through sensory neurons to the brain, where the information is interpreted.
5. What is the role of the brain in reflex actions?
Many reflex actions are controlled by the spinal cord. The brain receives information about the reflex action and can coordinate further responses. Some reflex actions, such as those involving the eyes, are controlled by the brain.
6. What happens when the spinal cord is injured?
An injury to the spinal cord may interrupt the transmission of nerve impulses between the brain and different body parts. Depending on the location and severity of the injury, it may affect movement, sensation and reflex actions.
7. What are receptors? What is their function?
Receptors are specialised cells or nerve endings that detect changes in the surroundings. They receive information such as light, sound, smell, taste, temperature and touch and send signals to the nervous system.
8. What are plant hormones?
Plant hormones are chemical substances that control and coordinate growth, development and responses to environmental changes in plants.
9. How does the movement of leaves of a sensitive plant differ from the movement of a shoot towards light?
The leaves of a sensitive plant fold when touched. This movement is caused by changes in water content and pressure in cells and does not depend on growth.
The shoot bends towards light due to unequal growth on its two sides. This movement is called phototropism.
10. Give an example of a plant hormone that promotes growth.
Auxin is a plant hormone that promotes cell elongation and helps in the growth of plant shoots.
11. How does chemical coordination take place in animals?
Chemical coordination in animals takes place through hormones. Endocrine glands release hormones directly into the blood. These hormones reach target organs and regulate different activities of the body.
12. Why is the use of iodised salt advisable?
Iodine is required by the thyroid gland to produce thyroxine. Thyroxine regulates metabolism. Iodine deficiency can cause goitre, in which the thyroid gland becomes enlarged. Therefore, iodised salt helps prevent iodine deficiency.
13. How does our body respond when adrenaline is released into the blood?
Adrenaline prepares the body for emergency situations. It increases heartbeat and breathing rate, directs more blood towards skeletal muscles and increases the supply of energy. This is called the fight-or-flight response.
14. Why are some patients of diabetes treated with insulin injections?
Insulin is a hormone produced by the pancreas. It helps regulate blood glucose levels. When the body does not produce enough insulin or cannot use it properly, blood glucose levels may rise. Insulin treatment helps control blood glucose levels in people who need it.
EXERCISE QUESTIONS AND ANSWERS
1. Which of the following is a plant hormone?
Answer: Auxin.
Auxin is a plant hormone that promotes cell elongation and helps regulate plant growth.
2. What is the function of the brain in the human body?
The brain is the main coordinating centre of the nervous system. It:
Receives information from different parts of the body.
Interprets sensory information.
Controls voluntary and involuntary activities.
Helps maintain balance and posture.
Controls thinking, memory, learning and emotions.
3. What is the difference between the nervous and hormonal mechanisms of control and coordination?
Nervous coordination:
It works through electrical impulses.
Messages travel through neurons.
Responses are generally quick.
Effects are usually short-lived.
It acts on specific muscles or glands.
Hormonal coordination:
It works through chemical substances called hormones.
Hormones are transported through blood.
Responses are generally slower.
Effects may last for a longer time.
Hormones act on specific target organs or tissues.
4. What is the difference between reflex actions and voluntary actions?
Reflex actions:
They are automatic and involuntary.
They occur quickly.
They are generally controlled by the spinal cord or brainstem.
Example: Pulling the hand away from a hot object.
Voluntary actions:
They are performed consciously.
They are generally controlled by the brain.
They may involve planning and decision-making.
Example: Writing, walking and drawing.
5. How are involuntary actions and reflex actions different?
Involuntary actions are activities that occur without conscious control, such as heartbeat and digestion.
Reflex actions are quick and automatic responses to specific stimuli, such as withdrawing a hand from a hot object.
Thus, reflex actions are a type of automatic response, but not all involuntary actions are reflex actions.
6. What happens when receptors do not function properly?
If receptors do not function properly, the body may fail to detect certain stimuli. As a result, appropriate responses may not occur. For example, damage to the receptors in the skin may reduce the ability to detect heat, cold or touch.
7. What is the role of the brain in controlling voluntary actions?
The cerebrum receives sensory information, processes it and makes decisions. It sends instructions through motor neurons to the muscles, producing voluntary movements.
8. Explain the structure and function of a neuron.
A neuron is the structural and functional unit of the nervous system.
Its main parts are:
Dendrites: Receive information from other neurons or receptors.
Cell body: Contains the nucleus and controls the activities of the neuron.
Axon: Carries electrical impulses away from the cell body.
Nerve endings: Pass the information to another neuron, muscle or gland.
9. How does a nerve impulse travel through a neuron?
A nerve impulse is received by the dendrites and passes through the cell body. It then travels along the axon to the nerve endings. At the nerve endings, chemicals are released to transmit the signal across the synapse to the next neuron or target cell.
10. What is a reflex arc? Explain its pathway.
A reflex arc is the pathway followed by nerve impulses during a reflex action.
The pathway is:
Stimulus → Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector muscle → Response.
For example, when a person touches a hot object, receptors in the skin detect heat and send signals to the spinal cord. The spinal cord sends instructions through motor neurons to the muscles, causing the hand to move away.
11. What are the functions of the forebrain, midbrain and hindbrain?
Forebrain:
Controls thinking, memory and intelligence.
Receives and interprets sensory information.
Controls voluntary movements.
Regulates activities such as hunger and thirst.
Midbrain:
Helps control visual and auditory reflexes.
Coordinates certain involuntary responses.
Hindbrain:
The cerebellum maintains balance and posture.
The pons helps regulate breathing.
The medulla controls involuntary activities such as heartbeat, blood pressure and breathing.
12. How does a plant shoot bend towards light?
When light falls on a plant shoot from one side, auxin accumulates more on the shaded side. Cells on the shaded side grow faster than cells on the illuminated side. As a result, the shoot bends towards the light. This movement is called positive phototropism.
13. How does the plant hormone auxin help in growth?
Auxin promotes cell elongation, particularly in shoots. It helps control directional growth and is responsible for movements such as bending of shoots towards light.
14. How do plants respond to gravity?
Plant roots generally grow towards gravity, while shoots generally grow away from gravity.
Roots show positive geotropism.
Shoots show negative geotropism.
15. How do plants respond to touch?
Some plants show movement in response to touch. For example, the leaves of Mimosa pudica fold when touched. This occurs due to changes in water pressure in specialised cells.
FEW IMPORTANT ADDITIONAL QUESTIONS AND ANSWERS
1. Define control and coordination.
Control and coordination is the process by which different organs and systems of an organism work together in a systematic manner to respond to internal and external changes.
2. What are the two main systems responsible for control and coordination in animals?
The two main systems are:
Nervous system
Endocrine system
The nervous system works through electrical impulses, while the endocrine system works through hormones.
3. What is a stimulus?
A stimulus is any change in the internal or external environment that produces a response in an organism.
Examples include light, sound, heat, cold, touch and smell.
4. What is a response?
A response is the reaction of an organism to a stimulus.
For example, withdrawing the hand after touching a hot object is a response.
5. What is a synapse?
A synapse is the small gap between two neurons or between a neuron and another target cell. Chemical substances called neurotransmitters help transmit signals across this gap.
6. What is the difference between sensory neurons and motor neurons?
Sensory neurons:
Carry nerve impulses from receptors towards the central nervous system.
Help the body receive information from the surroundings.
Motor neurons:
Carry nerve impulses from the central nervous system to muscles or glands.
Help produce a response.
7. Name the main parts of the human nervous system.
The main parts are:
Central nervous system – brain and spinal cord.
Peripheral nervous system – nerves connecting the central nervous system to different body parts.
8. What are the main parts of the human brain?
The human brain is broadly divided into:
Forebrain
Midbrain
Hindbrain
Each part performs specific functions and helps coordinate body activities.
9. What is the function of the spinal cord?
The spinal cord:
Transmits messages between the brain and the body.
Controls many reflex actions.
Helps coordinate certain movements.
10. What are plant movements? Give examples.
Plant movements are changes in the position or growth direction of plant parts in response to stimuli.
Examples:
Shoot bending towards light.
Roots growing towards gravity.
Tendrils coiling around a support.
Sensitive plant leaves folding when touched.
11. What is phototropism?
Phototropism is the directional growth movement of a plant part in response to light.
Example: A plant shoot bends towards sunlight.
12. What is geotropism?
Geotropism is the directional growth movement of plant parts in response to gravity.
Example: Roots grow towards gravity, while shoots grow away from gravity.
13. What is hydrotropism?
Hydrotropism is the directional growth of plant parts in response to water.
Example: Plant roots grow towards a source of water.
14. What is chemotropism?
Chemotropism is the directional growth of a plant part in response to a chemical stimulus.
Example: The pollen tube grows towards the ovule due to chemical signals.
15. What is the difference between tropic and nastic movements?
Tropic movements:
Directional growth movements.
Depend on the direction of the stimulus.
Usually involve growth.
Example: Shoot bending towards light.
Nastic movements:
Non-directional movements.
Do not depend on the direction of the stimulus.
May occur due to changes in water pressure in cells.
Example: Folding of Mimosa leaves when touched.
16. Name the major plant hormones and write their functions.
Auxin: Promotes cell elongation and helps in shoot growth.
Gibberellin: Promotes stem growth and seed germination.
Cytokinin: Promotes cell division and helps delay ageing in plant tissues.
Abscisic acid: Generally inhibits growth and helps plants respond to stress.
17. What are hormones?
Hormones are chemical messengers produced by endocrine glands. They are released into the blood and regulate different activities of the body, such as growth, metabolism and reproduction.
18. Name important endocrine glands and their hormones.
Pituitary gland: Growth hormone.
Thyroid gland: Thyroxine.
Pancreas: Insulin.
Adrenal glands: Adrenaline.
Testes: Testosterone.
Ovaries: Oestrogen and progesterone.
19. What is feedback mechanism in hormonal control?
A feedback mechanism regulates the amount of a hormone produced by a gland according to the body's requirements.
For example, when the level of thyroxine in the blood becomes sufficient, signals reduce the stimulation of the thyroid gland.
20. What is the role of insulin in the human body?
Insulin is a hormone produced by the pancreas. It helps regulate blood glucose levels by promoting the uptake and storage of glucose in body cells.
21. What is the role of adrenaline?
Adrenaline prepares the body to face emergency situations. It increases heartbeat and breathing rate and directs more blood towards skeletal muscles.
22. Why is the pituitary gland called the master gland?
The pituitary gland is often called the master gland because it produces hormones that regulate the activities of several other endocrine glands. However, its activity is itself controlled by the hypothalamus.
23. Why is the thyroid gland important?
The thyroid gland produces thyroxine, which regulates the metabolism of carbohydrates, proteins and fats. Iodine is essential for the production of thyroxine.
24. What is goitre?
Goitre is a condition in which the thyroid gland becomes enlarged. Iodine deficiency is one of its important causes because iodine is required for the production of thyroid hormones.
25. Why is coordination necessary in living organisms?
Coordination is necessary because different organs perform different functions. It ensures that these activities work together properly and helps organisms respond to changes in their surroundings.
IMPORTANT TERMS TO REMEMBER
Neuron – Structural and functional unit of the nervous system.
Synapse – Junction or gap between two neurons.
Reflex action – Quick and automatic response to a stimulus.
Reflex arc – Pathway followed by nerve impulses during a reflex action.
Receptor – Specialised structure that detects a stimulus.
Hormone – Chemical messenger produced by endocrine glands.
Auxin – Plant hormone that promotes cell elongation.
Phototropism – Growth movement in response to light.
Geotropism – Growth movement in response to gravity.
Hydrotropism – Growth movement in response to water.
Chemotropism – Growth movement in response to chemicals.
Transmitter – Chemical substance that helps carry signals across a synapse.
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