NCERT Solutions For Class 10 Science Chapter 7 Control and Coordination

NCERT Solutions For Class 10 Science Chapter 7 Control and Coordination

Question 1. What is geotropism? Describe an experiment to demonstrate positive and negative geotropism.
Answer:

The upward growth of shoots and the downward growth of roots in response to the pull of the earth or gravity is known as geotropism.

Experiment: Take a small healthy potted plant. Make a hole at the bottom of the pot. Tilt the pot so that it rests on its edge so that the plant becomes in a horizontal position. Place the tilted potted plant in a safe space.

• Water the plant from time to time. After some days, you will find the shoot growing upward, that is, away from the force of gravity showing negative geotropism, and the roots coming out of the bottom of the pot grow downward, that is, towards the force of gravity showing positive geotropism.
• (This upward growth of young shoots and downward growth of roots are seen due to the unilateral effect of gravity).

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Question 2. State the sequence of change that takes place in the human body when it prepares itself to protect itself from a scary or dangerous situation.
Answer:

1. Target organs or specific tissues on which it acts include the heart.
2. Under the influence of adrenaline, the heart beats faster to supply more oxygen to the heart muscles.
3. The blood supply to the digestive system and skin is reduced due to the contraction of muscles around small arteries in these organs This causes the diversion of the blood to skeletal muscles.
4. There is an increase in breathing rate. It happens because of the contraction of the diaphragm and rib muscles.
5. All these responses together enable the body to meet with the situation (emotional stress).
6. Thus, hormones secreted by the endocrine system act as a second way to control and coordinate in our body.

Question 3.

1. Name one organ each where growth hormone is synthesized in man and plant.
2. List the sequence of events that occur when a plant is exposed to unidirectional light, leading to the bending of a growing shoot. Also, name the hormone.

Answer:

1. The pituitary gland in men and shoot tip in plants.
2. Auxin diffuses towards the shady side and causes elongation of one side (shady side) resulting in bending. When light is coming from one side of the plant, auxin diffuses towards the shady side. This concentration stimulates the cells to grow longer on that side of the shoot which is away from the light and thus the shoot bends. The name of the hormone is Auxin.

Question 4.

1. Explain how auxins help in the bending of plant stems towards the light.
2. State the objective of the experiment, for which the experimental setup is shown in the given diagram.

Answer:

1. When a growing plant detects light, auxin synthesizes at the shoot tip to help the cells grow longer. When light comes from one side, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light and the plant appears to bend towards light.
2. The objective of the experiment is to show the phototropic movement of the plant.

Question 5. What is meant by reflex action? With the help of a labeled diagram trace the sequence of events that occur when we touch a hot object.
Answer:

Reflex action is defined as an unconscious, automatic, and involuntary response of the effector, i.e., muscle and gland to a stimulus which is monitored through the spinal cord.

A sequence of events when we touch a hot object are:

1. Receptor organ skin receives the stimulus and activates a sensory nerve impulse.
2. Sensory neuron carries the message in the form of sensory impulses to the spinal cord.
3. The spinal cord acts as a modulator. The neurons of the spinal cord transmit the sensory neural impulses to motor neurons.
4. The motor nerve conducts these impulses to the effector organ hand which responds by pulling back the hand away from the hot object.

Question 6. State the functions of plant hormones. Name four different types of plant hormones.
Answer:

Plant hormones help to coordinate growth, development, and responses in the environment. Four different types of plant hormones are Auxins, Gibberellins, Cytokinins, and Abscisic acid.

1. Auxins are the group of plant hormones synthesized at the shoot-tip of the plant body. These promote cell elongation, root formation, cell division, respiration, and other physiological processes like protein synthesis, water uptake, and protoplasmic permeability. Auxins also play an important role in the development of seedless fruits.
2. Gibberellins stimulate stem elongation, seed germination, and flowering. The maximum concentration of gibberellins is found in fruits and seeds.
3. Cytokinins are produced in dividing cells throughout the plant. In mature plants, cytokinins are produced in the root tips and are transported to the shoots. Cytokinins promote cell division and also help in breaking the dormancy of seeds and buds and regulate the phloem transport. Cytokinins delay the aging in leaves and promote the opening of stomata.
4. Abscisic acid is a growth inhibitor that reverses the growth-promoting effects of auxins and gibberellins. Its effects include wilting of leaves. It causes dormancy of seeds. It also promotes the closing of stomata.

Question 7.

1. Name the hormone which is released into the blood when its sugar level rises. Name the organ which produces this hormone and its effect on blood sugar levels. Also, mention the digestive enzymes secreted by this organ with one function of each.
2. Explain the need for Chemical communication in multicellular organisms.

Answer:

1. When the sugar level rises, the hormone insulin is released into the blood. Insulin is released in our body by the pancreas. When insulin is secreted in lower quantities by the pancreas, the blood sugar level of the concerned person increases. On the other hand, if the insulin is secreted in excess, the person suffers from low sugar in the blood.
2. Chemical communication is required in multicellular organisms to deal with emergency demands such as infection, trauma, dehydration, starvation, hemorrhage, extreme temperature, etc.

Question 8. A young boy met an accident while riding a bike. Patrolling police found the boy and brought him to a hospital for treatment. After the accident, the boy lost his memory completely. The left side of his body also suffered from paralysis.

1. What values were shown by police persons?
2. Which injured body part can cause paralysis?
3. What precautions should one take while riding a two-wheeler?

Answer:

1. The values shown by the police persons were truthful to duty and humanity.
2. Injury to the brain or spinal cord can cause paralysis.
3. Riders must wear helmets while riding a two-wheeler. One must drive at a controlled speed to avoid accidents.

Question 9. What is a reflex arc? Draw a neat labeled diagram of the components in a reflex arc. Why do impulses flow only in one direction in a reflex arc?
Answer:

The reflex arc is the pathway taken by the nerve impulses and responses in a reflex action, i.e., from the receptor organs like skin to the spinal cord and from the spinal cord to the effector organs like muscles.

Impulses flow only in one direction in a reflex arc, because each synapse in the reflex arc allows impulses to cross it in a single direction.

Question 10. With the help of a flow chart, highlight the various types of plant movements with suitable examples.
Answer:

Question 11.

1. Name the parts labeled A and B in the neuron drawn above.
2. Which part acquires the information in the neuron?
3. Through which part does the information travel?
4. In what form does this information travel?
5. Where is the impulse converted into a chemical signal for onward transmission?

Answer:

1. A- Dendrite B-Axon
2. The information in the neuron is acquired at the end of the dendrite tip.
3. The information travels from the dendrite to the cell body and then along the axon to its end.
4. The information travels in the form of an impulse.
5. The impulse is converted into a chemical signal at the end of the axon.

Function of thyroxine hormone:

It regulates carbohydrate, protein, and fat metabolism in the body to provide the best balance for growth.

The use of iodized salt is advisable because iodine is essential for the synthesis of thyroxin. In case of iodine deficiency in our diet, there is a possibility one can suffer from goiter, which is a disease of the swollen neck.

Question 12. Suggest six reflex actions of the body. Explain how the reflex arc is the same in all of them.
Answer:

1. Six reflex actions of the body are as follows:
2. When we see a speeding car moving towards us, we move aside.
3. We withdraw our hands from being pricked by a pin.
4. We withdraw our hands on touching a very hot substance.
5. We close our eyes to see the direct sun or extremely bright source of light.
6. We close our eyes on hear a loud noise.
7. We shiver on feeling cold.

The reflex arc in all the above cases is the same because in all the cases, the stimulus is received by sense organs Then this information is carried to the spinal cord through sensory nerves. Thus, information from the spinal cord is sent to the effectors such as muscles via motor neurons.

Question 13. Draw the structure of a neuron and explain its function.
Answer:

Neurons are the units that make up the nervous system. These are the structural and functional units of the nervous system. These carry messages over large distances in the body quickly.

A neuron (or nerve cell) has three components:

1. Cell body: It contains cytoplasm and nucleus.
2. Dendrites: These are shorter fibers on the body of neurons.
3. Axon: It is the longest fiber on the cell body of a neuron.

Question 14. What are the major parts of the brain? Mention the functions of different parts.
Answer:

Question 15. What constitutes the central and peripheral nervous systems? How are the components of the central nervous system protected?
Answer:

The central nervous system consists of the brain and spinal cord.

1. Brain: It is the main coordinating center in the body. It is lodged in the brain box or cranium which protects it. It is covered by membranes called meninges, which also help to protect it.
   • The space between the membranes and the brain is filled with cerebrospinal fluid which protects the brain from mechanical shock. The brain is broadly divided into three regions: fore-brain, mid-brain, and hind-brain.
2. Spinal cord: It is a long cylindrical structure. It begins from the medulla oblongata and extends downwards. It is enclosed in a bony cage called a Vertebral column that protects it.
   • It is also surrounded by meninges. It is concerned with spinal reflex actions and the conduction of nerve impulses to and from the brain.

Peripheral Nervous System (PNS)

It includes the following:

1. Cranial nerves have 12 pairs that emerge from the brain.
2. Spinal nerves 31 pairs that arise from the spinal cord and spread throughout the body.
3. Visceral nerves: They are a special kind of nerves that mostly arise from the spinal cord and are connected to the internal organs of the body. They carry both sensory and motor neurons. The PNS works according to our will.

Question 16. Mention one function for each of these hormones:

1. Thyroxin
2. Insulin
3. Adrenaline
4. Growth hormone
5. Testosterone.

Answer:

1. Thyroxin regulates carbohydrate, fat, and protein metabolism in the body to provide the best balance for growth.
2. Insulin regulates blood sugar levels.
3. Adrenaline increases heart rate and supply of blood to various organizers:
4. Growth hormone regulates growth and development.
5. Testosterone controls the changes in body features associated with puberty in males.

Question 17. Name various plant hormones. Also give their physiological effects on plant growth and development.
Answer:

Question 18. What are reflex actions? Give two examples. Explain a reflex arc.
Answer:

Reflex action is a rapid, automatic response to a stimulus that is not under the voluntary control of the brain i.e., it is an involuntary action. It is a simple form of behavior in which the same stimulus produces the same response every time, for example.,

1. If we unknowingly touch a hot plate, we immediately move our hand away from it.
2. A sharp thing like a nail touches our body.

Other examples are knee jerk, coughing, yawning, etc.

The pathway taken by nerve impulses in a reflex action is called the reflex arc. Reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. However, even after complex neuron networks have come into existence, the reflex arc continues. to be more efficient for quick responses.

Question 19. The nervous and hormonal systems together perform the function of control and coordination in human beings. Justify the statement.
Answer:

The working together of various organs of human beings in a systematic, controlled, and efficient way to produce a proper response to various stimuli is known as coordination. In humans, the nervous and hormonal systems together perform this control and coordination.

• The nervous system consists of receptors that receive stimuli from the surrounding environment and send the message conveyed by them to the spinal cord and brain in the form of electrical impulses through the sensory nerves.
• The motor nerves then transmit the response to the ‘effector’. The effectors are mainly the muscles and glands of our body.
• Thus, endocrine glands secreting hormones are directly or indirectly controlled by the nervous system.
• Hence, control and coordination in humans (or animals) depend on two things for transmitting information i.e., chemical signals of hormones and nerve impulses.
• If they depend upon only nerve impulses through nerve cells, a limited range of tissues would be stimulated.

Question 20. How does chemical coordination take place in animals?
Answer:

Different endocrine glands secrete different hormones. These hormones are released into the blood which carries them to specific tissues or organs called target tissues or target orgAnswer: In the target tissues, the hormone triggers a particular biochemical or physiological activity.

Question 21. Why is the flow of signals in a synapse from the axonal end of one neuron to the dendritic end of another neuron, but not the reverse?
Answer:

When an electrical signal reaches the axonal end of a neuron, it releases a chemical substance. This chemical diffuses towards the dendrite end of the next neuron where it generates an electrical impulse or signal.

Hence, the electrical signal is converted into a chemical signal at the axonal end. Since these chemicals are absent at the dendrite end of the neuron the electrical signal cannot be converted into a chemical signal.