NCERT Solutions for Class 10 Science CONTROL AND COORDINATION
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1) What is the difference between a reflex action and walking? Answer Reflex action is a process by which we do something without thinking about it or without being in control of reactions. It is done by only the spinal cord without the help of brain.
While walking is a process which is done by thinking or it is performed by the brain unlike reflex action. 2) What happens at the synapse between two nephrons? Answer The electrical impulses set off release of some chemicals at the synape between two nephrons. These chemicals cross the synapse and start a similar electrical impulse in a dendrite of the next neuron. 3) Which part of the brain maintains posture and equilibrium of the body? Answer Posture and equilibrium of the body is maintained by midbrain. 4) How do we detect the smell of an agarbatti (incense stick)? Answer The smell of agarbatti is detected by the forebrain. There are separate areas of association where sensory impulses or information are interpreted by putting them together. These impulses of smell are detected by forebrain.
5) What is the role of the brain in reflex action? Answer The nerves from all over the body meet in the bundle in the spinal cord. Reflex arcs are formed in the spinal cord itself although the information input also goes on to reach the brain.
6) What are plant hormones? Answer The chemical substances released by various part of plants to control growth and various activities are called plant hormones. 7) How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light? Answer The movement of leaves of the sensitive plant is neither towards nor away from stimulus like touch. While movement of shoot is towards stimulus like light. The movement of leaves of sensitive plants is not directional while the movement of shoot is directional.
8) Give an example of a plant hormone that promotes growth. Answer (i) Auxins help to increase the length of plants.
(ii) Gibberellins help in the growth of stem.
9) How do auxins promote the growth of a tendril around a support? Answer The tendrils are sensitive to touch. As these tendrils come in the contact with the support, the auxin diffuses towards the other side away from the support. So this part grows more rapidly than the other. This causes the tendril to circle around the support and thus climb upwards.
10) How does chemical coordination take place in animals? Answer Chemical coordination takes place in animals with \the help of some chemical substances called hormones. Hormones are secreted by endocrine glands. The timing and amount of hormones released are regulated by feedback mechanisms.
11) Why is the use of iodized salt advisable? Answer The use of iodized salt is advisable because iodine is necessary for the thyroid gland to produce thyroxine hormone. Thyroxine regulates carbohydrates, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxine.
12) How does our body respond when adrenalin secreted into the blood? Answer Adrenalin is secreted directly into the blood and is carried to different parts of the body. It acts on heart. As a result the heart beats faster in order to supply more oxygen to our muscles. These muscles regulate various movements of the body. 13) Why are some patients of diabetes treated by infections of insulin? Answer The patients of diabetes are treated by giving injections of insulin. Insulin is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects.
14) What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise? Answer the main function of receptors is to detect in formations from the environment. These receptors are located in our sense organs. There are some situations which receptors do not work properly, like mouth starts water when we feel hungry, touching a flame, knee – jerk, etc.
In these situations, they take enough time if these done by brain. To solve these problems, the nerves made muscles in a simpler way. This is done by the spinal cord.
15) Draw the structure of a neuron and explain its function. Answer Function of neuron: The neuron is the structure and functional unit of the nervous system. It contain following three parts:
(i) dendrites (ii) Cell body (iii) Axon
The impulses of information travel from dendrites to cell body. and then along the axon to its end. These impulses cross the synapse. at the end, the impulses travel from one neuron to the other up to the spinal cord or to the concerned part of body.
16) How does phototropism occur in plants? Answer The directional or tropic movement towards the light or away from the light is called phototropism. The shoots respond by bending towards light, while roots respond by bending away from the light.
17) Which signals will get disrupted in case of a spinal cord injury? Answer (i) All the signals are responses which pass from and to the brain through the spinal cord will get disturbed.
(ii) Reflex actions will be disrupted.
18) How does chemical coordination occur in plants? Answer In plants, stimulated cells release chemical compounds, which are called plant hormones. Different plant hormones help to coordinate growth development and responses to the environment. They are synthesized at placed away from where they act and simply diffuse to the area of action.
19) What is the need for a system of control and coordination in an organism? Answer Every little change in the environment evokes an appropriate movement in response. For example, if we want to talk to our friends in class, we whisper rather than shouting loudly. Thus, the movement to be made depends on the event that is triggering it. Therefore, such controlled movement must be connected to the recognition of various events in the environment, followed by only the correct movement in response. In other words, living organisms must use systems providing control and coordination. In multicellular organisms, specialized tissues are used to provide control and coordination activities.
20) How are involuntary actions and reflex actions different from each other? Answer Involuntary Action: (i) The action which we cannot do by thinking; called involuntary action. For example, beating of the heart (ii) Involuntary actions are controlled by the brain. Reflex Action: (i) An action i. e. a response which is immediate and does not need processing by the brain is called a reflex action. For example, immediate removal of hand on touching a hot plate (ii) Reflex actions are controlled by the spinal cord.
21) Compare and contrast nervous system and hormonal mechanisms for control and coordination in animals. Answer In human beings, he nervous system controls the various functions by small units called neurons. Neurons receive the information through sensory nerves and transfer them through motor nerves.
Besides this, certain important functions like sugar level, metabolism, growth and development, etc. are controlled by hormones secreted by various endocrine glands. Hence, it is true that nervous and hormonal systems together perform the function of control and coordination in human beings.
22) What is the difference between the manner in which movement in the sensitive plant and movement in our legs takes place? Answer Movement in sensitive plant: Movement in the sensitive plant leaves takes place in response to touch (shock) stimulus. When terminal pinnule is touched, the stimulus is conducted to its base and the pinnules droop down. This happens due to change (decrease) in osmotic pressure causing shrinkage. when the stimulus time is over, osmotic pressure increases and the cells swell, causing to the pinnules become normal. This is an example of growth independent movement.
Thus, movement happens at a point different from the point of touch (stimulus). So, the information that a touch has occurred is communicated through electrical – chemical means from cell to cell, but not through specialized tissues. Plant cells change in shape by changing the amount of water in them, resulting in swelling or shrinking, during movement. Movement in our legs: Our legs are provided with nerves which are connected to muscles. To lift the leg, the brain passes information to nerves.
The information travels as an electrical impulse. On reaching the leg muscles, the impulse is converted into a chemical signal and the muscles contract to lift the leg. Movement of legs takes place due to muscle contraction and relaxation, which is under the control of our nervous system.
In the nervous system, electrical impulses are generated for quick transmission of information. But there are limitations:
(i) Impulses will reach only those cells that are connected by the nervous tissue.
(ii) Once an electrical impulse is generated in a cell and transmitted, the cell takes some time to generate another impulse. That is, cells cannot continuously create and transmit electrical impulses.
Hormones are chemical messengers that diffuse to all cells of the body. The body cells using special, molecules on heir surfaces, recognize information and even transmit it. Hormones are synthesized at places away from where they act.Hormones can reach all cells of the body (through blood in animals) regardless of nervous connections, and it can be done steadily and persistently.
23) Name the system in animals which help in the process of control and coordination. Answer
(i) Nervous system
(ii) Hormonal (Endocrine) system
24) Name the largest cell in the human body. Answer
Nerve cell or neuron.
25) Have the old parts of the shoot and root changed direction? Answer
The old parts of roots and shoots of plant change their directions slightly (very less), while new parts move more.
26) What are the main divisions of nervous system? Answer The nervous system is broadly divisible into two parts:
(i) Central nervous system,
(ii) Peripheral nervous system
27) Give four examples of simple human reflexes. Answer
(i) Knee – jerk reflex in which the leg is involuntarily extended forward as a result of a sharp tap below the knee – ap in a relaxed (freely hanging) leg.
(ii) Closing of the eyelids when an object suddenly approaches the eye or when a strong beam of light is flashed cross.
(iii) Withdrawal of the hand on pricking a pin or a horn.
(iv) Movement of the diaphragm.
28) Design an experiment to demonstrate hydrotropism. Answer
Positive hydrotropism can be demonstrated with terminated seedlings, which are allowed to grow on ground. The soil below the roots is separated by a polythene partition. The left side is kept moist but the right side is kept ry.
The radicals at first grow in a downward direction due to the effect of gravity (positive geotropism), but after some time, the roots bend toward the moist soil (positive hydrotropism). This is evidently due to the closeness of the germinating roots to wate
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