In Text Questions
Page No: 119
Ques 1. What is the difference between a reflex action and walking?
Ques 2. What happens at the synapse between two neurons?
Ans: A very small gap that occurs between the last portion of axon of one neuron and the dendron of the other neuron is known as a synapse. It acts as a one way valve to transmit impulses in one direction only.
This uni-directional transfer of impulses occur as the chemicals are produced in only one side of the neuron i.e., the axon’s side. From axon, the impulses travel across the synapse to the dendron of the other neuron.
Ques 3. Which part of the brain maintains posture and equilibrium of the body?
Ans: Cerebellum, a part of the hindbrain is responsible for maintaining posture and equilibrium of the body.
Ques 4. How do we detect the smell of an agarbatti (incense stick)?
Ans: The thinking part of our brain is the fore-brain. It has separate areas that are specialized for hearing, smelling, sight, taste, touch, etc. The fore-brain also has regions that collect information or impulses from the various receptors.
When the smell of an incense stick reaches us, our fore-brain detects it. Then, the fore-brain interprets it by putting it together with the information received from other receptors and also with the information already stored in the brain.
Ques 5. What is the role of the brain in reflex action?
Ans: Reflex actions are sudden responses, which do not involve any thinking. For example, when we touch a hot object, we withdraw our hand immediately without thinking as thinking may take time which would be enough to get us burnt.
The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves (input) and responding to it quickly (output) is called a reflex arc. The reflex arcs −connections present between the input and output nerves − meet in a bundle in the spinal cord.
Reflex arcs are formed in the spinal cord and the information (input) reaches the brain. The brain is only aware of the signal and the response that has taken place. However, the brain has no role to play in the creation of the response.
Page No: 122
Ques 1. What are plant hormones?
Ans: Plant hormones are the fluids which are secreted within the plant also known as phytohormones. Plant hormones regulate the growth and development of the plant. Examples of plant hormones are auxin, gibberellins etc.
Ques 2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
|Movement of leaves of sensitive plant||Movement of shoot towards light|
|(i) Growth independent movement.|
(ii) Movement is non-directional i.e., it is neither towards nor away from the stimulus.
(iii) Such movements are referred as nastic movements.
(iv) Such movements are reversible.
|(i) Growth dependent movement.|
(ii) Movement is towards the source of stimulus (light). So it is a directional movement.
(in) Such movements are referred as tropic movements.
(iv) Such movements are irreversible.
(b) When tendrils come in contact with any support, the tip of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This is due to the fact that auxin secreted in the tip diffuses towards the side opposite to the point of contact. So this induces more growth on the side opposite to the point of contact. Thereby causing the tendril to circle around the object.
Folding of leaves of touching me not plant or sensitive plant (Mimosa pudica or Chhui-Mui) on being touched is an example of nastic movement. The movement is directed neither towards nor away from the stimulus. This movement is due to change in the turgor pressure of cells.
Ques 3. Give an example of a plant hormone that promotes growth.
Ans: Auxin is an example of a growth-promoting plant hormone.
Ques 4. How do auxins promote the growth of a tendril around a support?
Ans: Auxin is synthesized at the shoot tip. It helps the cell grow longer. When a tendril comes in contact with a support, auxin stimulates faster growth of the cells on the opposite side, so that the tendril forms a coil around the support. This makes the tendrils appear as a watch spring.
Ques 5. Design an experiment to demonstrate hydrotropism.
Ans: Take two small beakers and label them as A and B. Fill beaker A with water. Now make a cylindrical-shaped roll from a filter paper and keep it as a bridge between beaker A and beaker B, as shown in the figure.
Attach few germinating seeds in the middle of the filter paper bridge. Now, cover the entire set-up with a transparent plastic container so that the moisture is retained.
The roots of the germinating seeds will grow towards beaker A.
This experiment demonstrates the phenomenon of hydrotropism.
Page No: 125
Ques 1. How does chemical coordination take place in animals?
Ans: Chemical coordination takes place in animals with the help of hormones. Hormone is the chemical messenger that regulates the physiological processes in living organisms. It is secreted by glands. The regulation of physiological processes and control and coordination by hormones comes under the endocrine system.
The nervous system along with the endocrine system in our body controls and coordinates the physiological processes.
Ques 2. Why is the use of iodized salt advisable?
Ans: Iodine stimulates the thyroid gland to produce thyroxin hormone. It regulates carbohydrate, fat, and protein metabolism in our body. Deficiency of this hormone results in the enlargement of the thyroid gland. This can lead to goitre, a disease characterized by swollen neck. Therefore, iodized salt is advised for normal functioning of the thyroid gland.
Ques 3. How does our body respond when adrenaline is secreted into the blood?
Ans: Adrenalin is a hormone secreted by the adrenal glands in case of any danger or emergency or any kinds of stress. It is secreted directly into the blood and is transported to different parts of the body.
When secreted in large amounts, it speeds up the heartbeat and hence supplies more oxygen to the muscles. The breathing rate also increases due to contractions of diaphragm and rib muscles. It also increases the blood pressure. All these responses enable the body to deal with any stress or emergency.
Ques 4. Why are some patients of diabetes treated by giving injections of insulin?
Ans: Diabetes is caused due to less or no secretion of hormone insulin by pancreas. In such a person, blood sugar level is high. Insulin converts extra sugar present in blood into glycogen. Thus, patients suffering from diabetes are given insulin injection to control their blood sugar level.
Page No: 126
1. Which of the following is a plant hormone?
Ans: (d) Cytokinin is a plant hormone.
2. The gap between two neurons is called a
Ans: (b) The gap between two neurons is called a synapse.
3. The brain is responsible for
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Ans: (d) The brain is responsible for thinking, regulating the heart beat and balancing the body.
Ques 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?
Ans: Receptors are sensory structures (organs/tissues or cells) present all over the body. The receptors are either grouped in case of eye or ear, or scattered in case of skin.
Functions of receptors:
(i) They sense the external stimuli such as heat or pain.
(ii) They also trigger an impulse in the sensory neuron which sends message to the spinal cord.
When the receptors are damaged, the external stimuli transferring signals to the brain are not felt. For example, in the case of damaged receptors, if we accidentally touch any hot object, then our hands might get burnt as damaged receptors cannot perceive the external stimuli of heat and pain.
Ques 5. Draw the structure of a neuron and explain its function.
Functions of the three parts of a neuron:
Axon: It conducts messages away from the cell body.
Dendrite: It receives information from axon of another cell and conducts the messages towards the cell body.
Cell body: It contains nucleus, mitochondria, and other organelles. It is mainly concerned with the maintenance and growth.
Ques 6. How does phototropism occur in plants?
Ans: The growth movement in plants in response to light stimulus is known as phototropism. The shoots show positive phototropism and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source.
Some examples of phototropism are as follows:
(a) The flower head of sunflower is positively phototropic and hence it moves from east to west along with the sun.
(b) The ovary stalk of groundnut is positively phototropic before fertilization and becomes negatively phototropic after fertilization, so that the fruit is formed underground.
Ques 7. Which signals will get disrupted in case of a spinal cord injury?
Ans: The reflex arc connections between the input and output nerves meet in a bundle in the spinal cord. In fact, nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. In case of any injury to the spinal cord, the signals coming from the nerves as well as the signals coming to the receptors will be disrupted.
Ques 8. How does chemical coordination occur in plants?
Ans: In animals, control and coordination occur with the help of nervous system. However, plants do not have a nervous system.
Plants respond to stimuli by showing movements. The growth, development, and responses to the environment in plants is controlled and coordinated by a special class of chemical substances known as hormones.
These hormones are produced in one part of the plant body and are translocated to other needy parts. For example, a hormone produced in roots is translocated to other parts when required.
The five major types of phytohormone are auxins, gibberellins, cytokinins, abscisic acid, and ethylene. These phytohormones are either growth promoters (such as auxins, gibberellins, cytokinins, and ethylene) or growth inhibitors such as abscisic acid.
Ques 9. What is the need for a system of control and coordination in an organism?
Ans: The maintenance of the body functions in response to changes in the body by working together of various integrated body systems is known as coordination. All the movements that occur in response to stimuli are carefully coordinated and controlled.
In animals, the control and coordination movements are provided by nervous and muscular systems. The nervous system sends messages to and away from the brain. The spinal cord plays an important role in the relay of messages.
In the absence of this system of control and coordination, our body will not be able to function properly. For example, when we accidentally touch a hot utensil, we immediately withdraw our hand. In the absence of nerve transmission, we will not withdraw our hand and may get burnt.
Ques 10. How are involuntary actions and reflex actions different from each other?
Ans: Involuntary actions cannot be consciously controlled. For example, we cannot consciously control the movement of food in the alimentary canal. These actions are however directly under the control of the brain.
On the other hand, the reflex actions such as closing of eyes immediately when bright light is focused show sudden response and do not involve any thinking. This means that unlike involuntary actions, the reflex actions are not under the control of brain.
Ques 11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Nervous System Mechanism
Hormonal System Mechanism
It is consist of nerve impulses between PNS, CNS and Brain.
It consists of endocrine system which secretes hormones directly into blood.
The axons and dendrites transmit the information through a coordinated effort.
The information is transmitted or transported through blood.
The flow of information is rapid and the response is quick.
The information travels slowly and the response is slow.
Nerve impulses are not specific in their action.
Each hormone has specific actions.
Effects are short lived.
It has prolonged effects.
Ques 12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Movement in sensitive plants
Movement in our legs
The movement in a sensitive plant is a response to stimulus(touch) which is a involuntary action.
Movement in our legs is a voluntary action.
No special tissue is there for the transfer of information
A complete system CNS and PNS is there for the information exchange.
Plant cells do not have specialised protein for movements.
Animal cells have specialised protein which help muscles to contract.