NCERT Intext Question
Question 1. What is the difference between a reflex action and walking? Sol. Difference between reflex action and walking.
Sol. Difference between reflex action and walking.
Question 2. What happens at the synapse between two neurons?
Sol. Synapse is a very small region that occurs between the last portion of axon of one neuron and the dendrite of the other neuron. It acts as a one-way passage in which transmission of nerve impulse can takes place in one direction only. At synapse, the nerve ending of a nerve cell converts the nerve impulse into some chemical substance that travels through the gap towards the dendrite of succeeding neuron. The axon terminal of a neuron releases specialised chemicals called neurotransmitters. These chemicals travel through the synapse and reach the dendrites of the successive neuron. These chemical messengers cross the synapse and start an electrical impulse
Question 3. Which part of the brain maintains posture and equilibrium of the body?
Sol. Cerebellum, a part of hind brain, maintains the posture and equilibrium of the body.
Note: The cerebellum receives information from the sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements like posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity
Question 4. How do we detect the smell of an agarabatti (incense stick)?
Sol. Smell of an agarbatti (incense stick) is sensed by olfactory receptor present in the nose and then information is transmitted to olfactory lobe located in the forebrain which interpret the information and give us a perception of smell.
Note: The thinking part of our brain is the forebrain. it has separate areas that are specialised for hearing, smelling, sight, taste, touch, etc. The forebrain also has regions that collect information or impulses from the various receptors
Question 5. What is the role of the brain in reflex action?
Sol. Reflex actions are sudden involuntary responses which does not involve thinking. For example, when we touch a hot object, we withdraw our hand immediately without thinking. Though, spinal reflexes are produced in the spinal cord, but the message of reflex action taken also goes on to reach the brain. 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 known as reflex arc.
Reflex arcs are formed in the spinal cord but the information is still sent to the brain. The brain doesn’t have a significant response to it.
Question 6. What are plant hormones ?
Sol. Plant hormones, also known as phytohormones, are chemical substances produced in the cells of root and shoot tips. These chemicals are responsible for controlling growth of the plant body. Major plant hormones are auxins, gibberellins, ethylene, cytokinin, abscisic acid (ABA). These hormones are either growth promoters or growth inhibitors.
Question 7. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Question 8. Give an example of a plant hormone that promotes growth.
Sol. Growth promoting hormones that promotes growth are:
- Auxin promotes growth of cells.
- Gibberellin promote elongation of cells.
- Cytokinin promotes cell division.
Question 9. How do auxins promote the growth of a tendril around a support?
Sol. Tendril is a thread-like growth on the stems and leaves of the climbing plants. These tendrils are sensitive to touch.
Auxin, synthesised at the tip of the shoot, triggers the growth of tendril around a support. Auxin increase in concentration in the part of the tendril which is away from the support. This results in increased cell division in that part. The part which is nearer to the support has lesser rate of cell division. As a result, the external part of the tendril grows more than the internal part and the tendril coils around the support.
Question 10. Design an experiment todemonstrate hydrotropism.
Sol. The growth of plant parts towards or away from water is called hydrotropism. It is known that roots are positively hydrotropic in nature, i.e., they grow towards water in the soil.
This can be demonstrated by the activity given below:
Material: A trough, soil water and germinating seeds or baby plants, perforated card board sheet equal to the diameter of trough.
- Take a trough.
- Fix the perforated card board sheet in the trough vertically.
- Half fill one part of trough with soil and the other half or second part of the trough with water.
- Now fix the germinating seed or baby plants in the soil.
- Keep the whole apparatus in the sun in open place for few days.
Observations: After a few days, the following changes are observed:
- (The roots bend towards water.
- The shoot part bends away from water.
Result: The experiment confirms that :
- Water has positive effect on roots which is called positive hydrotropism.
- Water has negative effect on shoot (stem and other aerial parts) which is called as negative hydrotropism.
- Apparatus should be placed at open place in the Sun so that plants may get all the necessary conditions.
- Perforations in the cardboard sheet should neither be too big nor too small. Water should be diffused slowly.
Question 11. How does chemical coordination takes place in animals ?
Sol. Chemical coordination in animals takes place by the hormones which are secreted by several endocrine glands.
The hormones after secretion reach into blood and after that through blood, it reaches to the various parts of the body. For example, adrenaline which is secreted by adrenal gland and through blood it reaches to its target i.e. heart. As a result, the heart beats faster in order to supply more oxygen to the muscles and the target organs get more oxygen and satisfies its need of oxygen to work.
Question 12. Why is the use of iodised salt advisable?
Sol. A deficiency of iodine in the diet can cause a deficiency of thyroxine hormone in the body leading to a condition of enlarged thyroid gland called goiter (characterised by swollen neck) and an abnormally low level of thyroid hormones (called hypothyroidism). Therefore, people are advised to use iodised salt for cooking food so as to prevent goiter disease
Note: Iodine is essential for healthy brain development in the foetus and young child. It is a very important nutrient of our diet, as the body does not naturally produce iodine. Iodine is required to stimulate the thyroid gland to produce thyroxine hormone. Thyroxine help in tissue repair, regulate metabolism and promote proper growth and development. Without adequate amount of iodine, the thyroid enlarges in an attempt to keep up with the body’s demand for thyroid hormone.
Question 13. How does our body respond when adrenaline is secreted into the blood?
Sol. Adrenaline is a hormone secreted by the adrenal glands (medulla) 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 amount, it speeds up the heartbeat and hence supplies more oxygen to the muscles. The breathing rate also increases due to contraction of diaphragm and rib muscles. It also increases the blood pressure. All these responses enable the body to deal with any stress or emergency
Question 14. Why are some patients of diabetes treated by giving injections of insulin?
Sol. Insulin is a hormone secreted by pancreas that regulates the sugar level in the blood. When this hormone is not synthesised in proper amount then the sugar level in the blood rises and the persons suffers from a condition called diabetes. This is the reason why diabetic patients are treated by giving injections of insulin.
Note: Insulin injection works by helping move sugar from the blood into other body tissues where it is used for energy. It also stops the liver from producing more sugar.
Question 1. Which of the following is a plant hormone?
Sol. (d) Cytokinin is a plant hormone which helps in the cell division in plant root and shoot.
While insulin, thyroxine and oestrogen are animal hormones in which insulin helps to control blood glucose levels, thyroxine helps to control energy level, growth of the body and oestrogen help to regulate a woman’s menstrual cycle and playan important role in pregnancy.
Question 2. The gap between two neurons is called a
(a) dendrite. (b) synapse.
(c) axon. (d) impulse.
Sol. (b) The gap between two neurons is called a synapse. It is a gap across which a nerve cell can send an impulse to another neuron with the help of neurotransmitter. Dendrites and axon are the parts of neurons. Impulse is the signal that travel along the length of a nerve fibre & ends in the release of neurotransmitter.
Question 3. The brain is responsible for
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above
Sol. (d) The brain is the most complex organ in a vertebrate’s body. It is a part of central nervous system. It controls thoughts, memory, speech, movement and also function of many organs within our body.
Question 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 ?
Sol. Receptors are cells, tissues, and organs which are capable of receiving particular stimuli and initiate impulses to be picked up by sensory nerves. These nerves are located in our sense organs such as the inner ear, nose, tongue, eye, skin etc. In case, any of the receptors do not work properly then the person will not perceive that particular information, e.g., if our gustatory receptors located in tongue do not work properly then we will not be able to perceive the taste of food such as sour, sweet, salty or bitter.
Question 5. Draw the structure of a neuron and explain its function.
Sol. Structure of neuron: Neurons are the structural and functional unit of nervous system which is specialised to receive, conduct and transmit impulses. It consists of three basic parts- dendrites, cell body and axon.
[Refer Chapter at a Glance point 2 (a)]
Function of neuron: Dendrites of a neuron collect information from the receptors and pass it to the cell body in the form of electrical impulse. From the cell body, impulse passes along the axon to its end. At end of the axon, the electrical impulse results in the release of certain chemicals (neurotransmitters). These chemicals cross the gap (synapse) between the endings of the axon and dendrites of the next neuron and start a similar electric impulse in the dendrites.Thus, information received, travels along the neurons of a nerve to the effector muscles or gland.
Question 6. How does phototropism occur in plants?
Hint: Sunlight and auxin plays an important role.
Sol. Phototropism is a directional growth movement which occurs in response to unidirectional exposure of light.
When sunlight/light falls from one direction on the shoot, the growth hormone auxin diffuses towards the shady side of the shoot. This increased concentration of auxin stimulates the cells to grow longer on the shaded side of the shoot. This enhanced growth on one side cause bending of shoot towards light.
Question 7. Which signals will get disrupted in case of spinal cord injury? Sol. In case of spinal cord injury the following signals will be disrupted:
(i) Reflex actions will be disturbed because reflex arcs are located in the spinal cord. So, the quick responses needed to guard the body will not take place. The delayed responses may pose harm to the body. For example, delayed response to touching a hot object may cause burn of the body part.
(ii) Impulses from various body parts will not be communicated to brain.
(iii) Messages from brain to body parts will not be communicated.
Question 8. How does chemical coordination occur in plants ?
- Chemical coordination in plants occur through phytohormones.
- These are the chemical compounds which are produced in the cells of the tips of main stem and branches. These hormones are diffused from the originating cells to the neighbouring cells through diffusion. They are responsible for cell elongation, cell multiplication, opening of flowers etc. The important plant hormones are auxins, cytokinins, gibberellins, abscisic acid (ABA) and ethylene.
Question 9. What is the need for a system of control and coordination in an organism?
Sol. There are various organs and organ systems in a complex organism. These organ systems must be carefully controlled and coordinated for healthy survival of the organism. A lack of coordination between these systems can cause lot of troubles for the organism. In the body of an organism various chemicals are secreted from the glands of the endocrine system. These are referred as hormones which are responsible for the overall growth and development of an organism. All other daily decisions that include voluntary and involuntary action are controlled by central nervous system (CNS).
Question 10. How are involuntary actions and reflex actions different from each other?
Sol. Difference between involuntary actions and reflex actions.
Question 11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Sol. Comparison between nervous and hormonal mechanisms.
Question 12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs ?
Sol. Difference between movement in sensitive plants and the movement in legs of human being.
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