IN TEXT QUESTIONS (PAGE 119)
1: What is the difference between a reflex action and walking.
Ans:A reflex action is a rapid, automatic response to a stimulus. It does not involve any thinking. Walking, on the other hand, is a voluntary action. It is under our conscious control.
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 dendrite of the other neuron is known as a synapse. It acts as a one way valve to transmit impulses in one direction only. This one-directional transfer of impulses occurs 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 dendrite of the other neuron.
3: Which part of the brain maintains posture and equilibrium of the body.
Ans: Cerebellum, a part of hind brain is responsible for maintaining posture and the equilibrium of the body.
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 with the information received from other receptors and also with the information already stored in the brain.
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. and the brain has no role to play in the creation of the response.
IN TEXT QUESTION (PAGE 122)
1: What are plant hormones. Explain briefly.
Ans:Plant hormones or phytohormones are naturally-occurring organic substances. These are synthesized in one part of the plant body (in minute quantities) and are translocated to other parts when required. The five major types of phytohormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene. Gibberellins help in the growth of the stem. Auxins help in the growth of the stem. Cytokinins promote cell division. Abscisic acid is one example of a hormone which inhibits growth.
2: How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light
Ans:The movement of leaves of the sensitive plant, Mimosa pudica or “touch me not”, occurs in response to touch. This is done by plant cells by changing the amount of water in leaves. This movement is independent of growth. (The movement of shoot towards light is known as phototropism. This type of movement is directional and is growth dependent).
3: Give an example of a plant hormone that promotes growth.
Ans: Examples of plants growth hormones:
(a) Gibberellins help in the growth of the stem.
(b) Auxins help in the growth of the stem.
(c) Cytokinins promote cell division.
4: How do auxins promote the growth of a tendril around a support.
Ans: These tendrils are sensitive to touch. When they come in contact with any support, auxin (a growth hormone) diffuses from the part of the tendril in contact with the object to other side, which is not in the contact. Therefore the part of the tendril in the contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.
IN TEXT QUESTION (PAGE 125)
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 of the endocrine system hormones regulate the overall growth and development of the animals. The nervous system along with the endocrine system coordinates the physiological processes.
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.
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.
4: Why are some patients of diabetes treated by giving injections of insulin.
Ans: Diabetes is a disease in which the level of sugar in the blood is too high. Insulin, a hormone secreted by the pancreas, helps in regulating the blood sugar levels.