Observation: After a week when seeds are taken out, it is observed that roots grow in the direction of the porous pot. This shows hydrotropic movement in roots.
Question 2: What is the difference between a reflex action and walking?
Answer: Walking is a voluntary action and is part of routine activities. On the other hand, reflex action is involuntary and happens as a response to a sudden danger to a voluntary organ.
Question 3: What happens at the synapse between two neurons?
Answer: Transmission of nerve impulses between two neurons takes place at through the synapse. The axon terminal of a neuron releases specialized chemicals; called neurotransmitters. These chemicals travel through the synapse and reach the dendrites of the next neuron. The nerve impulses travel along with the neurotransmitters.
Question 4: Which part of the brain maintains posture and equilibrium of the body?
Question 5: How do we detect the smell of an agarbatti (incense stick)?
Answer: The olfactory receptors; present in the nostrils; pick the smell. They send signals to the brain. The brain interprets those signals and we detect the smell of an incense stick.
Question 6: What is the role of the brain in reflex action?
Answer: Brain has no direct involvement in reflex action. Reflex action is mainly controlled at the level of spinal cord.
Question 7: What are plant hormones?
Answer: Plant hormones are special chemicals which regulate the growth of various plant parts.
Question 8: 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 a nastic movement, i.e. it does not depend on the direction of the stimulus. On the other hand, the movement of a shoot towards light is a tropic movement, i.e. it depends on the direction from which light is coming.
Question 9: Give an example of a plant hormone that promotes growth.
Question 10: How do auxins promote the growth of a tendril around a support?
Answer: Auxin increases 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 11: How does chemical coordination take place in animals?
Answer: Chemical coordination in animals takes place through hormones. There are several endocrine glands which secrete various kinds of hormones. These hormones regulate different functions in the body. For example; insulin is a hormone which regulates the blood sugar level.
Question 12: Why is the use of iodised salt advisable?
Answer: Iodine is an important constituent of the hormone thyroxine. Iodine deficiency leads to a disease called goiter. Iodised salt is advised to prevent chances of goiter.
Question 13: How does our body respond when adrenaline is secreted into the blood?
Answer: Adrenaline is also known as ‘fight or flight’ hormone. It prepares the body for emergency situations. Increased secretion of adrenaline in the blood increases the blood supply to limbs and to the facial area. It increases the heart rate and breathing rate so that more oxygen could be supplied to the limbs. Slight precipitation also occurs on the temple and in palms. All of this shows readiness for a fight or; if need be; a flight from the scene.
Question 14: Why are some patients of diabetes treated by giving injections of insulin?
Answer: Insulin plays an important role in sugar metabolism. In some patients of diabetes insulin secretion is reduced. Insulin injection is given to such patients to compensate for reduced insulin secretion. Such cases of diabetes are called Insulin Dependent Diabetes Mellitus (IDDM).
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