1. What is the difference between a reflex action and walking?
Reflex action is involuntary, uncontrolled and unconscious actions in response to a stimulus.
Walking is voluntary, controlled and conscious action.
2. What happens at the synapse between two neurons?
At synapse, a neurotransmitter is produced at the end of axon of one nerve cell that reaches to the other nerve cell through the dendrite. Thus, information is transmitted from one neuron to another neuron.
3. Which part of the brain maintains posture and equilibrium of the body?
4. How do we detect the smell of an agarbatti (incense stick)?
The smell of agarbatti diffused in the air is detected by olfactory receptors in the nose. It produces an impulse which is sent to olfactory lobe by sensory nerves located in the forebrain. It responds to the information.
5. What is the role of the brain in reflex action?
There is no direct role for brain in reflex action. These are controlled by the spinal cord and the action takes place immediately before the information is sent to the brain.
1. What are plant hormones?
Plant hormones are the chemical substances which influence growth, flowering, development of plants etc.
E.g., auxins, gibberellins, cytokinins, abscisic acid and ethylene.
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: It is a nastic movement and the stimulus is touch. It is caused by the sudden loss of water from the swellings at the base of leaves. It is not a growth movement.
Movement of a shoot towards light: It is a tropic movement and the stimulus is light. It is caused by the unequal growth on the two sides of the shoot. It is a growth movement.
3. Give an example of a plant hormone that promotes growth.
4. How do auxins promote the growth of a tendril around a support?
Auxin is present at the tip of tendrils. When the tip of a tendril touches a support, the auxins move to the side of tip away from the support. So, that side of tendril grows faster and becomes longer than the side which is in contact with the support and makes the tendril bend around the support.
5. Design an experiment to demonstrate hydrotropism.
Take two beakers A and B.
In beaker A, add moist soil and sow the seeds.
In beaker B, add dry soil in one part and moist soil in another part and sow the seeds. Also, place an earthen pot filled with water near to it.
It was found that in beaker A, plants grows normally and roots will be straight.
In beaker B, plant grows towards the water.
This experiment shows that the plants grow towards the source of water (hydrotropism).
1. How does chemical coordination take place in animals?
In animals, chemical coordination takes place through the hormones secreted by various endocrine glands.
Endocrine glands secrete hormones into the blood that reach to the specific cells. The receptors on the cell surface detect the hormone. This causes biochemical changes and thereby physiological changes.
2. Why is the use of iodised salt advisable?
Thyroid gland needs iodine to produce thyroxin hormone. Thyroxin controls the metabolism of carbohydrates, fats and protein. Deficiency of thyroxin causes a disease called goitre.
3. How does our body respond when adrenaline is secreted into the blood?
· The heart beat increases to supply more oxygen to muscles.
· Blood pressure and sugar level increase.
· The breathing rate increases.
· Dilation of pupil.
· All these responses enable us to face situations of fear and anger.
4. Why are some patients of diabetes treated by giving injections of insulin?
Insulin regulates blood sugar (glucose) level. If this is not secreted in proper amount, the blood sugar level rises. This causes diabetes mellitus. To treat this, the diabetic patients are given injections of insulin.