Science – Control and Coordination
Long Answer Type Questions
Q.1) What is a synapse? What happens at the synapse between two neurons?
Ans) The synpase is the tiny gap between two adjacent neurons. The information acquired (like touching a hot object) at the end of a dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body and then along the axon to its end. At the end of axon, the electrical impulse sets off the release of some chemicals.
These chemicals cross the gap, or synapse and start an similar electrical impulse in a dendrite of the next neuron. This is the process how nervous impulses travel in the body. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscle cells or gland.
Q.2) 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) All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs such as the inner ear, the nose, the tongue and so on. So, gustatory receptors will detect taste, while olfactory receptors will detect smell. We detect that we are touching a hot object by the action of receptors present on various organs or tissues. If olfactory receptors do not work properly then we are not able to smell things like incense sticks, perfumes, aroma of food, etc.
Q.3) Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Ans) Comparison between nervous and hormonal mechanism-
| Nervous System | Hormonal System |
|---|---|
| It comprises of neurons (nerve cells). | It is made of secretary cells (glands). |
| In it, messages are transmitted in the form of electrical impulse. | In it, messages are transmitted in the form of chemicals called hormones. |
| Messages are transmitted along nerve fibre. | Messages are transmitted along blood stream. |
| Effect of message usually lasts for a very short while. | Effect of message lasts for a long time. |
| Messages travel quickly. | Messages travel slowly. |
Q.4) How does phototropism occur in plants?
Ans) Phototropism is the movement of plant parts in response to light. The shoot is positively phototropic as it moves towards light, whereas the root is negatively phototropic as it moves away from light.
Plants exhibit phototropism due to the action of auxins, synthesised at the shoot tip. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. The concentration of auxin initiates cell division and elongation in the shaded side and not in the side of the shoot exposed to light. This causes unequal growth on both sides of the shoot, with the shaded portion growing more than the side exposed to the sun. This causes the shoot to bend towards the light.