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Question : 17
Total: 27
(a) Why is the use of iodized salt advisable? Name the disease caused due to deficiency of iodine in our diet and state its one symptom.
(b) How do nerve impulses travel in the body? Explain.
OR
What is hydrotropism ? Design an experiment to demonstrate this phenomenon.
(b) How do nerve impulses travel in the body? Explain.
OR
What is hydrotropism ? Design an experiment to demonstrate this phenomenon.
Solution:
(a) Iodised salt is advisable because iodine is necessary for the formation of thyroxine hormone by thyroid gland. Goitre is the disease caused due to its deficiency.Symptom: The neck of the person appears to be swollen due to the enlargement of thyroid gland.(b) Two neurons are not joined to one another completely. There is a small gap between a pair of neuron. This gap is called synapse. The nerve impulse are carried out to this gap by the help of neuro transmitter (chemical substance). The conduction of nerve impulse through the synapse takes place in the form of electrical nerve impulse. When a stimulus acts on the receptor, an electrical impulse is produced with the help of chemical reaction. This electrical impulse passes through the synapse and then to the other neuron. Thus, in this way nerve impulses travel in the body.
OR
The movement of root of plants towards water is called hydrotropism.
Take two glass troughs A and B fill each one of them two-thirds with soil. In trough A plant a tiny seedling figure (a). In trough B plant a similar seedling and also place a small 'clay pot' inside the soil figure (b). Water the soil in trough A daily and uniformly. Do not water the soil in trough B but put some water in the clay pot buried in the soil. Leave both the troughs for a few days.
In trough A, the root of seedling gets water from both sides (because the soil is watered uniformly) in trough B, the roots gets water oozing out from the clay pot which is kept on the right side. So, the root of seedling in trough B grows and bends towards the source of water to the right side. The experiment shows that the root of a plant grows towards water. In other words, the root of a plant is positively hydrotropic.
OR
The movement of root of plants towards water is called hydrotropism.
Take two glass troughs A and B fill each one of them two-thirds with soil. In trough A plant a tiny seedling figure (a). In trough B plant a similar seedling and also place a small 'clay pot' inside the soil figure (b). Water the soil in trough A daily and uniformly. Do not water the soil in trough B but put some water in the clay pot buried in the soil. Leave both the troughs for a few days.
Now, dig up the seedlings carefully from both the trough without damaging their roots. We will find that the root of seedling in trough A is straight. On the other hand, the root of seedling in trough B is found to be bent to the right side (towards the clay pot containing water) figure (b)This can be explained as follows.
In trough A, the root of seedling gets water from both sides (because the soil is watered uniformly) in trough B, the roots gets water oozing out from the clay pot which is kept on the right side. So, the root of seedling in trough B grows and bends towards the source of water to the right side. The experiment shows that the root of a plant grows towards water. In other words, the root of a plant is positively hydrotropic.
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