CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 17(a)

(a) Iodine is necessary for the thyroid gland to make the hormone thyroxin, which regulates carbohydrate, protein and fat metabolism in the body for balanced growth. Iodised salt supplies this iodine through the diet, so its use is advisable. Disease: goitre. Symptom: a swollen neck (enlarged thyroid gland). (b) Information received at the tip of a dendrite of a nerve cell sets off a chemical reaction that creates an electrical impulse. The impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap (synapse) between the two neurons and start a similar electrical impulse in a dendrite of the next neuron. In this way the impulse travels from neuron to neuron, and finally to muscle cells or glands. Path: dendrite → cell body → axon → nerve ending → chemicals across the synapse → dendrite of the next neuron.