Question

Give reasons for the following.
(i) The nerve impulse travels in one direction.
(ii) Jamming of wooden doors and windows takes place during rainy season.
(iii) A cut plant wilts fast even if its cut end is dipped in water.
(iv) Urine excreted during summer months is hypertonic.
(v) A person had difficulty in focusing on nearer objects, as the age increases.

Answer 1

(i) Nerve impulse travels in one direction because nerve cells (neurons) connect to each other by synapse. The synapse (neurotransmitter vesicle) acts as a valve and allows the only one-way flow of nerve impulse due to the presence of neurotransmitter which is found on the one side of the synapse and receptors being on the other side.

(ii) Jamming of wooden doors and window takes place during the rainy season because of the dry wood swells due to the imbibition of water (moisture). Due to which its volume increases.

(iii) Root is necessary for the absorption of water. Without roots, there is no sufficient absorption of water. So, cut plants wilt fast even end is dipped in water due to less absorption of water.

(iv) It happens because during summer most of the water is lost from the body during perspiration. While in winter, there is no perspiration and the urine passed out is hypotonic.

(v) A person had difficulties in focusing on near objects, as the age increases because the abnormalities in the shape of the eyeball affect the working of the focusing part of the eye as the lens become more stiff and elastic with growing age, which makes it more difficult for the lens to change shape and thus it cannot manage the extra degree of focus (accommodation) needed for near objects.