Question

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

Answer 1

Hint:In order for a depolarization wave on nerve impulse to pass from cell to cell there are what we call synaptic junctions. This means that the nerve cells are lined up head to tail all the way down and other tracks and they are not connected but they have tiny gaps between them and the next cell. These tiny gaps are called a synapse.

Complete answer:I) The nerve impulse travels in one direction because nerve cells are connected to each other by synapse. The synapse is a neurotransmitter vesicle that allows only one-way flow of nerve impulse due to the presence of neurotransmitters which is found on the one side of the synapse and receptor on the other side of the synapse.
ii) Jamming of wooden doors and window takes place during the rainy season because the cell in the wood absorbs the water (moisture) from the atmosphere by the process of inhibition. Due to which its volume increases and the door swells up.
iii) Root is necessary for the absorption of water. In the absence of the root, there is no sufficient absorption of water. So, cut plants wilt fast even if its end is dipped into the water, due to less absorption of water.
iv) During summer the urine becomes more hypotonic because the Antidiuretic hormone (ADH) secretion from the pituitary gland decreases because during summer season water gets lost from our body at a large amount in the form of sweat than in winter.
v) A person facing difficulties in focusing on nearer objects as the age increases because the abnormalities in the shape of the eyeball affect the focusing part of the eye as the lens becomes more sticker and inelastic with growing age. As a result, it makes it more difficult for the lens to change its shape, and does it cannot manage their accommodation.

Note:Accommodation is a process by which the eye changes its optical power in order to maintain a clear image of focus on an object, as its distance may vary. Accommodation usually acts as a reflex but it can be consciously controlled.