Application Based Questions
Give reasons for the following statements.
1.Cells of a living organism are comparable to bricks of a building.
2. Nerve cells or neurons are long and branched in appearance.
3. Fertilised egg is considered as a single cell.
Answers
1. Both, bricks in a building and cells in the living organisms, are basic structural units [Fig. 8.2(a), (b)]. The buildings, though built of similar bricks, have different designs, shapes and sizes. Similarly, in the living world, organisms differ from one another but all are made up of cells. Cells in the living organisms are complex living structures unlike non-living bricks.
2. Nerve cells are usually very long and branched so that it helps in transmission of signals or electrical impulses over all parts of the body. They divide and re-divide and so cover a large surface area of the body and every portion receives the signals from the central nervous system.
3. The egg of reptiles and aves is already fertilised one in the female but develops into an offspring outside the body. Whereas in mammals the fertilized egg develops into an offspring inside the womb (uterus). Thus, zygote is a multiple cell and not the egg.