Question

Mention whether the following statements are True or False. Give reason in support of your answer. [5 MARKS]
(a) As you grow from childhood to adulthood, your skin cells divide only to replace such cells that are lost from the surface.
(b) The unfertilized human egg has half the number of chromosomes of the body cells.
(c) Nuclear membrane in a mitotically dividing cell remains intact up to the metaphase and disappears only in telophase.
(d) Mitotic cell division can be a mode of reproduction.
(e) Crossing-over between chromatids can occur only between homologous chromosomes.

Answer 1

Each Part: 1 Mark

(a) True. When we are adults, our cell population stays constant. The number of new cells produced equals the number of dying cells.
(b) True. Out of 23 pairs of chromosomes in humans, only single chromosome from each pair is passed on to the sex cells.
(c) False. Nuclear membrane remains intact up to early prophase but disappears in late prophase. It reappears in telophase.
(d) True. Mitotic cell division is an equational division in which the two daughter cells produced are identical to each other and even to their parent cell. Amoeba or bacteria just divide to produce two similar independent cells by mitotic cell division. However, in humans, only special cells in the reproductive organs undergo a special cell division called meiosis.
(e) True. During pairing, some chromatids of homologous chromosomes break and rejoin at points of intersection. It causes crossing-over.