Meiosis, mitosis & chromosome questions...?

Question

1. what affect does fertilisation have on the chromosome number of the cell?

2. chromosome copies are made before mitotic cell division so that...?

3. two organs in the human body where cell division occurs by mitosis are...?

4. two reasons for body cells to divide are... ?

Answer 1

1. When fertilization occurs, the chromosomes from the sperm and the chromosomes from the egg go together in one cell. Hence, from the chromosome number of each s*x cell, the chromosome number is doubled to equal the chromosome number of a non-s*x cell (i.e. typical somatic cell, like blood cell, muscle cell, etc)

2. The chromosomes carry the genetic information of the organism. The chromosome copies are made before mitotic cell division, so that this genetic information can be copied into the new cells.

3. Everywhere. The only cells not included in the count are egg cells (produced in the ovaries) and sperm cells (produced in the testicles). And I believe brain cells are also not included here, because at a certain age, brain cells cease to be produced.

4. 1st reason: Growth, especially during the younger years.

2nd reason: Healing and replacement of aged, damaged cells. This can easily be observed during the healing of a wound, or the healing of a broken bone.

Furthermore, cells have a certain life span (from skin cells having a lifespan of a few days, to bone cells having a lifespan of decades), so they have to be continually replaced. As we age, however, this capacity becomes weaker, so it becomes more difficult to replace worn-out cells. This appears in wrinkles and other evidence of degeneration in the body.