3.24a-c)- Mitosis

a) Understand that division of a diploid cell by Mitosis produces two cells which contain identical sets of chromosomes

The diploid number is the number of chromosomes in the nucleus. This can be abbreviated as 2n. Humans have 46 chromosomes so 2n=46.In the process known as mitosis a cell is divided to two cells - each with a nucleus. If we look at the nucleus we will find that each one will have a diploid nucleus.We often say that these cells are 

identical sometimes described as daughter cells. (same no. of chromosomes, same set of chromosomes)

b) Mitosis is performed through DNA replication, in this each chromosome replicates itself. The two copies are held together by a structure around the center region known as the centromere. They are known as a pair of chromatids. DNA replication takes place in the nucleus while its still intact. The process of DNA replication takes place inside the nucleus while its still inact. This is known as the interphase.

 

 

c) The stages of mitosis

Observing a cell down a microscope, we would normally see a nucleus has a spherical structure and would be unable to observe the chromosomes. It is during the interphase that the process of DNA replication occurs.

When the membrane breaks down and the chromosomes become visible as a pair of chromatids= Prophase.

 

The nucleus is gone, inside the cell, there is a network of protein molecules called spindle. These extend from one pole of a cell to the other. The pair of chromatids will join on one of the spindle fibres at the centromere.

Metaphase is when the pair of chromatids are attached to a spindle fibre by the centromere, characteristic of the metaphase is that the chromatid is in the middle across the equator of the cell.

In the Anaphase the fibre shortens pulling the chromatids apart and they move to the poles of the cell. The pair of chromatids are seperated. 

The last phase is called Telophase, in which the nucleus begins to reform around the chromosomes at either end of the cell. We see the formation of two nuclei at opposite ends of the cell.

Cytokinesis is where the cell splits into two, this is not part of mitosis. Here we see the nucleus that has reformed in the anaphase, the cell is beginning to move inwards, dividing the cytoplasm in half and the 

membrane fuses across the equator to form two cells. Both of these cells contain a chromosome.