1.6 cell division

Question 1

what is mitosis?

Answer 1

• the process of dividing a eukaryotic cell into two genetically identical nuclei
• Mitosis is an important process as it occurs when genetically identical nuclei are needed e.g. embryonic development, growth and asexual reproduction.
• Mitosis is a continuous process in which cytologists have divided into four main phases of events: prophase, metaphase, anaphase and telophase

Question 2

what happens in interphase?

Answer 2

• Each chromosome is converted from a single molecule into two DNA molecules called (sister) chromatids
• Prior to mitosis occurring, all the DNA in the nucleus must be replicated during the process of interphase

Question 3

what happens in prophase?

Answer 3

• Chromosomes condense and supercoil, becoming shorter and fatter.
• The nuclear membrane breaks down.
• Spindle fibres grow from the pole towards the equator of the cell.
• Each chromosome consists of two identical chromatids held together by a centromere.
• Nuclear membrane completely breaks down.

Question 4

what happens in metaphase?

Answer 4

• Spindle microtubules continue to grow and the spindle microtubules attach to the centromere of the chromosomes.
• Spindle fibres are put under tension to determine correct attachment.
• Chromosomes line up on the metaphase plate (equator).
• Centromeres divide and the sister chromosomes separate into two chromatids.

Question 5

what happens in anaphase?

Answer 5

• Chromatids are divided at the centromere to separate.
• The shortening of the spindle microtubules pull chromatids rapidly towards the two poles (opposite sides) of the cell.

Question 6

what happens in telophase?

Answer 6

• The chromatids reach the poles, and are called chromosomes.
• The spindle microtubules dissolve.
• The nuclear membrane reforms around the chromosomes at each pole of the cell.
• The chromatids decondense.
• The cell generally starts to divide into the two daughter cells (cytokinesis) by developing a cleavage furrow.
• In plant cells, the cell plate forms between the two cells.

Question 7

how do you work out the mitotic index?

Answer 7

= number of cells in mitosis / total number of cells