Mitosis

Question 1

What is the purpose of mitosis?

Answer 1

A type of cell division for growth and the repair of damaged tissue

Question 2

Where does mitosis occur?

Answer 2

In all body/somatic cells except those in sexual organs that undergo meiosis

Question 3

Describe the key stages of mitosis

Answer 3

1. Chromosomes replicate by DNA replication
2. The chromosomes shorten, thicken and become visible as chromatids
3. The chromatids line up along the cell equator
4. The two sister chromatids are separated by spindle fibres
5. The cell membrane pinches in and separates the single cell into two identical cells

Question 4

Why is it important that the cells are replicated correctly and are identical?

Answer 4

So that each cell has all the genetic information in order for it to carry out its intended function

Question 5

Before a cell can divide by mitosis, the DNA must replicate. Describe the steps of DNA replication.

Answer 5

1. Enzymes unwind the DNA double helix and unzip the two strands by breaking the hydrogen bases between the bases
2. A leading strand made up of single free nucleotides is constructed by an enzyme and it is complimentary (A-T, C-G) to one of the original DNA strands.
3. A lagging strand made up of okazaki fragments (1000-2000 bases long) is constructed by and enzyme and it is complimentary to the other original DNA strand
4. Two new DNA molecules are formed and they wind back into double helixes

Question 6

Why does DNA replication follow the base pairing rule?

Answer 6

By always following A-T and C-G, the two new DNA molecules will be exactly the same which means each of the two new cells will have the same genetic information so they can carry out their function

Question 7

DNA replication is describe as semi-conservative. What does this mean?

Answer 7

In each of the new DNA molecules, one strand is an original and one is newly made

Question 8

Why is DNA replication semi-conservative?

Answer 8

Each of the original strands acts as a template form making a new strand. By also following the base pairing rule, the two new DNA molecules will be identical and contain all the genetic information needed to carry out their function.

Question 9

How do cells know when to divide by mitosis?

Answer 9

When the cell gets bigger, its surface area to volume ration decreases. This makes is less efficient at supplying all parts of the cells gases and nutrients. Therefore it divides in two creating two new cells that are smaller. These smaller cells have a large surface area to volume ratio.

Question 10

At what stages in life is mitosis faster and why?

Answer 10

When organisms are young so they can grow bigger more quickly
For plants, in spring and summer because temperatures are warmer which makes the enzymes that control mitosis work at a faster rate
Mitosis requires energy so it there is large amounts of ATP provided by respiration

Question 11

At what locations is mitosis faster and why?

Answer 11

In cells that are likely to be damaged when carrying out their function and need to be replaced e.g. skin cells, liver cells, cheek cells
At the growing tips of shoots and roots to grow higher for more sunlight
Cancer cells - have lost the ability to stop dividing by mitosis