Cell Division

Question 1

Cell cycle

Answer 1

The cell cycle starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells. It consists of interphase and mitosis and the interphase is subdivided into three separate growth stages:

G1: cell grows and new organelles and proteins are made
Synthesis: cell replicates ready to be divided by mitosis
G2: cell keeps growing and proteins needed for cell division are made
Mitosis: the cycle starts and ends here.

Question 2

Interphase

Answer 2

During interphase cell carries out it’s normal functions but also prepares to divide. The cells DNA is unravelled and replicated to double its genetic content. The organelle are also replicated so it has spare ones and it’s ATP content is increased to proved energy needed for cell division.

Question 3

Mitosis

Answer 3

Mitosis is the cell division that occurs during the cell cycle. A parent cell divides to produce two genetically identical daughter cells. Mitosis is needed for the growth and repairing of damaged tissues.

Question 4

Structures of chromosomes in mitosis

Answer 4

The chromosomes are made up of two strands joined in the middle by a centromere.

The separate strands are chromatids

Two strands on the same chromosome are called sister chromatids.

There are two strands because each chromosome has already made an identical copy of itself during interphase. When mitosis is over the chromatids end up as one strand chromosomes in the new daughter cells.

Question 5

Prophase

Answer 5

The chromosomes condense getting shorter and fatter.

centrioles start moving to the opposite ends of the cell forming a network of protein fibres across it called the spindle.
The nuclear envelope breaks down and the chromosomes lie free in the cytoplasm

Question 6

Metaphase

Answer 6

The chromosomes line up along the middle of the cell and become attached to the spindle by their centromere

Question 7

Anaphase

Answer 7

The centromeres divide separating each pair of sister chromatids. The spindles contract pulling chromatids to opposite poles of the spindle, centromere first. This makes the chromatids appear v- shaped

Question 8

Telophase

Answer 8

The chromatids reach the opposite poles of the spindle they uncoil and become long and thin again. They’re now called chromosomes again. A nuclear envelope forms around each group of chromosomes so they’re now two nuclei. The cytoplasm divides (cytokinesis) and there are now two daughter cells that are genetically identical to the original cell and to each other. Mitosis is finished and starts the interphase part of the cell cycle to get ready for the next round of mitosis.

Question 9

What is cancer?

Answer 9

A tumour that causes Uncontrolled cell division

Question 10

What happens during cancer?

Answer 10

There’s a mutation in a gene that controls cell division so the cell grow out of control. The cells keeps on diving to make more and more cells which form a tumour.

Question 11

Cancer treatments

Answer 11

Some treatments for cancer are designed to control the rate of cell division in tumour cells by disrupting the cell cycle. This kills the tumour cells. Treatments don’t distinguish between tumour cells and healthy cells so they can also kills normal body cells that are dividing. However, tumour cells divide much more frequently than normal cells so the treatment is more likely to kill tumour cells