Cell Division

It means that all cells develop from pre-existing cells.

Chromosomes are coiled threads of DNA, which forms genes, and protein that become visible in the nucleus at cell division.

A gene is a section of DNA that controls the formation of a protein.

A haploid cell has one set of chromosomes while a diploid has two sets of chromosomes.

A homologous pair is two chromosomes of similar size with the same sequence of genes.

A cell cycle is the changes that occur in a cell between one cell division and the next.

Mitosis is a form of nuclear division in which one nucleus divides to form two nuclei, each containing the same number of chromosomes with identical genes.

• It allows single celled organisms to reproduce 2. In multicellular organisms it allows for growth and repair.

A tumour results when one or more cells lose the ability to control the rate of mitosis.

Cancer occurs when cells lose the ability to control the rate and the number of times mitosis takes place.

Meiosis is a form of nuclear division in which the four daughter nuclei contain half of the chromosome number of the parent nucleus.

A gamete is a haploid cell that are able to fuse with another gamete of the opposite sex.

• It allows for sexual reproduction, involving gametes, while still maintaining the parental chromosome number. • It allows for new combinations of genes to be formed, which will give rise to variations among organisms.

In animal cells, a cleavage furrow forms and deepens to produce two new cells. In plant cells, vesicles gather to form a cell plate, which forms new cell walls.