Edexcel Biology Gcse - Cell Division Part 2

A cell found in foetuses, embryos and some adult tissues that can give rise to a wide range of other cells.

Stem cells are cells that have not undergone differentiation. A cell which has not yet become specialised is called undifferentiated.

Made or put together

Using cloning technology for medicinal purposes. One example is to use a person's DNA to clone one of their organs for use in transplanting

The lump of cells formed as a result of uncontrolled cell division

A high energy part of the electromagnetic spectrum associated with sunburn and skin cancer

A space within the cytoplasm of plant cells that contains cell sap

A fertilised egg cell

For most of the time, DNA exists in the nucleus as thin strands.

When the cells containing nuclei are ready to divide, the DNA copies itself then coils and condenses to form chromosomes.

Each chromosome is made from a single molecule of DNA. Each section of this single molecule of DNA contains a code for the production of a particular protein called a gene.

Each human body cell contains 46 chromosomes. These can be arranged into 23 pairs. Each chromosome in a pair carries the same types of genes.

The 23rd pair is the sex chromosomes. In females, the two chromosomes are identical in shape. These are X chromosomes. Females are referred to as XX. In males, one of the chromosomes is different in shape. This is a Y chromosome. Males are referred to as XY.

Cells divide when:

an organism grows

an organism becomes damaged and needs to produce new cells for repair

organisms like bacteria reproduce asexually

The first stages of the cell cycle involve cell growth, then synthesis of DNA. The single strand of DNA that makes up each chromosome produces an exact copy of itself. After this a period of further growth occurs and the DNA is checked for errors. Mitosis occurs after this checking has been completed. Finally the cytoplasm of the cell separates and two cells are formed.

mitotsis is part of the cell cycle

The cell undergoes a type of cell division called mitosis. In mitosis, two cells called daughter cells are produced, each identical to the parent cell.

It is essential that any new cells produced contain genetic information that is identical to the parent cell.

length of time in phase = ((observed number of cells at that stage) ÷ (total number of cells observed)) x total length of time of cell cycle

Cells grow then divide by mitosis only when we need new ones. This is when we're growing or need to replace old or damaged cells.

malignant cells develop

| - malignant cells divide and invade the surrounding tissues

the existing tumour secretes chemicals

The chemicals stimulate the blood vessels to grow. They grow around the tumour

Cancer cells detach from the tumour and are transported into the blood.

A malignant cell squeezes through a blood capillary wall

The cell divides; a secondary tumour starts to grow

Carcinogens cause cancer by damaging DNA. Carcinogens cause mutations to occur. A single mutation will not cause cancer. Several are required for this to occur. For this reason, we are more likely to develop cancer as we get older.

Something that increases the likelihood of developing a disease is called a risk factor. There are several risk factors for various types of cancers including:

viruses linked with cancer, such as the human papilloma virus (HPV), being spread from person to person through sexual intercourse

the chemical carcinogens in cigarette smoke increasing the risk of lung cancer

alcohol intake is linked with certain cancers

exposure to ultraviolet radiation, part of which is ionising, during sunbathing or outdoor activities, leading to the development of skin cancers

diet, including fat and salt intake, increases the risk of cancer

exposure to ionising radiation increases the risk factor

| - exposure to chemical carcinogens

Animals and plants produced by sexual reproduction begin life as a single cell, a fertilised egg or zygote. These cells must divide by mitosis to produce a multicellular organism.

Mitosis happens throughout the bodies of animals but only occurs in specific regions of plants. These are called meristems and are found in the tips of roots and shoots. Here new cells are formed.