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Cell

The basic unit from which all living organisms are built up, consisting of a cell membrane surrounding cytoplasm and a nucleus.

Natural selection

The process in nature where the fittest individuals survive, reproduce and pass their characteristics on to their offspring.

Cell division

The process by which a parent cell divides into two daughter cells

Cell Cycle

Controlled sequence of events that results in cell division in the body cells.

Asexual reproduction

Reproduction not involving the fusion of gametes.

Organelles

A distinct part of the cell, such as the nucleus, ribosome or mitochondrion, which has structure and function.

Nucleus

The part of a cell that controls the cell function and contains the chromosomes.

Mutations

A change in the arrangement or amount of genetic material in a cell.

Multicellular

Made up of many cells

Mitosis

Division of a cell nucleus which results in each daughter cell having the same number of chromosomes as the parent cell.

Meiosis

The type of cell division, which occurs in the ovaries and testes, to produce cells with a haploid number of chromosomes.

Glossary

A list of often difficult or specialised words with their definitions.

Gametes

The sex cells (ova and sperm) that join together to form a new unique diploid cell in sexual reproduction.

Evolution

A theory, supported by much evidence, which suggests that the animal and plant species inhabiting the earth today are descended from simpler forms by a gradual process of change.

Enzymes

Reusable protein molecules which act as biological catalysts, changing the rate of chemical reactions in the body without being affected themselves

DNA

Deoxyribonucleic acid. This is the molecule which contains the genetic code. It coils up tightly inside chromosomes. DNA is a double helix made from two strands which are joined together by pairs of bases.

Chromosomes

A chromosome is like a packet of coiled up DNA. Humans have 23 pairs of chromosomes. They are in the nucleus of every human cell.

Cancer

A mass of abnormal cells which keep multiplying in an uncontrolled way.

Cell division – key process in growth, repair and reproduction

Inside your body, around 1 billion cells die every hour. In this time a similar number are made. The ability of cells to divide and make new cells is vital for life. In eukaryotic organisms, mitosis results in two daughter cells with identical copies of the parent cell DNA. Meiosis results in daughter cells with half the number of chromosomes of the parent cell. This is the type of cell division needed for sexual reproduction..

Contents

Why is cell division so important?

Whenever multicellular organisms grow, more cells are required. New cells are also needed all the time to replace those that wear out, or become damaged or destroyed. Mitosis is the key process here. The rate of mitosis varies greatly, depending on many factors including the life stage of an organism and the type of cells involved.

Flowers

Enzymes control cell reactions whatever the organism and wherever it is growing

The rate of mitosis is controlled within the cell cycle. This is a sequence of events including the replication of the DNA and the cell organelles prior to cell division, the division of the nucleus and the subsequent division of the cytoplasm with all its contents. If control of the cell cycle is lost, tumours and cancer may result.

All organisms need to reproduce. Many organisms produce identical offspring by asexual reproduction, and for that they need mitosis. Some organisms reproduce sexually, with gametes combining to produce a unique new individual containing genetic information from both parents. The formation of gametes depends on meiosis.

Mutations can arise during mitosis and meiosis. Mutations during mitosis often cause problems for the organism including cancer formation. Mutations during meiosis drive natural selection and evolution, but can also result in genetic diseases.

Cell Cycle

The cell cycle – key to health and disease

Photos by Anthony Short unless credited otherwise. Animations and diagrams by Edward Fullick throughout.

How to use this site

There are a number of interactive features in this e-source:

  • A glossary of terms: any word with a glossary entry is highlighted like this.
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