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Definition: cell ‡ from Cambridge Dictionary of Human Biology and Evolution

Smallest living biological functional and structural unit of an organism that displays the properties of growth, metabolism, energy cycles, and reproduction. Adjective: cellular. See eukaryotes and prokaryotes.

Summary Article: cell
From Philip's Encyclopedia

Basic biological unit of which all plant and animal tissues are composed. The cell is the smallest unit of life that can exist independently, with its own self-regulating chemical system. Most cells consist of a membrane surrounding jelly-like cytoplasm with a central nucleus. The nucleus is the main structure in which DNA is stored in chromosomes. Animal cells vary widely in shape. A red blood cell, for instance, is a biconcave disc, while a nerve cell has a long fibre. The cells of plants and algae are enclosed in a cell wall, which gives them a more rigid shape. prokaryotae cells, as in bacterial, also have a cell wall, but do not have nuclei or chromosomes; instead, they have a loop of DNA floating in the cytoplasm. More advanced cells (those that have nuclei), often have other membrane-bounded structures inside the cell, such as chloroplasts within a plant cell. Cells divide by duplicating the DNA and splitting the nucleus. This takes place by meiosis in sexual reproduction, and by mitosis in asexual reproduction. See also eukaryote; mitochondrion


Animal cells are made up of many different components called organelles. The most prominent is the nucleus (1), which contains all the information of the cell in the form of chromosomes. It is surrounded by the nuclear membrane (2) which contains many pores (3) which allow the nucleus to communicate with the rest of the cell. The centre of the nucleus, the nucleolus (4), generates ribosomes (5), which provide the cell with protein. They are found on the rough endoplasmic reticulum (6), a system of flattened sacs and tubes connected to the nuclear membrane. It brings the messenger RNA molecules, which control the creation of protein, to the ribosomes. The smooth endoplasmic reticulum (7) produces small spheres called vesicles (8) which provide the Golgi apparatus (9) with protein. The Golgi apparatus modifies, sorts and packs large molecules into other vesicles which bud off (10). They are sent to other organelles or secreted from the cell. The fusion of such vesicles with the cell membrane allows particles to be transported out of the cell (exocytosis) (11-13) or brought in (endocytosis) (14-17). Lysosomes (18) break down the molecules entering the cell into enzymes. The mitochondria (19) power the cell, using oxygen and food to generate energy in the form of ATP. ATP is then used in many metabolic processes essential for the cell to function.

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