in an animal, which, like all eukaryotic cells, has a cell membrane
, and a nucleus
, but in which the surface consists of the cell surface membrane only it does not have a cell wall. The cell surface membrane keeps the cell together by being strong, even though it is very thin and flexible. The membrane also controls what enters and leaves the cell. For example, nutrients need to be able to enter and waste materials to leave. The cell contains cytoplasm, in which is located a nucleus. This controls the activities of the cell.
An animal is made up of many thousands of cells, which are used as building blocks. However, as with a house, different types of building blocks are used in different places. Groups of similar cells form a tissue
. An example of this is the tissue forming the brain. One of the specialized cells found in this tissue is the neurone or nerve cell. The brain is an organ
made up of a number of different tissues.
The blood is a tissue consisting mainly of another type of specialized cell the red blood cell. Other specialized cells include the epithelium
and sperm cell.
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