Almost all animals and plants are made up of cells.
Animal cells have a basic structure. Below the basic structure is shown in the same animal cell, on the left viewed with the light microscope, and on the right with the transmission electron microscope.
|Cytoplasm||A jelly-like material that contains dissolved nutrients and salts and structures called organelles. It is where many of the chemical reactions happen.|
|Nucleus||Contains genetic material including DNA, which controls the cell's activities.|
|Cell membrane||Its structure is permeable to some substances but not to others. It therefore controls the movement of substances in and out of the cell.|
|Mitochondria||Organelles that contain the enzymes for respiration, and where most energy is released in respiration.|
|Ribosomes||A tiny structure where protein synthesis occurs.|
Most cells are specialised and are adapted for their function. Animals and plants therefore consist of many different types of cell working together. Most human cells are like most other animal cells.
There are many different types of cells in animals. Each type is specialised for a particular role. These ensure that the organism functions as a whole.
The head of the sperm contains the genetic material for fertilisation.
The acrosome in the head contains enzymes so that the sperm can penetrate an egg.
The middle piece is packed with mitochondria to release energy needed to swim and fertilise the egg.
The tail enables the sperm to swim.
The nerve cell is extended, so that nerves can run to and from different parts of the body to the central nervous system.
The cell has extensions and branches, so that it can communicate with other nerve cells, muscles and glands.
The nerve cell is covered with a fatty sheath, which insulates the nerve cell and speeds up the nerve impulse.
Muscle cells contain filaments of protein that slide over each other to cause muscle contraction. The arrangement of these filaments causes the banded appearance of heart muscle and skeletal muscle.
They contain many well-developed mitochondria to provide the energy for muscle contraction.
In skeletal muscle, the cells merge and the muscle fibres contract in unison.
Animal cells can be observed in a laboratory, using a light microscope.