Animal and plant cells have features in common
In animals and plants each cell is surrounded by a very thin cell surface membrane. This is also sometimes referred to as the plasma membrane.
Many of the cell contents are colourless and transparent so they need to be stained to be seen. Each cell has a nucleus, which is a relatively large structure that stains intensely and is therefore very conspicuous. The deeply staining material in the nucleus is called chromatin and is a mass of loosely coiled threads. This material collects together to form visible separate chromosomes during nuclear division. It contains DNA (deoxyribonucleic acid), a molecule which contains the instructions that control the activities of the cell. Within the nucleus an even more deeply staining area is visible, the nucleolus, which is made of loops of DNA from several chromosomes. The number of nucleoli is variable, one to five being common in mammals.
The material between the nucleus and the cell surface membrane is known as cytoplasm. Cytoplasm is an aqueous (watery) material, varying from a fluid to a jelly-like consistency. Many small structures can be seen within it. These have been likened to small organs and hence are known as organelles. An organelle can be defined as a functionally and structurally distinct part of a cell. Organelles themselves are often surrounded by membranes so that their activities can be separated from the surrounding cytoplasm. This is described as compartmentalisation. Having separate compartments is essential for a structure as complex as an animal or plant cell to work efficiently. Since each type of organelle has its own function, the cell is said to show division of labour, a sharing of the work between different specialised organelles.
The most numerous organelles seen with the light microscope are usually mitochondria (singular: mitochondrion). Mitochondria are only just visible, but films of living cells, taken with the aid of a light microscope, have shown that they can move about, change shape and divide. They are specialised to carry out aerobic respiration.
The use of special stains containing silver enabled the Golgi apparatus to be detected for the first time in 1898 by Camillo Golgi. The Golgi apparatus is part of a complex internal sorting and distribution system within the cell. It is also sometimes called the Golgi body or
Golgi complex.
Tags
BIOLOGY