Structure

Cells can be of variable shape, but their underlying structure is very well conserved. Different cell types represent modifications of basic cell structure by:

• loss or gain of organelles e.g. loss of nucleus in erythrocytes
• modification of basic structural components e.g. contractile filaments in motile tail of spermatozoa

There are two key cellular compartments:

• the nucleus, which sits within
• the cytoplasm or matrix compartment

Both are demarcated by membranes. Subcellular structures bounded by membranes are termed organelles. Protoplasm refers to the combination of nuclear and cytoplasmic compartments.