Human Cells and Cell Structure

Cells are the smallest living units of the human body, and all tissues and organs are built from them. A typical human cell is enclosed by a cell membrane, a thin barrier that controls which substances enter and leave, and it contains a watery interior called the cytoplasm in which specialised structures known as organelles carry out the cell's functions.

The nucleus is the cell's control centre, holding the genetic material and surrounded by a nuclear envelope; within it the nucleolus is involved in making the components of ribosomes. Ribosomes are the sites where proteins are assembled. The endoplasmic reticulum is a network of membranes that helps build and transport proteins and lipids, and the Golgi apparatus packages and modifies these products for use or export. Mitochondria release energy from nutrients through respiration, supplying the cell with usable chemical energy, while lysosomes contain enzymes that break down waste and worn-out parts. Unlike plant cells, human cells have no rigid cell wall, no chloroplasts and no large central vacuole, features that belong to plants.

Human cells specialise into many types suited to particular jobs. Among blood cells, red cells carry oxygen, while white cells defend the body. Lymphocytes are white cells of the immune system: B lymphocytes can mature into plasma cells that produce antibodies, and T lymphocytes coordinate and carry out immune responses. This division of labour, with each cell type built from the same basic toolkit of organelles, allows the body to perform its enormous range of functions.

Frequently asked questions

What is the function of the nucleus?

The nucleus stores the cell's genetic material and directs its activities; it is enclosed by a nuclear envelope and contains the nucleolus, which helps produce ribosome components.

What do mitochondria do?

Mitochondria release energy from nutrients through respiration, providing the cell with the usable chemical energy it needs to function.

How do human cells differ from plant cells?

Human cells lack the rigid cell wall, chloroplasts and large central vacuole found in plant cells, though both share organelles such as the nucleus, mitochondria and ribosomes.