Cell Structure and Organisation

General Cell Structure

Cells are the basic building blocks of life, and are derived from pre-existing cells through the process of cell division.
All cells are enclosed by a plasma membrane, which controls the movement of substances in and out of the cell.
The cytoplasm within the membrane is where most cellular activity occurs.

Eukaryotic cells have a membrane-bound nucleus and other specialised organelles, differing from prokaryotic cells, which lack these structures.
The nucleus contains the cell’s DNA and controls cellular activities by regulating gene expression.
The mitochondria are the sites of aerobic respiration in cells, and provide the ATP needed for cellular processes.
Ribosomes are the site of protein synthesis. They can be found in the cytoplasm and on the rough endoplasmic reticulum.

Prokaryotic cells are smaller and simpler in structure than eukaryotic cells. They lack a nucleus and membrane-bound organelles.
The genetic material is found in the nucleoid, a region of the cytoplasm, rather than a membrane-bound nucleus.
Plasmids are small circular pieces of extra-chromosomal DNA in prokaryotic cells, which often carry genes for antibiotic resistance.

In multicellular organisms, cells differentiate to become specialised for certain functions, forming tissues, organs, and organ systems.
Specialised cells may have adaptations to their shape or structure that help them carry out their function.
Example of specialised cells include red blood cells (transport oxygen), neurones (transmit nerve impulses), and epithelial cells (form barriers and line body cavities and organs).

Plant cells contain additional structures not found in most animal cells including a cell wall made of cellulose, which provides support and structure.
Chloroplasts are organelles present in photosynthetic cells in plants and algae, responsible for photosynthesis, converting light energy into chemical energy.
Plant cells also contain permanent vacuoles, containing cell sap, important for cell turgidity and storage of biochemicals.