Compare the structure and organisation of prokaryotic and eukaryotic cells

What this dot point is asking

You need to compare the two fundamental cell types, identifying the key structural differences and the features they share.

Two types of cell

All cells fall into one of two categories based on whether they have a true nucleus:

• Prokaryotic cells have no membrane-bound nucleus. Bacteria and archaea are prokaryotes.
• Eukaryotic cells have a membrane-bound nucleus. Animals, plants, fungi and protists are eukaryotes.

Features they share

Despite their differences, all cells share certain features, supporting the idea of common ancestry:

• a cell (plasma) membrane controlling what enters and leaves
• cytoplasm, the fluid where reactions occur
• DNA as genetic material
• ribosomes for protein synthesis

Prokaryotic cells

Prokaryotic cells are typically very small (about 1 to 10 micrometres). Their key features:

• No nucleus - the DNA is a single circular chromosome free in the cytoplasm, in a region called the nucleoid.
• No membrane-bound organelles - no mitochondria, no endoplasmic reticulum.
• A cell wall (made of peptidoglycan in bacteria) outside the membrane.
• Smaller (70S) ribosomes.
• Often extra small rings of DNA called plasmids, which can be exchanged between cells.

Eukaryotic cells

Eukaryotic cells are larger (about 10 to 100 micrometres) and far more compartmentalised:

• A true nucleus enclosed by a nuclear membrane, containing linear chromosomes.
• Membrane-bound organelles including mitochondria, endoplasmic reticulum, Golgi apparatus and (in plants) chloroplasts and a large vacuole.
• Larger (80S) ribosomes.
• Plant and fungal cells have a cell wall (cellulose in plants), but animal cells do not.

Why the comparison matters

The compartmentalisation of eukaryotic cells underpins the rest of this topic: organelles, membrane transport, respiration and photosynthesis all depend on the membrane-bound structures that prokaryotes lack.