Comparing cell types by their organelles

The big idea: Not every cell carries the same set of organelles (its internal structures).

We sort cells into types — prokaryotic or eukaryotic, and within eukaryotes animal, plant or fungal — by asking which organelles each one has and which it lacks.

A few structures are found in every cell. The rest are the distinguishing features that tell the cell types apart.

Organelle

A structure inside a cell that has a particular job (for example a nucleus, a mitochondrion or a chloroplast).

Prokaryotic cell

A cell with NO nucleus and NO membrane-bound organelles; its DNA is free in the cytoplasm (for example a bacterium).

Eukaryotic cell

A cell that keeps its DNA inside a nucleus and contains membrane-bound organelles (for example an animal, plant or fungal cell).

Membrane-bound organelle

An organelle wrapped in its own membrane, such as the nucleus, mitochondria or chloroplasts. Only eukaryotes have these.

Found in every cell: Four structures are present in all cells — prokaryotic and eukaryotic alike:

DNA, cytoplasm, a plasma membrane and ribosomes.

Because every cell has them, these four can never be the answer to 'name something that tells two cell types apart'.

The first split is prokaryotic vs eukaryotic, and it comes down to one structure: the nucleus.

A prokaryote has no nucleus and no membrane-bound organelles — its DNA floats free in the cytoplasm. A eukaryote keeps its DNA inside a nucleus and is packed with membrane-bound organelles such as mitochondria.

Then: animal vs plant (both eukaryotic): Animal and plant cells are both eukaryotic, so both have a nucleus, mitochondria, ribosomes and a plasma membrane.

Plant cells add three structures that animal cells do not have:

a cellulose cell wall, chloroplasts (for photosynthesis) and a large central vacuole.

So 'name an organelle in plant cells but not animal cells' is answered by chloroplast, large central vacuole or cellulose cell wall.

Watch the wording: cell wall is not unique to plants: Plants, fungi and many prokaryotes all have a cell wall — but the material differs: cellulose in plants, chitin in fungi, peptidoglycan in most bacteria.

So 'has a cell wall' does not prove a cell is a plant. Chloroplasts and a large central vacuole are the safer plant-only answers, because animals and fungi have neither.

A memory hook: Prokaryote = Plain (no nucleus, no membrane-bound organelles).

Plant = the extra three: wall, chloroplast, vacuole — the photosynthesis-and-support kit that animals skip.

How this is tested: A 1-mark State question often asks for one organelle found in plant cells but not animal cells — answer with chloroplast, large central vacuole or cellulose cell wall (one is enough).

A partner 1-mark State asks for one structure common to both prokaryotic and eukaryotic cells — answer ribosomes, plasma membrane, DNA or cytoplasm.

On Paper 2 a Distinguish or Compare question wants the differences set out side by side (prokaryote vs eukaryote, or animal vs plant).

✓ Why this scores full marks: Each point is a paired contrast — it says what the prokaryote does and what the eukaryote does.

A 'distinguish' answer that only describes one cell type ('eukaryotes have a nucleus') does not score — you must spell out the difference.