Common Features of Eukaryotic and Prokaryotic organisms

Living organisms are first split by whether their cells have a nucleus:

• Eukaryotes — cells contain a true nucleus (DNA enclosed in a membrane) and other membrane-bound organelles (e.g. mitochondria). The four eukaryote groups are plants, animals, fungi and protoctists.
• Prokaryotes — cells have no nucleus; the DNA is a single circular chromosome loose in the cytoplasm, plus small rings called plasmids. Bacteria are prokaryotes.

Feature	Eukaryote	Prokaryote (bacterium)
Nucleus	Yes (true nucleus)	No — circular DNA in cytoplasm
Plasmids	No	Yes
Membrane-bound organelles	Yes (e.g. mitochondria)	No
Size	Larger	Smaller
Examples	plants, animals, fungi, protoctists	Lactobacillus, Pneumococcus

Exam tip. The single most reliable way to identify a prokaryote is "no nucleus". Do not say "no cell wall" — bacteria do have a wall.

Plants (e.g. a cereal such as maize; a legume such as peas or beans)

• Multicellular.
• Cells contain chloroplasts → carry out photosynthesis to make their own food (autotrophic).
• Cell walls made of cellulose.
• Store carbohydrate as starch or sucrose.

Animals (e.g. mammals such as humans; insects such as the housefly and mosquito)

• Multicellular.
• No chloroplasts — cannot photosynthesise; take in ready-made food (heterotrophic).
• No cell walls.
• Usually have nervous coordination and can move their whole body.
• Store carbohydrate as glycogen.

Exam tip. Markers reject vague answers. "Plants have cell walls" earns little — write "plant cells have cellulose cell walls", because fungi and bacteria have walls too.

Fungi (e.g. Mucor, with the typical thread-like structure; yeast, which is single-celled)

• Cannot photosynthesise.
• Body is usually a mycelium made of thread-like hyphae that contain many nuclei (yeast is the single-celled exception).
• Cell walls made of chitin.
• Feed by saprotrophic nutrition — release digestive enzymes onto food outside the body, then absorb the soluble products.
• Store carbohydrate as glycogen.

Protoctists (e.g. Amoeba — animal-like, in pond water; Chlorella — plant-like, has chloroplasts; Plasmodium — a pathogen causing malaria)

• Microscopic and usually single-celled eukaryotes.
• A "mixed bag": some are more like tiny animals, others more like tiny plants, and some are pathogens.

Bacteria are the prokaryotes you must know:

• Microscopic and single-celled.
• Have a cell wall, cell membrane, cytoplasm and plasmids.
• No nucleus — the DNA is a single circular chromosome in the cytoplasm.
• Nutrition varies: a few photosynthesise, but most feed off other living or dead organisms.

Named examples from the spec:

• Lactobacillus bulgaricus — a rod-shaped bacterium used to make yoghurt from milk (useful, not a pathogen).
• Pneumococcus — a spherical bacterium that is a pathogen causing pneumonia.

Watch out. "Bacteria have no cell wall" is wrong — they do have a wall, just not cellulose. The defining prokaryote feature is no nucleus.

Paper 1 (4WSD0/1B) often gives a description or drawing and asks which group an organism belongs to. Work down a key:

1. Is there a nucleus? No → prokaryote (bacterium). Yes → eukaryote, continue.
2. Are there chloroplasts? Yes, with a cellulose wall → plant (multicellular) or plant-like protoctist (single-celled, e.g. Chlorella). No → continue.
3. Cell-wall material? Chitin → fungus. None → animal (multicellular) or animal-like protoctist (single-celled, e.g. Amoeba).

Examiner reports praise candidates who show this as a short numbered key rather than just listing features.