Distinguish between prokaryotic and eukaryotic cells in terms of their internal organisation.

IB DP Biology Standard Level (2023 syllabus) — A2.2 Cell structure · Distinguish · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Prokaryotic cells lack a membrane‑bound nucleus, whereas eukaryotic cells possess a nucleus surrounded by a double‑membrane nuclear envelope.
Prokaryotic cells do not contain membrane‑bound organelles, while eukaryotic cells have organelles such as mitochondria and endoplasmic reticulum.
Prokaryotic DNA is circular and located in a nucleoid that is not membrane‑bound; eukaryotic DNA is linear and confined within the nucleus.
Prokaryotic cells are generally smaller (≈1–10 µm) compared with eukaryotic cells (≈10–100 µm).

Examiner tips

Use the word ‘lack’ for prokaryotes and ‘possess’ for eukaryotes to show contrast.
Include the size comparison to hit the fourth point.
Mention the nucleoid vs. nuclear envelope to cover the DNA point.

Common mistakes

Confusing the size ranges or giving only one figure for both cell types.
Using ‘membrane‑bound’ for prokaryotes or omitting the double‑membrane description of the nucleus.

Mark scheme (4 marks)

Prokaryotic cells lack a membrane-bound nucleus, whereas eukaryotic cells possess a nucleus enclosed by a double membrane (nuclear envelope).
Prokaryotic cells lack membrane-bound organelles, whereas eukaryotic cells contain membrane-bound organelles such as mitochondria and endoplasmic reticulum.
Prokaryotic DNA is circular and located in a region called the nucleoid (not enclosed by a membrane), whereas eukaryotic DNA is linear and contained within the nucleus.
Prokaryotic cells are generally much smaller than eukaryotic cells (prokaryotes typically 1–10 µm; eukaryotes typically 10–100 µm).

Key terms in this question

eukaryotic cell