At GCSE
At GCSE you identify organelles in animal, plant and bacterial cells, and use the magnification formula. The differences between eukaryotic and prokaryotic cells and the use of light microscopes appear regularly.
GCSEA-LevelAQAEdexcelOCR
Cell Structure revision — GCSE & A-Level Biology
Cell structure is the foundation of every Biology specification. You need to identify organelles, link structure to function, and compare prokaryotic and eukaryotic cells. Microscopy questions about resolution and magnification appear in almost every series.
At A-Level you also study specialised cells, ultrastructure under the electron microscope, and the endosymbiotic origin of mitochondria and chloroplasts. AQA, Edexcel and OCR all reward precise organelle vocabulary.
At A-Level
At A-Level you study ultrastructure with electron microscopes, distinguish 70S from 80S ribosomes, and link organelle structure to function (e.g. cristae and oxidative phosphorylation, rER and protein secretion). Expect questions on resolution vs magnification and the endosymbiotic theory.
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Example flashcards
Q: Give three features unique to prokaryotic cells.
A: Circular DNA (no nucleus), 70S ribosomes, plasmids and a peptidoglycan cell wall.
Q: What is the function of the rough endoplasmic reticulum?
A: It synthesises and transports proteins made on its attached ribosomes.
Q: How do you calculate magnification?
A: Magnification = image size ÷ actual size. Always convert to the same units first.
Q: Why are cristae important in mitochondria?
A: They increase surface area for the electron transport chain and ATP synthase, increasing the rate of oxidative phosphorylation.
Quick summary
Cell Structure is a high-yield Biology topic for GCSE and A-Level students (AQA, Edexcel, OCR). At A-Level you study ultrastructure with electron microscopes, distinguish 70S from 80S ribosomes, and link organelle structure to function (e.g. Examiners reward precise definitions and applied explanations — focus on the core ideas and the small set of terms that come up every series.
Key terms
- Nucleus
- Mitochondrion
- Ribosome
- Endoplasmic reticulum
- Golgi apparatus
- Chloroplast
- Plasmid
- Magnification
- Resolution
Cell Structure FAQs
Why do mitochondria and chloroplasts have their own DNA?+
The endosymbiotic theory suggests they originated as free-living prokaryotes engulfed by an ancestral cell. Their 70S ribosomes and circular DNA support this.
What is the difference between magnification and resolution?+
Magnification is how many times bigger the image is than the object. Resolution is the smallest distance between two points that can still be distinguished.
Why are electron microscopes better for ultrastructure?+
Electrons have much shorter wavelengths than visible light, giving far higher resolution (down to ~0.1 nm), revealing organelles like ribosomes.
Are viruses cells?+
No — viruses lack cytoplasm, ribosomes and a cell membrane. They are non-cellular and only replicate inside host cells.
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