2.2Structures and Functions in Living Organisms
Cell structure — Edexcel Modular - OL Revision Notes & Topical Questions
10 min read 13 parts Lesson 2 of 12 1 quiz
Lesson summary
Cell structure Edexcel O Level Modular Biology notes: describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole1 mm = 1000 µm; 1 µm = 1000 nm.Prokaryotes have 70S ribosomes, eukaryotes 80S in cytoplasm.…
- Viruses are acellular
- Cell structure Edexcel O Level Modular Biology: what to do next
- Magnification
- Resolution
- Cell fractionation
- Eyepiece graticule
Part 1 of 6Key ideas
1 mm = 1000 µm; 1 µm = 1000 nm.
Prokaryotes have 70S ribosomes, eukaryotes 80S in cytoplasm.
Viruses are acellular
Viruses are acellular nucleic acid + capsid (± envelope).
Plant cells have a cellulose wall, vacuole with tonoplast, and plasmodesmata.
Part 2 of 6Syllabus points
Syllabus points
describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole
describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole
know the similarities and differences in the structure of plant and animal cells 2.5B explain the importance of cell differentiation in the development of specialised cells 2.6B understand the advantages and disadvantages of using stem cells in medicine
Part 3 of 6Process & sequence
1
Name the cell part shown.
2
State whether it is in plant cells, animal cells or both.
3
Give its structure in one line.
4
Give its function in one line.
5
Link structure to function with "so that".
- Name the part
- Where found
- Structure
- Function
Part 4 of 6Summary
What the symbols mean:
M = I ÷ A.
What the symbols mean: M = magnification (no unit) · I = image size · A = actual size; use the same unit for both (1 mm = 1000 μm)
Resolution of an electron microscope is much higher because electrons have a shorter wavelength.
Mitochondria and chloroplasts contain 70S ribosomes and circular DNA.
Part 5 of 6Keep going
Cell structure Edexcel O Level Modular Biology: what to do next
These Cell structure Edexcel O Level Modular Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Cell structure Edexcel O Level Modular Biology understanding with the practice questions below, then reread any Cell structure Edexcel O Level Modular Biology point you were unsure about before moving on.
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Previous lesson: 2.1 Level of organisation — Notes
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Next lesson: 2.3 Biological molecules — Notes
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Course: Edexcel Modular - OL — all units
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Official syllabus: Pearson Edexcel International GCSEs
Part 6 of 6Compare: Compare
| Organelle | Membrane | Structure | Function | Found in | Seen with |
|---|---|---|---|---|---|
| Nucleus | Double (envelope with pores) | Chromatin, nucleolus | Contains DNA; controls cell; makes rRNA | Eukaryotes | Light microscope |
| Rough ER | Single | Cisternae with 80S ribosomes | Protein synthesis and transport | Eukaryotes | Electron microscope |
| Smooth ER | Single | Cisternae, no ribosomes | Lipid and steroid synthesis | Eukaryotes | Electron microscope |
| Golgi body | Single | Stack of flattened sacs + vesicles | Modifies, packages proteins; makes lysosomes | Eukaryotes | Electron microscope |
| Mitochondrion | Double; inner folded (cristae) | Matrix, 70S ribosomes, circular DNA | Aerobic respiration – ATP | Eukaryotes | EM (just visible LM) |
| Chloroplast | Double + thylakoids | Grana, stroma, starch, 70S ribosomes | Photosynthesis | Plants, algae | Light microscope |
| Ribosome | None | Two subunits; 80S (cytoplasm) or 70S | Translation | All cells | Electron microscope |
| Lysosome | Single | Vesicle of hydrolytic enzymes | Digests old organelles, pathogens | Animal cells | Electron microscope |
| Centriole | None | Microtubules in 9 triplets | Spindle formation | Animal cells | Electron microscope |
Key terms
Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Magnification · Resolution · Eukaryote · Prokaryote · Organelle · Cell fractionation · Eyepiece graticule · Endosymbiosis
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. eukaryotic/prokaryotic, enzyme–substrate complex, active site, complementary).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Marked practiceQuizzes for this lesson
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