Cell biology — GCSE Biology Revision
Everything you need to revise cell biology for GCSE Biology: clear notes, the key facts and terms to learn, the mistakes that cost students marks, and practice questions with answers.
Revision notes
Eukaryotes and prokaryotes
Animal and plant cells are eukaryotic: their genetic material is enclosed in a nucleus. Bacterial cells are prokaryotic: they are much smaller, have no nucleus, and their DNA is a single loop, sometimes with extra small rings called plasmids.
Inside a cell
Most animal cells have a nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes. Plant cells also often have chloroplasts, a permanent vacuole filled with cell sap, and a cell wall made of cellulose that strengthens the cell.
Moving substances
Diffusion is the net movement of particles from an area of higher concentration to lower concentration. Osmosis is the diffusion of water through a partially permeable membrane. Active transport moves substances against a concentration gradient and needs energy from respiration.
Key facts
- Mitochondria are the site of aerobic respiration.|Ribosomes are where proteins are made.|Chloroplasts absorb light for photosynthesis.|Bacteria have a cell wall but it is not made of cellulose.|Mitosis produces two genetically identical cells.
Key terms
- Diffusion::Net movement of particles from higher to lower concentration.|Osmosis::Diffusion of water across a partially permeable membrane.|Active transport::Movement against a concentration gradient using energy from respiration.|Stem cell::An undifferentiated cell that can become many types of cell.
Common mistakes
- Saying cells "make" energy — respiration releases energy.|Forgetting that osmosis only applies to water.|Calling the cell wall a membrane.
Exam tips
- Magnification questions: use magnification = image size ÷ real size and convert units first.|For "compare" questions, give a similarity AND a difference.|Always state the direction of movement in diffusion answers.
Quick quiz
1. Which structure is the site of aerobic respiration?
- Nucleus
- Mitochondria
- Ribosome
- Cell membrane
Show answer
Mitochondria — Mitochondria contain the enzymes for aerobic respiration.
2. Which structure is found in plant cells but NOT animal cells?
- Ribosome
- Cytoplasm
- Cellulose cell wall
- Cell membrane
Show answer
Cellulose cell wall — Animal cells have no cell wall.
3. What is osmosis?
- Movement of any particle down a gradient
- Diffusion of water across a partially permeable membrane
- Movement using energy from respiration
- Movement of glucose into cells
Show answer
Diffusion of water across a partially permeable membrane — Osmosis is specifically about water.
4. Where is the genetic material in a bacterial cell?
- In a nucleus
- In mitochondria
- Free in the cytoplasm as a single loop
- In chloroplasts
Show answer
Free in the cytoplasm as a single loop — Prokaryotes have no nucleus.
5. Active transport requires:
- Light
- Energy from respiration
- A cell wall
- A concentration gradient going downhill
Show answer
Energy from respiration — It moves substances against the gradient.
Exam-style questions
Describe two differences between a bacterial cell and an animal cell. [2 marks]
Show mark scheme
- 1 mark for each correct difference, up to 2:
- No nucleus / DNA free in cytoplasm
- Has a cell wall
- Has plasmids
- Much smaller
A student views a cell. The image is 12 mm long and the magnification is ×400. Calculate the real length of the cell in micrometres (µm). [3 marks]
Show mark scheme
- Real size = image ÷ magnification (1)
- 12 ÷ 400 = 0.03 mm (1)
- 0.03 mm = 30 µm (1)
Explain why root hair cells need to use active transport to absorb mineral ions from the soil. [3 marks]
Show mark scheme
- Concentration of ions in soil is lower than in the cell (1)
- So ions move against the concentration gradient (1)
- Requires energy from respiration (1)
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