AQA GCSE Biology: Cell Biology — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Cell Biology revision notes

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Section A

1. Give three differences between a bacterial cell and an animal cell. [3]

2. State the three ways substances move into and out of cells, and say which require energy. [4]

Section B

3. An image of a cell is 60 mm wide at a magnification of ×1500.

(a) Calculate the real width in micrometres. [3] (b) Explain why an electron microscope allows sub-cellular structures to be seen that a light microscope cannot. [2]

4. Describe the cell cycle, including what happens in mitosis. [5]

5. Stem cells can be obtained from embryos or from adult bone marrow.

(a) Define a stem cell. [2] (b) Give one advantage of using embryonic rather than adult stem cells. [1] (c) Give one ethical objection to embryonic stem cell use. [1] (d) Explain what therapeutic cloning is and one benefit of it. [3]

6. Explain why an increase in surface area to volume ratio increases the rate of diffusion into a cell. [3]

7. Root hair cells and xylem cells are both specialised for their function in a plant.

(a) Describe how each is adapted to its function. [2] (b) Explain why plants, unlike most animals, can be cloned from cuttings. [2]

8. A cell is 0.02 mm across. Under a microscope its image measures 40 mm.

(a) Calculate the magnification, showing your unit conversion. [3] (b) State whether this magnification could be achieved using a light microscope, giving a reason based on the typical maximum magnification of light microscopes. [1]

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Answers

1. Bacteria have no nucleus — DNA is a single loop free in the cytoplasm [1]; they may have plasmids [1]; they have a cell wall [1]. (Also accept: much smaller; no mitochondria.)

2. Diffusion — no energy required [1]. Osmosis — the movement of water across a partially permeable membrane, no energy required [1] [1]. Active transport — requires energy from respiration [1].

3. (a) Real = 60 ÷ 1500 = 0.04 mm [1]; × 1000 [1] = 40 µm [1]. (b) The electron microscope has much higher resolution as well as higher magnification [1], so two points very close together can still be seen as separate — revealing structures such as ribosomes and internal membranes [1].

4. In the first stage the cell grows, the number of sub-cellular structures increases [1] and the DNA replicates to form two copies of each chromosome [1]. In mitosis, one set of chromosomes is pulled to each end of the cell [1] and the nucleus divides [1]. Finally the cytoplasm and cell membrane divide to form two genetically identical daughter cells [1].

5. (a) An undifferentiated cell [1] that can divide to produce more cells of the same type and differentiate into other specialised cell types [1]. (b) Embryonic stem cells can be made to differentiate into most different types of human cells, whereas adult stem cells can only form a limited range [1]. (c) The embryo is destroyed, and some people consider it to have the right to life [1]. (d) An embryo is produced with the same genes as the patient [1], so the stem cells taken from it are genetically identical to the patient [1] and will not be rejected by the immune system [1].

6. A larger surface area to volume ratio means there is more membrane area per unit of cytoplasm [1], so more substances can diffuse across at the same time [1] and the distance to the centre of the cell is shorter [1].

7. (a) A root hair cell has a large surface area for absorbing water (and dissolved minerals) from the soil [1]; a xylem cell is hollow, dead and strengthened with lignin, allowing water to flow through it easily and giving the plant structural support [1]. (b) Most animal cells differentiate early and lose the ability to change [1], whereas many plant cells retain the ability to differentiate for life, so a cutting can regrow the missing specialised cell types [1].

8. (a) Convert to the same units: 0.02 mm = 20 micrometres, 40 mm = 40 000 micrometres [1] magnification = 40 000 ÷ 20 [1] = ×2000 [1]. (b) Yes — light microscopes typically reach a maximum magnification of about ×2000, so this result is right at the upper limit of what one can achieve [1].

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Where marks are usually lost

• Saying bacteria have no DNA rather than no nucleus.
• Confusing magnification with resolution.
• Forgetting that DNA replicates before mitosis, not during it.
• Giving surface area alone rather than the ratio to volume.
• Not converting to the same units before calculating magnification, or before comparing a size given in mm with one given in micrometres.
• Assuming plant and animal cells differentiate in the same way — most animal cells lose this ability early, while many plant cells keep it.

Work through the Cell Biology revision notes alongside these questions: the notes summarise cell types, microscopy and stem cells in condensed form, while these questions test whether you can apply the magnification formula and the differentiation argument to a specific, unfamiliar example rather than just recall the definition.