Cell Biology
Cell biology is the study of the structure of animal, plant and bacterial cells and how they carry out life processes, including how substances move across cell membranes by diffusion, osmosis and active transport, and how cells divide by mitosis. It is usually the first topic in GCSE Biology and often involves calculating magnification from microscope images.
Before you start
No specific prerequisites - this is a good place to start.
Method
- Learn each organelle (nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, plus the plant-only chloroplast, cell wall and permanent vacuole) and its one-sentence function, and know which are missing from a bacterial cell.
- Memorise and practise the magnification formula: magnification = size of image / size of real object. Rearrange it to find image size or real size, and convert between mm, um and nm (1 mm = 1000 um = 1,000,000 nm).
- Distinguish the three ways substances move across membranes: diffusion (net movement down a concentration gradient, no energy needed), osmosis (diffusion of water across a partially permeable membrane) and active transport (movement against a gradient, using energy from respiration).
- For surface-area-to-volume-ratio questions, calculate the surface area and the volume separately, then simplify the ratio to the form n : 1.
- Learn the order of the cell cycle (growth and DNA replication, then mitosis, then division into two genetically identical daughter cells) and why organisms need it (growth, repair and asexual reproduction).
- For extended-writing questions on stem cells, give a scientific point about what stem cells can do, plus a balanced point weighing the medical benefit against the ethical objection.
Worked example
A student views a plant cell under a microscope. The image of the cell is 36 mm wide. The actual width of the cell is 0.045 mm. Calculate the magnification of the image.
- Write down the magnification formula: magnification = size of image / size of real object.
- Check that both measurements are in the same unit (both are already in mm).
- Substitute the values: magnification = 36 / 0.045.
- Calculate: 36 / 0.045 = 800.
- Final answer: the magnification is x800.
Practice questions
Type your answer and press Check to be marked straight away, or reveal the answer and mark yourself.
Q1Name the structure in a plant cell that controls the substances entering and leaving the cell.Show answer
Answer: The cell membrane.
Q2State one structure found in a bacterial cell but not in an animal cell.Show answer
Answer: Cell wall (also accept: plasmid(s), or a single loop of DNA free in the cytoplasm).
Q3A microscope has a x10 eyepiece lens and a x20 objective lens. Calculate the total magnification.Show answer
Answer: x200 (10 x 20)
Q4Convert 0.02 mm into micrometres (um).Show answer
Answer: 20 um (0.02 x 1000)
Q5A cube-shaped model cell has sides of length 3 cm. Calculate the surface area to volume ratio of the cube. Give your answer in the form n : 1.Show answer
Answer: 2 : 1 (surface area = 6 x 9 = 54 cm^2, volume = 27 cm^3, 54/27 = 2)
Q6A student views a red blood cell at a magnification of x2000. The image of the cell measures 20 mm across. Calculate the real width of the cell, giving your answer in micrometres (um).Show answer
Answer: 10 um (real size = 20/2000 = 0.01 mm = 10 um)
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
Calculate the surface area to volume ratio of a cube-shaped cell with sides of length 4 cm. Give your answer in the form n : 1.
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A student places a cylinder of potato in a concentrated sugar solution. Before the experiment the cylinder has a mass of 4.50 g. After 30 minutes in the solution, the cylinder has a mass of 3.87 g. Explain, in terms of water movement and concentration, why the potato lost mass, and calculate the percentage change in mass.
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Some medical conditions can be treated using stem cells. Stem cells can be taken from human embryos, or from adult tissue such as bone marrow. Evaluate the use of embryonic stem cells to treat human diseases. Your answer should consider both the potential benefits and the objections.
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See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the cell biology worksheet pack - 10 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 1 of GCSE Biology Workbook, the whole course as one free printable PDF.
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