Topic 2 of IGCSE Biology (Cambridge 0610) is organisation of the organism. You need to know the structure and function of animal and plant cells, the hierarchy from cell → tissue → organ → organ system, and how to calculate magnification. This revision guide covers each of these with clear descriptions and exam-style tips so you can label diagrams, state functions, compare cells, and do magnification calculations for full marks.

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Animal cell: structure and function

An animal cell has a cell membrane (surface membrane) that surrounds the cell and controls what enters and leaves. Inside is the cytoplasm, a jelly-like substance where many chemical reactions take place. The nucleus contains the genetic material (DNA) and controls the cell’s activities (e.g. growth, division). Mitochondria are where respiration happens: they release energy from glucose for the cell to use. Ribosomes are where proteins are made (protein synthesis). You may also see references to the endoplasmic reticulum and Golgi body; at minimum, know nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes and their functions.

In exams, “state the function” means one clear sentence (e.g. “The nucleus controls the cell’s activities and contains genetic material.”).

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Plant cell: structure and function

A plant cell has all the structures of an animal cell (cell membrane, cytoplasm, nucleus, mitochondria, ribosomes) plus three more. The cell wall is outside the cell membrane; it is made of cellulose and gives the cell support and shape. It is fully permeable (unlike the membrane). The chloroplasts contain chlorophyll and are where photosynthesis takes place; they are found mainly in leaves and green stems, not in roots. The large permanent vacuole contains cell sap (water, salts, sugars) and helps keep the cell firm (turgid) and supports the plant.

Do not say that chloroplasts are in “all” plant cells; they are mainly in cells that carry out photosynthesis (e.g. palisade mesophyll in the leaf).

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Comparing plant and animal cells

When you compare plant and animal cells, give both similarities and differences. Similarities: both have a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes. Differences: plant cells have a cell wall (animal cells do not); plant cells have chloroplasts (animal cells do not); plant cells have a large permanent vacuole (animal cells may have small temporary vacuoles). The cell wall is for support; the cell membrane controls what enters and leaves. Do not confuse the two: the cell wall is rigid and made of cellulose; the cell membrane is flexible and is the barrier between cytoplasm and the outside.

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Tissues, organs, and organ systems

A tissue is a group of cells of the same type working together (e.g. muscle tissue, xylem tissue). An organ is a structure made of several different tissues working together to carry out a function (e.g. the heart, the leaf, the stomach). An organ system is a group of organs working together (e.g. the circulatory system: heart, blood vessels, blood; the transport system in a plant: root, stem, leaf, xylem, phloem).

You may be asked to define these terms and give one example of each. For example: tissue – muscle tissue; organ – heart or leaf; organ system – circulatory system or digestive system.

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Magnification calculations

Magnification tells you how much bigger the image is than the real object. The formula is magnification = image size ÷ actual size. You must use the same units for image size and actual size (usually mm or µm). 1 mm = 1000 µm. If the image size is in cm, convert to mm (× 10) or µm (× 10 000) before dividing. Actual size = image size ÷ magnification. Always show your working and give the unit in the answer.

Example: Image size = 20 mm, actual size = 0.05 mm. Magnification = 20 ÷ 0.05 = 400. (No unit for magnification.) Example: Image size = 50 mm, magnification = 500. Actual size = 50 ÷ 500 = 0.1 mm (or 100 µm).

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Exam tips and command words

• Draw / Label: Use a sharp pencil; label lines should not cross; state the function if asked.
• State the function: One clear sentence (e.g. “Mitochondria release energy in respiration.”).
• Compare: Give similarities and differences (e.g. “Both have a nucleus; plant cells have a cell wall, animal cells do not.”).
• Calculate magnification: Use magnification = image size ÷ actual size; convert units so they are the same; show working; give units where needed.

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Common mistakes to avoid

• Confusing cell wall (plant; cellulose; support) with cell membrane (all cells; controls what enters/leaves).
• Saying chloroplasts are in all plant cells (they are mainly in leaves and green stems, not roots).
• Wrong magnification because units were mixed (e.g. image in cm, actual in µm, without converting).
• Forgetting to give the unit for actual size (e.g. mm or µm).

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Revision checklist

• Draw and label an animal cell and a plant cell with at least five parts each.
• State the function of nucleus, mitochondria, ribosomes, cell membrane, cell wall, chloroplast, vacuole.
• Define tissue, organ, organ system and give one example of each.
• Calculate magnification or actual size from a scale bar or given measurements; use the same units.

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Next steps

Book a free trial with an IGCSE Biology tutor to practise cell diagrams and magnification calculations, or explore Tutopiya’s learning portal for more revision resources.