Cells and levels of organisation — Edexcel International GCSE Biology
Levels of organisation, plant and animal cell structures and functions, cell differentiation and stem cells.
Revision notes
4 short notes, in the order of the specification. Each one in short:
Living things are organised in levels, each built from the one below: organelle, cell, tissue, organ, organ system and organism. A tissue is a group of cells with a similar structure and function. An organ, such as the stomach, is made of several different tissues working together to perform a specific function.
Animal and plant cells both have a nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes. Plant cells also have a cellulose cell wall for strength and support, a large permanent vacuole filled with cell sap that keeps the cell firm, and often chloroplasts, which contain chlorophyll to absorb light energy for photosynthesis.
Cell differentiation and specialised cells
Biology onlyDifferentiation is the process by which a cell becomes specialised for a particular job by gaining the structures it needs. For example, a root hair cell has a long projection giving a large surface area for absorbing water and mineral ions, and a nerve cell has a long axon that carries electrical impulses over long distances.
Stem cells in medicine
Biology onlyStem cells are cells that have not yet differentiated, so they can develop into different types of cell and may replace damaged or diseased cells, for example to treat diabetes or paralysis. Embryonic stem cells can become almost any cell type. Risks include tumours, passing on viruses, rejection by the immune system and ethical objections to using embryos.
Exam questions
6 exam-style questions (20 marks), each with its mark scheme.
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13 cards: flip them, mark what you knew, and practise the rest.
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The whole of structure and functions in living organisms on one page, so you can see where this subtopic fits.
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Quick check questions
Put these in order, smallest first: organ, cell, organelle, tissue, organ system.
Show answer
Organelle, cell, tissue, organ, organ system.
What is the function of the mitochondria?
Show answer
They are where aerobic respiration takes place, releasing energy for the cell.
Name three structures found in plant cells but not animal cells.
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Cell wall, chloroplasts and a large permanent vacuole.
Biology only What is differentiation?
Show answer
The process by which a cell becomes specialised for a particular job.
Biology only Give one disadvantage of using stem cells in medicine.
Show answer
They can divide out of control and form a tumour (or viruses could be passed on, or the immune system may reject them).
Frequently asked questions
Why do plant cells have a cell wall?
Plant cells have a cell wall to strengthen and support the cell. The wall is made of cellulose and lies outside the cell membrane. Animal cells do not have a cell wall. Together with the large vacuole of cell sap, which keeps the cell firm, the wall helps the plant hold its shape.
Why do plant cells have large vacuoles?
Plant cells have a large, permanent vacuole filled with cell sap, a solution of sugars and salts, which helps to keep the cell firm. Animal cells have no vacuole or only small, temporary ones. For Edexcel International GCSE Biology, learn the vacuole, cell wall and chloroplasts as the structures plant cells have but animal cells do not.
What is the difference between a tissue and an organ?
A tissue is a group of cells with a similar structure and function, while an organ is a group of different tissues working together to perform a specific function. The stomach is an organ because muscular tissue churns food, glandular tissue makes digestive juices and epithelial tissue covers its surfaces.
How are specialised cells adapted to their function?
Biology only Specialised cells gain structures during differentiation that suit their job. A root hair cell has a long projection for a large surface area to absorb water and mineral ions. A nerve cell has a long axon to carry impulses. A red blood cell has no nucleus, leaving more room for haemoglobin to carry oxygen.
Why are stem cells useful in medicine?
Biology only Stem cells are useful because they have not yet differentiated, so they can develop into different types of cell and could replace damaged or diseased cells. They might treat conditions such as diabetes or paralysis, or grow replacement tissues. However, they can form tumours, pass on viruses, be rejected by the immune system, and raise ethical concerns.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026