Cells and levels of organisation — Edexcel International GCSE Science (Double Award)
Levels of organisation from organelles to organisms, and the structures of plant and animal cells and what they do.
Revision notes
2 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.
Exam questions
4 exam-style questions (11 marks), each with its mark scheme.
Answer the questionsFlashcards
9 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of structure and functions in living organisms on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
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.
Show answer
Cell wall, chloroplasts and a large permanent vacuole.
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.
Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026