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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key concept
A typical animal cell contains a nucleus (houses DNA), cytoplasm (site of chemical reactions), cell membrane (controls entry and exit of substances), mitochondria (site of aerobic respiration) and ribosomes (site of protein synthesis).
Cell structure is foundational: nearly every topic in IGCSE Biology connects back to the cell. You must be able to draw and label an animal cell, state the function of each organelle, and compare animal cells with plant and bacterial cells. This guide covers Core and Supplement content.
Core Organelles and Their Functions
Organelle
Function
Nucleus
Contains genetic material (DNA) in the form of chromosomes. Controls cell activities and cell division.
Cytoplasm
Jelly-like substance where most chemical reactions take place. Contains enzymes for metabolic reactions.
Cell membrane
Partially permeable barrier that controls which substances enter and leave the cell. Made of a phospholipid bilayer with proteins (Supplement).
Mitochondria
Site of aerobic respiration. Glucose is broken down to release energy (ATP). Cells with high energy demands (e.g. Muscle cells, sperm cells) have many mitochondria.
Ribosomes
Site of protein synthesis. Found free in the cytoplasm or attached to rough endoplasmic reticulum.
Supplement Organelles
Extended-tier students also need to know:
Rough endoplasmic reticulum (RER): a network of membranes studded with ribosomes. Transports proteins made by the ribosomes.
Smooth endoplasmic reticulum (SER): makes and transports lipids.
Golgi apparatus (Golgi body): modifies, packages and secretes proteins. Think of it as the cell's "post office".
Why some cells have more mitochondria: Cells that require large amounts of energy: such as muscle cells, sperm cells and nerve cells: contain many mitochondria to provide the ATP needed for their functions.
Drawing an Animal Cell in Exams
When asked to draw a cell:
Use a sharp pencil with clear, continuous lines: no shading or colouring.
Draw the cell membrane as a single line (not a double line unless showing the phospholipid bilayer).
Show the nucleus as a large circle inside the cell with a visible nucleolus if specified.
Draw mitochondria as small oval shapes with internal folds (cristae for Supplement).
Show ribosomes as dots: they are too small to draw to scale.
Label lines must touch the structure and not cross each other.
Try a focused question (2 marks)
Explain why a muscle cell contains a large number of mitochondria. (2 marks)
Show the answer and marking guidance
Muscle cells require a lot of energy / ATP for contraction.
Mitochondria are the site of aerobic respiration, which releases this energy.
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Saying the nucleus "contains the cell" or "is the brain": state it contains DNA and controls cell activities.
Drawing a cell wall on an animal cell: only plant, fungal and bacterial cells have cell walls.
Confusing mitochondria with chloroplasts: mitochondria are for respiration (all cells), chloroplasts for photosynthesis (green plant cells only).