What are the parts of animal and plant cells, what do they do, and how are cells organised into organisms?
Identify the structures of animal and plant cells and their functions, compare the two cell types, and describe the organisation of cells into tissues, organs and systems
A focused answer to the O-Level Combined Science outcome on cells. The parts of animal and plant cells and their functions, the differences between them, and the levels of organisation from cell to organism.
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What this dot point is asking
SEAB wants you to name the structures inside animal and plant cells and state what each does, to compare the two cell types, and to describe how cells are organised into tissues, organs and systems. This is foundational biology: labelled-diagram and short-definition marks dominate, so the parts and their functions must be learnt precisely.
The answer
Structures common to animal and plant cells
Both cell types contain:
- Cell membrane: a thin layer that controls what enters and leaves the cell (partially permeable).
- Cytoplasm: a jelly-like substance where chemical reactions happen.
- Nucleus: contains the genetic material (DNA) and controls the cell's activities.
- Mitochondria: the site of aerobic respiration, releasing energy for the cell.
Extra structures in plant cells
Plant cells have three structures that animal cells lack:
- Cell wall: a rigid cellulose layer outside the membrane that supports the cell and stops it bursting.
- Chloroplasts: contain chlorophyll and are the site of photosynthesis.
- Large permanent vacuole: stores cell sap and keeps the cell firm (turgid) for support.
Comparing the two cell types
An animal cell has a membrane, cytoplasm, nucleus and mitochondria but no cell wall, no chloroplasts and only small temporary vacuoles. A plant cell has all of those plus a cell wall, chloroplasts and a large permanent vacuole, and it tends to have a fixed, often rectangular, shape because of the wall.
Levels of organisation
In a multicellular organism, cells are organised into larger units:
- a cell is the basic unit (e.g. a muscle cell),
- a tissue is a group of similar cells working together (e.g. muscle tissue),
- an organ is several different tissues working together (e.g. the heart),
- an organ system is several organs working together (e.g. the circulatory system),
- the organism is all the systems together.
Specialised cells
Cells are often specialised for their job: a red blood cell has no nucleus and is packed with haemoglobin to carry oxygen; a root hair cell has a long extension to absorb water. Structure is matched to function throughout biology.
Examples in context
Example 1. Why plant stems stand upright. The cellulose cell walls and turgid vacuoles of plant cells give the stem its rigidity, letting a non-woody plant hold itself up. When the cells lose water and become flaccid, the plant wilts, showing the support role of these plant-only structures.
Example 2. Sperm and egg cells as specialised cells. A sperm cell has a tail (flagellum) packed with mitochondria for swimming to the egg, and an egg cell is large with food stores. These specialisations illustrate how the same basic cell parts are adapted for very different functions.
Try this
Q1. Name the structure that controls what enters and leaves a cell, and the structure that contains the genetic material. [2 marks]
- Cue. The cell membrane controls what enters and leaves; the nucleus contains the genetic material.
Q2. State the function of mitochondria and say whether they are found in animal cells, plant cells, or both. [2 marks]
- Cue. Mitochondria are the site of aerobic respiration (release energy); they are found in both animal and plant cells.
Q3. Put these in order from smallest to largest: organ, cell, organism, tissue, organ system. [2 marks]
- Cue. Cell, tissue, organ, organ system, organism.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original4 marksA student examines a plant cell and an animal cell under a microscope. State two structures found in the plant cell but not in the animal cell, and for each one describe its function.Show worked answer →
Two structures found in the plant cell but not the animal cell (any two of):
Cell wall: a rigid layer of cellulose outside the cell membrane that supports the cell and gives it a fixed shape, and stops it bursting when full of water.
Chloroplast: contains chlorophyll, which absorbs light energy for photosynthesis so the plant can make food (glucose).
Large permanent vacuole: a sap-filled space that stores cell sap and helps keep the cell firm (turgid) for support.
Markers reward two correct plant-only structures, each with a correct function (for example cell wall for support and chloroplast for photosynthesis).
Original3 marksDefine the terms tissue and organ, and give one example of each from the human body.Show worked answer →
A tissue is a group of similar cells that work together to carry out a particular function. Example: muscle tissue (made of muscle cells that contract), or epithelial tissue.
An organ is a structure made of several different tissues working together to carry out a particular function. Example: the heart (or the stomach, lung, or kidney).
Markers reward a correct definition of a tissue as similar cells with a shared function, a correct definition of an organ as different tissues working together, and a valid example of each.
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