Plant cell structure
A plant cell has everything an animal cell has, plus a cellulose cell wall, chloroplasts for photosynthesis, and one large permanent vacuole.
One-hour paid trial · Same-day reply
The plant cell is the basic unit of plants. Its extra structures let plants make food, stay upright and store cell sap.
A plant cell is a eukaryotic cell that shares its core organelles with an animal cell, nucleus, cytoplasm, plasma membrane, mitochondria and ribosomes, but it also has three features an animal cell lacks: a cellulose cell wall, chloroplasts and a large permanent vacuole. Exam diagrams are usually drawn from a palisade or leaf cell, so these three extras are almost always what a comparison question turns on.
Parts and functions
| Part | Function |
|---|---|
| Cell wall | Made of cellulose; freely permeable; gives support and a fixed shape |
| Plasma membrane | Partially permeable; controls what enters and leaves the cell |
| Cytoplasm | Jelly-like medium where most chemical reactions of the cell take place |
| Nucleus | Controls the cell and contains the genetic material (chromosomes) |
| Chloroplast | Contains chlorophyll; the site of photosynthesis |
| Vacuole (with tonoplast) | Large and permanent; the tonoplast surrounds the cell sap, which keeps the cell turgid and stores dissolved substances |
| Mitochondria | Site of aerobic respiration, releasing energy as ATP |
| Ribosomes | Where proteins are made from amino acids |
How structure suits function
The DSKP expects you to link each extra structure to the job it does for the whole plant, not just to name it.
- Cellulose cell wall, strong but freely permeable, it resists the pressure of water entering by osmosis, so the cell becomes turgid and supports the plant without blocking the movement of substances.
- Chloroplasts, packed with chlorophyll and able to move within the cell towards the light, they capture the light energy needed for photosynthesis; leaf cells that face the light contain the most.
- Large permanent vacuole, filled with cell sap, it presses the cytoplasm against the wall to keep the cell turgid, and it stores sugars, salts and pigments.
- Fixed, box-like shape, because the wall holds the shape, plant cells pack together neatly to build firm tissues such as the palisade layer of a leaf.
- Mitochondria, release the ATP a plant cell needs for active transport of mineral ions into root cells and for other energy-using processes.
Related processes
The extra structures of a plant cell each drive a process from elsewhere in the syllabus. The chloroplasts carry out photosynthesis, using carbon dioxide and water to make glucose in the light.
The large vacuole and cell wall together are the basis of turgor: when water enters the cell by osmosis, the vacuole swells and pushes the cytoplasm against the wall, and this turgor pressure keeps soft tissues such as leaves and young stems firm and upright.
Because the cell wall is strong, a plant cell placed in distilled water becomes turgid rather than bursting, unlike an animal cell. In a concentrated solution water leaves the cell, the vacuole shrinks and the cell becomes flaccid; if this continues, the membrane pulls away from the wall (plasmolysis).
The mitochondria supply ATP for aerobic respiration and active transport, and protein synthesis runs from the nucleus to the ribosomes just as it does in an animal cell.
Common labelling errors
Worked question
Question (in the style of Paper 2 Section A): Diagram X shows a palisade cell from a leaf. Structure K forms the outer boundary and keeps the cell's shape; structure L is a green oval body; structure M is a large space filling most of the cell.
(a) Name K, L and M. [3 marks] (b) Explain how structure L suits its function. [2 marks] (c) The cell is placed in distilled water but does not burst. Explain why. [2 marks]
Model answer: (a) K is the cell wall; L is the chloroplast; M is the vacuole. (b) The chloroplast contains chlorophyll, which absorbs light energy for photosynthesis, and it can move within the cell towards the light.
(c) Water enters the cell by osmosis and the cell becomes turgid, but the cellulose cell wall is strong and resists the pressure, which stops the cell from bursting.
Marking note: in part (c) the mark for not bursting must credit the strong cell wall resisting the pressure, not just water entering.
Source:SRC-DSKP-EN
Frequently asked questions
What extra structures does a plant cell have compared with an animal cell?
Why does a plant cell become turgid instead of bursting in water?
What is the function of the large vacuole in a plant cell?
Related
One-hour paid trial · Same-day reply