A plant cell up close
A typical leaf cell is a rounded box shape, about 20–100 µm long, held in place by its wall. The living part inside the wall — the protoplast — contains a nucleus, cytoplasm and organelles, but much of the volume is taken up by a single large vacuole, which pushes the other organelles toward the edges.
The cell wall
Outside the cell membrane is a rigid cell wall made mostly of cellulose fibres. It gives the cell its shape, protects it, and stops it bursting when it takes in water. The wall is fully permeable, so water and dissolved substances pass through it freely; the membrane inside still controls what enters the cell. Neighbouring cells are linked through tiny channels in their walls called plasmodesmata.
Chloroplasts
Chloroplasts are where photosynthesis happens. They contain the green pigment chlorophyll, arranged on stacks of membranes called grana, surrounded by a fluid called the stroma. Like mitochondria, chloroplasts have their own DNA and ribosomes — evidence that both were once free-living bacteria taken in by an ancient cell (the endosymbiotic theory).
The central vacuole
The large central vacuole is filled with cell sap — water containing sugars, salts and pigments — and surrounded by a membrane called the tonoplast. When it is full, it presses the cytoplasm against the wall, making the cell firm (turgid). This turgor pressure keeps leaves and soft stems upright; when a plant loses water, its cells become flaccid and the plant wilts.
Organelles shared with animal cells
Plant cells also contain a nucleus, cell membrane, cytoplasm,mitochondria, ribosomes, endoplasmic reticulum and aGolgi apparatus, which do the same jobs as in animal cells. Plants need mitochondria too: they respire all the time to release energy from the glucose made by photosynthesis.
Specialised plant cells
- Palisade cells in leaves are packed with chloroplasts.
- Root hair cells have no chloroplasts but a long extension for absorbing water.
- Xylem cells die and lose their contents, leaving hollow tubes with thick walls.
- Guard cells change shape to open and close stomata.
Interesting facts
- Robert Hooke named cells in 1665 after looking at thin slices of cork: what he saw were the empty walls of dead plant cells.
- Cellulose, the main material of plant cell walls, is the most abundant organic polymer on Earth.
- Neighbouring plant cells are linked through their walls by tiny channels called plasmodesmata, so water, sugars and signals can pass directly from cell to cell.
- Chloroplasts can move inside a cell: in dim light they spread out to catch more light, and in very bright light they line up along the side walls to avoid damage.
- The colour of red cabbage, beetroot and many flowers comes from pigments dissolved in the central vacuole.
Key terms
- Cellulose
- A strong carbohydrate made of glucose units, forming the cell wall.
- Chlorophyll
- The green pigment that absorbs light for photosynthesis.
- Turgor
- The pressure of the cell contents against the cell wall.
- Plasmodesmata
- Channels through cell walls that connect the cytoplasm of neighbouring plant cells.
Why it matters
- Materials: cotton, paper and wood are made largely of cellulose from plant cell walls.
- Food and fibre: dietary fibre is mostly plant cell wall material that humans cannot digest.
- Biofuels: scientists are developing ways to break down cellulose into fuels.
- Gardening: watering restores turgor in wilting plants.
Common misconceptions
- “Plant cells don’t have mitochondria.” They do — plants respire like animals.
- “All plant cells have chloroplasts.” Cells in roots and other unlit tissues usually don’t.
- “The cell wall controls what enters the cell.” That is the membrane’s job; the wall is fully permeable.
Key takeaways
- Plant cells have a cellulose wall, chloroplasts and a large central vacuole, in addition to the organelles of animal cells.
- The wall gives support; turgor pressure from the vacuole keeps cells firm.
- Chloroplasts make food; mitochondria release its energy.
- Different plant cells are specialised for different jobs.
Model note: organelles are shown larger and fewer than in a real cell so that each can be seen and selected.