A level-readyAll subjects · Biology · WBI12 (Unit 2)
Plant cell ultrastructure
Plant cells have all the main eukaryotic organelles plus several extra structures linked to support, storage and photosynthesis.
Plant cell structures
These structures are found in plant cells in addition to the organelles all eukaryotic cells share.
| Structure | Function |
|---|---|
| Cellulose cell wall | Strength and support; resists bursting when the cell is turgid; freely permeable |
| Middle lamella | Layer of calcium pectate that cements neighbouring cells together |
| Plasmodesmata | Channels of cytoplasm through cell walls linking neighbouring cells, for transport and communication |
| Pits | Thin areas in walls where there is no secondary thickening, letting water pass between cells (for example between xylem vessels) |
| Chloroplast | Double membrane, stacks of thylakoids (grana) in a fluid stroma; site of photosynthesis |
| Amyloplast | Membrane-bound organelle that stores starch grains (for example in potato tubers and root cells) |
| Vacuole | Large permanent sac of cell sap; keeps the cell turgid, and stores substances |
| Tonoplast | Membrane around the vacuole; controls what enters and leaves it |
Comparing with animal cells
Animal cells have no cell wall, chloroplasts, amyloplasts or large permanent vacuole, and they store glycogen rather than starch. Animal cells have centrioles, which most plant cells lack. Both have a nucleus, ribosomes, ER, Golgi apparatus and mitochondria.
In electron micrographs, look for chloroplasts with stacked membranes, a thick wall with a middle lamella between cells, and a large vacuole bounded by the tonoplast.
Worked example
A cell from a potato tuber contains many large starch grains in membrane-bound organelles but no chloroplasts. What are the organelles, and why are there no chloroplasts?
- Membrane-bound starch stores are amyloplasts.
- Tubers grow underground with no light, so there is no photosynthesis.
Answer: Amyloplasts; the tuber does not photosynthesise.
Check yourself
- What is the middle lamella made of, and what does it do?
- Cellulose; it carries out photosynthesis
- Lignin; it stores starch
- Phospholipid; it surrounds the vacuole
- Calcium pectate; it holds neighbouring cells together
Show answer
Calcium pectate; it holds neighbouring cells together. Calcium pectate acts like a glue between cell walls.
- What are plasmodesmata?
- Starch-storing organelles
- Channels of cytoplasm through cell walls connecting neighbouring cells
- Membranes around vacuoles
- Thickened regions of xylem
Show answer
Channels of cytoplasm through cell walls connecting neighbouring cells. They allow transport and communication between cells.
- What is the function of an amyloplast?
- Photosynthesis
- Making ribosomes
- Controlling entry to the vacuole
- Storing starch
Show answer
Storing starch. Amylo- refers to starch.
- What is the tonoplast?
- The membrane surrounding the vacuole
- The cell wall
- A type of chloroplast
- A pore in the nucleus
Show answer
The membrane surrounding the vacuole. It controls movement into and out of the vacuole.
- What is the function of pits in xylem vessel walls?
- Storing starch
- Making the vessel stronger
- Allowing water to move sideways between vessels
- Photosynthesis
Show answer
Allowing water to move sideways between vessels. Pits are gaps in the lignified wall.
- Which structure is found in animal cells but not in most plant cells?
- Centrioles
- Mitochondria
- Ribosomes
- Golgi apparatus
Show answer
Centrioles. Most plant cells lack centrioles.
- What is a function of the large permanent vacuole?
- Making ATP
- Synthesising proteins
- Keeping the cell turgid
- Forming the spindle
Show answer
Keeping the cell turgid. Water in the vacuole pushes the cytoplasm against the wall.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.