Identify plant cell walls, plasmodesmata and vacuoles
Plant cell walls, plasmodesmata and the large permanent vacuole support shape, communication and cell water relations.
AS Level · Cambridge International Biology 9700, 2028–2030. Interpret only the structures supported by the provided image or description. Written practice is self-checked; it does not demonstrate practical microscopy competence.
Before you begin
- Recognise that organisms are made of cells and that a light microscope produces a magnified image.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the membrane around a plant-cell vacuole called?
What you will learn
- Recognise the plant cell wall, plasmodesmata, large permanent vacuole and tonoplast
- Outline the roles of these plant cell structures
Wall and plasmodesmata
The plant cell wall is outside the cell-surface membrane and is made mainly of cellulose in the cells considered here. It supports the cell and helps maintain its shape. The wall is not the selectively permeable cell boundary.
Plasmodesmata are channels through plant cell walls that connect the cytoplasm of adjacent cells. They allow communication and movement of some substances between neighbouring cells. The connecting membrane remains continuous through the channel.
Vacuole and tonoplast
A typical plant cell may contain a large permanent vacuole filled with cell sap. The tonoplast is the membrane surrounding the vacuole. The vacuole contributes to storage and helps maintain turgor when water enters the cell.
The vacuole is not the cytoplasm, and the tonoplast is not the cell-surface membrane. A plant cell image may show a large central region that displaces cytoplasm towards the edge.
Pause and explain
What do plasmodesmata connect?
Worked example
A plant-cell image shows a broad cellulose boundary and a large central compartment bounded by a membrane. Name the structures and describe one role of each.
Show the worked solution
- The broad outer boundary is the cell wall.
- The central compartment is the vacuole.
- Its membrane is the tonoplast.
Answer The cellulose wall supports the cell. The central compartment is a large permanent vacuole, whose surrounding membrane is the tonoplast. The vacuole stores cell sap and contributes to maintaining turgor.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State the positions of a plant-cell wall, cell-surface membrane and tonoplast.
Give me a hint
Move from the outside of the cell to the vacuole.
Compare my reasoning
- The wall is outside the cell-surface membrane.
- The tonoplast surrounds the vacuole within the cell.
From outside to inside: the cell wall lies outside the cell-surface membrane; the tonoplast surrounds the vacuole inside the cell.
Look for these in your work
- Wall and membrane ordered
- Tonoplast location stated
Explain how plasmodesmata support neighbouring plant cells.
Give me a hint
Think about connections through the walls.
Compare my reasoning
- Plasmodesmata pass through cell walls.
- They connect cytoplasm and allow communication or movement of some substances.
Plasmodesmata are channels through cell walls that connect the cytoplasm of adjacent plant cells, supporting communication and movement of some substances between them.
Look for these in your work
- Structure located
- Function linked
A central plant-cell compartment is labelled “cytoplasm.” Give a better label and one function.
Give me a hint
A large permanent vacuole can occupy the centre.
Compare my reasoning
- The compartment is the vacuole.
- It is enclosed by the tonoplast and stores cell sap.
The central compartment is the large permanent vacuole, bounded by the tonoplast. It stores cell sap and contributes to maintaining turgor.
Look for these in your work
- Correct structure
- Boundary or function included
Common mistakes
- Calling the tonoplast the cell-surface membrane
- Describing plasmodesmata as gaps that remove all cell boundaries
- Treating the cell wall as selectively permeable membrane
What can you explain now?
What is the membrane around a plant-cell vacuole called?
Compare with the explanation
Tonoplast
The tonoplast surrounds the vacuole.
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Make it stick
How do the wall, plasmodesmata, vacuole and tonoplast support plant cells?
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