Relate cilia and microvilli to cell surfaces
Cilia and microvilli are cell-surface specialisations with different structures and functions.
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
Which structure is associated with increasing surface area for absorption?
What you will learn
- Recognise cilia and microvilli in eukaryotic cells
- Distinguish cilia that move material from microvilli that increase surface area
Cilia are projections that can move material
Cilia are hair-like projections from a cell surface. Their internal microtubule arrangement supports movement. In groups, beating cilia can move fluid or particles across a cell surface, as in specialised tissues.
Cilia are not present on every cell. In a micrograph, look for repeated projections from the cell surface and use tissue context; a single uneven edge is not enough evidence.
Microvilli increase surface area
Microvilli are small projections of the cell-surface membrane that increase surface area. They can increase the area available for absorption, for example on epithelial cells lining the small intestine.
Microvilli are not motile cilia. A brush border may contain many microvilli that are too small to resolve individually in a light micrograph. Describing the increased surface area is the key structure-function link.
Pause and explain
What is a common role of cilia?
Worked example
A cell surface has many short projections and is specialised for absorption. Is this more consistent with cilia or microvilli?
Show the worked solution
- Absorptive projections increase surface area.
- Cilia are associated with movement.
Answer The projections are more consistent with microvilli because they increase surface area for absorption. Cilia are projections associated with movement of material across a cell surface.
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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.
Compare cilia and microvilli by their surface structure and main role.
Give me a hint
Use movement versus increased surface area.
Compare my reasoning
- Cilia are projections associated with movement.
- Microvilli increase surface area, often for absorption.
Cilia are hair-like projections that can move material across a cell surface. Microvilli are small surface projections that increase area available for absorption.
Look for these in your work
- Cilia role
- Microvilli role
An absorptive epithelial cell has a dense brush border. Identify the likely surface feature and explain its advantage.
Give me a hint
Connect the brush border with membrane area.
Compare my reasoning
- A brush border is consistent with many microvilli.
- More surface area can support absorption.
The brush border is consistent with many microvilli. Their increased cell-surface area can support absorption of substances.
Look for these in your work
- Likely feature
- Structure-function link
A student calls a row of surface projections “microvilli that sweep mucus away.” Correct the explanation.
Give me a hint
Assign the movement role to the right structure.
Compare my reasoning
- Cilia can beat to move mucus.
- Microvilli increase surface area.
Cilia are the projections that can beat to move mucus or other material across a cell surface. Microvilli increase surface area and are not the motile structures described.
Look for these in your work
- Cilia correctly identified
- Microvilli function distinguished
Common mistakes
- Saying microvilli beat to move material
- Saying cilia mainly increase absorptive surface area
- Assuming every epithelial cell has the same projections
What can you explain now?
Which structure is associated with increasing surface area for absorption?
Compare with the explanation
Microvilli
Microvilli increase the area of the cell surface.
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Make it stick
How do cilia and microvilli differ in structure and function?
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