Distinguish villi from microvilli
Explain two scales of increased internal absorptive surface.
Section B7.5 · Absorption
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall large and small nutrient molecules, cell membranes and enzyme specificity.
- Use the stated diagram keys and evidence; models are not to scale.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which surface faces the gut contents?
What you will learn
- Explain two scales of increased internal absorptive surface.
- Read a magnified cell inset without confusing structural scales.
Villi are tissue projections
Villi are finger-like multicellular projections of the small-intestine lining. They increase the internal surface available for absorption within the intestinal tube. Their value is the surface exposed to gut contents, not simply a larger external abdominal area.
A villus contains an epithelial surface with transport vessels inside. It is not an individual molecule or a single membrane bump on one cell.
Microvilli are cell-surface projections
Microvilli are much smaller projections of the lumen-facing epithelial-cell membranes. They further increase surface area at the cell scale. The diagram’s magnified cell inset must not be treated as a second full-size villus.
Together, villi and microvilli provide more area for absorption. Surface area is one adaptation; a short transport distance and removal of products also matter. More area alone does not prove every nutrient is absorbed instantly.
Sources for this lesson
Pause and explain
Which statement distinguishes the scales?
Worked example
A model shows a tissue finger and a magnified cell with many fine membrane projections. Name each level.
Show the worked solution
- Tissue projection: villus.
- Cell membrane projections: microvilli.
- Both increase internal surface area.
Answer Villus at tissue scale; microvilli at epithelial-cell membrane scale.
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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.
Explain how villi and microvilli support absorption.
Give me a hint
Use internal surface area.
Compare my reasoning
- Villi increase lining surface.
- Microvilli further increase epithelial-cell surface.
Both increase the internal surface area available for absorption, at different structural scales.
Look for these in your work
- Both structures.
- Correct area/function link.
A teaching sheet’s flat patch has area 20 units and its folded patch 60 units, with the same material. Find the area factor and explain the model’s useful analogy.
Give me a hint
Use 60/20.
Compare my reasoning
- Area factor is 3.
- More exposed surface can model an absorption adaptation.
Threefold exposed area; it models surface increase but not a measured threefold body absorption rate.
Look for these in your work
- Correct ratio.
- Limit the rate claim.
A picture labels a whole finger-like tissue projection “microvillus” and fine cell bumps “villi”. Correct it and explain the magnification issue.
Give me a hint
Match structural level.
Compare my reasoning
- Whole tissue projection: villus.
- Cell bumps: microvilli.
- Inset is magnified.
Swap the labels; the cell inset is magnified and is not at the same scale as the villus.
Look for these in your work
- Both corrections.
- Scale awareness.
Common mistakes
- Villus and microvillus are not synonyms.
- A magnified inset is not drawn to the same scale.
What can you explain now?
Which statement distinguishes the scales?
Compare with the explanation
Villi are multicellular projections; microvilli project from cell membranes.
The structural levels differ.
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Make it stick
Explain the two levels of surface increase without promising a fixed rate multiplier.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.