Calculate how subdivision exposes more surface
Connect unchanged volume with greater enzyme-accessible area.
Section 7.3 · Physical digestion
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
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 quantity stays the same when the stated cube is divided?
What you will learn
- Connect unchanged volume with greater enzyme-accessible area.
- Calculate total area while conserving the volume of material.
Expose the outside
Enzymes can act on exposed surfaces of food. Dividing a piece exposes surfaces that were previously inside it, increasing the surface available for enzyme action without changing the food molecules by the division itself.
For a cube of side length s, total surface area is 6s² and volume is s³. The cube is a teaching model: irregular food is not an exact cube, and a bigger surface does not alone establish the whole digestion rate.
Keep material quantity matched
A 2 cm cube has surface area 24 cm² and volume 8 cm³. Dividing it into eight 1 cm cubes keeps total volume 8 cm³ but gives total surface area 48 cm². The surface area doubles while the material quantity is unchanged.
Use equal starting material when comparing subdivision. Different enzyme amounts, temperature or substrate composition would provide additional rate explanations. Area predicts a useful mechanism, not a universal guarantee of doubled digestion speed.
Pause and explain
Why does subdivision support digestion?
Worked example
Compare one 2 cm cube with eight 1 cm cubes made from it.
Show the worked solution
- Original area: 6 × 2² = 24 cm².
- New area: 8 × 6 × 1² = 48 cm².
- Total volume remains 8 cm³.
Answer Surface area doubles from 24 to 48 cm² without changing total volume.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Calculate the surface area and volume of a 3 cm cube.
Give me a hint
Use 6s² and s³.
Compare my reasoning
- Area: 6 × 9 = 54.
- Volume: 27.
54 cm²; 27 cm³.
Look for these in your work
- Correct powers.
- Correct units.
The 3 cm cube becomes twenty-seven 1 cm cubes. Find total area and the area increase factor.
Give me a hint
Add all small-cube areas.
Compare my reasoning
- 27 × 6 = 162 cm².
- 162 ÷ 54 = 3.
162 cm², three times the original area; total volume remains 27 cm³.
Look for these in your work
- Correct total.
- Area factor and unchanged volume.
A subdivided food sample is also given twice as much enzyme. Can a faster result isolate the surface-area effect?
Give me a hint
Two variables differ.
Compare my reasoning
- Area and enzyme quantity both changed.
- Keep enzyme quantity matched in a new comparison.
No; match enzyme quantity and other conditions to isolate subdivision.
Look for these in your work
- Identify both variables.
- Give a controlled correction.
Common mistakes
- Do not add volumes as if material was created.
- Doubled area does not automatically prove doubled biological rate.
What can you explain now?
Why does subdivision support digestion?
Compare with the explanation
It exposes more surface for enzyme action.
More substrate surface becomes accessible.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the area mechanism without promising a fixed digestion-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.