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Class 9 · Biology

Cell size and exchange

Interactive explanation Gamified quiz, feedback & rewards

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NCERT chapter connection · Learning goals & preparation

By the end, you can…

  • Explain Total surface / total volume = 6/L
  • Change one input at a time and predict its effect before checking the model.
  • Apply the relationship in a quiz and explain the reasoning behind your answer.

Useful preparation: Living and non-living things, cells and reading labelled diagrams. Suggested previous stop: Population growth.

Exploration · Cell: The Building Block of Life
NCERT ePathshala current chapter index · checked 12 Nov 2026. This activity explores part of the chapter; it does not replace the textbook. Open official NCERT reference ↗

Interactive exploration · Class 9

Cell size and exchange

Class 9
Surface / volume (µm⁻¹)01.683.365.046.72110.520Cell side length (µm)Number of separate cells held at 1 · scale adjusts to values
The relationshipTotal surface / total volume = 6/L
01 · How to explore

Make the idea your own

  1. 1Read the inputs and predict what will change.
  2. 2Change one parameter while keeping the other fixed.
  3. 3Explain the result using the diagram and the live values.
02 · Take it further

Notice the pattern

This geometric model helps explain why small cells have more surface per unit volume.