Cell Size & Exchange — Practice · Grade 10 Science

Chapter: Cells, Membranes & Exchange

What this practice covers

By the end of Cell Size & Exchange you should be able to:

8 questions, numeric, multiple choice and written answer, each with a worked explanation.

Vocabulary used: surface area, volume, diffusion distance.

Problem 1

Find area/volume for a cube with side length 3 mm.
Answer and explanation

2 mm⁻¹

6/3 = 2.

Problem 2

Doubling a cube’s side makes its volume…
  1. 2 times larger
  2. 4 times larger
  3. 8 times larger
  4. unchanged
Answer and explanation

8 times larger

Volume depends on the cube of length.

Problem 3

How do a thin surface and folding help exchange?
Answer and explanation

Thinness shortens diffusion distance; folding increases exchange area.

Problem 4

Compare area/volume ratios for cubes of side 1 mm and 2 mm. Explain the reasoning in your own words.
Answer and explanation

The larger cube has half the area per unit volume.

At 1 mm, area=6 and volume=1, ratio=6 mm⁻¹.

At 2 mm, area=24 and volume=8, ratio=3 mm⁻¹.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 5

For L=3, find SA/V using 6L²/L³. Show the reasoning, not just the conclusion.
Hints

Both lengths use the same units.

Answer and explanation

54/27=2 inverse length units.

Problem 6

How can folds help a cell exchange materials without greatly increasing volume?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

They increase membrane area available for transport relative to the volume served.

Problem 7

Surface shape, thickness and delivery solve different exchange problemsSurface shape, thickness and delivery solve different exchange problemsSmooth exchange boundaryFolded exchange boundaryFolds add area within a similar footprint.Thin barriers shorten a diffusion path; circulation changes delivery.
Original smooth/folded boundary sections; the curves illustrate added area qualitatively and are not a measured organ surface or a fold-area calculation.
Interpret the supplied visual. Would more folds alone guarantee faster exchange if no useful gradient or pathway exists?
Answer and explanation

No. Area supports capacity, but driving conditions, permeability and supply/removal also determine rate.

A fold can increase exchange area within a compact region. A thin barrier reduces the distance across which a substance must move. Circulation maintains delivery and removal by bulk transport, affecting gradients at exchange surfaces. These mechanisms should not be collapsed into one vague explanation that every surface is “large.” Intestinal villi, respiratory surfaces and internal membranes use different combinations under their conditions. A structural observation supports a plausible function, but actual rates also need permeability, driving conditions and activity measurements.

No. Area supports capacity, but driving conditions, permeability and supply/removal also determine rate.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 8

A cube’s side length rises from 2 to 4 mm. Calculate area, volume and area/volume for both, then explain why “the larger one has less surface” is misleading.
Answer and explanation

At 2 mm: area 24 mm², volume 8 mm³, ratio 3 mm⁻¹. At 4 mm: area 96 mm², volume 64 mm³, ratio 1.5 mm⁻¹. Total surface increases while area per volume falls; actual exchange also depends on pathways and demand.

At 2 mm: area 24 mm², volume 8 mm³, ratio 3 mm⁻¹. At 4 mm: area 96 mm², volume 64 mm³, ratio 1.5 mm⁻¹. Total surface increases while area per volume falls; actual exchange also depends on pathways and demand.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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