Membrane Transport, Diffusion & Osmosis — Practice · Grade 7 Science

Chapter: Cells, Transport & Cellular Energy

What this practice covers

By the end of Membrane Transport, Diffusion & Osmosis you should be able to:

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

Vocabulary used: diffusion, concentration, osmosis, selectively permeable, equilibrium.

Problem 1

Why can particle count alone fail to show concentration?
Answer and explanation

Concentration depends on both amount and volume; counts in unequal volumes are not directly comparable.

Problem 2

Does diffusion equilibrium mean all particles stop?
Answer and explanation

No. Motion continues; opposing movements can balance so there is no net concentration change.

Problem 3

What must be known before predicting osmosis?
Answer and explanation

Which materials can cross, their concentrations, and relevant pressure or other conditions; a membrane is not universally permeable.

Problem 4

Is movement of a dissolved particle always osmosis?
Answer and explanation

No. Osmosis describes net water movement across a selective membrane; other particles and processes require their own explanation.

Problem 5

Illustrative model: equal-pressure compartments A and B start with equal volumes; A has 5 nonpenetrating solute particles per volume unit and B has 10. Water can cross; solute cannot. Predict initial net water movement, identify what crosses, and explain why equilibrium need not mean no motion.
Answer and explanation

Initial net water movement tends from A toward B under these simplified conditions. Water crosses; the stipulated solute does not. This can change concentrations and pressures, limiting later flow. At equilibrium water molecules can still move both ways even when there is no net change. The conclusion depends on the stated permeability and pressure assumptions.

Compare nonpenetrating solute concentrations.

Apply the stipulated water permeability.

Separate net movement from individual crossings.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A membrane is freely permeable to the solute in a second model. Can the previous nonpenetrating-solute prediction be copied unchanged?
Answer and explanation

No. Solute redistribution changes the relevant conditions. Determine permeability and concentrations before predicting water movement.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

What moves in the simple osmosis model?
  1. Only cell walls
  2. Water across the selective membrane
  3. Every solute equally
  4. Whole organ systems
Answer and explanation

Water across the selective membrane

Osmosis concerns net water movement across a selectively permeable membrane.

Problem 8

A model compartment has 12 solute units in 3 volume units. Find concentration.
Answer and explanation

4 solute units/volume unit

12/3=4 in the stated model units.

Browse all courses