Distinguish transport mechanisms
Distinguish transport mechanisms using supplied evidence and a solved model.
About 25 minutes, plus any extended practice
Supplied materials
- All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
- Paper or a browser document for a labeled drawing, table or explanation.
- Worked problem inputs: A permeable membrane separates solute at 8 and 2 mmol/L. Predict net passive movement and distinguish individual paths.
- Assessment case 1: A permeable membrane separates solute at 6 and 1 mmol/Lwithout a pump. What net tendency fits? Which inference or prediction is best supported?
- Assessment case 2: What is the most specific name for passive water movement across this selective membrane down its water-potential gradient? Supplied case: Water moves passively across a selective membrane down its water-potential gradient.
- Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Pump uses energy against concentration gradient.
- Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Vesicle carries material across boundary.
- Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Particles spread down their concentration gradient.
- Assessment case 6: A selective membrane passes water but not the supplied solute; passive water entry changes model cell volume. What fits? Which inference or prediction is best supported?
Learn the idea
Cell membranes regulate exchange. Diffusion follows concentration gradients; osmosis concerns water across a selectively permeable membrane. Active transport uses energy to move against a gradient in this simplified model.
Diffusion means net particle movement down concentration gradient. Osmosis means net water movement across selective membrane. Active transport means energy-dependent movement against gradient. Bulk transport means vesicles move larger quantities across membrane.
For the supplied mechanism problem, A permeable membrane separates solute at 8 and 2 mmol/L. Predict net passive movement and distinguish individual paths. Net diffusion is from the higher concentration toward the lower for that solute. Individual particles move both ways. If concentrations equilibrate, microscopic motion continues while net movement can balance.
- Read the supplied problem and mark the structures, processes or quantities named: A permeable membrane separates solute at 8 and 2 mmol/L. Predict net passive movement and distinguish individual paths.
- Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
- Write a causal explanation or calculation, showing how each observation supports the result.
- Compare your reasoning with the worked solution; name a condition that would change or limit the inference.
See the method in action
Worked supplied problem: A permeable membrane separates solute at 8 and 2 mmol/L. Predict net passive movement and distinguish individual paths. Solution: Net diffusion is from the higher concentration toward the lower for that solute. Individual particles move both ways. If concentrations equilibrate, microscopic motion continues while net movement can balance. This conclusion uses the stated observations and the mechanism explained above; it does not establish every unmeasured feature of a real organism, device or place.
Check your reasoning
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Helpful tips
- Use the feature “net particle movement down concentration gradient” to justify diffusion; do not sort by the name alone.
- Distinguish osmosis (net water movement across selective membrane) from a different process occurring in the same situation.
See the answer and explanation
Net passive solute movement is high-to-low while particles can move both ways.
Random microscopic motion plus the gradient produces a net tendency, not one-way individual paths.
Take it further
New membrane case: permeable solute is at 3 mmol/L outside and 9 inside. Expected: net passive movement for that solute is outward down its gradient; individual motion still occurs in both directions.
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More practice: try new cases
Choose an answer for each problem. Explain your method on paper, then use the feedback to decide what to revisit.
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Check the subject sources
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