Predict passive movement across a membrane
See this course’s project requirements
A labeled cell-function model with membrane transport predictions, cell-type comparisons and an explanation connecting cells to tissues and organs.
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What to include
- Classify supplied living and nonliving observations.
- Label major structures with their distinct functions.
- Compare typical plant, animal and bacterial cells and name an exception.
- Predict two passive-movement directions with permeability assumptions.
- Link cells, tissues and organs and repair the supplied flawed model.
- Include the six changed-case responses with explanations.
Review and revise
Use these criteria to check your work and choose what to improve.
- Method: applies the course-specific rules to the supplied cases with visible intermediate work.
- Accuracy: results agree with the stated facts, units, boundaries and independent checks.
- Reasoning: explains why the result follows and identifies a limitation or unresolved question.
- Transfer: completes changed cases and revises the final project when a relevant assumption changes.
Want more background?
The idea in everyday life
Paper model: compartments I and O have equal volume and pressure. Dye concentration I=8 units and O=2 units; membrane allows dye through. Separate water model: solute I=4 units and O=1 unit; solute cannot cross but water can. Units are supplied model concentrations, not a recipe.
Diffusion gives net movement of a permeable substance from higher to lower concentration; particles still move both ways. Osmosis is net movement of water across a selectively permeable membrane. For equal-pressure model compartments with nonpermeating solute, water tends toward the higher solute concentration. Actual cells have additional transport processes.
Predict passive movement across a membrane — worked practice
Diffusion gives net movement of a permeable substance from higher to lower concentration; particles still move both ways. Osmosis is net movement of water across a selectively permeable membrane. For equal-pressure model compartments with nonpermeating solute, water tends toward the higher solute concentration. Actual cells have additional transport processes.
Paper model: compartments I and O have equal volume and pressure. Dye concentration I=8 units and O=2 units; membrane allows dye through. Separate water model: solute I=4 units and O=1 unit; solute cannot cross but water can. Units are supplied model concentrations, not a recipe.
1. 1. Dye
Compare dye concentrations and mark net diffusion direction.
You should see: I to O because 8 is greater than 2.
2. 2. Motion
Separate net movement from motion of individual particles.
You should see: Dye can move both directions; more initially moves out than in.
3. 3. Water
Apply the separate water-model permeability conditions.
You should see: Net water movement O to I, toward higher nonpermeating solute.
4. 4. Boundary
State what has not been modeled.
You should see: Pumps, changing volume, pressure differences and real-cell regulation may change later behavior.
What to finish
Two directional membrane predictions with the conditions that support them.
Watch for this
Individual particles continue random motion. Equal concentration can produce balanced exchange, which differs from no motion.
How can I tell I understand it?
Reverse a concentration gradient and explain the changed initial direction.
Quick knowledge check
Answer all 3 questions. Get at least 2 right and the lesson completes automatically.
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Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.
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Source & access notes · checked 2026-10-01
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