Cell Transport
Students often see cell transport as a cluster of new terms. A steadier route is to connect Diffusion with Osmosis, then place Facilitated diffusion and Active transport into the same working picture.
Definition: Cell transport describes how substances cross a selectively permeable membrane. Passive transport moves substances down a concentration gradient without direct cellular energy. Active transport uses energy to move substances against a gradient or to move large materials through membrane vesicles.
What do you need to know about cell transport?
Use the visual as a recall tool: read the Diffusion box, cover it, and explain it from memory. Repeat that move for Osmosis, Facilitated diffusion, and Active transport; then explain how the four ideas connect.
What should you remember about cell transport?
| Idea | What it means |
|---|---|
| Diffusion | Net movement from higher concentration toward lower concentration. |
| Osmosis | Diffusion of water across a selectively permeable membrane. |
| Facilitated diffusion | Passive movement through a membrane protein. |
| Active transport | Energy-requiring movement, often against a concentration gradient. |
How can each anchor help you answer a question?
Diffusion as a question clue
Net movement from higher concentration toward lower concentration. A useful contrast is osmosis: diffusion of water across a selectively permeable membrane.
Osmosis as a question clue
Diffusion of water across a selectively permeable membrane. A useful contrast is facilitated diffusion: passive movement through a membrane protein.
Facilitated diffusion as a question clue
Passive movement through a membrane protein. A useful contrast is active transport: energy-requiring movement, often against a concentration gradient.
Active transport as a question clue
Energy-requiring movement, often against a concentration gradient. A useful contrast is diffusion: net movement from higher concentration toward lower concentration.
What else helps this topic make sense?
Tonicity predicts how a surrounding solution changes cell volume. An isotonic solution produces no net water shift, even though individual water molecules continue crossing both ways. A hypotonic solution drives net water entry, and a hypertonic solution drives net water loss. Plant cells respond differently from animal cells because a rigid cell wall limits expansion and allows internal pressure to build. Always identify the reference cell before naming the solution.
How does this idea work in a real question?
A cell placed in a solution with a higher solute concentration outside loses water by osmosis and shrinks. Water moves toward the side with the greater effective solute concentration because the membrane allows water to cross more readily than that solute.
For this example, first identify which of the four anchors is changing or acting. Follow its effect through the situation and name the result before comparing choices. This keeps your reasoning tied to evidence rather than to a familiar-looking term.
What is a reliable way to reason through it?
- Decide whether the question is mainly about Diffusion, Osmosis, Facilitated diffusion, or Active transport.
- Restate the job of the named idea before reading the answer choices.
- Use the Diffusion–Active transport map above to trace direction, cause, evidence, or outcome in the order supplied.
- Test the remaining choice against this specific warning: Particles move randomly in every direction during diffusion. The net movement is from higher to lower concentration because more particles begin on the crowded side.
What mistake should you watch for?
Particles move randomly in every direction during diffusion. The net movement is from higher to lower concentration because more particles begin on the crowded side.
If two choices survive, ask which one preserves the stated relationship between Diffusion and Osmosis. Then check it against Facilitated diffusion or Active transport if either appears in the prompt.
Watch a short lesson
The membrane-transport video compares passive and active routes and reinforces gradient-based reasoning. Pause the lesson when a diagram or process appears and connect it with the four anchors in this page’s visual.
Can you check your understanding?
Try these six checks from memory. Open an answer only after you have said or written your own response.
In your own words, what is the central idea in this lesson?
Check the answer
Cell transport describes how substances cross a selectively permeable membrane. Passive transport moves substances down a concentration gradient without direct cellular energy. Active transport uses energy to move substances against a gradient or to move large materials through membrane vesicles.
What should you remember about diffusion?
Check the answer
Net movement from higher concentration toward lower concentration.
What should you remember about osmosis?
Check the answer
Diffusion of water across a selectively permeable membrane.
What should you remember about facilitated diffusion?
Check the answer
Passive movement through a membrane protein.
What should you remember about active transport?
Check the answer
Energy-requiring movement, often against a concentration gradient.
What final check is most useful for a question about cell transport?
Check the answer
Compare the choice with the relationship among Diffusion, Osmosis, Facilitated diffusion, and Active transport. Then apply this warning: Particles move randomly in every direction during diffusion. The net movement is from higher to lower concentration because more particles begin on the crowded side.
Where does this fit in your science review?
The ATI TEAS Science Study Hub places this lesson inside the larger biology review. Continue with these connected lessons:
Recommended ATI TEAS resources
Keep this biology lesson in your science sequence. When you are ready to work on the mathematics section of the same exam, the resources below provide a separate set of lessons and practice.
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