Click image to open full size
Osmosis, Diffusion & Active Transport Cheat Sheet
A printable reference covering diffusion, osmosis, concentration gradients, facilitated diffusion, active transport, and tonicity for grades 8-12.
Related Tools
Related Labs
Related Worksheets
Related Infographics
This cheat sheet covers how substances move into and out of cells by diffusion, osmosis, facilitated diffusion, and active transport. Students need these ideas to understand cell survival, homeostasis, nutrient uptake, and waste removal. It also helps connect cell membranes to real biological examples such as plant wilting, red blood cell swelling, and mineral uptake by roots. The most important idea is that passive transport moves substances down a concentration gradient without using cellular energy. Osmosis is the diffusion of water across a selectively permeable membrane, while facilitated diffusion uses membrane proteins to move substances down the gradient. Active transport moves substances against the gradient and requires energy, usually from ATP.
Key Facts
- Diffusion moves particles from high concentration to low concentration until equilibrium is reached.
- Osmosis is the movement of water across a selectively permeable membrane from higher water concentration to lower water concentration.
- Passive transport does not require ATP because substances move down their concentration gradient.
- Facilitated diffusion moves molecules through channel or carrier proteins from high concentration to low concentration.
- Active transport requires energy because it moves substances from low concentration to high concentration.
- A hypertonic solution has more solute outside the cell, so water tends to leave the cell.
- A hypotonic solution has less solute outside the cell, so water tends to enter the cell.
- An isotonic solution has equal solute concentration inside and outside the cell, so there is no net water movement.
Vocabulary
- Concentration Gradient
- A difference in the amount of a substance between two areas.
- Diffusion
- The movement of particles from an area of higher concentration to an area of lower concentration.
- Osmosis
- The diffusion of water across a selectively permeable membrane.
- Facilitated Diffusion
- Passive transport that uses membrane proteins to help molecules cross the cell membrane.
- Active Transport
- The movement of substances across a membrane against their concentration gradient using energy.
- Tonicity
- A comparison of solute concentration outside a cell to solute concentration inside a cell.
Common Mistakes to Avoid
- Thinking all movement across a membrane uses energy, which is wrong because diffusion, osmosis, and facilitated diffusion are passive and do not require ATP.
- Confusing solute movement with water movement, which is wrong because osmosis specifically describes water moving across a selectively permeable membrane.
- Saying water moves toward lower solute concentration, which is wrong because water moves toward higher solute concentration when the membrane allows water through.
- Mixing up hypertonic and hypotonic solutions, which is wrong because hypertonic solutions draw water out of cells while hypotonic solutions push water into cells.
- Forgetting that facilitated diffusion still moves down the gradient, which is wrong because using a protein channel does not automatically make transport active.
Practice Questions
- 1 A cell has 5% solute inside and is placed in a solution with 10% solute. Will water move into the cell, out of the cell, or show no net movement?
- 2 A membrane separates side A with 30 oxygen molecules and side B with 80 oxygen molecules. In which direction will oxygen diffuse?
- 3 A plant root cell uses ATP to move mineral ions from low concentration in the soil into higher concentration inside the cell. What type of transport is this?
- 4 Explain why a freshwater organism may have problems if placed in saltwater, using osmosis and tonicity in your answer.