Science: Osmosis, Diffusion, and Active Transport
Comparing passive and active movement across cell membranes
Science: Osmosis, Diffusion, and Active Transport
Comparing passive and active movement across cell membranes
Biology - Grade 9-12
- 1
Define diffusion and describe the direction that particles move during diffusion.
Focus on how concentration changes from one place to another.
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. The particles spread out down their concentration gradient until they are more evenly distributed. - 2
Define osmosis and explain how it is related to diffusion.
Osmosis is the diffusion of water across a selectively permeable membrane. It is related to diffusion because water moves from an area with more available water and lower solute concentration to an area with less available water and higher solute concentration. - 3
What is active transport, and how is it different from diffusion and osmosis?
Compare whether energy is required.
Active transport is the movement of substances across a cell membrane using energy, usually in the form of ATP. It differs from diffusion and osmosis because it moves materials against their concentration gradient instead of down the gradient. - 4
A drop of food coloring is placed in a beaker of still water. After several minutes, the color spreads evenly through the water. Identify the process and explain why it happens.
This process is diffusion. The food coloring particles move randomly from the region where they are highly concentrated into regions where they are less concentrated until the color becomes evenly distributed. - 5
A cell is placed in a solution that has a higher solute concentration than the inside of the cell. Describe what happens to the cell and explain why.
Think about the direction water moves in a hypertonic solution.
Water will move out of the cell by osmosis because the outside solution has a higher solute concentration and lower water concentration than the inside of the cell. As water leaves, the cell will shrink. - 6
A plant cell is placed in distilled water. Predict what happens to the plant cell and explain your answer.
Water will move into the plant cell by osmosis because distilled water has a lower solute concentration than the cell. The central vacuole will fill, and the cell becomes turgid because the cell wall helps prevent it from bursting. - 7
Explain why oxygen entering a cell is usually considered passive transport.
Consider whether oxygen is moving with or against the concentration gradient.
Oxygen entering a cell is usually passive transport because oxygen molecules move from an area of higher concentration outside the cell to an area of lower concentration inside the cell without requiring cellular energy. This movement occurs by diffusion through the membrane. - 8
Some mineral ions are more concentrated inside root cells than in the soil. Explain how the root cells can still take in these ions.
Root cells can take in these mineral ions by active transport. Membrane proteins use energy from ATP to move the ions from the lower concentration in the soil to the higher concentration inside the cells. - 9
Compare a selectively permeable membrane with a membrane that is fully permeable.
Think about whether all particles can cross or only certain ones.
A selectively permeable membrane allows some substances to pass through while blocking others based on factors such as size, charge, or the presence of transport proteins. A fully permeable membrane allows all substances to pass through freely. - 10
Red blood cells are placed in a hypotonic solution. Describe what happens to the cells and explain the role of osmosis.
Water enters the red blood cells by osmosis because the solution outside the cells has a lower solute concentration than the cytoplasm. The cells swell, and they may burst because animal cells do not have a cell wall. - 11
A student says that diffusion stops completely when equilibrium is reached. Evaluate this statement.
Distinguish between particle motion and net movement.
The statement is not fully correct. At equilibrium, particles continue to move randomly, but there is no net movement in one direction because the concentrations are balanced. - 12
Complete the comparison: diffusion, osmosis, and active transport all move substances, but only one always requires energy. Identify which process requires energy and summarize the main difference in one or two sentences.
Active transport always requires energy. The main difference is that diffusion and osmosis are passive processes that move substances down their concentration gradients, while active transport uses energy to move substances against their concentration gradients.