Define diffusion.
Reveal answer
The net movement of particles from a region of higher concentration to a region of lower concentration.
Key words: net movement · concentration
2(d) MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS · RECALL
2.15 Diffusion, osmosis and active transport
18 recall questions. Answer from memory, reveal the answer, then rate yourself. Ratings stay on this device.
Ratings are saved in this browser on this device, under a KS4 key kept separate from International A Level recall. Written answers are temporary and cleared when you leave the page. Use Reset to clear the ratings on this device.
Define osmosis.
Reveal answer
The net movement of water molecules through a partially permeable membrane, from a dilute solution into a more concentrated one.
Key words: water · partially permeable
Define active transport.
Reveal answer
Movement of particles against a concentration gradient (low to high), using energy from respiration.
Key words: against · energy
Why do roots in waterlogged soil take up fewer mineral ions?
Reveal answer
Little oxygen → less aerobic respiration in root cells → less ATP → less active transport of ions.
Key words: oxygen · respiration · active transport
What is plasmolysis?
Reveal answer
When a plant cell loses water by osmosis so that the cytoplasm and membrane pull away from the cell wall.
Key words: plasmolysis · cell wall
What is a turgid cell?
Reveal answer
A plant cell full of water, with the vacuole pushing the cytoplasm against the cell wall.
Key words: turgid
What is meant by the term concentration gradient?
Reveal answer
A difference in concentration between two regions.
Key words: concentration gradient
What is meant by the term water potential?
Reveal answer
A measure of the tendency of water to move; pure water has the highest value under standard conditions.
Key words: water potential
What is meant by the term partially permeable?
Reveal answer
Allowing some particles to cross more readily than others.
Key words: partially permeable
What is meant by the term net movement?
Reveal answer
The overall movement after movement in both directions is considered.
Key words: net movement
What is meant by the term active transport?
Reveal answer
Energy-requiring movement across a membrane against a concentration gradient.
Key words: active transport
Three transport processes compared, Diffusion. Direction and requirement? Example?
Reveal answer
Direction and requirement: Particles move net high → low concentration; passive; membrane not always required. Example: Oxygen moving from an alveolus into blood.
Key words: Diffusion
Three transport processes compared, Osmosis. Direction and requirement? Example?
Reveal answer
Direction and requirement: Water moves net high → low water potential through a partially permeable membrane; passive. Example: Water entering a root hair cell.
Key words: Osmosis
Three transport processes compared, Active transport. Direction and requirement? Example?
Reveal answer
Direction and requirement: Solute moves low → high concentration through carrier proteins; requires energy released by respiration. Example: Mineral ions entering a root hair cell against the gradient.
Key words: Active transport
True or false, and why? “Particles stop moving at equilibrium.”
Reveal answer
False. Random movement continues, but equal movement in both directions gives no net change.
True or false, and why? “Osmosis is the movement of any molecule through a membrane.”
Reveal answer
False. Osmosis describes water molecules only.
True or false, and why? “A flaccid plant cell is necessarily plasmolysed.”
Reveal answer
False. Plasmolysis is a more extreme state in which the membrane pulls from the wall.
True or false, and why? “Active transport moves substances from high to low concentration.”
Reveal answer
False. It moves against the gradient, from lower to higher concentration.