Transport Across Membranes (B3)
Describe diffusion.
Answer: The net movement of particles from a region of higher concentration to a region of lower concentration due to random movement.
What type of molecule are enzymes?
Answer: Proteins
What gas is required for photosynthesis?
Answer: Carbon dioxide.
Name the structures where gas exchange occurs in the lungs.
Answer: Alveoli.
What type of signal travels along a neurone?
Answer: Electrical impulse.
What type of membrane is involved in osmosis?
Answer: A partially permeable membrane.
What is the name of the region where the substrate binds on an enzyme?
Answer: Active site.
State the word equation for photosynthesis.
Answer: Carbon dioxide + water → glucose + oxygen.
Which gas diffuses from alveoli into the blood?
Answer: Oxygen.
Name the neurone that carries impulses from receptors to the CNS.
Answer: Sensory neurone.
State two factors that increase the rate of diffusion.
Answer: Any two of: larger surface area, higher temperature, steeper concentration gradient, shorter diffusion distance.
What happens to enzyme activity above the optimum temperature?
Answer: The enzyme denatures and activity decreases.
Which tissue transports sucrose in plants?
Answer: Phloem.
State the balanced symbol equation for aerobic respiration.
Answer: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
Put these in order: receptor, motor neurone, sensory neurone, effector, relay neurone.
Answer: Receptor → sensory neurone → relay neurone → motor neurone → effector.
Name the condition of a plant cell placed in a concentrated solution.
Answer: Plasmolysed.
Explain why enzymes are specific.
Answer: The active site has a complementary shape to the substrate.
State two functions of xylem.
Answer: Transport of water and mineral ions; support.
Why does breathing rate increase during exercise?
Answer: To supply more oxygen and remove excess carbon dioxide.
State one advantage of reflex actions.
Answer: They are rapid and protect the body from harm.
Why does active transport require energy?
Answer: Because particles are moved against a concentration gradient using energy from respiration.
Explain how a change in pH can stop an enzyme working.
Answer: Extreme pH changes alter the shape of the active site, preventing enzyme–substrate complexes from forming
Explain how increased wind speed affects transpiration.
Answer: Wind removes water vapour around the leaf, maintaining a steep diffusion gradient and increasing transpiration rate.
Describe how oxygen debt is removed after vigorous exercise.
Answer: Increased breathing and heart rate supply oxygen so lactic acid can be transported to the liver and aerobically respired.
Explain why reflex actions do not involve conscious thought.
Answer: The impulse passes through the spinal cord instead of the brain, allowing a faster response.