IB DP Biology - B2.1 Membranes and membrane transport - IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Human cells maintain high intracellular K⁺ and high extracellular Na⁺ using the sodium–potassium pump, which actively transports ions against their concentration gradients using ATP.
✅ Answer: (A)
✅ Answer: (A)
Question
What applies to chemiosmosis?
A. It takes place in both cristae and thylakoid membranes.
B. It involves the movement of water across a semipermeable membrane.
C. It only takes place in the presence of sunlight and oxygen gas.
D. It uses ATP to pump hydrogen ions against the concentration gradient.
▶️Answer/Explanation
Answer: A. It takes place in both cristae and thylakoid membranes.
Explanation:
What is Chemiosmosis?
Chemiosmosis is the process where ATP is produced using the energy from a flow of hydrogen ions (H⁺) across a membrane through an enzyme called ATP synthase.
This occurs during:
- Cellular respiration in mitochondria (in the cristae)
- Photosynthesis in chloroplasts (in the thylakoid membranes)
Let’s analyze the options:
A. Correct – Chemiosmosis takes place in both cristae (mitochondria) and thylakoid membranes (chloroplasts) during ATP production.
B. Incorrect – This describes osmosis, which is the movement of water, not hydrogen ions.
C. Incorrect – Chemiosmosis does not require both sunlight and oxygen together; it occurs in photosynthesis (sunlight) and respiration (oxygen) separately.
D. Incorrect – ATP is not used to pump hydrogen ions. The electron transport chain creates the H⁺ gradient. Chemiosmosis uses that gradient to make ATP.
▶️ Answer/Explanation
Clathrin molecules assemble into a cage-like structure on the cytoplasmic side of the membrane, causing it to bend inward and form a budding vesicle.
✅ Answer: (B)
✅ Answer: (B)