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Energy and Respiration: Question 6

Syllabus 12.1

Multiple choice A2 1 mark

Living cells constantly need a supply of energy from the hydrolysis of ATP to drive processes that would not otherwise happen, while some other processes in a cell take place without any direct input of energy from ATP.

Which of the following processes in a cell requires energy directly from the hydrolysis of ATP?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall which cell processes need a direct input of energy

Many essential processes in a cell, such as active transport, muscle contraction, the synthesis of large molecules (for example proteins and DNA) and nerve impulse transmission, cannot occur spontaneously and need a continuous input of energy released by the hydrolysis of ATP. Other processes, however, are passive: they rely only on the random kinetic energy of particles moving down a concentration gradient (or, for water, down a water potential gradient) and need no direct ATP input.

  • Diffusion, facilitated diffusion and osmosis are all passive processes: molecules or ions move from a region of higher concentration (or water potential) to a region of lower concentration (or water potential), without any energy being supplied by the cell. Facilitated diffusion still needs a specific channel or carrier protein, but the protein does not use ATP. It simply provides a route through the membrane for a substance that would otherwise cross too slowly.
  • Active transport, by contrast, moves substances against their concentration gradient, from a region of lower to a region of higher concentration. This cannot happen spontaneously, so a carrier protein couples the process to the hydrolysis of ATP, using the energy released to change shape and move the substance across the membrane.

Step 2: Evaluate each option

  • A: correct. Moving ions against their concentration gradient is active transport, which requires energy directly from ATP hydrolysis.
  • B: incorrect. Diffusion of carbon dioxide down its concentration gradient is a passive process and needs no ATP.
  • C: incorrect. Osmosis is diffusion of water down a water potential gradient, so it is passive and needs no direct ATP input.
  • D: incorrect. Facilitated diffusion moves glucose down its concentration gradient through a channel protein; it is passive and, unlike active transport, does not use ATP.

Final answer

  • Only movement against a concentration gradient, such as active transport, requires energy directly from ATP hydrolysis, option A.