2018 · Q7
Which one of the following statements about transport mechanism in plants is correct?
general-sciencebiology-plants
- ADiffusion of ions and small molecules across cell membrane requires energy.
- BActive transport of ions and small molecules across cell membrane against concentration gradient requires energy.
- CCells conserve energy and no energy is required for transport of ions and small molecules against concentration gradient.
- DCells do not transport ions across their membrane as these are charged molecules.
Explanation
Active transport moves ions and small molecules across the cell membrane against their concentration gradient — thermodynamically uphill — and therefore requires metabolic energy (usually ATP). Diffusion moves substances down the gradient and needs no energy, ruling out statement A. Plant cells routinely transport charged ions (K+, NO3−) using channels and pumps, ruling out D. Statement C contradicts the very definition of active transport. Hence only B is correct.