Question 19

Sugar molecules enter a cell against a concentration gradient by the process of active transport.

Active transport is the mechanism through which sugar molecules move into a cell against their concentration gradient, requiring energy typically in the form of ATP to drive the process.

A) Osmosis

Osmosis specifically refers to the movement of water molecules across a semipermeable membrane and does not apply to the transport of sugar molecules. Therefore, this option is incorrect in the context of sugar transport.

B) Facilitated diffusion

Facilitated diffusion involves the movement of molecules across a membrane through protein channels, but it occurs down a concentration gradient and does not require energy. Since sugar molecules are entering against their gradient, this option is not applicable.

C) Active transport

Active transport is the correct answer as it allows sugar molecules to be transported into the cell against their concentration gradient, utilizing energy to move them from an area of lower concentration to an area of higher concentration.

D) Passive diffusion

Passive diffusion refers to the movement of substances across a membrane without the use of energy, occurring down their concentration gradient. Since sugar molecules are entering the cell against a gradient, this option is incorrect.

Conclusion

Active transport is the definitive mechanism for the movement of sugar molecules into cells against their concentration gradient, as it requires energy to facilitate this process. All other options fail because they either describe processes that do not involve energy or that occur down a concentration gradient, which does not apply to the movement of sugar in this context.