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In a yeast cell, chloride ions are pumped from a low concentration inside the cell to a high concentration of chloride ions through carrier molecules in the membrane. This movement is an example of:
A. endocytosis
B. exocytosis
C. diffusion
D. osmosis
E. active transport
The Correct Answer and Explanation is:
The correct answer is E. active transport.
Explanation:
The process described in the question involves the movement of chloride ions from a region of low concentration inside the yeast cell to a region of higher concentration outside the cell. This type of ion movement requires energy input because it is moving against the concentration gradient, from an area of lower concentration to one of higher concentration.
In biological systems, active transport refers to the movement of molecules or ions across a cell membrane against their concentration gradient, utilizing energy in the form of ATP (adenosine triphosphate). This is in contrast to passive transport methods, where substances move along their concentration gradient (from high to low concentration) without the use of energy.
Active transport often involves carrier proteins or pumps embedded in the cell membrane that facilitate the movement of ions or molecules. In this case, chloride ions are being actively pumped across the cell membrane using a specific protein, and this requires the hydrolysis of ATP to supply the necessary energy to transport the ions against the gradient.
Why the other options are incorrect:
- A. Endocytosis: This is a type of active transport where the cell membrane engulfs external material, forming vesicles to bring substances into the cell. However, the question involves the movement of ions across the membrane, not the ingestion of substances.
- B. Exocytosis: This process involves the removal of substances from the cell by vesicles fusing with the plasma membrane. Again, it does not apply here because the question concerns ion movement into the cell, not their removal.
- C. Diffusion: This is a passive process where substances move from an area of high concentration to low concentration, without requiring energy. The chloride ions in the question are moving against the gradient, so diffusion does not apply.
- D. Osmosis: This specifically refers to the movement of water molecules across a semipermeable membrane from an area of lower solute concentration to higher solute concentration. This process does not involve chloride ions in the context described.
Thus, the process described in the question is best explained by active transport.