Question

A Gram-negative cell is moving uric acid across the cytoplasmic membrane against its chemical gradient. Which of the following statements is true?

a. The exterior of the cell is probably electrically negative compared to the interior of the cell.
b. The acid probably moves by a passive means such as facilitated diffusion.
c. The acid moves by an active process such as active transport.
d. The movement of the acid requires phagocytosis.

Accepted Answer

Step 1: Understand the nature of the transport process described. The problem states that uric acid is moving across the cytoplasmic membrane against its chemical gradient, which means it is moving from a region of lower concentration to a region of higher concentration. Step 2: Recall that moving a substance against its concentration gradient requires energy input, which is characteristic of active transport mechanisms, not passive transport. Step 3: Evaluate the options: (a) concerns electrical charge differences, which may relate to membrane potential but does not directly explain movement against a chemical gradient; (b) suggests passive transport, which cannot move substances against their gradient; (c) suggests active transport, which fits the requirement of moving against the gradient; (d) involves phagocytosis, a process for engulfing large particles, not small molecules like uric acid. Step 4: Conclude that the correct statement must describe an active process, since energy is needed to move uric acid against its chemical gradient. Step 5: Therefore, the correct understanding is that the acid moves by an active process such as active transport.

Verified video answer for a similar problem:

Key Concepts

Active Transport

Passive Transport and Facilitated Diffusion

Membrane Potential in Gram-negative Bacteria