Question

(a) ... particles are moving against their concentration gradient. (b) ... particles are moving against their concentration gradient. (c) ... particles are moving with the use of atp. (d) ... particles are moving without the use of atp. diagrams show particle movement across a membrane (top and bottom).

Explanation:

To solve this, we analyze the particle movement:

Step 1: Analyze Concentration Gradient

In the top image, particles are more on the left (higher concentration) and fewer on the right (lower concentration). In the bottom image, particles move from left (high) to right (low) – with the concentration gradient (passive transport, no ATP needed for simple/passive, but here, if it’s facilitated diffusion, still no ATP). Wait, no – wait, the options: Let's check each:

• Option A: “because particles are moving against their concentration gradient” – No, they move with (high to low), so A is wrong.
• Option B: “because particles are moving against their concentration gradient” – Same as A, wrong.
• Option C: “because particles are moving with the use of ATP” – No, moving with gradient (passive) doesn’t need ATP. Wrong.
• Option D: “because particles are moving without the use of ATP” – Correct, as movement with concentration gradient (passive transport: simple or facilitated) doesn’t require ATP.

Answer:

D. because particles are moving without the use of ATP.