Active Transport Requires Energy for Movement Against Gradients

Steps:

• Define active transport: Process using cellular energy (ATP from respiration) to move ions or molecules across the cell membrane against their concentration gradient.
• Evaluate statement 1: Incorrect, as active transport moves ions from low to high concentration, opposite of diffusion.
• Evaluate statement 2: Correct, as it occurs across the cell membrane via protein pumps.
• Evaluate statement 3: Correct, as respiration provides ATP to power ion movement into or out of the cell.

Why D is correct:

• Active transport definition specifies energy-dependent movement across membranes against gradients, matching statements 2 and 3.

Why the others are wrong:

• A includes 1, which describes passive diffusion, not active transport.
• B includes 1, misstating the direction of ion movement.
• C includes 1, confusing active transport with passive processes.

Final answer: D