Active Transport Uses Energy for Ion Movement Across Membranes

Steps:

• Define active transport as the energy-requiring process that moves ions across cell membranes against their concentration gradient.
• Evaluate statement 1: Describes movement from high to low concentration, characteristic of passive diffusion, not active transport.
• Evaluate statement 2: Correctly indicates that active transport involves ions crossing the cell membrane toward regions of lower concentration in specific cellular contexts, like maintaining ion balances.
• Evaluate statement 3: Accurately states that respiratory energy (ATP) powers the transport of ions into or out of cells.

Why D is correct:

• Statements 2 and 3 align with the definition of active transport as an energy-driven process for ion translocation across membranes.

Why the others are wrong:

• A: Includes statement 1, which reverses the gradient direction.
• B: Includes statement 1, misrepresenting the transport mechanism.
• C: Includes statement 1, confusing it with passive processes.

Final answer: D