Question

Neutral solutes may move across the membrane by a process of _____A ____, ____B_____ the concentration gradient.

• A. (A – Simple diffusion), (B – Along)
• B. (A – Osmosis), (B – Against)
• C. (A – Active transport), (B – Against)
• D. (A – Osmosis), (B – Along)

Answer 1

Answer: (A)

The cell membrane is semi-permeable with the following functions:
1. Fat-soluble substances can channelize directly across the phospholipid layer.
2. Neutral solutes may move across the membrane through simple diffusion along the concentration gradient, i.e., from higher concentration to the lower.
3. Water may also move across this membrane from higher to lower concentration. The movement of water by diffusion is called osmosis.
4. The polar molecules cannot pass through the nonpolar lipid bilayer. They require a carrier protein of the membrane to facilitate their transport across the membrane called facilitated diffusion.
5. Some ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration. Such transport is an energy-dependent process, in which ATP is utilized and is called active transport, e.g., Na+/K+pump.