Which of the following is a property of protein-based active transport across cell membranes?

• A. It is a type of passive transport.
• B. It requires energy input, often in the form of ATP.
• C. It moves substances only down their concentration gradient.
• D. It does not involve any membrane proteins.

Answer: (B)

Verified step by step guidance

1. Understand the concept of active transport: Active transport is a process where substances are moved across a cell membrane against their concentration gradient, meaning from a region of lower concentration to a region of higher concentration.
2. Recognize the role of energy in active transport: Active transport requires energy input because moving substances against their concentration gradient is not energetically favorable. This energy is often provided in the form of ATP (adenosine triphosphate).
3. Identify the involvement of membrane proteins: Active transport relies on specific membrane proteins, such as pumps, to facilitate the movement of substances across the membrane. These proteins undergo conformational changes powered by ATP to transport molecules.
4. Distinguish active transport from passive transport: Passive transport does not require energy and moves substances down their concentration gradient, while active transport requires energy and moves substances against their concentration gradient.
5. Eliminate incorrect options: Based on the properties of active transport, discard options that describe passive transport, lack energy input, or do not involve membrane proteins. The correct property is that active transport requires energy input, often in the form of ATP.