Which statement about active transport is most accurate?

• A. Active transport requires energy, usually in the form of ATP, to move substances against their concentration gradient.
• B. Active transport is a type of passive transport.
• C. Active transport does not involve membrane proteins.
• D. Active transport only occurs when substances move down their concentration gradient.

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by understanding the concept of active transport. Active transport is a biological process where substances are moved across a cell membrane against their concentration gradient (from low concentration to high concentration). This process requires energy input.
2. Step 2: Recognize that the energy required for active transport is typically provided by ATP (adenosine triphosphate). ATP is hydrolyzed to release energy, which powers the transport proteins involved in this process.
3. Step 3: Note that active transport is distinct from passive transport. Passive transport does not require energy and involves substances moving down their concentration gradient (from high concentration to low concentration). Active transport, on the other hand, requires energy and moves substances against the gradient.
4. Step 4: Understand the role of membrane proteins in active transport. These proteins, such as pumps (e.g., sodium-potassium pump), are essential for facilitating the movement of substances against their concentration gradient. Active transport cannot occur without these specialized proteins.
5. Step 5: Evaluate the given statements based on the above information. The most accurate statement is: 'Active transport requires energy, usually in the form of ATP, to move substances against their concentration gradient.' The other statements are incorrect because active transport is not passive, involves membrane proteins, and does not occur when substances move down their concentration gradient.