Which of the following statements correctly describes coupled transport in cellular membranes?

• A. Coupled transport is a form of passive transport that does not require energy.
• B. Coupled transport involves the simultaneous movement of two substances across a membrane, where one substance moves down its concentration gradient and the other moves against its gradient.
• C. Coupled transport occurs only in the presence of a specific enzyme that facilitates the movement of substances.
• D. Coupled transport requires ATP to move substances against their concentration gradients.

Answer: (B)

Verified step by step guidance

1. Understand the concept of coupled transport: Coupled transport, also known as co-transport, involves the simultaneous movement of two substances across a cellular membrane. This process is often facilitated by transport proteins.
2. Identify the types of coupled transport: There are two main types of coupled transport - symport and antiport. Symport involves the movement of two substances in the same direction, while antiport involves the movement of substances in opposite directions.
3. Recognize the role of concentration gradients: In coupled transport, one substance typically moves down its concentration gradient (from high to low concentration), which provides the energy needed for the other substance to move against its concentration gradient (from low to high concentration).
4. Clarify the energy requirement: Coupled transport does not directly require ATP. Instead, it uses the energy from the movement of one substance down its concentration gradient to transport another substance against its gradient.
5. Evaluate the statements: Based on the understanding of coupled transport, identify the correct statement that describes the process accurately. The correct statement is: 'Coupled transport involves the simultaneous movement of two substances across a membrane, where one substance moves down its concentration gradient and the other moves against its gradient.'