Which of the following BEST explains whether cotransport is an active process or a passive process?
A.
It is active because ATP is needed to transport both chemicals across their concentration gradients.
B.
It is active because ATP is needed to establish a concentration gradient for one chemical to power the transport of the other chemical.
C.
It is passive because both chemicals move down their concentration gradients.
D.
It is passive because the movement of one chemical powers the movement of the other chemical.
B. It is active because ATP is needed to establish a concentration gradient for one chemical to power the transport of the other chemical.
The correct answer is B. It is active because ATP is needed to establish a concentration gradient for one chemical to power the transport of the other chemical. Cotransport is a process in which two different substances are transported across a biological membrane simultaneously. It involves the use of ATP to establish a concentration gradient for one of the substances, which then powers the transport of the other substance against its concentration gradient. This ATP-dependent movement of substances against their concentration gradients is what makes cotransport an active process rather than a passive one.
To determine whether cotransport is an active or passive process, let's analyze the options given:
A. This option suggests that cotransport is an active process because ATP is needed to transport both chemicals across their concentration gradients. This implies that energy in the form of ATP is required for the transport process, supporting the idea of active transport.
B. This option suggests that cotransport is an active process because ATP is needed to establish a concentration gradient for one chemical, which then powers the transport of the other chemical. Similarly to option A, this involves the use of energy in the form of ATP to drive the transport process.
C. This option suggests that cotransport is a passive process because both chemicals move down their concentration gradients. Passive processes typically occur when molecules move along their concentration gradients without the need for an external energy source like ATP.
D. This option suggests that cotransport is a passive process because the movement of one chemical powers the movement of the other chemical. This also implies that the process occurs without requiring ATP or other energy sources.
Based on the explanations provided, both options A and B propose that cotransport is an active process that requires ATP to transport the chemicals. On the other hand, options C and D suggest that cotransport is a passive process that occurs spontaneously along concentration gradients.
Therefore, the BEST explanation would be option A: "It is active because ATP is needed to transport both chemicals across their concentration gradients." This option represents the concept of active transport, where energy in the form of ATP is utilized to transport molecules against their concentration gradients.