Help needed with a past paper question

[the Teddy Piano]

Hey guys,

I was doing a past paper question when I came across this question,

So it is

what is needed for active transport of glucose into a cell?

Energy Glucose concentration outside the cell

A. needed Higher concentration than inside

B. needed Any concentration

C. not needed Higher concentration than inside

D. not needed Any concentration

I know that energy is needed in active transport, but when it came to the concentration outside the cell, I was confused.

To my understanding, if glucose is being transported into the cell, and since it's the active transport that needs energy, glucose should be transported against concentration gradient, right? If so, I think to make this happen, the concentration of glucose outside the cell should be lower than that inside the cell.

Can you guys please explain a little bit and help me pinpoint where I was wrong about my idea?

Thanks in advance.

Edited November 2, 2013 by the Teddy Piano

[Fiz]

I am not sure, but

Glucose is normally transported by facilitated diffusion down the concentration gradient, so no AT is required.

Yet, this question specifically asks for the concentration when the cell uses active transport to pump glucose, which means that the inside has a larger concentration than the outside.

But the question did not state this answer, so i cancel A as it is wrong, and i would definitely eliminate answers C,D as they are completely wrong. So i'd go with B.

[Sandwich]

Hey guys,

I was doing a past paper question when I came across this question,

So it is

what is needed for active transport of glucose into a cell?

Energy Glucose concentration outside the cell

A. needed Higher concentration than inside

B. needed Any concentration

C. not needed Higher concentration than inside

D. not needed Any concentration

I know that energy is needed in active transport, but when it came to the concentration outside the cell, I was confused.

To my understanding, if glucose is being transported into the cell, and since it's the active transport that needs energy, glucose should be transported against concentration gradient, right? If so, I think to make this happen, the concentration of glucose outside the cell should be lower than that inside the cell.

Can you guys please explain a little bit and help me pinpoint where I was wrong about my idea?

Thanks in advance.

As the above person said, eliminate C and D because you need energy. As for the concentration gradient, active transport is against the concentration gradient as you said, so B is correct. The concentration gradient is irrelevant as glucose can be transported whether the concentration is lower inside OR outside the cell. The concentration outside the cell may well be lower because glucose is being concentrated in the cell on account of the process of active transport - but it doesn't NEED to be lower in order for glucose to move from outside to inside the cell, because active transport doesn't rely at all on the concentration gradient. The key word in this question is "needed". Whether it is likely or not is irrelevant - it's whether it's necessary or not!