Cells lining kidney tubules function in the reabsorption of water from urine. In response to chemical signals, they reversibly insert additional aquaporins into their plasma membranes. In which of these situations would your tubule cells have the most aquaporins: after a long run on a hot day, right after a large meal, or after drinking a large bottle of water? Explain.

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Accepted Answer

Hello, everyone here's our next problem. It says poor ends are membrane proteins that help transport molecules by And we have choices of simple diffusion facilitated diffusion, active transport or all of the above. Well, let's think and recall from our content videos about the different types of transport of molecules across cell membranes. Because that's what we're talking about here in terms of diffusion or transport. So at the lowest level we talk about simple diffusion and that involves no help whatsoever by any sort of proteins, transport proteins or transporting molecules, anything like that. It just as it says, with simple molecules diffuse directly through the cell membrane and those would be small, non polar molecules that can make their way through um than the hydrophobic interior of the cell membrane. But that's not what we have here because we specifically have porn's which are membrane proteins. So we do not have simple diffusion since we've got a membrane protein helping the molecules go through. So now we move on to choice be facilitated diffusion. So, facilitated diffusion is when the transport is favored um it's going with or down, I should say, a concentration gradient. It doesn't need any energy to make it happen. But it does need some sort of helper. It needs a protein to get through the membrane to get across the membrane. And that is what we are having here because there's no sort of active transport. There's no use of energy by these proteins or carrier molecules or anything like that. The porn's just allow molecules to cross the cell membrane that wouldn't be able to diffuse by themselves. So, Choice B facilitated diffusion will be our answer. But for the sake of thoroughness, we'll just keep going here. Choice C active transport is when you require energy to transport across the membrane. So this would be when you're transporting compounds against a concentration gradient, higher concentration in the cell or outside of the cell, and you are transporting those molecules in the direction of higher concentration. So that requires an input of energy. It's active transport, but that's not what porn's do. So, Choice C is not our answer. And then obviously, Choice D all of the above cannot be correct, since we've only got one correct answer here. So porn czar membrane proteins that help transport molecules by choice be facilitated diffusion. Hope to see in the next video.

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Key Concepts

Aquaporins

Kidney Function and Water Reabsorption

Physiological Responses to Hydration Status