What statement best describes the difference in how water and glucose can move across a plasma membrane?

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Biology

Drew Hammond

29 February, 18:41

What statement best describes the difference in how water and glucose can move across a plasma membrane?

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Mayra Holloway · Answer 1

Water moves across a plasma membrane by osmosis while glucose moves across a plasma membrane by facilitated diffusion.

Animal cells are surrounded by a cell membrane. This membrane has tiny holes in it which allows small molecules (such as water molecules) to pass through but not large ones (such as glucose molecules). Due to this, the nature of the cell membrane is described as being partially (or selectively) permeable.

When the concentration of solutes such as salts in the cell cytoplasm fluids is higher, water molecules from the fluid outside the cell will simply leave this fluid and pass into the cell through the semi permeable membrane so that there is a balance of concentration between the outside and inside of the cell. This is osmosis.

Glucose on the other hand first binds to a carrier protein which then changes shape so that it can fit into the hole in the cell membrane. It is then carried in this fashion by the carrier protein through this hole and into the cell. This is facilitated diffusion.