Arrange the following molecules according to increasing rate of diffusion across a lipid bilayer without the aid of any membrane protein: glucose, Ca2 N2, H2O. N2 < H2O < glucose < Ca2 glucose < Ca2 < N2 < H2O Ca2 < glucose < H2O < N2

Ca2 < glucose < H2O < N2

Explanation:

The plasma membrane is a semipermeable membrane because it only allows selective molecules to cross through it. Gases are transported fast through simple diffusion so N2 will be diffused first.

H2O moves from high concentration to lower concentration by a type of simple diffusion called osmosis. Glucose are larger molecules that require transport proteins for moving along the concentration gradient. This is called facilitated diffusion.

Calcium ions require energy and membrane proteins to be transported across the cell membrane. Therefore the correct answer is Ca2 < glucose < H2O < N2.

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