Question

Of the following molecules, which would NOT be expected to be moved across a membrane by simple diffusion?

1) oxygen
2) fatty acids
3) water
4) glucose
5) dimethylurea

Answer 1

In simple diffusion, small nonpolar molecules can pass through a membrane, but larger polar molecules need transmembrane proteins. Glucose would not be expected to be moved across a membrane by simple diffusion.

Step-by-step explanation:

In simple diffusion, molecules move across a membrane from an area of higher concentration to an area of lower concentration. The molecules that can move across the membrane without any assistance are small, nonpolar molecules. Examples of such molecules include oxygen and carbon dioxide gases.

However, larger, polar molecules like glucose and dimethylurea cannot easily pass through the plasma membrane's lipid core due to their hydrophilic properties. These molecules need the help of various transmembrane proteins (channels) to transport themselves across the membrane.

Therefore, the molecule that would NOT be expected to be moved across a membrane by simple diffusion is glucose.