What does it mean for a membrane to be selectively permeable? only certain molecules are allowed to pass through. the membrane is rigid and only allows water to pass through. all types of molecules are able to pass into the cell. the membrane is rigid and nothing can enter or leave the cell.

a is the correct answer

Only certain molecules are allowed to pass through.

Correct A). Only certain molecules are allowed to pass through

The semi-permeability is the feature of the cell membrane, which show that the cell membrane allows the only selective molecule to move in and out of the cell. It only allows the movement of small molecules and ions such as sodium and potassium ions are able to move across the cell membrane. While all other molecules that are of a bigger size such as proteins are not allowed to pass through it.

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.