Mediated transport of polar molecules and ions across the plasma membrane utilizes a/n carrier that will bind to the substance, effecting a conformational change that allows movement across the membrane.
a) protein carrier
b) lipid carrier
c) porin carrier
d) all of the choices are correct

Option A) Protein carrier

Explanation:

The carrier proteins are those proteins that are involved in transfer of substances from one side to other side through plasma membrane. These are present in chloroplast, mitochondria and nucleolus.

The lipid carriers increases the absorption and solubility. These allows the transfer of non-polar molecules. The lipid carriers are used in drug delivery systems. So, this is an incorrect option.

The Porin carriers are present in the membrane of the bacteria. It allows the passive diffusion of molecules due to its large size. It only allows movement of hydrophillic substances.

The Polar molecules and ions moves across the biological membrane with the help of protein carrier. Thus, option A is correct.

the dark variety, as they are not visible on the dark tree barks

explanation: