Which of the following controls the permeability of the cell?

$A$ boy is studying the transport of a certain type of molecule into a cell. He finds that the transport slows down when the cells are poisoned with a chemical that inhibits energy production. Under normal circumstances,the molecules studied by the boy are probably transported by

Structure and function are correlatable in living organisms. Can you justify this by taking the plasma membrane as an example?

Carbohydrates are present in the plasmalemma in the form of

According to the fluid mosaic model (proposed by Singer and Nicolson),the plasma membrane is composed of:

Identify the structures marked as $A, B, C$ and $D$ with respect to the fluid mosaic model of the plasma membrane.