Cells transport molecules into the cell in many different ways. one method is through endocytosis, shown in the model. in endocytosis, the cell brings specific molecules it needs, finding fluid, into the cell. why does the structure of the plasma membrane make this type of transport necessary for fluids?

Yes structure of membrane is necessary to transport these fluids.

The method of transport of fluids into the cells by using the plasma membrane is called pinocytosis or endocytosis. In this method, first the cell finds a fluid that is suitable to be taken inside the cell for further necessities like nutrition, immunity etc. Then the cell produce some pseudopodia which covers up the fluid. Then a depression in cell membrane is seen engulfing the fluid and the margins of that depressed part approximates, resulting in punching off the portion of cell membrane into the cell, forming a secondary lysozome. This is seen in figure.

Without the help of the plasma membrane, the engulfing of the fluid by the cell is impossible, so plasma membrane structure is important for endocytosis.

equal distribution i think.

yes, because even though a theory has a  lot of evidence to support it, it is not always true