In a cell, what is the function of the cell membrane? a. it controls the entry and exit of substances b. it generates energy for the cell. c. it removes waste and stores ingested food. d. it only maintains the cell shape.

A

WHY?
Cell membrane is partially permeable, in order to control substances going in and out of the cell. This ensures that harmful substances do not enter the cell and that only useful substances that aids the cell in it's metabolism enters the cell.

for choice B, the only organelle that generates energy for the cell is called the mitochondria (plural = mitochondrion). The cell membrane doesn't have this function. Therefore it is wrong.

For option C, removes waste and stores ingested food refers to the function of transport vesicles and vacuoles. Although they are essentially made up of the same substance, phospholipid, their essentially different organelles. Besides this, cell membrane doesn't have the function to store food. Therefore option C is wrong.

For option D, Maintaining cell shape is the job of the Cell wall. Cell wall is made up of cellulose, a tough substance that forms a "shell" to give the cell it's shape and protect the cell from mechanical damage. The cell membrane is literally a fluid, where it's molecules are constantly moving inversely or across the plane, therefore, it has no capability to maintain the shape of the cell. Therefore, option D is wrong.

Hope I answered your question.