Question

all cells contain cell membranes. which of the following describes the composition of cell membranes?
call membranes are composed of carbohydrates chains, which allow all molecules to enter and leave the cell
call membranes are composed of cellulose, which provides rigidity for the cell
call membranes are composed of cytoplasm, which allows proteins to be excreted by the cell
call membranes are composed of lipid molecules, which provide a hydrophobic barrier to allow selective passage of molecules

Explanation:

To determine the correct description of cell membrane composition, we analyze each option:

• Option 1: Cell membranes are not composed of carbohydrate chains that allow all materials to freely enter/leave (they are selectively permeable). Eliminate.
• Option 2: Cellulose is a component of plant cell walls, not cell membranes. Eliminate.
• Option 3: Cytoplasm is inside the cell, not a component of the cell membrane. Eliminate.
• Option 4: Cell membranes are composed of lipid molecules (phospholipids) forming a hydrophobic barrier, enabling selective permeability. This matches the known structure (phospholipid bilayer with hydrophobic tails).

Answer:

The correct option is the one stating: "Cell membranes are composed of lipid molecules, which provide a hydrophobic barrier to allow selective passage of materials" (the last option in the list).