Quiz 5: A Closer Look at Cell Membranes


The white blood cells (WBCs) especially macrophages are phagocytic in nature. They engulf and break down the worn-out (dead) red blood cells (RBC) and removed from blood circulation in spleen and liver. In these organs, the break-down products of RBC are recycled. So, the worn-out RBCs are disposed of by WBC through phagocytosis or cell eating a type of endocytosis process.

The cell membranes are made up of mainly two components: phospholipids and proteins. The each phospholipid composed of phosphate-containing hydrophilic head and two hydrophobic fatty acid tails. These phospholipids and arranged in two layers. This is called a lipid bilayer. Hence, the correct option is ( c ) lipid bilayer and proteins. The bilayer in cell membrane is made up of phospholipids only. Carbohydrates and proteins do not form a bilayer. So, the options (a) and (b) are incorrect.

The Paramecium is surrounded by a hypotonic solution in which concentration of solutes is less than that of cytoplasm of Paramecium. We know that, water moves from low solute concentration to high solute concentration. So, water in solution surrounding the Paramecium moves constantly in to the cell which is then removed by the contractile vacuole.

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