Question

What is meant by the plasma membrane?

Answer 1

Hint: Cell membrane is also known as the plasma membrane or cytoplasmic membrane. It is the outermost covering of the animal cell. It (plasma membrane) separates the interior of the cell from the outside environment. The cell membrane is living and provides definite shape to the cell and holds the content of the cell.

Complete answer:The plasma membrane is a part of the cell. In animal cells, the cell membrane is the outermost covering of the cell, but in a plant cell, the cell membrane is surrounded by a cell wall. The cell membrane is semipermeable. The plasma membrane controls the movement of substances in and out of the cells and organelles.
Composition of the cell membrane -The cell membrane is made up of proteins, lipids, and carbohydrates.Proteins contribute 60-70%, lipids(phospholipids and cholesterol)contribute 20-40% and carbohydrates contribute 2-10%.
The structure of the cell membrane - The cell membrane is made up of phospholipid bilayer. Phospholipid molecules are made up of two regions - one is the phosphate head (hydrophilic)and one is the fatty acid tail(hydrophobic). These phospholipid molecules are placed in such a way that their head region is facing outward and the tail region is placed in between facing each other.
The fluid mosaic model-This is the most accepted model which explains the structure of the cell membrane. According to this model various structure present in the cell membrane are -
1.Cholestrol-This molecule is embedded in the hydrophobic region and provides rigidity and flexibility to the cell. When the temperature of the cell is high then this cholesterol molecule provides rigidity to the cell and the temperature of the cell is low, then the cholesterol molecule provides flexibility to the cell
2.Glycolipid- made up of carbohydrate molecule and lipid molecule.
3.Gylcoprotien-it is made up of carbohydrates and protein.
4.Protein-These are of two types -intrinsic and extrinsic. Intrinsic proteins are present in between two phospholipid membranes and extrinsic proteins are present externally to the phospholipid membrane.
The function of the cell membrane -The cell membrane is semipermeable, that is it allows the only movement of an only selected molecule across it. The cell membrane gives strength, support, and protection to the cell. Cell membrane helps in cell recognition and immunity.

Note: Aquaporin proteins help in the transportation of water. Nonpolar small molecules like oxygen and carbon dioxide are transported by diffusion. Some molecules like glucose, water ions are transported by passive transfer. Some ions like Na+, K+ are transported by active transfer.