Answer:
1. The three main functions of the cell membrane are:
- To act as a barrier or boundary between the cell and its environment, controlling the movement of substances in and out of the cell.
- To maintain the shape and integrity of the cell by providing structural support.
- To facilitate communication between the cell and its surroundings through various membrane proteins and receptors.
2. Hydrophilic refers to molecules that are attracted to water and can dissolve in it, while hydrophobic refers to molecules that repel water and are not soluble in it.
3. The structure of the cell membrane, which is composed of a phospholipid bilayer with embedded proteins and carbohydrates, allows it to selectively transport molecules and ions in and out of the cell, maintaining a balance of substances and preventing the buildup of harmful substances. The membrane also helps to regulate the cell's internal environment by responding to external signals and changing its permeability accordingly.
4. The structure of the cell membrane can be visualized as a fluid mosaic model, where the phospholipid bilayer acts as a fluid matrix with embedded proteins, carbohydrates, and cholesterol molecules. The hydrophobic tails of the phospholipids face inward, while the hydrophilic heads face outward towards the aqueous environments inside and outside the cell. The membrane also contains various types of proteins that serve different functions, such as transporters, channels, receptors, and enzymes.