In the plasma membrane, the phospholipid molecules are oriented so that the heads are facing the outside environment and the of the membrane. tails are facing the interior
A) hydrophilic, hydrophobic
B) ectothermic, endothermic
C) heterotrophic, autotrophic
D) autotrophic, heterotrophic
E) hydrophobic, hydrophilic
The Correct Answer and Explanation is :
Correct Answer:
A) hydrophilic, hydrophobic
Explanation:
The plasma membrane is a selectively permeable barrier composed primarily of a phospholipid bilayer, with embedded proteins, cholesterol, and carbohydrates. The structure and orientation of phospholipids in the bilayer are crucial for its function. Phospholipids are amphipathic molecules, meaning they have both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.
- Phospholipid Structure:
- Head: The “head” of a phospholipid is made up of a phosphate group attached to glycerol. This region is polar and hydrophilic due to its ability to interact with water molecules through hydrogen bonding.
- Tails: The “tails” consist of two long fatty acid chains, which are nonpolar and hydrophobic. These tails repel water and interact with each other instead.
- Orientation in the Bilayer:
In an aqueous environment, such as inside and outside the cell, phospholipids organize themselves into a bilayer:
- The hydrophilic heads face outward, toward the aqueous extracellular fluid and intracellular cytoplasm.
- The hydrophobic tails face inward, shielded from water, creating the interior of the bilayer.
- Functionality:
This arrangement:
- Maintains the membrane’s integrity and prevents water-soluble substances from freely crossing the membrane.
- Creates a dynamic barrier that supports membrane fluidity and flexibility.
- Allows selective transport of substances via embedded proteins, ensuring the cell’s internal environment is regulated.
- Significance:
The hydrophilic heads interacting with water enable the membrane to remain stable in an aqueous environment. Simultaneously, the hydrophobic core restricts the passage of polar molecules and ions, maintaining cellular homeostasis. This dual property of phospholipids ensures the plasma membrane serves as both a protective barrier and a medium for controlled interactions with the environment.