Question

What features of a biological membrane are major contributors to its selective permeability? a. phospholipid bilayer b. transport proteins c. glycolipids on the outer surface of the membrane d. peripheral membrane proteins e. both a and b

Short answer

The answer is e. Both a (the phospholipid bilayer) and b (the transport proteins) are major contributors to the selective permeability of a biological membrane.

Step-by-step solution

Identify the Components

The given components are phospholipid bilayer, transport proteins, glycolipids, and peripheral membrane proteins.

Understand the Function of Each Component

The phospholipid bilayer forms the basic structure of the biological membrane and allows or restricts the passage of certain substances. The transport proteins assist in the movement of substances that cannot easily pass through the lipid bilayer. The glycolipids on the outer surface of the membrane and the peripheral membrane proteins mainly serve other functions and do not have a significant impact on the selective permeability.

Select the Correct Answer

Based on the roles of each component, it can be concluded that both the phospholipid bilayer and the transport proteins are the major contributors to the selective permeability of a biological membrane.

Key concepts

Phospholipid Bilayer

The phospholipid bilayer forms the fundamental framework of a biological membrane. It's composed of two layers of phospholipids, with their hydrophobic tails facing inward and their hydrophilic heads facing outward. This orientation creates a barrier that is crucial for maintaining the integrity of cells.

The bilayer serves as a selective barrier due to its lipophilic nature. Hydrophobic or non-polar molecules can diffuse easily across the bilayer, while polar or charged particles are restricted. This unique structure ensures that essential molecules like oxygen and carbon dioxide pass freely, while others require assistance.

• Hydrophobic core: Blocks ions and polar molecules.
• Allows small and non-polar molecules to pass.

The phospholipid bilayer plays a critical role in selectively allowing substances to enter or exit the cell, maintaining an optimal internal environment.

Transport Proteins

Transport proteins are essential components embedded within the biological membrane. They are key contributors to the membrane's selective permeability, enabling substances that cannot diffuse through the lipid bilayer to enter or exit the cell.

These proteins come in various forms and serve various functions:

• Channel Proteins: Form open channels allowing specific molecules or ions to diffuse.
• Carrier Proteins: Bind and transport substances across the membrane by changing shape.

Some transport proteins require energy, often in the form of ATP, to actively transport molecules against a concentration gradient. This process is known as active transport, and it's crucial for maintaining concentration differences of ions and other critical substances across the membrane.

Biological Membrane

A biological membrane not only defines the boundary of a cell but also plays a multifunctional role in its physiology and interaction with the environment. It features a semipermeable nature, which is pivotal for various cellular processes.

The primary structure of a biological membrane consists of the phospholipid bilayer embedded with proteins and, in some cases, carbohydrates. This dynamic combination allows the membrane to be flexible and adapt to different conditions. The membrane's selective permeability helps in regulating the cell's chemical balance and energy usage, enabling cells to thrive in varying environments.

• Provides structural support and protection.
• Helps in communication and signal transduction with cellular surroundings.
• Aids in transport and compartmentalization of cellular processes.

Thus, the biological membrane plays a crucial role in the life of a cell, closely linked to its identity and functionality.