B2.1.1 Understanding Cell Membranes

Which of the following is NOT a component of the cell membrane?

• Phospholipids

• Ribosomes

• Cholesterol

• Proteins

Answer explanation

Ribosomes are not components of the cell membrane; they are involved in protein synthesis. In contrast, phospholipids, cholesterol, and proteins are essential components that make up the cell membrane structure.

What is the primary function of the cell membrane?

• To store genetic information.

• To provide structural support to the cell.

• To produce energy for the cell.

• To regulate the movement of substances in and out of the cell.

Answer explanation

The primary function of the cell membrane is to regulate the movement of substances in and out of the cell, maintaining homeostasis and allowing communication with the environment.

Which component of the membrane is primarily responsible for forming the bilayer?

• Phospholipids

• Cholesterol

• Proteins

• Carbohydrates

Answer explanation

Phospholipids are the primary components that form the bilayer of cell membranes. Their hydrophilic heads face outward while the hydrophobic tails face inward, creating a stable bilayer structure essential for membrane function.

What is the key difference between hydrophobic and hydrophilic substances?

• Hydrophobic substances repel water; hydrophilic substances attract water.

• Hydrophobic substances attract water; hydrophilic substances repel water.

• Hydrophobic substances are always solid; hydrophilic substances are always liquid.

• Hydrophobic substances dissolve in water; hydrophilic substances do not.

Answer explanation

The key difference is that hydrophobic substances repel water, making them non-polar and unable to mix with water, while hydrophilic substances attract water, being polar and able to dissolve in it.

What role do proteins play in the cell membrane?

• Proteins play roles in signaling, transport, structure, and cell recognition in the cell membrane.

• Proteins are only involved in the genetic material of the cell membrane.

• Proteins act as a barrier to prevent all substances from entering the cell.

• Proteins are primarily responsible for energy production in the cell membrane.

Answer explanation

Proteins in the cell membrane are crucial for various functions, including signaling, transport of substances, providing structural support, and facilitating cell recognition, making the first answer choice correct.

Which of the following substances can easily pass through the cell membrane?

• Ions (e.g., sodium, potassium)

• Charged molecules (e.g., amino acids)

• Large polar molecules (e.g., glucose)

• Small nonpolar molecules (e.g., oxygen, carbon dioxide)

Answer explanation

Small nonpolar molecules, like oxygen and carbon dioxide, can easily pass through the cell membrane due to their size and lack of charge, allowing them to diffuse freely. Other substances face barriers due to size or charge.

What is the term for the movement of water across a selectively permeable membrane?

• Diffusion

• Filtration

• Osmosis

• Evaporation

Answer explanation

The movement of water across a selectively permeable membrane is called osmosis. This process allows water to move from an area of lower solute concentration to an area of higher solute concentration, maintaining balance.

What is the function of cholesterol in the cell membrane?

• Cholesterol stabilizes cell membrane fluidity.

• Cholesterol acts as a primary energy source for the cell.

• Cholesterol is responsible for protein synthesis in the membrane.

• Cholesterol increases membrane permeability.

Answer explanation

Cholesterol plays a crucial role in maintaining cell membrane fluidity by preventing the fatty acid chains from packing too closely together, thus ensuring the membrane remains flexible and functional.

What is the fluid mosaic model?

• A diagram illustrating the process of photosynthesis.

• A theory explaining the movement of water in plants.

• A model that describes the rigidity of cell walls.

• The fluid mosaic model is a conceptual model that describes the structure of cell membranes as a dynamic and flexible arrangement of various molecules.

Answer explanation

The fluid mosaic model accurately describes cell membranes as dynamic structures composed of various molecules, unlike the other options which do not pertain to cell membrane structure.

What is the role of receptor proteins in the cell membrane?

• Receptor proteins transport nutrients into the cell.

• Receptor proteins provide structural support to the cell membrane.

• Receptor proteins act as enzymes to speed up chemical reactions.

• Receptor proteins facilitate communication between the cell and its environment by binding to signaling molecules.

Answer explanation

Receptor proteins are crucial for cell communication. They bind to signaling molecules, allowing the cell to receive and respond to external signals, which is essential for various cellular processes.