3.2.3 Cell Membrane Structure

What is the basic structure of all cell membranes, including cell-surface membranes and the membranes around cell organelles of eukaryotes?

• Double helix

• Fluid-mosaic model

• Solid matrix

• Crystal lattice

Answer explanation

The fluid-mosaic model describes the structure of all cell membranes, including cell-surface membranes and organelle membranes in eukaryotes. It highlights the fluid nature of the lipid bilayer and the mosaic of proteins embedded within.

In the fluid-mosaic model, which component is primarily responsible for restricting the movement of other molecules in the membrane?

• Phospholipids

• Proteins

• Cholesterol

• Glycoproteins

Answer explanation

Cholesterol is primarily responsible for restricting the movement of other molecules in the membrane by fitting between phospholipids, thereby stabilizing the membrane structure and reducing fluidity.

Which of the following is NOT a component of the fluid-mosaic model of membrane structure?

• Phospholipids

• Proteins

• Glycolipids

• Nucleic acids

Answer explanation

The fluid-mosaic model includes phospholipids, proteins, and glycolipids as key components of the cell membrane. Nucleic acids, however, are not part of this model, making it the correct answer.

What is the primary role of phospholipids in the cell membrane?

• Energy storage

• Structural framework

• Genetic information

• Enzymatic activity

Answer explanation

Phospholipids form the structural framework of the cell membrane, creating a bilayer that provides integrity and fluidity, essential for cell function. They do not primarily serve in energy storage, genetic information, or enzymatic activity.

Which component of the cell membrane is involved in cell recognition and signalling?

• Phospholipids

• Proteins

• Glycoproteins

• Cholesterol

Answer explanation

Glycoproteins are essential for cell recognition and signaling as they have carbohydrate groups attached, allowing cells to communicate and identify each other. This function is crucial for immune response and tissue formation.

What characteristic of the fluid-mosaic model allows for the movement of proteins within the membrane?

• Rigid structure

• Fluidity

• Fixed positions

• Solid state

Answer explanation

The fluidity of the fluid-mosaic model allows proteins to move laterally within the membrane, enabling dynamic interactions and functions. This characteristic is essential for cellular processes, unlike rigid or fixed structures.

Which of the following best describes the arrangement of phospholipids in the cell membrane?

• Randomly scattered

• Single layer

• Bilayer

• Triple layer

Answer explanation

The cell membrane is primarily composed of a phospholipid bilayer, where two layers of phospholipids arrange themselves with hydrophilic heads facing outward and hydrophobic tails inward, providing structure and fluidity.

How does cholesterol affect the fluidity of the cell membrane?

• Increases fluidity

• Decreases fluidity

• Has no effect

• Completely solidifies the membrane

Answer explanation

Cholesterol decreases the fluidity of the cell membrane by fitting between phospholipids, making the membrane less permeable and more rigid. This stabilizes the membrane structure, especially at higher temperatures.