Quiz: Cell Membrane Function and Transport — 10 perguntas

1. What is the structure of the cell membrane primarily composed of?

A. A single layer of glycoproteins forming a protective barrier.

B. A phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

C. A rigid layer of cellulose fibers providing support.

D. A lattice of protein fibers creating a fixed framework.

Answer: (B)

Explicação

The cell membrane is primarily composed of a phospholipid bilayer, which provides a semi-permeable barrier. Embedded within this bilayer are various proteins, cholesterol molecules, and carbohydrates, which contribute to its fluid mosaic structure. This composition allows the membrane to be flexible, dynamic, and functional in cellular processes such as transport, signaling, and interaction with the environment.

2. What is the primary structural component of the cell membrane that forms its semi-permeable barrier?

A. Glycocalyx

B. Phospholipid bilayer

C. Cholesterol

D. Integral proteins

Answer: (B)

Explicação

The phospholipid bilayer is the fundamental structure of the cell membrane, creating a semi-permeable barrier that regulates substance movement.

3. What ions does the sodium-potassium pump (Na+/K+ ATPase) move across the cell membrane, and in what quantities per ATP hydrolyzed?

A. It moves 4 Na+ ions out and 4 K+ ions in per ATP hydrolyzed.

B. It moves 1 Na+ ion out and 1 K+ ion in per ATP hydrolyzed.

C. It moves 2 Na+ ions out and 3 K+ ions in per ATP hydrolyzed.

D. It moves 3 Na+ ions out and 2 K+ ions in per ATP hydrolyzed.

Answer: (D)

Explicação

The sodium-potassium pump (Na+/K+ ATPase) moves 3 sodium ions (Na+) out of the cell and 2 potassium ions (K+) into the cell for each molecule of ATP hydrolyzed. This activity is essential for maintaining the cell's electrochemical gradients, which are critical for functions such as nerve impulse transmission and muscle contraction.

4. Which model describes the cell membrane as a dynamic, flexible structure composed of various molecules?

A. Phospholipid Model

B. Fluid Mosaic Model

C. Cholesterol Model

D. Glycocalyx Model

Answer: (B)

Explicação

The Fluid Mosaic Model describes the cell membrane as a flexible, dynamic structure made of phospholipids, proteins, cholesterol, and carbohydrates.

5. What is the primary role of membrane potential in cells?

A. To regulate the cell's pH balance

B. To facilitate electrical signaling in excitable cells

C. To synthesize ATP for cellular energy

D. To generate mechanical force for cell movement

Answer: (B)

Explicação

The membrane potential's main function is to facilitate electrical signaling, particularly in excitable cells like neurons and muscle cells. It allows these cells to rapidly respond to stimuli by generating and propagating electrical signals such as action potentials, which are essential for nerve communication and muscle contraction.

6. What role does cholesterol play in the cell membrane?

A. It acts as an enzyme in signal transduction.

B. It maintains membrane fluidity and stability.

C. It forms the carbohydrate-rich glycocalyx.

D. It facilitates the active transport of ions.

Answer: (B)

Explicação

Cholesterol molecules are interspersed within the phospholipid bilayer, helping to maintain membrane fluidity and stability.

7. Which components of the cell membrane are involved in cell recognition and immune response?

A. Integral proteins

B. Glycocalyx (glycoproteins and glycolipids)

C. Cholesterol molecules

D. Peripheral proteins

Answer: (B)

Explicação

The glycocalyx, composed of glycoproteins and glycolipids, plays roles in cell recognition, adhesion, and immune response.

8. Which type of membrane transport involves movement of substances without energy, driven by gradients?

A. Active transport

B. Facilitated diffusion

C. Endocytosis

D. Exocytosis

Answer: (B)

Explicação

Facilitated diffusion is a passive transport mechanism where molecules move along their concentration gradient with assistance from specific proteins.

9. What is an example of small, nonpolar molecules that diffuse freely through the membrane?

A. Glucose

B. Na+ ions

C. Oxygen (O₂)

D. Protein ions

Answer: (C)

Explicação

Oxygen, being small and nonpolar, diffuses freely through the phospholipid bilayer, unlike polar or larger molecules like glucose or ions.

10. Approximately when was the Fluid Mosaic Model proposed, and by whom?

A. 1925 by Robertson

B. 1972 by Singer and Nicolson

C. 1953 by Watson and Crick

D. 1980 by Alberts et al.

Answer: (B)

Explicação

The Fluid Mosaic Model was proposed in 1972 by Singer and Nicolson, fundamentally changing our understanding of membrane structure.