Question 1

Which of the following best explains why phospholipids spontaneously form bilayers in aqueous environments?

Accepted Answer

Their hydrophilic heads interact with water while their hydrophobic tails avoid water, resulting in a stable bilayer.

Question 2

A scientist observes that a certain fish species living in extremely cold water has a high proportion of unsaturated fatty acids in its cell membranes. What is the most likely evolutionary advantage of this adaptation?

Accepted Answer

Unsaturated fatty acids prevent membrane solidification at low temperatures, maintaining membrane fluidity.

Question 3

Which of the following statements about the fluid mosaic model is CORRECT?

Accepted Answer

Membrane proteins are embedded in a fluid bilayer of phospholipids and can move laterally within the membrane.

Question 4

A patient is found to be resistant to HIV infection. Genetic analysis reveals a mutation that prevents the expression of the CCR5 protein. Why does this mutation confer resistance?

Accepted Answer

HIV requires both the CD4 receptor and the CCR5 co-receptor to enter cells; without CCR5, HIV cannot infect the cell.

Question 5

Which of the following best describes the role of cholesterol in animal cell membranes at low temperatures?

Accepted Answer

Cholesterol prevents membrane solidification by disrupting the regular packing of phospholipids.

Question 6

A researcher labels membrane proteins in a mouse cell with a green marker and in a human cell with a red marker. After fusing the two cells, she observes that the markers mix over time. What does this experiment demonstrate?

Accepted Answer

Membrane proteins can move laterally within the plasma membrane.

Question 7

Which of the following is a function of membrane glycoproteins?

Accepted Answer

Serving as identification tags for cell-cell recognition.

Question 8

A native grass species is found growing in soil near a hot spring. Which of the following membrane adaptations would you expect to find in this plant?

Accepted Answer

A higher proportion of saturated fatty acids in its membrane lipids.

Question 9

Which of the following best explains why membrane proteins are often amphipathic?

Accepted Answer

They have hydrophobic regions that interact with the lipid bilayer interior and hydrophilic regions that interact with the aqueous environment.

Question 10

Which of the following is TRUE regarding the sidedness (asymmetry) of the plasma membrane?

Accepted Answer

The asymmetrical arrangement of proteins, lipids, and carbohydrates is established during membrane synthesis in the ER and Golgi apparatus.

Question 11

Which of the following best describes the movement of phospholipids within the plasma membrane?

Accepted Answer

They move rapidly and frequently switch positions with neighboring phospholipids within the same layer.

Question 12

Which of the following is NOT a function of membrane proteins?

Accepted Answer

Synthesis of DNA in the nucleus.

Question 13

A cell is exposed to a drug that blocks the addition of carbohydrates to proteins in the Golgi apparatus. Which of the following processes would be most directly affected?

Accepted Answer

Cell-cell recognition due to altered glycoprotein formation.

Question 14

Which of the following best explains why cholesterol is considered a 'fluidity buffer' in animal cell membranes?

Accepted Answer

It helps maintain membrane fluidity by restraining movement at moderate temperatures and preventing solidification at low temperatures.

Question 15

Which of the following scenarios best illustrates the importance of membrane fluidity for cell function?

Accepted Answer

A cell in a cold environment increases unsaturated fatty acids in its membrane to maintain protein function and permeability.

Question 16

Which of the following statements about the synthesis and transport of membrane components is CORRECT?

Accepted Answer

Glycoproteins and glycolipids are synthesized and modified in the ER and Golgi apparatus before being transported to the plasma membrane.

Question 17

Which of the following best explains why the four human blood types (A, B, AB, O) differ from each other?

Accepted Answer

They reflect variations in the carbohydrate part of glycoproteins on the surface of red blood cells.

Question 18

A bacterium is found in a hot spring with temperatures above $$70^\circC. $$Which of the following membrane adaptations would you expect to find?

Accepted Answer

Unusual lipids that prevent excessive membrane fluidity at high temperatures.

Question 19

Which of the following is a TRUE statement about the attachment of membrane proteins?

Accepted Answer

Some membrane proteins are attached to the cytoskeleton on the cytoplasmic side and to the extracellular matrix on the extracellular side.

Question 20

Which of the following best describes the difference between integral and peripheral membrane proteins?

Accepted Answer

Integral proteins penetrate the hydrophobic core of the lipid bilayer, while peripheral proteins are loosely bound to the membrane surface.

Membrane Structure and Function: The Fluid Mosaic Model

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