Question 1

Which property of phospholipids is primarily responsible for the formation of the plasma membrane bilayer?

Accepted Answer

Their amphipathic nature, having both hydrophilic and hydrophobic regions.

Question 2

A scientist observes that a cell membrane becomes more rigid as the temperature decreases. Which change in membrane composition would help maintain fluidity at lower temperatures?

Accepted Answer

Increase the proportion of unsaturated fatty acids in the membrane.

Question 3

Which of the following best describes the fluid mosaic model of the plasma membrane?

Accepted Answer

A bilayer of phospholipids with proteins embedded and moving within it.

Question 4

What is the main function of membrane carbohydrates in cell recognition?

Accepted Answer

They help cells distinguish 'self' from 'non-self' by binding to specific molecules.

Question 5

Which type of membrane protein penetrates the hydrophobic core of the lipid bilayer?

Accepted Answer

Integral membrane proteins

Question 6

A patient receives a blood transfusion with the wrong blood type. Which membrane component is most directly responsible for the immune reaction?

Accepted Answer

Cell-surface glycoproteins with specific carbohydrate chains

Question 7

Which of the following molecules can most easily cross the plasma membrane by simple diffusion?

Accepted Answer

Oxygen ($$\mathrm{O_2$})$$

Question 8

What is the effect of cholesterol on membrane fluidity at high and low temperatures?

Accepted Answer

It decreases fluidity at high temperatures and increases fluidity at low temperatures.

Question 9

Which equation best describes the net movement of molecules during diffusion?

Accepted Answer

$$J = -D \frac{dC}{dx}$$

Question 10

A researcher fuses a mouse cell and a human cell, each with differently labeled membrane proteins. After one hour, the labels are mixed throughout the hybrid cell membrane. What does this experiment demonstrate?

Accepted Answer

Membrane proteins can move laterally within the plane of the membrane.

Question 11

Which of the following statements about passive transport is correct?

Accepted Answer

It relies on the potential energy of the concentration gradient.

Question 12

A bacterium is found living in hot springs. Which membrane adaptation would you expect to find?

Accepted Answer

A membrane rich in saturated fatty acids.

Question 13

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

Accepted Answer

Energy storage

Question 14

Why do polar molecules such as glucose require transport proteins to cross the plasma membrane?

Accepted Answer

They are repelled by the hydrophobic core of the lipid bilayer.

Question 15

Which of the following best explains why the plasma membrane is described as 'selectively permeable'?

Accepted Answer

It allows some substances to cross more easily than others.

Question 16

During membrane synthesis, what determines the asymmetric distribution of proteins, lipids, and carbohydrates in the plasma membrane?

Accepted Answer

The processes occurring in the endoplasmic reticulum and Golgi apparatus.

Question 17

Which of the following is a real-world example of cell recognition mediated by membrane carbohydrates?

Accepted Answer

The determination of human blood types (A, B, AB, O).

Question 18

If a cell is placed in a solution with a higher concentration of solutes than inside the cell, which direction will water move by diffusion?

Accepted Answer

Out of the cell

Question 19

Which of the following statements about the movement of molecules across the plasma membrane is correct?

Accepted Answer

Each substance diffuses down its own concentration gradient independently.

Question 20

Which of the following best describes the role of the hydrophobic tails in the phospholipid bilayer?

Accepted Answer

They form the interior of the membrane, shielding themselves from water.

Chapter 7: Membrane Structure and Function – Study Notes

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