Question 1

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

Accepted Answer

Their amphipathic nature, with hydrophilic heads and hydrophobic tails, causes them to arrange so that tails are shielded from water and heads face outward.

Question 2

A cell membrane is described as a 'fluid mosaic.' Which property of the membrane does the term 'fluid' refer to?

Accepted Answer

The lateral movement of lipids and some proteins within the bilayer.

Question 3

Which of the following molecules would most easily cross a pure phospholipid bilayer without the aid of a protein transporter?

Accepted Answer

Oxygen ($$O_2)$$

Question 4

What is the main structural difference between saturated and unsaturated fatty acids, and how does this affect membrane fluidity?

Accepted Answer

Unsaturated fatty acids have one or more double bonds causing kinks, which increase membrane fluidity.

Question 5

A red blood cell is placed in a hypotonic solution. What will happen to the cell and why?

Accepted Answer

Water will enter the cell by osmosis, causing it to swell and possibly burst.

Question 6

Which of the following best describes the role of membrane proteins in the plasma membrane?

Accepted Answer

They perform specialized functions such as transport, signaling, and anchoring.

Question 7

Which of the following is an example of primary active transport?

Accepted Answer

The $$Na^+/K^+$$ pump using ATP to move ions against their concentration gradients.

Question 8

Why do cells rely on transport proteins for the movement of glucose across the plasma membrane?

Accepted Answer

Glucose is a large, uncharged polar molecule and cannot easily cross the hydrophobic core of the lipid bilayer.

Question 9

Which of the following statements about osmosis is correct?

Accepted Answer

Osmosis is the net movement of water from an area of high free water concentration to an area of low free water concentration across a semipermeable membrane.

Question 10

A mutation causes a membrane protein to lose its ability to change conformation. Which process would be most directly affected?

Accepted Answer

Active transport by carrier proteins, such as the $$Na^+/K^+$$ pump.

Question 11

Which of the following best explains why large, uncharged polar molecules like sucrose have low permeability across the phospholipid bilayer?

Accepted Answer

They cannot easily pass through the hydrophobic core of the membrane.

Question 12

Which of the following best describes the arrangement of phospholipids in a biological membrane?

Accepted Answer

Hydrophilic heads face outward toward water, and hydrophobic tails face inward, away from water.

Question 13

Which of the following is a property of the plasma membrane that allows it to maintain distinct internal and external environments?

Accepted Answer

Selective permeability

Question 14

What is the main function of the endomembrane system in eukaryotic cells?

Accepted Answer

To compartmentalize the cell and facilitate specialized functions by enclosing organelles with membranes.

Question 15

Which of the following best describes the process of facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient through a membrane protein, without energy input.

Question 16

A scientist observes that a certain membrane protein is only found on the cytoplasmic side of the plasma membrane. This protein is most likely:

Accepted Answer

A peripheral membrane protein.

Question 17

Which of the following best explains why flipping of phospholipids from one leaflet of the bilayer to the other is rare?

Accepted Answer

It requires the hydrophilic head to pass through the hydrophobic core, which is energetically unfavorable.

Question 18

Which of the following is a correct sequence of events for a protein destined to be secreted from a eukaryotic cell?

Accepted Answer

Synthesis on rough ER → transport to Golgi → packaging into vesicles → exocytosis

Question 19

Which of the following best describes the driving force for simple diffusion across a membrane?

Accepted Answer

The concentration gradient of the substance

Question 20

A patient is given an intravenous solution that is hypertonic relative to their blood plasma. What is the most likely effect on their red blood cells?

Accepted Answer

Water will leave the cells, causing them to shrink (crenate).

Lipids, Membranes, and Cell Compartments: Study Guide

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