Question 1

Which structural feature of unsaturated fatty acids is responsible for increasing membrane fluidity at lower temperatures?

Accepted Answer

The presence of cis double bonds that introduce kinks in the hydrocarbon tails, preventing tight packing.

Question 2

A cell membrane is described as 'fluid.' Which of the following factors would most likely decrease its fluidity?

Accepted Answer

Increasing the proportion of saturated fatty acids in the phospholipids.

Question 3

Which of the following best describes the amphipathic nature of phospholipids?

Accepted Answer

They contain both hydrophilic (polar) heads and hydrophobic (nonpolar) tails.

Question 4

Which of the following molecules can most easily diffuse through the hydrophobic interior of a cell membrane without the aid of a transport protein?

Accepted Answer

Oxygen ($O_2$)

Question 5

The Frye & Edidin (1970) experiment demonstrated that membrane proteins are able to move within the lipid bilayer. What property of the membrane does this experiment support?

Accepted Answer

Membrane fluidity

Question 6

Which of the following statements about cholesterol in animal cell membranes is correct?

Accepted Answer

Cholesterol acts as a fluidity buffer, restricting movement of phospholipids at high temperatures and preventing tight packing at low temperatures.

Question 7

Which type of membrane protein spans the entire lipid bilayer, having domains exposed to both the extracellular and cytoplasmic sides?

Accepted Answer

Transmembrane protein

Question 8

A scientist observes that a certain cell membrane contains a high percentage of unsaturated phospholipids during winter. What is the most likely reason for this adaptation?

Accepted Answer

To maintain membrane fluidity at lower temperatures.

Question 9

Which of the following is a correct description of facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient via membrane proteins without energy input.

Question 10

Which of the following best explains why ions and polar molecules cannot easily cross the lipid bilayer?

Accepted Answer

The hydrophobic interior of the bilayer repels charged and polar substances.

Question 11

Which of the following is the correct general formula for a saturated fatty acid with 16 carbons (palmitic acid)?

Accepted Answer

$C_{16}H_{32}O_2$

Question 12

Which of the following membrane models was disproven by the freeze-fracture method, which showed proteins embedded within the bilayer?

Accepted Answer

Davson-Danielli model

Question 13

Which of the following statements about osmosis is correct?

Accepted Answer

Osmosis is the movement of water across a semi-permeable membrane down its concentration gradient.

Question 14

Which of the following is a real-world example of a channel protein facilitating diffusion?

Accepted Answer

Aquaporin allowing water molecules to cross the membrane.

Question 15

Which of the following would most likely be found in the hydrophobic core of a membrane protein?

Accepted Answer

Nonpolar amino acid residues

Question 16

A mutation causes a cell to produce only saturated fatty acids in its membrane phospholipids. What is a likely consequence for the cell at low temperatures?

Accepted Answer

The membrane may become too rigid and lose permeability.

Question 17

Which of the following best describes the role of membrane fluidity in cellular function?

Accepted Answer

It allows membrane proteins to move to where their function is needed and maintains proper permeability.

Question 18

Which of the following is a correct description of a triglyceride molecule?

Accepted Answer

It consists of three fatty acids esterified to a glycerol backbone.

Question 19

Which of the following adaptations would you expect in the membrane lipids of bacteria living in hot springs (temperatures > 90°C)?

Accepted Answer

Unusual lipids that prevent excessive fluidity at high temperatures.

Question 20

Which of the following statements about peripheral membrane proteins is correct?

Accepted Answer

They are associated with the outer surfaces of the membrane and do not span the bilayer.

Biological Macromolecules and Membrane Structure & Function: Lipids and Membranes

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