Freeman bio chapter 6 practice questions

Why are lipids insoluble in water

​They are made mostly of nonpolar C–H bonds, which can’t form hydrogen bonds with water.

Saturated vs. unsaturated fatty acid

​Saturated: only single C–C bonds, maximum H, straight, solid at room temp. Unsaturated: one or more C=C double bonds causing kinks, liquid at room temp.

What is a fat (triglyceride) made of

​One glycerol + three fatty acids, joined by ester linkages formed in dehydration reactions.

Why aren’t fats considered polymers

​Their fatty acids aren’t linked together into a chain of repeating monomers; each attaches to glycerol.

Structure of a phospholipid

​Glycerol + phosphate-containing hydrophilic head + two hydrophobic hydrocarbon tails.

What does amphipathic mean

​Having both hydrophilic and hydrophobic regions (e.g., phospholipids, cholesterol).

Micelle vs. bilayer

​Micelle: small sphere, tails inward, typical of single-tailed free fatty acids. Bilayer: two sheets with tails facing each other, typical of phospholipids.

Why do bilayers form spontaneously if lipids become more ordered

​Clustering tails releases ordered water that was caged around them, so total entropy increases.

Which molecules cross a bilayer fastest

​Small, nonpolar molecules like O₂ and CO₂. Ions cross slowest.

Four things that decrease membrane permeability​Longer tails, more saturated tails, more cholesterol, lower temperature.

Define osmosis​

Diffusion of water across a selectively permeable membrane, from low solute concentration to high solute concentration.

Cell in a hypertonic solution

​Water leaves; the cell shrinks (crenation in red blood cells, plasmolysis in plant cells).

Cell in a hypotonic solution

​Water enters; animal cells swell and can lyse; plant cells become turgid.

Integral vs. peripheral protein

​Integral (transmembrane) spans the bilayer; peripheral attaches to one surface without crossing it.

What did the Frye–Edidin experiment show

​Mouse and human membrane proteins intermixed within about an hour in fused cells, so membrane proteins move laterally.

What is facilitated diffusion

​Passive movement down a gradient through a channel or carrier protein; no energy required.

Channel vs. carrier

​Channel: a pore that ions/molecules flow through. Carrier: binds the solute and changes shape to move it (e.g., GLUT-1).

What does the Na⁺/K⁺ pump do

​Uses ATP to move 3 Na⁺ out and 2 K⁺ in, both against their gradients (active transport).

Secondary active transport

​A gradient set up by a pump powers moving another substance against its own gradient; ATP isn’t used directly.

What goes wrong in cystic fibrosis

​The CFTR chloride channel is defective, so Cl⁻ can’t leave cells and secretions become thick.