Membrane Structures and Properties
Which part of a phospholipid is nonpolar and hydrophobic?
Phosphate group
Glycerol backbone
Fatty acid tails
Polar head group
3) Fatty acid tails
Which best describes simple diffusion?
Movement of molecules against their concentration gradient, requiring ATP
Movement of molecules from high concentration to low concentration without energy
Movement of water only
Transport using protein channels only
2) Movement of molecules from high concentration to low concentration without energy
Which statement best describes facilitated diffusion?
It requires ATP to move substances across a membrane.
It moves molecules down their concentration gradient through a protein.
It pumps molecules against their concentration gradient.
It allows only gases like oxygen and carbon dioxide to cross membranes.
2) It moves molecules down their concentration gradient through a protein.
What best defines active transport?
Movement of molecules from high to low concentration without energy.
Movement of molecules against their concentration gradient using energy.
Movement of gases like O₂ and CO₂ directly across the lipid bilayer.
Movement of water through aquaporins down its gradient.
2) Movement of molecules against their concentration gradient using energy.
Which of the following processes is used by white blood cells to engulf bacteria?
Exocytosis
Pinocytosis
Phagocytosis
Facilitated diffusion
Answer: 3) Phagocytosis
Which statement best describes the “fluid mosaic model” of membranes?
Proteins are fixed in place within the phospholipid bilayer.
Lipids and proteins can move laterally within the bilayer.
Cholesterol molecules form rigid patches that prevent fluidity.
Only lipids move, while proteins remain immobile.
2) Lipids and proteins can move laterally within the bilayer.
What process describes water moving across a semipermeable membrane?
Facilitated diffusion
Osmosis
Endocytosis
Exocytosis
2) Osmosis
Which molecule is most likely to require facilitated diffusion to cross a cell membrane?
Oxygen (O₂)
Carbon dioxide (CO₂)
Glucose
Fatty acid
3) Glucose
Which of the following is an example of active transport?
Oxygen entering a red blood cell.
Sodium being pumped out of a neuron.
Water moving into a plant root by osmosis.
Glucose entering a cell through a channel protein down its gradient.
Answer: 2) Sodium being pumped out of a neuron.
What is the main function of exocytosis?
Bringing water into the cell
Releasing large molecules or waste out of the cell using vesicles
Diffusion of gases across the membrane
Pumping ions against their concentration gradient
2) Releasing large molecules or waste out of the cell using vesicles
Which factor increases membrane fluidity?
Higher proportion of saturated fatty acids
Lower temperature
Higher proportion of unsaturated fatty acids
Absence of cholesterol
3) Higher proportion of unsaturated fatty acids
If a red blood cell is placed in pure distilled water, what happens?
Water enters the cell, and it bursts.
Water leaves the cell, and it shrinks.
No net water movement occurs.
The cell pumps ions to prevent water entry.
1) Water enters the cell, and it bursts.
Facilitated diffusion differs from simple diffusion because:
It can move substances against their concentration gradient.
It uses specific proteins to allow certain molecules through.
It always requires energy input.
It can only move ions, not neutral molecules.
2) It uses specific proteins to allow certain molecules through.
Why does active transport require energy?
Molecules move in random directions.
It moves substances down their concentration gradients.
It forces molecules into regions where they are already more concentrated.
It only transports gases like O₂.
3) It forces molecules into regions where they are already more concentrated.
Pinocytosis differs from phagocytosis in that pinocytosis:
Requires ATP, while phagocytosis does not
Engulfs small fluid droplets rather than large particles
Releases materials instead of taking them in
Uses carrier proteins rather than vesicles
2) Engulfs small fluid droplets rather than large particles
In a mammalian cell exposed to cold, cholesterol helps maintain membrane function by:
Breaking down fatty acid tails to generate heat.
Preventing fatty acid tails from packing too tightly.
Making the membrane more rigid at all temperatures.
Replacing unsaturated fatty acids with saturated ones.
Answer: 2) Preventing fatty acid tails from packing too tightly
Why does facilitated diffusion differ from simple diffusion?
Facilitated diffusion requires ATP, while simple diffusion does not.
Facilitated diffusion can move molecules against the concentration gradient.
Facilitated diffusion uses membrane proteins but does not require ATP.
Simple diffusion moves ions, while facilitated diffusion moves water.
3) Facilitated diffusion uses membrane proteins but does not require ATP.
Why does facilitated diffusion eventually level off (plateau) when measuring rate vs. concentration?
The concentration gradient disappears.
ATP is depleted.
Transport proteins become saturated.
The membrane becomes impermeable.
3) Transport proteins become saturated.
The sodium-potassium pump in animal cells moves:
3 Na⁺ out and 2 K⁺ in, using ATP.
2 Na⁺ in and 3 K⁺ out, using ATP.
Only Na⁺ out, without energy.
Only K⁺ in, without energy.
1) 3 Na⁺ out and 2 K⁺ in, using ATP.
A nerve cell releasing neurotransmitters at a synapse is an example of:
Endocytosis
Exocytosis
Facilitated diffusion
Osmosis
Answer: 2) Exocytosis
A researcher engineers cells with membranes containing only saturated fatty acids and no cholesterol. Predict the main effect on these cells at low temperatures.
Membranes will remain fluid and functional.
Membranes will become too rigid, reducing protein mobility.
Membranes will become too fluid, causing leakage of ions.
No change will occur compared to normal membranes.
Answer: 2) Membranes will become too rigid, reducing protein mobility.
Which situation is the best example of osmosis in living cells?
Oxygen moving into red blood cells
Glucose entering muscle cells via transport proteins
Water moving into plant root cells from soil with lower solute concentration
Sodium ions being pumped out of nerve cells using ATP
3) Water moving into plant root cells from soil with lower solute concentration.
Insulin helps cells take up glucose from the blood. Which is the most accurate description of this process?
Insulin increases the rate of glucose diffusion by opening ion channels.
Insulin triggers insertion of glucose transport proteins into the membrane, allowing facilitated diffusion.
Insulin directly pumps glucose into cells using ATP.
Insulin lowers the blood glucose gradient, so diffusion speeds up.
2) Insulin triggers insertion of glucose transport proteins into the membrane, allowing facilitated diffusion.
A cell is low on ATP. Which process would be most directly affected?
Diffusion of oxygen into the cell.
Osmosis of water across the membrane.
Uptake of glucose when extracellular concentration is lower than intracellular concentration.
Movement of carbon dioxide out of the cell.
3) Uptake of glucose when extracellular concentration is lower than intracellular concentration.
Which statement best explains why bulk transport requires energy?
Vesicles must fuse with or pinch off from the membrane, processes that require ATP.
Molecules move down their concentration gradient, which always costs energy.
Water passes freely through aquaporins, requiring ATP.
Simple diffusion of oxygen is energy-intensive.
Answer: 1) Vesicles must fuse with or pinch off from the membrane, processes that require ATP.