AP Biology : Understanding the Cell Membrane

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #61 : Understanding The Cell Membrane

In a lipid bilayer, lipid molecules either move laterally within their layer or flip transversely across the membrane. Which of the movements happens more readily?

Possible Answers:

Lateral movement

Flipping

Neither, no movement of lipids happens

Both happen at the same rate

None of these

Correct answer:

Lateral movement

Explanation:

In lipid bilayers, lipids molecules readily drift around laterally, they rarely flip across the membrane. Recall that the lipid bilayer can be depicted via the fluid mosaic model, as phospholipids and integral proteins are free to move laterally throughout the membrane. A flip (phospholipid from the inner leaflet to outer leaflet, or vice-versa) is thermodynamically unfavorable and does not occur as often as lateral movements. 

Example Question #62 : Understanding The Cell Membrane

Which of the following is not a major function of membrane proteins?

Possible Answers:

Attachment to cytoskeleton

Signal transduction

Cell-cell recognition

Protein chaperones

Transport

Correct answer:

Protein chaperones

Explanation:

Chaperons are proteins that help other proteins fold properly. There are found in the interior of the cell, usually associated with ribosomes and not the cell membrane. All other functions listed are carried out by membrane proteins.

Example Question #63 : Understanding The Cell Membrane

Which of the following molecules cannot pass through the membrane spontaneously?

Possible Answers:

Molecular oxygen

Methane

Ethane

Glucose

Pentane

Correct answer:

Glucose

Explanation:

Plasma membranes are selectively permeable. Small non polar molecules like molecular oxygen and hydrocarbons can pass through the membrane while larger charged molecules like glucose cannot, unless their transport is facilitated by a membrane protein.

Example Question #64 : Understanding The Cell Membrane

In order for a solute to pass through a cell membrane via diffusion, it must be all of the following except __________.

Possible Answers:

hydrophobic

lipophilic

nonpolar

small

charged

Correct answer:

charged

Explanation:

Only small, uncharged molecules that are nonpolar can cross the cell membrane via diffusion. For example, oxygen molecules can easily diffuse across the cell membrane. Ions like potassium and sodium can cross the cell membrane through other mechanisms, such as active transport or through ion channels, but they cannot cross via the mechanism of diffusion.

Example Question #65 : Understanding The Cell Membrane

While in the lab, a research student was interested in how temperature changes the fluidity of the plasma membrane. At physiologic pH, which of the following change to fluidity would be expected if we added more cholesterol?

Possible Answers:

Membrane would be destroyed

Cholesterol is not found in the cell membrane

Increased fluidity

No change in fluidity

Decreased fluidity

Correct answer:

Decreased fluidity

Explanation:

Cholesterol is a major component of the plasma membrane fluidity. If we add more of this molecule to a cell membrane in normal conditions, we would hinder the movement of other lipids and essentially cause them to be more compressed. This compression would lead to a decrease in the fluidity of the membrane.

Example Question #66 : Understanding The Cell Membrane

Which of the following proteins act as a carrier for transporting substances across the cell membrane?

Possible Answers:

Golgi apparatus

Peripheral protein

Integral protein

Glycoprotein

Mitochondria

Correct answer:

Integral protein

Explanation:

Peripheral proteins are located either on the inside or outside of the cell, but do not pass all the way through. Glycoproteins are located on the outside of the cell membrane. Mitochondria are located within the cell and make ATP. Golgi apparatus is also located within the cell, thus does not function for transport through the membrane. Integral proteins act as carrier proteins and allow substances to pass through the cell membrane from the inside to the outside of the cell (or outside to the inside).

Example Question #67 : Understanding The Cell Membrane

Which of the following types of cell transport requires energy? 

Possible Answers:

The transport of a particle across a selectively permeable membrane down its concentration gradient. 

The transport of a potassium ion across a selectively permeable membrane from an area of high concentration to low concentration. 

The transport of a particle across a selectively permeable membrane against its concentration gradient. 

The transport of a particle across a selectively permeable membrane with the assistance of the membrane's transport proteins. 

The diffusion of a water across a selectively permeable membrane against its concentration gradient. 

Correct answer:

The transport of a particle across a selectively permeable membrane against its concentration gradient. 

Explanation:

Active transport is when a particle moves against its concentration gradient through a selective membrane with the aid of energy. Moving down its concentration gradient and from a high to low concentration is simple diffusion. The movement of water down its concentration gradient is osmosis and moving a particle or ion through a protein is facilitated transport. These are all examples of passive transport. 

Example Question #68 : Understanding The Cell Membrane

Which of the following can not pass through the phospholipid bilayer of a cell by simple diffusion?

Possible Answers:

Nonpolar molecules

Glucose

Oxygen gas

Carbon dioxide

Testosterone

Correct answer:

Glucose

Explanation:

Glucose need a channel protein to pass through the membrane because it is too large. Substances that pass through the membrane via simple diffusion need to be relatively small and not charged. Carbon dioxide and oxygen gas are both small nonpolar molecules that can easily diffuse through the plasma membrane. 

Example Question #69 : Understanding The Cell Membrane

Which of the following types of transport is mediated by a membrane protein?

Possible Answers:

Two of these

All of these

Facilitated diffusion

Passive diffusion

Active transport

Correct answer:

Two of these

Explanation:

Only two choices are correct, facilitative diffusion and active transport because they both need carrier proteins for transport across the cell membrane. Simple diffusion does not require carrier proteins.

Example Question #70 : Understanding The Cell Membrane

Nonpolar molecules will typically pass though the plasma membrane via which mechanism?

Possible Answers:

Active transport

Secondary active transport

Facilitated diffusion

Passive diffusion

Correct answer:

Passive diffusion

Explanation:

Nonpolar molecules can pass through the plasma membrane with relative ease. Even larger nonpolar molecules, such as steroid hormones, can pass through the plasma membrane easily. Passing through the membrane without the need for assisting proteins is known as passive diffusion.

Facilitated diffusion involves the use of membrane channel proteins to allow molecules to pass (example: potassium leak channels). Active transport requires the metabolism of ATP to pump a molecule against its concentration gradient (example: sodium-potassium pump). Secondary active transport uses ATP to generate an electrochemical gradient, then uses the gradient to transport molecules and perform work (example: ATPase).

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