Practice Questions: Transport of Water and Solutes

Plasma membranes are selectively permeable. This means that

the plasma membrane allows some substances to enter or leave a cell more easily than others.

Assume you have a protein-free, artificial lipid bilayer. Which of the following solutes would cross at the greatest rate?

oxygen

Primary Active Transport

the process by which cells use ATP to move ions or molecules against their concentration gradient through specific transport proteins in the membrane

Secondary Active Transport

a process that uses the energy created by primary active transport to move other substances across a membrane against their concentration gradient, relying on the movement of ions or molecules that are moving down their gradient to drive the transport of the target substance.

Facilitated Diffusion

a passive transport process in which specific molecules move across a cell membrane via specialized protein channels or carriers, allowing them to cross the membrane along their concentration gradient without the use of energy

Simple diffusion

Simple diffusion is the passive movement of molecules or ions from an area of higher concentration to an area of lower concentration through a membrane, without the involvement of transport proteins or energy.

Osmosis

movement of a solvent from low concentration to high concentration

When the interior of a cell is in equilibrium with its environment, which of the following statements best describes the relative movement of molecules that can diffuse through the plasma membrane?

There is random and equal movement of molecules into and out of the cell.

Is osmosis passive?

yes!

Which of the following statements best describes a characteristic feature of osmosis?

In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.

A defect in which of the following molecules would dramatically reduce the rate of diffusion of water across cell membranes?

aquaporins

The solutions in the two arms of a U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal.

Which of the following is the most likely result when the system has reached equilibrium?

The water level will be higher in side A than in side B

White blood cells (WBCs) are more resistant to lysis than red blood cells (RBCs). When looking at a sample of blood for WBCs, what could you do to reduce interference from RBCs?

Mix the blood in a hypotonic solution, which will cause the RBCs to lyse.

Which statement about osmosis is correct?

The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.

Which of the following statements best describes a characteristic feature of membrane transport proteins?

They exhibit specificity for a particular type of molecule.

The transport of solutes across the cell membrane by facilitated diffusion and active transport is mediated by ________.

integral membrane proteins

If placed in tap water, an animal cell will undergo lysis, whereas a plant cell will not. What accounts for this difference?

the relative inelasticity and strength of the plant cell wall

What determines the direction that glucose is transported across the membrane through a passive transporter such as the Glut5 representative of the SWEET family of sugar transporters?

concentration gradient

The voltage across a membrane is called the ________.

membrane potential

What are the two forces that drive the diffusion of ions across the membrane? What is the combination of these forces called?

Chemical gradient - This is the difference in concentration of the ions across the membrane, which drives ions from an area of higher concentration to an area of lower concentration 

Electrical gradient - This is the difference in charge across the membrane, which influences the movement of ions based on their charge (positively charged ions are attracted to negative areas and repelled by positive areas, and vice versa) 

Combo = electrochemical gradient

Facilitated diffusion of ions across membranes through specific ion channels is driven by ________.

ion electrochemical gradients

Which of the following statements best describes the characteristic activities of a sodium-potassium pump?

The pump moves three sodium ions out of a cell and two potassium ions into a cell using energy from ATP hydrolysis.

Which of the following statements best explains why the sodium-potassium pump is an electrogenic pump?

It generates voltage across the membrane.

the main electrogenic pump in animals

sodium-potassium pump

The main electrogenic pump in plants, fungi, and bacteria

proton pump (H+ ATPase).

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Because phosphate import depends on a pH gradient across the membrane, phosphate transport is most likely an example of which of the following transport processes?

secondary active transport

A membrane-enclosed vesicle fuses with the plasma membrane and releases its contents to the extracellular fluid. This statement describes _____.

exocytosis

Cells such as bacteria are taken up by other cells such as white blood cells by which mechanism?

phagocytosis

Which of the following membrane activities requires energy from ATP hydrolysis?

movement of Na⁺ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid

Which of the following would decrease a cell's membrane potential?

a potassium channel

Imagine a small synthetic vesicle made from pure phospholipids (no proteins) enclosing an interior lumen containing 1 mM glucose and 1 mM sodium chloride. If the vesicle is placed in pure water, which of the following happens faster? 

water diffuses in

You are adrift in the Atlantic Ocean and, being thirsty, drink the surrounding seawater. This increases the concentration of salt in the extracellular fluid surrounding your cells and, as a result,

your cells shrivel as a result of the hypertonic environment they are in

A group of single-cell organisms collected from the ocean was brought into the lab for examination. The lab assistant was concerned that the water had become full of toxic waste products and so added clean water to the culture. All of the organisms died, and when they looked at them under the microscope, all they could see were bits and pieces of them scattered throughout the water. What likely happened?

The lab assistant added water that was hypotonic to the culture of organisms, and they ruptured. 

What is generally true of ion channels?

They exist in open or closed conformation.

If ATP production is blocked in an animal cell, the cell will swell up. Explain this observation. 

If ATP production is blocked in an animal cell, the sodium-potassium pump cannot function effectively, leading to the accumulation of sodium ions inside the cell. This increases osmotic pressure, causing water to flow into the cell and resulting in swelling, which may eventually lead to cell lysis