PhysioEx 1: Cell Transport Mechanisms and Permeability

The driving force for diffusion is

the kinetic energy of the molecules in motion

In diffusion, molecules move

from high concentration to low concentration

Which of the following dialysis membranes has the largest pore size?

200 MWCO

The reason sodium chloride didn’t diffuse left to right is that

the membrane pore size was too small

Glucose is a six-carbon sugar. Albumin is a protein with 607 amino acids. The average molecular weight of a single amino acid is 135 g/mol. There is no reason to run these solutes at the 20 MWCO because

glucose and albumin are both too large to pass

The rate of diffusion for urea

is slower than that for sodium because urea is a larger molecule

The effect of increasing the concentration of sodium chloride from 9 mM to 18 mM in the left beaker was to

increase the rate of diffusiondue to a greater concentration gradient.

Describe the difference between the rate of diffusion seen for sodium and urea.

Urea diffused more slowly because it is larger than sodium.

Which of the following solutes did not pass through any of the membranes?

albumin

When diffusion stops, we say the solution has reached

equilibrium

Describe two variables that affect the rate of diffusion.

The concentration gradient and the molecular size.

Why do you think the urea was not able to diffuse through the 20 MWCO membrane? How well did the results compare with your prediction?

The size of urea molecule may have been too big compare to the 20MWCO.

Describe the results of the attempts to diffuse glucose and albumin through the 200 MWCO membrane. How well did the results compare with your prediction?

Between glucose and albumin, glucose would be the only molecule pass through the 200MWCO because albumin is too big.

Put the following in order from smallest to largest molecular weight: glucose, sodium chloride, albumin, and urea.

NaCl < urea < glucose < albumin

Molecules need a carrier protein to help them move across a membrane because

they are lipid insoluble or they are too large

Which of the following is true of facilitated diffusion?

movement is passive and down a concentration gradient

Examples of solutes that might require facilitated diffusion include

All of the above

Which of the following would not affect the rate of facilitated diffusion?

the amount of intracellular ATP

What happened to the glucose transport rate when the glucose concentration was increased from 2 mM to 8 mM?

The glucose transport rate increased

Describe the conditions that resulted in the fastest rate of glucose transport.

700 glucose carries proteins and 8 mM glucose

Why do you think equilibrium wasn't reached?

The membrane proteins were saturated

What variable(s) increased the rate of facilitated diffusion of glucose?

increasing the concentration of glucose and increasing the number of membrane carriers.

For facilitated diffusion, increasing the concentration of glucose on one side of the membrane is the same as

making the concentration gradient steeper.

When all of the membrane carriers are engaged, or busy, we say they are

saturated

Na Cl had no effect on glucose transport because

sodium is not required for glucose transport in the simulation

Explain one way in which facilitated diffusion is the same as simple diffusion and one way in which it is different from simple diffusion.

Both are a passive diffusion, which mean they are similar in their movement. They both move molecules down the gradient. However, the facilitated diffusion uses protein to move molecules that are too large while simple diffusion only move the molecule that are small enough to pass through the membrane.

Which of the following is true of osmosis?

it is a type of diffusion

Which of the following occurs when a hypertonic solution is added to cells?

The cells shrink

The variable that affects osmotic pressure is

the concentration of nondiffusing solutes

The net movement of water would be into the cell in a

hypotonic solution

Why do you think there is no pressure change?

Sodium is able to diffuse through the pores.

Why do you think there was no pressure change?

There is no net movement of water because the solute concentrations are the same.

If you double the concentration of a nondiffusible solute that is on one side of a membrane, the osmotic pressure will

double

Which membrane did not allow Na Cl to pass through?

20 MWCO

When a solute is able to diffuse through a membrane

equilibrium is reached

Water diffuses

toward solutes

Describe one way in which osmosis is similar to simple diffusion and one way in which it is different.

Both method doesn’t require energy, however osmosis only move the water (solvent) molecule.

Solutes are sometimes measured in milliosmoles. Explain the statement, “Water chases milliosmoles.”

"Water chases milliosmoles" because when the solute concentration increases, the water concentration will decrease because water moves into areas of high concentration.

Filtration is a process that

is passive

Filtration is dependent upon a

hydrostatic pressure gradient

The filtrate

all of these answers are correct

An important place that filtration takes place in the body is in

the kidneys

The reason none of the solutes were present in the filtrate was that

the solutes were all too large to pass through

What does an increase in the driving pressure correspond to in the body?

an increase in blood pressure

After filtration, substances that pass through the filter are called the filtrate, which includes

all of the above

The top beaker in the simulation corresponds to

the blood capillary

Why was there not 100% recovery of the Na Cl solute with any of the membranes?

Some of the solute remained on the membrane filter

An increase in blood pressure would probably initially __________ filtration in the kidneys.

increase the rate of

The movement of sodium and potassium maintained by the Na -K pump

requires energy and is against a concentration gradient

The sodium-potassium pump is classified as a(n)

antiporter

The sodium-potassium pump moves _____ sodium ions and _____ potassium ions

3, 2

Solutes that require active transport for movement might be too large to pass or might be

lipid insoluble

Why did the sodium transport stop before the transport was completed?

The ATP was depleted

Why was the equilibrium for the solutes reached earlier?

There were more pumps for transport

What happened when you increased the amount of ATP dispensed with the same concentration of sodium and potassium on either side of the membrane?

More ions were transported

At what concentration of ATP were the sodium and potassium maximally transported?

3 mM ATP

What was the effect of adding more Na -K pumps to the simulated cell?

Transport of the ions was faster

Describe the effect of adding glucose carriers to the sodium and potassium transport.

There was no change in the transport rate because glucose is transported independently.

Describe the significance of using 9 mM sodium chloride inside the cell and 6 mM potassium chloride outside the cell, instead of other concentration ratios.

I believe this is based on the fact that 3 Na+ enter the cell while 2 K+ move out of the cell in order to keep the pump going.