Membrane Transport Review Questions

How are large molecules transported across cell membranes?

Transport proteins or vesicular transport (if very large)

How do passive transport and active transport differ?

-Active transport requires ATP, passive does not -Active moves a substance against its concentration gradient, while passive moves a substance down its concentration gradient

Define diffusion, osmosis, active transport, and passive transport.

-Diffusion: -Osmosis: -Active transport: requires ATP energy, moves against concentration gradient -Passive transport: does not require ATP, moves down concentration gradient

Name 3 functions of the sodium potassium pump.

-Maintain ionic gradients (important to resting potential) -Provides gradients for secondary active transporters -Maintains cell volume by keeping ionic concentrations constant.

The opening of membrane channels can be controlled by "gates". What factors can cause these gates to open?

-Mechanical stimulation -Ligand binding -Change in membrane voltage

What factors influence the rate of diffusion across a membrane?

-concentration gradient -permeability of molecule -membrane surface area -membrane thickness -temp(should not vary within the body) -molecular size

Crossing a membrane by simple diffusion can be distinguished from facilitated diffusion because: (multiple choice) A. Simple diffusion does not require energy: facilitated diffusion requires a source of ATP. B. Simple diffusion can only move material in the direction of a concentration gradient; facilitated diffusion moves materials with and against a concentration gradient. C. Simple diffusion is not saturable; facilitated diffusion rates are limited by the number of functional membrane proteins and can be saturated D. Simple diffusion is found only in prokaryotes while facilitated diffusion is found only in eukaryotes.

C. Simple diffusion is not saturable; facilitated diffusion rates are limited by the number of functional membrane proteins and can be saturated

If the vessels of the brain have a reduced amount of plasma proteins, what effect would you expect this to have on the volume of extracellular fluid surrounding the brain neurons?

Decrease in plasma proteins results in a decrease in osmotic pressure within the vessels. This results in fluid moving from the vessels into the ECF and increases the volume of the ECF causing cerebral edema (brain swelling due to fluid in the brain)

Can you give a few examples of where diffusion is important for proper physiological function?

Diffusion is important for gas exchange, transport of small molecules and membrane permeable drugs into cells (alcohol, nicotine, steroids, anesthetics, etc.).

Give examples of how membranes might be altered in a biological system to change the rate of diffusion.

Membranes could be altered by increasing the thickness of the diffusion barrier (ex: edema), alteration of membrane surface area (ex: emphysema), and in the case of water, insertion of more channels although this would not be diffusion as strictly defined.

Same question as above except solution A contains a 150 millimolar solution of sodium chloride and solution B contains a 300 millimolar solution of glucose. In which direction does osmosis occur?

No net movement the solutions are iso osmotic with respect to each other.

Two solutions (A and B) are separated by a semi-permeable membrane which only allows the passage of water. Solution A contains 600 millosmoles of sodium chloride and solution B contains 250 milliosmoles of sodium chloride. In which direction will osmosis occur?

Osmosis will occur from B to A (water moves towards salt, A contains more salt)

Is facilitated diffusion active or passive?

Passive

Lipid bilayers are differentially permeable to different types of molecules. Which types of molecules can readily cross such bilayers without the help of transport proteins? Name some of the physical properties of molecules that prevent them from freely diffusing across lipid bilayers.

Small uncharged lipid soluble molecules cross bilayers easily without help. Large molecules, charged molecules, and hydrophilic molecules do not diffuse readily across the membrane.

Which of the following processes could result in the net movement of a substance into a cell, if the substance is more concentrated in the cell than in the surroundings (ie movement against the substances concentration gradient) (multiple choice) a. active transport b. facilitated diffusion c. diffusion d. osmosis e. none of the above

a. active transport

Which statement is true? (multiple choice) a. A cell placed in an isotonic solution will swell. b. A cell placed in a hypotonic solution will swell c. A cell placed in a hypotonic solution will shrink. d. A cell placed in a hypertonic solution will remain the same size.

b. A cell placed in a hypotonic solution will swell

Which of the following is a characteristic of all carrier proteins in a plasma membrane? (multiple choice) a. They are peripheral membrane proteins b. Each exhibits a specificity for a particular type of molecule c. They require energy to function d. They work against diffusion

b. Each exhibits a specificity for a particular type of molecule

Oxygen, carbon dioxide, and other small molecules cross the plasma membrane through the process(es) of (multiple choice) a. osmosis. b. diffusion. c. endocytosis and exocytosis. d. active transport. e. facilitated diffusion.

b. diffusion

Which of the following substances would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer? (multiple choice) a. water b. O(2) c. phosphate ion (PO4 2-) d. testosterone

c. phosphate ion (PO4 2-)

All of the following statements about membrane structure and function are true EXCEPT (multiple choice) a. diffusion and osmosis do not require energy input from the cell b. voltage across the membrane depends on an unequal distribution of ions across the plasma membrane c. uniport proteins can co-transport two solutes by coupling diffusion with active transport in different directions

c. uniport proteins can co-transport two solutes by coupling diffusion with active transport in different directions

The sodium-potassium pump is an example of (multiple choice) a. simple diffusion b. facilitated diffusion. c. osmosis. d. active transport

d. active transport

Two similar-sized cells from different organisms are placed in a 0.5% sucrose solution. Cell A enlarges in size for a while, then stops; cell B continues to enlarge and finally ruptures. Which of the following was true at the beginning of the experiment? (multiple choice) a. cell A was hypoosmotic to the solution, and cell B was hyperosmotic b. cell A was hyperosmotic to the solution and cell B was hypoosmotic c. cell A was hyperosmotic to cell B d. cell B was hyperosmotic to cell A e. cell A and B are isoosmotic with respect to each other

d. cell B was hyperosmotic to cell A

In simple diffusion, (multiple choice) a. the rate of movement of molecules is controlled by temperature and molecular size. b. the movement of individual molecules is random. c. the movement of molecules of one substance is independent of the movement of any other substance. d. the net movement is away from the region of highest concentration. e. all of these

e. all of these

What are the membrane structures that function in active transport? (multiple choice) a. phospholipids b. carbohydrates c. cholesterol d. hydrophobic molecules e. integral proteins

e. integral proteins

What would happen to a cell placed in a hypertonic solution?

the cell will shrivel and die by a process known as plasmolysis

What would happen to a cell placed in a hypotonic solution?

the cell will swell and expand until it eventually burst through a process known as cytolysis

What would happen to a cell placed in an isotonic solution?

the cell would remain the same