Cell Transport: Simple Diffsion

Question 1

Define: Simple Diffusion

Answer 1

the unassisted net movement of a solute from a region where its concentration to a region where its concentration is lower

Question 2

What molecules use simple diffusion?

Answer 2

gases, non polar molecules, and small polar molecules (water, glycerol or ethanol)

Question 3

Oxygen can simply diffuse, how is this helpful in the red blood cells?

Answer 3

Allows red blood cells to take up oxygen in the lungs and release it into the capillaries of the tissues (uses concentration gradient, high oxygen in RBC, low in tissues)

Question 4

In what form is carbon dioxide transported?

Answer 4

HCO3-, bicarbonate ion

Question 5

Where does diffusion always move solutes?

Answer 5

Towards equilibrium

Question 6

How does diffusion tend toward minimum free energy?

Answer 6

free energy is minimized as molecules move down their concentration gradient (higher to lower energy)

Question 7

What is the driving force for diffusion?

Answer 7

Entropy, a randomization of molecules

Question 8

Define: osmosis

Answer 8

movement of water through a semipermeable membrane driven by a difference in solute concentration on the two sides of the membrane

Question 9

In terms of free energy, which way does the gradient go in osmosis?

Answer 9

from the side with higher free energy to the side with lower free energy

Question 10

What did Bangham do?

Answer 10

extracted lipids from cell membranes and when dispersed in water they form liposomes, ions were stuck in the vesicles for days, while oxygen exchanged rapidly

Question 11

What is a liposome?

Answer 11

small vesicles, each consisting of a closed, spherical, lipid bilayer that is devoid of membrane proteins

Question 12

What are the three main factors that affect diffusion of solutes?

Answer 12

size, polarity and charge

Question 13

How does size effect solubility across the membrane?

Answer 13

bilayers are more permeable to smaller molecules than larger. water, oxygen, carbon dioxide and molecules with a molecular weight under 100

Question 14

How does polarity effect solubility across the membrane?

Answer 14

as the lipid bilayer is polar on the outside but non-polar in the inside mostly non-polar molecules are able to simply diffuse across the bilayer

Question 15

How does water diffuse across the membrane?

Answer 15

membranes contain tiny pores that allow water to diffuse more quickly than predicted based on its polarity lipid movement

also provides temporary “holes” allowing water to move through the membrane

Question 16

How does charge affect solubility across the membrane?

Answer 16

molecules of water form a ‘shell of hydration’ around polar substances membranes maintain electrochemical potentials so they need to allow ions to move across the membrane in a controlled manner

Question 17

When thinking of the rate of simple diffusion in proportion to the concentration gradient:

Describe this relationship in terms of thermodynamics.

(Thermodynamics : Thermodynamics is a branch of physics concerned with heat and temperature and their relation to energy and work)

Answer 17

simple diffusion is always and exergonic process, requiring no input of energy

net flux will always be in the direction of minimum free energy

Question 18

When thinking of the rate of simple diffusion in proportion to the concentration gradient:

Describe this relationship in terms of kinetics.

(Kinetics : Kinetics (physics), the study of motion and its causes)

Answer 18

the net rate of transport for a substance is proportional to its concentration difference across the membrane over a broad concentraion range

Question 19

Describe what is happening in this figure in terms of the kinetics of simple diffusion and facilitated diffusion.

Answer 19

for simple diffusion the relationship between the rate of diffusion and solute concentration gradient is linear

for facilitated diffusion the relationship between the rate of diffusion and solute concentration is linear when the concentration gradient is small, but when the concentration increases the diffusion rate is hyperbolic