Cell Transport: Simple Diffsion Flashcards Preview

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Flashcards in Cell Transport: Simple Diffsion Deck (19):
1

Define: Simple Diffusion

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

2

What molecules use simple diffusion?

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

3

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

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)

4

In what form is carbon dioxide transported?

HCO3-, bicarbonate ion

5

Where does diffusion always move solutes?

Towards equilibrium

6

How does diffusion tend toward minimum free energy?

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

7

What is the driving force for diffusion?

Entropy, a randomization of molecules

8

Define: osmosis

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

9

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

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

10

What did Bangham do?

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

11

What is a liposome?

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

12

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

size, polarity and charge

13

How does size effect solubility across the membrane?

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

14

How does polarity effect solubility across the membrane?

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

15

How does water diffuse across the membrane?

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

16

How does charge affect solubility across the membrane?

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

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)

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

 

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

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)

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

19

 

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

Q image thumb

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