How Molecules Move Around The Body: Passive Transport

Question 1

What is the difference between active and passive transport?

Answer 1

Active:
-movement of molecules against a gradient (low to high conc)
-requires energy (ATP)
Passive:
-movement of molecules down a gradient (high to low conc)
-doesn’t require energy

Question 2

What are the 4 passive transport processes? Give an example of each

Answer 2

Diffusion:
-conc gradient
-oxygen uptake from lungs to blood
Convection:
-pressure gradient
-blood flow from heart to blood vessels 
Osmosis:
-osmotic pressure
-water uptake by cells
Electrochemical flux:
-electrical and conc gradient 
-APs in a nerve

Question 3

What is the rate of transport (J) equal to?

Answer 3

Energy difference/Resistance to transport

Question 4

What is Fick’s Law?

Answer 4

• the rate of movement increases as the conc difference and area increase
• Js= -DA(conc gradient diff/x)
• D= diffusion coefficient of solute
• A= area
• x= distance

Question 5

What factors affect the rate of diffusion and how?

Answer 5

Solute size:
-small solutes diffuse faster
Capillary density:
-higher capillary density= less distance= a larger conc gradient (C/x)
-e.g. in cardiac muscle
Distance between capillary and cell:
-less distance= quicker diffusion
-e.g. in alveoli
Metabolic activity:
-conc gradient increases as tissue con decreases
-this increases the conc difference
-tissue conc decreases due to faster usage of metabolites

Question 6

How does the membrane affect diffusion?

Answer 6

• if all of the cell membrane is available, transport is rapid
• if there’s only a small pore area, transport is slower
• saturation of carrier proteins during facilitated diffusion= slower transport

Question 7

What is the difference between how lipid-soluble and lipid-insoluble solutes travel through the membrane?

Answer 7

Lipid-soluble solutes:
-via simple diffusion
-e.g. oxygen, carbon dioxide, anaesthetics and glycerol
Lipid-insoluble solutes:
-go through aqueous pores/ion channels/specific protein carriers
-e.g. electrolytes, glucose, amino acids, plasma proteins, most therapeutic drugs

Question 8

What is permeability and how does it relate to Fick’s Law?

Answer 8

• it’s the ability of a molecule to cross a membrane

- in relation to Fick’s Law- Js=-PAC