S1: How Molecules Move Around the Body - Passive Transport

Question 1

What two mechanisms transport molecules around the body?

Answer 1

Passive

Active

Question 2

What is Passive Transport?

Answer 2

• Movement of molecules down a gradient

- Does not require energy

Question 3

What is Active Transport?

Answer 3

• Movement of molecules against a gradient

- Requires energy (uses ATP)

Question 4

List the four passive transport processes

Answer 4

Diffusion
Convection
Osmosis
Electrochemical flux

Question 5

What is diffusion?

Answer 5

It is molecules going down their concentration gradient

e.g. O2 uptake from the lungs

Question 6

What is convection?

Answer 6

It is molecules going down a pressure gradient

e.g. Blood flow from heart to blood vessels

Question 7

What is osmosis?

Answer 7

Water going down concentration(pressure) gradient

e.g. Water uptake by cells

Question 8

What is electrochemical flux?

Answer 8

Electrical and concentration gradient

e.g. Action potential in nerve

Question 9

What is the equation for rate of transport?

Answer 9

Rate of transport (J) = Energy difference / Resistance to transport (R)

Question 10

What is Darcy’s Law on blood flow?

Answer 10

Blood Flow = Pressure difference between arteries and veins/ Resistance produced by blood vessels

Question 11

What is Brownian motion?

Answer 11

The random, un-directional thermal motion of molecules - in diffusion

Question 12

List some properties of diffusion

Answer 12

• Brownian Motion
• No input from any other force
• Each molecules has a different properties
• Thermal Motion: Molecular Motion depends on absolution temperature (measured in kelvin)

Question 13

What is absolute zero and how does this affect diffusion?

Answer 13

Absolute zero is 0K or 273 degrees.

At this temperature there is no kinetic motion

Question 14

How fast is diffusion (equation)?

Answer 14

The time taken (t) for one randomly moving molecules to move a net distance (x) in one specific direction increases with the distance squared (x^2)
D= diffusion coefficient for molecule within the medium e.g. O2 in the water vs O2 in air

t=x^2/(2D)

Question 15

How does distance affect rate of diffusion?

Answer 15

Speed of diffusion decreases with increasing distance

Question 16

How is diffusion clinically important?

Answer 16

• Useful for transporting molecules over very short distances - Diffusion is very and an effective transport process on a cellular scale (nm and um)
• Not useful at transporting molecules over distances > mm - Diffusion is very slow at transporting molecules around the body
• Oxygen transport
• Limitations exposed in a heart attack - Infarcted area of cardiac muscle due to lack of O2 supply

Question 17

What is Fick’s Law (Js)?

Answer 17

• Processing controlling diffusion
• ‘Steady state diffusion down a constant concentration gradient’
• Units: m/t(Js)

Js=-Concentration gradient x area(A) x diffusion coefficient of solute(D)/distance (x)

Concentration gradient= concentration difference/distance

Question 18

What are the 4 factors of Fick’s law optimised in the body?

Answer 18

D= Solute size (small solutes diffuse faster)

A= Capillary density (areas of diffusion have high capillary and recruitment)

X= Distance between capillary and cell where diffusion is important is very small e.g. alveoli

Change in concentration changes according to metabolic activity

Question 19

Why is Fick’s law negative?

Answer 19

Molecules move down a concentration gradient

Question 20

What is D?

How does diffusion coefficient (D) change with different molecules?

Answer 20

D is greater for small molecules

D is smaller for large molecules

D is the ease of which a molecule moves through a solvent

Question 21

How do different solutes diffuse through the cell membrane?

Answer 21

Lipid soluble solutes: Diffuses across all cell membrane and is rapid

Lipid insoluble solutes:

1. It diffuses across a slow pore area via aqueous pores (gaps through capillary walls). It is slow.
2. Enter via specific protein carriers in the membrane where they enter by facilitated diffusion until the carriers become saturated.

Question 22

Give examples of lipid soluble solutes

Answer 22

Oxygen
Carbon Dioxide
Anaesthetics
Glycerol

Question 23

Give examples of lipid insoluble solutes

Answer 23

Electrolytes (NaCl)
Glucose
Amino Acids
Plasma Proteins
Most therapeutic drugs

Question 24

Give an example of a lipid soluble solute entering aqueous pores

Answer 24

Na+ through ion channel

Question 25

Give an example of a lipid soluble solute entering protein carrier

Answer 25

Glucose in brain

Question 26

Why can some molecules diffuse faster across the cell membrane?

Answer 26

The ability of a molecule to cross a membrane relates to its permeability.