Lecture 2

Question 1

Who showed that ability to cross the membrane unaided is proportional to fat solubility?

Answer 1

Randall et al.

They showed that as hydrophobicity increases, permeability increases.

Question 2

Why do cell walls not represent a barrier to movement of small molecules?

Answer 2

cellulose is spongey (holes between cellulose fibres)

Question 3

How does secondary active transport work?

Answer 3

It uses the free energy released when an ion (e.g. H+) is allowed to move down its electrochemical gradient, to move another substance against its gradient. Can be symport or antiport.

Question 4

What is a colligative property?

Answer 4

Any property that only depends on the number of molecules, not their type. (e.g. osmotic pressure)

Question 5

Why do aquaporins contain lots of alpha helices?

Answer 5

Alpha helices are especially good at passing through the membrane. *

Question 6

How might a dynamic equilibrium between osmosis and hydrostatic pressure be established?

Answer 6

A container of pure water and a salt solution within a rigid container are separated by a partially permeable membrane.

1. Water enters the salt solution via osmosis
2. Hydrostatic pressure increases.

Question 7

What is the van’t Hoff equation?

Answer 7

π=RTC
π- osmotic pressure (Pa)
R- ideal gas constant
T- absolute temperature (K)
C- concentration (Osml-1)

Question 8

What is water potential?

Answer 8

Water potential combines the effects of solute and pressure potentials.

Question 9

turgor pressure is a type of…

Answer 9

hydrostatic pressure

Question 10

How do animal cells cope without a cell wall?

Answer 10

By controlling the external solution (the extracellular fluid).

Question 11

Describe an experiment demonstrating diffusion.

Answer 11

Fluorescein dye was placed in the centre of a petri dish full of agar. (Agar stops convection currents as it is semi solid.)
Conclusion: diffusion is very slow (and increases exponentially with time?)

Question 12

What is the Einstein diffusion equation?

Answer 12

t=x^2/2D
x- distance
D-diffusion coefficient
(x^2 shows that at large distances diffusion is very slow, but short distances are okay)

Question 13

Ways of minimising diffusion distances.

Answer 13

1. being very small
2. being very flat
3. situating your most active tissue peripherally

Question 14

E-demanding mechanisms for speeding up movement of substances.

Answer 14

1. cytoplasmic streaming
2. polar auxin transport
3. axonal transport
4. bulk flow

Question 15

How does bulk flow work?

Answer 15

Fluid is moved down its mechanical energy gradient (e.g. hydrostatic pressure gradient)

Question 16

Darcy’s law of flow

Answer 16

Q=deltaP/R
flow: Qmlmin-1
P=pressure

(similar to Ohm’s law: I=V/R)

Question 17

What does Darcy’s law of flow show?

Answer 17

The rate of flow is proportional to the pressure gradient, but inversely proportional to resistance.