Lab - Week 1 Content - Membrane Transport

Question 1

What does the plasma membrane of most cells separate?

Answer 1

Intracellular and extracellular compartments

Question 2

T/F: the plasma membrane does permit the movement of certain substances between the ICF and ECF

Answer 2

True

Question 3

Have you revised membrane transport from week 1?

Answer 3

Yes

Question 4

Osmosis is the term given to the movement of any ___________ across a __________________________

Answer 4

Solvent

Selectively permeable barrier

Question 5

What kind of solutions are the ICF and ECF?

Answer 5

Aqueous solutions

Question 6

For our purposes what does osmosis refer to?

Answer 6

The movement of water across the plasma membrane

Question 7

What are a good model system in which to study osmosis?

Why?

Answer 7

Erythrocytes

Their plasma membrane is permeable to water but fairly impermeable to salts

Question 8

If erythrocytes are placed in a hypotonic solution then water will flow…?

What will happen if the process continues?

What is the name of the resulting process?

Answer 8

Into the cell, DOWN it’s concentration gradient and the cell will increase in volume.

The cell will eventually burst, expelling the haemoglobin into the surrounding fluid

Haemolysis

Question 9

If erythrocytes are placed in a hypertonic solution water will move…?

What will happen if the process continues?

What is the name of the resulting process?

Answer 9

Out of the cell

This will cause the cell to shrink

Process known as CRENATION

Question 10

If erythrocytes are placed in a hypertonic solution water will move…?

What will happen if the process continues?

What is the name of the resulting process?

Answer 10

Out of the cell

This will cause the cell to shrink

Process known as CRENATION

Question 11

What is the goal of the lab?

What kind of blood did we use?

Answer 11

To determine which aqeuous solutions are which

Sheeps blood

Question 12

What is the rough osmolarity of sheep erythrocyte ICF?

Answer 12

Roughly 300 mOsm/L

Question 13

How much of a drop of blood can we place on a slide with how much of the unknown, diluting solution?

Answer 13

1/10 of a drop of sheeps blood

1 drop of unknown solution

Question 14

It is very important that only a very small volume of blood is applied to the slide so that you can observe…?

Why?

How long do you have to examine the cells within?

Answer 14

The shape of the cells

If when you look down the microscope and see clumps of cells your results will be meaningless

1-2 minutes of applying the solution in order to observe the changes (crenation or haemolysis etc)

Question 15

If red blood cells are suspended in a solution containing a foreign substance to which the membrane is readily permeable, then this substance will…?

How long will this continue?

Answer 15

Rapidly diffuse into the cells down it’s concentration gradient.

This diffusion will continue until its concentration inside the cells is the same as its concentration outside the cells.

Question 16

What will the addition of extra solute to the normal intracellular constituents of the cells mean?

Answer 16

The effective concentration of water inside the cells is now less than it was previously.

As a result, water will move into the cell by osmosis and may cause haemolysis.

Question 17

The rate at which water moves into the cell depends on…?

Answer 17

the permeability of the cell membrane to the foreign substance.

Question 18

The time for haemolysis to occur will give an indication of…?

Answer 18

The permeability of the membrane to the substance

Question 19

What is the procedure to determine haemolysis?

Answer 19

1. Put 2mL of the solution into a plastic vial
2. Add two drops (only) of sheep blood to the vial, start the timer and mix gently
3. Note the time taken for the suspension to become translucent, due to haemolysis of the cells

Question 20

When is the end point of the haemolysis experiment?

How is the experiment facilitated?

Answer 20

When the solution changes from being a cloudy suspension to being translucent (not transparent).

By holding the tube against some text.

Practice as many times as you’d like with the Practice solution provided - make sure you’re comfortable at determining this end point before you continue

Question 21

What is the maximum cut off time for the haemolysis experiment we are recommended to use?

Answer 21

12 minutes

Question 22

What is the effect of the size of the solute on haemolysis time?

Why is this the case?

Answer 22

The result of these findings suggest that smaller molecules hemolysis faster as compared to larger molecules (extra: and the stronger the lipid-water partition coefficient the fast hemolysis can occur regardless of the size of the molecule)

This is due to the simple fact the plasma membrane is generally more permeable to smaller molecules as compared to larger one as they enter the cell effortlessly. So, the hemolysis rate is dependent on the size of the molecules

Question 23

How does relative lipid solubility effect haemolysis time?

Answer 23

The lipid solubility increases the permeability of the membrane, which increase hemolysis. This is because the formation of longer carbons will make lipids more soluble, thus reducing the molecular size of the lipid, which will then be easily passed out.

Question 24

What effect does temperature have on haemolysis time?

Answer 24

The rate of hemolysis was rapid at 5–10° and above 40°, but slow at around 25°. The results suggest the importance of membrane fluidity in hemolysis and the occurrence of phase separations of membrane lipids.

Question 25

Determine the haemolysis time for the 1M solution of urea at the different temperatures provided and enter the results in the table below (Temperature in celsius by haemolysis time)

What is the effect of temperature on haemolysis time?

How do you explain this result?

Answer 25

Question 26

Determine the haemolysis time for each of the solutions in the table below.

Answer 26

Question 27

From your observations, identify each of the numbered solutions and explain why you came to this conclusion:

Answer 27

Question 28

What is the effect of the size of the solute on haemolysis time?

How do you explain these observations?

Answer 28

Question 29

Answer 29

Question 30

Answer 30