Lab 1

Question 1

What was the aim of experiment one?

Answer 1

To measure the packed cell volume

Question 2

What is the packed cell volume?

Answer 2

This is the proportion of a column of blood cells occupied by cells (RBC, leukocytes, WBC) after they have been packed by centrifuging in a narrow micro-haematocrit tube

Question 3

What is the PCV also known as?

Answer 3

haematocrit

Question 4

Why were the red blood cells used in these experiments?

Answer 4

• they are red so it is easy to see
• they are free floating
• they have a phospholipid semipermeable membrane
• they have aquaporins so H2O can go in or out

Question 5

What will happen to the PCV when fluid enters the RBC?

Answer 5

It will increase

Question 6

What happens to the PCV when fluid move out of cells?

Answer 6

It will decrease

Question 7

What is haemolysis?

Answer 7

This is the cell bursting (RBC burst because they don’t have a cell wall)

Question 8

What is the aim of experiment 2?

Answer 8

to estimate the osmolarity of the fluid inside red blood cells by measuring the change in volume of each red blood cells exposed to solutions of impermeant (can’t cross membrane) of different osmolarities

Question 9

In experiment 2, why do we need to multiply the PCV value by 2?

Answer 9

This is because we did a 1:1 dilution when we mixed the saline’s with the whole blood so we multiply by 2 to get a PVC value that can be compared to the whole blood

Question 10

How did we calculate the final osmolarity of the saline and blood solutions?

Answer 10

We calculated the osmolarity of the NaCl solution from the concentration value for this solution. Because we added equal amounts of blood and saline, we can then calculate the final osmolarity of the blood + saline by finding the average osmolarity of the two solutions

Question 11

What is the relationship between osmolarity and PCV?

Answer 11

As the final osmolarity increases, the PCV initially increases. It reaches a maximum at 40%, then begins to decrease.

Question 12

What is the effect of a hyper osmotic solution on the PCV?

Answer 12

There are more solutes inside the solution than inside the cell which means that water leaves the cell. The cell shrivels up and so the solution is hypertonic and therefore the PCV decreases

Question 13

What is the difference between molarity and osmolarity?

Answer 13

Molarity refers to the molar concentration of solutes in a solution whereas osmolarity describes the total number of osmotically active particles in a solution.

Question 14

What is the difference between osmolarity and tonicity?

Answer 14

Osmolarity describes the total number of osmotically active particles in a solution whereas tonicity describes the observed effect a solution has on the cell volume

Question 15

What is the effect of a hypo-osmotic solution on the PCV?

Answer 15

There are less solutes inside the solution than inside the cell which means that water enters the cell. The cell swells and so the solution is hypotonic and therefore the PCV increases

Question 16

What would occur if the intracellular osmolarity of body cells was different from plasma osmolarity?

Answer 16

Water would move from one to the other and the cells could shrink of swell

Question 17

What was the aim of experiment 3?

Answer 17

This was to estimate the rate of osmosis using the haemolysis of red blood cells

Question 18

How did we know haemolysis has occurred in experiment 3?

Answer 18

The indicator line became visible against the illuminated background

Question 19

What is the relationship between the observed time for haemolysis and the difference in osmolarity? Why is this?

Answer 19

As the difference in osmolarity (between the NaCl solutions and the RBC) increases, the observed time for haemolysis decreases because there is a greater driving force and so H2O moves faster into the membrane

Question 20

What is the aim for experiment 4?

Answer 20

This is to illustrate the relative permeabilities of the red blood cell membrane to various substances by measuring the time for haemolysis

Question 21

Red blood cells, when places in either NaCl solution (154 mmol/L) or glucose solution (300 mmol/L), neither swell or shrink. Why is this?

Answer 21

This is because the rate of osmosis into the cell is equal and opposite to the rate of osmosis out of the cell.

Question 22

In a 300 mmol/L urea solution of red blood cells burst, yet in a 300 mmol/L NaCl solution, the cells shrink. Why is this?

Answer 22

• There is no Na+ or Cl- channel in the membrane of the RBC despite the concentration gradient being present; Na+ and Cl- can’t enter
• Urea can’t dissociate so the osmolarity is the same as the concentration. There is a channel for urea to enter the cell but it can’t leave. It enters the cell as there is a low concentration and water follows, making it hypertonic. The cell bursts