Practical 7 - Determination of the solute potential by measuring the degree of incipient plasmolysis

Question 1

What are equal in incipient plasmolysis?

Answer 1

The cell’s water potential and the solute potential

Question 2

What’s the value of the pressure potential in incipient plasmolysis?

Answer 2

0kPa

Question 3

Describe the movement of water when a cell’s in incipient plasmolysis

Answer 3

No net-movement of water
In equilibrium

Question 4

What type of external medium is a cell in to be in incipient plasmolysis?

Answer 4

Isotonic

Question 5

Describe the cell when under incipient plasmolysis

Answer 5

Not turgid or plasmolysed

Question 6

What do we put into the Petri dishes and how much?

Answer 6

10cm^3 of…
Distilled water
0.2, 0.4, 0.6, 0.8 moldm^-3 sodium chloride solution

Question 7

What do we put our solutions in?

Answer 7

Petri dishes

Question 8

How do we remove the upper epidermis of the onion leaf?

Answer 8

Insert the fine forceps tip just underneath
Keep the forceps parallel to the epidermis (so as not to penetrate the underlying mesophyll), grip the epidermis and, maintaining tension in the tissue, pull the epidermis off the mesophyll away from you and into the distilled water

Question 9

Where do you put the epidermis layer after removing it?

Answer 9

In distilled water

Question 10

Why is it important to keep the forceps handles parallel with the epidermis when removing it?

Answer 10

So as not to penetrate the underlying mesophyll

Question 11

How did we improve reliability in this experiment?

Answer 11

We put more than one epidermis layer in each concentration and calculated a mean

Question 12

What does putting more than one layer of epidermis in each concentration do?

Answer 12

Gives us reliable results

Question 13

How long did we leave the epidermis layer;s in their Petri dishes for?

Answer 13

At least 30 minutes

Question 14

Why does the tissue need to be spread carefully onto the microscope slide?

Answer 14

So as not to fold it

Question 15

How big of a square of tissue do we cut?

Answer 15

5cm x 5cm

Question 16

What do we apply to the tissue on the slide?

Answer 16

2 drops of bathing solution
Cover slip

Question 17

What do we do once the tissue samples are under the microscope?

Answer 17

Count the number of turgid and plasmolysed cells in field view under the x10 and x40 objective lens and repeat counts at all concentrations

Question 18

Which objective lens do we view the tissue with?

Answer 18

x10 and x40

Question 19

What goes on the x and y axis on the graph?

Answer 19

x - concentration of the bathing solution
y - mean % cells plasmolysed

Question 20

How do we work out the solute potential of the tissue sample?

Answer 20

Read the concentration of bathing solution that would produce plasmolysis in 50% of the cells on the graph and use the table to convert it to solute potential

Question 21

What happens to the tissue in solutions of lower molarities?

Answer 21

The solution has a higher water potential than the tissue
Water moves into the cell by osmosis
Cells are turgid

Question 22

What happens to the tissue in solutions of higher molarities?

Answer 22

The solution has a lower water potential than the tissue
Water leaves the cell by osmosis
Cells plasmolyse

Question 23

Under which conditions do the cells become turgid here?

Answer 23

Solutions of lower molarities

Question 24

Under which conditions do the cells plasmolyse here?

Answer 24

Solutions of higher molarities

Question 25

What percentage of the cells have plasmolysed in incipient plasmolysis?

Answer 25

50%

Question 26

What’s the pressure potential of the cell under incipient plasmolysis?

Answer 26

0kPa

Question 27

What’s the relationship between the water and solute potentials of the tissue in incipient plasmolysis?

Answer 27

Equal

Question 28

What does a range bar show?

Answer 28

The mean
The highest point
The lowest point

Question 29

What’s the name of the line drawn on a graph to show the highest ad lowest points as well as the mean?

Answer 29

Range bar

Question 30

What does a longer range bar mean?

Answer 30

Less repeatable data
Less reliable data

Question 31

How do we improve the reliability of this practical?

Answer 31

Observe more pieces of onion tissue from each solution and calculate a mean

Question 32

How do improve the accuracy of this experiment?

Answer 32

Use a narrower range around 50% plasmolysis