Practical 7 - Determination of the solute potential by measuring the degree of incipient plasmolysis Flashcards
What are equal in incipient plasmolysis?
The cell’s water potential and the solute potential
What’s the value of the pressure potential in incipient plasmolysis?
0kPa
Describe the movement of water when a cell’s in incipient plasmolysis
No net-movement of water
In equilibrium
What type of external medium is a cell in to be in incipient plasmolysis?
Isotonic
Describe the cell when under incipient plasmolysis
Not turgid or plasmolysed
What do we put into the Petri dishes and how much?
10cm^3 of…
Distilled water
0.2, 0.4, 0.6, 0.8 moldm^-3 sodium chloride solution
What do we put our solutions in?
Petri dishes
How do we remove the upper epidermis of the onion leaf?
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
Where do you put the epidermis layer after removing it?
In distilled water
Why is it important to keep the forceps handles parallel with the epidermis when removing it?
So as not to penetrate the underlying mesophyll
How did we improve reliability in this experiment?
We put more than one epidermis layer in each concentration and calculated a mean
What does putting more than one layer of epidermis in each concentration do?
Gives us reliable results
How long did we leave the epidermis layer;s in their Petri dishes for?
At least 30 minutes
Why does the tissue need to be spread carefully onto the microscope slide?
So as not to fold it
How big of a square of tissue do we cut?
5cm x 5cm
What do we apply to the tissue on the slide?
2 drops of bathing solution
Cover slip
What do we do once the tissue samples are under the microscope?
Count the number of turgid and plasmolysed cells in field view under the x10 and x40 objective lens and repeat counts at all concentrations
Which objective lens do we view the tissue with?
x10 and x40
What goes on the x and y axis on the graph?
x - concentration of the bathing solution
y - mean % cells plasmolysed
How do we work out the solute potential of the tissue sample?
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
What happens to the tissue in solutions of lower molarities?
The solution has a higher water potential than the tissue
Water moves into the cell by osmosis
Cells are turgid
What happens to the tissue in solutions of higher molarities?
The solution has a lower water potential than the tissue
Water leaves the cell by osmosis
Cells plasmolyse
Under which conditions do the cells become turgid here?
Solutions of lower molarities
Under which conditions do the cells plasmolyse here?
Solutions of higher molarities
What percentage of the cells have plasmolysed in incipient plasmolysis?
50%
What’s the pressure potential of the cell under incipient plasmolysis?
0kPa
What’s the relationship between the water and solute potentials of the tissue in incipient plasmolysis?
Equal
What does a range bar show?
The mean
The highest point
The lowest point
What’s the name of the line drawn on a graph to show the highest ad lowest points as well as the mean?
Range bar
What does a longer range bar mean?
Less repeatable data
Less reliable data
How do we improve the reliability of this practical?
Observe more pieces of onion tissue from each solution and calculate a mean
How do improve the accuracy of this experiment?
Use a narrower range around 50% plasmolysis
