1. Osmosis Experiment (Monday)

2. Your Research Question…
How does sucrose concentration affect the water content (rate of osmosis) in root vegetables (potatoes, sweet potatoes) ?
Or a more ‘correct’ scientific question:
Using sucrose solution as a reference point of known water potential, what is the water potential of white potatoes (Solanum tuberosum]/ Sweet potatoes (Ipomea batatas)?

3. Osmosis
‘Facilitated diffusion of water molecules from a region of their higher concentration (high water potential, dilute solution) to a region of their lower concentration (concentrated solution, low water potential, through a partially permeable membrane ’ Let’s remind ourselves… McGraw Hill animation

4. What are factors which affect osmosis?
Temperature: The higher the temperature, the higher the rate of osmosis
Concentration gradient across the semi-permeable membrane (Difference in water potential*)
Surface Area for osmosis
Pressure difference across the semi-permeable membrane (Difference in water potential*)

5. Check out the amyloplasts, storing starch granules…
Potato cells
Check out the amyloplasts, storing starch granules…

7. Designing an experiment

8. The fundamental cornerstone of ALL SCIENCE
The Scientific Method
The fundamental cornerstone of ALL SCIENCE

10. Words we will understand by the end of today…
Observation
Inference
Hypothesis…and the Null Hypothesis
Data – quantitative and qualitative
Variables
Controlled experiment
Control group

11. Why do all experiments require a hypothesis?
‘If... then…’ We must have a principle that we can objectively test We generally state the Null Hypothesis for cause-and-effect relationships

12. Based on our observations, we formulate a research question
Our research question is presented as a hypothesis, based on our biological reasoning
We typically present the Null hypothesis

13. Identify the experimental VARIABLES
Independent – what you change (X- axis)
Dependent – what you measure (Y-Axis)
Controlled – what remains constant (potential to influence experimental data)
(Uncontrolled – variables which may be hard to control) (potential to influence experimental data)
Ideally you should have all variables controlled, excepting one dependent and one independent variable

15. When does a hypothesis become a theory?
When a hypothesis is repeatedly confirmed by experiment and observation (USING THE SCIENTIFIC METHOD), it may become generally considered as a THEORY
THEORIES are the most reliable, rigorous, and comprehensive form of scientific knowledge
Some well known scientific theories:
Cell theory
Evolutionary theory
Theory of relativity
Climate change theory

16. Designing a controlled experiment

17. Designing a controlled experiment
Formulate a focused research question
Identify ALL of the relevant variables (independent, dependent, controlled, uncontrolled)that could influence outcome
Decide how to manipulate the independent variable – range
Decide how many repeats of the experiment you need to do
Decide if you are including a control (‘untreated’) group

18. How much data is enough?

19. Your Research Question…
How does sucrose concentration affect the rate of osmosis across potato cells? Or a more sophisticated question: Using sucrose solution as a reference point of known water potential, what is the water potential of white potatoes (Solanum tuberosum]?

20. (i.e. what will be your dependent variable?)
…So how could we ‘measure’ the effect of sucrose concentration on the rate of osmosis in potatoes?
(i.e. what will be your dependent variable?)

21. Other folks ideas… Mr Bozeman's tips
Rate of osmosis could be measured as mass change per unit time (gmin-1 or gh-1)
In a closed chamber, [where temperature was controlled, and not manipulated], rate of osmosis could be measured as pressure change per unit time (kPamin-1)

22. Identification of Independent, Dependent, controlled and measured variables

23. Make a table of accurately defined variables
Definition, Units
Independent
Dependent
Rate of osmosis
Controlled
Measured

24. Factors which affect osmosis
Sucrose concentration will be your independent variable (what you manipulate)
You must ensure that all other factors are controlled

25. Sucrose concentration
Results table
Sucrose concentration 1%
10%
25%
50%
Distilled water
Initial mass of potato (g ±0.01)
Final mass of potato (g ±0.01)
Change in mass (g ±0.01)
% change in initial mass

26. Is one set of results enough?
How could we improve the accuracy of our results?

27. Your Research Question…
How does sucrose concentration affect the rate of osmosis across potato cells? Or a more sophisticated question: Using sucrose solution as a reference point of known water potential, what is the water potential of white potatoes (Solanum tuberosum]?

28. Reminder: Water potential (y)
A term used to describe the ‘water concentration’of a cell or tissue
Pure water in a free standing solution has a water potential of zero, while most plant cells have a negative water potential.
All solutions have water potential < 0
A dilute solution has a relatively high water potential
A concentrated solution has a relatively low water potential

29. Water potential = solute potential + pressure potential

31. Do we know the water potential of sucrose solution?
How can that help us define the water potential of our potatoes?

32. Your challenge for next Monday/ Tuesday
Set up experiment
Collect and collate CLASS data on Google form
Calculate the mean and standard deviation of the % change in mass of the potato strips for each sucrose solution
GRAPH the mean and standard deviation of the % change in mass of the potato strips for each sucrose solution
Use your knowledge of osmosis to explain your results
Think of ways in which you could improve your experient to make your results more reliable