This isn’t preparation for Biology 2.1

1. This isn’t preparation for Biology 2.1 AIM: Carry out a short investigation that won’t help you prepare for Biology 2.1

2. Premise • Dried apricots are low in water – no surprises there – so if you place one in a beaker of water it will take up water by osmosis. No surprises there either as the cells are still intact so water will move from the beaker into the apricot because the water is moving from an area of high concentration (beaker) to an area of low concentration (apricot) across a selectively permeable membrane.

3. Task • Or will it? Your mission, should you choose to accept it (and you will) is to demonstrate that this uptake of water will occur and then explain it as succinctly and beautifully as I have in the previous slide which you will never, never, never see again. • Please note: it would be UNREASONABLE to expect you to compare your results with those of your fellow scientists or compare to any previous research, after all real scientists don’t do that

4. Equipment • You have one dried apricot and two friends (or maybe one dried apricot and two other people who might trade results with you), a beaker, water, thermometer, electric scales and a next-to-useless biology teacher who can give you “supervision” (whatever that means).

5. Apricots & Osmosis • Aim: • Hypothesis: • Independent Variable? • Dependent Variable • Controlled Variables • Number of Repeats • Method

6. What are you waiting for? Get started! I'm not doing the freaking thing for you! Results • You might like to make use of the following table (or not) Average Percentage Weight Change:

7. % Mass Change vs % of Original Weight • An apricot started at 10 grams and increased to 20g, an increase of 10 grams. % mass change = weight gain / initial weight x 100 = 10 / 10 x 100 = 100% % of original weight = final weight / initial weight x 100 = 20 / 10 x 100 = 200%

8. Conclusion • What did you results show? Discussion • Justify your conclusion in terms of the method you used. • This is about what you did to make it a fair test and why that means your conclusion is correct. • It isn’t about the things you cocked up or would do differently if you did it again. You’re never going to do it again so do it right in Bio 2.1! • Explain (using your vast knowledge of osmosis) the reason for the results you obtained. Evaluation

9. Other guff you should know after 3.5-5.5 of years of science at Johnnies… • Independent Variable (changing what? & valid range) • Dependent Variable (you’re measuring…?) • Controlled Variables (how!?) • Do experiment right! (method can be changed!) • Why do repeats? • How to draw a table, graph • Conclusion relates to purpose AND your data! • Discussion uses scientific knowledge to explain trend / pattern in results • Evaluate it. Justify what you have said is right by bragging about your: • Quantity of data • Wonderful independent variable range • Removal of sources of error • Removal of bias

10. Validity vs Reliability • Validity: the degree to which a study accurately reflects or assesses the specific concept that the researcher is attempting to measure. We achieve validity by: • Having a suitable range for our independent variable (at least five!) • Measuring all variables accurately (how many decimal places?) • Controlling all variables not being investigated (and stating how you controlled and measured them) • Anything else that you might have done to remove error and bias

11. A List of Controlled Variables Size of apricot Length of time Concentration for each repeat Glad wrap to prevent evaporation Same equipment Temperature of repeat Apricots from same bags (controls species variation, variation in dryness) Removed excess water from wet apricots

12. Validity vs Reliability • Reliability: the extent to which an experiment, test, or any measuring procedure yields the same result on repeated trials. • We achieve this by carrying out repeats (at least three!) and averaging the data

14. Practice Plan Design an experiment to find out what will happen in terms of osmosis to celery sticks placed in different salt concentrations. Background: concentration of salt in celery is 0.5 mol / L. You have lots of celery, 5 x 30cm sticks of celery each. Concs of salt solutions available. Distilled water, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1,1.2, 1.3, 1.4, 1.5 mol / L salt concs. Complete the following: Aim, Hypothesis, Variables (independent, dependent, controlled), Equipment, Method.

15. Observing Osmosis in a Cell

16. Observing Osmosis in a Cell • Problem • hard to see osmosis occurring in microscopic cells. • Solution • use a large cell like a chicken egg • Problem • shell impermeable to water. • Solution • remove shell (dissolve in acetic acid – vinegar) Reaction: Calcium carbonate + Acetic acid  H2O + CO2 + Calcium Acetate Chemists: write the formula, try to balance! (Acetic acid: CH3COOH, Acetate ion: CH3COO-)

17. Dissolve shell Place in water Weigh Measure 200mL sugar solution Put egg in, leave 48 hours. Weigh, measure solution volume Expect: egg mass drop, solution volume increase

18. Observations +30mins: Bubbles of CO2 on egg Observations +48hrs (day 3): • Place egg in 250mL of a hypertonic sugar solution Prediction: Observations +48hrs (day 5): - Egg: Liquid Volume Observations +48hrs (day 7): - Egg: Liquid Volume • Questions • What happened to the egg? Why? • What happened to the liquid volume? Why • What could you do to reverse what happened?

19. Elodea Plasmolysis

20. Elodea Plasmolysis Make a wet mount of elodea and add saltwater to the slide. Observe what happens to the cells after 15min. (make a control (no salt) for comparison). Observations: Conclusions: Questions: Is plasmolysis reversible? What could you do to test this?

22. See: http://www.biologycorner.com/worksheets/plants_and_salt.html For a clip on cytoplasmic streaming

23. Isotonic Concentration of Carrots Aim: to find out the isotonic concentration of carrots

24. Isotonic concentration of carrots • Write: • Aim • Independent variable • suitable range, how to change it • Dependent variable • what, how to measure • Controlled variable • List each and how to measure and check

26. Dummy Data

27. Questions What happened in distilled water? Explain What happened in the saltiest concentration? Explain How did you identify the isotonic concentration? How did you make sure the experiment was valid? How did you make sure the experiment was reliable?