Misconceptions in Scientific Inquiry

1. What is scientific inquiry? Misconceptions in Scientific Inquiry • Methods used by scientists • Nature of scientific knowledge • Historical examples : • Theory of spontaneous generation • What is the genetic material? • Cause of gastric ulcer - Marshall

2. Key steps of scientific inquiry: 1.Observation: Maggots are often found on rotten meat. Question: Where do the maggots come from? 2.Hypothesis: The maggots are hatched from eggs laid by flies. 3.Testing the hypothesis Predictions  Design experiments / observation If the hypothesis is correct, ….. Results: (a) No maggots were found inside Flask 1. (b) Maggots were found inside Flasks 2 and 3. Conclusion: The maggots were developed from eggs laid by flies.

3. Concept of assumptions What is the aim of the experiment? What do I actually measure? What is my assumption(s) ? What is the conclusion?

4. Only oxygen is used up during burning. • All oxygen in the air is used up. • No air has escaped from the gas jar. • All carbon dioxide released out during combustion is dissolved in water. Assumptions made:

5. What do you want to measure? Growth of seedlings • What parameter do you actually measure? • length of radicle, • fresh mass • dry mass How is this parameter related to what you want to measure?

6. What do you want to measure? • What parameter do you actually measure? • length of root • fresh mass • dry mass How is this parameter related to what you want to measure? Which assumptions may not hold true under specific situations?

7. We want to measure the growth of germinating seeds - formation of new cells or protoplasm. • We actually measure the increase in length of the root/the fresh mass /the dry mass of the seedlings. • Assumptions: all changes in the parameter we measure are caused by changes in the quantity of new cells or protoplasm. • The assumptions may not hold true in the following situations: • At the initial stage when the dry seeds are soaked in water, the increase in fresh mass of the seeds is not caused by growth but by the absorption of water. • The growth of a seedling during germination cannot be measured by the change in dry mass - affected by the oxidation of organic substances in respiration.

8. Aim? Assumptions? Conclusion? Van Helmont’s experiment [1668]

9. Aim of experiment To test the hypothesis:Plants absorb soil as food through the roots for growth. Assumption: Plants obtain their nutrients through the roots. Conclusion: (CE 2003 Q4) Plants do not absorb soil as food through the roots for growth. They absorb water through the roots.

10. Measuring the rate of transpiration using a bubble potometer What do you want to measure? What parameter do you actually measure? How is this parameter related to what you want to measure?

11. Measuring the rate of transpiration using a bubble potometer What is your assumption? The rate of water absorption is identical to the rate of transpiration. Under what situations will the assumption fail to hold true? • Using a dehydrated shoot • Transpiration rate >> rate of water absorption

12. Other examples: • To find out the water potential of potato cells by measuring the length or mass of potato cylinders • To measure the rate of respiration of mealworms using a respirometer • To compare the vitamin C content of fresh and boiled orange juice using DCPIP solution • To compare the sweet taste of green and red grapes using Benedict’s test • To find out which brand of tissue paper absorbs water best

13. Drawing conclusions from negative results Suppose you have performed a number of food tests on milk and got the following results: Benedict’s testIodine testBiuret testGrease spot test +++  ++ + What would be your conclusion on the food content of milk?

14. Drawing conclusions from negative results Corn plants were grown in fields A and B of different soil conditions. To test for N sufficiency in the soil, each field was separated into two plots. One plot was supplied with N fertiliser and the other plot without N fertiliser. After 15 weeks, the corn in the two fields was harvested. (a) What conclusion can you draw from the results of field A? (b) What conclusion can you draw from the results of field B?

15. Drawing conclusions from negative results (a) N is deficient in field A. (93%) (b) N is not deficient in field B. Besides N, the plants need other minerals. No conclusion about N content of Field B. 18%

16. Drawing conclusions from negative results (a) If germination occurs in set-up B but not in set-up A, what would be your conclusion? (b) If no germination occurs in both set-ups, what would be your conclusion?

17. Drawing conclusions from negative results (a) Water is necessary for germination. (96%) (b) Water is not necessary for germination. Besides water, other factors are necessary. No conclusion can be obtained.(31%)

18. Drawing conclusions from negative results Cognitive conflict What conclusion can be made if: (a) germination occurs in B but not in A. (b) germination occurs in both A and B. (c) no germination occurs in both A and B.

19. Misunderstanding on concept of hypothesis Investigations that do not need a hypothesis Problem: What are the effects of air currents on the rate of transpiration of a plant? Hypothesis: The rate of transpiration is greater in windy conditions than in still air.

20. Investigations that do not need a hypothesis Problem: What are the energy values of 3 food samples: cheese, peanut and biscuit? Hypothesis: It is hypothesized that peanut will generate the largest amount of energy and biscuit the lowest. It is because peanut is rich in oil, which can provide 2x of energy as that of biscuits, which is mainly made up of carbohydrates.

21. Further examples (p.102)

22. Investigations that involve hypothesis (p.103)

23. Students’ performance in exam questions 2005 CE Biology Q3(c) & (d) Marshall observed that all his ulcer patients had a type of bacteria called Helicobacter pylori’. He treated his patients with antibiotics What was Marshall’s hypothesis about gastric ulcer? • Gastric ulcer can be cured by antibiotics. • Helicobacter pylori can survive in the low pH of stomach. • The bacteria can be killed by antibiotics.

24. 2005 CE Bio Q3 How to test Marshall’s hypothesis? Wrong answers: Inject antibiotics into the patient’s body. If the hypothesis is correct, all bacteria will be killed. After injecting antibiotics, examine the cells of stomach under a high-power to check whether the bacteria are killed or not.

25. 2004 CE Bio Q2 What did Engelmann wish to find out by setting up the experiment? Wrong answer: Engelmann wanted to test the hypothesis that blue and red lights are most effective for photosynthesis. No hypothesis is needed.

26. 2000 CE Bio Q3 What was the aim of performing experiments? To determine whether the active substance for treating diabetes was a protein or a fat.

27. 2000 CE Bio Q3 If the active substance is a protein  predictions  Control and experimental set-ups

28. 2006 AL Biology 1 Q5 (a) Meat broth did not turn cloudy; no microbes found. (a) Meat broth turned cloudy; microbes found. • What is the hypothesis to be tested? • Which one is the control set-up, and which one the experimental set-up? • What conclusion can be drawn from the results?

29. Went’s experiment (1928) • Coleoptile tips are placed on the agar plate. • 2. The agar plate is cut into 12 blocks. • 3. The tips are removed from the coleoptiles. • 4. Agar block is place on one side of the decapitated coleoptile. • 5. The coleoptile bends to one side. • What is the hypothesis to be tested? • Which is the control set-up, and which the experimental set-up? • What conclusion can be drawn from the results?

30. What is the hypothesis to be tested? • Which is the control set-up, and which the experimental set-up? • What conclusion can be drawn from the results? Loewi’s experiment (1921)

31. What is the hypothesis to be tested? • Which is the control set-up, and which the experimental set-up? • What conclusion can be drawn from the results? In the 18th century, people noticed that a piece of meat, once in the stomach, was soon digested into a semi-fluid mass. There were two theories to account for this: the food was digested by the churning action of the stomach or by the action of digestive juice. A scientist swallowed a hollow wooden tube (2 cm long and 0.5 cm in diameter) with small holes containing a piece of meat. 2 days later, the wooden tube passed out of his body. It was found to be empty.

33. How to identify misconceptions • Ask high-order questions – informal /formal • - understanding • - application in different contexts • Students construct drawings/flow diagrams /concept maps • Discuss specific instances • Challenge students to ask questions

34. Informal preconceptions • Lack of prerequisite knowledge • Language – everyday meaning & scientific meaning • Compartmentalised concepts • Too many facts  rote learning • Inaccurate text or teaching Why misconceptions ?

35. Re-teaching • Cognitive conflicts • Generating a range of conceptual schemes • Using ideas in a range of situations • e.g. osmosis, grease-spot test Design teaching strategies

36. Osmosis Lock-and-key model Emulsion test & fat absorption Vitamin C & carnivore Egestion & excretion Blood pressure, flow rate, resistance Capillary network Tubal ligation & menstrual cycle Development of insecticide resistance Which came first, chicken or egg?