Testing hypotheses in scientific investigation

1
Testing hypotheses in scientific investigation
2
A study on predator-prey relationship-- Caro
--
3
(No Transcript)
4
(No Transcript)
5

• slow down the deer
• more conspicuous
• more vulnerable

6
Observation Deer leap when running away from a
cheetah.

• What question to ask?
• What to find out?

7
Problem

• Why does a deer occasionally leap when running
  away from a cheetah?

8

• What can you suggest ?

9
Tentative explanations

• Deer leap to survey immediate area for predators.
• Deer leap to warn other deer of danger.
• Deer leap to draw attention away from their
  vulnerable young.
• Deer leap to tell the predator that it has been
  seen.

10

• These tentative explanations are derived from
  Caro? prior knowledge of similar situations.
• A hypothesis is a tentative explanation proposed
  to account for some specific observation.

11

• Hypotheses
• -- not merely educated guesses based on an
  observation.
• Creating hypotheses requires background
  information as well as an element of guessing.
• Not all educated guesses are hypotheses.

12
Example

• Observation
• You taste a green apple find that it is sour.
• After tasting 2, 3 ...10 green apples, you also
  find them sour.

13

• What will you conclude ?
• All green apples are sour.
• Is this educated guess a hypothesis?

14

• It is a generalization --
• a general statement drawn from specific
  observation by induction.
• It does not attempt to offer an explanation for
  the observation.

15

• Based on this generalization, we can make the
  prediction that The next green apple will be
  sour?by deduction.
• The prediction will be true if the general
  statement ?All green apples are sour?is true.

16
By asking questions on the original observation,
the following process will lead to new knowledge
17
Problem Why are green apples sour? Hypotheses
1. Green apples lack sugar. 2. Green apples
contain many acids.
18
Testing hypotheses

• Caro? next step
• To find out which tentative explanations
  (hypotheses) is the best answer to the question.

19

• If deer leap to draw attention
• away from their more vulnerable offspring
  (hypothesis)
• then ..... (predictions?)

20
So what can you predict?
21
Prediction 1 Young, sexually immature deer
should not leap. Prediction 2 Adults who have no
young in the herd should not leap. Prediction
3 Isolated deer who are feeding alone should not
leap.
22

• If the hypothesis under consideration is correct,
  some experimental or observational situation will
  lead to one or more specific expected outcomes
  (predictions).

23

• These predictions are made by deduction from the
  hypothesis, but they differ in nature from the
  predictions derived from a generalized statement.

24

• He observed that
• sexually immature deer
• adults with no young
• isolated deer
• deer with offspring
• all leap at the same frequency when fleeing from
  a cheetah.

25

• With respect to the present hypothesis, Caro?
  results did not correspond well with his expected
  (predicted) results.

26

• Caro rejected this hypothesis.
• By testing other hypotheses in this way, Caro
  rejected all but the hypothesis that
• Deer leap to signal that the predator has been
  seen, thus the deer will be difficult to catch.

27
Support for this hypothesis came from the
following reasoning and evidence

• Hypothesis
• If deer leap to signal to the predator that it
  has been seen, so the deer will be difficult to
  catch ......

28

• Prediction 1
• then deer should leap so that the furs at their
  back are visible to the predator not to other
  deer.
• Prediction 2
• then solitary deer should leap just as often as
  those in groups.
• Prediction 3
• then predators should often abandon a chase if
  the deer leap early.

29

• Caro observed all of these expected outcomes
  (predictions) and therefore concluded that this
  hypothesis had been supported.

30
(No Transcript)
31
Examples from AL Biology

• Observation
• Green bananas are still raw. They taste flat but
  after storing for a few days, they become yellow
  taste sweet.

32
Problem ?

• What makes the banana sweet after storing for a
  few days?

33
Hypotheses

• 1. The green banana carries out photosynthesis
  to produce sugar during storage.
• 2. The starch in the raw banana changes into
  sugar during storage.

34

• Predictions for Hypothesis 1
• If H1, then .....
• Predictions for Hypothesis 2
• If H2, then .....

35
Methods of scientific investigation

• 1. Proposing a hypothesis to account for certain
  observation and testing its predictions by

36

• a) Performing experiment -
• a planned intervention in which a part of
  the natural world is manipulated in order to
  obtain data.

37

• b) Making planned structured observation -
• the objects cannot be brought into the lab
  processes which cannot be replicated
• (e.g. astronomy and geology).

38

• c) Historical explanations
• e.g.
• palaeontology evolutionary biology

39
2. Collecting data and information

• In initial exploration of a new area, the primary
  concern is often simply to gather data about the
  area.
• No theory (hypothesis) in mind.

40

• For most school students, a significant
  proportion of their first-hand experience of
  science is of this nature
• -- not involving hypothesis
• formulation testing.

41
Examples of this type of investigation

• Which is sweeter, the green grape or red grape?
• What food substances are present in the maize
  grain?
• What is the effect of heating on vitamin C
  content of fresh orange juice?

42

• Compare the protease activity of pineapple, kiwi
  fruit and papaya.
• Find the water potential of potato cells.
• What is the optimum temperature of salivary
  amylase?
• What keeps a cut flower longer?

43
(No Transcript)
44
Thank you !