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Gas bubbles from the pond weed Testing hypotheses in scientific investigation Observation Bubbles coming out from the pond weed. These are oxygen bubbles produced by the plants during photosynthesis. Betsy was not convinced of this explanation.

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gas bubbles from the pond weed
Gas bubbles from the pond weed

Testing hypotheses in

scientific investigation

observation
Observation

Bubbles coming out from the pond weed.

slide5
Betsy was not convinced

of this explanation.

slide6
The bubbles could be carbon dioxide, nitrogen or anything.

They could have been produced by respiration or other life processes.

problem for investigation
Problem for investigation:

What are the gas bubbles made up of ?

betsy made the following tentative explanations
Betsy made the following tentative explanations:
  • The gas is carbon dioxide produced by respiration of the pond weed.
  • The gas is oxygen produced by photosynthesis of the pond weed.
slide10
All living organisms undergo respiration which provides the energy for all life processes.

Green plants undergo photosynthesis in the presence of light to produce energy-rich food.

slide12
Creating hypotheses requires background information as well as an element of guessing (or imagination), but not all educated guesses are hypotheses.
observation14
Observation

You eat a banana & find that it has no seed inside.

After eating a second, third, & ... tenth banana, you also find them seedless.

slide18
This is not a hypothesis. It is a generalization --a general statement drawn from observation by a process known as induction.
slide20

Based on the generalization “All bananas are seedless”,what prediction(s) can you make (if you are given another banana)?

slide24

The following steps show how a scientific method can be used to build up knowledge from the same observation.

ask the pupils to suggest a problem question for investigation on basis of the original observation
Ask the pupils to suggest a problem (question) for investigation on basis of the original observation.
formulating hypotheses

Formulating hypotheses:

1. Banana plants do not have flowers.

2. Banana flowers do not produce pollen grains.

3. No fertilization takes place in the banana flower.

example 2
Example 2

Observation:

The sun has risen in the east every day in the past years.

generalization
Generalization:

The sun always rises

in the east.

prediction
Prediction:

The sun will rise in the east tomorrow.

problem
Problem:

Why does the sun rise in the east?

hypotheses
Hypotheses:

1. The sun moves around the earth.

2. The earth rotates on its axis from west to east.

slide37
Summarize the differences between a generalization and a hypothesis as derived from the same observation.
testing hypotheses
Testing hypotheses

Betsy’s next step:

Which alternative explanations (hypotheses) was the best answer to the question?

hypothesis 1
Hypothesis 1:

Ifthe gas is carbon dioxide produced by respiration of the pond weed…..

prediction 1
Prediction 1:

then the pond weed will produce the gas all the time.

prediction 2
Prediction 2:

then the gas will turn lime water milky.

based on the predictions betsy designed a number of experiments to test the hypothesis
Based on the predictions, Betsy designed a number of experiments to test the hypothesis.
slide44
Betsy watched the aquarium day & night  The pond weed produced the gas bubbles only in the presence of light.
slide48
Hypothesis 2:

If the gas is oxygen produced by photosynthesis of the pond weed …..

prediction 150

Prediction 1:

then the pond weed will only produce the gas in the presence of light.

prediction 251

Prediction 2:

thenthe gas will not turn lime water milky, but will be absorbed by alkaline pyrogallic solution.

slide53
Experimentsobserved all the expected outcomes (predictions). concluded that this hypothesis is supported.
the above investigation leads to the following conclusion
The above investigation leads to the following conclusion:

The gas bubbles are made up of oxygen produced by the pond weed during photosynthesis.

this conclusion can be taken as a new observation a starting point for further investigation

This conclusion can be taken as a new ‘observation’, a starting point for further investigation.

examples from al biology
Examples from AL Biology

Observation:

Green bananas taste flat but become yellow & taste sweet after storing for a few days.

hypotheses 1
Hypotheses 1:

The green banana carries out photosynthesis to produce sugar during storage.

hypothesis 2
Hypothesis 2:

The starch in the raw banana changes into sugar during storage.

slide67
Performing experiment
  • Making planned & structured observation
  • Historical explanations
examples
Examples
  • Which is sweeter, the green grape or red grape?
  • What food substances are present in the maize grain?
slide71
What is the effect of heating on vitamin C in fresh orange juice?
  • Compare the protease activity of pineapple, kiwi fruit and papaya.
slide72
Find the water potential of potato cells.

What is the optimum temperature of salivary amylase?

slide73
Study the responses of mealworms to external stimuli.

Which area of the hand is most sensitive to touch, heat, cold or pressure?