The scientific method

Observations

Identify a problem

Hypothesis

Predictions

Investigation

Results

Interpretations

Accept?

Modify?

Reject?

A study on the gas bubbles released from the pond weed

The aquarium in the biology laboratory was an attraction for Betsy and her classmates. While watching the colourful coral fish moving elegantly through the dense pond weed, they noticed that numerous small bubbles came out from the pond weed. They wondered what these bubbles were. Jackie said that these were oxygen bubbles produced by the plants during photosynthesis. Betsy was not quite convinced of this explanation. The bubbles could be carbon dioxide, nitrogen, or anything, and they could have been produced by respiration or other life processes. She wanted to perform an investigation to find out the answer herself.

Problem for investigation

What are the gas bubbles that come out from the pond weed?PROPOSING HYPOTHESIS

Betsy made the following tentative explanations (hypothesis)

Hypothesis 1: The gas is carbon dioxide produced by respiration of the pond weed.

Hypothesis 2: The gas is oxygen produced by photosynthesis of the pond weed

These hypotheses are derived from Betsy’s biological knowledge such as:

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.

MAKING PREDICTIONSHypothesis 1: If the gas is carbon dioxide produced by respiration of the pond weed.

Prediction 1: then the pond weed will produce the gas all the time.

Prediction 2: then the gas will turn lime water milky.

INVESTIGATIONSBetsy watched the aquarium day and night and found that the pond weed produced the gas bubbles only in the presence of light. She also collected the gas and found that it did not turn lime water milky.

Hypothesis 2: If the gas is oxygen produced by photosynthesis of the pond weed.

Prediction 1: then the pond weed will only produce the gas in the presence of light.

Prediction 2: then the gas will not turn lime water milky, but will be absorbed by alkaline pyrogallic solution.

After carrying out a number of experiments, Betsy concluded that this hypothesis had been supported.

CONCLUSION

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