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.
The bubbles could be carbon dioxide, nitrogen or anything. They could have been produced by respiration or other life processes.
Problem for investigation: What are the gas bubbles made up of ?
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.
These tentative explanations 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.
A hypothesis is a tentative explanation proposed to account for some specific observation.
Creating hypotheses requires background information as well as an element of guessing (or imagination), but not all educated guesses are hypotheses.
Observation You eat a banana & find that it has no seed inside. After eating a second, third, & ... tenth banana, you also find them seedless.
This is not a hypothesis. It is a generalization --a general statement drawn from observation by a process known as induction.
It does not attempt to offer an explanation for the observation.
Based on the generalization “All bananas are seedless”,what prediction(s) can you make (if you are given another banana)?
We can make the prediction “The next banana will also be seedless” by deduction.
The prediction will be true if the general statement “All bananas are seedless”is true.
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.
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 Observation: The sun has risen in the east every day in the past years.
What can you generalize from this observation?What can you predict from the generalization?
Generalization: The sun always rises in the east.
Prediction: The sun will rise in the east tomorrow.
Problem: Why does the sun rise in the east?
Hypotheses: 1. The sun moves around the earth. 2. The earth rotates on its axis from west to east.
Summarize the differences between a generalization and a hypothesis as derived from the same observation.
Testing hypotheses Betsy’s next step: Which alternative explanations (hypotheses) was the best answer to the question?
Hypothesis 1: Ifthe 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.
Based on the predictions, Betsy designed a number of experiments to test the hypothesis.
Betsy watched the aquarium day & night The pond weed produced the gas bubbles only in the presence of light.
Support for Hypothesis 2 may come from the following reasoning and evidence:
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.