Observing, recording, inferring, generalising, prediciting and testing.
Irene observed that when a water plant is placed in a sealed test tube with water that had been previously boiled and put in a dark cupboard it died. The set up is shown on the right.
She recorded the average height of the plants over the five day period.
Day |
Average
height |
Appearance |
1 |
5.5
cms |
bright
green in colour and standing tall |
2 |
5.0
cms |
green
in colour but starting to shrink |
3 |
4.3
cms |
brownish
tinge starting to appear |
4 |
2.1
cms |
plants
are brown and very sick looking |
5 |
1.3
cms |
it
appears the plants are dead. |
Irene inferred
(tried to explain her observations) that "It was the boiled water
that made the plants die. Plants need fresh water in order to survive."
She now formulated a hypothesis. A hypothesis is a generalisation
that seems true in most cases. It is made only after a number of observations
have taken place and been recorded.
Her hypothesis was as follows. "No plant can survive for more
than five days in water that had previously been boiled"
Irene predicted that if she placed plants in boiled water they would eventually die no matter how much light was available.
To test her hypothesis she set up the experiment on the left. We will see later how a proper experiment is set up.
Observe the outcome. Does the hypothesis need revising? Why?