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It's been a month since we set up this experiment, and there's some fascinating differences
between these beakers. In the two beakers that didn't have any soil, all the oil
has congealed into blobs on the surface and around the side of the glass.
And the two with soil,
they're completely different. All the water is clear of oil, except in beaker three
where there is just the remote trace of oil.
And in beaker four, no oil in the water whatsoever.
So what's happening here? Have we actually got bacteria in our soil that can
degrade the oil or has the oil just attached itself the soil particles
and is now sitting in sediment at the bottom?
If there is oil-munching bacteria in these soil samples, how effective are they?
The grease spot test will help determine this.
You also need to get all the other soil samples that your students brought in for testing
and compared them to these ones.
Now let's check the grease spots. I just took one or two samples each time just to demonstrate
the process. Obviously,
to reduce the error margin and get more statistically robust data, you're going to need
to do 10 or more samples from each beaker, each time you do the test.
Working on observation alone however, you can see in beaker 3 and 4
that there's an initial decline in the size of the grease spots. This stabilizes soon after
however.
My hypothesis for further testing, is that the oil in beaker 3 and 4 is simply
clinging to the soil particles and there's very little bacterial activity happening
to degrade the oil in these beakers.
A further test you could do, you could sterilize half of each soil sample.
This will kill the bacteria in the soil
and help you work out if the soul itself
is actually playing a role.
As is the nature of science, there are many more questions than answers that have come from
this experiment.
The microbial world is a fascinating one. In which the myriad microbes
play a vital role in sustaining the life of this planet.
Hopefully, this prac will arouse curiosity and get students thinking about this invisible part of our
ecosystems.