3.2.1 Living organisms vary and this variation is influenced by genetic and environmental factors.
- Variation exists between members of a species.
- The need for random sampling, and the importance of chance in contributing to differences between samples.
- The concept of normal distribution about a mean.
- Understanding mean and standard deviation as measures of variation within a sample.
Taken from AQA A Level Biology Specification
The classic thing to do here is measure the students to get some data that they can graph and analyse. Maybe height, eye colour, hand span, can they roll their tongue etc. The problem I’ve always had is not having enough students to get enough data to get a good normal curve. I could send the students out of class to measure as many other students they can find hanging around the campus but let’s face it that’s a lot of lesson time for them to have a cup of coffee and halfheartedly go to the LRC to convince some skivers to get measured.
I could send them outside to measure some leaves which would be fine if there were some leaves to measure, or I could get them to measure some seeds in the class but that could mean we all slightly insane.
So what I needed was something that could be measured easily, preferably in the class room and with large enough numbers to get some good graphs… Then it hit me.
In a tube of smarties there must be about 30 sweets, that’s a good data set and the colours of the sweets can be recorded (discrete data) and their masses can be measured (continuous variation). This can be done in the class nice an easily and the fact they are sweets gives it a little hook that should hopefully keep the students interested a bit. The colour of the sweet could be considered a ‘genetic variation’ and the mass ‘genes and the environment’. As long as the students recognise the limitations of the model then I couldn’t see why it wouldn’t work as an activity.
My Technician wasn’t convinced, he thought that the variation of the mass wouldn’t be measurable as they are product of an industrial process and the checks and balances would mean that it wouldn’t work.
Then I had a second idea….
The addition of a peanut to the sweet would add in an extra random factor meaning that the masses of the sweets should be different enough to be measurable.
So I decided to have a go and buy both as I was convinced we could get a data set out of the smarties. I bought some tubes of smarties and the little snack sized bags of peanut M&Ms you can buy. If you want you could buy the large packs and split them up into beaker for different groups (or maybe you could spread them out on a tray and model random sampling?) but I liked the idea of giving each group their own pack.
If I was that kind of teacher I would have made a worksheet that had a pretend story associated with it giving Latin names to the ‘species’ of sweets (Chocolatus smartius, Peanutis mandmis) but I’m not. Gave the students some instructions and away we went.
Results
Smarties Colour
Bars: 95% CI
Smarties Mass
Average mass: 1.17g SD:0.07
Peanut M&Ms Colour
Bars: 95% CI
Peanut M&Ms Mass
Average mass: 2.23g SD:0.46
If you want the raw data it is available here, or have a go yourself.
Graphs constructed using the excellent Excel plugin Merlin (if you teach A Level Biology you have to get your students to use this).
I think it seemed to work, students had an opportunity to discuss which graph they would choose to plot and why as well as calculate standard deviation and discuss what that actually meant. It acted as a springboard to discuss variation in biological organisms and how you would go about measuring them successfully.
