3.1.1 The experiment

Follow Janet’s instructions in the video (or use your activity booklet [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]   PDF) to conduct the experiment. You will need about 1 tablespoon of sugar and approximately 200 ml of water in each large glass. This sugar will act as food for your yeasts to consume.

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[MUSIC PLAYING]

JANET SUMNER

In this experiment we're going to look at life in action and investigate some of the ingredients that make life work. Now most organisms need air to breathe and some kind of energy source to live. And by energy, we usually mean food.

But in order to thrive and multiply, conditions need to be just right. And that's what we're going to investigate. We're going to use a very simple form of life.

This is baker's yeast, and it's alive. It's a tiny single celled kind of a fungus. And given food and air, it will grow and multiply.

But we're going to see which kind of conditions it likes best. And to do that, I'm going to make up a series of sugar solutions. Before you start, print off the glass diagram from your study journal so that you can record which sugar solution is which.

I've got four glasses each with a spoonful of sugar in, and I'm going to add the same amount of water to each. So this first one, I'm going to add cold water.

In the next one, I'm going to put in the same amount of just boiled water from the kettle, but be careful you don't crack the glass. In the final two, I'm going to put the same amount of water that's at body temperature or blood temperature. So I've just tested that with my finger.

Now give them a quick stir. Cold water. Boiling water. Blood warm, and blood warm.

So now I'm going to add a sachet of yeast to each glass. Then I'm going to mark off the level of the water on the side of the glass. Now this last glass, I'm going to cover with cling film to restrict the amount of air that the yeast has to work with.

Set your experiment up in the same way, so we can compare results. I'm going to give this five minutes and see if anything's happened.

[MUSIC PLAYING]

Well that's five minutes up and the yeast is clearly sprung into action because it started to produce a foam. This foam is the result of the yeast using the oxygen in the air to digest the sugar. It's producing a gas as a waste or byproduct.

In this particular case, it's carbon dioxide. And that's the process that makes bread rise in the same way as its doming and making the cling film rise here. Now to monitor the experiment - and keep track of the process - I'm going to measure the thickness of the foam and record how it changes over time.

So this one is 2 centimetres thick after five minutes. And this one is 2 centimetres thick. I'll give that another five minutes, and then I'll come back and make another measurement.

[MUSIC PLAYING]

Well that's 10 minutes up, and this one - which was the boiling water - doesn't seem to be doing very much at all. This one - which was the cold water - appears to be just starting to produce a very thin layer of foam. And these two are still doing really well, and producing more foam.

I'm just going to measure the thickness again. This foam has gone up to 6 centimetres. And this one is 5 centimetres. Now to find out what these observations mean and to interpret the results, you'll need to join in with the online discussion.

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Take care to label your glasses with which variables you’ve changed – you don’t want to get them mixed up. If the environmental conditions are suitable, the yeasts will grow and multiply quite quickly – you shouldn’t need more than 30 minutes to complete this experiment. Remember that boiling water can crack glassware, so be careful to let the water cool a bit first.

Carefully observe and record which glasses have conditions suitable for the yeasts to grow and which ones have conditions that restrict its growth.

You will have the opportunity to discuss your results in the next section.