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Do you like to watch your favourite team show off their talents? Are you happy when they win? Sometimes it’s fun to be a spectator. All you have to do is cheer. Let’s be spectators in temperature races featuring that special competitor, the yeast cell.

Yeast is a tiny mold made up of a single cell. Yeast has the remarkable ability to turn sugar into alcohol and carbon dioxide gas. If there are more yeast cells, naturally, sugar is turned into alcohol and carbon dioxide gas at a faster rate. The happier the yeast is kept, the faster it grows and the more product it produces. Let’s see if temperature has any effect on how happy the yeast is and thus on how fast it grows and how much product it produces.

Your supplies will include styrafoam bowls (at least 5), weighing balance, thermometer, measuring spoons, measuring cups, plastic spoons, stir sticks,

yeast (fresh dry yeast), sugar and water, warm and cold.

You start by placing one half cup of water at 10 degrees C in a bowl. Add 10 ml or 2 tsp of sugar. Stir until the sugar disappears. The sugar is now in solution in the water. (You can tell by the sweet taste that the sugar is still there, only you can’t see it.)   Add 30 ml or 2 tbsp of yeast to your bowl and weigh the bowl right away. Leave the bowl on the scale. Record the weight and allow the bowl to sit 10 minutes. Record the weight again. Is there any change? This bowl was Team A.

Next do the same thing with water that is at 20 degrees C. This was team B.

Next do the same thing with water at 30 degrees C.  This was team C. Lastly do the same thing with water at 40 degrees C. This was team D. If you are really keen, try the same thing with water at 45 degrees C. This is team E.

Why do some of the teams suffer a loss of weight? Make a graph which plots weight loss against temperature.  (temperature on the horizontal axis and weight loss on the vertical axis) Oh yes, the winner is the team with the most weight loss.

The happier the yeast is, the faster it will grow. That means more cells all happily digesting sugar and turning it into alcohol and gas. The amount of gas produced is an indication of how fast the yeast is growing.

Have you measured anything that gives you an indication how fast the yeast is growing? Final clue … the faster that gas is produced, the faster it escapes from the water and thus the more weight that is lost. Thus, the biggest loser is actually the winner!

Can the yeast grow indefinitely in your system? What will stop the reaction?

What would happen if you regularly removed some of the old liquid and then added an equal amount of fresh sugar solution.

There is a song that says “You can learn a lot of things from the flowers, especially in the month of June!” But here you can learn a lot of things from a simple fungus, the yeast cell. And we can do it at any time of the year!


Margaret Helder
April 2019

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