Keeping A Creature Alive

I tried out this experiment with my friends over the science eureka course.

1) We placed 2 table spoons of sugar into a beaker and dissolved it with warm water (using a stirrer)

2) We then added 5g of yeast into the beaker and continued to stir

3) Once the yeast and the sugar are fully mixed, we poured the mixture into a conical flask

4) We then stretched a balloon over the mouth of the flask, ensured that it is air tight, then left it there for 10 mins

What did we observe and why?

a) The balloon inflated

b) The yeast fed on the glucose and respired, exhaling carbon dioxide. However, this isn't totally why the volume of gas in the bottle increases and inflates the balloon. If you react a sugar with oxygen, you form as much carbon dioxide as the oxygen you started with. The carbon dioxide produced will be the same volume and the oxygen taken in, so there would be no increase in volume and the balloon would not inflate. So, yeast had another trick. If there is lots of food about in the form of sugar but not enough oxygen, the yeast can generate energy by breaking down the sugar into ethanol (alcohol) and carbon dioxide. There is not much oxygen in the air above the bottle and even less in the water so the yeast breaks the sugar straight down to alcohol and carbon dioxide. This form extra gas of carbon dioxide, thus increasing the volume of gas and inflating the balloon.

We also learnt new terms Aerobic and Anaerobic.

Aerobic is breathing in the presence of oxygen.

Anaerobic is breathing without the presence of oxygen.

I Wonder?

I was amazed by the results. I did not expect yeast to be able to respire just like us! Although yeast may seem lifeless, it can even partially inflate a balloon in ten minutes!

AMAZING!