Respiration + Gas Exchange

In Biology, we are working on, as the title shows, respiration & breathing. Today we analysed the Activity 11.3, in page 143, from our Biology Coursebook. This one focuses on invstigating the production of carbon dioxide (CO2) by anaerobic respiration. Later we had to answer the following questions:

A1. Why is it important to boil water?

Boiling the water is important because, doing so will take away any dissolved air.

A2. Why must the sugar solution be cooled before adding the yeast?

The sugar solution has to be cooled before the yeast is added because if the yeast is added when water is hot, the molecules will die, without releasing carbon dioxide for the experiment.

A3. What is the liquid paraffin for?

The liquid paraffin, by trickling it gently with a pipett, is used for separating the living yeast from the air in the test tube.

A4. What happened to the limewater or the hydrogencarbonate indicator solution in each of your pieces of apparatus? What does this show?

Due to the carbon dioxide released by the living yeast in the first test tube, the lime water or the hydrogencarbonate indicator solution turned cloudy. However, in the second test tube, as the boiled yeast is dead and does not breath, releasing carbon dioxide, the limewater prevailed clear.

A5. What new substance would you expect to find in the sugar solution containing living yeast at the end pf the experiment?

I would find ethanol, as living yeast releases this new substance, in anaerobic respiration. (glucose => ethanol + carbon dioxide)


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