Arjun mixes flour, water, a spoon of sugar and a little yeast…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Arjun mixes flour, water, a spoon of sugar and a little yeast. He leaves the dough in a warm place for two hours, and it doubles in size. Which kind of respiration happens in the dough? Name its two products, and say which one makes the dough rise.
Need a reminder? The key ideaShow
Respiration releases the energy of glucose. Glucose is split into pyruvate in the cytoplasm. Without oxygen, yeast makes ethanol and carbon dioxide, and muscles make lactic acid: about 2 ATP for each glucose. With oxygen, in the mitochondria, pyruvate becomes carbon dioxide and water: about 38 ATP for each glucose.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The kind of respiration. Inside the dough there is little oxygen, so the yeast respires anaerobically. This is fermentation.
Step 2. The products. The yeast breaks the sugar down into ethanol and carbon dioxide.
Step 3. The rising. The carbon dioxide forms small bubbles of gas, trapped in the dough. The bubbles make it swell. The ethanol escapes when the bread is baked.
Answer: anaerobic respiration (fermentation); the products are ethanol and carbon dioxide, and the carbon dioxide makes the dough rise.
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