Baking
1.13
Yeast is also used in baking bread. Yeast is mixed with flour and some sugar. The ingredients are mixed together thoroughly and the dough is left to rise before baking it. 3
Explain why sugar is added to dough.
4
Why does the dough rise?
5
What happens to the alcohol made during bread production?
The biochemistry of fermentation The equation for fermentation is: glucose → ethanol + carbon dioxide (energy released) Anaerobic respiration is much less efficient than aerobic respiration. It produces only around a nineteenth as much energy. But in situations where there’s little oxygen, it means that cells can stay alive, and the amount of energy produced is still enough to keep single cells running. Certain plant cells can also use alcoholic fermentation to obtain their energy. These include plants that grow in marshes, where oxygen is in short supply. Pollen grains can also respire anaerobically. Without oxygen, we would die. But when actively contracting, our muscles run short of oxygen. They are able to respire anaerobically for short periods of time. Lactic acid, and not ethanol, is produced. glucose → lactic acid (energy released) 6
Explain why it is helpful for pollen grains to respire anaerobically.
7
Write down the equation for fermentation.
8
For anaerobic respiration in muscle:
Figure 1.44 Dough is kneaded to mix the ingredients.
Did you know? Yeast is unable to use the starch in barley for respiration. Maltsters germinate the barley grains first to break down the starch into sugar.
KEY SKILLS You must be able to compare aerobic and anaerobic respiration: the need for oxygen, the products and the amount of energy transferred.
• write down the word equation • work out the symbol equation.
Google search: 'anaerobic respiration in yeast, anaerobic respiration in muscle, fermentation'
75047_P012_047.indd 39
39
5/20/16 10:11 AM