PART 2: Anaerobic Respiration For Food

What three food making processes require a form of anaerobic respiration to take place

1. Bread making

2. Production of Beer & Wine

3. Production of Yogurt

Explain how bread is made using anaerobic respiration

• Yeast is a single-celled organism that can respire well both aerobically and anaerobically

• At the start of preparing the dough, the yeast respires aerobically, therefore producing water and carbon dioxide (this gas makes the dough rise)

• When the oxygen runs out the yeast switches to respiring anaerobically

• Since the yeast has now begun alcoholic fermentation, not all the glucose gets broken down and is converted into carbon dioxide and alcohol

• The alcohol evaporates and the yeast die (their optimal temp is around 40°C) during baking due to very high temperatures in the oven

What is the sugar source used by the yeast in bread making

Glucose (from the flour of the bread)

What does alcoholic fermentation have to do with anaerobic respiration

Alcoholic fermentation is a type of anaerobic respiration. It is how organisms like yeast respire anaerobically

🧠 Quick memory trick

• Anaerobic respiration = umbrella term (no oxygen)

• Alcoholic fermentation = one branch of that (used by yeast)

Define alcoholic fermentation

When a sugar (e.g. glucose) is partially broken down by yeast (or a certain bacteria) into CO2, ethanol and ATP in the absence of oxygen

What single-celled organism produces beer and wine. And by what process?

Yeast - through alcoholic fermentation

In this case, what is the sugar source in

• a) the wine

• b) the beer

• a) sugar from the grapes

• b) sugar source is maltose (from germinating barley seeds) - hops is added too

What does the yeast do in the production of wine and beer

It respires anaerobically by breaking down the sugar from the barely or grapes (depending on whether wine or beer is going to be produced)

into → carbon dioxide + ethanol + energy

What happens to the energy produced by the yeast

It uses it for survival

Do the yeast stay alive in the beer or wine

No, they eventually die out either due to

• the alcoholic concentration being too high

• they run out of sugar to respire with

What type of anaerobic respiration is used to produce yogurt

Lactic acid fermentation

How is lactic acid fermentation different to alcoholic fermentation

• Alcoholic fermentation: products = carbon dioxide + ethanol + energy

• Lactic acid fermentation: products = lactic acid + energy

What organisms respire anaerobically by lactic acid fermentation

• humans and animals

• some bacteria eg. Lactobacillus in yogurt production

What is the difference between how the lactobacillus respire anaerobically and how humans do

• They both use lactic acid fermentation

• Only the sugar source is different (lactobacillus → lactose), (humans → glucose

What is the microorganism needed in the production of yogurt

A bacteria - Lactobacillus

How does Lactobacillus help in making yoghurt from milk?

• It uses the sugars, lactose, from fresh milk as its energy source for respiration

• When the lactobacillus respires (anaerobically) it produces lactic acid

• The lactic acid causes the milk to coagulate (clump up/curd) which sours and thickens it

What is a word equation to summarize the process of lactic acid fermentation the lactobacillus undergoes during the production of yogurt?

Lactose → Lactic Acid + Energy