Question

compare (similarities) and contrast (differences) aerobic and anaerobic cellular respiration:
similarities:

differences:

what are the two types of fermentation?
and

why does bread rise if you use yeast?

Explanation:

1. Compare (similarities) and contrast (differences) aerobic and anaerobic cellular respiration:

Similarities:

• Both aerobic and anaerobic respiration are types of cellular respiration, which means they are processes that cells use to generate energy (in the form of ATP, adenosine triphosphate).
• Both start with the process of glycolysis. In glycolysis, glucose (a 6 - carbon sugar) is broken down into two molecules of pyruvate (a 3 - carbon compound), and a small amount of ATP (2 ATP molecules) and NADH (nicotinamide adenine dinucleotide, reduced form) are produced.

Differences:

• Presence of Oxygen: Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen.
• Location: Aerobic respiration takes place in the cytoplasm (for glycolysis) and the mitochondria (for the Krebs cycle and electron transport chain). Anaerobic respiration occurs entirely in the cytoplasm.
• End Products:
• In aerobic respiration, the end products are carbon dioxide ($\ce{CO_2}$), water ($\ce{H_2O}$), and a large amount of ATP (about 30 - 32 ATP per glucose molecule). The overall reaction is $\ce{C_6H_{12}O_6 + 6O_2 -> 6CO_2 + 6H_2O + ATP}$.
• In anaerobic respiration, the end products depend on the type of organism. In animals (including human muscle cells during intense exercise), the end product is lactic acid. In yeast and some bacteria, the end products are ethanol (alcohol) and carbon dioxide. The amount of ATP produced is much less (only 2 ATP per glucose molecule) compared to aerobic respiration.
• Energy Yield: Aerobic respiration yields a large amount of ATP (30 - 32 ATP per glucose), while anaerobic respiration yields a small amount of ATP (2 ATP per glucose).

2. What are the two types of fermentation?

The two main types of fermentation are:

• Lactic Acid Fermentation: This occurs in muscle cells of animals (when there is a lack of oxygen) and in some bacteria (like the bacteria used to make yogurt). In lactic acid fermentation, pyruvate (produced from glycolysis) is converted into lactic acid. The reaction is $\ce{Pyruvate + NADH -> Lactic Acid + NAD^+}$.
• Alcoholic Fermentation: This occurs in yeast and some bacteria. In alcoholic fermentation, pyruvate is first converted into acetaldehyde (with the release of carbon dioxide), and then acetaldehyde is converted into ethanol (alcohol). The overall reaction is $\ce{Pyruvate -> Acetaldehyde + CO_2}$ (first step), and $\ce{Acetaldehyde + NADH -> Ethanol + NAD^+}$ (second step).

3. Why does bread rise if you use yeast?

Yeast is a single - celled fungus that can perform alcoholic fermentation. When yeast is added to bread dough, it uses the sugars (like glucose) present in the dough as a source of energy.

• During alcoholic fermentation, yeast breaks down glucose (from the flour in the dough or added sugars) through glycolysis and then alcoholic fermentation.
• One of the products of alcoholic fermentation in yeast is carbon dioxide ($\ce{CO_2}$). The carbon dioxide gas is trapped within the gluten network of the dough. As more and more carbon dioxide is produced, the dough expands or "rises" because the gas bubbles push the dough outward, making the bread light and fluffy. Also, the ethanol produced during fermentation evaporates during the baking process.

Answer:

1. Compare (similarities) and contrast (differences) aerobic and anaerobic cellular respiration:

Similarities:

• Both aerobic and anaerobic respiration are types of cellular respiration, which means they are processes that cells use to generate energy (in the form of ATP, adenosine triphosphate).
• Both start with the process of glycolysis. In glycolysis, glucose (a 6 - carbon sugar) is broken down into two molecules of pyruvate (a 3 - carbon compound), and a small amount of ATP (2 ATP molecules) and NADH (nicotinamide adenine dinucleotide, reduced form) are produced.

Differences:

• Presence of Oxygen: Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen.
• Location: Aerobic respiration takes place in the cytoplasm (for glycolysis) and the mitochondria (for the Krebs cycle and electron transport chain). Anaerobic respiration occurs entirely in the cytoplasm.
• End Products:
• In aerobic respiration, the end products are carbon dioxide ($\ce{CO_2}$), water ($\ce{H_2O}$), and a large amount of ATP (about 30 - 32 ATP per glucose molecule). The overall reaction is $\ce{C_6H_{12}O_6 + 6O_2 -> 6CO_2 + 6H_2O + ATP}$.
• In anaerobic respiration, the end products depend on the type of organism. In animals (including human muscle cells during intense exercise), the end product is lactic acid. In yeast and some bacteria, the end products are ethanol (alcohol) and carbon dioxide. The amount of ATP produced is much less (only 2 ATP per glucose molecule) compared to aerobic respiration.
• Energy Yield: Aerobic respiration yields a large amount of ATP (30 - 32 ATP per glucose), while anaerobic respiration yields a small amount of ATP (2 ATP per glucose).

2. What are the two types of fermentation?

The two main types of fermentation are:

• Lactic Acid Fermentation: This occurs in muscle cells of animals (when there is a lack of oxygen) and in some bacteria (like the bacteria used to make yogurt). In lactic acid fermentation, pyruvate (produced from glycolysis) is converted into lactic acid. The reaction is $\ce{Pyruvate + NADH -> Lactic Acid + NAD^+}$.
• Alcoholic Fermentation: This occurs in yeast and some bacteria. In alcoholic fermentation, pyruvate is first converted into acetaldehyde (with the release of carbon dioxide), and then acetaldehyde is converted into ethanol (alcohol). The overall reaction is $\ce{Pyruvate -> Acetaldehyde + CO_2}$ (first step), and $\ce{Acetaldehyde + NADH -> Ethanol + NAD^+}$ (second step).

3. Why does bread rise if you use yeast?

Yeast is a single - celled fungus that can perform alcoholic fermentation. When yeast is added to bread dough, it uses the sugars (like glucose) present in the dough as a source of energy.

• During alcoholic fermentation, yeast breaks down glucose (from the flour in the dough or added sugars) through glycolysis and then alcoholic fermentation.
• One of the products of alcoholic fermentation in yeast is carbon dioxide ($\ce{CO_2}$). The carbon dioxide gas is trapped within the gluten network of the dough. As more and more carbon dioxide is produced, the dough expands or "rises" because the gas bubbles push the dough outward, making the bread light and fluffy. Also, the ethanol produced during fermentation evaporates during the baking process.