Question

model 2 – krebs cycle
mitochondrial matrix
outer mitochondrial membrane
inner mitochondrial membrane
▲ = pyruvic acid (3 c)
❋ = carbon dioxide (1 c)

1. according to model 2, what happens to pyruvic acid during the krebs cycle?
2. according to model 2, where does the change identified in the previous question occur?
3. note the number of atoms of carbon in pyruvic acid and explain why three molecules of carbon dioxide are produced.

Explanation:

For question 8:

The model shows pyruvic acid (3-carbon) entering the Krebs cycle, and carbon dioxide (1-carbon) is released as a product. The pyruvic acid is broken down, with its carbon atoms released as CO₂, while the remaining energy is used to generate NADH, FADH₂, and ATP.

For question 9:

The diagram labels the location of the Krebs cycle components (NAD⁺, FAD, ADP) as the mitochondrial matrix, which is the space inside the inner mitochondrial membrane.

For question 10:

Pyruvic acid has 3 carbon atoms. During the Krebs cycle, each pyruvic acid molecule is fully oxidized, with each of its 3 carbon atoms being released individually as a 1-carbon carbon dioxide molecule, resulting in 3 total CO₂ molecules per pyruvic acid.

Answer:

1. Pyruvic acid (3-carbon) is broken down, and its carbon atoms are released as three molecules of carbon dioxide (1-carbon each), while the energy from the breakdown is used to produce NADH, FADH₂, and ATP.
2. The changes to pyruvic acid occur in the mitochondrial matrix.
3. Pyruvic acid contains 3 carbon atoms. During the Krebs cycle, each of these 3 carbon atoms is removed one at a time and released as a single-carbon carbon dioxide molecule, so three carbon dioxide molecules are produced to account for all the carbon in the original pyruvic acid.