Chapter 9: Cellular Respiration and Fermentation

Question 1

What is cellular respiration?

Answer 1

The extraction of energy from food which all living organisms are capable of doing.

Question 2

How is energy extracted in cellular respiration?

Answer 2

Through ATP (adenosine triphosphate).

Question 3

______ is necessary in organisms in order to extract the maximum amount of energy.

Answer 3

Oxygen (O2)

Question 4

What happens during cellular respiration?

Answer 4

Fuel (like glucose) is oxidized (completely broken down) to produce ATP, and the O2 is reduced to H2O.

Question 5

Where in the cell does energy extraction take place?

Answer 5

In the mitochondia.

Question 6

Describe the FIVE molecules that produced in cellular respiration.

Answer 6

1. ATP (adenosine triphosphate): The primary energy currency of the cell
   - 36-38 ATP per glucose molecule
   - When is it produced: glycolysis, citric acid cycle, and oxidative phosphorylation
2. NADH (nicotinamide adenine dinuleotide): Electron carriers that store energy in the form of high-energy electrons. Electrons carried by NADH have more energy compared to FADH2.
   - ~10 NADH per glucose molecule
   - When is it produced: glycolysis and citric acid cycle
3. FADH2 (flavin adenine dinucleotide): electron carriers that store energy in the form of high-energy electrons.
   - ~2 FADH2 per glucose molecule
   - When is it produced: citric acid cycle
4. CO2 (carbon dioxide): A waste product generated and released into the bloodstream, eventually exhaled from the body.
   - 6 CO2 per glucose molecule
   - When is it produced: cytric acid cycle (during breakdown of glucose)
5. H2O (water): O2 combines with protons and electrons to form H2O molecules as a byproduct and as the final step of cellular respiration.
   - ~6 H2O per glucose molecule
   - When is it produced: oxidative phosphorylation (in the ETC)

Question 7

What is substrate level phosphorylation?

Answer 7

The process in which a phosphate group is transferred directly FROM a substrate molecule TO a molecule of ADP, thereby forming ATP.
- does NOT involve the ETC or chemiosmosis.
- does NOT need O2 to take place.

Question 8

What are the four stages of cellular respiration?

Answer 8

1. Glycolysis
2. Pyruvate oxidation
3. Citric Acid cycle
4. Oxidative phosphorylation

Question 9

What happens during glycolysis? Where does it occur?

Answer 9

Glucose (six carbon) enters the cell and broken down into to pyruvate (two groups of three carbon) using two molecules of ATP.

Occurs in the cytoplasm.

Question 10

What are the key outputs of glycolysis?

Answer 10

2 ATP, 2 NADH, 2 pyruvate

Question 11

In the intermediate step, pyruvate transported across the membrane into the mitochondrial matrix ONLY IF ______ is present.

Answer 11

Oxygen (O2)

Question 12

What happens in pyruvate oxidation and where does it occur?

Answer 12

If oxygen is present, pyruvate transported across the membrane into the mitochondrial matrix, where each pyruvate molecule is broken down and converted to a two-carbon molecule called acetyl-CoA (substrate).

This occurs in the mitochondrial matrix.

Question 13

What are the key outputs of pyruvate oxidation?

Answer 13

2 acetyl-Coa, 2 NADH, 2 CO2

Question 14

What happens in the Krebs Cycle and where does it occur?

Answer 14

The citric acid cycle (krebs cycle) takes place by further breaking down the pyruvate to produce energy carriers. This cycle also releases carbon dioxide as a waste product.

Occurs in the mitochondrial matrix.

Question 15

Describe the steps of the Citric Acid Cycle.

Answer 15

1. Acetyl-CoA enters the cycle and combines with Oxaloacetate to create Citrate.
2. Citrate goes through a series of transformations where atoms are rearranged, leading to the release of two molecules of CO2.
3. While the atoms are rearranging, high-energy electrons are transferred to the electron carriers NAD+ and FAD, forming NADH and FADH2.
4. At the end of the cycle, oxaloacetate is regenerated, ready to combine with another molecule of acetyl-CoA to start the cycle again.

Question 16

What are the key outputs of the Krebs Cycle?

Answer 16

2 ATP, 6 NADH, 2 FADH2, 2 CO2 per cycle.

Question 17

What happens in Oxidative Phosphorylation and where does it occur?

Answer 17

Oxidative Phosphorylation is the transfer of electrons from NADH and FADH2 (electron carriers) → to the electron transport chain (ETC). As the electrons move across the ETC, energy is released and used to pump protons (H+) across the inner membrane against their gradient, creating an electrochemical gradient.

Occurs in the inner mitochondrial membrane.

Question 18

What is the Electron Transport Chain?

Answer 18

A series of membrane proteins that can accept, reduce, and transfer electrons.

Question 19

What is chemiosmosis?

Answer 19

A mechanism for generating ATP by harnessing the energy stored in the proton gradient across membranes.

Question 20

The enzyme involved that synthesizes ATP is called __________.

Answer 20

ATP Synthase

Question 21

If oxygen is not available, pyruvate stays in the _____ and can be fermented into ______ or ________.

Answer 21

cytoplasm, alcohol, acetaldehyde.

Question 22

Anaerobic VS Aerobic

Answer 22

Anaerobic respiration occurs in the absence of oxygen, while Aerobic respiration occurs when oxygen is present.

Question 23

Define Fermentation.

Answer 23

Fermentation is an anaerobic process that occurs in the absence of oxygen, and it allows cells to continue generating ATP through glycolysis when oxygen is limited.

Question 24

Describe the process of fermentation.

Answer 24

In fermentation, pyruvate is converted into other compounds such as ethanol (alcohol) or lactate (lactic acid) to regenerate NAD+ and sustain glycolysis.

Question 25

How is ATP generated during the Krebs Cycle?

Answer 25

Through substrate level phosphorylation.

Question 26

Where is oxygen consumed in cellular respiration?

Answer 26

In the Electron Transport Chain

Question 27

What is the role of O2 in cellular respiration?

Answer 27

Serves as the final electron acceptor in the electron transport chain.

Question 28

What is proton motive force?

Answer 28

The proton motive force (PMF) is a form of electrochemical potential energy that is generated by the uneven distribution of protons (H+) across a membrane.

Question 29

Explain in general terms how redox reactions are involved in energy exchanges.

Answer 29

Because they often involve the transfer of electrons from one molecule to another, accompanied by a transfer of energy.

Question 30

Explain where and how the respiratory electron transport chain creates a proton gradient.

Answer 30

rETC creates a proton gradient across the inner mitochondrial membrane. As electrons are passed along the chain from one complex to another, they lose energy, creating a concentration gradient of protons across the inner mitochondrial membrane.

Question 31

Distinguish between fermentation and anaerobic respiration.

Answer 31

Fermentation is a simpler process primarily aimed at regenerating NAD⁺ to keep glycolysis going, while anaerobic respiration involves more complex reactions and can yield more ATP in the absence of oxygen.

Question 32

Distinguish between obligate aerobes and facultative anaerobes.

Answer 32

Obligate aerobes strictly require oxygen for their metabolism, while facultative anaerobes can adapt to varying oxygen conditions and use alternative metabolic pathways when oxygen is unavailable.