Cell respiration

Question 1

What is the main goal of cellular respiration?

Answer 1

To convert glucose into ATP for cellular energy.

Question 2

What are the five stages of cellular respiration?

Answer 2

Glycolysis, pyruvate oxidation, citric acid cycle, oxidative phosphorylation, ATP synthase.

Question 3

Where does glycolysis occur?

Answer 3

In the cytoplasm.

Question 4

Where do the citric acid cycle and oxidative phosphorylation occur?

Answer 4

In the mitochondrial matrix and inner mitochondrial membrane, respectively.

Question 5

What is the overall equation for cellular respiration?

Answer 5

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP

Question 6

How much ATP is produced in aerobic respiration?

Answer 6

~30-32 ATP per glucose molecule.

Question 7

What type of reaction is cellular respiration?

Answer 7

A redox reaction where glucose is oxidized, and oxygen is reduced.

Question 8

Why is cellular respiration more efficient than fermentation?

Answer 8

Because oxidative phosphorylation allows for a higher ATP yield.

Question 9

What is the role of electron carriers like NADH and FADH₂?

Answer 9

They transfer high-energy electrons to the electron transport chain.

Question 10

What is the difference between substrate-level phosphorylation and oxidative phosphorylation?

Answer 10

Substrate-level phosphorylation generates ATP directly in glycolysis and the citric acid cycle, whereas oxidative phosphorylation relies on the electron transport chain and chemiosmosis

Question 11

What happens to oxygen in cellular respiration?

Answer 11

It is reduced to water (H₂O).

Question 12

Why are NADH and FADH₂ important?

Answer 12

They shuttle electrons to the electron transport chain.

Question 13

How do electrons move through the electron transport chain?

Answer 13

They move from high to low energy, releasing energy to pump protons.

Question 14

What happens if oxygen is unavailable?

Answer 14

The electron transport chain stops, and ATP production ceases.

Question 15

Why does NADH contain more energy than ATP?

Answer 15

It carries high-energy electrons, which drive ATP synthesis.

Question 16

What is the role of cytochrome proteins in the electron transport chain?

Answer 16

They pass electrons down the chain and help generate the proton gradient.

Question 17

Why does FADH₂ generate less ATP than NADH?

Answer 17

It enters the electron transport chain later, pumping fewer protons.

Question 18

How is the potential energy in glucose transferred to ATP?

Answer 18

Through a series of redox reactions.

Question 19

Why does ATP synthase need oxygen indirectly?

Answer 19

Oxygen is needed to keep the electron transport chain running, allowing ATP synthesis.

Question 20

What are the two main phases of glycolysis?

Answer 20

Energy investment and energy payoff.

Question 21

What is the net ATP gain from glycolysis?

Answer 21

2 ATP per glucose molecule.

Question 22

What are the final products of glycolysis?

Answer 22

2 pyruvate, 2 ATP, 2 NADH.

Question 23

What enzyme regulates glycolysis?

Answer 23

Phosphofructokinase (PFK).

Question 24

Why doesn’t glycolysis require oxygen?

Answer 24

It is an anaerobic process.

Question 25

What happens to pyruvate after glycolysis?

Answer 25

It enters pyruvate oxidation or undergoes fermentation.

Question 26

How many ATP are invested in glycolysis?

Answer 26

2 ATP are consumed in the energy investment phase.

Question 27

What role does NAD⁺ play in glycolysis?

Answer 27

It accepts electrons, forming NADH.

Question 28

What enzyme catalyzes the first step of glycolysis?

Answer 28

Hexokinase.

Question 29

Why is glycolysis considered an ancient metabolic pathway?

Answer 29

Because it occurs in all organisms, including those that existed before oxygen was abundant.

Question 30

Where does pyruvate oxidation occur?

Answer 30

In the mitochondrial matrix.

Question 31

What enzyme complex catalyzes pyruvate oxidation?

Answer 31

Pyruvate dehydrogenase complex (PDC).

Question 32

What are the products of pyruvate oxidation per pyruvate?

Answer 32

1 Acetyl-CoA, 1 NADH, and 1 CO₂.

Question 33

How many NADH are produced per glucose?

Answer 33

2 NADH.

Question 34

Why is CO₂ released in this step?

Answer 34

Due to decarboxylation of pyruvate.

Question 34

What happens to Acetyl-CoA?

Answer 34

It enters the citric acid cycle.

Question 35

What would happen if pyruvate oxidation were blocked?

Answer 35

The citric acid cycle would stop, preventing ATP production.

Question 36

Does pyruvate oxidation directly produce ATP?

Answer 36

No, but it generates NADH.

Question 37

Why does pyruvate oxidation require oxygen indirectly?

Answer 37

Oxygen is needed for NADH oxidation in the ETC.

Question 38

Why is Acetyl-CoA important in metabolism?

Answer 38

It is a key intermediate linking carbohydrates, fats, and proteins to the citric acid cycle.

Question 39

Where does the Citric Acid Cycle occur?

Answer 39

In the mitochondrial matrix.

Question 40

What molecule starts the Citric Acid Cycle?

Answer 40

Acetyl-CoA, which combines with oxaloacetate to form citrate.

Question 41

What are the products of one turn of the Citric Acid Cycle?

Answer 41

3 NADH, 1 FADH₂, 1 ATP, 2 CO₂.

Question 42

How many ATP are produced per glucose in this cycle?

Answer 42

2 ATP per glucose (since the cycle runs twice).

Question 43

Why is the Citric Acid Cycle a "cycle"?

Answer 43

Oxaloacetate is regenerated at the end to restart the process.

Question 44

How many NADH are produced per glucose in this cycle?

Answer 44

6 NADH (3 per cycle, runs twice per glucose).

Question 45

What happens to the CO₂ released in the cycle?

Answer 45

It is exhaled as a waste product.

Question 46

What happens if the Citric Acid

Answer 46

Cycle stops ATP production would drastically decrease, and metabolism would slow down.

Question 47

What is the main purpose of the Citric Acid Cycle?

Answer 47

To generate NADH and FADH₂ for oxidative phosphorylation.

Question 48

Where does oxidative phosphorylation occur?

Answer 48

In the inner mitochondrial membrane.

Question 49

What are the two main components of oxidative phosphorylation?

Answer 49

The Electron Transport Chain (ETC) and Chemiosmosis.

Question 50

What is the role of NADH and FADH₂?

Answer 50

They donate high-energy electrons to the ETC.

Question 51

What is chemiosmosis?

Answer 51

The movement of H⁺ ions across the membrane to power ATP synthase.

Question 52

What is the final electron acceptor?

Answer 52

Oxygen (O₂), which forms water (H₂O).

Question 53

What would happen if the ETC stopped working?

Answer 53

ATP production would cease, leading to cell death.

Question 54

How does cyanide poisoning affect oxidative phosphorylation?

Answer 54

It blocks Complex IV, preventing electron transfer to oxygen.

Question 55

What is ATP synthase?

Answer 55

An enzyme that synthesizes ATP using the proton gradient.

Question 56

Why is oxidative phosphorylation the most efficient ATP producer?

Answer 56

Because it harnesses the full energy potential of NADH and FADH₂.

Question 57

Why is fermentation necessary in the absence of oxygen?

Answer 57

To regenerate NAD⁺ and keep glycolysis running.

Question 58

What are the two main types of fermentation?

Answer 58

Lactic acid fermentation and alcohol fermentation.

Question 59

Why does fermentation produce less ATP than aerobic respiration?

Answer 59

It does not use oxidative phosphorylation.

Question 60

What happens to pyruvate in lactic acid fermentation?

Answer 60

It is converted to lactic acid.

Question 61

What happens to pyruvate in alcohol fermentation?

Answer 61

It is converted to ethanol and CO₂.

Question 62

How many ATP are produced per glucose in fermentation?

Answer 62

Only 2 ATP.

Question 63

Which enzyme converts pyruvate to lactic acid?

Answer 63

Lactate dehydrogenase.

Question 64

Which organisms use alcohol fermentation?

Answer 64

Yeast and some bacteria.

Question 65

How does fermentation impact muscle performance?

Answer 65

It produces lactic acid, causing muscle fatigue. 10. Why is fermentation considered inefficient? Because much of the energy remains trapped in the fermentation byproducts.

Question 66

Why is fermentation considered inefficient?

Answer 66

Because much of the energy remains trapped in the fermentation byproducts.

Question 67

Why was anaerobic respiration important in early life?

Answer 67

Early Earth had little oxygen, so cells needed alternative energy pathways.

Question 68

What organisms still use anaerobic respiration today?

Answer 68

Some bacteria and archaea in oxygen-poor environments.

Question 69

How does anaerobic respiration differ from fermentation?

Answer 69

It uses an electron transport chain, while fermentation does not.

Question 70

What are common final electron acceptors in anaerobic respiration?

Answer 70

Sulfate (SO₄²⁻), nitrate (NO₃⁻), iron (Fe³⁺).

Question 71

How did mitochondria evolve?

Answer 71

From aerobic bacteria that were engulfed by ancestral eukaryotes

Question 72

How do lipids enter cellular respiration?

Answer 72

Fatty acids undergo hydrolysis and oxidation to form Acetyl-CoA.

Question 73

Which macromolecule produces the most ATP per gram?

Answer 73

Lipids (fats) because they have more high-energy bonds.

Question 74

How does gluconeogenesis relate to cellular respiration?

Answer 74

It converts non-carbohydrate sources (e.g., amino acids) into glucose.

Question 75

Why do starving individuals break down muscle protein?

Answer 75

To supply amino acids for gluconeogenesis, maintaining blood glucose levels. This only occurs once glycogen and triglyceride stores are gone.

Question 76

Why is it important to regulate cellular respiration?

Answer 76

To prevent excessive ATP production and ensure energy is used efficiently.

Question 77

What inhibits phosphofructokinase (PFK; i.e. inhibits glycolysis)?

Answer 77

High ATP and citrate levels.

Question 78

What stimulates phosphofructokinase (PFK)?

Answer 78

High ADP and AMP levels (indicating low energy).

Question 79

Why does citrate inhibit glycolysis?

Answer 79

It signals that the Citric Acid Cycle has enough substrates.

Question 80

How does feedback inhibition maintain metabolic balance?

Answer 80

By adjusting the speed of respiration based on ATP and NADH levels.

Question 81

How many ATP are produced in aerobic respiration?

Answer 81

~30-32 ATP per glucose.

Question 82

How many ATP are produced in glycolysis?

Answer 82

Net 2 ATP.

Question 83

How many ATP are produced in the Citric Acid Cycle?

Answer 83

2 ATP per glucose.

Question 84

Which stage produces the most ATP?

Answer 84

Oxidative phosphorylation (~26-28 ATP per glucose).

Question 85

How much ATP does fermentation produce?

Answer 85

Only 2 ATP per glucose.

Question 86

Why does FADH₂ generate less ATP than NADH?

Answer 86

It enters the ETC later, pumping fewer protons.

Question 87

Why is aerobic respiration more efficient than anaerobic?

Answer 87

Oxygen allows full oxidation of glucose, maximizing ATP yield.

Question 88

What happens if ATP production stops?

Answer 88

The cell dies due to lack of energy.

Question 89

How does anaerobic respiration differ from fermentation?

Answer 89

Anaerobic respiration uses an electron transport chain, while fermentation does not.

Question 89

Why does oxidative phosphorylation require oxygen?

Answer 89

Oxygen is the final electron acceptor, allowing the ETC to function.