Biology 20: Chapter 5 Part 2
Cellular Respiration
KEY
Glycolysis & Fermentation
1. What organisms trap sunlight & store it in carbohydrates? Photoautotrophs.
2. What organisms (more than 1) break down carbohydrates to release energy from cells? All
3. What is the main energy currency of a cell? ATP
4. Define cellular respiration. C6H12O6 (s) (glucose) + 6O2 (g)  6CO2 (g) + 6H2O (l) + ENERGY (36 ATP)
A biochemical pathway that releases stored food energy and transfers that energy to ATP.
5. What process begins cellular respiration & does it produce much ATP? Glycolysis. 2 net ATP/
glucose molecule.
6. If there is no oxygen in cells, the products of glycolysis enter anaerobic (or fermentation)
pathways that yield no additional ATP.
7. Fermentation is anaerobic because no oxygen is used.
8. If oxygen is present in cells, the glycolysis products enter the aerobic respiration pathway.
9. Does aerobic respiration produce much ATP? Yes. 36 net ATP for every molecule of
glucose (including 2 net ATP from glucolysis).
10. What simple sugar starts glycolysis? Glucose
11. In glycolysis, glucose is broken into 2 molecules of pyruvate or pyruvic acid in the
cytoplasm of the cell.
12. In which part of the cell does fermentation occur? Cytoplasm. Is oxygen involved? No.
13. Name the 2 types of fermentation. Lactate (or lactic acid) & Ethanol (or alcohol) fermentation.
14. Lactic acid fermentation helps make cheese & yogurt and also occurs in animal and some
bacteria cells (or muscle) cells during heavy exercise.
15. What effect does lactic acid have on muscle cells? Fatigue & soreness. Evidence of
conversion to aerobic respiration during strenuous muscle exercise.
16. Yeasts carry on what type of fermentation? Alcohol or ethanol fermentation
1
Biology 20: Chapter 5 Part 2
17. What alcohol is made in alcoholic fermentation? Ethanol
18. One molecule of sugar produces 4 kilocalories of energy. (**Don’t need to know this.)
Aerobic Respiration
19. Aerobic respiration requires what gas? Oxygen
20. How much more ATP does aerobic respiration produce than glycolysis alone? 34 ATP/
glucose molecule
21. Name and summarize the 4 major stages of aerobic respiration.
1. Glycolysis: (sugar splitting- technically anaerobic, but needed to start aerobic resp)
C6H12O6(s) (Glucose) + 2ADP + 2Pi
 2 Pyruvate (3-Carbon Molecules) + 2ATP
2. Conversion of Pyruvate to Acetyl-CoA:
When oxygen is available, pyruvate enters the matrix of the mitochondrion.
NAD+ = Nicotinamide Adenine Dinucleotide & Acetyl-CoA = Acetyl Coenzyme A
2 Pyruvate + 2CoA + 2 NAD+  2 Acetyl-CoA + 2 CO2 + 2 NADH
3. The Krebs Cycle:
4. The Electron Transport Chain:
The NADH and FADH2 from the Krebs cycle
donate their electrons to the electron carriers
in the electron transport chain. As electrons
are passed from one carrier to the next, the
energy that is released is used to pump
hydrogen ions across the mitochondrial
inner membrane into the intermembrane
space, creating a concentration gradient. The
energy stored in the gradient is used to
generate ATP by chemiosmosis.
22. What is completed in the Krebs cycle? The conversion of Acetyl CoA to carbon dioxide
and water, the transfer of energy to ATP, the release of H+ and reduction of NADP and
FAD, electrons to the electron transport chain.
23. The energy carrier NAD+ is reduced to what substance? NADH
2
Biology 20: Chapter 5 Part 2
24. Which part of aerobic respiration makes most of the ATP (cell’s energy)? Electron Transport
25. Where do these reactions take place in the cell?
Anaerobic glycolysis in the cytoplasm.
Aerobic Krebs Cycle & ETS in mitochondria.
26. What is the mitochondrial matrix & what product of glycolysis diffuses into this matrix?
The mitochondrial matrix is a fluid filled area of
the mitochondrial interior into which pyruvate
is passively transported by diffuse
27. What is found inside the mitochondrial matrix to help catalyze the reactions of the Krebs
cycle? Enzymes involved with the Krebs Cycle
28. What is acetyl CoA & to what does it combine? Acetyl CoA is a 2-carbon molecule that is
the product of the chemical reaction of 2 Pyruvate + 2CoA + 2 NAD+ in the mitochondrial
matrix. It combines to the 4-carbon molecule (oxaloacetate) as it enters the Krebs Cycle.
29. Define Krebs cycle. A biochemical pathway that involves the metabolism of pyruvate
into carbon dioxide and a 4-carbon molecule (oxaloacetate) in order to generate energy to
form ATP and to free electrons for the Electron Transport System.
OR
Acetyl-CoA enters the Krebs cycle by combining with a four-carbon compound. During
the Krebs cycle, two carbon atoms are fully oxidized to carbon dioxide, NAD+ and FAD
(Flavin Adenine Dinucleotide) are reduced to NADH and FADH2, and a small amount of
ATP is produced.
3
Biology 20: Chapter 5 Part 2
30. The first acid produced in the Krebs cycle is citrate or citric acid.
31. Two energy carriers are reduced in the Krebs cycle; NAD+ becomes NADH and FAD
becomes FADH2.
32. Is any ATP made in the Krebs cycle? Yes, 1 ATP/Krebs Cycle or 2 ATP/ glucose molecule.
33. What gas is a waste product produced in the Krebs cycle? Carbon dioxide
34. The electron transport system is the second part of aerobic respiration.
35. Where does the ETS take place in eukaryotic cells? Across the mitochondrial inner
membrane into the intermembrane space.
36. ATP is made in the ETS when NADH and FADH2 release hydrogen ions.
37. What gas serves as the final acceptor of electrons in the ETS (electron transport system)?
oxygen
38. Write the equation for this gas accepting electrons at the end of the ETS. 2H+ + 2e- + ½O2 H20
39. What is the final product of the ETS? ATP (or H20)
40. How many ATPs of energy are made during glycolysis? 2 net ATP
41. How many ATPs of energy are made during the Krebs cycle? 1/cycle. 2/glucose molecule.
42. Each FADH can generate how many ATPs of energy? 2 ATP
43. Each NADH can generate how many ATPs of energy? 3 ATP (or 2 if NADH is from glycolysis)
44. 10 (including 2 from glycolysis) NADH molecules & 2 FADH molecules are made by
aerobic respiration.
45. How many ATP molecules are made by the electron transport system? 32 ATP
46. What is the maximum number of ATP molecules that can be produced from each glucose
molecule? 36 ATP (or 38 gross ATP)
47. Write the summary equation for cellular respiration.
C6H12O6 (s) (glucose) + 6O2 (g)  6CO2 (g) + 6H2O (l) + ENERGY (36 ATP)
4
Biology 20: Chapter 5 Part 2
Draw out a summary of the entire cellular respiration cycle from memory. Once you are finished
check your answers and fill in anything you missed.
Formation of Acetyl-CoA:
2 Pyruvate + 2CoA + 2 NAD+  2 Acetyl-CoA + 2 CO2 + 2 NADH
5