BIO 101 - Cellular respiration (lecture 7 notes) Big picture: cells break down glucose to make ATP. Overall equation: C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy. Eukaryotes get roughly 30-32 ATP per glucose (older textbooks say 36-38). 1. Glycolysis - Happens in the cytoplasm. Does NOT need oxygen. - Glucose (6 carbons) is split into 2 pyruvate (3 carbons each). - Uses 2 ATP early on and makes 4 ATP, so the net gain is 2 ATP, plus 2 NADH. 2. Pyruvate oxidation - Pyruvate enters the mitochondrial matrix. - Each pyruvate becomes acetyl-CoA, releasing 1 CO2 and making 1 NADH. 3. Krebs cycle (citric acid cycle) - In the mitochondrial matrix. Acetyl-CoA joins oxaloacetate to make citrate. - Per glucose (two turns of the cycle): 2 ATP, 6 NADH, 2 FADH2 and 4 CO2. 4. Electron transport chain + chemiosmosis - On the inner mitochondrial membrane. NADH and FADH2 hand their electrons to protein complexes. - Energy from the electrons pumps H+ across the membrane, building a proton gradient. - H+ flows back through ATP synthase, which makes most of the ATP (about 26-28 per glucose). - Oxygen is the final electron acceptor and ends up as water. With no oxygen the chain backs up. 5. No oxygen? Fermentation - Glycolysis can keep going if NAD+ is regenerated. - Lactic acid fermentation (muscle cells): pyruvate -> lactate. - Alcohol fermentation (yeast): pyruvate -> ethanol + CO2. - Only the 2 ATP from glycolysis per glucose. Exam traps - Most ATP comes from the electron transport chain, not from glycolysis or the Krebs cycle. - CO2 is released in pyruvate oxidation and in the Krebs cycle: 6 CO2 per glucose in total. - The water in the overall equation is made at the end of the electron transport chain, not in glycolysis.
BIO 101 · sample notes
Cellular respiration: the notes, and the study tools StudyProofs made from them
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1. The notes
2. Notes StudyProofs made (7)
Overview of Cellular Respiration
Cells break down glucose to make ATP. Overall equation: C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy. Eukaryotes get roughly 30-32 ATP per glucose.
Source: “Big picture: cells break down glucose to make ATP. Overall equation: C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy. Eukaryotes get roughly 30-32 ATP per glucose (older textbooks say 36-38”
Glycolysis
Happens in the cytoplasm. Does NOT need oxygen. Glucose (6 carbons) is split into 2 pyruvate (3 carbons each). Uses 2 ATP early on and makes 4 ATP, so the net gain is 2 ATP, plus 2 NADH.
Source: “1. Glycolysis - Happens in the cytoplasm. Does NOT need oxygen. - Glucose (6 carbons) is split into 2 pyruvate (3 carbons each). - Uses 2 ATP early on and makes 4 ATP, so the net gain is 2 ATP, plus 2 NADH”
Pyruvate Oxidation
Pyruvate enters the mitochondrial matrix. Each pyruvate becomes acetyl-CoA, releasing 1 CO2 and making 1 NADH.
Source: “2. Pyruvate oxidation - Pyruvate enters the mitochondrial matrix. - Each pyruvate becomes acetyl-CoA, releasing 1 CO2 and making 1 NADH”
Krebs Cycle
In the mitochondrial matrix. Acetyl-CoA joins oxaloacetate to make citrate. Per glucose (two turns of the cycle): 2 ATP, 6 NADH, 2 FADH2 and 4 CO2.
Source: “3. Krebs cycle (citric acid cycle) - In the mitochondrial matrix. Acetyl-CoA joins oxaloacetate to make citrate. - Per glucose (two turns of the cycle): 2 ATP, 6 NADH, 2 FADH2 and 4 CO2”
Electron Transport Chain + Chemiosmosis
On the inner mitochondrial membrane. NADH and FADH2 hand their electrons to protein complexes. Energy from the electrons pumps H+ across the membrane, building a proton gradient. H+ flows back through ATP synthase, which makes most of the ATP (about 26-28 per glucose). Oxygen is the final electron acceptor and ends up as water.
Source: “4. Electron transport chain + chemiosmosis - On the inner mitochondrial membrane. NADH and FADH2 hand their electrons to protein complexes. - Energy from the electrons pumps H+ across the membrane, building a proton gradient. - H+ flows…”
Fermentation
Glycolysis can keep going if NAD+ is regenerated. Lactic acid fermentation (muscle cells): pyruvate -> lactate. Alcohol fermentation (yeast): pyruvate -> ethanol + CO2. Only the 2 ATP from glycolysis per glucose.
Source: “5. No oxygen? Fermentation - Glycolysis can keep going if NAD+ is regenerated. - Lactic acid fermentation (muscle cells): pyruvate -> lactate. - Alcohol fermentation (yeast): pyruvate -> ethanol + CO2. - Only the 2 ATP from glycolysis per…”
Exam Traps
Most ATP comes from the electron transport chain, not from glycolysis or the Krebs cycle. CO2 is released in pyruvate oxidation and in the Krebs cycle: 6 CO2 per glucose in total. The water in the overall equation is made at the end of the electron transport chain, not in glycolysis.
Source: “Exam traps - Most ATP comes from the electron transport chain, not from glycolysis or the Krebs cycle. - CO2 is released in pyruvate oxidation and in the Krebs cycle: 6 CO2 per glucose in total. - The water in the overall equation is made…”
3. Flashcards (8)
Prompt
What is the overall equation for cellular respiration?
Answer
C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy.
Source: “Big picture: cells break down glucose to make ATP. Overall equation: C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy”
Prompt
Where does glycolysis occur?
Answer
In the cytoplasm.
Source: “Happens in the cytoplasm. Does NOT need oxygen”
Prompt
What is produced during pyruvate oxidation?
Answer
1 CO2 and 1 NADH per pyruvate.
Source: “Each pyruvate becomes acetyl-CoA, releasing 1 CO2 and making 1 NADH”
Prompt
How many ATP are produced in the Krebs cycle per glucose?
Answer
2 ATP.
Source: “Per glucose (two turns of the cycle): 2 ATP, 6 NADH, 2 FADH2 and 4 CO2”
Prompt
What is the final electron acceptor in the electron transport chain?
Answer
Oxygen.
Source: “Oxygen is the final electron acceptor and ends up as water”
Prompt
What happens during fermentation?
Answer
NAD+ is regenerated, allowing glycolysis to continue.
Source: “Glycolysis can keep going if NAD+ is regenerated”
Prompt
Where is most ATP produced during cellular respiration?
Answer
In the electron transport chain.
Source: “Most ATP comes from the electron transport chain, not from glycolysis or the Krebs cycle”
Prompt
How many CO2 are released per glucose during cellular respiration?
Answer
6 CO2.
Source: “CO2 is released in pyruvate oxidation and in the Krebs cycle: 6 CO2 per glucose in total”
4. Quiz (4)
1. What is the net gain of ATP from glycolysis?
- A. 0 ATP
- B. 2 ATP
- C. 4 ATP
- D. 36 ATP
Show the answer
B. 2 ATP
Glycolysis uses 2 ATP and produces 4 ATP, resulting in a net gain of 2 ATP.
Source: “Uses 2 ATP early on and makes 4 ATP, so the net gain is 2 ATP, plus 2 NADH”
2. What is produced in the Krebs cycle?
- A. 2 ATP, 6 NADH, 2 FADH2, 4 CO2
- B. 4 ATP, 2 NADH, 2 FADH2, 6 CO2
- C. 2 ATP, 4 NADH, 2 FADH2, 4 CO2
- D. 2 ATP, 6 NADH, 4 FADH2, 2 CO2
Show the answer
A. 2 ATP, 6 NADH, 2 FADH2, 4 CO2
The Krebs cycle produces 2 ATP, 6 NADH, 2 FADH2, and 4 CO2 per glucose.
Source: “Per glucose (two turns of the cycle): 2 ATP, 6 NADH, 2 FADH2 and 4 CO2”
3. According to the notes, what does the energy from the electrons do in the electron transport chain?
Reworded by a person on 2026-10-12
- A. It splits glucose into two pyruvate
- B. It turns pyruvate into lactate
- C. It pumps H+ across the membrane, building a proton gradient
- D. It releases CO2
Show the answer
C. It pumps H+ across the membrane, building a proton gradient
The electron transport chain pumps H+ ions across the membrane, creating a proton gradient used to produce ATP.
Source: “Energy from the electrons pumps H+ across the membrane, building a proton gradient”
The question as StudyProofs wrote it
What is the primary function of the electron transport chain?
- A. To produce ATP
- B. To oxidize NADH
- C. To pump H+ ions (its answer key)
- D. To produce CO2
4. What type of fermentation occurs in muscle cells?
- A. Alcohol fermentation
- B. Lactic acid fermentation
- C. Both
- D. Neither
Show the answer
B. Lactic acid fermentation
Muscle cells undergo lactic acid fermentation, converting pyruvate to lactate.
Source: “Lactic acid fermentation (muscle cells): pyruvate -> lactate”
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