🔥 Chapter 7: Cellular Respiration

📚 Section 1: Vocabulary Matching ⏱ ~5 min

Match each cellular respiration term with its correct definition.

🔬 Section 2: Key Figures ⏱ ~5 min

Study these key OpenStax figures. Click each image to reveal its description.

Figure 7.3 NAD⁺ is the oxidized form; NADH is the reduced form. NAD⁺ accepts two electrons and one H⁺ to become NADH. This electron carrier shuttles high-energy electrons to the electron transport chain, where their energy is used to make ATP.

🔍 Click to reveal description

Figure 7.7 Glycolysis has two phases: The energy-investment phase uses 2 ATP to phosphorylate glucose. The energy-payoff phase produces 4 ATP and 2 NADH. Net gain: 2 ATP, 2 NADH, and 2 pyruvate per glucose molecule. Occurs in the cytoplasm without oxygen.

🔍 Click to reveal description

Figure 7.11 The citric acid cycle (Krebs cycle): Acetyl CoA (2C) joins oxaloacetate (4C) to form citrate (6C). Through 8 steps, it releases 2 CO₂, produces 3 NADH, 1 FADH₂, and 1 ATP (GTP) per turn. The cycle turns twice per glucose molecule.

🔍 Click to reveal description

Figure 7.12 The electron transport chain (ETC): Located in the inner mitochondrial membrane. NADH and FADH₂ donate electrons to a series of protein complexes (I-IV). As electrons pass through, energy is used to pump H⁺ ions into the intermembrane space, creating a proton gradient. Oxygen is the final electron acceptor, forming water.

🔍 Click to reveal description

Figure 7.13 ATP synthase is a molecular machine embedded in the inner mitochondrial membrane. H⁺ ions flow down their concentration gradient through the enzyme, causing it to rotate like a turbine. This mechanical energy drives the phosphorylation of ADP → ATP. This process is called chemiosmosis.

🔍 Click to reveal description

Figure 7.16 Fermentation regenerates NAD⁺ so glycolysis can continue without oxygen. Lactic acid fermentation (in muscles) converts pyruvate to lactate. Alcohol fermentation (in yeast) converts pyruvate to ethanol + CO₂. Neither pathway produces additional ATP beyond glycolysis's 2 ATP.

🔍 Click to reveal description

🔢 Section 3: Order the Steps ⏱ ~5 min

Put these stages of aerobic cellular respiration in the correct order by clicking the numbers. Click a step, then click where you want to place it.

• ? Electron Transport Chain & Oxidative Phosphorylation — produces ~34 ATP using NADH and FADH₂
• ? Glycolysis — glucose → 2 pyruvate + 2 ATP + 2 NADH (in cytoplasm)
• ? Fermentation — anaerobic alternative when O₂ is absent; regenerates NAD⁺
• ? Pyruvate Oxidation & Citric Acid Cycle — produces CO₂, NADH, FADH₂ (in mitochondrial matrix)

Click the step numbers to assign order (1, 2, 3, 4):

✅ Section 4: Concept Check ⏱ ~8 min

Test your understanding of cellular respiration.

1. How many net ATP molecules are produced directly by glycolysis from one glucose molecule?

4 ATP

2 ATP

36 ATP

0 ATP

💡 Need a hint?

Glycolysis uses 2 ATP in the investment phase and produces 4 ATP in the payoff phase. What's the net?

Why this is correct: Glycolysis invests 2 ATP to phosphorylate glucose, then produces 4 ATP by substrate-level phosphorylation. Net gain = 4 - 2 = 2 ATP. It also produces 2 NADH, which can later produce more ATP through the ETC if oxygen is present.

2. What is the final electron acceptor in the electron transport chain?

NADH

CO₂

ATP

O₂ (oxygen)

💡 Need a hint?

This is why we need to breathe! Without this molecule, the ETC cannot function.

Why this is correct: Molecular oxygen (O₂) is the final electron acceptor in the ETC. After electrons pass through all the protein complexes, O₂ picks them up along with H⁺ ions to form water (H₂O). Without oxygen, the ETC backs up and cells must resort to fermentation for energy.

4. What is the primary purpose of fermentation?

To produce large amounts of ATP

To break down glucose completely into CO₂ and H₂O

To regenerate NAD⁺ so glycolysis can continue

To transport electrons to oxygen

💡 Need a hint?

Without oxygen, NADH piles up. What does glycolysis NEED to keep running?

Why this is correct: Without oxygen, the ETC can't accept electrons from NADH, so NAD⁺ runs out. Fermentation solves this by converting NADH back to NAD⁺ (while converting pyruvate to lactate or ethanol). This lets glycolysis keep producing its 2 ATP per glucose — not much, but enough for survival.

💡 Section 5: Apply Your Knowledge ⏱ ~5 min

Answer these short response questions (minimum 30 characters each).

Question 1

Why does cyanide poisoning kill so quickly? (Hint: Cyanide blocks Complex IV of the electron transport chain.)

Question 2

During intense exercise, your muscles burn and feel fatigued. Using your knowledge of cellular respiration and fermentation, explain what is happening at the cellular level.

🎯 Section 6: Final Reflection ⏱ ~2 min

Write a brief reflection: How does cellular respiration connect to photosynthesis? Why do both plants AND animals need cellular respiration? (Minimum 100 characters)