Cellular Respiration

Grade 12 · Biology

Semester 2 | Period 4 | Week 23

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Subject: Biology

Semester: 2

Period: 4

Week: 23

School Name:
Teacher’s Name:
Subject: Biology
Grade Level: Grade 12
Date: Week 23
Lesson Duration: 45 minutes
Week & Period: Week 23, Period IV
Topic: Cellular Respiration
Sub-topic: Glycolysis, Link Reaction, Krebs Cycle, ETC, ATP Synthesis, Coenzymes, Pyruvate, and Oxygen Debt

 

Learning Objectives

By the end of this lesson, learners should be able to:

  1. Describe the glycolysis process and identify its final product.
  2. Explain the fate of pyruvate under aerobic and anaerobic conditions.
  3. Discuss the link reaction and steps of the Krebs Cycle.
  4. Identify the reactions in cellular respiration: decarboxylation, dehydrogenation, oxidative phosphorylation.
  5. Explain the role of coenzymes (NAD and FAD) in respiration.
  6. Describe the electron transport chain (ETC) and the role of electron carriers.
  7. Outline how ATP is synthesized in mitochondria.
  8. Define oxygen debt and explain anaerobic respiration in muscle cells.

 

Previous Knowledge

Learners understand the difference between aerobic and anaerobic respiration, and the importance of ATP.

 

Instructional Materials

  • Diagram of mitochondrion with labeled stages
  • Flowchart of glycolysis → Krebs → ETC
  • Colored paper arrows to demonstrate movement of electrons
  • Animation or video showing ATP synthesis (if available)
  • Labeled NAD and FAD molecule charts

 

Lesson Development – ABC Model

A – Anticipation (Warm-up Activity)

Time: 5–7 minutes
Ask learners: “If we remove oxygen from the body, how will cells still get energy?”
Write their responses and then introduce the term oxygen debt and link to the need for efficient respiration.

 

B – Building Knowledge (Main Lesson)

Time: 25–30 minutes

  1. Glycolysis:
  • Occurs in cytoplasm.
  • One glucose molecule is split into two molecules of pyruvate.
  • 2 ATP and 2 NADH are formed.
  • No oxygen needed.
  1. Link Reaction (Preparatory Step):
  • Pyruvate enters mitochondria.
  • Converted to Acetyl CoA and CO₂ is released.
  • NAD+ is reduced to NADH.
  1. Krebs Cycle (Citric Acid Cycle / TCA Cycle):
  • Acetyl CoA enters the cycle.
  • Series of decarboxylation (release of CO₂) and dehydrogenation (hydrogen atoms picked up by NAD or FAD).
  • Generates: 2 ATP, 6 NADH, 2 FADH₂.
  1. Electron Transport Chain (ETC):
  • NADH and FADH₂ donate electrons.
  • Electrons move through flavoproteins, quinones, and cytochromes.
  • This flow pumps protons and forms ATP through oxidative phosphorylation.
  • Oxygen is the final electron acceptor → water is formed.
  1. ATP Synthesis:
  • About 34 ATP produced in ETC.
  • Total ATP from one glucose: 36–38 ATP.
  1. Role of Coenzymes (NAD and FAD):
  • Carry electrons from glycolysis and Krebs cycle to ETC.
  1. Fate of Pyruvate:
  • Aerobic condition: enters mitochondria for Krebs cycle.
  • Anaerobic condition:
    • In yeast: Pyruvate → ethanol + CO₂
    • In muscles: Pyruvate → lactic acid → causes fatigue → oxygen debt during recovery.

 

Learners’ Activities

  • Sequence game: Arrange the stages of respiration in order.
  • Group chart work: Label a mitochondrion and point where each reaction happens.
  • Individual task: Match coenzymes with their functions.
  • Classroom demo: Pass a ball (representing electrons) through a human “ETC” line.

 

C – Consolidation (Conclusion & Assessment)

Time: 8–10 minutes

Quick Questions:

  1. What are the three main stages of cellular respiration?
  2. What is the function of NAD in respiration?
  3. Why does lactic acid build up in muscles?
  4. What happens to ATP if ETC stops?

Homework:

  • Draw and label a diagram showing glycolysis, link reaction, Krebs cycle, and ETC.
  • State two examples of organisms that use anaerobic respiration.

 

Short Notes (Summarized Recap)

  • Glycolysis splits glucose into pyruvate (2 ATP produced).
  • In presence of oxygen, pyruvate enters mitochondria → Krebs → ETC.
  • NAD and FAD carry high-energy electrons to ETC.
  • ETC releases most of the ATP during respiration.
  • No oxygen = anaerobic respiration → fermentation or lactic acid.
  • Oxygen debt is the body’s need for extra oxygen to remove lactic acid.

 

Extra Instructions for Expanded Work

Expanded Notes:

  • Full diagram of each stage
  • Equation for each major reaction
  • List all ATP totals per stage

Assignment:

  • Research: Compare alcoholic fermentation in yeast and muscle fatigue in humans.
  • Creative task: Build a respiration model with labeled paths for glucose, oxygen, CO₂, ATP.

 

Differentiation / Inclusive Strategies

  • Visuals for all pathways.
  • Sentence starters for written work.
  • Oral presentation option for learners who struggle with writing.

 

Teacher Reflection

  • Were learners able to follow the biochemical sequence of respiration?
  • Did visual aids and models improve understanding of the abstract concepts?