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Respiration

Subject: Biology
Topic: 5
Cambridge Code: 0610 / 0970 / 5090

Overview​

Respiration - Release of energy from organic molecules

Two Types​

  1. Aerobic - With oxygen
  2. Anaerobic - Without oxygen

Purpose: Produce ATP (energy currency of cells)

Aerobic Respiration​

C6H12O6+6O2→6CO2+6H2O+energy (ATP)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}

Glucose is commonly used substrate (can use fats, proteins)

Energy released: ~2880 kJ per mole glucose

Location: Mitochondrion​

Mitochondrial structure:

  • Outer membrane: Permeable
  • Inner membrane: Highly folded (cristae)
  • Matrix: Inner space
  • DNA and ribosomes present

Stages of Aerobic Respiration​

Glycolysis​

Location: Cytoplasm

Process:

  • Glucose (6 carbons) → Pyruvate (3 carbons × 2)
  • Net gain: 2 ATP, 2 NADH

Steps:

  1. Glucose activated (uses 2 ATP)
  2. Glucose split into two 3-carbon molecules
  3. Oxidized, releasing energy (produces 4 ATP)

Net: 2 ATP produced

Location: Mitochondrial matrix

Process:

  • Pyruvate (3C) → Acetyl-CoA (2C)
  • Releases CO₂
  • Produces NADH
  • Occurs twice per glucose

Krebs Cycle (Citric Acid Cycle)​

Location: Mitochondrial matrix

Occurs: 2 turns per glucose

Inputs: Acetyl-CoA (2C)

Outputs per turn:

  • 3 NADH (reducing agents)
  • 1 FADH₂ (reducing agent)
  • 1 ATP
  • 2 CO₂

Electron Transport Chain​

Location: Inner mitochondrial membrane

Process:

  • NADH and FADH₂ oxidized
  • Electrons transferred through proteins
  • Releases energy
  • Energy pumps H⁺ ions
  • H⁺ gradient produces ATP (chemiosmosis)

ATP produced: ~32-34 ATP per glucose

Anaerobic Respiration​

Occurs: Without oxygen

Location: Cytoplasm

Glucose → Pyruvate (glycolysis) → Lactate or Ethanol

In Animals​

Glucose→Pyruvate→Lactate\text{Glucose} \rightarrow \text{Pyruvate} \rightarrow \text{Lactate}

  • Pyruvate reduced to lactate
  • NAD⁺ regenerated (allows glycolysis to continue)
  • Only 2 ATP produced per glucose

Problem: Lactate accumulates, causes fatigue

In Plants/Yeast​

Glucose→Pyruvate→Ethanol+CO2\text{Glucose} \rightarrow \text{Pyruvate} \rightarrow \text{Ethanol} + CO_2

  • Pyruvate decarboxylated to ethanol
  • NAD⁺ regenerated
  • 2 ATP produced per glucose

Uses: Fermentation, brewing

Comparing Aerobic and Anaerobic​

FeatureAerobicAnaerobic
Oxygen requiredYesNo
LocationMitochondriaCytoplasm
ATP per glucose~32-342
ProductsCO₂, H₂OLactate or Ethanol
DurationLong-term energyShort-term emergency

Respiratory Quotient (RQ)​

RQ=CO2 producedO2 consumedRQ = \frac{CO_2 \text{ produced}}{O_2 \text{ consumed}}

Carbohydrate: RQ = 1 Protein: RQ = ~0.9 Fat: RQ = ~0.7

Measuring Respiration​

Respiration Rate​

Oxygen consumed: Using respirometer CO₂ produced: Using lime water Heat released: Using thermometer

Respirometer​

Airtight container with organism Measures gas volume changes KOH absorbs CO₂ produced

Key Points​

  1. Aerobic: Glucose + O₂ → CO₂ + H₂O + ATP
  2. Anaerobic: Glucose → Lactate/Ethanol + ATP
  3. Glycolysis in cytoplasm, Krebs in matrix
  4. NADH and FADH₂ key carriers to ETC
  5. Aerobic produces 32-34 ATP, Anaerobic produces 2
  6. Mitochondria structure relates to function

Practice Questions​

  1. Write equation for aerobic respiration
  2. Describe glycolysis
  3. Explain Krebs cycle
  4. How does electron transport produce ATP?
  5. Compare aerobic vs anaerobic
  6. Calculate RQ for different substrates

Revision Tips​

  • Learn all stages in order
  • Know ATP yield per stage
  • Understand mitochondrial structure
  • Practice respirometer calculations
  • Know when anaerobic occurs
  • Distinguish lactate vs ethanol fermentation