3.2.3Additional lessons
Cell Respiration Skills — IB Biology SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 56 of 142
Curriculum Equation Key معادلة التنفس الخلوي الهوائي الموزونة - Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP) | جلوكوز + أكسجين ← ثاني أكسيد كربون + ماء + طاقة
Location & Specifications: الميتوكوندريا (Mitochondria) والسيتوسول.
Part 1 of 6Equations
Aerobic respiration
- Aerobic respiration C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, with release of energy that makes ATP.
Human anaerobic
- Human anaerobic In humans glucose is converted to lactate without oxygen, releasing a small amount of ATP.
Yeast anaerobic
- Yeast anaerobic C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂, producing ethanol and carbon dioxide, with a small amount of ATP.
ATP yield
- ATP yield Aerobic respiration releases far more ATP per molecule of glucose than anaerobic respiration.
Site
- Site Glycolysis occurs in the cytoplasm, and the aerobic stages take place in the mitochondria.
Part 2 of 6Using a Respirometer
1
Place the organisms, such as germinating seeds or insects, in a sealed tube with potassium hydroxide or soda lime.
2
The absorbent removes carbon dioxide, so any change in gas volume is due to oxygen use.
3
Connect a capillary tube with a drop of coloured liquid that moves as the pressure falls.
4
Record the movement of the drop at regular intervals and keep the temperature constant.
5
Calculate the volume of oxygen used per minute, usually per gram of organism.
Part 3 of 6Variables and Controls
Variables and Controls
Temperature
- Temperature Raising temperature increases respiration rate until enzymes denature, so use a water bath.
Control tube
- Control tube Use glass beads of the same volume instead of organisms, to check for changes in pressure or temperature.
Respiratory quotient
- Respiratory quotient The ratio of carbon dioxide produced to oxygen consumed is about 1.0 when glucose is respired.
Replicates
- Replicates Repeat each condition and calculate a mean for greater reliability.
Part 4 of 6Interpreting Results
Interpreting Results
Temperature
- Temperature A rise in temperature increases the rate of oxygen use in germinating seeds until enzymes denature.
Seeds
- Seeds Germinating seeds respire quickly, whereas dormant seeds have a very low rate of respiration.
Limitations
- Limitations Gas volume changes with temperature and pressure, so a control tube is needed.
Part 5 of 6Worked Example
Question
- In a respirometer the coloured drop moves 30 mm in 10 minutes along a capillary of radius 1 mm.
- Calculate the volume of oxygen used per minute.
- Volume = πr²d = π × 1² × 30 = 94.2 mm³.
- Rate = 94.2 ÷ 10 = 9.42 mm³ per minute.
Answer About 9.4 mm³ of oxygen per minute (example data).
Part 6 of 6Exam Checklist & Tips
3.2.3 – Key Points for the Exam
- Aerobic respiration Release of energy from glucose using oxygen, producing carbon dioxide and water.
- Anaerobic respiration Release of energy from glucose without oxygen.
- Respirometer Apparatus for measuring the rate of oxygen use or carbon dioxide production.
- Fermentation Anaerobic respiration in yeast, producing ethanol and carbon dioxide.
Common Mistakes
- Writing that anaerobic respiration releases no ATP, when it releases a small amount.
- Giving lactate as the product of yeast respiration, when yeast makes ethanol and carbon dioxide.
- Leaving out the absorbent for carbon dioxide, so the volume change does not show oxygen use.
- Stating that respiration is the same as breathing; respiration happens in cells.
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Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.