CIE iGCSE Co-ordinated Sciences-B12. Respiration- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B12. Respiration – Study Notes
CIE iGCSE Co-ordinated Sciences-B12. Respiration – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- State the uses of energy in living organisms, including: muscle contraction, protein synthesis, cell division, growth, the passage of nerve impulses and the maintenance of a constant body temperature
- Describe aerobic respiration as the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy
- State the word equation for aerobic respiration as:
glucose + oxygen → carbon dioxide + water - State the balanced symbol equation for aerobic respiration as:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O - Describe anaerobic respiration as the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen
- State that anaerobic respiration releases much less energy per glucose molecule than aerobic respiration
- State the word equation for anaerobic respiration in muscles during vigorous exercise as:
glucose → lactic acid - State that lactic acid builds up in muscles and blood during vigorous exercise causing an oxygen debt
Supplement
- Outline how the oxygen debt is removed after exercise, limited to:
(a) continuation of fast heart rate to transport lactic acid in the blood from the muscles to the liver
(b) continuation of deeper and faster breathing to supply oxygen for aerobic respiration of lactic acid
(c) aerobic respiration of lactic acid in the liver
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Uses of Energy in Living Organisms
📌 Introduction
All living things need a continuous supply of energy, mainly released by respiration. This energy is stored in ATP and used for many vital processes.
🌱 Main Uses of Energy
- Muscle Contraction
Energy needed for sliding of actin & myosin filaments.
Allows movement (walking, running, pumping of heart, breathing). - Protein Synthesis
Energy required to join amino acids into polypeptide chains.
For making enzymes, hormones, antibodies, structural proteins. - Cell Division
Mitosis and meiosis require energy.
For chromosome movement, spindle formation, and cytokinesis. - Growth
Building new cells, tissues and organs.
Involves synthesis of macromolecules + cell division. - Passage of Nerve Impulses
Nerve cells use energy to pump ions across membranes.
Maintains resting potential and allows transmission of electrical signals. - Maintenance of a Constant Body Temperature
In warm-blooded animals (birds & mammals).
Heat from respiration maintains 37 °C in humans for enzyme activity.
📊 Summary Table
| Use of Energy | Explanation |
|---|---|
| Muscle contraction | Movement of body & organs |
| Protein synthesis | Building enzymes, hormones, cell structures |
| Cell division | Growth, repair, reproduction |
| Growth | Formation of new tissues |
| Nerve impulses | Active transport of ions for signal transmission |
| Constant temperature | Heat from respiration keeps enzymes active |
⚡ Quick Recap
Energy uses = MPC GNC
Muscle contraction
Protein synthesis
Cell division
Growth
Nerve impulses
Constant temperature
👉 Memory hook: “My Pet Cat Grows Neatly Constantly.”
Aerobic Respiration
📌 Introduction
Respiration is the process by which cells release energy from food molecules. In aerobic respiration, oxygen is required.
🌱 Definition
Aerobic respiration = a series of chemical reactions in cells that use oxygen to break down nutrient molecules (mainly glucose), releasing energy.
🔬 Word Equation
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)
⚡ Key Features
- Takes place mostly in the mitochondria.
- Requires oxygen.
- Breaks down glucose completely.
- Releases a large amount of energy (much more than anaerobic respiration).
- Energy released is used for: muscle contraction, growth, protein synthesis, nerve impulses, maintaining temperature, etc.
📊 Summary Table
| Aspect | Aerobic Respiration |
|---|---|
| Oxygen requirement | Yes |
| Breakdown of glucose | Complete |
| Products | CO₂ + H₂O |
| Energy released | Large amount (ATP) |
| Site in cell | Mitochondria |
⚡ Quick Recap
Definition: Respiration using oxygen.
Equation: Glucose + O₂ → CO₂ + H₂O + energy.
Main point: Complete breakdown of glucose, high energy yield.
👉 Memory hook: “O₂ in, Energy out.”
Aerobic Respiration – Word Equation
📌 Introduction
Aerobic respiration is the process in which cells release energy from glucose using oxygen. It is the most efficient way to produce energy for living organisms.
🌱 Word Equation
Glucose + Oxygen → Carbon dioxide + Water
- Glucose → main nutrient (sugar) broken down.
- Oxygen → required for complete breakdown.
- Carbon dioxide → waste gas removed by lungs.
- Water → waste, often lost through sweat or urine.
Energy is released during this process and stored in ATP molecules, used for all cellular activities.
🔬 Key Points
- Takes place mainly in mitochondria.
- Oxygen is essential.
- Releases a large amount of energy compared to anaerobic respiration.
- Products are CO₂ and H₂O.
📊 Summary Table
| Component | Role |
|---|---|
| Glucose | Nutrient broken down for energy |
| Oxygen | Needed to fully oxidize glucose |
| Carbon dioxide | Waste, exhaled by lungs |
| Water | Waste, also used in cells |
| Energy | Captured as ATP for cell processes |
⚡ Quick Recap
Equation: Glucose + O₂ → CO₂ + H₂O
Key idea: Oxygen helps break glucose completely, releasing lots of energy.
👉 Memory tip: “Sugar + air → energy + CO₂ + H₂O.”
Aerobic Respiration – Balanced Symbol Equation
📌 Introduction
Aerobic respiration is the process by which cells release energy from glucose in the presence of oxygen. It is the most efficient way to produce energy in living organisms.
🌱 Balanced Symbol Equation
\[ \mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + Energy\,(ATP)} \]
- C₆H₁₂O₆ (Glucose) → nutrient molecule broken down.
- 6O₂ (Oxygen) → required to fully oxidize glucose.
- 6CO₂ (Carbon dioxide) → waste, exhaled.
- 6H₂O (Water) → waste, also used in cells.
- Energy → stored as ATP for cellular processes.
🔬 Key Points
- Takes place mainly in the mitochondria.
- Oxygen is essential for complete breakdown of glucose.
- Produces a large amount of energy compared to anaerobic respiration.
- The equation is balanced: same number of C, H, and O atoms on both sides.
📊 Summary Table
| Component | Role |
|---|---|
| C₆H₁₂O₆ | Nutrient for energy |
| 6O₂ | Oxidizes glucose completely |
| 6CO₂ | Waste, exhaled |
| 6H₂O | Waste, also used in metabolism |
| Energy (ATP) | Powers cell activities |
⚡ Quick Recap
Equation: \[ \mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + Energy} \]
Key idea: Oxygen fully breaks down glucose → CO₂ + H₂O + lots of energy.
👉 Memory tip: “1 sugar + 6 oxygens → 6 CO₂ + 6 waters + energy.”
Anaerobic Respiration
📌 Introduction
Not all energy-releasing processes require oxygen. In anaerobic respiration, cells release energy by breaking down nutrients without oxygen. This happens when oxygen is insufficient, such as during intense exercise.
🌱 Definition
Anaerobic respiration = a series of chemical reactions in cells that break down nutrient molecules (mainly glucose) to release energy without using oxygen.
🔬 Word Equations
- In animals (lactic acid formation):
Glucose → Lactic acid + Energy (ATP) - In plants and yeast (alcoholic fermentation):
Glucose → Ethanol + Carbon dioxide + Energy (ATP)
⚡ Key Points
- Takes place in cytoplasm (not mitochondria).
- Releases less energy than aerobic respiration.
- Produces lactic acid in animals → can cause muscle fatigue.
- Produces ethanol + CO₂ in plants/yeast → basis for bread and alcohol fermentation.
- Useful when oxygen is limited or unavailable.
📊 Summary Table
| Feature | Animals | Plants / Yeast |
|---|---|---|
| Oxygen needed | No | No |
| End products | Lactic acid | Ethanol + CO₂ |
| Energy released | Small amount (ATP) | Small amount (ATP) |
| Site in cell | Cytoplasm | Cytoplasm |
⚡ Quick Recap
Definition: Energy release without oxygen.
Animals: Glucose → lactic acid + ATP
Plants/Yeast: Glucose → ethanol + CO₂ + ATP
Less efficient than aerobic respiration.
👉 Memory trick: “No O₂ → small energy, lactic acid or alcohol made.”
Energy Release in Anaerobic Respiration
📌 Key Point
Anaerobic respiration releases much less energy per glucose molecule than aerobic respiration.
Reason: Glucose is partially broken down without oxygen, so fewer ATP molecules are produced.
📊 Comparison Table
| Type of Respiration | Energy Released per Glucose | Key Note |
|---|---|---|
| Aerobic | Large amount (≈36–38 ATP) | Complete breakdown of glucose |
| Anaerobic | Small amount (≈2 ATP) | Incomplete breakdown of glucose |
⚡ Quick Recap
Aerobic = lots of energy (O₂ present).
Anaerobic = little energy (O₂ absent).
👉 Memory tip: “No oxygen → tiny energy.”
Anaerobic Respiration in Muscles
📌 Introduction
During vigorous exercise, muscles may not get enough oxygen for aerobic respiration. In such cases, energy is released anaerobically.
🌱 Word Equation
Glucose → Lactic acid + Energy (ATP)
Glucose → sugar broken down for energy.
Lactic acid → waste product that can accumulate in muscles → causes fatigue.
Energy → released in small amounts to support muscle contraction.
🔬 Key Points
- Takes place in cytoplasm.
- Oxygen not required.
- Energy yield is much less than aerobic respiration.
- Produces lactic acid, which may cause muscle soreness.
📊 Summary Table
| Aspect | Anaerobic Respiration in Muscles |
|---|---|
| Oxygen needed | No |
| Word equation | Glucose → Lactic acid + Energy |
| Energy released | Small amount (ATP) |
| Site | Cytoplasm |
| Side effect | Lactic acid build-up → fatigue |
⚡ Quick Recap
Equation: Glucose → Lactic acid + Energy
Key idea: Muscles produce energy quickly without oxygen.
👉 Memory trick: “Glucose → Lactic acid when O₂ is low.”
Lactic Acid and Oxygen Debt
📌 Key Point
During vigorous exercise, muscles may not get enough oxygen for aerobic respiration.
Anaerobic respiration then occurs, producing lactic acid.
Lactic acid builds up in muscles and diffuses into the blood.
This causes an oxygen debt, which is the extra oxygen needed after exercise to:
- Break down lactic acid into CO₂ and H₂O
- Restore normal oxygen levels in blood and tissues
⚡ Quick Recap
Vigorous exercise → anaerobic respiration → lactic acid ↑
Oxygen debt = extra O₂ required after exercise to remove lactic acid
👉 Memory tip: “Run hard → lactic acid → repay oxygen later.”
Removal of Oxygen Debt
📌 Introduction
After vigorous exercise, lactic acid builds up in muscles due to anaerobic respiration. The oxygen debt is the extra oxygen required to remove this lactic acid and restore normal conditions.
🌬️ Steps in Oxygen Debt Removal
(a) Fast heart rate continues
The heart keeps beating faster after exercise.
Purpose: transport lactic acid from muscles through the blood to the liver.
(b) Deeper and faster breathing continues
Breathing remains rapid and deep even after stopping exercise.
Purpose: supply extra oxygen for aerobic breakdown of lactic acid.
(c) Aerobic respiration of lactic acid in the liver
Lactic acid is converted back into glucose or carbon dioxide + water.
This occurs via aerobic respiration in liver cells, using the extra oxygen supplied.
📊 Summary Table
| Step | Mechanism | Purpose |
|---|---|---|
| Fast heart rate | Moves blood quickly | Transport lactic acid from muscles to liver |
| Deep & fast breathing | Extra oxygen intake | Provides O₂ for lactic acid breakdown |
| Aerobic respiration in liver | Lactic acid → glucose/CO₂ + H₂O | Removes lactic acid, repays oxygen debt |
⚡ Quick Recap
Oxygen debt = extra oxygen needed after exercise.
Steps to remove it: Fast heart rate → Deep breathing → Aerobic respiration of lactic acid
👉 Memory tip: “Heart pumps, lungs breathe, liver fixes.”