CIE iGCSE Co-ordinated Sciences-B3.1 Diffusion - Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B3.1 Diffusion – Study Notes
CIE iGCSE Co-ordinated Sciences-B3.1 Diffusion – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
- Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement
- State that some substances move into and out of cells by diffusion through the cell membrane
- Describe the importance of diffusion of gases and solutes in living organisms
- Investigate the factors that influence diffusion, limited to: surface area, temperature, concentration gradient and distance
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Diffusion
📌 Definition
Diffusion = net movement of particles from a region of higher concentration → to a region of lower concentration (down a concentration gradient), due to random movement of particles.
🔑 Key Points
- Happens in gases, liquids, and dissolved substances.
- Particles are always moving randomly → this causes spreading out.
- Continues until particles are evenly distributed (concentration equal everywhere).
- Does not need energy (passive process).
🌱 In Cells
Cell membranes are partially permeable → only certain small molecules can diffuse through.
Examples:
- Oxygen (O₂) diffuses into cells for respiration.
- Carbon dioxide (CO₂) diffuses out of cells as waste from respiration.
- Water (H₂O) also moves by diffusion (and osmosis).
📖 Example
- When a cell is using oxygen in respiration → concentration of O₂ inside the cell drops.
- Oxygen molecules diffuse in from outside (where concentration is higher).
- At the same time, CO₂ produced inside diffuses out.
📊 Summary Table
| Feature | Diffusion |
|---|---|
| What moves? | Particles (gas, liquid, dissolved substances) |
| Direction | High → Low concentration |
| Gradient | Down a concentration gradient |
| Energy needed? | No (passive) |
| Cell examples | O₂ in, CO₂ out, water moves too |
⚡ Quick Recap
Diffusion = random spreading, high → low concentration.
Passive process (no energy).
Key in cells: O₂ in, CO₂ out.
Diffusion Across the Cell Membrane
📌 Key Statement
Some substances move into and out of cells by diffusion through the cell membrane.
🔑 Examples
- Oxygen (O₂) → diffuses into cells for respiration.
- Carbon dioxide (CO₂) → diffuses out of cells as a waste product.
- Water (H₂O) → small molecules can diffuse too (also via osmosis).
🌱 Note
- The cell membrane is partially permeable → allows only certain small molecules to pass through.
- Diffusion always goes down a concentration gradient (high → low).
- This process is passive → no energy required.
⚡ Quick Recap
Movement through cell membrane = diffusion.
Substances: O₂ in, CO₂ out, H₂O too.
Needs no energy, only concentration difference.
Importance of Diffusion in Living Organisms
📌 Introduction
Diffusion is essential for survival because it allows cells to exchange gases and solutes with their surroundings without using energy.
🔑 Importance in Living Organisms
1. Gas Exchange (Respiration)
- Oxygen (O₂) diffuses into cells → needed for aerobic respiration.
- Carbon dioxide (CO₂) diffuses out of cells → waste product removed.
- In humans: diffusion occurs in alveoli of lungs (O₂ in, CO₂ out).
2. Nutrient Transport
- In small intestine → digested food molecules (e.g. glucose, amino acids) diffuse into blood capillaries.
- In plants → minerals like nitrates diffuse into root hair cells.
3. Waste Removal
- Cells get rid of harmful by-products (e.g. CO₂, urea in kidneys) by diffusion.
4. Equal Distribution of Substances
- Molecules like water, salts, and dissolved gases spread evenly in cells → maintains balance inside/outside.
⚡ Factors Affecting Diffusion (Rate)
- Surface Area → bigger area = faster diffusion (e.g. microvilli in intestine, alveoli in lungs).
- Temperature → higher temp = faster diffusion (molecules move quicker).
- Concentration Gradient → steeper gradient = faster diffusion (maintained by haemoglobin binding O₂ in RBCs).
- Distance → shorter path = faster diffusion (thin membranes help).
📊 Summary Table
| Factor | Effect on Diffusion | Example in Biology |
|---|---|---|
| Surface area ↑ | Faster diffusion | Microvilli, alveoli |
| Temperature ↑ | Faster diffusion | Active warm-blooded animals |
| Steeper gradient | Faster diffusion | O₂ into RBC (haemoglobin maintains gradient) |
| Shorter distance | Faster diffusion | Thin alveolar + capillary walls |
📝 Quick Recap
Diffusion = passive, no energy.
Essential for O₂ in, CO₂ out, nutrients in, wastes out.
Rate ↑ with ↑ surface area, temperature, gradient; rate ↓ if distance ↑.
Investigating Factors Affecting Diffusion
📌 Introduction
Diffusion rate can change depending on certain factors. In biology experiments, we usually test how surface area, temperature, concentration gradient, and distance affect diffusion.
🔑 Factors Affecting Diffusion
1. Surface Area
- Larger surface area = more space for particles to pass through.
- Example: microvilli in intestine increase SA for faster nutrient absorption.
- Experiment idea: Compare diffusion through small vs large agar blocks.
2. Temperature
- Higher temperature → molecules move faster (more kinetic energy).
- Diffusion happens more quickly at warmer temperatures.
- Experiment idea: Use dye diffusion in water at hot vs cold temperatures.
3. Concentration Gradient
- Steeper gradient = faster diffusion.
- Example: O₂ diffuses rapidly into red blood cells because haemoglobin keeps the internal O₂ concentration low.
- Experiment idea: Different sugar concentrations diffusing into dialysis tubing.
4. Distance
- Shorter distance = quicker diffusion (less travel path).
- Example: Alveoli walls are extremely thin → allows fast gas exchange.
- Experiment idea: Compare diffusion through thin vs thick layers of agar gel.
📊 Summary Table
| Factor | Effect on Diffusion | Example in Organism |
|---|---|---|
| Surface Area ↑ | Faster diffusion | Microvilli, alveoli |
| Temperature ↑ | Faster diffusion | Warm-blooded animals |
| Steeper Gradient | Faster diffusion | O₂ into RBCs |
| Distance ↓ | Faster diffusion | Thin alveolar walls |
⚡ Quick Recap
SA ↑ → faster
Temp ↑ → faster
Gradient ↑ → faster
Distance ↓ → faster