IB MYP 4-5 Biology-Diffusion- Study Notes - New Syllabus
IB MYP 4-5 Biology-Diffusion- Study Notes – New syllabus
IB MYP 4-5 Biology-Diffusion- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Simple diffusion
- Facilitated diffusion
- Factors affecting diffusion rate
Diffusion – Simple Diffusion
What is Diffusion?
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.
In simple terms, particles naturally move from crowded spaces to areas where there is more room. This movement continues until the particles are evenly spread out – this is called equilibrium.
Simple Diffusion
Simple diffusion is the most basic type of diffusion. It does not require any energy (ATP). It happens directly through the cell membrane, especially for small and non-polar molecules.
Examples of Simple Diffusion
- Oxygen (O₂) entering cells from the blood.
- Carbon dioxide (CO₂) leaving cells as a waste product.
- Small molecules like ethanol and urea passing through the membrane.
Key Features
| Feature | Simple Diffusion |
|---|---|
| Energy Needed? | No (Passive process) |
| Direction | High → Low concentration |
| Uses Protein Carriers? | No |
| Examples | Oxygen, Carbon dioxide |
Memory Trick
“C T S S D” helps you remember the 5 key factors:
- Concentration
- Temperature
- Surface area
- Size of molecule
- Distance
Why Is It Important?
- Take in oxygen for respiration
- Remove carbon dioxide, a waste product
- Maintain the right balance of small molecules
Factors That Affect the Rate of Diffusion
- Concentration Gradient: A bigger difference = faster diffusion.
- Temperature: Higher temperature = particles move faster.
- Surface Area: Larger surface area = faster diffusion.
- Size of the Molecule: Smaller particles move more easily.
- Distance: Shorter distance = quicker diffusion.
Facilitated Diffusion
What is Facilitated Diffusion?
Facilitated diffusion is a type of passive transport where particles move across a cell membrane with the help of proteins. Just like simple diffusion, it moves substances from high concentration to low concentration – but with a little help!
Why Do We Need Help Sometimes?
- Too big (like glucose)
- Charged or polar (like ions)
These cannot pass directly through the lipid bilayer. So, they need help from protein channels or carrier proteins in the membrane.
How It Works
Facilitated diffusion uses special transport proteins to move substances without using energy.
There are two main types of transport proteins:
- Channel proteins = form tiny pores for specific ions (like Na⁺ or K⁺) to pass through.
- Carrier proteins = change shape to move molecules (like glucose) across the membrane.
Key Features
| Feature | Facilitated Diffusion |
|---|---|
| Energy Needed? | No (Still Passive) |
| Direction | High → Low concentration |
| Protein Involved? | Yes (Channels or Carriers) |
| Moves What? | Glucose, ions, amino acids |
Tip
Facilitated = “With Help”
Just remember: It’s still passive, just not alone!
Examples
- Glucose entering a muscle cell with help from a glucose carrier.
- Sodium (Na⁺) and Potassium (K⁺) ions moving through channel proteins.
- Chloride (Cl⁻) ions passing through chloride channels.
Simple vs Facilitated Diffusion
| Feature | Simple Diffusion | Facilitated Diffusion |
|---|---|---|
| Uses proteins? | No | Yes |
| Molecules moved | Small, non-polar | Larger, polar/charged |
| Energy? | No | No |
Factors Affecting Diffusion Rate
Diffusion is the movement of particles from an area of high concentration to low concentration, but how fast this happens depends on a few key factors.
1. Concentration Gradient
The steeper the gradient, the faster the diffusion. A large difference between concentrations on either side of the membrane causes particles to spread out quickly.
Example: Oxygen diffuses faster into a cell when there’s a lot outside and very little inside.
2. Temperature
Higher temperature = more kinetic energy = faster particle movement. So, diffusion happens faster in warmer conditions.
Example: Diffusion of dye in hot water happens much faster than in cold water.
3. Surface Area
A larger surface area means more space for particles to pass through. Cells with lots of membrane folds (like microvilli) absorb materials faster.
Cells are small and often folded to increase surface area for faster transport!
4. Particle Size
Smaller molecules diffuse faster than larger ones. Large molecules take more time to squeeze through membrane pores.
Example: Oxygen (O₂) diffuses faster than glucose.
5. Distance (Thickness of Membrane)
The shorter the distance, the faster diffusion occurs. Thin membranes help substances move across more quickly.
Example: Lung alveoli have thin walls to speed up gas exchange.
6. Type of Molecule
Lipid-soluble and non-polar molecules diffuse easily through the cell membrane. Charged or polar molecules need help (facilitated diffusion).
Summary Table
| Factor | Effect on Diffusion |
|---|---|
| Steeper concentration gradient | Faster diffusion |
| Higher temperature | Faster diffusion |
| Larger surface area | Faster diffusion |
| Smaller particle size | Faster diffusion |
| Thinner membrane | Faster diffusion |
| Lipid-soluble molecule | Diffuses more easily |
Real-Life Application
Fish gills and human lungs are adapted to maximize diffusion by having:
- Large surface area
- Thin surfaces
- Moist membranes
- Steep concentration gradients