Edexcel iGCSE Biology-3.1 Transport in unicellular organisms- Study Notes- New Syllabus
Edexcel iGCSE Biology-3.1 Transport in unicellular organisms- Study Notes- New syllabus
Edexcel iGCSE Biology-3.1 Transport in unicellular organisms- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
3.1 understand why simple, unicellular organisms can rely on diffusion for movement of substances in and out of the cell
Diffusion in Simple Unicellular Organisms
📝 Introduction
All living organisms need to take in substances (like oxygen, nutrients) and remove wastes (like carbon dioxide).
In simple unicellular organisms (e.g., amoeba), diffusion alone is enough for this exchange.
🔑 Reasons Why Diffusion is Enough
- Small Size
Only one cell thick → substances do not have to travel far. - Large Surface Area to Volume Ratio (SA:V)
Cell surface is large compared to the tiny volume inside.
Diffusion can supply enough materials to meet the cell’s needs. - Low Metabolic Demand
Unicellular organisms have relatively low energy needs compared to multicellular organisms.
Simple diffusion is sufficient to provide oxygen and remove carbon dioxide. - Direct Contact with Environment
Whole cell is in contact with the surrounding medium (water/air).
No need for transport systems.
📊 Summary Table
| Feature | Effect |
|---|---|
| Small size | Short diffusion distance |
| Large SA:V ratio | More surface for exchange |
| Low energy needs | Diffusion is enough |
| Direct exposure | Easy exchange with surroundings |
⚡ Quick Recap
Unicellular = small + large SA:V → diffusion works.
No transport system needed.
Diffusion supplies O₂ + nutrients, removes CO₂ + waste.