Edexcel iGCSE Biology- 3.20 Excretion in Flowering Plants- Study Notes- New Syllabus
Edexcel iGCSE Biology- 3.20 Excretion in Flowering Plants- Study Notes- New syllabus
Edexcel iGCSE Biology- 3.20 Excretion in Flowering Plants- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
3.20 understand the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf
Waste Gases in Plants – CO₂ & O₂
📝 Introduction
Plants, like all living organisms, carry out metabolic processes (photosynthesis + respiration).
These processes produce waste gases:
- Carbon dioxide (CO₂) → from respiration.
- Oxygen (O₂) → from photosynthesis.
These gases leave the plant mainly through stomata on the leaf surface.
🔬 Origin of Waste Gases
🔹 Carbon Dioxide (CO₂)
Produced in aerobic respiration in mitochondria:
Glucose + Oxygen → Carbon dioxide + Water + Energy
CO₂ diffuses out of cells → into air spaces of leaf → out via stomata.
🔹 Oxygen (O₂)
Produced in photosynthesis (light reactions in chloroplasts):
Carbon dioxide + Water → Glucose + Oxygen
O₂ diffuses out of cells → into air spaces of leaf → out via stomata.
🍂 Loss of Waste Gases Through Stomata
- Stomata = tiny pores on underside of leaf, controlled by guard cells.
- Day (light): Photosynthesis > Respiration → O₂ is main waste → diffuses out.
- Night (dark): No photosynthesis, only respiration → CO₂ is main waste → diffuses out.
📊 Summary Table
| Process | Waste Gas Produced | When? | How it Leaves |
|---|---|---|---|
| Respiration | CO₂ | Day & Night | Diffuses out via stomata |
| Photosynthesis | O₂ | Day (light present) | Diffuses out via stomata |
⚡ Quick Recap
CO₂ → waste of respiration.
O₂ → waste of photosynthesis.
Both gases leave the leaf via stomata.
Day → O₂ mainly lost. Night → CO₂ mainly lost.