🌱 Photosynthesis: C3 vs C4 Plants & Photorespiration
Here’s a simple breakdown of how plants make food and why some are more efficient than others!
🔬 Photorespiration: The “Oops” Moment in Plants
- What is it?
A process where plants use oxygen instead of carbon dioxide during photosynthesis.
• Happens only in C3 plants (like wheat, rice) 🌾, not in C4 plants (like maize, sugarcane) 🌽. - Why does it happen?
The enzyme RuBisCO (the most abundant enzyme on Earth! 🌍) can bind to both CO₂ and O₂.
• Equation:
\[ \text{RuBP} + O_2 \xrightarrow{\text{RuBisCO}} \text{Phosphoglycerate} + \text{Phosphoglycolate} \] - Consequences:
• No sugars or ATP are made 🚫🍬⚡
• CO₂ is released and ATP is wasted 😔
• Reduces photosynthesis efficiency in C3 plants.
🌿 Key Differences: C3 vs C4 Plants
| Characteristics | C3 Plants | C4 Plants |
|---|---|---|
| Cell type for Calvin cycle | Mesophyll | Bundle sheath |
| Cell type for initial CO₂ fixation | Mesophyll | Mesophyll |
| Number of cell types fixing CO₂ | One: Mesophyll | Two: Bundle sheath + Mesophyll |
| Primary CO₂ acceptor | RuBP | PEP |
| Carbons in primary CO₂ acceptor | 5 (RuBP) | 3 (PEP) |
| Primary CO₂ fixation product | PGA (3C) | OAA (4C) |
| Carbons in primary fixation product | 3 | 4 |
| Has RuBisCO? | Yes | Yes |
| Has PEP Case? | No | Yes |
| Cells with RuBisCO | Mesophyll | Bundle sheath |
| CO₂ fixation rate (high light) | Low | High |
| Photorespiration at low CO₂ | High | Negligible |
| Photorespiration at high CO₂ | Negligible | Negligible |
| Temperature optimum | 20-25°C | 30-40°C |
| Examples | Wheat, rice, soybeans | Maize, sugarcane, sorghum |
💡 Why C4 Plants Rock!
- No photorespiration: They pump CO₂ into bundle sheath cells, making RuBisCO use CO₂ (not O₂) 👍
- More efficient: Higher yields, better in hot climates ☀️, and fix CO₂ faster under bright light
⚡ NEET Must-Knows!
- RuBisCO’s dual role: Fixes CO₂ (carboxylase) or O₂ (oxygenase → photorespiration)
- C4 plants avoid photorespiration via spatial separation of steps (mesophyll + bundle sheath)
- Photorespiration wastes energy (ATP/CO₂ loss) and lowers C3 plant efficiency
- C4 plants use PEP carboxylase (no O₂ binding) for initial CO₂ fixation → higher productivity
- Temperature tolerance: C4 plants thrive at 30-40°C; C3 plants prefer 20-25°C
🌟 Quick Summary
- C3 plants: Photorespiration = 🌧️ “Rain on their parade”
- C4 plants: No photorespiration = ☀️ “Sunny skies ahead”!
Use this table to ace those plant-comparison questions! 💪✨
