Factors Affecting Photosynthesis
Photosynthesis depends on internal factors (inside the plant) and external factors (environment). The slowest factor at any time controls the overall rate! ⏱️
⚖️ Key Rule: Law of Limiting Factors
When many factors affect a process, the one closest to its lowest needed level controls the speed. For example:
- Even with perfect light and CO₂, low temperature stops photosynthesis ❄️
- Fixing the limiting factor (e.g., warming the plant) restores photosynthesis ☀️
🌞 1. Light
- At low light: Photosynthesis rate ↗️ as light ↗️ (straight-line relationship).
- At high light: Rate stops increasing (saturation at 10% of full sunlight!) because other factors become limiting.
- Too much light: Breaks down chlorophyll 😵 and reduces photosynthesis.
Note: Light is rarely limiting in nature (except for shady forest plants 🌳).
☁️ 2. Carbon Dioxide (CO₂)
- Major limiting factor! 🌍 Atmosphere has very little CO₂ (0.03–0.04%).
- Upto 0.05% CO₂ ↗️ photosynthesis rate. Beyond that, it harms plants long-term ⚠️.
- C₃ vs. C₄ plants react differently:
- C₄ plants (e.g., corn): Saturate at 360 μlL⁻¹ CO₂
- C₃ plants (e.g., wheat): Need >450 μlL⁻¹ CO₂ to saturate 🌾
Fun fact: Greenhouses pump extra CO₂ for tomatoes/bell peppers 🍅🌶️ to boost yields!
🌡️ 3. Temperature
- Affects dark reactions (enzyme-driven 🧪). Light reactions are less sensitive.
- C₄ plants like higher temperatures.
- C₃ plants prefer cooler temps.
- Tropical plants handle heat better than temperate ones 🌴 vs. 🍂.
💧 4. Water
- Not directly limiting, but indirect effects:
- Water stress → shuts stomata 😶 → less CO₂ enters leaves.
- Water stress → wilting leaves → smaller surface area for photosynthesis.
NEET Must-Knows! 📚
- Blackman’s Law: The factor nearest its minimum level controls photosynthesis rate.
- C₃ vs. C₄ plants: Different CO₂ saturation points (360 μlL⁻¹ vs. >450 μlL⁻¹).
- Light saturation at just 10% of full sunlight 🌤️.
- Water’s role: Stress closes stomata → less CO₂ → slower photosynthesis.
- Temperature: Controls dark reactions; C₄ plants prefer hotter temps than C₃.
Keep these in mind—they’re golden for exams! 💛
