Action Spectrum
Effectiveness of Different Wavelengths
Light comes in different colors (wavelengths) – red, blue, green, etc.
- Not all colors are equally useful for photosynthesis.
- Some are absorbed well, while others are reflected.
The action spectrum tells us which colors of light are most effective for photosynthesis.
Method of Determining Action Spectrum
Here’s how scientists determine it:
- A plant is exposed to different colors (wavelengths) of light one by one.
- For each color, they measure how much oxygen the plant produces.
- This data is then used to create a graph – called the action spectrum.
This graph shows us which colors are most useful for photosynthesis.
Historical Discovery
The first action spectrum was made in 1883 by T. W. Engelmann, a German scientist.
- He worked on Spirogyra, a type of green algae.
- When he exposed it to different colors of light, he saw:
- Blue and red light caused the most photosynthesis (more oxygen released).
- Green light was the least effective (most of it is reflected, which is why leaves look green).
Role of Carbon Dioxide in Photosynthesis
Function of CO₂
Carbon dioxide (CO₂) is one of the raw materials in photosynthesis.
- Inside the plant cell, CO₂ is used in reactions that make sugar molecules.
- These reactions are powered by ATP and NADPH, two energy-rich molecules made during the light reactions.
So, CO₂ provides the carbon atoms that end up in glucose (C₆H₁₂O₆).
Entry of CO₂ into the Leaf
- CO₂ enters the leaf through stomata – tiny openings mostly found on the underside of leaves.
- Once inside, CO₂ dissolves in water in the cell walls of mesophyll cells (the main cells where photosynthesis occurs).
Key Points:
- Stomata act like tiny mouths or gates.
- They open to let CO₂ in and close to prevent water loss.
- The opening and closing of stomata is controlled by the plant depending on its needs and environmental conditions.
✅ Summary
So students, today we learned how important light, carbon dioxide, and pigments are in the process of photosynthesis. This process is nature’s magic — turning air, water, and sunlight into food and oxygen. It’s why plants are so important for life on Earth.
We also learned how at different times of the day, the balance between photosynthesis and respiration can shift — and at one special time called the compensation point, they exactly cancel each other out.
Photosynthesis doesn’t happen randomly — it’s affected by the color of light, the amount of carbon dioxide, and even the structure of the leaf.