📊 Results:

• Group A (heavy oxygen in water) released oxygen-18.
• Group B (heavy oxygen in carbon dioxide) released normal oxygen.

✅ This clearly showed: the oxygen released by plants comes from water, not from carbon dioxide.

Thus, Van Neil’s hypothesis was proved correct.

🔁 Release of Hydrogen and Role of NADP

When water is split during photosynthesis, two things are released:

• Hydrogen
• Oxygen

We already discussed that oxygen goes out into the air. But what happens to hydrogen?

🧪 Hydrogen is not wasted. It plays a very important role.

This hydrogen is used to reduce a special helper molecule called:

NADP – Nicotinamide Adenine Dinucleotide Phosphate

When NADP combines with hydrogen, it becomes:

NADPH – this is a form of stored energy

Think of NADPH as a delivery truck, carrying hydrogen and energy to another part of the plant cell, where glucose (sugar) will be made.

🌱 So, in summary:

• Water is split into hydrogen and oxygen
• Hydrogen + NADP → NADPH (energy carrier)
• NADPH helps turn CO₂ into glucose

🎨 Role of Photosynthetic Pigments

🌿 What are Photosynthetic Pigments?

These are special colored substances found in chloroplasts of plant cells. They help plants absorb light — just like solar panels absorb sunlight.

They are found in structures called thylakoid membranes (tiny compartments inside the chloroplasts).

The main pigments are:

• Chlorophyll a – the main pigment
• Chlorophyll b
• Xanthophylls
• Carotenes

These pigments are responsible for capturing sunlight and starting the process of photosynthesis.

🌈 Absorption of Light – How does it work?

Light is made up of many colors or wavelengths — red, blue, green, etc. Each pigment absorbs specific colors better than others.

💡 For example:

• Chlorophyll a absorbs blue and red light best
• It does not absorb green well — that’s why most plants appear green, because green light is reflected, not absorbed

Light behaves like tiny packets of energy called photons. When a pigment absorbs a photon:

• An electron inside the pigment jumps to a higher energy level
• This is called an excited state
• The energy from this excited electron is used to start the chemical reactions of photosynthesis

📚 Simple Example:
Imagine a solar-powered toy. Sunlight hits the toy’s panel, and the energy runs the motor. In the same way, sunlight hits chlorophyll, and the energy is used to make food in the plant.