Photosynthesis

Definition

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll, carbon dioxide, and water. It converts light energy into chemical energy.

Basic Process

During photosynthesis, plants take in carbon dioxide from the atmosphere and water from the soil. Using sunlight as an energy source, and with the help of chlorophyll, they convert these into glucose (sugar) and oxygen. The overall word equation is:

Carbon Dioxide + Water + Light Energy (Chlorophyll) → Glucose + Oxygen

Factors Affecting Photosynthesis

1. Light: Light provides the energy for the process. The rate of photosynthesis increases with light intensity up to a certain point.
2. Carbon Dioxide (CO₂): CO₂ is a raw material. An increase in CO₂ concentration generally increases the rate of photosynthesis, provided other factors are optimal.
3. Water: Water is also a raw material. A shortage of water can reduce the rate of photosynthesis.
4. Chlorophyll: The green pigment that absorbs light energy. Without chlorophyll, photosynthesis cannot occur.

Significance of Photosynthesis

• Food Production: It is the primary source of food for almost all life on Earth, either directly (plants) or indirectly (animals eating plants or other animals).
• Oxygen Release: It releases oxygen into the atmosphere, which is essential for the respiration of most living organisms.
• Carbon Cycle: It helps in maintaining the balance of carbon dioxide and oxygen in the atmosphere.

Experiment to Demonstrate Photosynthesis Process

Aim: To show that sunlight is necessary for photosynthesis.

Setup:

1. Take a potted plant and destarch it by keeping it in a dark room for 2-3 days. (This ensures that any starch present in the leaves is used up).
2. Cover a part of one of its leaves with a black paper clip or aluminum foil on both sides, ensuring no light reaches the covered part.
3. Keep the potted plant in sunlight for 6-8 hours.
4. Pluck the covered leaf and remove the black paper.
5. Boil the leaf in water for a few minutes (to break down cell walls).
6. Then, boil the leaf in alcohol (in a water bath) to remove the chlorophyll (decolorization). The leaf will turn pale white.
7. Wash the leaf with water and then dip it in a dilute solution of iodine.

Observation:

• The part of the leaf that was exposed to sunlight turns blue-black (indicating the presence of starch).
• The part of the leaf that was covered with black paper remains yellowish-brown (indicating the absence of starch).

Conclusion: This experiment shows that sunlight is necessary for photosynthesis to produce starch.