How Does the Process of Photosynthesis Occur in Green Plants?

Photosynthesis in green plants is the process by which they convert light energy into chemical energy in the form of glucose (sugar), using carbon dioxide and water.

Here's a breakdown of how this process occurs:

1. Absorption of Light Energy:

• Green plants contain a pigment called chlorophyll, located within organelles called chloroplasts, primarily in the leaves.
• Chlorophyll absorbs light energy, particularly in the red and blue regions of the electromagnetic spectrum. Green light is reflected, which is why plants appear green.

2. Uptake of Water and Carbon Dioxide:

• Water is absorbed from the soil by the plant's roots through a process called osmosis. The water is then transported to the leaves through the xylem vessels.
• Carbon dioxide is taken in from the atmosphere through small pores on the leaves called stomata. The stomata also allow for the release of oxygen, a byproduct of photosynthesis.

3. The Two Stages of Photosynthesis:

Photosynthesis is divided into two main stages: the light-dependent reactions and the light-independent reactions (Calvin Cycle).

a) Light-Dependent Reactions (Occur in the thylakoid membranes of the chloroplasts):

• Light energy absorbed by chlorophyll is used to split water molecules into hydrogen ions (H+), electrons, and oxygen. This process is called photolysis.
• The electrons are passed along an electron transport chain, releasing energy that is used to generate ATP (adenosine triphosphate), an energy-carrying molecule, and NADPH, another energy-carrying molecule.
• Oxygen is released as a byproduct into the atmosphere.

b) Light-Independent Reactions (Calvin Cycle) (Occur in the stroma of the chloroplasts):

• The ATP and NADPH produced in the light-dependent reactions provide the energy and reducing power needed to convert carbon dioxide into glucose.
• Carbon dioxide from the atmosphere is "fixed" or incorporated into an organic molecule using an enzyme called RuBisCO.
• Through a series of reactions, the carbon is ultimately used to create glucose (C6H12O6).
• The Calvin Cycle regenerates its starting molecule, allowing the process to continue.

4. Summary Equation:

The overall chemical equation for photosynthesis is:

6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂

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

In essence, green plants use sunlight, water, and carbon dioxide to create glucose (their food) and release oxygen as a byproduct. This process is vital for life on Earth, as it provides the oxygen we breathe and forms the base of most food chains.