How does photosynthesis work step by step?

What is Photosynthesis?

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. This process primarily occurs in the chloroplasts of plant cells and can be summarized by the following equation:

$$ 6 \mathrm{CO}_2 + 6 \mathrm{H}_2O + \text{light energy} \longrightarrow C_6H_{12}O_6 + 6 \mathrm{O}_2 $$

Step-by-Step Process

1. Light-Dependent Reactions

• Location: Thylakoid membranes of the chloroplast
• Inputs: Water ($\mathrm{H}_2O$) and light energy
• Process: Light energy splits water molecules, releasing oxygen ($\mathrm{O}_2$), and produces ATP and NADPH (energy carriers).

2. Light-Independent Reactions (Calvin Cycle)

• Location: Stroma of the chloroplast
• Inputs: Carbon dioxide ($\mathrm{CO}_2$), ATP, and NADPH
• Process: ATP and NADPH are used to convert $\mathrm{CO}_2$ into glucose ($C_6H_{12}O_6$).

Worked Example

Calculate the amount of oxygen produced when 12 molecules of water are used in photosynthesis.

The balanced equation:

$$ 6 \mathrm{CO}_2 + 12 \mathrm{H}_2O + \text{light energy} \longrightarrow C_6H_{12}O_6 + 6 \mathrm{H}_2O + 6 \mathrm{O}_2 $$

Step 1: Identify the ratio from the equation:
12 molecules of water yield 6 molecules of oxygen.

Step 2: Calculate oxygen produced:

$$ \text{If } 12 \mathrm{H}_2O \to 6 \mathrm{O}_2, \text{ then } 12 \mathrm{H}_2O \text{ produces } 6 \mathrm{O}_2 $$

Answer:
12 molecules of water produce 6 molecules of oxygen during photosynthesis.

Takeaways

• Photosynthesis converts light energy into chemical energy in glucose.
• It consists of light-dependent (energy capture) and light-independent (sugar synthesis) stages.
• Oxygen is released as a byproduct when water is split during the light-dependent reactions.