GPT on Question 12, Sep 17

Photosynthesis is the process plants, algae, and some bacteria use to convert light energy into chemical energy stored in sugar.

The overall equation

\[
6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2
\]

In words:

carbon dioxide + water + light → glucose + oxygen

Where it happens

In plants, photosynthesis mainly occurs in leaf cells inside structures called chloroplasts. Chloroplasts contain chlorophyll, the green pigment that absorbs light—especially red and blue wavelengths.

The two main stages

• 1.Light-dependent reactions
• •Occur in the chloroplast’s thylakoid membranes.
• •Chlorophyll absorbs sunlight.
• •Water molecules are split, releasing oxygen.
• •Light energy is converted into temporary chemical energy in molecules called ATP and NADPH.

• 2.The Calvin cycle
• •Occurs in the chloroplast’s stroma.
• •Uses carbon dioxide from the air.
• •Uses ATP and NADPH from the first stage to build sugar molecules.
• •These sugars can later be used for energy, growth, or storage.

Why photosynthesis matters

• •It produces much of the oxygen in Earth’s atmosphere.
• •It provides plants with energy-rich sugars.
• •It supports most food chains: animals obtain this stored energy by eating plants or other animals.
• •It removes carbon dioxide from the atmosphere.

A simple way to think about it is: plants use sunlight to turn water and carbon dioxide into food, releasing oxygen as a byproduct.