IB Biology Topic C1.3.1: Transformation of Light Energy to Chemical Energy Notes

Photosynthesis Converts Light Energy into Chemical Energy

1. Photosynthesis is the process that captures light energy and stores it as chemical energy in carbon compounds.
2. It takes place in the chloroplasts of plants, algae, and some bacteria.
3. This one process is the entry point for energy into almost every ecosystem on Earth.

Photosynthesis Happens in Two Linked Stages

1. Light-dependent stage
   1. This stage captures light energy and stores it briefly in the energy carriers ATP and reduced NADP.
2. Light-independent stage
   1. This stage uses the ATP and reduced NADP to build carbon compounds such as glucose.
3. The first stage supplies the energy that the second stage spends, so the two stages depend on each other.

Photosynthesis Is the Base of Energy Flow in Ecosystems

1. Plants and other photosynthetic organisms are called producers because they make the carbon compounds that store energy.
2. These compounds form the base of the food chain, passing energy to consumers that eat the producers.
3. Photosynthesis is how light energy from the Sun first enters the living world.

Without photosynthesis, energy could not enter most ecosystems and life as we know it could not be sustained.

Where This Topic Leads Next

1. The details of how carbon dioxide becomes glucose are covered in the next topic.
2. The step-by-step mechanisms of both stages are HL content in later topics.