Photosynthesis

This course is a part of Biology, a 31-course Topic series from Khan Academy.

There's a lot of carbon in your body - in DNA, proteins, carbohydrates, fats, and other key biological molecules. How did that carbon get there? Drumroll... photosynthesis! Learn how plants and other photosynthetic organisms use light energy to make sugars from carbon dioxide and water, bringing both chemical energy and readily usable carbon into Earth’s global ecosystem.

This course contains 4 segments:

Intro to photosynthesis

Get an overview of photosynthesis! Learn more about the stages of photosynthesis, as well as why this process is so important to human life and to the global ecosystem.

The light-dependent reactions

How do you turn light energy into chemical energy? Find out how plants perform this amazing energy transformation. We'll dive into the properties of light, how chlorophylls and other pigments absorb light, and how the absorbed energy is stored in chemical bonds.

The Calvin cycle

In the Calvin cycle, energy storage molecules from the light-dependent reactions are used to capture (fix) carbon dioxide molecules and build sugars. Learn more about how this important cycle works.

Photorespiration: C3, C4, and CAM plants

The Calvin cycle enzyme rubisco is essential...but it also has a bad habit. Rubisco sometimes acts on oxygen rather than carbon dioxide, leading to a carbon-wasting side process called photorespiration. Learn about the strategies C4 and CAM plants use to minimize photorespiration.