recap

10.1 recap

The light reactions of photosynthesis convert light energy into chemical energy. The light-independent reactions use that chemical energy to reduce CO2 to carbohydrates. While most photosynthetic organisms use water as the electron donor for reduction of CO2, some use other molecules, such as hydrogen sulfide (H2S).

learning outcomes

You should be able to:

  • Use experimental evidence to explain the source of the O2 produced in oxygenic photosynthesis.

  • Describe the relationship between the light reactions and the light-independent reactions of photosynthesis.

Question 1

What is the relationship between the light reactions and the light-independent reactions of photosynthesis?

The light reactions convert light energy into chemical energy in the form of ATP and NADPH. In the light-independent reactions, ATP and NADPH power the fixation of CO2 to form carbohydrate. NADP and ADP are regenerated.

Question 2

What is the experimental evidence that water is the source of the O2 produced during photosynthesis?

Researchers used the isotope 18O to show that the O2 produced during photosynthesis came from water labeled with 18O and not from carbon dioxide labeled with 18O.

We will describe the light reactions and the light-independent reactions separately. We’ll begin the next section by discussing the physical nature of light and the specific photosynthetic molecules that capture its energy.