5. A scientist proposes using radioactive tracers to demonstrate that the carbon atoms from carbon dioxide end up incorporated into glucose molecules as the result of photosynthesis. In order to test this hypothesis, the scientist conducts the following experiment:

1. A group of plants are illuminated with light of a wavelength that is optimal for photosynthesis.
2. The light is turned off, and the plants are kept in darkness for all remaining steps in the investigation.
3. Radiolabeled CO ₂ is introduced to the plants.
4. After 30 minutes, plant leaves are homogenized and glucose extracted from the cell homogenate.
5. Radiolabels are found in the glucose samples.

Explain why the radiolabel was present in the homogenate. Describe the role of light in the synthesis of ATP and NADPH and how the absence of light may have affected this process. (5 points)