Photosynthesis

Autotrophs are organisms that convert light energy to chemical energy through photosynthesis. In light-dependent reactions, ATP and NADPH are produced through photosystems of electron transport in the thylakoid inner membranes (where molecules of water are stripped to provide electrons to these ETC systems!), then in the light-independent reactions that ATP and NADPH are used to produce sugars from CO2 in the atmosphere! If we weren’t already so habituated to the facts of photosynthesis, it would seem like an impossible fantasy of science fiction.

Here are a few questions to help you test your understanding. Post your responses to the comments.

1. Use the following labels for the diagram below: NADPH, CO2, LIGHT, O2, ATP, SUGAR/CH2O, LIGHT REACTIONS IN THYLAKOID MEMBRANES, CALVIN CYCLE IN STROMA, H20 
2. Below is an image of an action spectrum (relative rates of photosynthesis under different wavelengths of light) and an absorption spectrum (the different wavelengths of light absorbed by chlorophylls a). Indicate which line (solid or dotted) represents the absorption spectrum and which represents the action spectrum of a plant performing photosynthesis. Why are these lines different?
3. How are the electron “holes” filled in chlorophyll P680+? and, P700+?
4. Specify the terms for the blanks of the diagram below. Which of these provide chemical energy and reducing power to the Calvin cycle?
5. Why is neither O2 nor NADPH generated by cyclic electron flow?
6. How is ATP produced by cyclic electron flow? (be specific by referring to elements of the ETC).
7. What does rubisco do?
8. Refer to the diagram below to answer these questions: What are the three phases (a, b, and c) of the Calvin cycle? What are the key molecules (d to o)?
9. What is the cause of photorespiration and what are the consequences?