Chapter 7

In photosynthesis, ________ is oxidized and __________ is reduced. a. water... oxygen b. carbon dioxide \(\ldots\) water c. water ... carbon dioxide d. glucose ... carbon dioxide

Which of the following are produced by reactions that take place in the thylakoids and consumed by reactions in the stroma? a. \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) b. ATP and NADPH c. ATP, NADPH, and CO \(_{2}\) d. ATP, NADPH, and \(\mathrm{O}_{2}\)

When light strikes chlorophyll molecules in the reaction-center complex, they lose electrons, which are ultimately replaced by a. splitting water. b. oxidizing NADPH. c. the primary electron acceptor. d. the electron transport chain.

The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why? (Explain your answer.) a. It is often too cold at night for these reactions to take place. b. Carbon dioxide concentrations decrease at night. c. The Calvin cycle depends on products of the light reactions. d. Plants usually close their stomata at night.

Which of the following does not occur during the Calvin cycle? a. carbon fixation b. oxidation of NADPH c. consumption of ATP d. release of oxygen

Why is it difficult for \(\mathrm{C}_{3}\) plants to carry out photosynthesis in very hot, dry environments such as deserts? a. The light is too intense and destroys the pigment molecules. b. The closing of stomata keeps \(\mathrm{CO}_{2}\) from entering and \(\mathrm{O}_{2}\) from leaving the plant. c. They must rely on photorespiration to make ATP. d. \(\mathrm{CO}_{2}\) builds up in the leaves, blocking carbon fixation.

How is photosynthesis similar in \(\mathrm{C}_{4}\) plants and CAM plants? a. In both cases, the light reactions and the Calvin cycle are sepa. rated in both time and location. b. Both types of plants make sugar without the Calvin cycle. c. In both cases, rubisco is not used to fix carbon initially. d. Both types of plants make most of their sugar in the dark.

Explain why a poison that inhibits an enzyme of the Calvin cycle will also inhibit the light reactions.

What do plants do with the sugar they produce in photosynthesis?

Explain what is meant by saying the light reactions convert solar energy to chemical energy.

Continue your comparison of electron transport and chemiosmosis in mitochondria and chloroplasts. In each case, a. where do the electrons come from? b. how do the electrons get their high potential energy? c. what picks up the electrons at the end of the chain? d. how is the energy released as electrons are transferred down the electron transport chain used?

Will increasing atmosphericlevels of \(\mathrm{CO}_{2}\) make you sneeze as well as itch? Scientists studying the effects of rising \(\mathrm{CO}_{2}\) levels have looked at ragweed, whose pollen is the primary allergen for fall hay fever. They grew ragweed in three levels of \(\mathrm{CO}_{2}\) : a pre- industrial concentration of \(280 \mathrm{ppm}\), a year 2000 level of 370 ppm, and a projected level of \(600 \mathrm{ppm}\). They found that pollen production increased by \(131 \%\) and \(320 \%\) in the plants exposed to the recent and projected \(\mathrm{CO}_{2}\) levels, respectively. What was the hypothesis of this experiment? Do the results support the hypothesis? Given what you know about climate change, what other variables would you like to test, and what other measurements would you like to take?

Most scientific experts agree that climate change is already occurring and has potentially catastrophic consequences for all of life on Earth. The Paris Agreement of 2015 represented a global consensus on the need to reduce greenhouse gas emissions. However, in 2017 the United States announced its intention to withdraw from the Agreement in \(2020 .\) Go online to research and summarize the main agreements reached in this historic global climate accord and the U.S. government's reasons for withdrawing. What roles do you think scientists, politicians, and citizens will need to play to cut emissions and limit global warming?