Thinking Scientifically

1. Photosynthesis takes place in plants, algae, and some microbes. How does it affect a meat-eating animal?

2. What color would plants be if they absorbed all wavelengths of visible light? Why?

3. How did Priestley and Ingenhousz’s experiments follow the scientific method?

4. A mutant strain of corn lacks carotenoids. Seedlings must be grown in the absence of oxygen, and as photosynthesis begins, the oxygen it generates must be removed for the plants to live. Why must the oxygen be removed?

5. When vegetables and flowers are grown in greenhouses in the winter, their growth rate greatly increases if the CO2 level is raised to two or three times the level in the natural environment. What is the biological basis for the increased rate of growth?

Additional Questions and Terms

1. The National Aeronautics and Space Administration (NASA) operates a program to establish "controlled ecological life-support systems," also known as space farms, to be used aboard spacecraft. These closed life-support systems are based on plants, using light as the only energy input. Use your knowledge of photosynthesis to explain how a space farm might operate.

2. How might you measure the efficiency of photosynthesis? Why is it more difficult to measure photorespiration?

3. A plant is exposed to an environment where the proportion of oxygen is increased from the normal value (21%) to 42%. This appears to have no effect on the plant's photosynthetic rate. What kind of plant is this, in terms of the type of photosynthesis that it conducts? How do you know?

4. Suppose rubisco is genetically altered so that it loses its ability to fix oxygen. What effect might this have on corn as compared to rice?

5. Why must electron transport in photosynthesis be unidirectional?

6. Some photosynthetic bacteria use hydrogen sulfide (H2S) instead of water in photosynthesis. They produce sulfur instead of oxygen. How do these bacteria demonstrate that the oxygen source in photosynthesis is water rather than CO2?