Photosynthesis

Can plants use the sugar they produce during photosynthesis to directly power the work of the cell? Explain. (See figures 8.10,8.11, and 9.6).

The light reactions of photosynthesis supply the Calvin cycle with

1. light energy.
2. CO₂ and ATP.
3. H₂O and NADPH.
4. ATP and NADPH.

Explain how the use of an oxygen isotope helped elucidate the chemistry of photosynthesis.

Which of the following sequences correctly represents the flow of electrons during photosynthesis?

(A)\({\rm{NADPH}}\, \to {{\rm{O}}_{\rm{2}}} \to {\rm{C}}{{\rm{O}}_{\rm{2}}}\)

(B) \({{\rm{H}}_{\rm{2}}}{\rm{O}}\, \to {\rm{NADPH}}\, \to {\rm{Calvin}}\,{\rm{Cycle}}\)

(C) \({{\rm{H}}_{\rm{2}}}{\rm{O}}\, \to {\rm{photosystem}}\,{\rm{I}}\, \to {\rm{photosystem}}\,{\rm{II}}\)

(D)\({\rm{NADPH}}\, \to {\rm{electron transport chain }} \to {{\rm{O}}_{\rm{2}}}\)

How is photosynthesis similar in C₄ plants and CAM plants?

(A) In both cases, only photosystem I is used.

(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.

Which of the following statements is a correct distinction between autotrophs and heterotrophs?

(A) Autotrophs, but not heterotrophs, can nourish themselves, beginning with CO₂ and other nutrients that are inorganic.

(B) Only heterotrophs require chemical compounds from the environment.

(C) Cellular respiration is unique to heterotrophs.

(D) Only heterotrophs have mitochondria.

Which of the following does not occur during the Calvin cycle?

(A) carbon fixation

(B) oxidation of NADPH

(C) release of oxygen

(D) regeneration of the CO₂ acceptor

In mechanism, photophosphorylation is most similar to

(A) substrate-level phosphorylation in glycolysis.

(B) oxidative phosphorylation in cellular respiration.

(C) carbon fixation.

(D) reduction of NADP+.

Which process is most directly driven by light energy?

(A). creation of a pH gradient by pumping protons across the thylakoid membrane.

(B) reduction of NADP+ molecules 

(C) transfer of energy from pigment molecule to pigment molecule

(D) ATP synthesis.

Scientific evidence indicates that the CO₂ added to the air by the burning of wood and fossil fuels is contributing to global warming, a rise in global temperature. Tropical rain forests are estimated to be responsible for approximately 20% of global photosynthesis, yet the consumption of large amounts of CO₂ by living trees is thought to make little or no net contribution to reduction of global warming. Explain why this might be the case. (Hint: What processes in both living and dead trees produce CO₂?).

Scientific evidence indicates that the CO₂ added to the air by the burning of wood and fossil fuels is contributing to global warming, a rise in global temperature. Tropical rain forests are estimated to be responsible for approximately 20% of global photosynthesis, yet the consumption of large amounts of CO₂ by living trees is thought to make little or no net contribution to reduction of global warming. Explain why this might be the case. (Hint: What processes in both living and dead trees produce CO₂?)

The following diagram represents an experiment with isolated thylakoids. The thylakoids were first made acidic by soaking them in a solution at pH 4. After the thylakoid space reached pH 4, the thylakoids were transferred to a basic solution at pH 8. The thylakoids then made ATP in the dark. (See Concept 3.3 to review pH.).

Draw an enlargement of part of the thylakoid membrane in the beaker with the solution at pH 8. Draw ATP synthase. Label the areas of high H+ concentration and low H+ concentration. Show the direction protons flow through the enzyme and show the reaction where ATP is synthesized. Would ATP end up in the thylakoid or outside of it? Explain why the thylakoids in the experiment were able to make ATP in the dark.

Life is solar powered. Almost all the producers of the biosphere depend on energy from the sun to produce the organic molecules that supply the energy and carbon skeletons needed for life. In a short essay (100–150 words), describe how the process of photosynthesis in the chloroplasts of plants transforms the energy of sunlight into the chemical energy of sugar molecules.

Watermelon snow” in Antarctica is caused by a species of photosynthetic green algae that thrives in subzero temperatures (Chlamydomonas nivalis). These algae are also found in highaltitude year-round snowfields. In both locations, UV light levels tend to be high. Based on what you learned in this chapter, propose an explanation for why this photosynthetic alga appears reddish-pink.

How do the CO₂ molecules used in photosynthesis reach and enter the chloroplasts inside the leaf cell? (See Concept 7.2)

The Calvin Cycle requires ATP and NADPH, products of light reactions. If a classmate asserted that the light reactions don’t depend on the Calvin cycle and, with continual light, could just keep on producing ATP and NADPH, how would you respond?

According to the graph, which wavelengths of light drive the highest rates of photosynthesis?

What color of light is least effective in driving photosynthesis? Explain.

In the light reactions, what is the initial electron donor? Where do the electrons finally end up? 

In an experiment, isolated chloroplasts placed in an illuminated solution with the appropriate chemicals can produce ATP synthesis. Predict what would happen to the synthesis rate if a compound is added to the solution that makes membranes freely permeable to hydrogen ions.

To synthesize one glucose molecule, the Calvin cycle uses __________molecules of CO₂, _________molecules of ATP, and ________molecules of NADPH.

How are the larger numbers of ATP and NADPH molecules used during the Calvin cycle consistent with the high value of glucose as an energy source?

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

Redraw the cycle in Figure 10.19 using numerals to indicate the numbers of carbons instead of gray balls, multiplying at each step to ensure that you have accounted for all the carbons. In what forms do the carbon atoms enter and leave the cycle?

Review Figures 9.9 and 10.19. Discuss the roles of intermediate and product played by glyceraldehydes 3-phosphate (G3P) in the two processes shown in these two figures. 

To explore the relationship between the two variables, it is useful to graph the data in a scatter plot and then draw a regression line. (a) First, place the labels for the dependent and independent variables on the appropriate axes. Explain your choices. (b) Now plot the data points for corn and velvet left using a different symbol for each set of data, and add a key for the two symbols. (For additional information about graphs, see the Scientific Skills Review in Appendix F.)

Draw a “best fit” line for each set of points. A best-fit does not necessarily pass through all or even most points. Instead, it is a straight line that passes as close as possible to all data points from that set. Draw a best-fit line for each set of data. Because the placement of the line is a matter of judgment, two individuals may draw slightly different lines for a given set of points. The line that actually fits best, a regression line, can be identified by squaring the distances of all points to any candidate line, then selecting the line that minimizes the sum of the squares. (See the graph in the scientific skills Exercise in Chapter 3) for an example of a linear regression line. Excel or other software programs, including those on a graphical calculator, can plot regression lines once data points are entered. Using either Excel or a graphical calculator, enter the data points for each data set and have the program draw the two regression lines. Compare them to the lines drawn.

Describe the trends shown by the regression lines in your scatter plot. (a) Compare the relationship between the increasing concentration of CO₂ and the dry mass of corn to that for velvetleaf. (b) Considering that velvetleaf is a weed invasive to cornfields, predict how increased CO₂ concentration may affect interactions between the two species. 

Based on the data in the scatter plot, estimate the percentage change in dry mass of corn and velvetleaf plants if atmospheric CO₂ concentration increased from 390 ppm(current levels) to 800 ppm. (a) What is the estimated dry mass of corn and velvetleaf plants at 390ppm? 800 ppm? (b) To calculate the percentage change in mass for each plant. Subtract the mass at 390 ppm from the mass at 800ppm(change in mass), divide by the mass at 390ppm (initial mass), and multiply by 100. What is the estimated percentage change in dry mass for corn? For velvet leaf? (C) Do these results support the conclusion from the other experiments that C₃ plants grow better than C₄ plants under increased CO₂ concentration? Why or why not?

Describe how photorespiration lowers photosynthetic output for plants.

The presence of only PSI, not PSII, in the bundle-sheath cells of C₄ plants has an effect on O₂ concentration. What is that effect, and how might that benefit the plant?

Refer to the discussion of ocean acidification in Concept 3.3. Ocean acidification and changes in the distribution of C₃ and C₄ plants may seem to be very different problems, but what do they have in common? Explain.

How would you expect the relative abundance of C₃ versus C₄ and CAM species to change in a geographic region whose climate becomes much hotter and drier, with no change in CO₂ concentration?