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Chapter 10: 10.4-2CC (page 206)

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?

Short Answer

Expert verified

No oxygen (O2) is produced without PSII in the bundle sheath cells of C4 plants. The absence of O2 eliminates the issue of O2 competing with carbon dioxide (CO2) for Rubisco binding in the bundle sheath cells.

Step by step solution

01

Meaning of PSI and PSII

The photosystem is a huge complex that comprises pigments and proteins to harvest light. They are the units of chlorophyll molecules that absorb the light energy of the sun to drive photosynthesis.

Photosystem I (PSI) and photosystem II (PSII) are the two types of photosystems (PSII). PSI is called P700, while PSII is called P680. In photosynthesis, PSII supplies PSI with high-energy electrons, which are transferred to NADP+ to form NADPH.

02

Effect of PSII on O2 concentration

Light is absorbed by one of PSII's pigments in the presence of sunlight. It then emits a high-energy electron, transfers it to an acceptor molecule, and replaces it with a water electron. O2 is released as a result of the water splitting.

The function of PSII is to divide split oxygen molecules and protons as effectively as possible. As a result, the bundle sheath cells do not generate oxygen in the absence of PSII.

03

The absence of PSII is beneficial for C4 plants

Rubisco is an enzyme that catalyzes the reaction of RuBP (ribulose 1.5-bisphosphate) with CO2 to produce phosphoglyceric acid, the first stage in the Calvin cycle. This enzyme, on the other hand, has a high affinity for oxygen. When there is a lot of oxygen around, it attaches to oxygen instead of carbon dioxide.

O2 is not generated in bundle sheath cells because PSII is missing. Rubisco successfully interacts with carbon dioxide in the absence of oxygen, initiating the Calvin cycle. As a result, C4 plants benefit from the absence of PSII in bundle sheath cells.

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Most popular questions from this chapter

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.

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Draw a 鈥渂est fit鈥� 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.

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.

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