AP Biology Campbell Active Reading Guide Chapter 10 – Photosynthesis

1. Define the terms "autotroph" and "heterotroph".

Autotrophs (producers) sustain themselves without consuming anything derived from other organisms. Heterotrophs (consumers) live by eating compounds produced by other organisms.

2. Draw a picture of the chloroplast and label the stroma, thylakoid, thylakoid space, inner membrane, and outer membrane.

(Diagram not yet available)

3. Write out the formula for photosynthesis (net consumption of water formula).

6CO₂ (Carbon Dioxide) + 6H₂O (Water) + Light Energy → C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen)

4. Using ¹⁸O as the basis for your discussion, explain how we know that oxygen released in photosynthesis comes from water.

O₂ released from plants was only labeled with ¹⁸O if water was the source of the tracer, not carbon dioxide.

5. a. Explain what occurs in the light reactions stage of photosynthesis. Be sure to use NADP⁺ and "photophosphorylation" in your discussion.

1. Light is absorbed and electrons are transferred to NADP⁺ from H₂O, forming NADPH. 2. H₂O is split and O₂ is released. 3. ATP is generated via chemiosmosis, through photophosphorylation.

5. b. Explain the Calvin Cycle, utilizing the term "carbon fixation" in your discussion.

The Calvin cycle occurs in the stroma, where CO₂ from the air is incorporated into organic molecules (sugars) through carbon fixation, using ATP and NADPH.

6. Label the figure displaying a simple coordination of reactions in chloroplast.

(Diagram not yet available)

7. What are the colors of the visible spectrum?

(in increasing energy and decreasing wavelength) red, orange, yellow, green, blue, indigo, violet

8. Explain the relationship between wavelength and energy.

The shorter the wavelength, the greater the energy of the photon.

9. Explain the correlation between an absorption spectrum and an action spectrum.

An absorption spectrum graphs a pigment’s light absorption vs. wavelength, while an action spectrum graphs the effectiveness of wavelengths in driving photosynthesis.

10. Describe how Englemann was able to form an action spectrum long before the invention of a spectrophotometer.

He used bacteria to measure the rates of photosynthesis in filamentous algae.

11. A photosystem is composed of a protein harvesting complex called a _______-_______ complex surrounded by several _____-__________ complexes.

reaction-center, light harvesting

12. Label the following diagram and explain the role of the components of the photosystem listed below: (parts a, b, c)

(Diagram not yet available)

12. a. Reaction center complex – (Explain the role)

The reaction center complex is where absorbed light energy (photons) are transferred to two chlorophyll a molecules, which excite and transfer an electron to the primary electron acceptor.

12. b. Light-harvesting complex – (Explain the role)

The light harvesting complex is full of chlorophyll pigment molecules which absorb light energy (photons) and transfer the energy through other pigment molecules to the primary electron acceptor.

12. c. Primary Electron Acceptor – (Explain the role)

A structure that accepts electrons, becomes reduced, and transfers electrons through an electron transport chain.

13. (Possible correction of typo) Photosystem 1 (PS I) has at its reaction center a special pair of chlorophyll a molecules called P700. What is the explanation for this name?

The chlorophyll molecules absorb red light of this wavelength (700) the best.

13. (Possible correction of typo) Photosystem 2 (PS II) has at its reaction center a special pair of chlorophyll a molecules called P680. What is the explanation for this name?

The chlorophyll molecules absorb red light of this wavelength (680) the best.

14. What is the name of the chlorophyll a at the reaction center of PS I?

P700

15. Label the following diagram of Linear Electron Flow.

(Diagram not yet available)

16. a. What is the source of energy that excites the electrons in photosystem II?

photon of light

16. b. What compound is the source of electrons for linear electron flow?

the P680 chlorophyll molecules

16. c. What is the source of O₂ in the atmosphere?

Combination of individual O atoms from splitting of H₂O in PSII

16. d. As electrons fall from photosystem II to photosystem I, the cytochrome complex uses the energy to pump __ ions. This builds a proton gradient that is used in chemiosmosis to produce what molecule? __

H⁺, ATP

16. e. In photosystem I, NADP⁺ reductase catalyses the transfer of the exited electron and H⁺ to NADP⁺ to form ______.

NADPH

17. In cyclic electron flow, no water is split; there is no production of ______, and there is no release of ___.

NADPH, O₂

18. Describe four ways that chemiosmosis is similar in photosynthesis and cellular respiration.

1. Both use electron flow to pump H⁺ across membrane. 2. Both use proton motive force of H⁺ diffusing back across membrane to generate ATP. 3. Both use ATP synthase complex to form ATP. 4. Both use similar electron carriers in electron transport chains (cytochrome family).

19. Use two key differences to explain how chemiosmosis is different in photosynthesis and cellular respiration.

1. In mitochondria, electrons for the ETC are extracted from organic molecules, while in chloroplasts, the source of electrons for the ETC is water. 2. ?

20. Label all components in this diagram.

(Diagram not yet available)

21. List the three places in the light reactions where a proton-motive force is generated by increasing the concentration of H⁺ in the stroma.

Potentially Incorrect 1. H⁺ from split H₂O 2. H⁺ pumped across membrane by cytochrome complex 3. Removal of H⁺ from stroma when NADP⁺ is reduced to NADPH.

22. To summarize, note that the light reactions store chemical energy in _____ and ______, which shuttle the energy to the carbohydrate-producing _____ cycle.

ATP, NADPH, Calvin

23. The carbohydrate produced directly from the Calvin cycle is not glucose, but the three-carbon compound _____. Each turn of the Calvin cycle fixes one molecule of CO₂; therefore, it will take 3 turns of the Calvin cycle to net one G3P.

G3P, 3

24. Explain the important events that occur in the carbon fixation stage of the Calvin cycle.

3CO₂ molecules attach to RuBP and are catalyzed by Rubisco. This produces an unstable intermediate that splits into 3-phosphoglycerate.

25. The enzyme responsible for carbon fixation in the Calvin cycle, and possibly the most abundant protein on Earth, is ______.

Rubisco

26. In phase two, the reduction stage, what molecule will donate electrons, and is therefore the source of the reducing power?

NADPH

27. In this reduction stage, the low-energy acid 1,3-biphosphoglycerate is reduced by electrons from NADPH to form the three-carbon sugar _____.

G3P

28. [In regards to the Calvin cycle] This means that we start with ___ carbons distributed in three RuBPs. After fixing three molecules of CO₂ using the enzyme ______, the Calvin cycle forms six G3Ps with a total of ___ carbons. At this point, the net gain of carbons is ___, or one net G3P molecule.

15, rubisco, 18, 3

29. Explain how the regeneration of RuBP is accomplished.

5 G3P molecules are rearranged into 3 RuBP, spending 3 ATP in the process.

30. The net production of one G3P requires ___ molecules of ATP and ___ molecules of NADPH.

9, 6

31. Explain what is meant by a C₃ plant.

C₃ plants produce 3-phosphoglycerate as a first product.

32. What happens when a plant undergoes photorespiration?

Photorespiration is when rubisco binds to O₂ instead of CO₂ on very hot, dry days, resulting in a loss of CO₂ and energy for the plant.

33. Explain how photorespiration can be a problem in agriculture.

Rice, wheat, and soybeans are all C₃ plants, and thus lose much energy and mass from intensive photorespiration.

34. Explain what is meant by a C₄ plant.

C₄ plants have an alternate mode of carbon fixation that fixes a 4 – carbon compound as a first product.

35. Explain the role of PEP carboxylase in C₄ plants, including key differences between it and rubisco.

PEP carboxylase fixes carbon efficiently when stomata are partially closed, because of its high affinity of CO₂ and no affinity for O₂.

36. Explain how changes in leaf architecture help isolate rubisco in regions of the leaf that are high in CO₂, but low in O₂.

In C₄ plants, mesophyll cells pump CO₂ into bundle-sheath cells, keeping CO₂ concentration high enough so that Rubisco will more likely bind with it.

37. Using figure 10.19 in your text as a guide, explain the three key events – indicated by the arrows below – in the C₄ pathway.

1. PEP carboxylase adds CO₂ to PEP. 2. A 4 – carbon compound conveys atoms of CO₂ into a bundle-sheath cell via plasmodesmata. 3. In bundle sheath cells, CO₂ is released and enters the Calvin Cycle

38. Compare and contrast C₄ plants with CAM plants. (Two key similarities, two key differences)

No differences listed yet Both C₄ and CAM plants have evolved to adapt to arid conditions, and both transform CO₂ into an organic intermediate before the Calvin cycle.

39. Explain this statement: "Only the green cells of a plant are the autotroph while the rest of the plant is a heterotroph.

The rest of the plant depends on the organic material generated via photosynthesis in green cells.

40. Label the following diagram, then summarize additional information for the Calvin Cycle reactions.

(Diagram not yet available) Light reactions: – carried out by molecules in the thylakoid membrane – converts light energy to the chemical energy of ATP and NADPH – splits H₂O and releases O₂ to the atmosphere Calvin Cycle Reactions: – Takes place in the stroma – Uses ATP and NADPH to convert CO₂ to G3P – Returns ADP, inorganic phosphate, and NADP⁺ to the light reactions