Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

9. Photosynthesis

Light Reactions of Photosynthesis

General Biology

9. Photosynthesis

Light Reactions of Photosynthesis

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5:01 minutes

Problem 9c

Textbook Question

Predict how the following conditions would affect the production of O₂, ATP, and NADPH and state whether noncyclic or cyclic electron flow would occur in each:
(3) blue and red photons hit a chloroplast, but a proton channel has been introduced into the thylakoid membrane, so it is fully permeable to protons.

Verified step by step guidance

Understand the role of blue and red photons in photosynthesis: Blue and red photons are absorbed by chlorophyll pigments in the chloroplasts, which are crucial for driving the light-dependent reactions of photosynthesis.

Recognize the impact of a proton channel in the thylakoid membrane: Normally, the thylakoid membrane is impermeable to protons, allowing a proton gradient to form during the light-dependent reactions. This gradient is essential for ATP synthesis via chemiosmosis.

Consider the effect on ATP production: With the thylakoid membrane fully permeable to protons, the proton gradient cannot be maintained. This disrupts ATP synthesis because the energy from the gradient is used by ATP synthase to convert ADP to ATP.

Analyze the impact on O2 and NADPH production: The absorption of blue and red photons will still drive the splitting of water molecules, releasing O2 and providing electrons for the electron transport chain. However, the lack of a proton gradient may affect the efficiency of NADPH production.

Determine the type of electron flow: Noncyclic electron flow typically occurs when both ATP and NADPH are produced. Given the disruption in ATP synthesis, cyclic electron flow might be favored to compensate for the lack of ATP production, although this would not produce NADPH or O2.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. It involves two main stages: the light-dependent reactions and the Calvin cycle. The light-dependent reactions occur in the thylakoid membranes of chloroplasts, where light energy is used to produce ATP and NADPH, essential for the Calvin cycle.

Electron Transport Chain

The electron transport chain is a series of protein complexes located in the thylakoid membrane that facilitates the transfer of electrons from water to NADP+, forming NADPH. This process also generates a proton gradient across the thylakoid membrane, which is crucial for ATP synthesis. The flow of electrons can be cyclic or noncyclic, affecting the production of ATP and NADPH.

Proton Gradient and ATP Synthesis

The proton gradient across the thylakoid membrane is essential for ATP synthesis during photosynthesis. Protons are pumped into the thylakoid lumen, creating a concentration gradient. ATP synthase uses this gradient to convert ADP to ATP. If the membrane is permeable to protons, the gradient dissipates, reducing ATP production and potentially altering electron flow from noncyclic to cyclic.

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Related Practice

Textbook Question

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⁺.

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Textbook Question

Which of the following is a false statement about photosynthesis?

a. During the light-independent reactions, electrons and ATP from the light reactions combine with atmospheric carbon dioxide to produce sugars.

b. The light-independent reactions take place in the chloroplast stroma.

c. Oxygen produced during the light-independent reactions is released into the atmosphere.

d. Chlorophyll absorbs blue and red light and reflects green light.

e. The end product of photosynthesis is a carbohydrate such as glucose.

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Textbook Question

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

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Textbook Question

Which of the following correctly identify a role of the ATP produced in the light-capturing reactions? Select True or False for each statement.

T/F It is used by rubisco to fix CO₂ to RuBP.

T/F It serves the same role as ATP produced by mitochondria.

T/F It is used to regenerate RuBP from G3P molecules.

T/F It is used to produce G3P molecules

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Textbook Question

Predict how the following conditions would affect the production of O₂, ATP, and NADPH and state whether noncyclic or cyclic electron flow would occur in each:

(2) blue and red photons hit a chloroplast, but no NADP⁺ is available

942

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Textbook Question

Predict how the following conditions would affect the production of O2, ATP, and NADPH and state whether noncyclic or cyclic electron flow would occur in each: (1) Only blue photons hit a chloroplast

1097

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Textbook Question

Predict how the following conditions would affect the production of O₂, ATP, and NADPH and state whether noncyclic or cyclic electron flow would occur in each:

(1) Only blue photons hit a chloroplast

667

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Textbook Question

An investigator exposes chloroplasts to 700-nm photons and observes low O₂ production, but high ATP production. Which of the following best explains this observation?

a. The electrons from water are directly transferred to NADP⁺, which is used to generate ATP.

b. Photosystem II is not splitting water, and the ATP is being produced by cycling electrons via photosystem I.

c. The O₂ is being converted to water as a terminal electron acceptor in the production of ATP.

d. Electron transport has stopped and ATP is being produced by the Calvin cycle.

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