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

Stages of Photosynthesis

General Biology

9. Photosynthesis

Stages of Photosynthesis

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Multiple Choice

In green plants, what is the correct sequence of photosystems during the light-dependent reactions of photosynthesis, and what does each photosystem primarily produce?

Photosystem II acts first, producing ATP, followed by Photosystem I, which produces NADPH.

Photosystem I acts first, producing ATP, followed by Photosystem II, which produces NADPH.

Photosystem I acts first, producing NADPH, followed by Photosystem II, which produces ATP.

Photosystem II acts first, producing NADPH, followed by Photosystem I, which produces ATP.

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Verified step by step guidance

Understand that the light-dependent reactions of photosynthesis occur in the thylakoid membranes of chloroplasts and involve two photosystems: Photosystem II (PSII) and Photosystem I (PSI). These photosystems work together to convert light energy into chemical energy in the form of ATP and NADPH.

Recall that Photosystem II (PSII) is the first photosystem to act. It absorbs light energy, which excites electrons in chlorophyll molecules. These high-energy electrons are passed to the electron transport chain, and water molecules are split (photolysis) to replace the lost electrons, releasing oxygen as a byproduct.

As the excited electrons move through the electron transport chain, their energy is used to pump protons (H⁺) into the thylakoid lumen, creating a proton gradient. This gradient drives ATP synthesis via ATP synthase, producing ATP.

Next, the electrons from Photosystem II are transferred to Photosystem I (PSI). PSI absorbs light energy, further exciting the electrons. These high-energy electrons are then used to reduce NADP⁺ to NADPH, a key molecule for the Calvin cycle.

Summarize the sequence: Photosystem II acts first, producing ATP, followed by Photosystem I, which produces NADPH. This sequence is essential for providing the energy and reducing power needed for the light-independent reactions of photosynthesis.