Chapter 10: Photosynthesis: Energy from Sunlight

• What is the primary function of photosynthesis?

  To capture energy from sunlight and convert it to chemical energy
• What are the two main products of photosynthesis?

  ATP and NADPH
• How does photosynthesis utilize carbon dioxide?

  It converts CO₂ into more complex carbon compounds
• What type of organisms are autotrophs?

  Plants, algae, and cyanobacteria
• What distinguishes heterotrophs from autotrophs?

  Heterotrophs must consume other organisms for food
• What is the source of O₂ released during photosynthesis?

  Water
• What are the two main pathways involved in photosynthesis?

  • Light-dependent reactions: Convert light energy to ATP and NADPH
  • Carbon-fixation reactions (Calvin cycle): Use ATP and NADPH to produce carbohydrates
• What is light in the context of photosynthesis?

  A form of electromagnetic radiation
• How is the amount of energy in light related to its wavelength?

  The amount of energy is inversely proportional to its wavelength
• What are photons?

  Particles of light
• What happens when a photon hits a molecule?

  It can be bounced off, passed through, or absorbed
• What effect does absorbed energy have on an electron in a molecule?

  It boosts the electron into a shell farther from the nucleus, making the molecule unstable
• What is the major pigment in photosynthesis?

  Chlorophyll a
• What is the role of chlorophyll a in photosynthesis?

  It absorbs blue and red light and scatters green
• What are light-harvesting complexes?

  Structures that capture light energy and transfer it to reaction centers
• What happens to energy when a pigment molecule absorbs a photon?


  The energy is quickly released and passed to other pigment molecules
• What is the final electron acceptor in the light-dependent reactions of photosynthesis?

  NADP⁺
• What is the role of water in photosystem II?

  Water provides electrons when chlorophyll gives up its electron
• What is the first product of CO₂ fixation in the Calvin cycle?

  3PG
• What enzyme catalyzes the reaction of CO₂ and RuBP?

  Ribulose bisphosphate carboxylase/oxygenase (rubisco)
• What are the three main steps of the Calvin cycle?

  Fixation of CO₂, reduction of 3PG to G3P, and regeneration of RuBP
• What is G3P used for in plants?

  It is converted to glucose, fructose, and starch
• How does light stimulate the Calvin cycle?

  It induces pH changes in the stroma that activate rubisco
• What happens to rubisco's affinity for CO₂ and O₂ under high O₂ conditions?

  Oxygenase activity is favored, reducing net carbon fixation
• What are the differences between C₃ and C₄ plants in CO₂ fixation?

  • C₃ plants: First product is 3PG; photorespiration occurs on hot days
  • C₄ plants: First product is oxaloacetate; no photorespiration on hot days
• What is the role of PEP carboxylase in C₄ plants?

  It catalyzes the reaction of CO₂ and PEP to form oxaloacetate
• How do C₄ plants prevent photorespiration?

  They concentrate CO₂ around rubisco in bundle sheath cells
• What is the advantage of C₄ plants in warm, dry climates?

  They do not experience photorespiration and maintain high photosynthesis rates
• What is Crassulacean acid metabolism (CAM)?

  A process where stomata are open at night and closed during the day to conserve water
• What percentage of sunlight energy is transformed into chemical energy during photosynthesis?

  5%
• How does rising atmospheric CO₂ affect photosynthesis?

  Higher CO₂ concentration generally leads to increased photosynthesis
• What is a potential downside of increased CO₂ for C₃ crops?

  The parts we eat, such as seeds, may not grow more