3.4.A—Describe the photosynthetic processes and structural features of the chloroplast that allow organisms to capture…

Describe the photosynthetic processes and structural features of the chloroplast that allow organisms to capture and store energy.

• Photosynthesis is the series of reactions that use carbon dioxide (CO2), water (H2O) and light energy to make carbohydrates and oxygen (O2).
  • i. Photosynthetic organisms capture energy fr om the sun and produce sugars that can be used in biological processes or stored.
  • ii. Photosynthesis first evolved in pr okaryotic organisms.
  • iii. Scientific evidence supports the claim that pr okaryotic (cyanobacterial) photosynthesis was responsible for the production of an oxygenated atmosphere.
  • iv. Prokaryotic photosynthetic pathways w ere the foundation of eukaryotic photosynthesis.
• Stroma and thylakoids are found within the chloroplast.
  • i. The stroma is the fluid within the inner chloroplast membrane and outside the thylakoid. The carbon fixation (Calvin cycle) reactions of photosynthesis occur in the stroma.
  • ii. The thylakoid membranes contain chlorophyll pigments organized into two photosystems, as well as electron transport proteins.
  • iii. Thylakoids are organized in stacks called grana. The light reactions of photosynthesis occur in the grana.
• The light reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture energy present in light to yield ATP and NADPH, which power the production of organic molecules in the Calvin cycle. This provides energy for metabolic processes.
• Exclusion: Memorization of the steps in the Calvin cycle, the structure of the molecules, and the names of the enzymes involved, with the exception of ATP synthase, is beyond the scope of the AP Exam.