Bio 2

• Introduction to Photosynthesis


  Feb 26, 2024
• Unit 2: Energy and Metabolism (4 Weeks)


  • Energy flow in biochemical reactions and cellular processes
  • Enzymes
  • Photosynthesis
  • Glycolysis and fermentation
  • Cellular respiration
• This lecture covers how photosynthesis feeds life on earth, plant cell anatomy relating to photosynthesis, the two stages of photosynthesis, light as electromagnetic radiation, and pigments and their functions in nature
• Photosynthesis


  A metabolic pathway that uses light (energy) to power the assembly of carbohydrates (sugars) from CO2 and H2O, and feeds most of the life on earth
• Autotrophs (Producers)


  Organisms that make their own food by harvesting energy directly from the environment, obtain carbon from inorganic forms (i.e. CO2)
• Heterotrophs (Consumers)


  Organisms that get their carbon from breaking down organic molecules assembled by autotrophs (photosynthesizers)
• Photosynthesis


  1. Light-dependent reactions

  2. Light-independent reactions (The Calvin Cycle)
• Chloroplasts


  • Where photosynthesis is made possible
  • Light-dependant reactions are carried out by molecules in the thylakoid membrane
  • Reactions occur in the stroma (cytosol-like fluid)
• Light-dependent reactions


  1. Converts light energy to chemical bonds in ATP

  2. Splits water to make O2 and free electrons (-)

  3. Loads H+ and electrons onto NADP+ to make NADPH
• Light-independent reactions


  1. Uses energy from NADPH and ATP (no light required) to build sugars from CO2 and water

  2. NADP+ and ADP are recycled to work again
• Theodor Engelmann's experiments in 1882 showed that blue and red light was best for driving photosynthesis
• Electromagnetic radiation


  • Light moves across space in waves, with distance between crests called wavelength (nm)
  • Light also carries energy in packets called photons
• Photosynthetic and accessory pigments

  • Organic molecules that act like antennae, absorbing energy from specific wavelengths
  • Chlorophyll a is the most common photosynthetic pigment, absorbing violet, red, orange light
  • Accessory pigments (chlorophyll b, carotenes) help maximize absorption and perform other functions
• Wavelengths that are not absorbed are reflected, giving plants their color
• Chlorophylls are the most abundant pigment in green plants, but other pigments are also present
• Chlorophylls are recycled first when plants go into dormancy, and anthocyanin synthesis sometimes increases as well