Food Procurement: Photosynthesis

• Photosynthesis

  A biological process that can capture energy (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism

  
• Trophic levels


  • Photoautotrophs ("self-feeders using light")
  • Heterotrophs ("other feeders")
  • Chemoautotrophs

  
• Photoautotrophs


  • Use light to manufacture their own food through photosynthesis
  • Examples: plants, algae, cyanobacteria
• Heterotrophs


  • Rely on the sugars produced by photosynthetic organisms for their energy needs
  • Examples: animals, fungi, and most other bacteria
• Chemoautotrophs


  • Organisms that extract energy from inorganic chemical compounds to synthesize sugar (group of bacteria)
• Photosynthesis is vital because it evolved as a way to store the energy in solar radiation as high-energy electrons in the carbon-carbon bonds of carbohydrate molecules

  
• Carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration
• Photosynthesis


  1. Sunlight is converted into chemical energy

  2. Water (H2O) is split into oxygen (O2)

  3. Carbon dioxide (CO2) is fixed into sugars (C6H12O6)

  
• Photosynthesis reaction


  6 CO2 + 6 H2O → C6H12O6 + 6 O2

  
• Mesophyll


  • Middle layer of the leaf
• Chloroplast


  • Organelle where photosynthesis takes place

  
• Granum


  • A stack of thylakoids
• Stroma


  • Liquid-filled space surrounding the granum
• Thylakoids


  • Stacked, disc-shaped structures
• Chlorophyll


  • Pigment embedded in the thylakoid membrane

  
• Chlorophyll absorbs all wavelength colors of light (harvest light energy packets or photons) except green

  
• Major Chlorophylls


  • Chlorophyll a
  • Chlorophyll b
  • Chlorophyll c
  • Chlorophyll d
  • Bacteriochlorophyll
• Carotenoids


  • Photosynthetic pigments found in fruit
• Examples of carotenoids


  • Red of tomato (lycopene)
  • Yellow of corn seeds (zeaxanthin)
  • Orange of an orange peel (β-carotene)
• Parts of photosynthesis


  • Light reaction (Light Dependent Reactions)
  • Calvin-Bensen-Bassham cycle/Calvin Cycle (Light Independent Reactions)

  
• Light reaction


  • Need to capture light energy to power photosynthesis
  • Take place in the thylakoids
  • Pigments in the thylakoid membranes form protein complexes called PHOTOSYSTEMS to harvest photons

  
• Calvin cycle


  • Do not need light energy to power their reactions
  • Occur in the stroma
  • Carbon dioxide is fixed into glucose
• Energy carrying molecules


  • ATP (Adenosine Triphosphate)
  • NADP+ (nicotinamide adenine dinucleotide phosphate)

  
• Energy carrying molecules move energy from light-dependent reactions to light-independent reactions where the energy is released
• Photosystem II (PSII)


  • The electron comes from the splitting of water

  
• Photosystem II (PSII)


  1. Absorbs photons

  2. Transfers energy to reaction center

  3. Splits water molecules

  4. Produces protons and oxygen

  
• ATP synthesis


  1. Protons pass through ATP synthase

  2. ATP synthase attaches a phosphate group to ADP to make ATP
• Photosystem I (PSI)


  • The electron comes from the chloroplast electron transport chain
  • Charges up the energy carrier molecule NADP+ into NADPH

  
• The light reactions temporarily store energy in the form of ATP and NADPH to fuel the Calvin cycle
• Calvin cycle


  1. Fixation: CO2 is fixed into an unstable intermediate by RuBisCO

  2. Reduction: ATP and NADPH convert 3-PGA into glyceraldehyde 3-phosphate (G3P)

  3. Regeneration: Some G3P is used to produce glucose, others are recycled to regenerate RuBP