Photosynthesis

• photo = light

  synthesis = building up
• photosynthesis - biological process by which green plants convert light energy into chemical energy to be stored in food molecules
• for photosynthesis to occur;

  • light
  • chlorophyll pigment
  • water
  • carbon dioxide
• light exhibits properties of waves and particles
• from long wave to short wave;

  • long radio waves (2, 4)
  • radio, tv (6, 8)
  • microwave (10)
  • infrared rays (14)
  • uv rays(16)
  • x-rays (18)
  • gamma rays (20-24)
• visible light is between uv and infrared
• light is composed of small particles or packets of energy called photons
• the amount of energy in a photon depends on the wavelength of light
• the shorter the wavelength is, the more energy there is and vice versa
• absorption of a photon bumps an electron to a higher-energy orbital
• different pigments absorb light differently
• in plants and algae, photosynthesis takes place in the chloroplasts
• chloroplast contains chlorophyll, one of the group of light-trapping pigments
• veins;

  • xylem
  • phloem
  • bundle sheath
• spongy mesophyll cells - tissue in the leaf which contains chloroplasts
• stroma - fluid matrix
• chloroplast is enclosed by;

  • outer membrane
  • inner membrane
• the inner membrane encloses a fluid region, the stroma, which contains most of the enzymes required to produce carbohydrate molecules
• suspended in the stroma is a third system of membranes that forms an interconnected set of flat, disc like sacs called thylakoids
• lumen is also known as thylakoid space
• thylakoid membrane - contain several kinds of pigment
• several kinds of pigments

  • chlorophyll a
  • chlorophyll b
  • carotenoids
  • phycobilins
• chlorophyll a - the pigment that initiates photosynthesis. blue green in color
• chlorophyll b - accessory pigment that also participates in photosynthesis. yellow green in color
• carotenoids - accessory photosynthetic pigment, yellow to orange pigment
• phycobilins - blue/red pigment found in cyanobacteria and red algae
• photosynthesis may take place in two series of step

  • light-dependent reaction
  • light independent reaction
• the light-dependent reaction

  • light energy is converted to chemical energy
  • occurs in thylakoid membrane
  • during light reaction, there are 2 possible routes for electron flow; cyclic electron flow & noncyclic electron flow
• cyclic electron flow;

  • occurs in the thylakoid membrane
  • uses photosystem 1 only
  • p700 reaction center - chlorophyll a
  • uses electron transport chain (etc)
  • generates atp only
  • pigments absorb light energy & excite e- of chlorophyll a to produce atp
• noncyclic electron flow

  • occurs in the thylakoid membrane
  • uses photosystem 1 & 2
  • p680 reaction center (ps 2) - chlorophyll a
  • p700 reaction center ( ps 1) - chlorophyll a
  • usses electron transport chain (etc)
  • generates 02, atp, and nadph
• in noncyclic electron flow, h2o is split in ps2 and atp is made, while the energy carrier nadph is made in ps1
• chemiosmosis;

  • powers atp synthesis
  • takes place across the thylakoid membrane
  • uses etc and atp synthase enzyme
  • h+ move down their concentration gradient through channels of atp synthase forming atp from adp
• light-dependent reaction

  • begins as chlorophyll absorbs light energy, which causes one of its electrons to move to a higher energy state
  • the energized electron is transferred to an acceptor molecule and is replaced by an electron from water
  • during this process, water is split and molecular oxygen is released
  • some of the energy of the energized electrons is used to make atp
  • in addition, nadp+ becomes reduced, forming nadph
• electron transport chain - each electron is passed from one electron carrier to another; losing energy as it goes. this energy is used to pump hydrogen ions across the thylakoid membrane
• nadp - is a hydrgoen carrier picking up h+ from the thylakoid and transporting them to the calvin cycle
• atp synthase - catalyzes the production of atp from adp and inorganic phosphate