Chapter 7:  Photosynthesis

I.  solar energy is the basis for energy on the earth

          A.  food chain: the passage of food energy from one organism to another

                    1.  autotroph: an organism that captures solar energy (Producers)

                    2.  heterotroph: an organism that feeds on an another (Consumers)

                              a.  herbivore: plant eater

                              b.  carnivore: meat eater

                              c.  omnivore: eats both plants and animals

          B.  photosynthesis: use sunlight as a source of energy to produce a

               carbohydrate,

solar energy + CO₂ + H₂O -> C₆H₁₂O₆ + O₂

          C.  photons: packet of light that travels in waves

          D.  electromagnetic spectrum: from short to long waves of solar radiation

                    1.  gamma, x-rays, ultraviolet, visible, infrared, microwaves, radio

                         waves

                    2.  visible light: Red, Orange, Yellow, Green, Blue, Indigo, Violet

                         (ROY G BIV)

II.  chloroplasts

          A.  pigments:

                    1.  chlorophyll a and b: absorb violet, blue, and red light best, reflect green

                    2.  carotenoids: absorb violet, blue, and green light best, reflect yellow-orange

          B.  history

                    1.  Joseph Priestley (1733-1804) lit a candle in a jar, found a plant

                         could "renew" the air

                    2.  Jan Ingenhousz (1730-99) identified the gas plants give off as

                         oxygen

                    3.  Nicholas de Saussure (1767-1845) increase in weight of the

                         plant is due to CO₂

                    4.  Julius Sachs (1832-97) green chlorophyll is confined to

                         chloroplasts

                    5.  F.F.Blackman (1905) suggested there were two stages, "photo"

                         and "synthesis"

                    6.  C.B.  van Niel (1930) showed O₂ given off came from H₂O

          C.  structure of chloroplasts

                    1.  stroma: fluid inside the chloroplasts (syrup)

                    2.  thylakoids: flattened sacs that form the grana (granny's

                         pancakes)

                              a.  contains chlorophyll

                              b.  energized electrons and H+ are sent to the stroma to

                                   reduce CO₂ to C₆H₁₂O₆

          D.  photosynthesis

                    1.  light-dependent reaction: in the grana, energy capturing

                         reaction,

H₂O + energy + NADP -> O₂ + NADPH + ATP

                    2.  light-independent (dark) reaction: in the stroma, synthesis

                         reaction,

ATP + NADPH + CO₂ -> C₆H₁₂O₆ + NADP

III.  solar energy captured (light reaction)

          A.  cyclic electron pathway: simplest electron pathway

                    1.  Photo System I (PS I): electrons are excited

                    2.  Goes to the electron transport system -> ATP

                    3.  Electron returns to PS I

          B.  noncyclic electron pathway:

                    1.  PS II: electrons are excited -> electron transport system -> ATP,

                        electron -> PS I

                    2.  splits H₂O, produces O₂ and H⁺ picked up by carrier

                    3.  NADP⁺ + H⁺ + 2e^- -> NADPH

          C.  chemisomotic theory: flow of H⁺ in membranes produces ATP

                    1.  thylakoid space: stores and accumulates H⁺

                    2.  photophosphorylation: P + energy + ADP <-> ATP

                    3.  by ATP synthase enzyme

IV.  carbohydrate is synthesized (dark reaction), don't need light to happen

          A.  use ATP and NADPH from the light reaction

          B.  Calvin cycle (C₃ cycle): (for Melvin Calvin in 1961)

                    1.  named C₃ cycle as first molecule has 3 carbons - PGA

                    2.  CO₂ fixation: attachment of CO₂ to RuBP (C₅) -> 2 PGA (C₃)

                    3.  CO₂ reduction: ATP + PGA + NADPH -> PGAL + ADP + NADP

                    4.  regeneration of RuBP from 5 out of every 6 PGALs

                    5.  PGAL -> glucose -> sucrose, starch, or cellulose

V.  Photorespiration: in the presence of light (photo) O₂ is taken up and CO₂ is

     released (respiration) in the mitochondria

          A.  stomates: openings in the leaves through which water can leave and

               CO₂ can enter

          B.  hot, dry weather causes stomates to close to conserve water

          C.  when stomates are closed, CO₂ decreases in leaf, O₂ increases

                because of photosynthesis

          D.  it slows down photosynthesis when there is too much O₂

VI.  Photosynthesis adaptations to hot, dry climate when stomates need to close

      when it's hot

          A.  C₃ plants most common, fixes CO₂ directly

                    1.  Mesophyll cells contain chloroplasts

                    2.  are arranged in parallel layers

          B.  C₄ plants: (corn, sugar cane): fix CO₂ to C₄ molecule first before Calvin

               Cycle

                    1.  Pumps C₄ into bundle sheath cells to store C for when it's

                        needed

                    2.  Mesophyll cells arranged concentrically around the bundle

                         sheath cells

                    3.  Photorespiration does not occur, because CO₂ is sent to bundle

                        sheath cells

                    4.  Sugarcane, corn, bermuda grass, crabgrass

          C.  CAM plant: cactus, succulents

                    1.  fix CO₂ by forming C₄ molecule at night when stomates can

                         open without losing much water

                    2.  store CO₂ in vacuole in messophyl cells

                    3.  low photosynthesis rate, due to low amount of CO₂

                    4.  succulents, cacti survive under stressful conditions