Photosynthesis

HideShow resource information
View mindmap
  • Photosynthesis
    • Cholorplasts
      • small, flattened organelles
      • double membrane = chloroplast envelope
      • thylakoids (fluid filled sacs) stack = grana
      • grana = linked by (lamellae) thylakoid membrane
      • Pigments
        • chlorophyll a chlorophyll b carotene
        • coloured substances that absorb light energy
        • found in thylakois membranes - attached to proteins forming a photosystem
        • PSI absorbs light best at 700nm, PSII absorbs light best at 680nm
      • stroma = gel-like substance containing enzymes, sugars, organic acids and oil droplets
      • Adaptations
        • chloroplast envelope = keeps reactants for photosynthesis close to reaction sites
        • thylakoids = large surface area to allow as much light energy as possible to be absorbed
        • thylakoids = lots of ATP synthase present to produce ATP in the LDR
        • stroma = contains enzymes, sugars and organic acids for LDR to take place
    • Light Dependent Reaction
      • LDR
        • requires light energy
        • takes place in thylakoid membrane of chloroplasts
        • light energy = absorbed by pigments and converted to chemical energy
        • light energy is used to add a phosphate group to ADP (forming ATP) and reduce NADP
        • ATP transfers energy + reduced NADP transfers hydrogen to the LDR
        • H20 is oxidised to O2
      • Non-Cyclic Phosphorylation
        • 1
          • light energy = absorbed by PSII which excites electrons in chlorophyll
          • electrons move to a higher energy level and move along electron transport chain to PSI
        • 2
          • the electrons that have left PSII need to be replaced
          • light energy splits water into protons (H+ ions) and electrons and oxygen
          • 2H2O -> 4H+ and O2
        • 3
          • excited electrons lose energy as they move along the electron transport chain
          • energy is used to transport protons into thylakoid membrane
          • thylakoid now has a higher concentration of protons
          • protons move down concentration gradient into stroma via ATP synthase (energy from this forms ATP)
        • 4
          • light energy = absorbed by PSI - excites electrons to an evn higher level
          • protons and electrons = transferred to NADP from stroma, forming reduced NADP
      • Cyclic Phosphorylation
        • only uses PSI
        • electrons from the chlorophyll are passed back to PSI via electron carriers
        • electrons are recycled and can repeatedly flow through PSI
        • only produces small amounts of ATP
    • Light Independent Reaction
      • Info
        • involves reduction of CO2 (it's combined with hydrogen during a series of reactions
          • triose phosphate is formed - it's used to make gluose + other useful organic substances
        • energy and H+ ions provided by ATP and reduced NADP from the LDR are needed to keep the cycle going
        • the starting component (ribulose biphosphate) is regenerated
      • The Calvin Cycle
        • takes place in stroma of chloroplasts
        • reduces CO2 (it's combined with hydrogen during reactions)
          • produces triose phosphate (used to make glucose)
        • needs energy and H+ ions to keep it going (provided by ATP and reduced NADP from LDR)
        • 3
          • 5 out of every 6 molecules of TP produced aren't used to make hexose sugars, but to regenerate RuBP
            • regenerating RuBP uses rest of ATP produced by LDR
        • 2
          • ATP from LDR provides energy to reduce GP to triose phosphate (TP)
            • reduction reaction requires H+ ions from reduced NADP (and LDR) -> reduced NADP = recycled to NADP
              • TP = converted to organic compounds e.g. glucose
        • 1
          • CO2 enters leaf through stomata, then diffuses into stroma pf chloroplast
            • CO2 = combined with ribulose phosphate (RuBP) - a 5-carbon compound
              • produces unstable 6-carbon compound -> breaks down into 2 molecules of 3-carbon compound: glycerate 3-phosphate (GP)
                • ribose biphosphate carboxylase (rubisco) catalyses reaction between CO2 and RuBP
      • Organic Substances
        • Carbohydrates: simple sugars (glucose) made my joining 2 TP molecules, and polysaccharides (starch/cellulose) made by joining 2 hexose sugars in different ways
        • Amino acids: some = made from GP
        • Nucleic acids: sugar in RNA = made using TP
        • Lipids: made using glycerol synthesised from TP, and fatty acids synthesised from GP
      • 6 turns = 1 glucose
        • 6 turns requires 18 ATP and 12 reduced NADP from the LDR
        • 5 out of 6 TP are used to regenerate RuBP
  • glucose has 6 carbons so 2 TP molecules are needed to form 1 glucose molecule
    • cycle must turn 6 times to produce 2 molecules of TP that can be used to make 1 glucose
    • 3 turns of calvin cycle = 1 TP produced (used to make glucose)
      • 6 turns = 1 glucose
        • 6 turns requires 18 ATP and 12 reduced NADP from the LDR
        • 5 out of 6 TP are used to regenerate RuBP

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes resources »