M5:S5 Photosynthesis

• Photosynthesis

  The process where energy from light is used to make glucose from carbon dioxide and water
• Respiration

  The process where living cells release energy from glucose
• Biological processes that need energy

  • DNA replication
  • Cell division
  • Protein synthesis
  • Motility (movement) (for microorganisms)
  • Photosynthesis
  • Active transport
  • Muscle contraction
  • Maintenance of body temperature (for animals)
• Without energy, these biological processes would stop and the plant or animal would die
• Photosynthesis

  Carbon dioxide + Water + Light energy -> Glucose + Oxygen
• Plants can make their own food glucose through photosynthesis
• Animals can't make their own food, so they obtain glucose by eating plants (or other animals), then respire the glucose to release energy
• Respiration

  Glucose + Oxygen -> Carbon dioxide + Water + Energy
• Aerobic respiration

  Respiration using oxygen
• Anaerobic respiration

  Respiration without oxygen
• Metabolic pathway

  A series of small reactions controlled by enzymes, e.g. respiration and photosynthesis
• Phosphorylation

  Adding phosphate to a molecule
• Photophosphorylation

  Adding phosphate to a molecule using light
• Photolysis

  The splitting of a molecule using light energy
• Hydrolysis

  The splitting of a molecule using water
• Decarboxylation

  The removal of carbon dioxide from a molecule
• Dehydrogenation

  The removal of hydrogen from a molecule
• Redox reactions

  Reactions that involve oxidation and reduction
• Oxidation

  Losing electrons, may have lost hydrogen or gained oxygen
• Reduction

  Gaining electrons, may have gained hydrogen or lost oxygen
• Coenzyme

  A molecule that aids the function of an enzyme, usually by transferring a chemical group
• NADP

  A coenzyme used in photosynthesis that transfers hydrogen from one molecule to another
• NAD, coenzyme A, FAD

  Coenzymes used in respiration that transfer hydrogen from one molecule to another
• Chloroplasts

  • Small, flattened organelles found in plant cells where photosynthesis takes place
  • Have a double membrane called the chloroplast envelope
  • Contain thylakoids (fluid-filled sacs) stacked into structures called grana
  • Contain photosynthetic pigments like chlorophyll a, chlorophyll b and carotene
  • Contain their own circular DNA
• Photosystems

  • Contain primary pigments (reaction centres) and accessory pigments (light-harvesting systems)
  • Photosystem I absorbs light best at 700nm, Photosystem II absorbs light best at 680nm
• Stroma

  The gel-like substance in the chloroplast surrounding the thylakoids, containing enzymes, sugars and organic acids
• Carbohydrates produced by photosynthesis and not used straight away are stored as starch grains in the stroma
• Light-dependent reaction

  The stage of photosynthesis that needs light energy, takes place in the thylakoid membranes and converts light energy to chemical energy in the form of ATP and reduced NADP
• Light-independent reaction

  Also called the Calvin cycle, the stage of photosynthesis that uses the ATP and reduced NADP from the light-dependent reaction to convert carbon dioxide into glucose
• Light-dependent reaction

  Light energy absorbed by photosynthetic pigments -> ATP formed by photophosphorylation -> NADP reduced -> Water oxidised to oxygen
• Thin layer chromatography can be used to separate and identify the photosynthetic pigments in plants
• Thin layer chromatography

  Grind leaves with solvent -> Extract pigments into solvent layer -> Apply to chromatography plate -> Develop plate with solvent -> Pigments separate and can be identified by their Rf values
• Photophosphorylation

  The process of using light energy to add a phosphate group to ADP to form ATP
• Non-cyclic photophosphorylation

  Light energy absorbed -> Water split into protons, electrons and oxygen -> NADP reduced -> ATP formed
• Cyclic photophosphorylation

  Light energy absorbed -> Electrons cycled back to photosystem -> ATP formed
• Chromatography

  1. Separation of pigments (solutes)

  2. Calculation of R, value

  3. Identification of pigments
• R, value

  Distance traveled by solute / distance traveled by solvent
• Light-Dependent Reaction

  1. Making ATP from ADP and inorganic phosphate (photophosphorylation)

  2. Making reduced NADP from NADP

  3. Splitting water into protons, electrons and oxygen (photolysis)
• Photophosphorylation

  Process of making ATP from ADP and inorganic phosphate
• Non-cyclic Photophosphorylation

  Produces ATP, reduced NADP and O2