5.2 Photosynthesis Stores Energy in Organic Compounds

• Equation for photosynthesis

  6CO2(g) + 6H2O + energy -> C6H12O6(s) + O2
• What does photosynthesis mean?

  Photo = light

  Synthesis = to put together
• What is the reaction of when the two sets of reactions that make up photosynthesis?

  Light-dependent and light-independent reactions.
• What happens during light-dependent reactions?

  Solar energy is trapped and used to generate two high-energy compounds: ATP and NADPH (reduced nicotinamide adenine dinucleotide phosphate).
• What happens during light-independent reactions?

  The energy of ATP and the reducing power of NADPH are used to reduce carbon dioxide to make glucose.
• What does glucose convert to for storage?

  Starch
• What is a pigment?

  A compound that absorbs certain wavelengths of visible light while reflecting others that give the pigment a specific colour.
• What do the pigments within the thylakoid membranes do?

  Absorb light energy
• What is a photosynthetic pigment?

  A compound that traps light energy and passes it on to other chemicals, which use the energy to synthesize high-energy compounds.
• Why does chlorophyll not absorb green light?

  Light-reflecting and light absorbing characteristics of pigments
• What colour(s) does chlorophyll solution absorb?

  Red and blue light while it transmits or reflects green light.
• What is the absorbance spectrum?

  A graph that shows relative amounts of light of different colours that a compound observes.
• What is beta-carotene?

  A member of a very large class of pigments called carotenoids.
• What colour(s) do carotenoids absorb?

  Blue and green light, so they are yellow, orange, and red in colour.
• What is beta-carotene responsible for?

  The orange colour of the carrots.
• What can beta-carotone be converted to?

  Vitamin A -> Retinal (the visual pigment for your eyes).
• What is the action spectrum show?

  The relative effectiveness of different wavelengths of light for promoting photosynthesis.
• What are photosystems?

  The clusters chlorophyll and other pigments are arranged in the thylakoid membranes.
• How many photosystems do the chloroplasts plants and algae have and what are they?

  Two photosystems: Photosystem I (PSI) and Photosystem II (PSII).
• How did the two photosystems get their names?

  They are named for the order in which scientists discovered them, not for their sequence in the process of photosynthesis.
• What are each photosystems made up of?

  Pigment molecules that include one dozen or more chlorophyll molecules, and a few carotenoids molecules.
• Why are the H+ ions unable to diffuse back across the thylakoid when they are forced from the stroma to the thylakoid space?

  The membrane is impermeable to the charged particles.
• What structure is embedded in the thylakoid membrane and what does it provide for the H+ ions?

  The ATP synthase provides the only pathway for the H+ ions to move down their concentration gradient.
• What is the pathway of the ATP synthase linked to?

  A mechanism that bonds a free phosphate group to an ADP molecule to form ATP.
• What is the linking of the movement of H+ ions to the production of ATP called?

  Chemiosmosis.
• What cycle has a series of reactions by which carbohydrates are synthesized?

  Calvin-Benson cycle
• What is the first stage of the Calvin-Benson cycle and what is it about?

  Carbon dioxide fixation is when the carbon atom in CO2 is chemically bonded to a pre-existing molecule in the stroma.
• What is the five-carbon molecule in the stroma called?

  RuBP (ribulose biphosphate)
• What is the equation for the reaction of the six-carbon compound being unstable and immediately breaks down into two identical three-carbon compounds?

  CO2 + RuBP -> unstable C6 -> 2 C3
• What is the second stage of the cycle?

  Reduction: The three-carbon compounds converting to a higher energy state by being activated by ATP then reduced by NADPH.
• What is the result of the three-carbon compounds activated by ATP and reduced by NADPH result to?

  Two molecules of PGAL (glyceraldehyde 3-phosphate)
• What is the third stage of the cycle?

  Replacing RuBP: Most of the reduced PGAL molecules are used to make more RuBP. The energy ATP provides is required to break and reform chemical bonds to make the five-carbon RuBP from PGAL.