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Photosynthesis and Calvin Cycle - General Biology

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Termini in questo insieme (27)

  • Photosynthesis
    The process by which plants, algae, and some prokaryotes convert light energy into chemical energy stored in sugars, using CO₂ and water and releasing O₂.
  • Autotroph
    An organism that makes its own organic molecules from inorganic sources such as CO₂ and H₂O, without consuming other organisms; the producers of the biosphere.
  • Photoautotroph
    An autotroph that uses light energy to make organic compounds (e.g., plants, algae, cyanobacteria).
  • Heterotroph
    An organism that cannot make its own food and must obtain organic molecules by consuming other organisms or their products; the consumers of the biosphere.
  • Chloroplast
    The organelle in plants and algae that is the site of photosynthesis; enclosed by a double membrane and contains chlorophyll.
  • Stomata
    Microscopic pores on the leaf surface through which CO₂ enters and O₂ exits the leaf.
  • Chlorophyll
    The green pigment in thylakoid membranes that absorbs light energy to drive the synthesis of organic molecules.
  • Thylakoid
    A flattened membranous sac inside a chloroplast; its membrane contains chlorophyll-bearing photosystems and electron transport chain components.
  • Summary equation for photosynthesis
    6 CO₂ + 12 H₂O + light energy → C₆H₁₂O₆ + 6 O₂ + 6 H₂O; often simplified to 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂.
  • Redox reactions in photosynthesis
    Water is oxidized (loses electrons, releasing O₂) and CO₂ is reduced (gains electrons and H) to form sugar; light energy boosts electrons to a higher energy level.
  • Light reactions
    The first stage of photosynthesis in thylakoid membranes; water is split, O₂ released, and ATP and NADPH produced.
  • Calvin cycle
    The second stage of photosynthesis in the stroma; uses ATP and NADPH to reduce CO₂ to sugar.
  • NADP⁺ / NADPH
    An electron carrier; NADP⁺ is reduced to NADPH by light reactions, and NADPH provides electrons for the Calvin cycle.
  • Photon
    A fixed quantity of light energy; a discrete packet of light with energy inversely related to its wavelength.
  • Photosystem II (PS II)
    The photosystem that functions first in light reactions; its reaction-center chlorophyll a (P680) absorbs best at 680 nm and splits water.
  • Photosystem I (PS I)
    The photosystem whose reaction-center chlorophyll a (P700) absorbs best at 700 nm; reduces NADP⁺ to NADPH.
  • Linear electron flow
    Electron flow from water to PS II, through electron transport chain to PS I, and finally to NADP⁺; produces ATP, NADPH, and O₂.
  • Cyclic electron flow
    Electrons from PS I cycle back to the electron transport chain instead of NADP⁺; produces ATP but no NADPH or O₂.
  • Chemiosmosis in chloroplasts
    H⁺ pumped into thylakoid space by electron transport chain; proton-motive force drives H⁺ back through ATP synthase to make ATP.
  • Carbon fixation
    The incorporation of carbon from CO₂ into an organic molecule; the first phase of the Calvin cycle.
  • Rubisco
    The enzyme that catalyzes the first step of carbon fixation, attaching CO₂ to RuBP; the most abundant protein in chloroplasts.
  • 3-Phosphoglycerate
    The three-carbon compound formed when the unstable six-carbon intermediate splits after carbon fixation.
  • Phase 2: reduction (Calvin cycle)
    Each 3-phosphoglycerate receives a phosphate from ATP and is reduced by NADPH electrons, forming glyceraldehyde 3-phosphate (G3P).
  • Glyceraldehyde 3-phosphate (G3P)
    The three-carbon sugar that is the direct product of the Calvin cycle; used to build glucose and other organic compounds.
  • Role of ATP in the Calvin cycle
    Provides energy (phosphate groups) for the reduction phase and for regenerating RuBP.
  • Role of NADPH in the Calvin cycle
    Provides high-energy electrons that reduce 3-phosphoglycerate to G3P.
  • Calvin cycle totals
    To make one G3P, the cycle uses 3 CO₂, 9 ATP, and 6 NADPH; ATP and NADPH are regenerated by light reactions.