Bio1151 Chapter 10 Photosynthesis
  1. Plants and other                  are the            of ecosystems.

    Photoautotrophic organisms can make organic molecules from light:

  2. plants
  3. multicellular algae such as kelp
  4. some unicellular protists such as Euglena
  5. prokaryotes such as cyanobacteria and
  6. purple sulfur bacteria
  7. Photoautotrophs can convert solar energy into the           energy in food by a process called                 .

    Visible light makes up a small range of the electromagnetic spectrum.

      Electromagnetic radiation ranges from the short wavelengths (high energy) of gamma and UV waves to the long wavelengths (low energy) of infrared and radio waves.

      Visible light occupies a narrow band within the electromagnetic spectrum.

  8. Photosynthesis is a        process where water is           and carbon dioxide is          to          .

    In a redox reaction, one substance loses electrons (oxidation) and energy while another gains electrons (reduction) and energy. In Photosynthesis, water is oxidized and carbon dioxide is reduced. Compare this to respiration, where glucose is oxidized and oxygen is reduced.
  9. In plants, photosynthesis occurs in organelles called chloroplasts, which contain              pigment molecules.

    In plants, chloroplasts are found mainly in the mesophyll cells of a leaf.

    The stomata are openings in the leaf that allow gas exchange with the atmosphere.

    Leaf structure review:

      A chloroplast has a double membrane.

      The inner membrane encloses a fluid stroma.

      A third membrane called thylakoid is stacked to form structures called grana and contains the photosynthetic pigment chlorophyll

    The chlorophyll molecules in leaves absorb wavelengths of light other than green.

    Most of the green wavelengths are reflected, so humans perceive leaves as green.


      Chlorophyll molecules are pigments that absorb most wavelengths of light other than green. Carotenoids absorb wavelengths other than yellow and orange.
  10. There are two major stages: the        reactions and the         cycle (light-independent reactions).

    Overview of photosynthesis.

    The light reactions use light energy to make ATP and NADPH.

    The Calvin cycle uses the energy molecules from the light reactions to convert CO[2] into sugar.

    This process also requires H[2]O and releases O[2].


    • The light reactions occur in the            , where chlorophyll pigments absorb light and excite some electrons.

      Excitation of electrons.

      When a chlorophyll pigment absorbs a photon of light, electrons are excited to an unstable high-energy state.

      When the electrons fall back to the ground state, the energy is released.

      This energy can be visualized by illuminating a solution of chlorophyll and observing the light (fluorescence) and heat.

      A spinach battery:

    • Each excited electron is passed through two               where the energy is used to produce      and        .

      Light reactions: electron flow in photosystems.
    • Light energy from a photon is passed among chlorophyll molecules.
    • The energy is eventually captured in an electron from water in Photosystem II.
    • The splitting of the electron donor, water, releases oxygen.
    • The electron passes through an electron transport chain (ETC).
    • The energy from the electron is used to generate ATP.
    • Another photon excites chlorophyll molecules of Photosystem I.
    • Energy is passed among electrons to a 2nd ETC.
    • Energy from this 2nd ETC is stored in the electron acceptor NADPH.


      As electrons pass along the ETC, protons are pumped from the stroma into the thylakoid space, forming a H^+ gradient.

      The protons diffuse back to the stroma by chemiosmosis, and powers the ATP synthase to make ATP.

      These light reactions store chemical energy in NADPH and ATP, which are used in the Calvin cycle.


    • The Calvin cycle occurs in the         to synthesize        from carbon dioxide.

    In the Calvin cycle, which occurs in the stroma, the ATP and NADPH from the light reactions drive the synthesis of sugars.

    In most plants, three molecules of CO[2] that enter the Calvin cycle produces one molecule of G3P (a three-carbon sugar); these are called C3 plants.

    Two molecules of G3P can combine to form one glucose.


      C3 Plants rice wheat soybean
  11.     plants are adapted to hot, dry climates by incorporating CO2 into       -carbon as the substrate in the Calvin cycle.

    C4 plants are adapted to hot, dry climates, when their stomata are partially closed to conserve water. The enzyme PEP carboxylase has a higher affinity for CO[2] than rubisco and produces the four-carbon product oxaloacetate in mesophyll cells, then exported to bundle sheath cells. This adaptation maintains a CO[2] concentration in the bundle sheath that favors photosynthesis over photorespiration. Review:

      C4 plants such as sugarcane, corn, and switchgrass preface the Calvin cycle with a four-carbon compound as its first product.
  12. The production of          carbon compounds from            CO2 is called         fixation.

    A review of photosynthesis.

    The light reactions and the Calvin cycle occur in chloroplasts of plant cells.

    The various organic compounds produced by photosynthesis provides energy in ecosystems.

    The incorporation of CO[2] into organic material is called carbon fixation.