Topic 8.3: Photosynthesis

Essential Idea:  Light energy is converted into chemical energy.
At SHS, Topic 8.3 is taught in the following class unit(s):

Statements & Objectives:

8.3.U1  Light-dependent reactions take place in the intermembrane space of the thylakoids.
  • State the location of the light dependent reactions of photosynthesis.
  • State that the light dependent reactions of photosynthesis include:
    • Photoactivation
    • Photolysis
    • Electron transport
    • Chemiosmosis
    • ATP synthesis
    • ​Reduction of NADP to NADPH + H+
8.3.U2  Light –independent reactions take place in the stroma.
  • State that the light dependent reactions convert light energy into chemical energy in the form of ATP and NADH.
8.3.U3  Reduced NADP and ATP are produced in the light-dependent reactions.
  • State the location of the light independent reactions of photosynthesis.
  • State that the light independent reactions of photosynthesis include:
    • Carbon fixation
    • Carboxylation of RuBP
    • Production of triosphosphate
    • ATP and NADPH as energy sources
    • ATP used to regenerate RuBP
    • ATP used to produce carbohydrates​
8.3.U4  Absorption of light by photosystems generates excited electrons.
  • Define photosystem and reaction center.
  • State that the light dependent reactions of photosynthesis begin at Photosystem II.
  • Outline process of photoactivation of the reaction center chlorophyll.  
  • State that in photoactivation at Photosystem II, the reaction center chlorophyll is oxidized and the plastoquinone (Pq) is reduced.
8.3.U5  Photolysis of water generates electrons for use in the light-independent reactions.
  • State that to replace the electrons lost during photoactivation, the reaction center chlorophyll takes electrons by splitting water.
8.3.U6  Transfer of excited electrons occurs between carriers in thylakoid membranes.
  • Draw a cross section of the thylakoid membrane to show the path of transfer of excited electrons, inclusive of Photosystem II, ATP synthase, an electron transport chain (with Pq first) and Photosystem II.
8.3.U7  Excited electrons from Photosytem II are used to contribute to generate a proton gradient.
  • State that electrons pass from plastoquinone (Pq) through a chain of electron carrier molecules.
  • State that the energy released by the movement of electrons is used to pump protons across the thylakoid membrane, from the stroma into the thylakoid lumen.
  • State that the result of the electron transport chain is a proton gradient, with a high concentration of protons in the thylakoid lumen.
8.3.U8  ATP synthase in thylakoids generates ATP using the proton gradient.
  • State that in chemiosmosis, ATP is generated as protons move down their concentration gradient through ATP synthase.
8.3.U9  Excited electrons from Photosytem I are used to reduce NADP.
  • State that photoactivation of the reaction center chlorophyll in photosystem I excites electrons which pass through a different electron transport chain.
  • State that the electrons of Photosystem I are used to reduce NADP+ to form NADPH.
  • State that NADPH is an electron carrier molecule.
  • State that the electrons from the Photosystem II electron transport chain are used to replace the electrons lost during photoactivation of Photosystem I.
8.3.U10  In the light-independent reaction a carboxylase catalyzes the carboxylation of ribulose-bisphosphate.
  • Define carbon fixation and carboxylation.
  • State that carbon fixation occurs in the chloroplast stroma.
  • State that the 5-carbon molecule ribulose bisphosphate (RuBP) is carboxylated by CO2, forming 2 3-carbon molecules called glycerate-3-phosphate (G3P).
  • State that the enzyme that catalyzes the carboxylation of RuBP is called ribulose bisphosphate carboxylase (rubisco).
8.3.U11  Glycerate 3-phosphate is reduced to triose phosphate using a reduced NADP and ATP.
  • State that ATP (from the light dependent reaction) provides the energy for NADPH (from the light dependent reaction) to reduce G3P, forming a three carbon carbohydrate, triose phosphate. ​
8.3.U12  Triose phosphate is used to regenerate RuBP and produce carbohydrates.
  • State that in the Calvin Cycle, triose phosphate is used to regenerate RuBP and create glucose.
  • State that six turns of the Calvin Cycle are needs to produce one molecule of glucose.
8.3.U13  Ribulose bisphosphate is reformed using ATP.
  • State that ATP is used to regenerate RuBP from triose phosphate.
8.3.U14  The structure of the chloroplast is adapted to its function in photosynthesis.
  • Outline how chloroplast structure could evolve through natural selection.
  • State evidence that suggests chloroplast were once free living prokaryotes.
8.3.A1  Calvin’s experiment to elucidate the carboxylation of RuBP.
  • Outline Calvin’s “lollipop” experiment, including the role of:
    • Radioactive carbon-14
    • Green algae
    • Air with CO2
    • Light
    • Varying the time of light exposure
    • Heated alcohol
    • Chromatography
    • Autoradiography
8.3.S1  Annotation of a diagram to indicate the adaptations of a chloroplast to its function.
  • Draw and label a diagram of the chloroplast.
  • State the function of the following chloroplast structures:  double membrane, thylakoids, pigment molecules, thylakoid lumen, and stroma.
8.3.NOS  Developments in scientific research follow improvements in apparatus- sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation.
  • State that the discovery of the radioactive 14C isotope allowed Calvin to determine the pathway of the light independent reactions of photosynthesis.
"When we try to pick out anything by itself, we find it hitched to everything else in the Universe." 
 John Muir,   1911