Biology: Photosynthesis

  1. Photosynthesis transforms solar energy into the __________ energy of a carbohydrate.
    Chemical Energy
  2. Name the 3 photosynthetic organisms.
    • Plants
    • Algae
    • Cyanobacteria
  3. What is the primary function of photosynthesis?
    The primary function of photosynthesis is to capture light energy, convert some of this light energy into chemical energy, and store this chemical energy in molecules of carbohydrates (such as phosphoglyceraldehyde, glucose, or starch).
  4. The leaf of a flowering plant contains __________ tissue in which cells are specialized to carry on photosynthesis.
    Mesophyll tissue
  5. What are the raw materials for photosynthesis?
    Water and Carbon Dioxide
  6. Carbon Dioxide in the air enters a leaf through small openings called ___________.
  7. __________are molecules that absorb wavelengths of light.
    • Pigments.
    • Most pigments absorb only some wavelengths; they reflect or transmit the other wavelengths.
  8. Pigments found in chloroplasts are capable of absorbing various portions of ___________ light.
    Visible light.
  9. How do photosynthetic organisms differ?
    Photosynthetic organisms differ by the type of chlorophyll they utilize.
  10. Chlorophyll a & Chlorophyll b absorb which colors of light?
    • Blue
    • Violet
    • Red

    *Because green is not absorbed, it is reflect, which is why plant leaves appear green to us.
  11. Carotenoids, which play an accessory role in photosynthesis, absorb which colors of light?
    Violet-blue-green range
  12. What color are carotenoids?
    • Shades of yellow and orange.
    • These pigments become noticeable during the fall when the chlorophyll breaks down.
  13. The light reaction occurs in the __________ of the chloroplast.
    Thylakoid membrane
  14. The light reactions consist of two electron pathways. Both pathways transform solar energy into chemical energy. Both pathways produce ATP. However, only one produces NADPH. Which pathway is it?
    A. Cyclic electron pathway
    B. Non-Cyclic electron pathway
    Non-Cyclic electron pathway
  15. What are the results of the Noncyclic pathway of the light reactions?
    Hint: 4 main results.
    • -Water is oxidized ---> yielding H+, e-, and O2.
    • -NADP+ becomes NADPH (gains an electron--->reduced)
    • -ATP is produced
    • -Oxygen is released

    ***The NADPH produced, will be used in the Calvin cycle in the stroma to reduce CO2 to a carbohydrate
  16. The cyclic pathway of the light reaction only has one result. What is it?
    produces 1 ATP!
  17. This series of reactions utilizes carbon dioxide from the atmosphere to produce carbohydrates?
    A. Light reactions
    B. Calvin Cycle
    Calvin Cycle
  18. What are the 3 main steps of the Calvin Cycle?
    • 1. Carbon Dioxide Fixation
    • 2. Carbon Dioxide Reduction
    • 3. Regeneration of RuBP
  19. What happens during the fixation of carbon dioxide?
    • During this reaction, carbon dioxide from the atmosphere is attached to RuBP (a 5 carbon molecule).
    • After attaching, the result is 6 carbon molecule.
    • This 6 carbon molecule splits into two 3 carbon molecules, called 3-phosphoglycerate (PGA)
  20. What is the enzyme that speeds up the reaction in fixating carbon dioxide?
    • RuBP carboxylase, or rubisco.
    • *This protein makes up 20-50% of the protein content in chloroplasts!
  21. What happens during the reduction of carbon dioxide?
    • -The 3 carbon molecule called PGA (3-phosophoglycerate) undergoes reduction to PGAL.
    • -The NADPH produced from the light reaction is used in this step!
    • -Carbohydrate (Glucose) is produced at this step
    • -As PGA becomes PGAL, ATP becomes ADP+ P
    • also, NADPH becomes NADP+ (loses electron, oxidized)
    • This sequence signifies the reduction of carbon dioxide to a carbohydrate because R-CO2 becomes R-CH2O ?? pg 125.
  22. How many PGAL molecules are needed to form glucose?
    Two PGAL molecules
  23. How many PGALs are needed to reform 3 RuBP?
    • 5 PGALs.
    • Thus, it takes 3 turns of the cycle to have a net gain of one PGAL.
  24. What makes PGAL so important?
    PGAL is the first reactant in a number of plant cell metabolic pathways.
  25. What types of plants use RuBP carboxylase to CO2 to RuBP in mesophyll cells?
    A. C3 plants
    B. C4 plants
    C. CAM plants
    C3 plants
  26. In C3 plants, what happens to the stomata during hot weather?
    • The stomata allows water to leave, and CO2 to enter.
    • If the weather is hot and dry, the stoma closes to prevent water from exiting.
    • Because the stomata is closed, CO2 is unable to enter.
    • Thus, CO2 concentration is decreasing, while O2 (by product of photosynthesis) is increasing.
    • ---when O2 rises in C3 plants, it combines with RuBP instead of CO2.
    • ----The result is ONE PGA and the release of CO2. ------->THIS IS CALLED PHOTORESPIRATION.
    • *C4 photosynthesis avoids photorespiration
  27. What enzyme do C4 plants use to fix CO2 to PEP (Phosphoenolpyruvate, resulting to oxaloacetate?

    PEP + CO2 -----------> oxaloacetate
    Enzyme: PEP carboxylase (PEP Case)

    PEP + CO2 -----------> oxaloacetate
  28. Why don't C4 plants undergo photorespiration?
    • Photorespiration does not occur in C4 leaves because PEP unlike RuBP, does NOT combine with O2.
    • Even when the stomata are closed, CO2 is delivered to the Calvin cycle in the bundle sheath cells.
  29. What is CAM photosynthesis?
    • CAM plants use PEPCase to fix some CO2, forming C4 molecules, which are stored in large vacuoles in mesophyll cells
    • **CAM plants open their stomata at night.
    • During the day, the stomata closes.
    • This is due to the conservation of water.
    • **This allows CAM plants to live under stressful conditions**
    • -C3 plants live in moderate conditions
    • C4- hott weather
    • CAM- extreme conditions

    example of CAM plant: pineapple!
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Biology: Photosynthesis