Chapter 10 Study ?’s (part 1): Photosynthesis in Nature
1) Distinguish between the following terms: autotroph, photoautotroph, heterotroph, and
decomposer. Give an example of each. Indicate which are producers or consumers.
Autotroph: organisms that produce their own food (“producers”); ex: plants, cyanobacteria, bacteria at deep
sea thermal vents (no light)
Photoautotroph: specific type of autotroph that uses light as the energy source to make
carbohydrates; ex: plants & cyanobacteria
Chemoautotroph: produce organic compounds w/o light; ex: sulfur deep sea vent organisms
Heterotroph: organisms that obtain organic material by consuming other organisms (“consumers”); ex:
animals, fungi
Decomposer: heterotroph that obtains organic material by consumer dead organisms; ex: fungi,
bacteria
2a) What parts of a plant have chloroplasts? All green parts
Where are chloroplasts mainly found? Mesophyll cells of leaves
2b) How many chloroplasts are found per square millimeter of leaf surface? 500,000 chloroplasts per mm2
of leaf surface
How many chloroplasts are found in each mesophyll cell? 30-40
2c) How do the cells of a leaf accomplish gas exchange (i.e. O2 and CO2)? Through stomata
How does water enter the plant? Receive water through roots
How do leaf cells receive water and export sugar? water and synthesized sugar are transported through
veins
2d) Specifically, where is the green pigment chlorophyll found? Thylakoid membrane
3) Sketch and label a chloroplast
4a) Write the NET chemical equation for photosynthesis.
6 CO2 + 6 H2O + light energy  C6H12O6 + 6O2
4b) How does this reaction compare to that of cellular respiration? Almost the reverse; type of energy
different
5a) Summarize the experimental results of C.B. van Niel. What did he hypothesize was the source of oxygen
gas in photosynthesis? Water
Why? He was studying bacteria that made their organic material with CO2 but they did not
release O2. Bacteria used H2S instead of water and they released S as a waste product instead.
5b) How did scientists confirm van Niel’s hypothesis? (Summarize their experiments and results)
Used O-18 (heavy isotope); the O2 that came from plants was labeled with O-18 ONLY if the water was
the source of the tracer. If CO2 had the heavy O-18 isotope, the released O2 was NOT labeled.
6) In the space below, create a chart in which you compare the two major phases of photosynthesis: the light
reactions and the Calvin cycle. In your chart include: the location (be specific!), the main function, and the
inputs/outputs of each.
LOCATION
MAIN
INPUTS
OUTPUTS
FUNCTION
LIGHT
Thylakoid
Convert light
Water, light,
Oxygen, NADPH,
DEPENDENT
membrane
energy to the
NADP+, ADP & Pi ATP
REACTIONS
chemical energy of
“photo”
ATP & NADPH
LIGHT
Stroma
Make
NADPH, ATP,
Water,
INDEPENDENT
carbohydrate
CO2
carbohydrate,
REACTIONS
(sugar) using ATP
ADP, NADP+
-CALVIN CYCLE
& NADPH from
“synthesis”
the Light Dep.
reactions
7) What 2 energy molecules are generated during the light reactions? ATP & NADPH
8) How is the ATP generated during photosynthesis different (in terms of use) from the ATP generated in
cellular respiration? Photophosphorylation; ATP is generated because sunlight “powers” an electron
transport chain which creates proton motive force; no sunlight used in cellular respiration
9a) Define the “action spectrum” of photosynthesis.
Rate of photosynthesis graphed against wavelength of light
9b) Draw the action spectrum of photosynthesis.
9b) Explain the relationship between the action spectrum and the absorption
spectrum of photosynthetic pigments in green
plants.
The more a wavelength of light is absorbed by the
pigments in the plant, the more photosynthesis that
can occur. That is why the shape of the absorption
spectrum graph looks similar to the action spectrum
graph.