Name Answer Key
Date:
Period:
1. Define photosynthesis
The conversion of _Light energy_____ into__organic molecules/glucose______ in plants. (1 p. 65)
2. Write a balanced symbol equation for the process of photosynthesis.
6CO2 + 6 H2O + Sunlight  C6H12O6 + 6 O2
3. Glucose is a product of photosynthesis. It can be used directly in respiration, stored as starch or
converted to glucose.
a. Distinguish between the functions of starch and cellulose.
Starch: Stores energy in plants
Cellulose: Structural molecule in found in cell wall of plants
4. Distinguish between action and absorption spectra for photosynthesis.
Action: Shows rate of photosynthesis at different wavelengths
Absorption: Shows each pigments (chlorophyll a, b, and carotenoids) ability to absorb sunlight at
different wavelengths.
5. Summarize the two main stages of photosynthesis:
Input
Outcome
Light energy is used to…
Light-dependent
reactions
Light
independent
reactions
Sunlight, H2O, NADP+, ADP
NADPH, ATP, Oxygen
ATP, NADPH, CO2
C6H12O6, NADP+, ADP
Name Answer Key
Date:
Period:
A limiting factor is the one factor which is in shortest supply or is preventing the rate of a reaction from
increasing. If this factor were increased, rate of reaction would increase until another plateau was
reached (a different factor is then limiting).
7. Outline the effects of the following variables on the rate of photosynthesis.
Sketch and annotate a graph for each one.
Light intensity
Photosynthetic rate increases as light
intensity concentration increases until certain
point where it plateaus. At high intensities,
chloroplasts are working at maximum
efficiency, and photosynthetic pigments are
absorbing light at maximum rate.
Note: light intensity is not the same as wavelength or frequency. Light intensity refers to the amount of light of a given
wavelength which is available to the plant. Light intensity is high at the equator, in the summer or at midday.
Temperature
Photosynthetic rate increases with
temperature until an optimum temperature
is reached. Higher temperatures decrease
rate of reactions. Enzymes denature at higher
temps.
Carbon dioxide concentration
Photosynthetic rate increases as CO2
concentration increases until certain point
where it plateaus. At maximum point, CO2 is
being fixed at its maximum rate. Similar to
enzyme and substrate concentration. Rubisco
can only combine RuBP and CO2 at a
maximum rate.
Name Answer Key
Date:
Period:
8.2/C4 Photosynthesis
8.
Photosynthesis consists of two stages: light dependent and light independent reactions.
a. Define photolysis The splitting of H2O into electrons (replace electrons in photosystem II)
hydrogen ions (used in chemiosmosis to produce ATP) and oxygen (which leaves as product)
using energy from the sunlight.
b. Define photophosphorylation The production of ATP using energy from photons, the
electron transport chain and chemiosmosis, which produces a concentration gradient of H+ that power
ATP synthase.
c. Define carbon fixation The conversion of inorganic carbon dioxide into an organic molecule.
This happens in photosynthesis by combining RuBP with CO2 using the enzyme rubisco in the calvin
cycle.
9. Annotate the diagram below to explain the light-dependent reactions of photosynthesis.
Include photolysis, photophosphorylation (and chemiosmosis), movement of electrons,
generation of a H+ gradient using a proton pump, reduction of NADP+ by ferredoxin.
Sunlight
H
+
H+
e-
NADP Reductase
e-
eeH+ + O2 + eH+
H2O
H
H
H+
+
H
+
H+
H+
H
+
H+
Chlorophyll molecules in photosystem II absorb photons and transfer the energy to electrons, which then jump to
H+ pass through an electron transport chain to photosystem I. As they move,
the primary electron acceptor and
chemiosmosis occurs, which is when
hydrogen ions are pumped into the lumen where a concentration gradient is
H+
created. The hydrogen ions then move down the gradient into the stroma through ATP synthase. As they pass
+
through ATP synthase, ADP is combined
with phosphorus to make ATP. This is photophosphorylation. In
photosystem I, photons are absorbed again and transferred to ferrodoxin, NADP reductase then uses the electrons
to reduce NADP+ to form NADPH. Photolysis occurs when water is split, using energy from sunlight, into electrons,
hydrogen, and oxygen. The electrons replace the electrons that were lost in photosystem II.
Name Answer Key
Date:
Period:
10. Identify the two products of the light-dependent reactions which are carried through to the
light- independent reactions.
o NADPH
o ATP
11. In the space below, draw a diagram to explain the cycle of reactions that occur in the lightindependent stages of photosynthesis. Include carboxylation of RuBP to glycerate-3-phosphate
by rubisco, reduction to triose phosphate, formation of glucose phosphate and reformation of
RuBP.
RuBP and CO2 are combined through the process of carbon fixation using the enzyme rubisco. This forms
a 6 carbon intermediate that is immediately broken down into two molecules of glycerate-3-phosphate.
Glycerate-3-phosphate is then phosphorylated and reduced using ATP and NADPH (from the light
independent reactions) into glyceraldehyde-3-phosphate (G3P/triose phosphate). G3P will then either
leave the cycle and become a molecule of glucose, or be recycled into RuBP. 5 molecules of G3P will be
used to regenerate 3 molecules of RuBP using ATP from the light dependent reactions. 1 molecule of
G3P will leave and become glucose when it combines with another molecule of G3P.