©THEBRIGHTSTARS 2024
EEB 162 Final Exam Questions With Correct
Answers.
1. Please explain C4 photosynthesis, using the following terms: HCO3-, PEP carboxylase,
mesophyll, Kranz Anatomy, plasmodesmata, malate, separation of pathways in space, water use
efficiency - answer✔C4 photosynthesis reduces photorespiration by concentrating CO2 near
rubisco. In mesophyll cells, CO2 is transformed to HCO3-, which is fixed to 3-carbon PEP by
PEP carboxylase. This reaction will produce a 4 carbon compound, often malate. Malate then
diffuses through plasmodesmata to bundle sheath cells. C4 plants have Kranz anatomy, an
enlarged bundle sheath with lots of chloroplasts. In the bundle sheath cells, malate is
decarboxylated to 3-carbon pyruvate and CO2, which is released to the bundle sheath
chloroplasts. The CO2 enters the full C3 Calvin cycle reactions in the bundle sheath. C4 plants
that do not have Kranz anatomy use separation of pathways in space (separating the PEP
carboxylase reactions from the Calvin cycle reactions within the cell). C4 plants have improved
water use efficiency (almost double C3 plants). C4 plants open stomata less for the same amount
of CO2 fixation under high irradiance, allowing them to lose less water.
2. a. Why does C4 photosynthesis have a cost? Please describe direct and indirect costs. -
answer✔(Direct)-Regeneration of PEP consumes 2 ATP
(IDirect)-If O2 was low and photorespiration did not occur, C4 plants require more quanta of
light per CO2 than C3 plants for the same CO2 fixation.
2.b. Under what conditions would C4 plants have an advantage over C3 plants? -
answer✔Higher temps, C3 plants increase photorespiration strongly, because Rubisco reacts
quicker with 02 and 02 becomes more soluble at higher temps.
C4 plants can lose less water, and so keep their leaf water potentials higher during transpiration,
and so operate effectively on drier soils.
2.c. Under what conditions would C3 plants have an advantage over C4 plants? Please explain
why. - answer✔As CO2 levels increase, it is possible that C3 species may be favored and
replace C4 grasses in the world's arid zones. However temp. increase along with CO2, not clear
if photorespiration would really be lower overall in C3 plants.
, ©THEBRIGHTSTARS 2024
What three possible environmental conditions might promote the evolution of the C4
photosynthetic pathway? Why? - answer✔C4 tends to originate in arid regions, implicating
heat, drought and or salinity as
important conditions promoting C4 evolution.
1)Implicating heat
2)Drought
3)Salinity
-Competitive advantage when resources are limited
-When hot, CO2 comes out of solution faster.
-C4 can maintain photosynthesis in drier soils, even when CO2 levels are low. As stomata closes,
CO2 rate in declines. C4 have an enzyme with high affinity, which can work efficiently in low
[CO2], an advantage in drier soils.
4. Please explain CAM photosynthesis, using the following terms: stomata, Rubisco, malate,
PEP carboxylase, water-use efficiency - answer✔CAM is like C4 in that PEP carboxylase fixes
HCO3-, and then releases CO2 to C3. CAM is like C4 where photosynthesis reduces
photorespiration by concentrating CO2 near rubisco. But CAM allows increased CO2
concentration by fixing HCO3- with PEP carboxylase at night (when the stomata open in CAM
plants). The malate is stored in the vacuole. The PEP is generated by the breakdown of starch
from the chloroplast. During the day (when stomata are closed), the malate is released from the
vacuole, and breaks down to pyruvate and CO2 in the chloroplast, and the light reactions and C3
Calvin cycle run. CAM leads to a huge water use efficiency (10x higher than C3 plants) b/c
stomata open only at night when CAM operates. CAM plants often have very water-resistance
cuticles, CAM photosynthesis is very expensive, due to additional metabolic costs and slow
photosynthetic rates
5. How are sun leaves adapted to capture light and CO2 effectively? Please name six different
features of their cells and tissues. - answer✔1)Epidermis is transparent, with convex cells that
can act as lenses to focus light to chloroplasts within the leaf.
2)Palisade cells allow penetration of light via vacuoles and intercellular airspaces (light
channeling).
3)Spongy mesophyll has honeycombed airspaces that reflect and refract light (light scattering).
4)Sun leaves are thicker, with more layers of palisade mesophyll to allow direct light to penetrate
the leaf. Intercellular area is maximized for CO2 capture.
EEB 162 Final Exam Questions With Correct
Answers.
1. Please explain C4 photosynthesis, using the following terms: HCO3-, PEP carboxylase,
mesophyll, Kranz Anatomy, plasmodesmata, malate, separation of pathways in space, water use
efficiency - answer✔C4 photosynthesis reduces photorespiration by concentrating CO2 near
rubisco. In mesophyll cells, CO2 is transformed to HCO3-, which is fixed to 3-carbon PEP by
PEP carboxylase. This reaction will produce a 4 carbon compound, often malate. Malate then
diffuses through plasmodesmata to bundle sheath cells. C4 plants have Kranz anatomy, an
enlarged bundle sheath with lots of chloroplasts. In the bundle sheath cells, malate is
decarboxylated to 3-carbon pyruvate and CO2, which is released to the bundle sheath
chloroplasts. The CO2 enters the full C3 Calvin cycle reactions in the bundle sheath. C4 plants
that do not have Kranz anatomy use separation of pathways in space (separating the PEP
carboxylase reactions from the Calvin cycle reactions within the cell). C4 plants have improved
water use efficiency (almost double C3 plants). C4 plants open stomata less for the same amount
of CO2 fixation under high irradiance, allowing them to lose less water.
2. a. Why does C4 photosynthesis have a cost? Please describe direct and indirect costs. -
answer✔(Direct)-Regeneration of PEP consumes 2 ATP
(IDirect)-If O2 was low and photorespiration did not occur, C4 plants require more quanta of
light per CO2 than C3 plants for the same CO2 fixation.
2.b. Under what conditions would C4 plants have an advantage over C3 plants? -
answer✔Higher temps, C3 plants increase photorespiration strongly, because Rubisco reacts
quicker with 02 and 02 becomes more soluble at higher temps.
C4 plants can lose less water, and so keep their leaf water potentials higher during transpiration,
and so operate effectively on drier soils.
2.c. Under what conditions would C3 plants have an advantage over C4 plants? Please explain
why. - answer✔As CO2 levels increase, it is possible that C3 species may be favored and
replace C4 grasses in the world's arid zones. However temp. increase along with CO2, not clear
if photorespiration would really be lower overall in C3 plants.
, ©THEBRIGHTSTARS 2024
What three possible environmental conditions might promote the evolution of the C4
photosynthetic pathway? Why? - answer✔C4 tends to originate in arid regions, implicating
heat, drought and or salinity as
important conditions promoting C4 evolution.
1)Implicating heat
2)Drought
3)Salinity
-Competitive advantage when resources are limited
-When hot, CO2 comes out of solution faster.
-C4 can maintain photosynthesis in drier soils, even when CO2 levels are low. As stomata closes,
CO2 rate in declines. C4 have an enzyme with high affinity, which can work efficiently in low
[CO2], an advantage in drier soils.
4. Please explain CAM photosynthesis, using the following terms: stomata, Rubisco, malate,
PEP carboxylase, water-use efficiency - answer✔CAM is like C4 in that PEP carboxylase fixes
HCO3-, and then releases CO2 to C3. CAM is like C4 where photosynthesis reduces
photorespiration by concentrating CO2 near rubisco. But CAM allows increased CO2
concentration by fixing HCO3- with PEP carboxylase at night (when the stomata open in CAM
plants). The malate is stored in the vacuole. The PEP is generated by the breakdown of starch
from the chloroplast. During the day (when stomata are closed), the malate is released from the
vacuole, and breaks down to pyruvate and CO2 in the chloroplast, and the light reactions and C3
Calvin cycle run. CAM leads to a huge water use efficiency (10x higher than C3 plants) b/c
stomata open only at night when CAM operates. CAM plants often have very water-resistance
cuticles, CAM photosynthesis is very expensive, due to additional metabolic costs and slow
photosynthetic rates
5. How are sun leaves adapted to capture light and CO2 effectively? Please name six different
features of their cells and tissues. - answer✔1)Epidermis is transparent, with convex cells that
can act as lenses to focus light to chloroplasts within the leaf.
2)Palisade cells allow penetration of light via vacuoles and intercellular airspaces (light
channeling).
3)Spongy mesophyll has honeycombed airspaces that reflect and refract light (light scattering).
4)Sun leaves are thicker, with more layers of palisade mesophyll to allow direct light to penetrate
the leaf. Intercellular area is maximized for CO2 capture.
