What happens if all the stomata on a C3 plant are closed during the day? What about C4 and
CAM plants?
In a C3 plant, the stroma is open during the day (as they are not in hot and dry environments) and
is closed at night. This occurs because during the day the plant wants to bring in as much light as
possible to aid in the production of ATP. They allow CO2 to enter the plant and go to the Calvin
Cycle to produce glucose so the plant can thrive. If the stroma was to be closed during
photorespiration then the plant would not be able to thrive as there is no CO2 entering the plant,
no CO2 means no food, and no food means the plant will die. Oxygen will also accumulate to
compete with the CO2 for the enzyme with ribusco - which will also impact the production of
glucose in the Calvin Cycle
C4 plants have a different mechanism for coping with carbon fixation, so they are resistant to
lower CO2 levels that would result from the closed stomata during the day. In a CAM plant, the
stroma is open at night and closed during the day (as these plants are located within hot and dry
places, ex. cactus). The plant opens its stroma at night to allow CO2 to enter the plant. Inside the
mesophyll of C4 and CAM plants, CO2 combines with PEP to make oxaloacetate then into
malate. Malate is then transported to the bundle sheath cells where it can be stored in vacuoles.
During the day, when the stomata are closed, malate can be decarboxylated to allow CO2 and
enter the Calvin Cycle to produce glucose.
An alien plant contains chlorophyll a and b pigment in photosystem I and carotenoid in
photosystem II. The plant is placed in a room with no windows and the only source of light is
green light shining from a lamp. What will happen to the plant?
Photosystem II has carotenoids. Since carotenoid absorbs green light, it can still receive the
electron from water, energize at the reaction centre p680, and pass on to the electron transport
chain. As the energized electrons are passed onto the b6f complex, it pumps H+ ions from the
stoma into the lumen to create the electrochemical gradient. It is still possible that ATP synthase
can still use the EC gradient to create ATP through photophosphorylation during chemiosmosis.
However, since photosystem I contains chlorophyll a and b, which does not absorb green light.
With only green light available, photosystem I would not be able to reenergize the electrons since
it reaches photosystem I at the reaction centre p700. Without the electrons being reenergized, it is
unable to provide the energy to NADP reductase to reduce NADP+ to NADPH. Without
NADPH, the Calvin Cycle cannot fix carbon in glucose.
A chemical used to control weeds damages the b6f complex. Is this chemical an effective way to
control weeds? Why or why not.
If the bf6 complex was damaged, it is unable to pump H+ ions from the stroma to the thylakoid
space to create the electrochemical gradient after receiving the energized electrons from
photosystem II. Also, electrons will not be passed onto photosystem I. If electrons are not passed
onto photosystem I, there would be no electrons gaining energy within the photosystem I and
therefore NADPHs cannot be produced. If no NADPHs are produced, then light independent
CAM plants?
In a C3 plant, the stroma is open during the day (as they are not in hot and dry environments) and
is closed at night. This occurs because during the day the plant wants to bring in as much light as
possible to aid in the production of ATP. They allow CO2 to enter the plant and go to the Calvin
Cycle to produce glucose so the plant can thrive. If the stroma was to be closed during
photorespiration then the plant would not be able to thrive as there is no CO2 entering the plant,
no CO2 means no food, and no food means the plant will die. Oxygen will also accumulate to
compete with the CO2 for the enzyme with ribusco - which will also impact the production of
glucose in the Calvin Cycle
C4 plants have a different mechanism for coping with carbon fixation, so they are resistant to
lower CO2 levels that would result from the closed stomata during the day. In a CAM plant, the
stroma is open at night and closed during the day (as these plants are located within hot and dry
places, ex. cactus). The plant opens its stroma at night to allow CO2 to enter the plant. Inside the
mesophyll of C4 and CAM plants, CO2 combines with PEP to make oxaloacetate then into
malate. Malate is then transported to the bundle sheath cells where it can be stored in vacuoles.
During the day, when the stomata are closed, malate can be decarboxylated to allow CO2 and
enter the Calvin Cycle to produce glucose.
An alien plant contains chlorophyll a and b pigment in photosystem I and carotenoid in
photosystem II. The plant is placed in a room with no windows and the only source of light is
green light shining from a lamp. What will happen to the plant?
Photosystem II has carotenoids. Since carotenoid absorbs green light, it can still receive the
electron from water, energize at the reaction centre p680, and pass on to the electron transport
chain. As the energized electrons are passed onto the b6f complex, it pumps H+ ions from the
stoma into the lumen to create the electrochemical gradient. It is still possible that ATP synthase
can still use the EC gradient to create ATP through photophosphorylation during chemiosmosis.
However, since photosystem I contains chlorophyll a and b, which does not absorb green light.
With only green light available, photosystem I would not be able to reenergize the electrons since
it reaches photosystem I at the reaction centre p700. Without the electrons being reenergized, it is
unable to provide the energy to NADP reductase to reduce NADP+ to NADPH. Without
NADPH, the Calvin Cycle cannot fix carbon in glucose.
A chemical used to control weeds damages the b6f complex. Is this chemical an effective way to
control weeds? Why or why not.
If the bf6 complex was damaged, it is unable to pump H+ ions from the stroma to the thylakoid
space to create the electrochemical gradient after receiving the energized electrons from
photosystem II. Also, electrons will not be passed onto photosystem I. If electrons are not passed
onto photosystem I, there would be no electrons gaining energy within the photosystem I and
therefore NADPHs cannot be produced. If no NADPHs are produced, then light independent
