Introduction to Photosynthesis
Where do the enzymatic reactions of the Calvin cycle take place?
stroma of the chloroplast
Where does light-dependent reactions occur in plant cells?
thylakoid of chloroplast
Which molecule is the source of oxygen produced during photosynthesis?
Give the CORRECT order of light-independent reaction events.
carbon fixation—reduction—regeneration
What is the main pigment that absorbs light for photosynthesis?
chlorophyll a
What products of the light reactions are utilized in the Calvin cycle?
ATP and NADPH
What is the main function of NADPH?
A. speeds up chemical reactions in the cell absorbs
B. chemical energy from food breakdown
C. absorbs sunlight to excite high-energy electrons
D. carries high-energy electrons from light reactions
D. carries high-energy electrons from light reactions
If CO₂ levels are low, which of the following is the most likely effect on photosynthesis?
A. The production of G3P slows down.
B. ATP and NADPH are still consumed rapidly.
C. Electron flow through the ETC is stopped.
D. Oxygen production increases steadily.
A. The production of G3P slows down.
What molecule combines with CO₂ at the start of the Calvin cycle?
RuBP
Which of the following processes is involved in Photosystem II?
A. reduction of CO2
B. splitting of H2O
C. formation of G3P
D. oxidizing of NADPH
B. splitting of H2O
How are electrons in Photosystem I replenished during the light reactions?
A. By electrons from water splitting
B. By electrons from ATP hydrolysis
C. By electrons from carbon dioxide fixation
D. By electrons from the electron transport chain
D. By electrons from the electron transport chain
How many G3P molecules are needed to regenerate six RuBP?
10
Photosynthesis is a redox process. In the overall reaction:
6CO2 + 6H2O + light → C6H12O6 + 6O2
Which molecule is reduced and which is oxidized during photosynthesis?
A. CO₂ is reduced, H₂O is oxidized
B. H₂O is reduced, CO₂ is oxidized
C. CO₂ is reduced, O₂ is oxidized
D. Glucose is oxidized, H₂O is reduced
A. CO₂ is reduced, H₂O is oxidized
How do hydrogen ions flow from the stroma to the thylakoid space during the light reactions?
A. By being pumped using energy from the electron transport chain
B. By moving down their concentration gradient through ATP synthase
C. By being carried along with electrons from Photosystem I
D. By binding to NADPH and moving across the membrane
A. By being pumped using energy from the electron transport chain
If the thylakoid membrane became leaky to ions, what would most likely happen during the light reactions?
A. ATP production would stop
B. NADPH production would stop
C. Water splitting would stop
D. Electron transfer from PSII to PSI would stop
A. ATP production would stop
Which of the following steps of the Calvin cycle requires NADPH?
A. Fixation of CO₂ to RuBP
B. Reduction of 3-phosphoglycerate to G3P
C. Regeneration of RuBP from G3P
D. Production of ATP and NADPH
B. Reduction of 3-phosphoglycerate to G3P
A plant is placed in an environment where light intensity is normal, but CO₂ concentration is extremely low. What is the direct effect on the process of photosynthesis?
A. ATP and NADPH production slows down
B. Water splitting and oxygen production stop
C. Glucose and cellulose production are reduced
D. Electron flow through Photosystem II to I fails
C. Glucose and cellulose production are reduced
A plant is placed under a light that only excites Photosystem II but not Photosystem I. Predict what will happen during the light-dependent reactions.
A. ATP will be produced, but NADPH production will be limited
B. NADPH will be produced, but ATP production will be limited
C. Both ATP and NADPH production will stop completely
D. Water splitting and oxygen release will increase in production.
A. ATP will be produced, but NADPH production will be limited
A mutation blocks the primary electron acceptor in Photosystem II. Predict the immediate effect on the light-dependent reactions.
A. Electron flow stops, reducing ATP and NADPH production
B. ATP continues normally, but NADPH cannot be produced
C. Oxygen production stops, but ATP and NADPH continue
D. Electron flow stops, but NADPH production continues
A. Electron flow stops, reducing ATP and NADPH production
A scientist blocks the activity of Rubisco in a plant while light and CO₂ are abundant. Predict what will happen in the Calvin cycle.
A. G3P is produced normally, but RuBP cannot be regenerated
B. CO₂ cannot be fixed, so G3P and glucose production stop
C. ATP and NADPH are not used, and the light reactions stop
D. Oxygen production is halted, but the Calvin cycle continues
B. CO₂ cannot be fixed, so G3P and glucose production stop