Mix of multiple choice, true/false, and fill-in-the-blank
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Estimated time: 20–25 minutes
QUESTION 1
What are the two main products of the light reactions that are used in the Calvin cycle?
✅ Correct! The light reactions produce ATP (energy) and NADPH (reducing power), which are used in the Calvin cycle to fix CO₂ into sugars. Oxygen is a byproduct, not used in the Calvin cycle.
QUESTION 2
Photosystem II (PSII) has its reaction center pigment called P680 because it absorbs light most efficiently at ______ nm.
✅ Correct! P680 absorbs light at 680 nm, while photosystem I (PSI) has P700 that absorbs at 700 nm. These are named for their peak absorption wavelengths.
QUESTION 3
What are the three phases of the Calvin cycle in correct order?
✅ Correct! The Calvin cycle has three phases: (1) Carbon fixation (CO₂ + RuBP → 3-PGA), (2) Reduction (3-PGA → G3P using ATP and NADPH), and (3) Regeneration of RuBP.
QUESTION 4
What is the most abundant protein on Earth, responsible for fixing CO₂ in the Calvin cycle?
✅ Correct! Rubisco (ribulose bisphosphate carboxylase/oxygenase) is the most abundant protein on Earth. It catalyzes the first step of carbon fixation but also has an oxygenase activity that leads to photorespiration.
QUESTION 5
Which of the following is a C4 plant?
✅ Correct! Maize (corn) is a C4 plant, along with sugarcane, sorghum, and millet. Wheat, rice, and potato are C3 plants. C4 plants have Kranz anatomy and use PEP carboxylase for initial CO₂ fixation.
QUESTION 6
What specialized leaf anatomy do C4 plants have that concentrates CO₂ around rubisco?
✅ Correct! Kranz anatomy (German for "wreath") describes the arrangement of bundle sheath cells surrounded by mesophyll cells in C4 plants. This structure allows CO₂ to be concentrated in bundle sheath cells, suppressing photorespiration.
QUESTION 7
When do CAM plants open their stomata to fix CO₂?
✅ Correct! CAM plants (like cacti and pineapple) open their stomata at night to fix CO₂ into malic acid, which is stored in vacuoles. During the day, stomata close to conserve water, and the stored CO₂ is released for the Calvin cycle.
QUESTION 8
True or False: Photorespiration increases at high temperatures and reduces photosynthetic efficiency.
✅ Correct! It's True. Photorespiration increases at high temperatures because rubisco's affinity for O₂ increases more than for CO₂. This wasteful process can reduce photosynthetic efficiency by 30-50% in C3 plants at high temperatures.
QUESTION 9
In the yield equation (Yield = Light interception × RUE × HI), what does HI stand for?
✅ Correct! Harvest Index (HI) is the proportion of total plant biomass that is harvestable product (grain, fruit, tuber, etc.). Modern wheat varieties have HI ~0.5 compared to traditional varieties ~0.3.
QUESTION 10
Which photosynthetic type typically has higher Radiation Use Efficiency (RUE)?
✅ Correct! C4 plants typically have higher Radiation Use Efficiency (1.5-2.0 g biomass/MJ) than C3 plants (1.0-1.5 g/MJ) because they suppress photorespiration and concentrate CO₂. CAM plants have variable RUE depending on conditions.
QUESTION 11
Leaf Area Index (LAI) measures:
✅ Correct! Leaf Area Index (LAI) is the total one-sided leaf area per unit ground area (m² leaf/m² ground). An LAI of 3-5 is optimal for most crops to intercept 95% of light.
QUESTION 12
Teff (Eragrostis tef), an important Ethiopian staple, is which photosynthetic type?
✅ Correct! Teff is a C3 plant, like wheat, rice, and barley. It grows well in the Ethiopian highlands where temperatures are moderate. In warmer lowlands, C4 crops like sorghum and millet are more common.
📊 Section 2.1 Complete!
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Great job! Review the explanations for any questions you missed.
📌 Section 2.1 Complete!
You have completed all units in Section 2.1: Photosynthesis. You should now be able to:
Explain how light reactions capture energy and produce ATP/NADPH
Describe the three phases of the Calvin cycle and the role of rubisco
Compare C3, C4, and CAM photosynthetic adaptations
Understand how photosynthesis relates to crop yield (light interception, RUE, harvest index)
Apply this knowledge to horticultural management
👉 Next: In Section 2.2, we'll explore Respiration and its role in plant energy metabolism.
Plant Biochemistry for Horticulture · HORT 202 · Dilla University · Last updated March 2026