Photosynthesis Applications and Implications 3 — Questions and Answers
Question 1: Vertical farming uses LED lights tuned to specific wavelengths to maximize crop growth. Which combination is most effective for photosynthesis?
- Green and yellow
- Blue and red (Correct answer)
- White and ultraviolet
- Orange and infrared
Correct answer: Blue and red
Blue light (~450 nm) and red light (~680 nm) match chlorophyll absorption peaks, making them the most energy-efficient choices.
Question 2: Global ocean warming threatens marine ecosystems partly because warmer water holds less dissolved CO2. What photosynthesis-related consequence does this have for phytoplankton?
- Phytoplankton switch to C4 photosynthesis
- Reduced carbon fixation rates and decreased primary productivity (Correct answer)
- Increased chloroplast count per cell
- Phytoplankton grow faster due to enzyme acceleration
Correct answer: Reduced carbon fixation rates and decreased primary productivity
Less dissolved CO2 limits the substrate available for carbon fixation, reducing phytoplankton primary productivity.
Question 3: Which statement best explains why C4 crops like sugarcane are preferred for bioethanol production in tropical regions?
- They fix nitrogen directly from the atmosphere
- Their C4 pathway minimizes photorespiration, yielding more biomass per unit of water (Correct answer)
- They require no CO2 for photosynthesis
- They store energy exclusively as glucose rather than sucrose
Correct answer: Their C4 pathway minimizes photorespiration, yielding more biomass per unit of water
C4 plants concentrate CO2 around RuBisCO, suppressing wasteful photorespiration and improving biomass yield under hot, sunny conditions.
Question 4: Scientists are engineering crops with modified RuBisCO enzymes. What is the primary goal of this modification?
- To allow plants to grow in total darkness
- To increase CO2 specificity and reduce oxygenase activity that causes photorespiration (Correct answer)
- To eliminate the need for chlorophyll
- To produce crops that photosynthesize using infrared light
Correct answer: To increase CO2 specificity and reduce oxygenase activity that causes photorespiration
RuBisCO can mistakenly bind O2 instead of CO2; engineering higher CO2 specificity would reduce photorespiration and increase yield.
Question 5: A solar panel farm and a cropland of equal area are compared for energy capture efficiency. Why do most crop plants convert less than 1% of incoming solar energy into stored biomass?
- Plants reflect all ultraviolet light
- Most wavelengths are not absorbed by chlorophyll, and metabolic costs further reduce net energy storage (Correct answer)
- Plants use only night-time energy
- Stomata block most incoming radiation
Correct answer: Most wavelengths are not absorbed by chlorophyll, and metabolic costs further reduce net energy storage
Chlorophyll absorbs only a fraction of the solar spectrum, and respiration, photorespiration, and other metabolic losses further reduce net yield.
Question 6: Which biotechnology application uses knowledge of the light-dependent reactions to engineer organisms that produce pharmaceutical compounds?
- CRISPR gene editing of soil bacteria
- Photobioreactors cultivating engineered algae that use photosynthesis to power compound synthesis (Correct answer)
- Hydroponic systems with synthetic fertilizers
- Tissue culture of plant embryos in the dark
Correct answer: Photobioreactors cultivating engineered algae that use photosynthesis to power compound synthesis
Photobioreactors harness algal photosynthesis to provide the ATP and NADPH needed to drive biosynthesis of target compounds.
Question 7: Ocean acidification from dissolved anthropogenic CO2 paradoxically provides more carbon for photosynthesis yet harms coral reefs. Why?
- Acidic water destroys chlorophyll in zooxanthellae
- The pH drop disrupts carbonate chemistry needed for coral skeleton formation, even if CO2 rises (Correct answer)
- Acidic oceans block sunlight from reaching corals
- Coral zooxanthellae require alkaline conditions to absorb CO2
Correct answer: The pH drop disrupts carbonate chemistry needed for coral skeleton formation, even if CO2 rises
Lower pH reduces carbonate ion availability, preventing corals from building their calcium carbonate skeletons despite increased CO2.
Photosynthesis Applications and Implications 3
Vertical farming uses LED lights tuned to specific wavelengths to maximize crop growth.
Which combination is most effective for photosynthesis?