BioInteractive Outputs and Ecological Roles of Photosynthesis 1 — Questions and Answers
Question 1: What are the overall reactants and products of the photosynthesis equation?
- Reactants: CO2 + H2O + light; Products: glucose + O2 (Correct answer)
- Reactants: O2 + glucose; Products: CO2 + H2O
- Reactants: CO2 + O2; Products: glucose + H2O
- Reactants: glucose + light; Products: CO2 + H2O
Correct answer: Reactants: CO2 + H2O + light; Products: glucose + O2
The overall equation of photosynthesis is: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2.
Question 2: How does photosynthesis contribute to the oxygen content of Earth's atmosphere?
- Photosynthetic organisms have released O2 as a byproduct for billions of years, creating the modern atmosphere (Correct answer)
- Photosynthesis consumes O2 from the atmosphere
- O2 is produced only by deep-sea photosynthesis
- Photosynthesis converts N2 to O2
Correct answer: Photosynthetic organisms have released O2 as a byproduct for billions of years, creating the modern atmosphere
The Great Oxygenation Event ~2.4 billion years ago resulted from cyanobacteria releasing O2 via photosynthesis, fundamentally changing Earth's atmosphere.
Question 3: What is gross primary productivity (GPP) in an ecosystem?
- The total rate of carbon fixation by photosynthesis before subtracting respiration losses (Correct answer)
- The carbon remaining after plant respiration
- The amount of carbon consumed by herbivores
- The net gain of biomass by the entire food web
Correct answer: The total rate of carbon fixation by photosynthesis before subtracting respiration losses
GPP is the total rate at which photosynthetic organisms fix CO2 into organic compounds, before any energy is consumed by their own cellular respiration.
Question 4: What is net primary productivity (NPP)?
- GPP minus the carbon lost to plant respiration, representing energy available to consumers (Correct answer)
- Total carbon fixed by photosynthesis
- Carbon stored in soil organic matter
- Energy used by animals for growth
Correct answer: GPP minus the carbon lost to plant respiration, representing energy available to consumers
NPP = GPP − plant respiration; it represents the organic matter actually available to support herbivores and higher trophic levels.
Question 5: How does photosynthesis influence the global carbon cycle?
- It removes CO2 from the atmosphere and stores carbon in organic molecules, partially offsetting emissions (Correct answer)
- It releases CO2 into the atmosphere
- It has no significant effect on atmospheric CO2 on human timescales
- It converts methane to CO2
Correct answer: It removes CO2 from the atmosphere and stores carbon in organic molecules, partially offsetting emissions
Globally, photosynthesis fixes roughly 120 Gt of carbon per year, making it the dominant mechanism for removing atmospheric CO2 and forming the base of the carbon cycle.
Question 6: Why is photosynthesis considered the foundation of most food webs on Earth?
- It converts light energy into chemical energy stored in organic molecules that all other organisms depend on (Correct answer)
- It produces O2 that animals use for cellular respiration only
- It directly feeds all organisms in a food web
- It is the only way plants can survive
Correct answer: It converts light energy into chemical energy stored in organic molecules that all other organisms depend on
Photosynthesis produces the organic carbon compounds that primary consumers (herbivores) eat, which in turn supports higher trophic levels in almost every ecosystem.
BioInteractive Outputs and Ecological Roles of Photosynthesis 1
What are the overall reactants and products of the photosynthesis equation?