Ecology Ecosystem Energy Flow Questions and Answers — Questions and Answers
Question 1: Which of the following best describes the relationship between Gross Primary Production (GPP) and Net Primary Production (NPP)?
- NPP is the total energy captured by producers, while GPP is the energy available to consumers.
- GPP and NPP are identical measures of the total solar energy converted to biomass.
- NPP is the energy remaining from GPP after producers have accounted for their own metabolic needs through respiration. (Correct answer)
- GPP is the rate of biomass accumulation by consumers, whereas NPP is the rate for producers.
Correct answer: NPP is the energy remaining from GPP after producers have accounted for their own metabolic needs through respiration.
Gross Primary Production (GPP) is the total rate at which solar energy is captured by producers during photosynthesis. However, producers must use some of this energy for their own life processes, such as cellular respiration. Net Primary Production (NPP) is the rate at which energy is stored as biomass by producers and made available to other trophic levels. Therefore, NPP is calculated as GPP minus the energy lost to producer respiration (NPP = GPP - R).
Question 2: In a terrestrial food web, a rabbit eats grass, and a fox eats the rabbit. In this chain, the rabbit functions as which of the following?
- A secondary consumer
- A primary consumer (Correct answer)
- A producer
- A decomposer
Correct answer: A primary consumer
Producers, like grass, create their own food, typically through photosynthesis. Primary consumers are herbivores that feed on producers. The rabbit eats grass, making it a primary consumer. Secondary consumers, like the fox, are carnivores or omnivores that feed on primary consumers.
Question 3: The '10% Rule' of energy transfer between trophic levels explains why which of the following is true?
- The biomass of producers is typically much smaller than the biomass of top carnivores.
- Ecosystems can support an infinite number of trophic levels.
- Energy is recycled efficiently, with 10% being permanently destroyed at each level.
- Food chains are generally limited to four or five trophic levels. (Correct answer)
Correct answer: Food chains are generally limited to four or five trophic levels.
The 10% Rule states that, on average, only about 10% of the energy from one trophic level is incorporated into the next. The remaining 90% is used for metabolic processes or lost as heat to the environment. This significant energy loss at each step limits the total number of trophic levels an ecosystem can support, as there is insufficient energy to sustain populations at higher levels.
Question 4: If the producer level in a grassland ecosystem contains 25,000 kcal/m²/year of energy, approximately how much energy would be expected to be available to the tertiary consumers?
- 2,500 kcal/m²/year
- 250 kcal/m²/year
- 25 kcal/m²/year (Correct answer)
- 2.5 kcal/m²/year
Correct answer: 25 kcal/m²/year
Following the 10% rule of energy transfer: Primary consumers would have access to 10% of 25,000 kcal, which is 2,500 kcal. Secondary consumers would have access to 10% of 2,500 kcal, which is 250 kcal. Tertiary consumers would then have access to 10% of 250 kcal, which is 25 kcal/m²/year.
Question 5: Which group of organisms is essential for returning nutrients from dead organic matter back into the soil, making them available for producers?
- Tertiary consumers
- Primary consumers
- Autotrophs
- Decomposers (Correct answer)
Correct answer: Decomposers
Decomposers, such as bacteria and fungi, play a critical role in ecosystem energy flow and nutrient cycling. They break down dead organisms and waste products from all trophic levels, releasing inorganic nutrients back into the environment (e.g., soil or water), which producers can then use to grow.
Question 6: What is the ultimate source of energy for the vast majority of ecosystems on Earth?
- Geothermal heat from the Earth's core
- Chemical energy from inorganic compounds
- Solar radiation (Correct answer)
- Kinetic energy from wind and tides
Correct answer: Solar radiation
For nearly all ecosystems on Earth, the ultimate energy source is the sun. Producers, or autotrophs, capture solar energy through photosynthesis and convert it into chemical energy (glucose), which then flows through the rest of the food web. Exceptions like deep-sea hydrothermal vent communities exist, but they represent a small fraction of the biosphere.
Ecology Ecosystem Energy Flow Questions and Answers
Which of the following best describes the relationship between Gross Primary Production (GPP) and Net Primary Production (NPP)?