CLEP - Biology Ecosystems and Energy Flow Questions and Answers — Questions and Answers
Question 1: In a terrestrial ecosystem, if the producers (plants) contain 10,000 kcal of energy, approximately how much energy would be available to the secondary consumers?
- 10,000 kcal
- 1,000 kcal
- 100 kcal (Correct answer)
- 10 kcal
Correct answer: 100 kcal
Energy transfer between trophic levels is inefficient, with only about 10% of the energy from one level being incorporated into the next. Primary consumers (herbivores) would have access to about 1,000 kcal (10% of 10,000). Secondary consumers, which feed on primary consumers, would then have access to about 100 kcal (10% of 1,000).
Question 2: A lake is contaminated with a persistent, fat-soluble pesticide. Which of the following organisms would likely contain the highest concentration of this pesticide in its tissues?
- A large predatory fish (Correct answer)
- Phytoplankton
- A small fish that feeds on zooplankton
- Zooplankton
Correct answer: A large predatory fish
This scenario describes biomagnification, where the concentration of a toxin increases at successively higher levels in a food chain. The pesticide is absorbed by phytoplankton, which are eaten by zooplankton, which are eaten by small fish, which are then consumed by the large predatory fish. At each step, the toxin becomes more concentrated, resulting in the highest levels in the apex predator.
Question 3: Which of the following best defines Net Primary Productivity (NPP)?
- The total rate of photosynthesis in an ecosystem.
- The total biomass of all producers in an ecosystem.
- The rate of decomposition by bacteria and fungi.
- The rate of energy storage as biomass that is available to consumers. (Correct answer)
Correct answer: The rate of energy storage as biomass that is available to consumers.
Gross Primary Productivity (GPP) is the total amount of energy captured by producers via photosynthesis. Producers use some of this energy for their own cellular respiration (R). Net Primary Productivity (NPP) is the energy that remains (NPP = GPP - R) and is stored as new biomass, making it available to the herbivores in the ecosystem.
Question 4: The process by which certain bacteria convert atmospheric nitrogen gas (N2) into ammonia (NH3), a form usable by plants, is known as:
- Denitrification
- Nitrogen fixation (Correct answer)
- Ammonification
- Nitrification
Correct answer: Nitrogen fixation
Nitrogen fixation is the essential process that converts inert atmospheric nitrogen (N2) into ammonia (NH3) and other nitrogenous compounds that plants can absorb. This is primarily carried out by nitrogen-fixing bacteria, which can be free-living in the soil or live in symbiotic relationships with plants like legumes.
Question 5: Why is a pyramid of energy in an ecosystem always depicted as upright?
- There is a progressive loss of energy at each successive trophic level. (Correct answer)
- The biomass of producers is always greater than the biomass of consumers.
- Organisms at higher trophic levels are generally larger than those at lower levels.
- Decomposers at the top of the pyramid recycle energy back to the producers.
Correct answer: There is a progressive loss of energy at each successive trophic level.
The structure of an energy pyramid is dictated by the second law of thermodynamics. As energy flows from one trophic level to the next, a significant portion (around 90%) is lost as metabolic heat. This inefficiency means the total energy available at each successive level is always less than the level below it, resulting in a mandatory upright pyramid shape.
Question 6: In an ecosystem, what is the primary role of detritivores, such as bacteria and fungi?
- To convert solar energy into chemical energy.
- To regulate the population sizes of primary consumers.
- To serve as the primary food source for apex predators.
- To recycle essential chemical nutrients back into the soil. (Correct answer)
Correct answer: To recycle essential chemical nutrients back into the soil.
Detritivores, or decomposers, play a critical role in nutrient cycling. They break down dead organic matter (detritus) from all trophic levels, releasing inorganic nutrients like carbon and nitrogen back into the environment. These recycled nutrients are then available for uptake by producers, completing the cycle and sustaining the ecosystem.
CLEP - Biology Ecosystems and Energy Flow Questions and Answers
In a terrestrial ecosystem, if the producers (plants) contain 10,000 kcal of energy, approximately how much energy would be available to the secondary consumers?