SAT - Biology Subject Ecosystems and Energy Flow Questions and Answers — Questions and Answers
Question 1: In a terrestrial ecosystem, if the primary producers generate 10,000 kcal/m²/year of energy, approximately how much energy would be available to the tertiary consumers?
- 1,000 kcal/m²/year
- 100 kcal/m²/year
- 10 kcal/m²/year (Correct answer)
- 1 kcal/m²/year
Correct answer: 10 kcal/m²/year
The transfer of energy between trophic levels is generally inefficient, with only about 10% of the energy from one level being incorporated into the next. This is known as the 10% rule. Primary producers (10,000 kcal) are eaten by primary consumers (10% of 10,000 = 1,000 kcal). Primary consumers are eaten by secondary consumers (10% of 1,000 = 100 kcal). Secondary consumers are eaten by tertiary consumers (10% of 100 = 10 kcal).
Question 2: Which of the following processes is essential for converting atmospheric nitrogen into a form usable by plants?
- Denitrification
- Nitrogen fixation (Correct answer)
- Photosynthesis
- Transpiration
Correct answer: Nitrogen fixation
Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into ammonia (NH3) or other nitrogenous compounds that plants can absorb and utilize. This process is primarily carried out by certain bacteria.
Question 3: The process by which the concentration of a persistent toxin, such as mercury or DDT, increases in the tissues of organisms at successively higher trophic levels is known as:
- Bioremediation
- Eutrophication
- Bioaccumulation
- Biomagnification (Correct answer)
Correct answer: Biomagnification
Biomagnification (or bioamplification) is the increasing concentration of a substance in organisms at successively higher levels in a food chain. These substances are often persistent and not easily broken down or excreted. Bioaccumulation refers to the buildup of a substance within a single organism over its lifetime, whereas biomagnification describes the increase across multiple trophic levels.
Question 4: A volcanic eruption creates a new island of barren rock. Over time, lichens and mosses begin to grow on the rock, followed by grasses, shrubs, and eventually trees. This entire sequence of community development is an example of:
- Climax community
- Secondary succession
- Primary succession (Correct answer)
- Trophic cascade
Correct answer: Primary succession
Primary succession is the ecological succession that occurs in an environment devoid of vegetation and usually lacking topsoil. It starts on newly formed or exposed land, such as bare rock from a volcanic eruption. Secondary succession occurs when an existing community has been cleared by a disturbance that leaves the soil intact.
Question 5: Net Primary Productivity (NPP) is the rate at which an ecosystem's producers create biomass. It is calculated by which of the following formulas?
- NPP = Gross Primary Productivity + Respiration
- NPP = Gross Primary Productivity / Respiration
- NPP = Respiration - Gross Primary Productivity
- NPP = Gross Primary Productivity - Respiration (Correct answer)
Correct answer: NPP = Gross Primary Productivity - Respiration
Gross Primary Productivity (GPP) is the total rate at which solar energy is captured by producers during photosynthesis. Producers use some of this energy for their own metabolic processes (cellular respiration). The remaining energy, stored as biomass, is the Net Primary Productivity (NPP), which is available to consumers. Therefore, NPP = GPP - R (Respiration).
Question 6: In the carbon cycle, which process removes carbon dioxide from the atmosphere and incorporates it into organic molecules?
- Decomposition
- Photosynthesis (Correct answer)
- Respiration
- Combustion
Correct answer: Photosynthesis
Photosynthesis is the primary process that removes carbon dioxide from the atmosphere. Plants and other autotrophs use CO2, water, and sunlight to create glucose (an organic molecule) and oxygen. Respiration, decomposition, and combustion are processes that release carbon dioxide back into the atmosphere.
SAT - Biology Subject Ecosystems and Energy Flow Questions and Answers
In a terrestrial ecosystem, if the primary producers generate 10,000 kcal/m²/year of energy, approximately how much energy would be available to the tertiary consumers?