Pre AP Biology -ECO 2.3 Food Webs and Transfer of Energy in Ecosystems- MCQ Exam Style Questions -New Syllabus 2025-2026
Pre AP Biology -ECO 2.3 Food Webs and Transfer of Energy in Ecosystems- MCQ Exam Style Questions – New Syllabus 2025-2026
Pre AP Biology -ECO 2.3 Food Webs and Transfer of Energy in Ecosystems- MCQ Exam Style Questions – Pre AP Biology – per latest Pre AP Biology Syllabus.
▶️ Answer/Explanation
The correct answer is c.
A grazing food web is defined by its start with living photosynthetic producers.
Primary consumers (herbivores) must be present to graze upon these living plants.
Secondary consumers (carnivores) are needed to represent the higher trophic levels.
Options including detritivores or decomposers refer to the detrital food web.
In a grazing web, energy flows from producers $\rightarrow$ herbivores $\rightarrow$ carnivores.
Including all three groups ensures the experimental model mimics natural energy transfer.
▶️ Answer/Explanation
A: B. the Sun.
Level A is at the bottom of the pyramid, representing the producers.
Producers are autotrophs that synthesize their own food.
They utilize light energy to power photosynthesis.
Thus, the original source of energy is the Sun.
A: B. \(20,000\) ; \(180,000\)
According to the \(10\%\) rule, only \(10\%\) of energy transfers to the next level.
Energy transferred to Level D \(= 200,000 \times 0.10 = 20,000 \text{ J}\).
The remaining \(90\%\) is lost as heat or waste.
Energy lost \(= 200,000 – 20,000 = 180,000 \text{ J}\).
▶️ Answer/Explanation
Phytoplankton are producers that convert solar energy into chemical energy via photosynthesis.
In an ecological pyramid, producers must have the largest biomass and population to support higher levels.
As energy moves up the food chain (from larvae to frogs to trout), approximately $90\%$ of energy is lost as heat.
Because only $10\%$ of energy is transferred to each succeeding level, fewer organisms can be supported at the top.
Therefore, a massive base of phytoplankton is required to sustain a very small number of apex predators like trout.
▶️ Answer/Explanation
Energy transfer in an ecosystem is always inefficient, with only about $10\%$ of energy moving to the next level.
Producers must contain the most energy to support the subsequent trophic levels.
As energy is lost as heat and through metabolic processes, each higher level receives significantly less energy.
Model B represents this “Energy Pyramid” where the base (producers) is the largest.
The narrowing shape reflects the decreasing energy available to primary, secondary, and tertiary consumers.
A stable ecosystem requires this broad base of producers to maintain higher-level consumers.
▶️ Answer/Explanation
A. Answer: C
The cell membrane contributes to homeostasis by acting as a selectively permeable barrier.
This means it regulates the passage of substances, allowing essential materials like water and nutrients to enter while keeping harmful substances out.
Option A is incorrect because a completely solid membrane would prevent necessary exchanges.
Option B is incorrect because cells need to transport ions and nutrients, not just water.
Option D is incorrect because unregulated transport would disrupt the internal balance.
A. Answer: B
The correct statement is: “The cell membrane maintains homeostasis by allowing water to exit the cell.”
In a high-salinity environment (hypertonic solution), the salt concentration outside the cell is higher than inside.
Water naturally moves from an area of high water concentration (inside) to low concentration (outside) via osmosis.
By allowing water to exit, the cell balances its internal concentration with the environment, preventing damage.
A. Answer: A
To test the hypothesis, the experiment must vary the salt concentration (the independent variable) while keeping the cell type constant.
Option A correctly uses the same cell type across different concentrations and measures size frequently to determine the speed of water movement.
Option B is incorrect because it uses only one concentration, so no comparison can be made.
Options C and D introduce a confounding variable (different fish species) and fail to measure the rate of change over time.
A. Answer: C
The food web shows a direct energy flow: Algae → Zooplankton → Finger Mullet.
If the algae population decreases, the zooplankton will have less food available, causing their population to decline.
With fewer zooplankton to eat, the finger mullet population will also decrease due to a lack of food resources.
This illustrates the “bottom-up” effect where changes at the producer level impact all higher consumer levels.
A. Answer: Statements 1, 3, and 6
Statement 1: The food web diagram shows only one arrow pointing to the red drum, coming from the finger mullet, meaning it is its sole energy source.
Statement 3: Phytoplankton are producers that create glucose and oxygen through photosynthesis; these products support the entire ecosystem, including the heron.
Statement 6: Energy is highest at the producer level (phytoplankton) and decreases by approximately 90% at each trophic level as heat.
Statements 2, 4, and 5 are false because seagrass is a producer (not consumer), algae produce their own glucose, and top predators have the least available energy.