AP Biology Quiz: Energy Flow Through Ecosystems

What this quiz covers

This quiz focuses on Energy Flow Through Ecosystems, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Consumer-to-consumer efficiency is 5%, which is lower than the producer-to-consumer efficiency of 12%. (correct answer)
2. Consumer-to-consumer efficiency is 12%, which is higher than the producer-to-consumer efficiency of 5%.
3. Both efficiencies are 100% because termites and aardvarks convert all ingested energy to biomass.
4. Producer-to-consumer efficiency is 60% because 4,800 kJ is close to 40,000 kJ in magnitude.
5. Efficiencies cannot be compared because producers measure energy while consumers measure matter only.

Explanation: This question compares energy flow efficiencies between different trophic level transfers. Producer-to-consumer efficiency (grasses to termites) is 12% (4,800/40,000 = 0.12). Consumer-to-consumer efficiency (termites to aardvarks) is 5% (240/4,800 = 0.05). This shows that consumer-to-consumer transfer (5%) is less efficient than producer-to-consumer transfer (12%), supporting answer A. Answer B reverses these values, confusing which transfer is more efficient. To compare efficiencies between different trophic transfers, calculate each percentage separately and recognize that herbivore efficiency often exceeds carnivore efficiency.

Question 2

1. The detrital pathway supports more predator biomass energy than the grazing pathway in this ecosystem. (correct answer)
2. The grazing pathway supports more predator biomass energy because producers directly feed predators.
3. Both pathways support equal predator biomass energy because energy transfer is always 10% per step.
4. Predator biomass energy is higher on the grazing pathway because detritus contains no energy.
5. Neither pathway can support predators because energy is recycled back to producers each step.

Explanation: This question tests energy flow analysis through different ecosystem pathways. The detrital pathway shows 360 kJ in predators from 6,000 kJ in detritivores (6% efficiency). The grazing pathway shows 240 kJ in predators from 3,000 kJ in grazers (8% efficiency). While the grazing pathway has higher efficiency, the detrital pathway supports more total predator biomass energy (360 kJ > 240 kJ) because it starts with more energy at the detritivore level. Answer D incorrectly claims detritus contains no energy, ignoring that dead organic matter is an important energy source. When comparing pathways, consider both the efficiency and the absolute energy values at each level.

Question 3

1. Zooplankton biomass energy would most likely decrease to about 600 kJ over the interval. (correct answer)
2. Zooplankton biomass energy would most likely increase to about 2,400 kJ over the interval.
3. Small fish biomass energy would most likely remain near 120 kJ because consumers regulate energy flow.
4. Small fish biomass energy would most likely increase because less producer energy reduces respiration losses.
5. Zooplankton biomass energy would most likely stay constant because energy cycles within ecosystems.

Explanation: This question requires analyzing energy flow to predict ecosystem changes when producer energy decreases. The original transfer efficiency from phytoplankton to zooplankton is 10% (1,200/12,000 = 0.10). If phytoplankton energy drops to 6,000 kJ and the same 10% efficiency applies, zooplankton would receive 600 kJ (6,000 × 0.10 = 600). This matches answer A, showing that energy at higher trophic levels decreases proportionally when producer energy decreases. Answer E incorrectly claims energy cycles within ecosystems, confusing energy flow (one-way) with nutrient cycling (circular). When producer energy changes, multiply the new producer value by the original transfer efficiency to predict consumer energy.

Question 4

1. About 10% transfers from producers to herbivores, and about 8% from herbivores to carnivores. (correct answer)
2. Energy transfer is 100% efficient because all consumed biomass becomes new consumer biomass.
3. More energy is transferred to carnivores than to herbivores because carnivores are higher trophic level.
4. Matter is lost between trophic levels, so energy transfer cannot be calculated from biomass values.
5. About 8% transfers from producers to herbivores, and about 10% from herbivores to carnivores.

Explanation: This question tests your ability to analyze energy flow through trophic levels by calculating transfer efficiencies. From producers to herbivores, 5,000 kJ out of 50,000 kJ transfers, which equals 10% (5,000/50,000 = 0.10). From herbivores to carnivores, 400 kJ out of 5,000 kJ transfers, which equals 8% (400/5,000 = 0.08). These calculations match answer A exactly. Answer B incorrectly assumes 100% efficiency, ignoring that organisms lose most energy through respiration, movement, and heat production. To solve energy transfer problems, calculate the percentage by dividing energy at the higher level by energy at the lower level, then multiply by 100.

Question 5

1. The new predator would store about 9 kJ/m$^2$/yr as new biomass. (correct answer)
2. The new predator would store about 900 kJ/m$^2$/yr as new biomass.
3. The new predator would store about 90 kJ/m$^2$/yr as new biomass.
4. The new predator would store about 9,000 kJ/m$^2$/yr as new biomass.
5. The new predator would store increasing energy because predators concentrate energy from prey.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, A, is supported because each existing transfer shows about 10% efficiency, with zooplankton storing 900 kJ/m²/yr (10% of 9,000) and small fish storing 90 kJ/m²/yr (10% of 900). Applying the same efficiency, the new predator would store 10% of 90 kJ/m²/yr, which is 9 kJ/m²/yr, reflecting ongoing energy loss through metabolic processes. This prediction uses the pattern of diminishing energy availability at higher trophic levels due to incomplete transfer. A tempting distractor, E, is wrong because it assumes predators concentrate energy upward, a misconception ignoring the second law of thermodynamics and energy dissipation. To analyze similar problems, identify the transfer efficiency pattern and multiply the last level's energy by that efficiency to predict the next.

Question 6

1. Rabbits store about 20% of plant energy because 900 is one-twentieth of 18,000.
2. Hawks store about 5% of rabbit energy because 45 is one-twentieth of 900. (correct answer)
3. Plants store about 5% of hawk energy because producers depend on consumer biomass.
4. Energy increases from rabbits to hawks because hawks consume many rabbits.
5. Rabbits are secondary consumers because their stored energy exceeds hawk stored energy.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, B, is supported because hawks store 45 kJ/m²/yr, which is 5% of rabbits' 900 kJ/m²/yr, as 45 is indeed one-twentieth of 900. This low efficiency underscores energy losses in predation, including hunting costs and uneaten prey. Rabbits store 5% of plant energy, maintaining consistency in transfer logic. A tempting distractor, A, is wrong because it incorrectly states 20% for rabbits while using one-twentieth (which is 5%), a misconception from arithmetic error. To analyze similar problems, verify percentages by division and check fractional descriptions for accuracy.

Question 7

1. Energy transfer between trophic levels is roughly 10% at each step in this chain. (correct answer)
2. Crabs receive 200 kJ/m$^2$/yr directly from cordgrass because energy bypasses snails.
3. Energy increases at higher trophic levels because consumers combine energy from many producers.
4. Snails are decomposers, so their biomass energy should exceed cordgrass biomass energy.
5. Energy is conserved within the chain, so total stored energy across levels must equal 20,000 kJ/m$^2$/yr.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, A, is supported because snails store 2,000 kJ/m²/yr, exactly 10% of cordgrass's 20,000 kJ/m²/yr, and crabs store 200 kJ/m²/yr, 10% of snails', demonstrating consistent trophic transfer. This pattern arises from energy losses via heat, excretion, and uneaten biomass, adhering to the 10% rule. The data illustrate unidirectional energy flow, decreasing at each step. A tempting distractor, C, is wrong because it suggests energy increases upward, a misconception confusing energy accumulation with the reality of dissipation. To analyze similar problems, verify if transfers approximate 10% by calculating ratios and assess overall flow direction.

Question 8

1. Energy loss is smallest from mosses to lemmings because 400 kJ is greater than 40 kJ.
2. About 5% of producer energy is stored as new biomass in lemmings. (correct answer)
3. Foxes must be primary consumers because their biomass energy is lower than lemmings.
4. Energy transfer exceeds 50% at each step because tundra ecosystems have low productivity.
5. Energy increases upward because predators accumulate energy from multiple prey individuals.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, B, is supported because lemmings store 400 kJ/m²/yr, which is 5% of mosses' 8,000 kJ/m²/yr, indicating significant energy loss at the primary consumer level. This low efficiency may relate to tundra constraints like short growing seasons affecting productivity transfer. Foxes then store 10% of lemming energy, showing variable losses but overall reduction. A tempting distractor, A, is wrong because it focuses on absolute values rather than percentages, a misconception ignoring relative efficiency. To analyze similar problems, calculate the percentage of producer energy reaching each consumer level to quantify cumulative losses.

Question 9

1. Energy transfer is most efficient from frogs to grasshoppers because frogs store less energy overall.
2. Approximately 10% of producer NPP is stored as new biomass in primary consumers. (correct answer)
3. Energy is recycled between trophic levels, so frog biomass energy returns to grasses each year.
4. Most energy is transferred upward, so frog biomass should exceed grasshopper biomass in kJ/m$^2$/yr.
5. The second transfer is more efficient because 120 kJ is closer to 1,200 than 1,200 is to 12,000.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, B, is supported because the energy stored in grasshoppers is 1,200 kJ/m²/yr, which is exactly 10% of the 12,000 kJ/m²/yr from grasses, indicating typical trophic efficiency where only a fraction of energy is transferred. Similarly, the transfer to frogs is 120 kJ/m²/yr, also 10% of the grasshopper energy, showing consistent loss due to respiration, heat, and uneaten biomass. This logic aligns with the 10% rule in ecology, where approximately 10% of energy is passed to the next level as new biomass. A tempting distractor, E, is wrong because it misinterprets efficiency by focusing on absolute differences rather than ratios, a common misconception of proportional energy transfer. To analyze similar problems, always calculate the percentage of energy transferred between levels by dividing the biomass energy of the consumer by that of its prey.

Question 10

1. Seals will have higher biomass production because longer food chains concentrate energy at the top.
2. Penguins will have higher biomass production because fewer trophic transfers reduce cumulative energy loss. (correct answer)
3. Both tops will have equal biomass production because they start with identical phytoplankton production.
4. Seals will have higher biomass production because energy increases with each consumer level.
5. Both tops will have near-zero biomass production because energy is recycled back to producers each step.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by comparing biomass production in marine food chains with different lengths. With ~10% efficiency per transfer, the shorter chain to penguins accumulates less cumulative loss, yielding higher top-level biomass (100 kJ/m²/yr) compared to the longer chain to seals (10 kJ/m²/yr). This occurs because each additional trophic level introduces more energy dissipation through respiration and waste, reducing available energy for top consumers. Therefore, choice B is correct in predicting higher penguin biomass due to fewer transfers. A tempting distractor is choice A, which is wrong because it assumes longer chains concentrate energy, a misconception that reverses the actual pattern of energy dilution up the chain. To compare food chains, multiply the initial production by the efficiency raised to the power of the number of transfers for accurate top-level estimates.

Question 11

1. Trophic efficiency increases at higher levels because lizards store a larger fraction of insect energy.
2. Trophic efficiency from producers to insects is about 5%, and from insects to lizards is about 10%. (correct answer)
3. Energy transfer is 100% efficient because all shrub energy becomes insect biomass each year.
4. Matter transfer is lower than energy transfer, so lizards must gain more mass than insects lose.
5. Energy stored at each level is similar, indicating minimal loss as energy moves through the chain.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, B, is supported because insects store 250 kJ/m²/yr, which is 5% of the shrubs' 5,000 kJ/m²/yr, indicating lower efficiency possibly due to desert conditions affecting consumption. Lizards then store 25 kJ/m²/yr, which is 10% of the insects' energy, showing variation in transfer rates between levels. This reflects how energy is lost at each step through respiration and unconsumed matter, with efficiencies often around 5-20%. A tempting distractor, E, is wrong because it claims similar energy storage across levels, a misconception overlooking the pyramid of energy and progressive losses. To analyze similar problems, compute efficiencies as percentages between consecutive levels and compare them to typical ecological ranges.

Question 12

1. Energy transfer from grasses to mice is about 5%, and from mice to owls is also about 5%. (correct answer)
2. Energy transfer from grasses to mice is about 20%, and from mice to owls is about 10%.
3. Energy transfer from grasses to mice is about 50%, because mice consume many grass plants.
4. Energy transfer from mice to owls is about 0.25%, because 20 is 0.25% of 8,000.
5. Energy transfer is identical to biomass transfer, so percent efficiency cannot be calculated.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by determining transfer efficiencies in a grassland chain. Both grass-to-mouse (400/8,000 = 5%) and mouse-to-owl (20/400 = 5%) transfers show ~5% efficiency, reflecting significant losses from uneaten biomass, digestion inefficiencies, and heat at each step. This low but consistent rate is plausible in ecosystems with high metabolic demands or sparse consumption. Therefore, choice A is accurate in stating ~5% for both transfers. A tempting distractor is choice B, which incorrectly calculates grass-to-mouse as 20% due to a misreading of the ratio, exemplifying a percentage calculation misconception. To evaluate chains, compute individual level-to-level ratios separately for a clear picture of energy dynamics.

Question 13

1. Bird biomass production would be about 3 kJ/m$^2$/yr, reflecting another ~10% transfer step. (correct answer)
2. Bird biomass production would be about 30 kJ/m$^2$/yr, because birds occupy the top trophic level.
3. Bird biomass production would be about 300 kJ/m$^2$/yr, because birds can access insect energy directly.
4. Bird biomass production would be about 6,000 kJ/m$^2$/yr, because producer energy supports all consumers equally.
5. Bird biomass production would be about 0 kJ/m$^2$/yr, because energy cannot move beyond secondary consumers.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by forecasting biomass in an extended coastal chain. Assuming continued ~10% efficiency, bird biomass would be about 10% of lizard biomass (30 kJ/m²/yr), or 3 kJ/m²/yr, as each added level incurs further energy loss through typical ecological processes. This extension maintains the observed pattern from producers (6,000 kJ) to insects (300 kJ) to lizards (30 kJ). Choice A correctly predicts this outcome based on the given efficiency. A tempting distractor is choice B, which overestimates at 30 kJ by assuming top-level privilege without losses, a misconception ignoring progressive energy reduction. When modeling additions to chains, apply the established efficiency to the immediate prior level for reliable predictions.

Question 14

1. Fish store about 0.5% of the algae biomass energy because energy is lost at each transfer step. (correct answer)
2. Fish store about 5% of the algae biomass energy because only one transfer separates fish from algae.
3. Fish store about 50% of the algae biomass energy because consumers convert most food to biomass.
4. Fish store more energy than algae because energy accumulates at higher trophic levels in ponds.
5. Fish store the same energy as algae because energy is conserved and therefore equally distributed.

Explanation: This question analyzes energy flow through two consumer levels above primary producers. Fish store 100 kJ while algae store 20,000 kJ, giving a ratio of 100/20,000 = 0.005 = 0.5%. This matches answer A, showing how energy diminishes across two trophic transfers (algae → larvae → fish). Answer B incorrectly assumes only one transfer exists, missing that fish are secondary consumers eating primary consumers (larvae). To determine relative energy storage across multiple levels, divide the higher-level consumer energy by the producer energy to find the overall transfer efficiency.

Question 15

1. Energy stored in biomass decreases by roughly a factor of 10 at each higher trophic level here. (correct answer)
2. Energy stored in biomass increases at higher trophic levels because consumers have more complex tissues.
3. Energy stored in biomass remains constant because energy is conserved within organisms across levels.
4. Energy stored in biomass decreases because matter is destroyed during feeding interactions.
5. Energy stored in biomass is greatest in snakes because they are the top consumers in the chain.

Explanation: This question analyzes energy flow patterns across multiple trophic levels in a meadow ecosystem. The energy decreases by approximately a factor of 10 at each level: plants (100,000) to grasshoppers (9,000) is 9% transfer, grasshoppers to frogs (900) is 10% transfer, and frogs to snakes (90) is 10% transfer. This consistent pattern of roughly 10% efficiency between levels supports answer A. Answer B incorrectly suggests energy increases at higher levels, violating the second law of thermodynamics. To identify energy flow patterns, calculate the ratio between consecutive trophic levels and look for consistent transfer efficiencies.

Question 16

1. About 9,000 kJ/m$^2$/yr, because energy is conserved through trophic transfers.
2. About 900 kJ/m$^2$/yr, because zooplankton pass most energy directly to large fish.
3. About 90 kJ/m$^2$/yr, because large fish receive energy equal to small fish growth.
4. About 9 kJ/m$^2$/yr, assuming ~10% transfer efficiency from small fish to large fish. (correct answer)
5. About 0 kJ/m$^2$/yr, because predators cannot convert prey energy into biomass.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by predicting biomass production in a lake food web based on trophic transfers. Given the pattern of 9,000 kJ/m²/yr in phytoplankton decreasing to 900 in zooplankton and 90 in small fish, each step shows about 10% transfer efficiency, so large fish, feeding on small fish, would likely store around 9 kJ/m²/yr. This prediction follows the logic that energy is lost at each level through respiration, excretion, and incomplete consumption, leaving only a fraction available for the next trophic level. Thus, choice D is supported as it applies the ~10% efficiency to the small fish biomass. A tempting distractor is choice A, which is incorrect due to the misconception that energy is conserved without losses, ignoring the second law of thermodynamics that dictates energy dissipation in ecosystems. When predicting energy flow, extend observed transfer efficiencies to higher levels by multiplying the lower level's biomass by the efficiency percentage.

Question 17

1. Overall efficiency from producers to owls is $35/10{,}000=0.35\%$ for biomass energy stored. (correct answer)
2. Overall efficiency from producers to owls is $35/700=5\%$ because owls eat lemmings directly.
3. Overall efficiency from producers to owls is $700/10{,}000=7\%$ because owls depend on plants.
4. Overall efficiency is 35% because 35 kJ is the energy available to the entire ecosystem.
5. Overall efficiency cannot be computed because energy is recycled between trophic levels each season.

Explanation: This question examines energy flow efficiency across multiple trophic levels in a tundra ecosystem. The overall efficiency from producers to owls is calculated by dividing owl energy by producer energy: 35/10,000 = 0.0035 = 0.35%. This matches answer A exactly, showing how energy diminishes across two trophic transfers. Answer B incorrectly calculates efficiency using only the intermediate level (lemmings), missing the complete producer-to-top-consumer pathway. To find overall efficiency across multiple levels, divide the final consumer's energy by the original producer's energy, not by intermediate levels.

Question 18

1. Transfer efficiency is about 5%, indicating most producer energy is not converted to rodent biomass. (correct answer)
2. Transfer efficiency is about 50%, because 250 kJ is half of 5,000 kJ.
3. Transfer efficiency is about 95%, because only 250 kJ is missing from the producers.
4. Transfer efficiency cannot be estimated without measuring decomposer biomass in the soil.
5. Energy transfer is 0%, because energy cannot move between trophic levels in deserts.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by calculating transfer efficiency between producers and primary consumers in a desert. The rodent biomass of 250 kJ is 5% of the shrub biomass of 5,000 kJ, indicating low transfer efficiency where most producer energy is lost to heat, decomposition, or not consumed. This low efficiency is typical in ecosystems due to factors like indigestible plant material and consumer metabolism, supporting that substantial energy is not converted to consumer biomass. Choice A correctly identifies this ~5% transfer. A tempting distractor is choice B, which errs by miscalculating the percentage as 50% instead of 5%, stemming from the misconception of inverting the ratio or confusing halves with percentages. For evaluating trophic transfers, always divide the higher level's energy by the lower level's to find the precise efficiency percentage.

Question 19

1. Sunfish would support fewer top predators because only about 60 kJ/m$^2$/yr is available above them. (correct answer)
2. Snails are producers because their biomass energy is closer to plants than to sunfish.
3. Energy is conserved across trophic levels, so plants must lose exactly 5,340 kJ/m$^2$/yr as matter.
4. Energy transfer from plants to snails is 60% because 600 is 60% of 6,000.
5. Energy transfer from snails to sunfish is 1% because 60 is 1% of 6,000.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, A, is supported because sunfish store 60 kJ/m²/yr, leaving limited energy for higher predators due to 10% transfer efficiencies observed from plants to snails and snails to sunfish. This implies fewer or smaller top predators, as energy pyramids narrow upward. The pattern shows progressive reduction, limiting biomass at apex levels. A tempting distractor, D, is wrong because it calculates 60% transfer incorrectly (600 is 10% of 6,000), a misconception from misapplying percentages. To analyze similar problems, project energy availability to hypothetical higher levels using observed efficiencies to predict ecosystem limits.

Question 20

1. Songbirds would support a larger biomass than caterpillars because higher trophic levels are more efficient.
2. About 90% of energy is transferred at each step because the numbers decrease by a factor of 10.
3. Approximately 10% of energy stored in caterpillar biomass is stored in songbird biomass. (correct answer)
4. Energy is recycled to producers, so leaf biomass energy should increase when songbirds increase.
5. Caterpillars occupy a higher trophic level than songbirds because they have more stored energy.

Explanation: This question assesses the skill of analyzing energy flow through ecosystems by examining biomass energy storage across trophic levels. The correct answer, C, is supported because songbirds store 150 kJ/m²/yr, which is 10% of the caterpillars' 1,500 kJ/m²/yr, highlighting the fraction of energy converted to consumer biomass. This transfer reflects losses from incomplete consumption and metabolic inefficiencies. Similarly, caterpillars store 10% of leaf energy, confirming the pattern of energy diminution. A tempting distractor, B, is wrong because it claims 90% transfer, a misconception inverting the typical 10% efficiency rule. To analyze similar problems, focus on the ratio of energy in consecutive levels to determine transfer percentages and trophic relationships.