AP Environmental Science Quiz: Food Chains And Food Webs

What this quiz covers

This quiz focuses on Food Chains And Food Webs, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Environmental Science.

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. They are always trophic level 1 because they start the chain
2. They operate outside a single trophic level by breaking down material from all levels (correct answer)
3. They are always tertiary consumers
4. They transfer energy upward to producers

Explanation: Trophic levels structure consumers, but decomposers like bacteria and fungi break down dead matter from all levels, recycling nutrients without a fixed level. Energy flows from phytoplankton (1) to zooplankton (2), sardines (3), dolphins (4), but decomposers process detritus separately. They are vital for nutrient return to producers, sustaining the web. Unlike consumers, they don't hunt but decompose. This role operates outside standard levels, emphasizing their unique ecosystem function.

Question 2

1. Anchovies
2. Copepods (correct answer)
3. Tuna
4. Sharks

Explanation: In marine food webs, trophic levels begin with producers like phytoplankton (level 1), followed by primary consumers (level 2) that eat them directly. Copepods are primary consumers as they feed on phytoplankton, gaining energy from producers. Higher consumers like anchovies (level 3), tuna (level 4), and sharks (level 5) eat those below. Decomposers recycle nutrients but are not consumers. This classification shows how energy diminishes upward, supporting vast producer bases for fewer top predators. Identifying primary consumers highlights the foundation of ocean productivity.

Question 3

1. Shrubs → rabbit → fox
2. Shrubs → insect → lizard → fox (correct answer)
3. Fox → lizard → insect → shrubs
4. Fungi → shrubs → insect → fox

Explanation: Trophic levels trace energy: level 1 producers (shrubs), level 2 primary (insect/rabbit), level 3 secondary (lizard), level 4 tertiary (fox eating lizard). Fox eating rabbit is level 3 (secondary). The pathway shrubs → insect → lizard → fox reaches tertiary consumer (level 4). Other paths are shorter, reversed, or start with decomposers. This shows multiple web pathways. Tertiary consumers receive least energy.

Question 4

1. Producer, because it lives on the fox
2. Consumer, because it obtains energy from the fox (correct answer)
3. Decomposer, because it breaks down fox tissue into nutrients
4. Primary consumer, because it eats grass through the fox

Explanation: Trophic levels focus on energy sources, with consumers obtaining energy from other organisms, including parasites like ticks that feed on hosts. Energy flows from producers through consumers, with parasites as specialized consumers. The tick is a consumer because it derives energy from the fox's blood. It is not a producer, decomposer (which acts on dead matter), or primary consumer (does not eat producers directly). Parasites fit into consumer categories, often as secondary or higher. This role affects host health and energy allocation in webs.

Question 5

1. Energy flows from hawks to songbirds to caterpillars to oak trees
2. Energy flows from oak trees to caterpillars to songbirds to hawks (correct answer)
3. Energy flows from decomposers to producers to consumers
4. Energy flows from wolves to deer to oak trees

Explanation: Energy flow in ecosystems follows a unidirectional path from producers to consumers, never in reverse. Producers like oak trees capture solar energy through photosynthesis and convert it into chemical energy stored in their tissues. This energy then flows to primary consumers (herbivores) when they eat the producers, then to secondary consumers when they eat the herbivores, and so on. In this forest food web, energy flows from oak trees to caterpillars (primary consumers), then from caterpillars to songbirds (secondary consumers), and finally from songbirds to hawks (tertiary consumers). This represents the fundamental principle that energy enters ecosystems through producers and flows upward through successive trophic levels, with significant energy loss at each transfer.

Question 6

1. Grass: 2; Rabbit: 1; Fox: 3; Decomposers: 4
2. Grass: 1; Rabbit: 2; Fox: 3; Decomposers: break down all levels (correct answer)
3. Grass: 1; Rabbit: 3; Fox: 2; Decomposers: producers
4. Grass: 4; Rabbit: 3; Fox: 2; Decomposers: 1

Explanation: Trophic levels are numbered starting with producers at level 1, then increasing with each consumer level. In this grassland chain, grass is the producer at trophic level 1, as it converts solar energy into chemical energy through photosynthesis. Rabbits eat the grass, making them primary consumers at trophic level 2. Foxes eat rabbits, placing them as secondary consumers at trophic level 3. Decomposers like fungi and bacteria don't fit into a single trophic level because they break down dead organic matter from all levels - dead grass, rabbits, and foxes. They recycle nutrients back into the soil for producers to use, playing a crucial role in nutrient cycling. Energy flows linearly through the main chain (grass → rabbit → fox), while decomposers work across all levels to complete the nutrient cycle.

Question 7

1. Cordgrass
2. Grasshopper
3. Frog (correct answer)
4. Heron

Explanation: In food chains, organisms are organized into trophic levels based on their feeding relationships. Producers (like cordgrass) occupy the first trophic level, primary consumers (herbivores like grasshoppers) occupy the second level, and secondary consumers (carnivores that eat herbivores) occupy the third level. In this coastal marsh chain, cordgrass is the producer, grasshoppers are primary consumers because they eat the plant directly, and frogs are secondary consumers because they eat the grasshoppers. Herons would be tertiary consumers as they eat the frogs. Energy flows from the sun to producers, then to primary consumers, secondary consumers, and so on, with approximately 90% of energy lost at each transfer due to metabolism and heat.

Question 8

1. Owls are producers because they are at the top of the web
2. Snakes can be secondary consumers and tertiary consumers depending on what they eat (correct answer)
3. Grasshoppers are decomposers because they eat plants
4. Energy flows from hawks to snakes to frogs to grasses

Explanation: In food webs, organisms can occupy different trophic levels depending on what they eat, demonstrating the complexity of real ecosystems. Snakes in this meadow web eat both frogs and mice, placing them at different trophic levels based on their prey. When snakes eat frogs (which eat grasshoppers that eat grass), they are tertiary consumers at level 4. When snakes eat mice (which eat grass directly), they are secondary consumers at level 3. This flexibility in feeding relationships is common in food webs and differs from simple food chains. Grasses are producers, not grasshoppers which are primary consumers. Owls are predators (consumers), not producers. Energy always flows from producers upward, not from top predators downward. The statement correctly identifies how snakes can function at multiple trophic levels within the same ecosystem.

Question 9

1. Sea urchins decrease, and kelp decreases
2. Sea urchins increase, and kelp decreases (correct answer)
3. Sea urchins increase, and kelp increases
4. Sea urchins decrease, and kelp increases

Explanation: This question illustrates a classic trophic cascade, where changes at one trophic level cause opposite effects at alternating levels below. Sea otters are keystone predators that control sea urchin populations through predation. When sea otter populations decline substantially, their predation pressure on sea urchins is reduced. This allows sea urchin populations to increase dramatically. Since sea urchins are voracious grazers of kelp, their population explosion leads to overgrazing and a significant decrease in kelp forests. This cascade demonstrates top-down control where predators indirectly benefit the producers by controlling herbivore populations. The loss of sea otters can transform entire kelp forest ecosystems into barren urchin-dominated areas, showing the critical importance of apex predators in maintaining ecosystem balance.

Question 10

1. Prairie grasses
2. Rabbit
3. Frog (correct answer)
4. Hawk

Explanation: Trophic levels represent the position of organisms in a food chain based on their source of energy. Level 1 consists of producers (prairie grasses), level 2 contains primary consumers that eat producers (rabbits and grasshoppers), and level 3 includes secondary consumers that eat primary consumers. In this grassland system, frogs occupy trophic level 3 because they eat grasshoppers, which are primary consumers. The energy flow follows: prairie grasses (level 1) → grasshoppers (level 2) → frogs (level 3) → snakes (level 4) → hawks (level 5). Each organism can only be assigned to one trophic level based on its primary food source, even though some organisms may feed at multiple levels in complex food webs.

Question 11

1. Small fish decrease, causing zooplankton to increase
2. Small fish increase, causing zooplankton to decrease (correct answer)
3. Zooplankton increase, causing algae to decrease
4. Hawks increase because snakes increase immediately

Explanation: In this pond food web, bass are predators that eat small fish, helping control their population. When bass are removed, their prey (small fish) lose a major predator and will likely increase in population in the short term. As small fish populations grow, they will consume more of their prey - the zooplankton. This increased predation pressure will cause zooplankton populations to decrease. This demonstrates top-down control in food webs, where removing a top predator causes cascading effects down the trophic levels. The effects on algae and other organisms would take longer to manifest as the changes work through the food web. Energy continues to flow from producers (algae) up through the consumers, but population dynamics shift when key predators are removed.

Question 12

1. Grass decreases because lions will eat more grass
2. Grass increases because one major herbivore is gone (correct answer)
3. Grass remains unchanged because decomposers control grass
4. Grass decreases because lizards will eat more grass

Explanation: Trophic levels in a food web represent the positions organisms occupy based on their role in energy transfer, starting with producers at level 1 that convert sunlight into chemical energy through photosynthesis. Primary consumers (herbivores) at level 2 eat producers, secondary consumers at level 3 eat primary consumers, and so on, with energy decreasing at each level due to the 10% rule where only about 10% of energy is passed on. In this savanna food web, grass is the producer, zebras and grasshoppers are primary consumers, lizards are secondary consumers, lions are tertiary consumers, and decomposers recycle nutrients. Removing zebras, a major herbivore, reduces the consumption of grass, allowing grass populations to increase in the short term as less biomass is eaten. This demonstrates top-down control where the absence of a primary consumer benefits the producer. Lions do not eat grass, and lizards eat grasshoppers, not grass, so they do not directly affect grass levels. Decomposers influence nutrient cycling but do not control grass population directly in the short term.

Question 13

1. Zooplankton
2. Phytoplankton
3. Jellyfish (correct answer)
4. Decomposers

Explanation: Trophic levels structure food webs by energy acquisition: producers (level 1) like phytoplankton photosynthesize, primary consumers (level 2) like zooplankton eat them, secondary consumers (level 3) eat primary consumers, and higher levels follow. Energy diminishes up the chain due to respiration and waste, following the 10% efficiency rule. Jellyfish, eating zooplankton, occupy level 3 as secondary consumers in this web. Small fish also eat zooplankton, making them secondary, while seabirds and sea turtles are tertiary. Decomposers recycle nutrients but are not consumers. This classification shows how energy flows from autotrophs to heterotrophs, supporting biodiversity.

Question 14

1. Snails
2. Dragonfly nymphs
3. Small fish (correct answer)
4. Herons

Explanation: Trophic levels in this pathway: cattails (1), snails (2), dragonfly nymphs (3), small fish (4), herons (5). Energy flows sequentially upward with losses. Small fish are at level 4, eating tertiary-level nymphs (wait, nymphs eat snails (2), so nymphs 3, fish 4). This positions fish as quaternary consumers in this chain. Webs allow varying levels per path. Identifying levels aids in energy pyramid construction.

Question 15

1. Snake and frog populations increase due to reduced predation (correct answer)
2. Rabbit population decreases due to fewer producers
3. Grasshopper population decreases because frogs decrease
4. Bacteria population disappears because hawks are gone

Explanation: Trophic levels define energy positions, with producers at 1, primary consumers at 2, secondary at 3, tertiary at 4, and decomposers recycling matter outside the main levels. Energy flows upward but diminishes, influencing population sizes. Removing hawks (tertiary consumers) reduces predation on snakes and frogs (secondary consumers), likely causing their populations to increase. This is a top-down trophic cascade effect. Rabbits and grasshoppers may indirectly benefit, but producers do not decrease. Bacteria persist as decomposers regardless of hawks.

Question 16

1. Sea urchins decrease, causing kelp to increase
2. Sea urchins increase, causing kelp to decrease (correct answer)
3. Kelp increases because it becomes a consumer
4. Sea otters increase because sea urchins increase

Explanation: Trophic levels enable cascades where removing top predators disrupts balance: level 1 kelp, level 2 urchin, level 3 otter. Energy flows upward, but predation controls populations. Removing otters allows urchins to increase, overgrazing kelp, causing kelp decrease. Urchins do not decrease without predators. Kelp remains producer, otters do not increase. This classic example shows keystone species' role in stability.

Question 17

1. Snake
2. Vole (correct answer)
3. Hawk
4. Grass

Explanation: Primary consumers (trophic level 2) eat producers directly, like voles eating grass (level 1) in this chain, followed by snakes (3) and hawks (4). Energy flows from grass to vole to snake to hawk, decreasing each step. The vole is primary as the first consumer. This distinguishes herbivores from carnivores. Understanding helps trace energy paths and predict biomass distributions.

Question 18

1. Mouse (correct answer)
2. Robin
3. Oak tree
4. Fungi

Explanation: Food webs are complex networks of interconnected food chains, where organisms can occupy multiple trophic roles depending on what they eat. Producers like the oak tree are at level 1, primary consumers eat producers (level 2), and secondary consumers eat primary consumers (level 3). Energy flows from producers to consumers, but organisms like omnivores can feed at different levels. In this web, the mouse can act as a primary consumer by eating oak tree parts (e.g., acorns) and as a secondary consumer by potentially eating caterpillars, which are primary consumers. This dual role makes the mouse versatile, allowing it to switch food sources based on availability. In contrast, the robin primarily eats caterpillars (secondary consumer), and the oak tree is a producer, while fungi are decomposers. Understanding such flexibility shows how food webs provide resilience compared to simple chains.

Question 19

1. Snowy owl populations decrease due to less prey (correct answer)
2. Lichens decrease because fewer lemmings recycle nutrients
3. Arctic foxes increase because they switch to eating lichens
4. Wolves increase because they can eat snowy owls

Explanation: In tundra ecosystems, food webs are relatively simple with few alternative prey options for predators. When lemming populations decline sharply, their predators - snowy owls and arctic foxes - lose a major food source. Snowy owls, being specialized predators that rely heavily on lemmings, will likely experience population decreases due to reduced prey availability. They may emigrate to find food elsewhere or experience reduced breeding success and survival. Arctic foxes might be somewhat buffered if they can switch to alternative prey or scavenging, but they too will be negatively impacted. This demonstrates how population fluctuations at one trophic level can cascade through the food web, particularly affecting specialist predators that depend heavily on a single prey species.

Question 20

1. Snake
2. Hawk
3. Rabbit (correct answer)
4. Decomposer (fungus)

Explanation: Primary consumers are herbivores that feed directly on producers (plants) and occupy the second trophic level in a food chain. In this meadow ecosystem, clover serves as the producer at the first trophic level. Both mice and rabbits eat the clover directly, making them both primary consumers at trophic level 2. These herbivores convert plant material into animal biomass, making energy available to higher trophic levels. Snakes and foxes are secondary consumers (trophic level 3) because they eat the primary consumers, while hawks are tertiary consumers (trophic level 4) feeding on secondary consumers. The question asks specifically about primary consumers, and among the options given, only the rabbit fits this category as it feeds directly on the producer.