Food Webs and Energy Flow in Aquatic Ecosystems

Which of the following best describes a food web?

• A simple chain showing one pathway of energy flow in an ecosystem.

• A complex model with many interconnected pathways through which energy flows in an ecosystem.

• A diagram showing only producers in an ecosystem.

• A list of all animals in an ecosystem.

Answer explanation

A food web is a complex model that illustrates the various interconnected pathways of energy flow among different organisms in an ecosystem, unlike a simple chain or a list of producers.

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What is the main role of producers in a food web?

• They consume other organisms for energy.

• They produce their own usable energy and provide energy for the entire food web.

• They decompose dead organisms.

• They only eat herbivores.

Answer explanation

Producers, like plants, create their own energy through photosynthesis. They form the base of the food web, supplying energy to herbivores and, subsequently, to higher trophic levels, making them essential for ecosystem functioning.

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Which of the following organisms is an example of a producer in an aquatic ecosystem?

• Green turtle

• Mollusk

• Algae

• Fish

Answer explanation

Algae are primary producers in aquatic ecosystems, converting sunlight into energy through photosynthesis. In contrast, green turtles, mollusks, and fish are consumers that rely on producers for food.

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Why are first-level consumers also called primary consumers?

• Because they produce their own food.

• Because they consume producers.

• Because they eat other consumers.

• Because they are always carnivores.

Answer explanation

First-level consumers, or primary consumers, are called so because they consume producers, which are typically plants or autotrophs. They rely on these producers for energy, making them essential in the food chain.

Green turtles and mollusks are examples of which category in an aquatic ecosystem?

• Producers

• Decomposers

• First-level or primary consumers

• Top predators

Answer explanation

Green turtles and mollusks are primary consumers in an aquatic ecosystem as they feed on producers like seagrass and algae, making them essential for energy transfer in the food web.

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Explain how energy flows from producers to first-level consumers in a food web.

• Producers eat first-level consumers, transferring energy.

• First-level consumers eat producers, obtaining energy produced by photosynthesis.

• Producers and first-level consumers share energy equally.

• Energy flows only between first-level consumers.

Answer explanation

Energy flows from producers to first-level consumers when the latter eat the former, obtaining energy produced by photosynthesis. This process is essential for sustaining the food web.

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Given an aquatic ecosystem, predict what might happen to the population of first-level consumers if the population of algae decreases significantly.

• The population of first-level consumers would likely increase.

• The population of first-level consumers would likely decrease.

• The population of first-level consumers would remain unchanged.

• The population of first-level consumers would become producers.

Answer explanation

If the population of algae decreases, first-level consumers, which rely on algae for food, would have less available energy and resources. This would likely lead to a decrease in their population.

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What is the main role of second-level or secondary consumers in a freshwater aquatic ecosystem?

• They produce their own food through photosynthesis.

• They prey on primary consumers.

• They decompose dead organic matter.

• They only eat plants.

Answer explanation

In a freshwater aquatic ecosystem, second-level or secondary consumers primarily prey on primary consumers, which are herbivores. This role helps maintain the balance of the ecosystem by controlling the population of primary consumers.

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Which of the following best describes a third-level or tertiary consumer in a freshwater aquatic ecosystem?

• A small fish that eats algae.

• A large carnivore or omnivore that consumes secondary consumers.

• An organism that only eats plants.

• A decomposer that breaks down dead material.

Answer explanation

A third-level or tertiary consumer is typically a large carnivore or omnivore that preys on secondary consumers, making the correct choice a large carnivore or omnivore that consumes secondary consumers.

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According to the food web, what type of consumer is a small fish in an aquatic ecosystem?

• Primary consumer

• Secondary consumer

• Tertiary consumer

• Producer

Answer explanation

In an aquatic ecosystem, small fish typically feed on primary consumers like zooplankton. Therefore, they are classified as secondary consumers, as they occupy the second trophic level in the food web.