Food Chains and Webs Practice Questions

Correct answer: Primary producers

Producers, or autotrophs, use photosynthesis to capture energy from sunlight and store it in organic molecules. This process provides the foundational energy source for all subsequent levels in the food chain.

Correct answer: An organism that consumes dead organic matter

Detritivores, such as earthworms and woodlice, consume decaying organic matter (detritus). By breaking down large pieces of waste, they assist decomposers in recycling nutrients back into the ecosystem.

Correct answer: It is lost as heat and used for metabolic processes.

Most energy consumed by an organism is used for life processes like movement, growth, and reproduction, or is lost to the environment as heat. Therefore, only a small fraction of the energy is available to be incorporated into new biomass for the next consumer.

Correct answer: Frog

The grass is the producer, the grasshopper is the primary consumer (herbivore), and the frog is the secondary consumer because it eats the primary consumer. The snake and hawk represent tertiary and quaternary consumers, respectively.

Correct answer: Pyramid of Numbers

While energy pyramids are always upright because energy is lost at each level, a pyramid of numbers can be inverted. For example, thousands of insects (primary consumers) might feed on a single large oak tree (producer).

Correct answer: Apex predators

This phenomenon is known as biomagnification. Because top predators eat many organisms from the levels below them, persistent toxins accumulate and reach much higher concentrations at the top of the food web.

Correct answer: The flow of energy between organisms

The arrows in a food web point from the organism being eaten to the organism that eats it. This signifies the transfer of chemical energy and nutrients from the 'prey' to the 'predator'.

Correct answer: Great White Shark

An apex predator sits at the top of the food web and has no natural predators of its own within that ecosystem. In many marine environments, the Great White Shark occupies this terminal trophic position.

Correct answer: Producer population will decrease due to overgrazing by herbivores.

This is an example of a trophic cascade. Without wolves to control the population of herbivores (like deer), the herbivore population grows and consumes more vegetation, leading to a decline in producers.

Correct answer: Sunlight availability

Abiotic factors are non-living components of an ecosystem. Sunlight is the primary abiotic energy source that limits the rate of photosynthesis in producers, thereby limiting the energy available to the entire food web.

Correct answer: Chemoautotroph

Chemoautotrophs, often found in deep-sea hydrothermal vent communities, use chemical energy from substances like hydrogen sulfide to synthesize organic compounds. They serve as the producers in ecosystems where sunlight cannot reach.

Correct answer: Omnivores

Omnivores, such as humans, bears, and pigs, occupy multiple trophic levels. This flexibility allows them to adapt to changes in food availability within a food web.

Correct answer: The total dry weight of organic matter at each level

Biomass is the total mass of living tissue within a given trophic level. Pyramids of biomass typically narrow toward the top because there is less energy available to support a large mass of higher-level consumers.

Correct answer: Phytoplankton

Phytoplankton are the microscopic producers in aquatic environments. In the Antarctic, they are the primary source of energy, which is then consumed by krill (primary consumers) and subsequently by larger animals.

Correct answer: Nutrient supply and producer productivity limiting higher trophic levels

Bottom-up control occurs when the population of higher trophic levels is determined by the availability of resources and the productivity of the producers at the base. If nutrients increase, the entire food web may see a rise in population.

Correct answer: Energy loss at each level leaves too little energy to support more levels.

Because roughly 90% of energy is lost as heat at each transfer, the amount of energy available to the top levels eventually becomes too small to support a viable population of even higher-level predators.

Correct answer: They recycle nutrients by breaking down organic remains.

Fungi and bacteria are decomposers. They complete the cycle of matter by breaking down dead organisms into simple inorganic nutrients, which can then be reused by producers.

Correct answer: Keystone species

Keystone species, like sea otters or beavers, play a vital role in maintaining the structure of a food web. Their presence or absence can trigger significant changes across multiple trophic levels.

Correct answer: A cow eating grass

Primary consumers are herbivores that feed directly on producers. In this example, the cow is the primary consumer because it eats the grass (producer).