Ecosystems Matter and Energy Flashcards

In a forest ecosystem, a deer eats plants, a wolf eats the deer, and fungi break down the wolf's remains after it dies. Which of the following correctly describes the flow of energy in this ecosystem?

Answer: Energy flows from the sun to the plants, then to the deer, and then to the wolf. Energy is transferred to the fungi from the wolf's remains.

Energy in most ecosystems originates from the sun and is captured by producers (plants) through photosynthesis. This energy is then transferred to primary consumers (deer) and then to secondary consumers (wolf). When the wolf dies, decomposers (fungi) obtain energy by breaking down its organic matter. Unlike matter, energy is not recycled; it flows through the ecosystem and is lost as heat at each transfer.

A biomass pyramid models the amount of living organic matter at each trophic level. In a stable grassland ecosystem, which trophic level would be expected to have the greatest amount of biomass?

Answer: Producers (e.g., grasses)

Producers form the base of the biomass pyramid and have the largest amount of living organic matter. This is because only a fraction of the energy and biomass from one trophic level is transferred to the next level above it. Therefore, the total mass of producers must be greater than the primary consumers they support, and so on up the pyramid.

A student is designing a model to illustrate the cycling of carbon in an ecosystem. To accurately represent the process, which of the following components is essential to include as a mechanism that returns carbon dioxide to the atmosphere?

Answer: Cellular Respiration

Cellular respiration is a process by which organisms (including plants, animals, and decomposers) break down organic compounds (like glucose) to release energy, with carbon dioxide being a primary waste product released back into the atmosphere. Photosynthesis removes CO2 from the atmosphere, transpiration releases water vapor, and nitrogen fixation converts nitrogen gas.

If the primary producers in a marine food web store 25,000 kcal of energy, approximately how much energy would be available to the tertiary consumers in that same food web?

Answer: 25 kcal

Only about 10% of the energy from one trophic level is transferred to the next. Therefore, primary consumers would receive about 2,500 kcal (10% of 25,000). Secondary consumers would receive about 250 kcal (10% of 2,500). Tertiary consumers would receive approximately 25 kcal (10% of 250).

Which of the following statements best describes the primary difference between how matter and energy move through an ecosystem?

Answer: Matter is cycled within the ecosystem, while energy flows through it.

The key principle of ecosystem dynamics is that matter (like carbon, nitrogen, and water) is continuously cycled between living and nonliving components. In contrast, energy flows in one direction: from the sun, through the trophic levels, and is eventually lost as heat. It is not recycled.

In an aquatic ecosystem, a sudden increase in agricultural runoff leads to eutrophication and a subsequent 'dead zone' where dissolved oxygen levels are extremely low. This condition is known as hypoxia. Which process is most directly inhibited in organisms living in this dead zone?

Answer: Aerobic cellular respiration

Aerobic cellular respiration is the process that uses oxygen to break down food molecules and release energy. In a hypoxic (low oxygen) environment, organisms that rely on this process cannot survive. Anaerobic respiration does not require oxygen. While the causes of the dead zone relate to photosynthesis (algal blooms), the direct process inhibited in animals by the lack of oxygen is aerobic respiration.