Ecosystems: Energy Flow and Matter Cycling — HS Environmental Science practice questions

Which statement about ecosystems is correct?

1. Energy cycles, while matter flows one way
2. Energy flows one way, while matter cycles
3. Both energy and matter cycle
4. Both energy and matter flow one way

Answer: B — Energy flows one way, while matter cycles

B) Correct — Sunlight enters and leaves as heat; atoms are reused. A) Reverses the two. C) Energy is lost as heat and must keep entering. D) Matter such as carbon and nitrogen is recycled.

Decomposers such as fungi and bacteria:

1. make food from sunlight
2. return nutrients to the soil
3. are the top predators
4. remove energy from the sun

Answer: B — return nutrients to the soil

B) Correct — They break down dead matter so nutrients can be reused. A) Producers do this. C) Decomposers feed on dead matter. D) Energy enters through producers.

Which pair of processes moves carbon in opposite directions?

1. Respiration and combustion
2. Combustion and decomposition
3. Evaporation and condensation
4. Photosynthesis and cellular respiration

Answer: D — Photosynthesis and cellular respiration

D) Correct — Photosynthesis removes CO₂; respiration releases it. A) Both release CO₂. B) Both release CO₂. C) Are steps of the water cycle.

Which cycle has no significant gas phase in the atmosphere?

1. Phosphorus cycle
2. Carbon cycle
3. Nitrogen cycle
4. Water cycle

Answer: A — Phosphorus cycle

A) Correct — Phosphorus moves through rocks, soil, water, and organisms. B) Has a large atmospheric pool of CO₂. C) The atmosphere is 78% N₂. D) Includes water vapor.

Producers capture 10,000 kcal. Using the 10% rule, about how much reaches tertiary consumers?

1. 1,000 kcal
2. 100 kcal
3. 1 kcal
4. 10 kcal

Answer: D — 10 kcal

D) Correct — 10,000 → 1,000 (primary) → 100 (secondary) → 10 (tertiary). A) Is the amount for primary consumers. B) Is the amount for secondary consumers. C) Is one level too many.

Transpiration is:

1. water soaking into the ground
2. water vapor turning into clouds
3. water vapor released from plant leaves
4. water flowing over land into streams

Answer: C — water vapor released from plant leaves

C) Correct — It moves large amounts of water into the air. A) Is infiltration. B) Is condensation. D) Is runoff.

Burning fossil fuels moves carbon from:

1. rock and sediment into the atmosphere
2. the atmosphere into rock
3. the ocean into the atmosphere
4. living plants into the soil

Answer: A — rock and sediment into the atmosphere

A) Correct — Coal, oil, and gas store carbon from ancient organisms. B) Reverses the direction. C) Fossil fuels are stored underground. D) Describes leaf litter and decomposition.

A food web differs from a food chain because a food web:

1. shows only one path of energy
2. includes no producers
3. shows how matter moves but not how energy moves
4. shows many connected feeding relationships

Answer: D — shows many connected feeding relationships

D) Correct — Most organisms eat, and are eaten by, more than one species. A) Describes a food chain. B) Every food web starts with producers. C) Both show who eats whom.

Nitrogen fixation is the process in which:

1. bacteria convert nitrate back into N₂ gas
2. bacteria convert ammonia into nitrate
3. bacteria convert N₂ gas into ammonia
4. plants release nitrogen gas from leaves

Answer: C — bacteria convert N₂ gas into ammonia

C) Correct — Many fixing bacteria live in nodules on legume roots. A) Is denitrification. B) Is nitrification. D) Plants cannot fix or release N₂ this way.

At deep-sea hydrothermal vents, the producers are bacteria that:

1. use sunlight to make food
2. eat dead fish that sink down
3. use chemical energy to make food
4. absorb heat directly as food

Answer: C — use chemical energy to make food

C) Correct — Chemosynthesis uses compounds such as hydrogen sulfide. A) No sunlight reaches the deep sea. B) Describes decomposers or scavengers. D) Organisms cannot use heat as food.

Nitrogen cycle?

N2 → fixation by bacteria → ammonia → nitrites → nitrates → plants → animals → decomposition → back.

Producer?

Makes own food (plants, algae). Base of food chain.

Water cycle?

Evaporation → condensation → precipitation → collection → repeats. Driven by sun.

Trophic levels?

Producers (1st), primary consumers (2nd), secondary (3rd), tertiary (4th).