HS Environmental Science practice questions and exam guide

Which biome has permanently frozen subsoil and no trees?

1. Taiga
2. Tundra
3. Desert
4. Grassland

Answer: B — Tundra

B) Correct — Permafrost and a short growing season keep plants low. A) Has coniferous forests. C) Is defined by low rainfall, and can be hot or cold. D) Has deep, thawed soils.

Which statement is a hypothesis rather than an observation?

1. More nitrate will increase algae growth
2. The pond water looks green
3. The nitrate level was 5 mg/L
4. Algae covered half of the pond's surface on Monday

Answer: A — More nitrate will increase algae growth

A) Correct — A hypothesis is a testable prediction. B) Is an observation. C) Is a measurement. D) Is an observation.

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.

A population grows 2% per year. Using the rule of 70, about how long until it doubles?

1. 35 years
2. 140 years
3. 50 years
4. 20 years

Answer: A — 35 years

A) Correct — Doubling time ≈ 70 ÷ growth rate (%) = 70 ÷ 2. B) Multiplies 70 × 2. C) Divides 100 by 2. D) Divides 70 by 3.5, not 2.

Highways split a forest into small patches. Which solution best helps wildlife move between patches?

1. Wildlife corridors
2. Wider highways
3. Removing predators
4. Planting a single crop between patches

Answer: A — Wildlife corridors

A) Correct — Strips of habitat or overpasses connect fragments. B) Would increase fragmentation. C) Does not reconnect habitat. D) Monocultures provide poor habitat.

Overgrazing harms grasslands by:

1. adding too many nutrients to the soil
2. removing plant cover so soil erodes
3. increasing plant diversity
4. raising groundwater levels

Answer: B — removing plant cover so soil erodes

B) Correct — Bare soil is blown and washed away. A) Overgrazing strips plants and soil. C) Usually decreases it. D) Has the opposite effect.

About what share of Earth's water is fresh water?

1. About 50%
2. About 30%
3. About 97%
4. About 3%

Answer: D — About 3%

D) Correct — Most of that is frozen in ice caps and glaciers. A) Most water is salty ocean water. B) Far too high. C) Is the share of salt water.

A catalytic converter in a car reduces:

1. carbon dioxide emissions from the exhaust
2. the amount of fuel the engine burns
3. noise from the engine
4. carbon monoxide, NOₓ, and unburned fuel

Answer: D — carbon monoxide, NOₓ, and unburned fuel

D) Correct — It converts them to CO₂, N₂, and water. A) It actually produces CO₂ from CO. B) It cleans exhaust; it does not save fuel. C) A muffler reduces noise.

Melting Arctic ice speeds up warming because:

1. ice releases CO₂ as it melts
2. open water reflects more sunlight
3. ice blocks the greenhouse effect
4. darker ocean water absorbs more sunlight

Answer: D — darker ocean water absorbs more sunlight

D) Correct — This loss of reflectivity (albedo) is a positive feedback. A) The main effect is reduced reflection. B) Reverses the effect. C) Ice does not block greenhouse gases.

A major drawback of nuclear fission power is:

1. high CO₂ emissions during operation
2. output that depends on the weather
3. long-lived radioactive waste
4. short plant lifetimes

Answer: C — long-lived radioactive waste

C) Correct — It stays dangerous for thousands of years; safe long-term storage is a challenge. A) Nuclear plants emit very little CO₂. B) Describes wind and solar. D) Plants often run 40 years or more.

Microplastics are a concern because they:

1. dissolve quickly in water
2. persist and enter food webs
3. are too small to affect organisms
4. come only from fishing nets

Answer: B — persist and enter food webs

B) Correct — They last for centuries and are found in oceans, soil, and even human blood. A) They persist. C) Animals eat them. D) They come from many sources.

The National Environmental Policy Act (NEPA) requires federal agencies to:

1. ban all pollution
2. charge a carbon tax
3. prepare environmental impact statements
4. require recycling in every state

Answer: C — prepare environmental impact statements

C) Correct — Major federal projects must study their environmental effects. A) NEPA does not ban pollution. B) NEPA sets no tax. D) NEPA does not mandate recycling.

Sustainable agriculture practices?

Crop rotation, cover crops, integrated pest management, no-till, organic.

Catalytic converters vs scrubbers?

Catalytic converters (cars) turn CO, NOₓ, and unburned fuel into CO₂, N₂, and water. Scrubbers (smokestacks) remove SO₂.

Personal actions for environment?

Reduce energy, walk/bike/transit, eat less meat, reduce waste, support conservation, vote.

Ecosystem?

Community of organisms + their physical environment, interacting.

Population pyramid?

Graph showing age + sex distribution. Shape indicates demographics.

Worked example — Radioactive half-life: Plutonium-239 has a half-life of ~24,000 years. If a sample contains 800 g today, how much remains after 72,000 years (assuming no removal)?

Step 1 — Find number of half-lives: 72,000 ÷ 24,000 = 3 half-lives. Step 2 — Apply halving: 800 → 400 (1) → 200 (2) → 100 g (3). Step 3 — Interpret: 100 g remains after 72,000 years. This is why high-level nuclear waste storage must be secure for hundreds of thousands of years — a key challenge for nuclear power.