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DSST Environmental Science study materials
DSST Environmental Science study resources

DSST Environmental Science practice questions

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Question 1Integrated subject knowledge, evidence and application

In ecology, what is the best distinction between a habitat and a niche?

  1. A habitat is where an organism lives; a niche is its role and resource use Correct answer.
  2. A habitat is a feeding level; a niche is a climate zone
  3. A habitat is always smaller than a niche
  4. A habitat describes genes; a niche describes chromosomes

Explanation

A habitat is the physical place where an organism lives. A niche includes how the organism uses resources, interacts with other organisms, and fits into ecosystem processes.

Question 2Integrated subject knowledge, evidence and application

Why does less energy usually reach each higher trophic level in a food chain?

  1. Most energy is lost as heat through metabolism and maintenance Correct answer.
  2. Energy is created only by top predators
  3. Decomposers block energy from moving upward
  4. Matter disappears at each feeding step

Explanation

Energy transfer between trophic levels is inefficient because organisms use much of the energy they consume for respiration, movement, growth, and heat loss. This is why food chains are usually short and top predators are less abundant.

Question 3Integrated subject knowledge, evidence and application

A bee obtains nectar while pollinating a flowering plant. Which relationship is most directly illustrated?

  1. Parasitism
  2. Mutualism Correct answer.
  3. Predation
  4. Amensalism

Explanation

Mutualism occurs when both species benefit from an interaction. The bee receives food, and the plant gains pollen transfer that can support reproduction.

Question 4Integrated subject knowledge, evidence and application

A lake supports about the same maximum biomass of fish year after year unless nutrient levels or habitat change. What ecological idea does this best represent?

  1. Primary succession
  2. Carrying capacity Correct answer.
  3. Speciation
  4. Ecological footprint

Explanation

Carrying capacity is the maximum population size or biomass that an environment can sustain over time given available resources and limiting factors. It can change when food, habitat, predation, disease, or water quality changes.

Question 5Integrated subject knowledge, evidence and application

Which situation is the clearest example of primary succession?

  1. A forest regrows from roots after a low-intensity fire
  2. Lichens and mosses colonize newly exposed bare rock Correct answer.
  3. A lawn is replaced by shrubs after mowing stops
  4. A flooded field returns to grassland after water drains

Explanation

Primary succession begins where no developed soil community exists, such as newly exposed rock. Pioneer species help create organic matter and soil, allowing later plants to establish.

Question 6Integrated subject knowledge, evidence and application

After a wildfire, grasses and shrubs quickly grow from surviving seeds in the soil. Which process is occurring?

  1. Secondary succession Correct answer.
  2. Genetic drift
  3. Biomagnification
  4. Desalination

Explanation

Secondary succession occurs after a disturbance removes some organisms but leaves soil, seeds, roots, or microbes behind. Recovery is usually faster than primary succession because the foundation for regrowth remains.

Question 7Integrated subject knowledge, evidence and application

Sea otters eat sea urchins, and without otters, urchins can overgraze kelp forests. Why are sea otters often described as a keystone species in this system?

  1. They are always the most numerous organism in the ecosystem
  2. Their effect on community structure is large relative to their abundance Correct answer.
  3. They convert sunlight into chemical energy
  4. They eliminate all competition among kelp species

Explanation

A keystone species has a disproportionately large effect on ecosystem structure and function. By controlling urchins, otters help maintain kelp habitat that supports many other species.

Question 8Integrated subject knowledge, evidence and application

Which factor is density-dependent for a population of deer in a forest?

  1. A severe winter storm
  2. Competition for limited forage Correct answer.
  3. A volcanic eruption
  4. A regional drought caused by weather patterns

Explanation

Density-dependent factors become stronger as population density increases. Competition for food, disease transmission, and some forms of predation intensify when more individuals occupy the same area.

Question 9Integrated subject knowledge, evidence and application

Why can high genetic diversity help a population survive environmental change?

  1. It gives the population more variation on which natural selection can act Correct answer.
  2. It prevents mutations from ever occurring
  3. It makes every individual identical
  4. It removes the need for reproduction

Explanation

Genetic diversity increases the chance that some individuals carry traits suited to new diseases, climate shifts, or resource changes. Those individuals can survive and reproduce, helping the population persist.

Question 10Integrated subject knowledge, evidence and application

If a top predator is removed and herbivores increase enough to reduce plant cover, what has most likely occurred?

  1. A trophic cascade Correct answer.
  2. Primary productivity doubling
  3. Nitrogen fixation
  4. Thermal stratification

Explanation

A trophic cascade happens when a change at one trophic level causes indirect effects across other levels. Removing predators can increase herbivores and reduce plant biomass.

Question 11Integrated subject knowledge, evidence and application

Which statement best compares matter and energy in ecosystems?

  1. Both matter and energy are permanently destroyed by decomposers
  2. Matter cycles through ecosystems, while energy flows through and is dissipated as heat Correct answer.
  3. Energy cycles endlessly, while matter moves only once
  4. Neither matter nor energy moves through food webs

Explanation

Atoms such as carbon, nitrogen, and phosphorus are recycled through biogeochemical cycles. Energy enters mainly as sunlight, moves through trophic levels, and is eventually lost as heat.

Question 12Integrated subject knowledge, evidence and application

Which process makes atmospheric nitrogen available to plants in forms such as ammonium?

  1. Nitrogen fixation by certain bacteria Correct answer.
  2. Photosynthesis by mammals
  3. Condensation of water vapor
  4. Ozone formation in the stratosphere

Explanation

Nitrogen fixation converts atmospheric N2 into biologically usable nitrogen compounds. Bacteria in soil and root nodules are major natural agents of this process.

Question 13Integrated subject knowledge, evidence and application

Conifer needles and a waxy coating are adaptations commonly useful in cold or dry conditions because they primarily help trees do what?

  1. Reduce water loss Correct answer.
  2. Increase soil salinity
  3. Absorb animal protein
  4. Prevent all fires

Explanation

Needle-like leaves and waxy cuticles reduce water loss when liquid water is limited by freezing or dry conditions. These traits are common in many conifer-dominated biomes.

Question 14Integrated subject knowledge, evidence and application

Why can an introduced species become invasive in a new ecosystem?

  1. It may lack natural predators or competitors that limited it in its original range Correct answer.
  2. It automatically increases native biodiversity
  3. It always has lower reproductive capacity than native species
  4. It cannot use resources in the new habitat

Explanation

An introduced species can spread rapidly if predators, parasites, competitors, or diseases from its original range are absent. Invasive species may outcompete native species and alter habitat or food webs.

Question 15Integrated subject knowledge, evidence and application

A bird nests in a tree and gains shelter while the tree is neither helped nor harmed. Which interaction is this?

  1. Mutualism
  2. Commensalism Correct answer.
  3. Competition
  4. Parasitism

Explanation

Commensalism benefits one organism while the other is not significantly affected. The bird gains nesting space, while the tree has no meaningful benefit or harm in the scenario.

Question 16Integrated subject knowledge, evidence and application

A small population enters a new habitat with abundant food and few predators. Which growth pattern is most likely at first?

  1. Exponential growth Correct answer.
  2. Immediate extinction
  3. Zero growth at all times
  4. Linear decline only

Explanation

Populations can grow exponentially when resources are abundant and limiting factors are weak. This early growth usually slows later as resources become limiting.

Question 17Integrated subject knowledge, evidence and application

Which set of traits is most typical of an r-selected species?

  1. Few offspring, late maturity, high parental care
  2. Many small offspring, early maturity, little parental care Correct answer.
  3. Only asexual reproduction and no dispersal
  4. Large body size and very long generation time

Explanation

r-selected species tend to produce many offspring quickly in variable environments, with relatively little parental investment per offspring. These traits favor rapid population growth when opportunities appear.

Question 18Integrated subject knowledge, evidence and application

A road splits a continuous forest into small patches. Which ecological effect is most likely?

  1. Greater edge habitat and reduced movement for some interior species Correct answer.
  2. Instant elimination of all species in both patches
  3. Complete prevention of invasive species
  4. No change in gene flow or microclimate

Explanation

Fragmentation increases edges, changes light and moisture conditions near boundaries, and can reduce movement among patches. Interior-sensitive species may decline even if some edge-adapted species increase.

Question 19Integrated subject knowledge, evidence and application

Which organisms are often important pioneer species during succession on bare mineral surfaces?

  1. Lichens and mosses Correct answer.
  2. Large grazing mammals
  3. Deep-sea fish
  4. Mature canopy trees only

Explanation

Pioneer species tolerate harsh conditions and help build soil or organic matter. Lichens and mosses can colonize bare surfaces and prepare the area for later species.

Question 20Integrated subject knowledge, evidence and application

A reindeer population grows beyond the food supply on an island and then rapidly declines. What ecological pattern does this describe?

  1. Overshoot followed by dieback Correct answer.
  2. Stable carrying capacity with no fluctuation
  3. Primary productivity with no consumers
  4. Mutualism replacing competition

Explanation

Overshoot occurs when a population temporarily exceeds the carrying capacity of its environment. Resource depletion, starvation, disease, or stress can then cause a dieback.

Question 21Integrated subject knowledge, evidence and application

In a food web, an organism that eats plants is classified as which trophic role?

  1. Primary consumer Correct answer.
  2. Primary producer
  3. Decomposer
  4. Tertiary consumer

Explanation

Herbivores are primary consumers because they eat producers directly. They occupy the trophic level above plants and algae.

Question 22Integrated subject knowledge, evidence and application

What is the main ecological role of decomposers?

  1. Recycle nutrients by breaking down dead organisms and wastes Correct answer.
  2. Prevent all predation
  3. Convert every pollutant into oxygen
  4. Stop succession permanently

Explanation

Decomposers such as fungi and bacteria break down organic matter and return nutrients to soil, water, and food webs. Without them, nutrients would remain locked in dead material.

Question 23Integrated subject knowledge, evidence and application

How does net primary productivity differ from gross primary productivity?

  1. Net primary productivity equals gross primary productivity minus energy used by producers in respiration Correct answer.
  2. Net primary productivity is always larger than gross primary productivity
  3. Gross primary productivity excludes photosynthesis
  4. Net primary productivity measures only animal respiration

Explanation

Gross primary productivity is the total rate at which producers capture energy through photosynthesis. Net primary productivity is what remains after producers use some of that energy for their own respiration.

Question 24Integrated subject knowledge, evidence and application

Which factor is most clearly density-independent for a coastal bird population?

  1. A hurricane that destroys nesting habitat Correct answer.
  2. Disease transmission increasing in crowded nests
  3. Competition for limited nest sites
  4. Predation increasing where nests are clustered

Explanation

Density-independent factors affect populations regardless of their density. A hurricane can damage habitat whether the bird population is small or large.

Question 25Integrated subject knowledge, evidence and application

Why are long-lived top predators often monitored for mercury contamination?

  1. Mercury can biomagnify through food webs Correct answer.
  2. Mercury disappears before reaching consumers
  3. Top predators produce mercury from sunlight
  4. Mercury is a necessary macronutrient for predators

Explanation

Persistent contaminants such as methylmercury can become more concentrated at higher trophic levels. Top predators may accumulate high body burdens because they eat many contaminated prey over time.

Question 26Integrated subject knowledge, evidence and application

Wetlands that store floodwater, filter sediment, and provide nursery habitat are examples of what broader idea?

  1. Ecosystem services Correct answer.
  2. Genetic drift
  3. Point-source emissions
  4. Ozone depletion

Explanation

Ecosystem services are benefits people receive from ecosystems, including water purification, flood control, habitat, pollination, and recreation. Wetlands provide several of these services at once.

Question 27Integrated subject knowledge, evidence and application

Two grasslands each contain five plant species. In one grassland, all five are equally common; in the other, one species dominates. What differs most directly between them?

  1. Species evenness Correct answer.
  2. Latitude
  3. Gross primary productivity by definition
  4. The number of trophic levels only

Explanation

Species richness counts how many species are present, while evenness describes how equally individuals are distributed among those species. The two grasslands have the same richness but different evenness.

Question 28Integrated subject knowledge, evidence and application

Why can predator and prey populations show repeated cycles over time?

  1. Predator numbers can rise after prey increase, then prey decline as predation pressure grows Correct answer.
  2. Predators always reproduce before prey are born
  3. Prey populations cannot respond to resource availability
  4. Predators and prey never affect one another

Explanation

Prey abundance can support predator population growth after a time lag. Higher predator abundance can then reduce prey, followed by predator decline when food becomes scarce.

Question 29Integrated subject knowledge, evidence and application

What is the difference between a fundamental niche and a realized niche?

  1. The realized niche is the portion actually occupied after competition, predation, and other limits Correct answer.
  2. The fundamental niche includes only predators
  3. The realized niche is always larger than the fundamental niche
  4. Both terms mean the exact same thing

Explanation

A fundamental niche is the full range of conditions and resources a species could use in the absence of limiting biotic interactions. The realized niche is the narrower role it actually occupies in nature.

Question 30Integrated subject knowledge, evidence and application

During photosynthesis, carbon is primarily moved from which reservoir into plant biomass?

  1. Atmospheric carbon dioxide Correct answer.
  2. Solid granite
  3. Molecular nitrogen
  4. Stratospheric ozone

Explanation

Photosynthesis takes carbon dioxide from the air or water and fixes it into organic molecules. That stored carbon becomes plant biomass and can move through food webs.

Question 31Integrated subject knowledge, evidence and application

Greenhouse gases contribute to warming mainly because they do what in the atmosphere?

  1. Absorb and re-emit outgoing infrared radiation Correct answer.
  2. Block all incoming visible sunlight
  3. Remove all water vapor from clouds
  4. Convert nitrogen gas into oxygen

Explanation

Greenhouse gases absorb some outgoing infrared radiation emitted by Earth's surface and atmosphere. This slows heat loss to space and strengthens the greenhouse effect when concentrations rise.

Question 32Integrated subject knowledge, evidence and application

Which human activity is a major direct source of added carbon dioxide to the atmosphere?

  1. Burning fossil fuels for energy Correct answer.
  2. Planting native trees
  3. Protecting wetlands from drainage
  4. Using gravity to move water downhill

Explanation

Combustion of coal, oil, and natural gas releases carbon that was stored underground into the atmosphere as CO2. This is a major driver of human-caused climate change.

Question 33Integrated subject knowledge, evidence and application

Which set of sources is most closely associated with methane emissions?

  1. Livestock digestion, landfills, and natural gas systems Correct answer.
  2. Only nuclear power plants
  3. Photosynthesis by forests
  4. Desalination membranes

Explanation

Methane is emitted by anaerobic decomposition in landfills, digestion in ruminant livestock, fossil fuel production and transport, and wetlands. It is a potent greenhouse gas over shorter time horizons than CO2.

Question 34Integrated subject knowledge, evidence and application

Why can cities be warmer than nearby rural areas on hot days?

  1. Dark pavement, buildings, and reduced vegetation absorb and retain heat Correct answer.
  2. Cities contain no greenhouse gases
  3. Concrete reflects all solar energy back to space
  4. Urban trees prevent all heat storage

Explanation

The urban heat island effect occurs when built surfaces absorb heat, vegetation is reduced, and waste heat is released. This can raise local temperatures and worsen heat stress.

Question 35Integrated subject knowledge, evidence and application

Excess nitrogen and phosphorus runoff enters a lake and triggers a dense algal bloom followed by low dissolved oxygen. What is this process called?

  1. Eutrophication Correct answer.
  2. Primary succession
  3. Ozone depletion
  4. Thermal inversion

Explanation

Eutrophication occurs when nutrient enrichment stimulates algal growth. When algae die and decompose, microbial respiration can deplete dissolved oxygen and harm aquatic life.

Question 36Integrated subject knowledge, evidence and application

A pipe from a factory discharging treated wastewater into a river is best described as what type of pollution source?

  1. Point source Correct answer.
  2. Nonpoint source
  3. Biological magnifier
  4. Renewable source

Explanation

A point source is a single identifiable location such as a pipe, ditch, or smokestack. Nonpoint pollution is diffuse, such as runoff from many lawns or fields.

Question 37Integrated subject knowledge, evidence and application

Acid deposition is most directly associated with emissions of which pollutants?

  1. Sulfur dioxide and nitrogen oxides Correct answer.
  2. Oxygen and helium
  3. Sodium chloride and water vapor
  4. Argon and neon

Explanation

Sulfur dioxide and nitrogen oxides can react in the atmosphere to form sulfuric and nitric acids. These acids return to Earth in rain, snow, fog, or dry particles and can affect soils, lakes, and structures.

Question 38Integrated subject knowledge, evidence and application

Which statement correctly distinguishes stratospheric ozone from ground-level ozone?

  1. Stratospheric ozone helps block UV radiation; ground-level ozone is a harmful air pollutant Correct answer.
  2. Both are always beneficial wherever they occur
  3. Ground-level ozone protects skin from UV better than stratospheric ozone
  4. Stratospheric ozone is the same as carbon monoxide

Explanation

Ozone high in the stratosphere absorbs much harmful ultraviolet radiation. Near the ground, ozone is a component of smog that can damage lungs and vegetation.

Question 39Integrated subject knowledge, evidence and application

How can habitat fragmentation increase extinction risk for some species?

  1. It can isolate small populations, reduce gene flow, and increase edge effects Correct answer.
  2. It always increases the size of every habitat patch
  3. It prevents all human access to ecosystems
  4. It guarantees higher genetic diversity

Explanation

Fragmentation breaks continuous habitat into smaller patches, which may isolate populations and make them more vulnerable to local extinction. Edge effects, roads, and reduced dispersal can further stress interior species.

Question 40Integrated subject knowledge, evidence and application

Why is salinization a common concern in irrigated agriculture in dry regions?

  1. Evaporation can leave dissolved salts behind in the soil Correct answer.
  2. Rainfall always removes all salts instantly
  3. Salt is produced only by insects
  4. Irrigation water contains no dissolved minerals

Explanation

Irrigation water often contains dissolved salts. In dry climates, high evaporation and poor drainage can concentrate salts in soil, reducing crop productivity.

Question 41Integrated subject knowledge, evidence and application

Overgrazing can contribute to desertification primarily by doing what?

  1. Removing vegetation cover and increasing erosion Correct answer.
  2. Increasing deep forest shade in deserts
  3. Adding unlimited organic matter to soil
  4. Creating permanent wetlands

Explanation

When livestock remove too much plant cover, soil is exposed to wind and water erosion. In drylands, this can degrade land and reduce the ability of vegetation to recover.

Question 42Integrated subject knowledge, evidence and application

Which statement best distinguishes bioaccumulation from biomagnification?

  1. Bioaccumulation occurs within an organism over time; biomagnification increases concentrations at higher trophic levels Correct answer.
  2. Bioaccumulation means energy loss; biomagnification means photosynthesis
  3. Both terms describe only clean water
  4. Biomagnification occurs only in rocks and never in organisms

Explanation

Bioaccumulation is the buildup of a substance in an individual organism. Biomagnification is the increase in concentration of certain persistent substances as they move up a food chain.

Question 43Integrated subject knowledge, evidence and application

A power plant releases warm water into a river. Why can this thermal pollution harm fish?

  1. Warmer water holds less dissolved oxygen and can stress temperature-sensitive species Correct answer.
  2. Warm water always contains more oxygen than cold water
  3. Temperature has no effect on aquatic organisms
  4. All fish require boiling water

Explanation

Raising water temperature can lower dissolved oxygen availability and increase metabolic stress for aquatic organisms. Sudden temperature changes can also disrupt reproduction and community composition.

Question 44Integrated subject knowledge, evidence and application

Fine particulate matter is a concern because it can do what?

  1. Penetrate deep into the lungs and affect respiratory and cardiovascular health Correct answer.
  2. Make air pollution impossible to measure
  3. Remove all nitrogen from soil
  4. Destroy gravity

Explanation

Small particles can be inhaled deeply and are associated with respiratory and cardiovascular effects. Particulate pollution is one of the criteria pollutant categories regulated for public health protection.

Question 45Integrated subject knowledge, evidence and application

Why are endocrine-disrupting chemicals difficult to evaluate in environmental health studies?

  1. They may cause effects at low doses, during sensitive life stages, or after delayed exposure periods Correct answer.
  2. They are always visible to the naked eye
  3. They are harmless by definition
  4. They affect only rocks and never organisms

Explanation

Endocrine disruptors can interfere with hormone signaling, so timing and developmental stage may matter as much as dose. Effects may be subtle, delayed, or population-level, making assessment challenging.

Question 46Integrated subject knowledge, evidence and application

A small isolated habitat patch supports fewer species than a large nearby patch. Which concept helps explain this pattern?

  1. Island biogeography Correct answer.
  2. Combustion efficiency
  3. Primary sewage treatment
  4. Ozone titration only

Explanation

Island biogeography predicts that larger and less isolated habitat patches generally support more species because colonization is easier and extinction risk is lower. The idea is often applied to habitat fragments as well as true islands.

Question 47Integrated subject knowledge, evidence and application

Deforestation can affect the environment by doing which of the following?

  1. Reducing habitat, changing water flow, and releasing stored carbon Correct answer.
  2. Increasing forest interior habitat everywhere
  3. Preventing all soil erosion
  4. Eliminating the carbon cycle

Explanation

Removing forests can reduce biodiversity, alter evapotranspiration and runoff, increase erosion, and release carbon stored in trees and soils. The impact depends on scale, location, and land use after clearing.

Question 48Integrated subject knowledge, evidence and application

Why are microplastics considered an environmental concern?

  1. They can persist, be ingested by organisms, and transport additives or contaminants Correct answer.
  2. They immediately biodegrade into harmless nutrients in all conditions
  3. They exist only in outer space
  4. They are too large for any animal to ingest

Explanation

Microplastics are small plastic particles that can persist in water, soil, and organisms. Their size makes ingestion possible, and their surfaces or additives can be associated with chemical exposure concerns.

Question 49Integrated subject knowledge, evidence and application

Melting sea ice can accelerate warming because darker ocean water absorbs more solar energy than reflective ice. What type of process is this?

  1. Positive feedback Correct answer.
  2. Negative feedback
  3. Primary treatment
  4. Genetic bottleneck

Explanation

A positive feedback amplifies an initial change. Ice loss lowers albedo, allowing more absorption of solar energy, which can contribute to further warming and additional ice loss.

Question 50Integrated subject knowledge, evidence and application

Why can heavy metals such as lead or mercury remain environmental hazards for long periods?

  1. They are elements and do not break down into harmless substances by biodegradation Correct answer.
  2. They vanish after one rainfall
  3. They become oxygen when exposed to sunlight
  4. They are living organisms that die quickly

Explanation

Heavy metals are chemical elements, so they cannot be biodegraded into simpler harmless components. They may change chemical form or location, but persistence and toxicity can make them long-term hazards.