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GTLE Subject Specialism Integrated Science study materials
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GTLE Subject Specialism Integrated Science practice questions

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Question 1Diversity of Matter and Materials (living and non-living)

Which feature is shared by all living organisms but is not shown by a crystal of table salt?

  1. A regular internal structure
  2. The ability to exist as a solid
  3. A definite chemical composition
  4. The ability to reproduce Correct answer.

Explanation

Living things share a set of characteristics including reproduction, growth, response to stimuli and metabolism. A salt crystal has a fixed composition and regular lattice but cannot reproduce or metabolise. Reproduction is therefore the feature that separates the living from the non-living here.

Question 2Diversity of Matter and Materials (living and non-living)

A student compares a plant cell with a copper wire. Which statement correctly identifies a property of the wire that the cell does not have?

  1. It conducts electricity because of delocalised electrons Correct answer.
  2. It contains atoms arranged in a lattice
  3. It has mass and occupies space
  4. It can be seen with a light microscope

Explanation

Metals conduct electricity because their outer electrons are delocalised and free to move through the lattice. A living plant cell contains ions in solution but no free electron sea, so it is not an electrical conductor in the metallic sense. The other options apply to both objects.

Question 3Diversity of Matter and Materials (living and non-living)

Which group contains only substances that are elements?

  1. Carbon dioxide, iron, nitrogen
  2. Air, sulfur, carbon
  3. Water, oxygen, iron
  4. Oxygen, iron, sulfur Correct answer.

Explanation

An element is a pure substance made of only one kind of atom. Oxygen, iron and sulfur each consist of a single type of atom, so all three are elements. The other groups each contain a compound or a mixture.

Question 4Diversity of Matter and Materials (living and non-living)

Which statement best describes the difference between a compound and a mixture?

  1. A compound can be separated by filtration, while a mixture cannot
  2. A compound has a fixed composition by mass, while a mixture can vary in composition Correct answer.
  3. A compound is always a liquid, while a mixture may be solid, liquid or gas
  4. A mixture always contains only two substances, while a compound may contain many

Explanation

In a compound the constituent elements are chemically combined in fixed proportions by mass, and the compound has properties different from those elements. In a mixture the components are not chemically combined, so the proportions can vary and the components keep their own properties.

Question 5Diversity of Matter and Materials (living and non-living)

A beaker contains a clear liquid. When it is heated gently, a white solid appears and a gas that turns limewater milky is released. The original liquid is best classified as:

  1. A heterogeneous mixture
  2. A compound Correct answer.
  3. An element
  4. A homogeneous mixture

Explanation

Heating produces a new solid and a new gas, showing a chemical change with a fixed decomposition pattern typical of a compound. A mixture would not decompose into new substances on gentle heating in this way. The clear, uniform appearance also rules out a heterogeneous mixture.

Question 6Diversity of Matter and Materials (living and non-living)

Which property of a substance is a chemical property rather than a physical property?

  1. Its solubility in water
  2. Its melting point
  3. Its reaction with oxygen Correct answer.
  4. Its density

Explanation

A chemical property describes how a substance behaves in a chemical reaction, producing new substances. Reaction with oxygen is such a change. Melting point, density and solubility describe the substance without changing its identity.

Question 7Diversity of Matter and Materials (living and non-living)

A sample of a metal is hammered into a thin sheet and then drawn into a wire. Which pair of properties does this demonstrate?

  1. Hardness and solubility
  2. Brittleness and conductivity
  3. Malleability and ductility Correct answer.
  4. Elasticity and density

Explanation

Malleability is the ability to be hammered into thin sheets, and ductility is the ability to be drawn into wires. Metals show both because layers of ions can slide over each other without the metallic bond breaking. The two processes therefore demonstrate these two properties.

Question 8Diversity of Matter and Materials (living and non-living)

Which observation provides the strongest evidence that a change is chemical rather than physical?

  1. A gas is produced that has different properties from the starting materials Correct answer.
  2. A solid changes shape when pressed
  3. A liquid boils and forms a vapour
  4. A solid dissolves and the liquid becomes coloured

Explanation

A chemical change produces new substances with properties different from the reactants. A gas that behaves differently from the starting materials indicates such a change. Dissolving, boiling and reshaping leave the substance chemically unchanged.

Question 9Diversity of Matter and Materials (living and non-living)

Which statement correctly describes the arrangement of particles in a crystalline solid compared with an amorphous solid?

  1. Both types have identical particle arrangements but differ only in colour
  2. Crystalline particles form a repeating three-dimensional pattern, while amorphous particles are disordered Correct answer.
  3. Crystalline solids contain no particles, while amorphous solids do
  4. Crystalline particles are randomly arranged, while amorphous particles form a repeating pattern

Explanation

In a crystalline solid the particles are packed in a regular, repeating three-dimensional lattice, which gives sharp melting points and cleavage along planes. In an amorphous solid such as glass the particles are disordered, giving a range of softening temperatures.

Question 10Diversity of Matter and Materials (living and non-living)

A jewellery maker wants a metal that is hard, resistant to corrosion and attractive in colour. Which choice best fits these requirements for a ring?

  1. Pure sodium
  2. Pure copper
  3. Stainless steel Correct answer.
  4. Pure sulfur

Explanation

Stainless steel is an alloy of iron with chromium and nickel, giving hardness and corrosion resistance suitable for jewellery. Its metallic lustre also makes it attractive. The other options are either too reactive, too soft or non-metallic.

Question 11Diversity of Matter and Materials (living and non-living)

Why is an alloy such as brass usually harder than the pure metal it is based on?

  1. The added atoms make the material a compound with ionic bonds
  2. The alloy contains no metal atoms at all
  3. The added atoms have different sizes and disrupt the sliding of layers of atoms Correct answer.
  4. The alloy has a lower melting point, which makes it harder

Explanation

In an alloy, atoms of different sizes replace some atoms in the metal lattice. These differently sized atoms distort the layers, making it harder for them to slide over one another, so the alloy is harder than the pure metal.

Question 12Diversity of Matter and Materials (living and non-living)

Which property makes ceramics such as fired clay useful for making oven dishes?

  1. They are heat-resistant and poor conductors of heat Correct answer.
  2. They melt at low temperatures
  3. They conduct heat very well
  4. They are good electrical conductors

Explanation

Ceramics are held together by strong ionic and covalent bonds, giving high melting points and low thermal conductivity. This allows an oven dish to withstand high temperatures and to insulate the food from direct heat.

Question 13Diversity of Matter and Materials (living and non-living)

Which statement about polymers is correct?

  1. All polymers are naturally occurring substances
  2. Polymers cannot be shaped or moulded
  3. Polymers are always good conductors of electricity
  4. Polymers are large molecules made from many small repeating units Correct answer.

Explanation

A polymer is a large molecule built from many small monomer units joined together in long chains. The chains can be natural, such as cellulose, or synthetic, such as polythene. Their chain structure allows many polymers to be moulded when heated.

Question 14Diversity of Matter and Materials (living and non-living)

A farmer compares clay soil with sandy soil. Which statement correctly describes a difference in their properties?

  1. Sandy soil contains more humus than clay soil in all cases
  2. Clay soil drains water quickly, while sandy soil holds water tightly
  3. Both soils have identical particle sizes and drainage
  4. Clay soil holds water well but has poor air spaces, while sandy soil drains freely Correct answer.

Explanation

Clay particles are very small, so the soil has tiny pore spaces that hold water but leave little air. Sand particles are larger, giving big pore spaces through which water drains freely. This difference in particle size explains the contrasting drainage.

Question 15Diversity of Matter and Materials (living and non-living)

Which of the following is the best example of a non-renewable material resource?

  1. Timber from a managed forest
  2. Water in a river used for irrigation
  3. Solar energy captured by panels
  4. Petroleum used to make plastics Correct answer.

Explanation

Petroleum formed over millions of years from buried organic matter and is used far faster than it forms, so it is non-renewable. Timber, solar energy and river water are replenished on human timescales when managed responsibly.

Question 16Diversity of Matter and Materials (living and non-living)

A sample of air is passed through a filter that removes all solid particles, then cooled until water vapour condenses. The remaining gas is mainly nitrogen and oxygen. This shows that air is:

  1. A single pure substance with a fixed formula
  2. A mixture of gases that can be separated by physical means Correct answer.
  3. An element with variable composition
  4. A compound of nitrogen and oxygen

Explanation

Air can be separated into its components by physical processes such as filtration and condensation, and its composition varies slightly with location. These are characteristics of a mixture, not a compound or element.

Question 17Diversity of Matter and Materials (living and non-living)

Which statement correctly explains why ice floats on water?

  1. Ice is denser than liquid water because it is colder
  2. Ice contains dissolved air that makes it lighter
  3. Ice has a different chemical formula from water
  4. Ice is less dense than liquid water because its lattice holds the molecules further apart Correct answer.

Explanation

When water freezes, hydrogen bonds hold the molecules in an open hexagonal lattice with more space between them than in the liquid. This makes ice less dense than liquid water, so it floats. The chemical formula of ice and water is the same.

Question 18Diversity of Matter and Materials (living and non-living)

Which change of state involves particles gaining energy and moving further apart?

  1. Evaporation Correct answer.
  2. Condensation
  3. Deposition
  4. Freezing

Explanation

Evaporation is the change from liquid to gas, in which particles gain kinetic energy and escape from the liquid surface into a much larger volume. Condensation, freezing and deposition all release energy as particles come closer together.

Question 19Diversity of Matter and Materials (living and non-living)

A student heats a pure crystalline solid and observes that it melts sharply at 80 degrees Celsius, while an amorphous solid softens gradually over a range. What is the best explanation?

  1. The crystalline solid has a regular lattice that breaks down at one temperature Correct answer.
  2. The amorphous solid contains no particles
  3. The amorphous solid has a higher melting point than the crystalline solid
  4. The crystalline solid is a mixture of many substances

Explanation

In a crystalline solid all the particles are held in a regular lattice with bonds of similar strength, so the lattice collapses at a single temperature. An amorphous solid has bonds of varying strength and disorder, so it softens gradually over a range.

Question 20Diversity of Matter and Materials (living and non-living)

Which everyday material is best classified as a composite?

  1. Glass-reinforced plastic used in boat hulls Correct answer.
  2. Table salt
  3. Pure aluminium foil
  4. Distilled water

Explanation

A composite combines two or more materials with different properties so that the product has improved characteristics. Glass-reinforced plastic combines glass fibres for strength with a plastic matrix for flexibility and lightness.

Question 21Diversity of Matter and Materials (living and non-living)

Which statement best explains why metals are good conductors of electricity while ionic solids such as sodium chloride are not, when both are solid?

  1. Metals contain water, which carries the current
  2. Metals contain free-moving delocalised electrons, while ions in the solid are fixed in the lattice Correct answer.
  3. Metal atoms are larger than ions, so charge moves more easily
  4. Ionic solids contain no charged particles at all

Explanation

In a metal, outer electrons are delocalised and can move throughout the structure, carrying charge. In a solid ionic compound the ions are held rigidly in the lattice and cannot move, so the solid does not conduct; it conducts only when molten or dissolved.

Question 22Diversity of Matter and Materials (living and non-living)

Which property of diamond makes it suitable for use as a cutting tool?

  1. It has a giant covalent structure with very strong bonds in three dimensions Correct answer.
  2. It melts at a low temperature
  3. It is a good conductor of electricity
  4. It is soft and flexible

Explanation

Diamond consists of carbon atoms each bonded covalently to four others in a rigid three-dimensional network. Breaking the tool would require breaking many strong covalent bonds, so diamond is extremely hard and useful for cutting.

Question 23Diversity of Matter and Materials (living and non-living)

A substance is found to be made of two or more elements chemically combined in fixed proportions, and it can be broken down only by chemical means. The substance is:

  1. A compound Correct answer.
  2. An alloy
  3. An element
  4. A mixture

Explanation

A compound consists of two or more elements chemically combined in fixed proportions by mass and can be decomposed only by chemical reactions. A mixture can be separated physically, while an element contains only one kind of atom.

Question 24Diversity of Matter and Materials (living and non-living)

Which observation about a material suggests that it is a heterogeneous mixture rather than a homogeneous one?

  1. It has the same composition throughout when examined closely
  2. Different parts of the sample show different colours and textures Correct answer.
  3. It has a fixed chemical formula
  4. It melts sharply at one temperature

Explanation

A heterogeneous mixture has visibly different regions with different compositions, such as granite or soil. A homogeneous mixture is uniform throughout, and a fixed formula or sharp melting point indicates a pure substance.

Question 25Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

In a food web, which organisms occupy the first trophic level and form the base of every grazing food chain?

  1. Decomposers such as fungi and bacteria
  2. Primary producers such as plants and algae Correct answer.
  3. Secondary consumers such as small predators
  4. Primary consumers such as herbivores

Explanation

The first trophic level is always occupied by primary producers, which convert light or chemical energy into organic matter through photosynthesis or chemosynthesis. All other trophic levels depend on the organic carbon these producers synthesize.

Question 26Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Which process returns carbon locked in dead plant material back to the atmosphere as carbon dioxide?

  1. Cellular respiration by decomposers Correct answer.
  2. Nitrogen fixation by soil bacteria
  3. Transpiration from leaves
  4. Weathering of silicate rock

Explanation

Decomposers such as fungi and bacteria respire as they break down organic matter, releasing carbon dioxide to the atmosphere. This respiration is a key return pathway in the carbon cycle.

Question 27Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Which statement best describes the role of nitrogen-fixing bacteria in the nitrogen cycle?

  1. They convert nitrate into nitrogen gas that escapes to the atmosphere
  2. They break down proteins in dead organisms into ammonium ions
  3. They convert atmospheric N2 into ammonia compounds usable by plants Correct answer.
  4. They oxidise ammonia into nitrite during nitrification

Explanation

Nitrogen-fixing bacteria, including rhizobia in root nodules, reduce inert atmospheric nitrogen gas to ammonia, which is then assimilated into organic compounds. This step is the main natural input of usable nitrogen to ecosystems.

Question 28Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Energy transfer between successive trophic levels is inefficient. Approximately what proportion of energy is typically passed from one level to the next?

  1. About 90 percent
  2. About 10 percent Correct answer.
  3. About 50 percent
  4. About 1 percent

Explanation

Roughly 10 percent of the energy at one trophic level is incorporated into biomass at the next, with the rest lost mainly as heat through respiration. This explains why food chains rarely have more than four or five links.

Question 29Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

In the water cycle, which process moves water vapour from the atmosphere into liquid form on cool surfaces?

  1. Runoff
  2. Condensation Correct answer.
  3. Evaporation
  4. Infiltration

Explanation

Condensation is the change of water from vapour to liquid, occurring when moist air cools below its dew point. It forms clouds, dew and fog and precedes precipitation.

Question 30Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Which term describes the variety of species and genetic variation present within a given ecosystem?

  1. Primary productivity
  2. Trophic efficiency
  3. Carrying capacity
  4. Biodiversity Correct answer.

Explanation

Biodiversity encompasses species richness, genetic diversity and ecosystem diversity within a defined area. It is a measure of biological variety, not of population size or energy flow.

Question 31Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Which pair of organisms represents a mutualistic relationship in an ecosystem?

  1. Lynx and snowshoe hare in a predator-prey cycle
  2. Leguminous plants and nitrogen-fixing rhizobia in root nodules Correct answer.
  3. Barnacles attached to a whale's skin without affecting it
  4. Tapeworms and the mammals whose intestines they inhabit

Explanation

In mutualism both partners benefit: the plant supplies carbohydrates while rhizobia supply fixed nitrogen. This exchange raises the fitness of both organisms.

Question 32Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A lake receives excess nitrate and phosphate from farmland runoff. Which sequence of events is most likely to follow?

  1. Rapid sedimentation, then reduced decomposition, then oxygen rise
  2. Increased water clarity, then plant decline, then nutrient loss
  3. Algal bloom, then decomposition, then oxygen depletion and fish kills Correct answer.
  4. Oxygen depletion, then algal bloom, then increased fish growth

Explanation

Nutrient enrichment triggers rapid algal growth; when the algae die, decomposers consume dissolved oxygen as they break them down. The resulting hypoxia can kill fish and other oxygen-dependent organisms, a process called eutrophication.

Question 33Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A population of rabbits grows rapidly after a mild winter, then its growth slows as food becomes scarce. Which factor is acting as a density-dependent limit?

  1. A volcanic ash fall
  2. Competition for limited food Correct answer.
  3. Seasonal day length
  4. A sudden early frost

Explanation

Density-dependent factors intensify as population density rises, so competition for food, disease and predation have stronger effects in crowded populations. Food shortage is the classic example of such a negative feedback on population growth.

Question 34Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

In the carbon cycle, which human activity most directly increases the flux of carbon from long-term geological stores to the atmosphere?

  1. Burning fossil fuels such as coal and oil Correct answer.
  2. Planting fast-growing forests
  3. Irrigating paddy fields
  4. Applying nitrogen fertiliser to crops

Explanation

Fossil fuels hold carbon that was removed from the short-term cycle over millions of years; combustion returns it rapidly to the atmosphere. This transfer from a geological reservoir is the dominant anthropogenic carbon flux.

Question 35Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A food chain is: grass, grasshopper, frog, snake, hawk. If the grass contains 20,000 kJ of energy, roughly how much energy reaches the snake assuming 10 percent transfer efficiency?

  1. 20 kJ Correct answer.
  2. 2 kJ
  3. 200 kJ
  4. 2,000 kJ

Explanation

With 10 percent transfer per step, the grasshopper receives 2,000 kJ, the frog 200 kJ and the snake 20 kJ. Each transfer step multiplies the previous value by 0.1.

Question 36Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Which feature of the phosphorus cycle distinguishes it from the carbon and nitrogen cycles?

  1. It cycles only through the atmosphere and never enters living tissue
  2. It lacks a significant gaseous phase and moves mainly through rock, soil and water Correct answer.
  3. It relies on bacteria to reduce atmospheric gas into ammonia
  4. It depends entirely on lightning to convert atmospheric gas into usable form

Explanation

Phosphorus is released mainly by weathering of phosphate minerals and cycles through soil, water and organisms, with no major atmospheric reservoir. This makes it a sedimentary cycle rather than a gaseous one.

Question 37Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Two species of warbler feed in different parts of the same tree, reducing direct competition. This is best described as which ecological concept?

  1. Competitive exclusion
  2. Bioaccumulation
  3. Primary succession
  4. Resource partitioning Correct answer.

Explanation

Resource partitioning is the division of a shared resource so that species use different parts or types, allowing coexistence. It reduces the intensity of interspecific competition.

Question 38Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

In a climax community, net ecosystem production is close to zero. What does this imply?

  1. Decomposers are absent from the ecosystem
  2. Gross primary production is roughly balanced by total respiration of the community Correct answer.
  3. Photosynthesis has stopped entirely within the ecosystem
  4. No energy is lost as heat from the ecosystem

Explanation

Net ecosystem production equals gross primary production minus ecosystem respiration. Near zero means carbon fixed by producers is almost equal to carbon released by plants, animals and decomposers.

Question 39Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Lichens and mosses colonise bare rock after a glacier retreats, gradually building soil for later plants. This sequence is an example of which process?

  1. Secondary succession
  2. Nitrogen fixation
  3. Eutrophication
  4. Primary succession Correct answer.

Explanation

Primary succession begins on newly exposed substrate with no pre-existing soil or seeds, so pioneer species like lichens must first create soil. Secondary succession instead follows a disturbance where soil already exists.

Question 40Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Why can persistent organic pollutants such as DDT reach higher concentrations in top predators than in the water or soil where they were released?

  1. They dissolve readily in water and are diluted at each trophic level
  2. They are rapidly excreted, so predators absorb them directly from water
  3. They are converted into minerals that predators ingest from soil
  4. They are fat-soluble and resist breakdown, so they accumulate along food chains Correct answer.

Explanation

Fat-soluble, persistent compounds are stored in body fat and poorly metabolised, so each consumer retains the burden of all the prey it eats. This biomagnification raises concentrations at higher trophic levels.

Question 41Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A keystone predator is removed from a rocky shore community. Which outcome is most consistent with the keystone species concept?

  1. All other species increase equally because predation has stopped
  2. The community remains unchanged because predators do not affect prey
  3. A dominant prey species expands and displaces other species, lowering diversity Correct answer.
  4. Primary productivity stops immediately because herbivores are absent

Explanation

A keystone predator exerts disproportionate influence by controlling a competitively dominant prey species. Removing it allows that prey to monopolise space or resources, reducing overall species diversity.

Question 42Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Which statement correctly describes the role of denitrification in the nitrogen cycle?

  1. It converts nitrogen gas to ammonia inside root nodules
  2. It converts ammonium to nitrite in the soil
  3. It converts nitrate to nitrogen gas, returning nitrogen to the atmosphere Correct answer.
  4. It converts plant proteins into nitrate for storage

Explanation

Denitrifying bacteria use nitrate as an electron acceptor in anaerobic conditions, reducing it to nitrogen gas that escapes to the atmosphere. This closes the nitrogen cycle by returning nitrogen to the atmospheric reservoir.

Question 43Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A freshwater pond has a large input of organic sewage. Which change to the dissolved oxygen profile is expected downstream of the discharge?

  1. A rise in oxygen because sewage kills decomposers
  2. No change because oxygen is not involved in decomposition
  3. A sharp oxygen sag as bacteria respire while decomposing the sewage Correct answer.
  4. A steady rise in oxygen because nutrients feed algae immediately

Explanation

Sewage supplies abundant organic matter, and aerobic bacteria consume dissolved oxygen as they decompose it, producing an oxygen sag. Oxygen recovers further downstream once the organic load is broken down.

Question 44Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A model of a lake ecosystem shows that doubling the nutrient input raises algal biomass only slightly because light becomes limiting. Which concept does this illustrate?

  1. A limiting factor controlling productivity Correct answer.
  2. Primary succession
  3. A keystone species effect
  4. Competitive exclusion between algae

Explanation

When one resource is abundant but another, such as light, is scarce, the scarce resource limits productivity. Adding more nutrients then produces little response, consistent with Liebig's law of the minimum.

Question 45Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

In a stable predator-prey model, why does the predator population peak slightly after the prey population?

  1. Predators reproduce faster than prey and overshoot immediately
  2. Prey numbers are controlled by day length, which peaks later each year
  3. Predators migrate before prey numbers fall
  4. Predator growth depends on prey availability, so predator numbers respond with a lag Correct answer.

Explanation

Predator reproduction and survival track prey abundance, so predator numbers rise only after prey have increased and then fall after prey decline. This time lag produces the characteristic offset cycles seen in coupled predator-prey systems.

Question 46Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

A carbon budget for a forest shows gross primary production of 1,200 g C m-2 yr-1, plant respiration of 600, and heterotroph respiration of 500. What is the net ecosystem production?

  1. 100 g C m-2 yr-1 Correct answer.
  2. 1,200 g C m-2 yr-1
  3. 700 g C m-2 yr-1
  4. 600 g C m-2 yr-1

Explanation

Net ecosystem production equals gross primary production minus total respiration (plant plus heterotroph). Here 1,200 minus 600 minus 500 leaves 100 g C m-2 yr-1, a small net carbon sink.

Question 47Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

Two islands of equal area differ: one has high habitat heterogeneity and the other is uniform. Based on island biogeography and habitat diversity theory, which prediction is most reasonable?

  1. The heterogeneous island supports fewer species because it fragments populations
  2. Both islands support identical species numbers because area is equal
  3. The uniform island supports more species because competition is stronger there
  4. The heterogeneous island supports more species because it offers more distinct niches Correct answer.

Explanation

Greater habitat heterogeneity provides a wider range of niches and resources, allowing more species to coexist without excluding one another. Area matters, but at equal area the structurally diverse island should hold more species.

Question 48Systems and Cycles in the Environment (ecosystems, matter and energy cycles)

In the nitrogen cycle, a waterlogged soil becomes anaerobic. Which shift in microbial activity is most likely?

  1. Nitrogen fixation ceases because oxygen is absent
  2. Nitrification accelerates while denitrification stops
  3. Nitrification slows while denitrification increases, releasing nitrogen gas Correct answer.
  4. Both nitrification and denitrification stop entirely

Explanation

Nitrifying bacteria require oxygen, so waterlogging inhibits nitrification, while denitrifying bacteria thrive in anaerobic conditions and reduce nitrate to nitrogen gas. This is why waterlogged fields lose nitrogen to the atmosphere.

Question 49Energy and Matter Transformations (forces, energy, waves, electricity)

A 4 kg block is pushed across a frictionless horizontal surface by a constant 12 N force directed along the surface. What is the magnitude of the block's acceleration?

  1. 48 m/s²
  2. 8 m/s²
  3. 0.33 m/s²
  4. 3 m/s² Correct answer.

Explanation

Newton's second law states that the net force equals mass times acceleration, so a = F/m. Dividing 12 N by 4 kg gives 3 m/s². Because the surface is frictionless, the applied force is the only horizontal force.

Question 50Energy and Matter Transformations (forces, energy, waves, electricity)

A book rests on a horizontal table. Which statement correctly describes the reaction partner to the gravitational force the Earth exerts on the book?

  1. It is the weight of the table acting downward.
  2. It is the normal force the table exerts on the book.
  3. It is the friction force between the book and the table.
  4. It is the gravitational force the book exerts on the Earth. Correct answer.

Explanation

Newton's third law pairs act on two different bodies and are of the same type. The reaction to Earth pulling the book is therefore the book pulling the Earth with an equal gravitational force. The normal force is a separate contact force that happens to balance the book's weight in this situation.