10 questions, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 10
An adult lizard of a hypothetical species is kept alone in a cage at a constant 25 °C. It is not growing or reproducing and moves very little, yet it slowly loses mass if it is not fed. Which statement best explains why the lizard continues to use energy?
Answer and reasoning
AIts small movements use energy; a body that does not move uses none. A student who thinks energy is used only for movement picks this. Movement adds to an animal's energy use, but every living cell uses energy all the time to maintain its organization, so a motionless animal still uses energy.
BIt generates heat from its metabolism to hold its body at a steady 25 °C. A student who thinks every animal uses metabolic heat to keep its body temperature constant picks this. A lizard is an ectotherm; its body stays near 25 °C because the cage does, not because its metabolism generates heat to hold it there.
CIts body mass is being converted into the energy that is keeping it alive. A student who thinks matter is converted into energy picks this. The lizard breaks down stored molecules and transfers their chemical energy to ATP; the atoms are not converted into energy but leave the body mainly as CO₂ and H₂O, which is why its mass falls.
DIts cells use energy to maintain their organization and internal state.Correct Even at rest, cells use energy for processes such as active transport across membranes and the replacement of worn-out molecules, which keep the organism organized and its internal conditions stable. With no food, the energy comes from stored molecules, so the lizard slowly loses mass.
The model shows the life cycle of a hypothetical species of water flea in which reproduction changes with food availability. According to the model, how would the genetic variation among the offspring produced in a pond change when food becomes scarce?
Answer and reasoning
AIt would increase, as eggs made by meiosis would be fertilized by sperm from males.Correct In the model, plentiful food is linked with eggs made by mitosis that develop without fertilization, giving offspring genetically like their mother. Scarce food is linked with males, eggs made by meiosis and fertilization: meiosis and fertilization combine alleles in new ways, so the offspring vary more.
BIt would increase, as scarce food would cause the new mutations that the offspring need. A student who thinks mutations arise because organisms need them picks this. Mutations are random with respect to need; the model shows that the increase in variation comes from sexual reproduction, through meiosis and fertilization.
CIt would increase, as each mother's genes would change to suit the food that she finds. A student who thinks organisms change their genes to suit their conditions and pass the changes on picks this. A mother's genes are not altered by her food supply; variation increases because offspring are now produced sexually.
DIt would decrease, as scarce food would make females switch to asexual reproduction. A student who thinks asexual reproduction is the low-energy option used when food is scarce picks this. The model shows the reverse: unfertilized eggs develop when food is plentiful, and sexual reproduction occurs when food is scarce.
An ecologist is studying a lake. Which statement correctly describes a level of ecological organization in the lake?
Answer and reasoning
AAll the organisms in the lake, without its water, light or nutrients, form its ecosystem. A student who thinks an ecosystem includes only living things picks this. All the organisms in the lake form a community; adding the abiotic factors (water, light, nutrients) makes it an ecosystem.
BAll the fish, plants and invertebrates in the lake together form a single population. A student who thinks a population can include several species picks this. A population is a group of one species; organisms of many species together form a community.
CAll the populations of different species in the lake together form a community.Correct A community is all the populations of different species that live and interact in an area. A population is one species; an ecosystem adds the abiotic factors; a biome is a large region containing many ecosystems.
DThe lake with its organisms, water, light and nutrients is by itself a biome. A student who thinks a biome is a single local ecosystem picks this. A lake with its organisms and abiotic factors is an ecosystem; a biome is a large region with a characteristic climate and many ecosystems.
Which flowchart best represents the flow of energy through a grassland food chain?
Answer and reasoning
ASunlight → grasses → grasshoppers → decomposers → back to the grasses as energy A student who thinks energy is recycled picks this. Decomposers return atoms (nutrients) to the soil, but the energy they obtain is released as heat; producers get their energy from sunlight, not from decomposers.
BSunlight → grasses → grasshoppers → birds, with energy lost as heat at each stepCorrect Energy enters as sunlight captured by producers, passes in organic molecules from grasses to grasshoppers to birds (arrows show the direction energy moves), and at each step much of it is released as heat, which leaves the ecosystem.
CBirds → grasshoppers → grasses → sunlight, with heat lost by each of the organisms A student who reads food-chain arrows as 'eats' picks this. Arrows show the direction in which energy moves, from the organism eaten to the one that eats it, so they point from sunlight toward the birds.
DGrasses → grasshoppers → birds, with the grasses as the original source of the energy A student who thinks producers create energy picks this. Grasses capture energy from sunlight; they do not make it, so the flowchart must begin with sunlight.
During a summer, a large tree takes up thousands of liters of water from the soil through its roots. Which statement best describes what happens to most of this water?
Answer and reasoning
AMost of it stays stored in the tree's wood and leaves for the rest of its life. A student who thinks plants keep the water they absorb picks this. A tree holds some water in its tissues, but most of what it absorbs passes through it and is lost to the air by transpiration.
BMost of it evaporates from its leaves and returns to the air as vapor.Correct Most of the water absorbed by the roots moves up through the plant and evaporates from the leaves (transpiration), returning to the atmosphere. Only a small fraction is held in the tree's tissues or used in photosynthesis.
CMost of it is built into the sugars and the new wood that the tree makes. A student who thinks water is a plant's main food picks this. Water is a reactant in photosynthesis, but only a small fraction of the water absorbed is used this way.
DMost of it is used up inside the tree's cells and then ceases to exist. A student who thinks matter used by organisms ceases to exist picks this. Water molecules are not destroyed; most leave the tree as vapor and continue through the water cycle.
A student places an aquatic plant in a sealed tube of water containing an indicator that shows changes in CO₂ concentration, and keeps the tube in darkness for 24 hours. An identical tube with no plant is kept beside it as a control. Which result should the student predict?
Answer and reasoning
ACO₂ rises in the tube with the plant, as its cells still release CO₂ in the dark.Correct In darkness, no photosynthesis takes place, but the plant's cells continue cellular respiration, releasing CO₂ into the water. The control tube has no organism, so its CO₂ concentration should not change.
BNeither tube changes, as plants take in CO₂ rather than release it. A student who thinks plants do not carry out cellular respiration picks this. Plant cells respire at all times, releasing CO₂; in the dark, this release is not offset by photosynthesis.
CCO₂ falls in the tube with the plant, as living plants take in CO₂ at all times. A student who thinks plants photosynthesize whenever they are alive picks this. Photosynthesis needs light, so in darkness the plant cannot take in CO₂ by photosynthesis.
DNeither tube changes, as the plant turns its sugar into energy and releases nothing. A student who thinks sugar is converted into energy picks this. In cellular respiration the atoms of sugar are rearranged into CO₂ and H₂O, so CO₂ is released while energy is transferred to ATP.
Bean plants grown in a soil low in nitrogen grow well when their roots form nodules containing certain bacteria, but poorly when no nodules form. Which statement best explains this?
Answer and reasoning
AThe nodules are plant organs that take in N₂ and turn it into protein. A student who thinks legumes fix nitrogen themselves picks this. The fixation is carried out by the bacteria living in the nodules, not by the plant's own cells; plants without the bacteria grow poorly.
BThe nodules let more N₂ from the air reach the roots, where it is used directly. A student who thinks plants can use N₂ directly picks this. Plants cannot use N₂; it must first be fixed into NH₃ by microorganisms.
CThe bacteria convert N₂ from the air into NH₃, which the plant then uses.Correct Nitrogen-fixing bacteria in the nodules convert atmospheric N₂ into NH₃ (which ionizes to NH₄⁺). The plant assimilates this fixed nitrogen into proteins and nucleic acids, so it can grow in soil that is low in nitrogen.
DThe bacteria make nitrogen out of the sugars the plant gives to them. A student who thinks atoms of one element can be made from another picks this. Sugars contain carbon, hydrogen and oxygen; the bacteria use their energy to fix nitrogen atoms that come from N₂ in the air.
In a hypothetical forest, the acorn crop was measured each autumn for eight years, and the density of mice, which feed heavily on acorns in winter, was measured the following summer. The graph shows the data. Which claim is supported by the data?
Answer and reasoning
AHigher mouse densities in summer caused the acorn crops to be larger. A student who thinks a correlation shows causation in either direction picks this. Each acorn crop was measured before the mouse density it is paired with, so the mice could not have caused it.
BMouse density kept rising from year to year whatever the acorn crop. A student who thinks populations keep growing regardless of food picks this. The graph shows mouse density depended on the acorn crop: it was low after small crops and high after large ones, not set by the passage of time.
CYears with larger acorn crops were followed by higher mouse densities.Correct The points rise from about 8–9 mice per ha after crops under 100 kg/ha to 35–38 mice per ha after crops over 350 kg/ha. More food energy available in winter is associated with a larger mouse population the next summer.
DMouse density was unrelated to the acorn crop, as the points are not on a line. A student who thinks variables are related only if points lie exactly on a line picks this. The points scatter, but there is a clear upward trend.
A large volcanic eruption fills the atmosphere with fine ash that greatly reduces the sunlight reaching a region for two years. Which statement best describes the most likely effect on the region's land ecosystems?
Answer and reasoning
AProducers decline, but consumers are unaffected, as they do not depend on sunlight. A student who thinks only producers depend on sunlight picks this. Consumers obtain their energy from organic matter made by producers, so less light means less energy for consumers too.
BLittle changes overall, as decomposers recycle enough energy to replace light. A student who thinks energy is recycled by decomposers picks this. Energy flows through ecosystems and is lost as heat; decomposers cannot replace the energy input from sunlight.
CTop predators are least affected, as they hold the most energy in the food web. A student who thinks top predators hold the most energy picks this. Top predators have the least energy available to them, because energy is lost at every transfer, so they are often among the first to be affected.
DPrimary productivity falls, so each trophic level has less energy available to it.Correct With less sunlight, photosynthetic producers capture less energy, so less energy is stored in organic matter. Consumers at every level obtain their energy, directly or indirectly, from producers, so the energy available to them falls and the ecosystem is disrupted.
Which measurement would best estimate the primary productivity of a meadow?
Answer and reasoning
AThe rate at which producers make new organic matter on each square meterCorrect Primary productivity is the rate at which producers, such as photosynthetic plants, capture energy and store it in organic matter. It is measured per unit area per unit time, for example as new organic matter per square meter per year.
BThe amount of sunlight energy that falls on each square meter of the meadow A student who thinks primary productivity is the light reaching an area picks this. Only a small fraction of incoming sunlight is captured by producers; productivity measures what is captured.
CThe total mass of all organisms present in the meadow on a single day A student who confuses biomass with productivity picks this. The mass present on one day is an amount, not a rate; productivity is how fast new organic matter is made.
DThe amount of new energy that producers create from carbon dioxide and water A student who thinks producers create energy picks this. Producers capture light energy and store it in organic molecules made from CO₂ and water; they do not create energy.
In preparation: 0 of 13 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
8.2.A.1 Energy use by organisms Fix
Energy use by organisms
Organisms use energy to organize, grow, reproduce and maintain homeostasis. Even an organism at rest uses energy continuously, for example for active transport and for building and replacing molecules.
Homeostasis
The maintenance of relatively stable internal conditions, such as body temperature or solute concentrations, despite changes in the external environment. Maintaining homeostasis requires energy.
Endotherm
An organism that uses thermal energy generated by its metabolism to maintain a homeostatic body temperature, such as a mammal or bird. As its surroundings become colder, an endotherm loses heat faster and generally must increase its metabolic rate to replace it.
Ectotherm
An organism that lacks efficient internal mechanisms for maintaining body temperature, so its body temperature depends largely on its surroundings; examples include most reptiles, amphibians, fish and invertebrates. Its metabolic rate generally rises and falls with its body temperature.
Behavioral thermoregulation
Regulation of body temperature by behavior, such as moving into the sun or shade or aggregating with other individuals. Many ectotherms keep their body temperature within a range this way.
Net energy gain
The condition in which an organism takes in more energy than it uses. The surplus results in energy storage, growth of the organism and increased reproductive output.
Net energy loss
The condition in which an organism uses more energy than it takes in. It results in loss of mass, a decrease in reproductive output and, eventually, the death of the organism.
Students often think Energy is used mainly for movement, so an animal that is not moving uses little or no energy. In fact Yes. Its cells continuously use energy to keep up their organization and internal conditions, for example by active transport across membranes and by replacing worn-out molecules. This is why a resting animal that is not fed slowly uses up its stored molecules.
Students often think Every animal uses heat from its metabolism to keep its body temperature constant, as humans do. In fact No. Endotherms use thermal energy generated by metabolism to maintain a homeostatic body temperature. Ectotherms lack efficient internal mechanisms for this; their body temperature depends largely on their surroundings, although many regulate it by behavior.
8.2.A.2 Reproductive strategy and energy availability Fix
Reproductive strategy and energy availability
Different organisms use various reproductive strategies in response to energy availability, such as reproducing in particular seasons or storing energy before reproducing. Some organisms, such as water fleas and aphids, alternate between asexual and sexual reproduction in response to energy availability.
Students often think When conditions become difficult, the mutations that offspring need are produced in response. In fact No. Mutations arise at random with respect to an organism's needs. A harsh environment does not produce the particular mutations that would help. Genetic variation among offspring comes from mutations, which arise at random, and, in sexual reproduction, from meiosis and fertilization.
Students often think Organisms change their genes during their lifetime to suit their environment and pass these changes on to their offspring. In fact No. An organism's genes are not altered to suit the conditions it meets, and traits acquired during an organism's life are not passed to its offspring through its genes.
8.2.B.1 Population Fix
Population
A group of individuals of the same species living in the same area.
Community
All the populations of different species that live and interact in the same area.
Ecosystem
A community of organisms together with the abiotic (nonliving) factors of the environment with which they interact, such as water, light, temperature and nutrients.
Biome
A large geographic region characterized by its climate and typical communities, such as tundra, desert or tropical rain forest. A biome contains many ecosystems.
Students often think An ecosystem is all the living things in an area; nonliving factors such as water and light are separate from it. In fact No. An ecosystem consists of a community of organisms together with the abiotic (nonliving) factors of their environment, such as water, light, temperature and nutrients, which they interact with.
Students often think A population is all the organisms living in an area, whatever their species. In fact No. A population is a group of individuals of the same species living in the same area. All the populations of the different species living and interacting in an area make up a community.
8.2.B.2 Energy flow Fix
Energy flow
The one-way movement of energy through an ecosystem: energy enters mainly as light captured by producers, passes between trophic levels in organic molecules, and leaves as heat. Energy is not recycled, so ecosystems need a continuous energy input.
Biogeochemical cycle
The cycling of an element or compound, such as water, carbon, nitrogen or phosphorus, between the environment and organisms. Each cycle demonstrates the conservation of matter, and the cycles are interdependent.
Conservation of matter
The principle that atoms are not created or destroyed in biological or chemical processes; they are rearranged into new molecules and moved between places.
Students often think Food, fat or other matter is converted into energy when it is used, and energy (such as light) can be converted into matter. In fact No, not in biological processes. In cellular respiration, the atoms in food molecules are rearranged into CO₂ and H₂O while chemical energy is transferred to ATP and released as heat. In photosynthesis, light energy is captured in the bonds of sugars made from the atoms of CO₂ and H₂O. Atoms are conserved throughout.
Students often think Energy is recycled in ecosystems: decomposers return the energy in dead organisms to the soil, where producers take it up again. In fact No. Energy flows through an ecosystem: it enters mainly as light captured by producers, passes from one trophic level to the next in organic molecules, and is eventually lost as heat. Matter, including carbon and nitrogen atoms, is what cycles; decomposers return matter, not usable energy, to producers.
8.2.B.3 Reservoir (abiotic and biotic) Fix
Reservoir (abiotic and biotic)
A place where matter in a biogeochemical cycle is stored. Abiotic reservoirs include the atmosphere, oceans, surface water, soil and rocks; biotic reservoirs are living organisms. Processes move matter between reservoirs.
Students often think Only nonliving parts of the environment, such as air, water and rock, are reservoirs; organisms just pass matter through without storing it. In fact Yes. Biogeochemical cycles include biotic reservoirs (living organisms and their tissues, such as the wood of trees) as well as abiotic reservoirs (such as the atmosphere, oceans and rocks). Carbon can be held in a tree's wood for many years.
Students often think Carbon locked in rock has left the cycle for good and is no longer part of it. In fact No. Rocks such as limestone are slow abiotic reservoirs. Carbon can be held in them for very long times but returns to other reservoirs through processes such as weathering and volcanic activity.
8.2.B.4 Hydrologic (water) cycle Fix
Hydrologic (water) cycle
The movement and storage of water within the hydrosphere. Reservoirs include oceans, surface water, the atmosphere and living organisms; processes include evaporation, condensation, precipitation and transpiration.
Transpiration
The loss of water vapor from plants, mainly through their leaves. It returns most of the water a plant absorbs to the atmosphere.
Students often think Water absorbed by plants stays stored in the plant, so plants hold back water from the cycle. In fact No. Most of the water that a plant absorbs through its roots moves through the plant and evaporates from its leaves by transpiration, returning to the atmosphere. Only a small fraction is held in the plant's tissues or used in reactions such as photosynthesis.
Students often think The water cycle is a purely physical cycle of evaporation, condensation and precipitation, and living organisms play no part in it. In fact Yes. Living organisms are reservoirs in the water cycle, and plants move large amounts of water from soil to the atmosphere by transpiration. Removing vegetation changes how much water returns to the atmosphere and how much runs off.
8.2.B.5 Carbon cycle Fix
Carbon cycle
The recycling of carbon atoms through Earth's biosphere into organisms as carbohydrates and back into the atmosphere as CO₂. At the highest level it can be simplified into photosynthesis, cellular respiration, decomposition and combustion.
Decomposition
The breakdown of dead organic matter and wastes by decomposers such as bacteria and fungi. Their cellular respiration releases carbon as CO₂, and the process releases nutrients such as ammonium and phosphate.
Combustion
Burning of organic material, such as wood or fossil fuels, which combines its carbon with oxygen and releases it to the atmosphere as CO₂.
Students often think Plants get the carbon that makes up most of their body from the soil or from fertilizer. In fact Most of a plant's carbon comes from CO₂ taken in from the air (or water) and fixed in photosynthesis. Soil supplies water and mineral nutrients such as nitrate and phosphate, but very little of a plant's carbon.
Students often think Plants do not carry out cellular respiration; they photosynthesize instead, so they only take in CO₂ and never release it. In fact Yes. Plant cells carry out cellular respiration at all times, releasing CO₂, in the light and in the dark. In the light, photosynthesis usually takes in CO₂ faster than respiration releases it, which hides the release; in the dark, only the release is seen.
8.2.B.6 Nitrogen fixation Fix
Nitrogen fixation
The conversion of nitrogen gas (N₂) into ammonia (NH₃), which ionizes to ammonium (NH₄⁺) by acquiring hydrogen ions from the soil solution. In soil it is carried out by nitrogen-fixing microorganisms, some living in the root nodules of legumes.
Assimilation (nitrogen)
The uptake of inorganic nitrogen, such as NH₄⁺ and NO₃⁻, by producers and its incorporation into organic molecules such as proteins and nucleic acids.
Ammonification
The conversion of organic nitrogen in dead organisms and wastes into ammonia/ammonium by decomposers.
Nitrification
The conversion of ammonium (NH₄⁺) into nitrate (NO₃⁻) by nitrifying microorganisms in the soil.
Denitrification
The conversion of nitrate (NO₃⁻) into nitrogen gas (N₂) by denitrifying microorganisms, returning nitrogen to the atmosphere, its largest reservoir.
Students often think Plants take nitrogen gas directly from the air, through their leaves or roots, to make proteins. In fact No. Plants cannot use N₂. They assimilate nitrogen from the soil, mainly as ammonium (NH₄⁺) and nitrate (NO₃⁻), which are produced by the activities of microorganisms such as nitrogen-fixing and nitrifying bacteria.
Students often think Nitrifying bacteria are the ones that fix nitrogen from the air, so nitrification and nitrogen fixation are the same step. In fact No. Nitrogen fixation converts N₂ gas into NH₃ (which ionizes to NH₄⁺). Nitrification is a different step, carried out by other soil microorganisms, that converts NH₄⁺ into nitrate (NO₃⁻).
8.2.B.7 Phosphorus cycle Fix
Phosphorus cycle
The cycling of phosphorus: weathering of rocks releases phosphate (PO₄³⁻) into soil and groundwater; producers take it in and incorporate it into biological molecules; consumers obtain it by eating; it returns to the soil by decomposition and excretion. The cycle has no major atmospheric reservoir.
Students often think Like carbon and nitrogen, phosphorus moves between organisms and the atmosphere as a gas. In fact No. The phosphorus cycle has no major atmospheric reservoir. Phosphate (PO₄³⁻) enters soil and groundwater by the weathering of rocks, is taken in by producers, passes to consumers and returns to the soil by decomposition and excretion.
Students often think Producers make their own phosphorus, as they make their own food in photosynthesis. In fact No. Producers take in phosphate from the soil or water and incorporate it into biological molecules such as nucleic acids, ATP and phospholipids. The phosphate originally comes from the weathering of rocks and is recycled by decomposition and excretion.
8.2.C.1 Energy availability and population size Fix
Energy availability and population size
The amount of energy available to a population, for example as food, affects births and deaths, so changes in energy availability can result in changes in population size.
Students often think If two variables are correlated, either one can be taken as the cause of the other. In fact No. A correlation shows that two variables change together. Which variable could cause the other has to be decided from other information, such as which change came first or an experiment in which one variable is manipulated.
Students often think Populations tend to grow steadily over time whatever the amount of food available. In fact No. When the energy available changes, population size can change too. When less food energy is available, fewer offspring are produced and more individuals die, so a population can shrink; when more is available, it can grow.
8.2.C.2 Ecosystem disruption by energy change Fix
Ecosystem disruption by energy change
A change in energy availability, such as reduced sunlight, can disrupt an ecosystem by reducing primary productivity and the energy available to every trophic level.
Trophic level
A feeding position in a food chain or web: producers; primary, secondary, tertiary and quaternary consumers; and decomposers.
Energy pyramid
A diagram showing the energy stored at each trophic level per unit area per unit time. Energy decreases at each higher level because much is used for maintenance and lost as heat, which limits the number of trophic levels an ecosystem can support.
Food chain and food web
Diagrams of feeding relationships in which arrows point from the organism eaten to the organism that eats it, showing the direction of energy and matter transfer. A food web links many food chains, so a change in producers can affect all other trophic levels.
Students often think The arrows in a food chain point from the eater to what it eats, so an arrow means 'eats'. In fact Arrows point from the organism that is eaten to the organism that eats it, showing the direction in which energy and matter move. For example, grass → grasshopper means the grasshopper eats the grass.
Students often think A change in a population or a step of a cycle affects only the parts directly connected to it. In fact No. Because populations are linked through food webs and nutrient cycles, a change in one population (or one step of a cycle) can affect populations and processes that are not directly linked to it, through intermediate links.
8.2.D.1 Autotroph Fix
Autotroph
An organism that captures energy from physical (light) or chemical sources in the environment and uses it to make organic molecules from inorganic ones; a producer.
Photosynthetic organism
An autotroph that captures energy present in sunlight and stores it in organic molecules made from CO₂ and water, contributing to primary productivity.
Primary productivity
The rate at which producers capture energy and store it in organic matter, expressed per unit area per unit time.
Chemosynthetic organism
An autotroph that captures energy from small inorganic molecules in its environment, such as hydrogen sulfide, and uses it to make organic molecules; chemosynthesis can occur in the absence of oxygen.
Students often think Producers make energy, so plants are the original source of the energy in a food chain. In fact No. Producers capture energy; they do not create it. Photosynthetic organisms capture light energy, and chemosynthetic organisms capture energy from small inorganic molecules, storing it in the chemical bonds of the organic molecules they make.
Students often think Plants carry out photosynthesis and take in CO₂ whenever they are alive, whether or not they are in the light. In fact No. Photosynthesis captures energy from light, so without light it cannot take place. In darkness, a plant's cells continue to carry out cellular respiration, which releases CO₂.
8.2.D.2 Heterotroph Fix
Heterotroph
An organism that obtains energy and carbon by consuming organic matter derived from autotrophs; it metabolizes carbohydrates, lipids and proteins as energy sources. Heterotrophs include carnivores, herbivores, omnivores, decomposers and scavengers.
Decomposer
A heterotroph, such as a fungus or bacterium, that obtains energy and matter by breaking down dead organic matter and wastes.
Scavenger
A heterotroph that feeds on the bodies of dead animals that it did not kill.
Students often think Everything an animal digests and absorbs becomes part of its body; only the undigested food in feces is lost. In fact No. Much of the energy in absorbed food is released by cellular respiration to power the animal's activities and maintenance, and leaves the animal as heat. Only the remainder is stored in new biomass.
Students often think Exactly 10% of the energy at one trophic level is passed to the next in every case, so data can be ignored. In fact No. About 10% is a rough average used for illustration. The fraction transferred varies among organisms and ecosystems and must be calculated from the data given.
21 more questions. Every wrong answer here is a real mistake students make, and you see why it is wrong as soon as you answer.
Question 1 of 21
In a field study, the body temperature of a lizard of a hypothetical species, an ectotherm, was recorded through one day, together with the temperature of the air in shade and of the ground in direct sun. The lizard was seen moving between sunny and shaded spots. The graph shows the data. Which claim is supported by the data?
Answer and reasoning
AIts body temperature matched the shade air temperature at each reading from 06:00 to 18:00. A student who thinks an ectotherm's temperature simply equals that of its surroundings picks this. At 12:00 the lizard was at 36 °C while the shade air was at 29 °C; by moving into the sun it kept its body warmer than the shade.
BFrom 10:00 to 16:00, its body temperature varied less than the temperature in sun or in shade.Correct From 10:00 to 16:00 the lizard's body temperature stayed between 34 °C and 36 °C, while the shade air ranged from 24 °C to 30 °C and the sunlit ground from 36 °C to 47 °C. Moving between sun and shade, an ectotherm can regulate its temperature behaviorally.
CIts body temperature stayed below the temperature of the air in the shade all day long. A student who thinks 'cold-blooded' animals are always cold picks this. From 08:00 onward the lizard's body was warmer than the shade air, by as much as 11 °C at 10:00.
DIt held its body temperature steady by generating heat from its own metabolism. A student who thinks every animal keeps a steady temperature with metabolic heat picks this. Nothing in the data shows heat production; the lizard is an ectotherm that was seen moving between sun and shade, which is how it gained and avoided heat.
Two hypothetical animal species, X and Y, of similar body mass were each kept resting for several hours in a chamber at three air temperatures, and their body temperatures were measured. The table shows the results. Predict how the rate of energy use of species X would change if the air temperature were lowered from 30 °C to 10 °C.
Answer and reasoning
AIt would decrease, as the colder air slows the chemical reactions in its cells. A student who thinks cold slows every animal's metabolism picks this. X's body does not cool: it stays near 38 °C, so its reactions do not slow, and holding that temperature in colder air requires more heat production.
BIt would stay the same, as X keeps its body temperature nearly constant. A student who thinks a constant body temperature costs no extra energy picks this. X keeps its temperature constant only by replacing the extra heat lost to colder air, so its energy use rises.
CIt would increase, as X must make more heat to replace its faster heat loss.Correct X's body temperature stays near 38 °C at every air temperature, so it is an endotherm. In colder air it loses heat faster and keeps its body temperature constant only by generating more thermal energy by metabolism, so its rate of energy use rises.
DIt would stay the same, as X is resting in the chamber rather than moving. A student who thinks energy is used mainly for movement picks this. A resting endotherm still uses energy continuously, and in colder air it must generate more heat to hold its body temperature, so its energy use rises.
On a cool morning, an ecologist counted the lizards of a hypothetical ectothermic species in sunlit and shaded patches of a habitat. The table shows the counts. The null hypothesis is that the lizards are distributed between sunlit and shaded patches in proportion to the area of each. Using a chi-square test at p = 0.05, which conclusion is supported?
Answer and reasoning
AReject the null hypothesis, as χ² = 12.96 is greater than the critical value of 3.84.Correct Expected counts are 0.5 × 100 = 50 in each type of patch. χ² = (68 − 50)²/50 + (32 − 50)²/50 = 6.48 + 6.48 = 12.96. With 2 − 1 = 1 degree of freedom, the critical value at p = 0.05 is 3.84; 12.96 > 3.84, so the departure from the expected counts is unlikely to be due to chance alone.
BFail to reject the null hypothesis, as a χ² of 12.96 shows a close fit to the expected counts. A student who thinks a large χ² means a good fit picks this. χ² measures how far the observed counts are from the expected ones; 12.96 is well above the critical value of 3.84, so the fit is poor and the null hypothesis is rejected.
CReject the null hypothesis; this proves that the lizards bask in order to warm their bodies. A student who thinks rejecting the null hypothesis proves an explanation picks this. The test shows only that the lizards were not distributed in proportion to area; it is consistent with behavioral warming but does not prove why they were in the sun.
DReject the null hypothesis, since the observed counts are not exactly 50 in each type of patch. A student who thinks any departure from the expected counts disproves the null hypothesis picks this. Chance alone makes counts differ somewhat from 50; the null hypothesis is rejected here because χ² = 12.96 exceeds the critical value of 3.84, not because the counts are unequal.
Working Expected count in each patch type = 0.5 × 100 = 50. χ² = (68 − 50)²/50 + (32 − 50)²/50 = 324/50 + 324/50 = 6.48 + 6.48 = 12.96. Degrees of freedom = 2 classes − 1 = 1; critical value at p = 0.05 = 3.84. Because 12.96 > 3.84, reject the null hypothesis: the lizards were not distributed in proportion to area.
Female fish of a hypothetical species were each fed a fixed daily ration for 4 weeks. The table shows the mean change in body mass and the mean number of eggs produced per female at each ration. Which claim is supported by the data?
Answer and reasoning
AEvery ration tested led to at least some gain in body mass, even the smallest ration. A student who thinks any food eaten adds to body mass picks this. At 0.5 g and 1.0 g the females lost mass (−3.2 g and −0.6 g): the energy in these rations was less than the energy they used.
BEggs were produced only at rations that also gave the females a net gain in body mass.Correct At rations of 0.5 g and 1.0 g, females lost mass (a net loss of energy) and produced no eggs. At 1.5 g and above, they gained mass and produced eggs, and both the gain in mass and the number of eggs rose as the ration increased.
CFemales given the smallest rations laid the most eggs, so that some young would survive. A student who thinks organisms short of energy reproduce more to help their species survive picks this. Females on the two smallest rations laid no eggs; reproduction requires energy, and they had a net loss.
DThe number of eggs per female stayed about the same across all the rations tested. A student who thinks reproductive output is fixed regardless of energy intake picks this. The mean number of eggs rose from 0 to 130 as the ration increased.
In a population of a hypothetical songbird, a cold spring reduces the number of insects the birds eat for six weeks, so that most adults take in less energy each day than they use. Which prediction about the adults is best supported?
Answer and reasoning
AThey lose body mass but lay as many eggs as they would in a good year. A student who thinks the number of offspring is fixed regardless of energy intake picks this. Producing eggs takes a great deal of energy, so a net loss of energy reduces reproductive output.
BThey lay more eggs than usual so that their population survives the shortage. A student who thinks organisms in danger reproduce more for the good of the species picks this. Birds do not plan for their species; with a net loss of energy, they have less energy to put into eggs, not more.
CThey rest more and so use no stored energy, keeping their body mass steady. A student who thinks only movement uses energy picks this. Resting reduces energy use, but cells still use energy to stay organized and, in an endotherm such as a bird, to generate body heat, so stored energy is still used.
DThey lose mass, lay fewer eggs, and those whose stores run out die.Correct A net loss of energy means stored molecules are used up, so the birds lose mass. With less energy available, reproductive output falls, and individuals whose stores run out die.
Nesting females of a hypothetical bird species were given no extra food (control), a low food supplement or a high food supplement during the breeding season (n = 25 nests per group). The graph shows the mean clutch size of each group. Which conclusion is best supported by the data?
Answer and reasoning
AThe high supplement probably increased clutch size; the data do not show an effect of the low one.Correct The high-supplement bar (4.1 to 4.7 eggs) does not overlap the control bar (2.9 to 3.5), so that difference is likely to be real. The low-supplement bar (3.2 to 3.8) overlaps the control bar, so the data do not establish a difference, although they do not rule out a small one.
BBoth supplements increased clutch size, since both means are higher than the control's mean. A student who thinks any difference in means shows an effect picks this. The low-supplement mean (3.5) is above the control mean (3.2), but the ±2 SE bars overlap, so this difference may be due to chance.
CThe high supplement likely increased clutch size; the low supplement had no effect on it. A student who thinks overlapping error bars prove no effect picks this. The overlap of the low-supplement and control bars means the data do not show a difference; it does not prove that the low supplement had no effect.
DNeither supplement changed clutch size, which is set by the genes of each female bird. A student who thinks reproductive output is fixed by genes regardless of energy picks this. The high-supplement bar does not overlap the control bar, so the data indicate that more food energy led to larger clutches.
Working Error bars are ±2 SE, so each spans mean ± 0.3: control 2.9–3.5; low supplement 3.2–3.8; high supplement 4.1–4.7. High vs control: no overlap (4.1 > 3.5), so the difference is likely significant. Low vs control: the bars overlap (3.2–3.5), so the data do not establish a difference.
A student plans to test whether a net loss of energy reduces egg production in a hypothetical insect species. Thirty adult females will each be fed half of their normal daily food for two weeks, and the eggs each one lays will be counted. Which additional group would be the most appropriate control?
Answer and reasoning
AThirty adult females of the same species given no food at all under the same conditions A student who thinks a control must receive none of the factor being tested picks this. Starved females test a much more severe deficit; they do not show what normal egg production is, so they cannot serve as the baseline.
BNo other group, since counting the eggs laid by thirty females already gives enough data A student who thinks a large sample makes a control unnecessary picks this. Without a group on the normal ration, there is no way to tell whether thirty females on half rations laid fewer eggs than they otherwise would.
CThirty similar females on their usual daily food, kept under identical conditionsCorrect The control should differ from the experimental group only in the variable being tested. Females of the same species, age and conditions given the normal ration show how many eggs are laid without an energy deficit, so any difference can be attributed to the reduced food.
DThirty adult females of a related insect species fed their normal daily food A student who thinks any separate group can serve as a control picks this. These females differ in species as well as in diet, so a difference in egg numbers could be caused by either variable.
A student seals soil, water, a small plant, and some soil animals in a clear glass container and places it where it receives light. After three months the plant has grown, and the mass of the sealed container and its contents is unchanged. Which reasoning best accounts for both observations?
Answer and reasoning
AThe light energy that entered the container was converted into the matter of the new plant tissue. A student who thinks energy can be converted into matter picks this. Light provides the energy to make sugars, but the atoms in the new tissue came from CO₂, water and minerals already present; that is why the mass did not change.
BBoth energy and matter were recycled inside the container, so nothing needed to enter it from outside. A student who thinks energy is recycled picks this. Matter cycles inside the container, but energy is lost as heat at every step, so the system depends on light entering from outside.
CThe matter used up by the animals was balanced by an equal amount of new matter that the plant made. A student who thinks matter is used up and made by organisms picks this. Neither animals nor plants destroy or create matter: they rearrange atoms, which pass between organisms and the air, water and soil.
DAtoms already in the container were rearranged into new plant tissue, and light supplied the energy for this.Correct Matter is conserved: the plant built its new tissue from atoms already in the container (carbon from CO₂ released by the organisms' respiration, plus water and minerals), so the total mass did not change. Energy is not recycled, so the container needed light entering from outside to power photosynthesis.
In a hypothetical forest, ammonium nitrate (NH₄NO₃) fertilizer was added to some plots each year for five years, while control plots received none. The graph shows the mean net carbon uptake by the producers in each group of plots in the fifth year. Which statement best relates these results to biogeochemical cycles?
Answer and reasoning
AThe cycles are linked: nitrogen supply limited how much carbon the producers took in from CO₂.Correct The error bars do not overlap, so the plots with added nitrogen probably took up more carbon. Producers need nitrogen to make proteins, nucleic acids and chlorophyll, so the amount of carbon they fix can depend on nitrogen: the carbon and nitrogen cycles are interdependent.
BThe added nitrogen atoms were changed into the extra carbon the trees took in and stored. A student who thinks atoms of one element can be changed into another picks this. Nitrogen atoms remain nitrogen; the extra carbon came from CO₂ in the air, fixed in photosynthesis.
CThe cycles are independent of each other, so the difference between the plots is due to chance. A student who thinks biogeochemical cycles are independent picks this. The ±2 SE bars do not overlap, so the difference is unlikely to be due to chance; the result shows the cycles are linked through the producers.
DThe fertilizer enriched the soil, and producers take most of their carbon from the soil. A student who thinks plants get their carbon from soil picks this. Producers take in carbon as CO₂ from the air; the fertilizer supplied nitrogen (NH₄NO₃ contains no carbon), which allowed them to fix more CO₂.
In a forest, carbon is found in CO₂ in the atmosphere, in the wood of living trees, and in limestone rock beneath the soil. Which statement correctly classifies these stores of carbon?
Answer and reasoning
AThe atmosphere and limestone are reservoirs, but trees only pass carbon on and store none. A student who thinks organisms cannot be reservoirs picks this. Trees hold carbon in their wood for many years; living organisms are biotic reservoirs.
BThe atmosphere and the trees are reservoirs, but carbon in the rock has left the cycle for good. A student who thinks carbon in rock is permanently lost from the cycle picks this. Limestone is a slow abiotic reservoir; its carbon can return to the atmosphere and oceans through processes such as weathering.
CThe atmosphere is abiotic, and the trees and limestone, which was made from shells, are biotic. A student who thinks anything formed by organisms is a biotic reservoir picks this. Limestone may have formed from ancient shells, but it is rock, not living tissue, so it is an abiotic reservoir.
DThe atmosphere and limestone are abiotic reservoirs; living trees are a biotic one.Correct Biogeochemical cycles include abiotic reservoirs (such as the atmosphere, oceans and rocks) and biotic reservoirs (living organisms). Carbon in living wood is held in a biotic reservoir until it is respired, eaten or decomposed.
Three hypothetical watersheds of equal size each receive 1,000 mm of precipitation per year. The table shows how this water leaves each watershed. Which claim is supported by the data?
Answer and reasoning
AThe trees used up much of the water that fell, so less of it returned to the atmosphere. A student who thinks plants keep or use up the water they absorb picks this. The forest returned the most water to the atmosphere (600 mm), 450 mm of it by transpiration.
BPlant cover changed how much water ran off but not how much returned to the atmosphere. A student who thinks living organisms play no part in the water cycle picks this. Water returned to the atmosphere ranged from 600 mm (forest) to 100 mm (paved), mainly because of differences in transpiration.
CWhere plants grew, more of the precipitation returned to the atmosphere than from paved land.Correct Water returned to the atmosphere is transpiration plus evaporation: forest 450 + 150 = 600 mm, grassland 300 + 150 = 450 mm, paved land 0 + 100 = 100 mm. Plants returned water to the atmosphere by transpiration, so less of the precipitation ran off.
DSome of the precipitation on the forest was destroyed, as that watershed had the least runoff. A student who thinks matter can be used up picks this. In each watershed, transpiration, evaporation and runoff add up to 1,000 mm, so all the water is accounted for; the forest's water left mostly as vapor.
The diagram is a model of the carbon cycle. Suppose a toxin killed most of the decomposers in the soil of a forest for several years. According to the model, which change would be expected?
Answer and reasoning
ACarbon in the soil would decrease, as decomposers are what move dead matter's carbon into soil. A student who thinks decomposition returns carbon to the soil rather than to the air picks this. The model shows decomposition (arrow 5) moving carbon from dead organic matter to the atmosphere as CO₂ released by decomposers' respiration; without decomposers, carbon builds up in dead organic matter instead.
BCarbon would build up in dead organic matter, as less of it would return to the air.Correct Arrow 5 (decomposition) carries carbon from dead organic matter to the atmosphere through the respiration of decomposers. Without decomposers, this flow falls while dead matter keeps arriving along the dashed lines, so carbon accumulates in dead organic matter.
CThe producers would stop growing, as decomposers supply the energy they take from soil. A student who thinks energy is recycled through decomposers picks this. Producers obtain energy from sunlight (arrow 1); decomposers return atoms such as nitrogen and phosphorus, not usable energy.
DDead organic matter would still rot away by itself, so no carbon would build up in it. A student who thinks dead matter decays on its own picks this. Decay is carried out by living decomposers; without them, dead matter is broken down only very slowly and accumulates.
The diagram is a model of the nitrogen cycle in a soil. Suppose the soil lacked the microorganisms that carry out nitrification. According to the model, which change would be expected?
Answer and reasoning
AThe plants would be unaffected, as they obtain their nitrogen directly from N₂ in the air. A student who thinks plants use atmospheric N₂ directly picks this. The model shows plants assimilating nitrogen only from NH₄⁺ and NO₃⁻ in the soil; they cannot use N₂.
BLess N₂ would be converted into NH₄⁺, so the amount of NH₄⁺ in the soil would fall. A student who confuses nitrification with nitrogen fixation picks this. Fixation (N₂ → NH₄⁺) is a different step; without nitrification, NH₄⁺ would tend to build up because it is no longer converted to NO₃⁻.
CThe amount of NO₃⁻ would fall, but no other step or box in the cycle would be affected. A student who thinks a change affects only directly linked parts picks this. Denitrification uses NO₃⁻, so it would also decrease, and NH₄⁺ would tend to accumulate.
DLess NO₃⁻ would form, so less nitrogen would return to the atmosphere by denitrification.Correct Nitrification converts NH₄⁺ to NO₃⁻. Without it, little NO₃⁻ forms, and because denitrification starts from NO₃⁻, less nitrogen would be returned to the atmosphere as N₂: a change in one step affects a step it is not directly linked to.
A student hypothesizes that the nitrogen fixed in the root nodules of bean plants is fixed by bacteria in the nodules, not by the bean plants themselves. Which investigation would best test this hypothesis?
Answer and reasoning
AGrow beans in sterilized nitrogen-free soil, half given the nodule bacteria, and compare plant nitrogen.Correct Sterilized, nitrogen-free soil removes other nitrogen sources and bacteria, and inoculating only half the plants makes the bacteria the only difference between groups. More nitrogen in the inoculated plants would support the hypothesis.
BGrow beans and corn in nitrogen-free soil with the bacteria present, and compare plant nitrogen. A student who thinks the bean plant itself fixes nitrogen picks this. Comparing two plant species tests a difference between plants, not whether the bacteria are responsible.
CGrow beans with the bacteria in nitrogen-free soil and others in no soil, and compare their nitrogen. A student who thinks a control should lack everything picks this. Plants with no soil differ in many ways besides the bacteria (water, minerals, support), so differences could not be attributed to the bacteria.
DGrow 500 beans with the bacteria in nitrogen-free soil and measure the nitrogen in every plant. A student who thinks a large sample replaces a control picks this. Without beans grown without the bacteria, there is nothing to compare with, so the role of the bacteria cannot be judged.
The diagram is a model of the phosphorus cycle. Which statement about the phosphorus cycle is supported by the model?
Answer and reasoning
ALike carbon, phosphorus enters producers from the atmosphere as a gas. A student who thinks every nutrient cycles through the air picks this. The model has no atmospheric box; producers take in phosphate from soil and groundwater.
BProducers make their own phosphate during photosynthesis and pass it to consumers. A student who thinks producers make all the substances they contain picks this. In the model, producers take up phosphate that came from rocks; photosynthesis makes sugars, not phosphate.
CPhosphorus in an organism leaves the cycle for good when the organism dies. A student who thinks matter is lost when organisms die picks this. The model shows phosphorus in dead organisms and wastes returning to the soil by decomposition.
DPhosphorus enters food webs from weathered rock, with no atmospheric reservoir.Correct In the model, phosphate (PO₄³⁻) is released into soil and groundwater by the weathering of rocks, taken up by producers, passed to consumers and returned by decomposition and excretion. No box represents the atmosphere, unlike the carbon and nitrogen cycles.
In a hypothetical forest, phosphate enters the soil mainly from the slow weathering of rock. Every 20 years, the trees are harvested and the wood is removed instead of being left to decompose. Which prediction about the soil's phosphate over many harvests is best supported?
Answer and reasoning
AIt would stay the same, as phosphate would be replaced from the air like nitrogen. A student who thinks phosphorus has an atmospheric reservoir picks this. Phosphorus has no major atmospheric form; it is replaced mainly by the slow weathering of rock.
BIt would decline, as phosphorus in the removed wood no longer returns by decomposition.Correct Phosphorus taken up by the trees is in their wood. When the wood is removed, that phosphorus leaves the forest instead of returning to the soil by decomposition, and slow weathering replaces it only slowly, so soil phosphate declines over many harvests.
CIt would stay the same, as matter is conserved and so it cannot leave the forest. A student who misapplies conservation of matter picks this. Atoms are not destroyed, but they can be carried away: phosphorus in the harvested wood leaves the forest.
DIt would rise, as the regrowing young trees make new phosphate while they grow. A student who thinks producers make their own phosphate picks this. Trees take phosphate from the soil; regrowth draws down the soil's phosphate rather than adding to it.
The diagram shows energy pyramids for two hypothetical ecosystems. Ecosystem A receives full sunlight; ecosystem B is heavily shaded. Which statement best explains why ecosystem B supports no tertiary consumers?
Answer and reasoning
AB's decomposers return less energy to its producers, so the cycle of energy cannot reach a fourth level. A student who thinks energy is recycled picks this. Producers capture their energy from sunlight, not from decomposers; B has fewer levels because less light energy is captured at its base.
BB lacks the right kinds of species; how much energy is captured does not set how many levels there are. A student who thinks the number of trophic levels depends only on the species present picks this. Because energy is lost at every transfer, the energy captured by producers limits how much reaches each higher level, and B's base captures far less than A's.
CLess energy is captured at B's base, so too little reaches a fourth level to support a population.Correct In both pyramids, each level holds roughly a tenth or less of the energy of the level below. B's producers capture 6,000 kJ/m² per year, so its secondary consumers hold only 45; a fourth level would receive only a few kJ/m² per year, too little to support a population of tertiary consumers.
DTertiary consumers hold more energy than any level below them, more than B's producers could supply. A student who thinks top predators hold the most energy picks this. Pyramid A shows tertiary consumers holding the least energy (18 kJ/m² per year); the limit in B is that too little energy reaches the top, not that top consumers hold the most.
The diagram shows a food web in a lake. Sediment from a construction site clouds the water and reduces the biomass of algae by half for one season. Predict the effect on the bass population.
Answer and reasoning
AIt would not change, as the bass do not feed directly on the algae themselves. A student who thinks a change affects only directly linked populations picks this. The bass depend on algae indirectly through both of their prey, so a fall in algal biomass reaches them.
BIt would decrease, as less energy would reach it through each of its food chains.Correct Both of the bass's food chains begin with algae (algae → zooplankton → minnows → bass and algae → snails → crayfish → bass). With half the algal biomass, less energy enters both chains, so less reaches the bass, and its population is likely to decrease.
CIt would not change, as decomposers would recycle the dead algae's energy to the bass. A student who thinks energy is recycled picks this. Decomposers release the energy in dead algae as heat; it does not return to the food chains that lead to the bass.
DIt would increase, since fewer algae would be eating the zooplankton and snails. A student who reads the arrows as pointing from eater to eaten picks this. The arrows point from the food to the organism that eats it: zooplankton and snails eat the algae, not the reverse.
At a deep-sea hydrothermal vent, where no sunlight reaches, microorganisms obtain energy by oxidizing hydrogen sulfide (H₂S) released from the vent and use it to make organic molecules from CO₂. Tube worms and clams at the vent depend on these microorganisms. Which statement best describes the microorganisms?
Answer and reasoning
AThey are heterotrophs, since they get energy by consuming chemicals rather than by capturing light. A student who thinks any organism that takes in chemicals for energy is a heterotroph picks this. Heterotrophs consume organic matter made by other organisms; these microorganisms make organic molecules from CO₂ using energy from an inorganic molecule.
BOrganisms like these can capture energy only where O₂ is present, as all energy capture uses O₂. A student who thinks all energy capture requires oxygen picks this. Chemosynthetic organisms capture energy from small inorganic molecules, and some of them do this in environments with no oxygen at all, so energy capture does not always require O₂.
CThey create the energy for the vent community by converting molecules of H₂S into energy. A student who thinks matter is converted into energy picks this. The microorganisms transfer chemical energy released when H₂S is oxidized; the atoms of H₂S are rearranged into other substances, not turned into energy.
DThey are autotrophs that capture chemical energy from inorganic molecules to make organic matter.Correct Chemosynthetic organisms capture energy from small inorganic molecules, such as H₂S, and use it to make organic molecules from CO₂. Because they make their own organic matter from inorganic sources, they are autotrophs and are the producers of the vent community.
The table shows what happened to the energy in the leaves eaten in one day by a caterpillar of a hypothetical moth species. The remainder of the energy was stored in the caterpillar's new biomass. How much of the energy from that day's feeding is stored in new biomass and so is available to the next trophic level?
Answer and reasoning
A0.36 kJCorrect Energy stored in new biomass = energy eaten − energy lost in feces − energy released by cellular respiration = 2.40 − 1.12 − 0.92 = 0.36 kJ. Only this energy, incorporated into the caterpillar's tissues, can pass to an animal that eats it.
B1.28 kJ A student who thinks all absorbed food becomes body tissue picks this, subtracting only the feces: 2.40 − 1.12 = 1.28 kJ. The 0.92 kJ released by cellular respiration is used for maintenance and lost as heat.
C0.24 kJ A student who applies an exact 10% rule picks this: 0.10 × 2.40 = 0.24 kJ. The data give the actual losses, which show that 0.36 kJ (15% of the energy eaten) was stored.
D2.40 kJ A student who thinks all the energy eaten is passed on picks this. Most of the 2.40 kJ was lost in feces or released as heat in cellular respiration.
Working Energy stored in new biomass = energy eaten − energy in feces − energy released by cellular respiration = 2.40 kJ − 1.12 kJ − 0.92 kJ = 0.36 kJ (15% of the energy eaten).
A bracket fungus grows on a fallen tree trunk. It releases enzymes that digest the wood, absorbs the products, and uses them to grow. Which statement correctly classifies the fungus?
Answer and reasoning
AIt is an autotroph, since, like a plant, it stays rooted in one place and does not hunt. A student who thinks fungi are plants that make their own food picks this. The fungus does not photosynthesize; it obtains organic molecules from the wood, so it is a heterotroph.
BIt is a heterotroph that returns the wood's energy to the soil for the trees to reuse. A student who thinks energy is recycled in ecosystems picks this. The fungus releases the energy it obtains from the wood as heat through cellular respiration; it returns atoms such as nitrogen and phosphorus to the soil, not energy the trees can reuse.
CIt is a heterotroph, a decomposer using organic matter that a producer originally made.Correct The fungus obtains energy and carbon by digesting and absorbing organic molecules from the dead wood, which the tree made by photosynthesis. Organisms that consume organic matter are heterotrophs; those that break down dead organic matter are decomposers.
DIt is a decomposer, not a heterotroph, as it breaks down wood for the forest, not for energy. A student who thinks decomposers break down dead matter only for the ecosystem picks this. The fungus uses the digested wood as its own source of energy and matter, so it is a heterotroph as well as a decomposer.
Compiled from the AP Biology Course and Exam Description (effective Fall 2025) and our question bank · Specialist review in progress. How these pages are made · Free, no account
