C4.2 Transfers of energy and matter
Practice exam-style IB Biology questions for Transfers of energy and matter, aligned with the syllabus and grouped by topic.
Question 1
A pond ecosystem is considered an open system. What can cross the boundary of this ecosystem?
A.
Both energy and matter
B.
Neither energy nor matter
C.
Energy only
D.
Matter only
Question 2
In a food chain, grass → rabbit → fox, what does the arrow from grass to rabbit represent?
A.
The rabbit is eaten by the grass
B.
Chemical energy in grass passes to the rabbit
C.
The rabbit passes heat energy to the grass
D.
Carbon dioxide diffuses from the grass to the rabbit
Question 3
What is the immediate energy source for saprotrophic fungi growing on fallen leaves?
A.
Heat released from the surrounding soil
B.
Chemical energy in carbon compounds in dead organic matter
C.
Inorganic nitrate ions in the leaf litter
D.
Light absorbed by chlorophyll in fungal hyphae
Question 4
What correctly describes an autotroph?
A.
It synthesizes carbon compounds from simple inorganic substances using an external energy source.
B.
It obtains carbon compounds only by ingesting other organisms.
C.
It occupies only the highest trophic level in a food chain.
D.
It releases enzymes onto dead organic matter and absorbs the products.
Question 5
Iron-oxidizing bacteria are chemoautotrophs. What supplies the energy they use for carbon fixation?
A.
Digestion of proteins from dead animals
B.
Combustion of fossil fuels in oxygen
C.
Oxidation of iron(II) ions to iron(III) ions
D.
Absorption of visible light by chlorophyll
Question 6
State one example of energy entering a forest ecosystem.
[1]
Outline two ways in which matter can leave the same forest ecosystem.
[1]
Question 7
Distinguish between photoautotrophs and chemoautotrophs. [2]
Question 8
A caterpillar feeds on oak leaves and is then eaten by a blue tit. What trophic level is the blue tit in this food chain?
A.
Producer
B.
Secondary consumer
C.
Tertiary consumer
D.
Primary consumer
Question 9
What is a cause of reduced energy availability at successive trophic levels?
A.
Energy content per gram of tissue always decreases at higher trophic levels.
B.
All biomass at one trophic level is consumed by the next level.
C.
Some ingested material is egested without being absorbed.
D.
Respiration converts carbon dioxide into food biomass.
Question 10
A fungus secretes protease onto dead wood containing animal remains and absorbs amino acids. What process follows absorption to make fungal proteins?
A.
Assimilation of absorbed amino acids into fungal biomass
B.
Egestion of amino acids as faeces
C.
Carbon fixation from atmospheric carbon dioxide
D.
Combustion of amino acids to form peat
Question 11
In a carbon cycle diagram, which flux transfers carbon from atmospheric carbon dioxide to producer biomass?
A.
Respiration
B.
Photosynthesis
C.
Egestion
D.
Feeding
Question 12
A community contains phytoplankton, water fleas, small fish and herons. Small fish feed on water fleas. Herons feed on small fish. Water fleas feed on phytoplankton.
Construct a food chain using these organisms.
[1]
State what the arrows in the food chain represent.
[1]
Question 13
Explain why not all chemical energy in producer biomass is transferred to primary consumers. [3]
Question 14
A student burns dry plant material beneath a tube containing water to estimate the energy content of the biomass.
State the temperature change needed for the calculation.
[1]
Outline two reasons why this method may underestimate the true energy content of the biomass.
[1]
Question 15
Define primary production.
[1]
Outline how net primary production differs from gross primary production.
[1]
Question 16
The graph shows the energy available at successive trophic levels in a grassland food chain.
Identify the trophic level with the greatest energy available.
[1]
Describe the trend in energy availability through the food chain.
[1]
Calculate the percentage transfer of energy from producers to primary consumers using the values shown.
[1]
Explain one reason for the low percentage transfer between these trophic levels.
[1]
Question 17
The graph shows light intensity with depth at two lake sites and the measured rate of photosynthesis by phytoplankton.
State how light intensity changes with depth at both sites.
[1]
Compare the depth at which photosynthesis becomes very low in the clear-water and turbid-water sites.
[1]
Suggest why primary production is lower in the turbid-water site.
[1]
Question 18
A wetland is a carbon sink over one year. What must be true for that year?
A.
Feeding transfers carbon directly from consumers to atmospheric carbon dioxide.
B.
Respiration releases more carbon dioxide than photosynthesis removes.
C.
Combustion releases carbon dioxide faster than peat accumulates.
D.
Photosynthesis removes more carbon dioxide than respiration releases.
Question 19
Why can energy not be recycled through an ecosystem in the same way as chemical elements?
A.
Heat produced in respiration cannot be gathered by organisms to rebuild chemical energy in food chains.
B.
Atoms of carbon are converted into atoms of oxygen during feeding.
C.
Photosynthesis produces heat but no chemical energy.
D.
Energy is destroyed when organisms respire.
Question 20
What units are most suitable for measuring primary production in a terrestrial biome?
A.
g C m⁻² yr⁻¹
B.
cm³ O₂ g⁻¹
C.
mol CO₂ dm⁻³
D.
kJ kg⁻¹ °C⁻¹
Question 21
Why is secondary production usually lower than primary production in an ecosystem?
A.
Heterotrophs convert some carbon compounds into carbon dioxide and water during respiration.
B.
Heterotrophs fix more carbon dioxide than autotrophs.
C.
Consumers have no anabolic reactions.
D.
Autotrophs never respire carbon compounds.
Question 22
What mainly causes the long-term upward trend in the Keeling Curve?
A.
Seasonal photosynthesis in northern hemisphere forests
B.
Combustion of fossil fuels and land-use change
C.
Conversion of atmospheric carbon dioxide into peat every winter
D.
Daily changes in oxygen concentration at Mauna Loa
Question 23
What describes a major interaction between photosynthesis and aerobic respiration at a global scale?
A.
Photosynthesis uses oxygen released by aerobic respiration.
B.
Aerobic respiration depends on oxygen maintained by photosynthesis, while photosynthesis depends on carbon dioxide released by respiration.
C.
Photosynthesis and respiration both recycle heat into chemical energy.
D.
Aerobic respiration fixes carbon dioxide into glucose for plants.
Question 24
What is the key reason matter can be recycled in ecosystems?
A.
Energy released as heat is converted back into producer biomass by decomposers.
B.
All elements are permanently locked in living organisms.
C.
Consumers create new atoms during assimilation.
D.
Atoms of chemical elements are conserved and can move between biotic and abiotic pools.
Question 25
The boxes in a carbon cycle diagram are labelled: atmospheric carbon dioxide, producer biomass, consumer biomass and dead organic matter.
Identify the process transferring carbon from atmospheric carbon dioxide to producer biomass.
[1]
Identify the process transferring carbon from producer biomass to consumer biomass.
[1]
Explain how carbon in dead organic matter can return to atmospheric carbon dioxide.
[1]
Question 26
Explain why food chains rarely contain more than four or five trophic levels. [4]
Question 27
A python digests a swallowed rat over several days.
State why proteins and nucleic acids in the rat must be digested before absorption.
[1]
Explain how digestion and assimilation allow secondary production in the python.
[1]
Question 28
A deep-ocean community occurs below the depth reached by light. Tube worms live near vents where reduced inorganic chemicals are released.
State why photosynthesis cannot be the local energy source for producers in this community.
[1]
Suggest how carbon compounds can still be produced in this community.
[1]
Question 29
A drained peatland is rewetted as part of a restoration project.
State the condition under which an ecosystem is a carbon sink.
[1]
Explain why waterlogged peat can sequester carbon.
[1]
Question 30
A 0.80 g dry seed sample is completely burned beneath 50.0 g of water. The water temperature rises by 18.0 K. Use Eᵦ = (m𝓌cΔT) / mᵦ and c = 4.18 J g⁻¹ K⁻¹.
Calculate the energy released by the seed sample.
[1]
Calculate the energy content in kJ g⁻¹.
[1]
Question 31
Outline why combustion of coal has a different carbon-cycle significance from combustion of recently grown wood. [3]
Question 32
Explain the dependence of aerobic organisms on photosynthesizing organisms and the dependence of photosynthesis on respiration. [4]
Question 33
A forest was monitored for carbon dioxide exchange over one year. Negative net exchange indicates uptake of CO₂ by the forest, and positive net exchange indicates release of CO₂.
Identify the season in which the forest acts most strongly as a carbon sink.
[1]
State one month or period when the forest acts as a carbon source.
[1]
Explain how photosynthesis and respiration determine whether the forest is a sink or a source.
[1]
Suggest one reason why the forest may release CO₂ during winter.
[1]
Question 34
The food web shows feeding relationships in a rocky shore community.
Identify one producer in the food web.
[1]
Identify one organism that can act as a secondary consumer in one food chain.
[1]
Explain why one named organism in the web may occupy different trophic levels.
[1]
Question 35
A student used simple combustion calorimetry to estimate energy content of three types of dry biomass.
| Biomass sample | Mass burned / g | Water mass / g | Initial temp / °C | Final temp / °C | Temp rise / °C |
|---|---|---|---|---|---|
| Wood shavings | 0.80 | 100 | 21.0 | 41.4 | 20.4 |
| Dry leaves | 0.75 | 100 | 21.2 | 36.3 | 15.1 |
| Rice husk | 0.90 | 100 | 21.1 | 39.5 | 18.4 |
Identify the biomass sample with the highest estimated energy content.
[1]
Calculate the energy content of one named sample using the data in the table and the formula Eᵦ = (m𝓌cΔT) / mᵦ.
[1]
State one variable that should be controlled when comparing the samples.
[1]
Suggest why all estimates are likely to be lower than the true energy contents.
[1]
Question 36
Explain the two main features of the Keeling Curve: the annual fluctuation and the long-term increase. [4]
Question 37
Explain the role of decomposers in the recycling of chemical elements in ecosystems. [4]
Question 38
The graph shows atmospheric CO₂ concentration measured at two monitoring stations: one remote oceanic station and one station near a large forested land mass.
Compare the annual fluctuations at the two stations.
[1]
Explain the long-term trend common to both stations.
[1]
Suggest why remote monitoring stations are useful for estimating global atmospheric CO₂.
[1]
Question 39
The table compares net primary production in four biomes.
| Biome | NPP / g C m⁻² yr⁻¹ |
|---|---|
| Tropical rainforest | 2200 |
| Temperate grassland | 600 |
| Tundra | 140 |
| Desert | 90 |
Identify the biome with the highest net primary production.
[1]
Calculate how many times greater the highest value is than the lowest value.
[1]
Suggest two abiotic factors that could explain differences in net primary production among the biomes.
[1]
State the correct units for net primary production shown in the table.
[1]
Question 40
Iron-oxidizing bacteria were grown in acidic water containing iron(II) ions. The graph shows changes in iron(II) concentration and bacterial biomass over time.
Describe the change in iron(II) concentration over time.
[1]
Describe the change in bacterial biomass over time.
[1]
Suggest how the bacteria obtain energy for increasing biomass.
[1]
Question 41
Outline how chemical energy enters and moves through a simple grazing food chain.
[1]
Explain why energy flow through the food chain is not the same as recycling of matter.
[1]
Question 42
Construct a possible food chain from the following organisms: algae, mayfly larva, trout, kingfisher.
[1]
Discuss why a food web is a more useful model than a single food chain for representing a community.
[1]
Question 43
The diagram shows energy and carbon transfers for a population of herbivorous insects feeding on leaves.
| Transfer | Description | Direction | Carbon flux / g C m⁻² yr⁻¹ |
|---|---|---|---|
| A | Leaf carbon consumed | leaves → insects | 120 |
| B | Faecal carbon | insects → faeces | 65 |
| C | Respiratory carbon loss | insects → CO₂ | 38 |
Identify the input to the insect population that represents ingestion.
[1]
Calculate assimilation using the values shown for ingestion and egestion.
[1]
Calculate secondary production using the values shown for assimilation and respiration.
[1]
Explain why secondary production is lower than ingestion.
[1]
Question 44
The table shows estimated carbon dioxide released by combustion of different carbon stores in one region during a dry year.
| Carbon store | Main ignition or use | CO2 release / Mt yr⁻¹ |
|---|---|---|
| Recent biomass | Wildfire and crop burning | 18.4 |
| Peat | Drained peatland fires | 46.7 |
| Coal | Electricity generation | 32.5 |
| Oil | Transport fuels | 21.8 |
| Natural gas | Heating and industry | 12.6 |
Identify the store that contributed the greatest carbon dioxide release.
[1]
Compare the likely time scales over which carbon in biomass and peat accumulated before combustion.
[1]
Suggest why human activity can increase carbon dioxide release from peatlands.
[1]
Explain why combustion is a carbon flux to the atmosphere.
[1]
Question 45
State two features of a correctly constructed energy pyramid.
[1]
Explain why energy pyramids usually narrow at higher trophic levels and how this restricts food-chain length.
[1]
Question 46
Define biomass and primary production.
[1]
Compare and contrast primary production and secondary production in ecosystems.
[1]
Question 47
Outline two biological carbon fluxes that should be included in a carbon cycle diagram.
[1]
Discuss how ecosystems can act as carbon sinks or carbon sources, including the roles of photosynthesis, respiration, decomposition and combustion.
[1]
Question 48
State two patterns shown by the Keeling Curve.
[1]
Evaluate the explanation that the annual fluctuation and long-term trend in atmospheric CO₂ have the same cause.
[1]
Question 49
Distinguish between autotrophs and heterotrophs.
[1]
Explain how autotrophs and heterotrophs obtain, transform and use carbon compounds and energy in ecosystems.
[1]
Question 50
Outline why all living organisms require a continuous supply of chemical elements.
[1]
Discuss why matter can be recycled in ecosystems but energy cannot.
[1]
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