IB Biology HL C4.2 Transfers of Energy and Matter Questions

Practise IB Biology HL C4.2 by tracing energy flow, nutrient cycling, biomass transfer, productivity and carbon fluxes across trophic levels.

Exam points

Define ecosystems as open systems exchanging energy and matter with their surroundings.
Trace chemical energy through producers, consumers and decomposers, and construct or interpret food chains and food webs.
Classify autotrophs and heterotrophs, including consumers, detritivores, decomposers and saprotrophs, by energy/carbon source and digestion.
Explain respiration as chemical-energy release producing ATP and CO2 with heat loss, and deduce trophic levels including omnivory or parasitism.
Construct, calculate and interpret energy pyramids and transfer efficiency using trophic labels, energy units, respiration, heat, uneaten biomass, egestion and excretion.
Explain why respiratory heat cannot be recycled and how inefficient energy transfer limits food-chain length and higher-level biomass.
Distinguish gross and net primary production and calculate or interpret productivity data with units.
Construct and interpret carbon-cycle and carbon-budget evidence, identifying stores, fluxes, sinks, sources and CO2 release from combustion.
Analyse Keeling-curve data to distinguish long-term atmospheric CO2 rise from seasonal photosynthesis and respiration oscillations.
Trace recycling of carbon and other elements through decomposers, inorganic nutrients and producer uptake, distinguishing matter recycling from one-way energy flow.

Covered syllabus points

C4.2.1—Ecosystems as open systems C4.2.2—Sunlight as principal energy source C4.2.3—Chemical energy flow C4.2.4—Food chains and food webs C4.2.5—Supply to decomposers C4.2.6—Autotrophs as self-feeders C4.2.7—Energy sources C4.2.8—Heterotrophs C4.2.9—Energy release C4.2.10—Trophic levels C4.2.11—Energy pyramids C4.2.12—Energy reductions C4.2.13—Heat loss C4.2.14—Restrictions on trophic levels C4.2.15—Primary production C4.2.16—Secondary production C4.2.17—Carbon cycle diagrams C4.2.18—Carbon sinks and sources C4.2.19—CO₂ release during combustion C4.2.20—Keeling Curve analysis C4.2.21—Dependence between respiration and photosynthesis C4.2.22—Recycling of all chemical elements

[Maximum number: 1]

An investigation into food web interactions was conducted in mesocosms in the Mediterranean Sea, off the coast of France. The effects of the addition of soil and fish on bacterial populations were tested.

Each of the mesocosms is an open ecosystem. State the property that makes the mesocosms open ecosystems.

[Maximum number: 4]

The mass of an individual organism can affect its physiology and feeding ecology. The diagram shows the relative mass of carbon (black) and total wet mass (grey) of a marine crustacean, Calanus hyperboreus and a jellyfish, Bathocyroe fosteri.

Two crustacean silhouettes representing relative masses: a larger grey outline for wet mass and a smaller black outline for carbon mass.

Two jellyfish silhouettes representing relative masses: a large grey silhouette for wet mass and a small black silhouette for carbon mass. The key identifies the two shadings.

(a)

State one process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.

[ 1 ]

(b)

Explain how energy enters, flows through and is lost from marine food chains.

[ 3 ]

[Maximum number: 2]

A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.

Diagram of a valley glacier surrounded by mountains, with curved bands in front of the glacier and branching meltwater streams crossing the exposed valley floor.

Compare and contrast food chains and food webs.

[Maximum number: 3]

Explain how energy enters, flows through and is lost from marine food chains.

[Maximum number: 1]

Marine sediments form at the bottom of oceans. These sediments contain organic material from the surface waters. Scientists analysed samples drilled from the floor of the north Pacific Ocean, representing 86 million years of sedimentation. Graph A shows the data for oxygen concentrations in 28 metres of sediment and graph B shows the oxygen consumption per cell in 22 metres of sediment measured in femtomoles ( $\mathrm{fmol}=10^{-15} \mathrm{~mol}$ ).

Two sediment-depth plots with depth increasing downward from 0 to 30 m. Graph A plots oxygen concentration in micromoles per cubic decimetre; graph B plots oxygen consumption in femtomoles per cell per day on a logarithmic horizontal scale.

State a possible source of food for the microbial community in the sediments.

[Maximum number: 1]

What is the classification of an organism that is able to make organic compounds from inorganic nutrients?

Autotroph

Consumer

Detritivore

Saprotroph

[Maximum number: 1]

The Chinese pangolin (Manis pentadactyla) is a critically endangered species that has declined in numbers by 80 % since 2000 . It inhabits both forest and grassland, where it uses long, powerful claws to open ant and termite nests and ingests the insects using a long, sticky tongue.

State with a reason whether pangolins are autotrophic or heterotrophic.

[Maximum number: 1]

State one process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.

[Maximum number: 2]

Explain what information is needed to find the trophic level of pangolins.

[Maximum number: 6]

Ecologists sometimes display data from an ecosystem using a diagram called a pyramid of energy. Describe what is shown in pyramids of energy.

pyramid of energy shows the flow of energy from one trophic level to the next (in a community);
units of pyramids of energy are energy per unit area per unit time $/ \mathrm{kJ} \mathrm{m}^{-2} \mathrm{yr}^{-1}$ ;
bar width is proportional to the energy stored (in the biomass) in that trophic level;
the first/lowest trophic level is producers;
second level is primary consumers/herbivores;
third level of secondary consumers/carnivores;
only a small amount (10 to 20 % ) of energy of one level is passed to the next;
bar width/energy stored in the trophic level decreases (proportionally) as you go up each level;
pyramid shows that there is a limit to the length of food chains;

Award any of the above marking points to a correctly drawn and clearly labelled pyramid.

[Maximum number: 3]

Outline how the energy flow through food chains limits their length.

a. only a small proportion/20 \%/10\% «of energy» can pass from one trophic level to the next

OR large proportion/80 \%/90\% lost between one trophic level and the next

b. energy released by respiration AND lost as heat

c. energy losses due to uneaten parts/undigested parts/feces/egestion

d. not enough energy for $4^{\text {th }} / 5^{\text {th }} /$ later stages of a food chain

OR

more energy available if feeding at an earlier stage in a food chain

[Maximum number: 1]

Plankton are major producers in marine ecosystems. Only a small proportion of the energy harvested by plankton is passed to the primary consumers. Which process in phytoplankton results in the largest loss of energy that could otherwise be utilized by consumers?

Reproduction

Homeostasis

Excretion

Respiration

[Maximum number: 1]

Animals in the highest trophic level of a food chain will often be the largest in body size but will be few in numbers. What accounts for the small numbers?

Food eaten by animals at the highest trophic level has a lower energy content per gram

Energy losses through the food chain

Conversion of heat energy into chemical energy

Biomass of producers is small

[Maximum number: 6]

Remote sensing satellites are used to monitor the Earth's ecosystems. One measure of ecosystem status is leaf area index (LAI), which is the total area of leaves in square metres per square metre ( $\mathrm{m}^{2} \mathrm{~m}^{-2}$ ) of the Earth's surface. The graph shows LAI estimates, calculated using data from the Global Inventory Monitoring and Modelling System (GIMMS), during the period from 1981 to 2011. The data points are monthly averages in four latitudinal zones in the northern hemisphere.

(a)

The data in the graph show a long-term trend in global LAI.

[ 2 ]

(i)

Global ecosystem modelling suggests that most of the change in LAI is due to increases in atmospheric carbon dioxide. Explain how rising atmospheric carbon dioxide ( $\mathrm{CO}_{2}$ ) concentration could cause the observed change in LAI.

[ 2 ]

(b)

The 2015 Paris Agreement sets out an international framework for avoiding dangerous climate change. A key aspect is conserving and enhancing sinks of greenhouse gases, including forests.

Free air carbon dioxide enrichment (FACE) experiments are being used to investigate whether increases in atmospheric $\mathrm{CO}_{2}$ concentration will cause biomass increases in existing forests. Three FACE experiments have been running for at least ten years in young, developing forests. Photosynthesis rates are measured in 25 to 30 m diameter plots. In control plots, carbon dioxide concentrations remain at current atmospheric levels (ambient CO2). In treatment plots, the CO2 concentration is raised by 50 % (elevated $\mathrm{CO}_{2}$ ).

The table gives some details of these experiments and the highest annual net primary production recorded during the period of the experiment. Net primary production is the mass of carbon absorbed and fixed by photosynthesis in plants that is not released due to plant respiration.

State the effect of elevated $\mathrm{CO}_{2}$ on net primary production in these young, developing forests.

[ 1 ]

(c)

In each forest, there are two or three trial plots per CO2 treatment. The bar chart shows the allocation of carbon from net primary production to different parts of the trees in these trial plots.

Evaluate the evidence from the bar chart that increases in carbon dioxide cause increases in carbon storage in young, developing forests.

[ 3 ]

[Maximum number: 2]

The diagram shows a simplified marine food web in an area of the North Pacific Ocean.

Marine food web with arrows from kelp and algae to sea urchins; algae to mussels and clams; diatoms to fish; sea urchins, mussels and clams to sea otters; fish to harbour seals, sea lions and orcas; and sea otters, harbour seals and sea lions to orcas.

Explain reasons for the feed conversion ratio in fish being lower than in cattle.

[Maximum number: 7]

Many biological processes are cyclical. Examples of cycles can be found at the level of the cell, the organism and the ecosystem.

Describe processes in the carbon cycle that produce or use carbon dioxide.

[Maximum number: 2]

The graph shows carbon dioxide ( $\mathrm{CO}_{2}$ ) concentration in the atmosphere during the past 800000 years. The data was produced by measuring the $\mathrm{CO}_{2}$ concentration of air bubbles trapped in cores of Antarctic ice.

The graph shows long-term fluctuations in atmospheric $\mathrm{CO}_{2}$ concentration of about 80 ppm . The decreases in $\mathrm{CO}_{2}$ concentration are probably due to oceans acting as a sink by holding large quantities of dissolved $\mathrm{CO}_{2}$ .

Identify two other examples of natural sinks that can remove carbon from the carbon cycle and reduce atmospheric $\mathrm{CO}_{2}$ concentration.

[Maximum number: 3]

The graph shows global $\mathrm{CO}_{2}$ contributions from the use of fuels since 1825. Emissions estimates for the years since 1950 are based on energy data from the United Nations while emissions estimates for years prior to 1950 have been constructed using a variety of sources.

(a)

Calculate the percentage increase in the use of liquid fuels from 1950 to 1975.

[ 1 ]

$\text { « } \frac{(2250-300) \times 100}{300}=\text { » } 650 \text { «\%» }$

(b)

Referring to the data, compare and contrast the changes in the use of the different fuels between 1950 and 1975.

[ 2 ]

[Maximum number: 1]

The graph shows data collected at Mauna Loa, USA, for monthly mean carbon dioxide concentration.

What causes the decreases in monthly mean carbon dioxide concentration each year?

Combustion increases.

Respiration increases.

Decomposition increases.

Photosynthesis increases.

[Maximum number: 2]

Where high amounts of ammonium ions are present in agricultural areas, gaseous ammonia can be released into the atmosphere. This ammonia can dissolve and be carried across distances and then be deposited through precipitation. In a study of the effects of deposition of ammonium in a forest, soil samples were taken starting at the forest edge next to an open field and moving toward the centre of the forest.

List two sources of the ammonium in the forest soils apart from deposition in rainfall.

All question bank results loaded

a	activity of soil microorganisms/ammonification/nitrogen fixation
b	urine/feces/other nitrogenous waste
c	dead organisms
d	fertilizers «on edge of forest»

Covered syllabus points

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