Transfer Of Energy & Matter

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Ecosystems as Open Systems

An ecosystem is a group of organisms interacting with each other and with the non-living parts of their environment.
Ecosystems contain both biotic (living) and abiotic (non-living) components; abiotic factors include salinity, pH, temperature, light intensity and mineral availability.
Ecosystems are open systems: both energy and matter can enter and exit.
Energy enters mainly as sunlight and flows through the ecosystem as stored chemical energy; it can also enter in the tissues of migrating organisms.
Matter enters when organisms arrive and leaves when organisms or dead matter are removed, e.g. timber being cut and taken away.
Most organisms remain in the ecosystem their whole lives, so matter and energy are largely recycled within it; ecosystems are largely self-contained.
Earth is a closed system: energy can enter and leave, but matter is recycled and cannot enter or leave.

A food chain

Energy Flow in Ecosystems

The sun is the initial source of energy for most food chains; light energy is converted to chemical energy by producers during photosynthesis.
Photosynthesis produces organic molecules (carbon compounds) including glucose, lipids and amino acids.
Chemical energy stored in plant tissues passes to the primary consumer when the plant is ingested, and on to secondary consumers when the primary consumer is eaten.
When an organism dies, the chemical energy in its tissues passes to detritivores and saprotrophs.
In food chains and food webs, arrows represent the transfer of energy (as stored chemical energy in carbon compounds) and biomass from one trophic level to the next by feeding.
A food web shows how several food chains in an ecosystem are connected; most species have more than one food source and are food for more than one consumer.
Some food chains do not rely directly on sunlight, e.g. those at deep sea volcanic vents and in caves, where bacteria gain energy from chemical processes.

Energy pyramids for a marine ecosystem and a savanna ecosystem

Obtaining Carbon Compounds: Autotrophs and Heterotrophs

An organism's mode of nutrition is how it gains organic molecules to fuel respiration.
Autotrophs synthesise their own organic molecules from simple inorganic substances; because they do not rely on other organisms they are called producers.
Photoautotrophs use light energy to fix carbon dioxide into organic molecules; examples include green plants, algae and cyanobacteria.
Chemoautotrophs obtain energy by oxidising inorganic chemicals, e.g. some bacteria oxidise Fe²⁺ to Fe³⁺; they act as producers in habitats without light, such as deep sea vents.
Heterotrophs gain carbon compounds by ingesting the tissues of other organisms, then digest and assimilate them into new molecules.
Types of heterotroph include consumers, detritivores and saprotrophs.
Respiration releases energy by the oxidation of carbon compounds such as glucose; it occurs in both autotrophs and heterotrophs and releases heat as a by-product.

Decomposers and Nutrient Cycling

Inorganic nutrients enter the food chain and are converted into carbon compounds locked inside the tissues of living organisms.
Because the supply of inorganic nutrients is finite, they must be released when organisms die.
Decomposition breaks down dead organisms, dead parts of organisms and waste products, converting carbon compounds back into inorganic nutrients.
Detritivores begin decomposition by breaking apart tissues; saprotrophs release enzymes that break down organic molecules, releasing inorganic nutrients.
Saprotrophs absorb some nutrients themselves, and the rest becomes available to other organisms such as producers.
In a functioning ecosystem the elements organisms need are constantly recycled: producers take in inorganic nutrients, consumers gain organic nutrients by ingestion, and decomposers return nutrients to the environment.
Elements cycled through ecosystems include carbon, nitrogen, calcium, phosphorus, sulfur and potassium.

Fungi as decomposers

Trophic Levels

Trophic levels describe an organism's position in a food chain and indicate how many organisms energy has passed through.
Level 1 = producers; level 2 = primary consumers (herbivores); level 3 = secondary consumers (carnivores); level 4 = tertiary consumers; level 5 = quaternary consumers.
Energy from sunlight enters the food chain at the first trophic level, where producers convert light energy into chemical energy.
Apex predators are at the top of the food chain and have no predators; their stored chemical energy can pass to decomposers when they die.
Some species occupy more than one trophic level because they have a varied diet, e.g. sparrowhawks can be at the third, fourth and fifth trophic levels in different food chains.

Trophic levels

Pyramids of Energy and Energy Losses

Pyramids of energy show the energy contained in the biomass at each trophic level; the length of each bar represents the energy present.
They should be drawn to scale, are always widest at the base, and show a stepped decrease at each level; units are energy per unit area per year, e.g. kJ m⁻² yr⁻¹.
Roughly 10% of the energy is passed on at each trophic level; around 90% is lost to the environment.
Energy is lost through incomplete consumption (e.g. roots, bones), incomplete digestion (e.g. cellulose, fur egested as faeces), heat loss during respiration, and excretion of metabolic waste such as urea.
Some organisms die without being consumed, so their energy is lost to the environment; detritivores and saprotrophs decompose uneaten parts and undigested waste.
Heat is lost to the environment by radiation at every trophic level and during decomposition.
Food chains rarely have more than four or five trophic levels because too little energy remains to support a predator higher up.
Biomass decreases at each trophic level, producing a pyramid shape, but the energy stored per unit mass does not change.

Energy loss along a food chain

Primary and Secondary Production

Primary production is the accumulation of carbon compounds in the biomass of autotrophs (producers) during photosynthesis.
Primary production is faster in biomes with more sunlight, optimum temperatures and higher rainfall, e.g. tropical forests.
The rate of primary production is expressed as biomass per unit area (or volume) per unit time, e.g. g m⁻² yr⁻¹ or g m⁻³ yr⁻¹ for aquatic habitats.
Secondary production is the accumulation of biomass in the tissues of heterotrophs after they ingest other organisms.
Not all ingested energy becomes new biomass; carbon is lost as carbon dioxide during respiration and energy is lost in metabolic waste such as water and urea.
The rate of secondary production is calculated by subtracting respiratory losses from the stored energy ingested, so it is always lower than primary production.

Pyramid of energy

The Carbon Cycle

The carbon cycle is the collection of processes by which carbon is transferred between stores.
Carbon exists in organic forms (e.g. carbohydrates and proteins in biomass) and inorganic forms (e.g. carbon dioxide in the atmosphere and hydrogen carbonate ions in the oceans).
Carbon stores are called pools or sinks (e.g. oceans, fossil fuels, living organisms); processes of transfer are called fluxes (e.g. dissolving, combustion, photosynthesis).
A carbon sink takes up and stores carbon, e.g. plants photosynthesising, oceans dissolving carbon dioxide, and fossil fuels or peat forming over long periods.
A carbon source releases carbon, e.g. burning plant material or the decay of dead or waste material.
If photosynthesis exceeds respiration there is a net uptake of carbon dioxide (the organism acts as a sink); if respiration exceeds photosynthesis there is a net release (the organism acts as a source).
Combustion of fossil fuels (coal, oil, natural gas), peat and biomass releases carbon dioxide and water; burning fossil fuels and peat releases carbon locked up for millions or thousands of years.

The carbon cycle

The Keeling Curve and Atmospheric Carbon Dioxide

The Mauna Loa Observatory, Hawaii, has recorded atmospheric carbon dioxide levels since 1958; the dataset is named after Charles Keeling.
The Keeling curve shows seasonal fluctuations in carbon dioxide concentration.
Levels decrease in whichever hemisphere is in spring and summer because photosynthesis removes carbon dioxide from the atmosphere.
Levels rise again in autumn and winter when photosynthesis rates decrease and respiration, decomposition and combustion dominate.
The overall upward trend is caused by human activities, especially the combustion of fossil fuels, which releases carbon dioxide faster than photosynthesis can remove it.

Interaction Between Autotrophs and Heterotrophs

Photosynthesis takes in carbon dioxide and produces carbon compounds and oxygen, which is the source of atmospheric oxygen on Earth.
Aerobic respiration uses oxygen and releases carbon dioxide as a waste product, which can be used in photosynthesis.
Both autotrophs and heterotrophs respire aerobically.
The combined photosynthesis of all photosynthetic organisms removes huge volumes of carbon dioxide and releases huge volumes of oxygen, while combined respiration does the reverse.
This exchange is a major interaction between autotrophs and heterotrophs and creates huge annual carbon fluxes on Earth.

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1.What is the initial source of energy for most food chains?
Easy
- ASunlight
- BHeat from the Earth's core
- CChemical energy in detritus
- DATP stored in producers
2.Which row correctly identifies the mode of nutrition of an autotroph and a heterotroph?
Easy
- AAutotroph: synthesises organic molecules from inorganic substances; Heterotroph: ingests carbon compounds from other organisms
- BAutotroph: ingests carbon compounds from other organisms; Heterotroph: synthesises organic molecules from inorganic substances
- CAutotroph: uses light energy to produce ATP only; Heterotroph: uses chemical energy to produce ATP only
- DAutotroph: obtains carbon compounds from dead organisms; Heterotroph: obtains carbon compounds from living organisms
3.In a functioning ecosystem, organisms are constantly recycled.
Easy
True or false?
4.Which of the following is an example of a chemoautotroph?
Medium
- AA bacterium that oxidises iron to produce ATP
- BA green plant that carries out photosynthesis
- CA fungus that absorbs nutrients from dead wood
- DA herbivore that eats grass
5.The arrows in a food chain represent the transfer of:
Medium
- AEnergy in the form of stored chemical energy in carbon compounds
- BBiomass only, not energy
- CInorganic nutrients from the abiotic environment
- DHeat energy from one trophic level to the next
6.Which of the following are reasons why energy is lost between trophic levels? (select all that apply)
Medium
- ANot all parts of the food organism are eaten
- BNot all ingested food is digested, so some is egested as faeces
- CHeat is lost to the environment during respiration
- DEnergy is lost when organisms excrete waste products such as urea
- EEnergy is converted into matter during photosynthesis
7.Which of the following correctly defines an ecosystem?
Easy
- AA group of organisms interacting with each other and with the non-living parts of the environment
- BAll the organisms of the same species living in a given area
- CThe non-living components of an environment only
- DA community of organisms and its interactions with other communities only
8.In a pyramid of energy, what do the units typically represent?
Medium
- AEnergy per unit area per year (e.g. kJ m⁻² year⁻¹)
- BBiomass per unit area (e.g. g m⁻²)
- CNumber of individuals per trophic level
- DEnergy per individual organism (e.g. kJ per organism)

Plus de questions

9.Which of the following is a carbon sink?
Medium
- AA growing forest that takes up carbon dioxide during photosynthesis
- BThe combustion of coal in a power station
- CThe respiration of animals in an ecosystem
- DThe decomposition of dead plant material by fungi
10.Detritivores obtain inorganic nutrients from the abiotic environment and convert them to organic molecules during photosynthesis.
Easy
True or false?
11.Decomposition is fundamental in ensuring that ecosystems remain unsustainable over long periods of time.
Easy
True or false?
12.Which of the following best describes the role of saprotrophs in nutrient cycling?
Medium
- AThey release enzymes that break down organic molecules in dead tissues, releasing inorganic nutrients
- BThey ingest dead organic matter and digest it internally
- CThey convert light energy into chemical energy
- DThey fix atmospheric nitrogen into organic compounds
13.Match each trophic level to its description.
Medium
- Producers
- Primary consumers
- Secondary consumers
- Tertiary consumers
- Organisms that produce their own carbon compounds using light energy
- Herbivores that feed on plant tissue
- Carnivores that are predators of primary consumers
- Carnivores that are predators of secondary consumers
14.Arrange the following processes in the order they occur during the decomposition of dead plant material.
Medium
- Detritivores break apart tissues
- Saprotrophs release enzymes to break down organic molecules
- Inorganic nutrients are released into the soil
- Producers take up inorganic nutrients
15.Which of the following statements about ecosystems as open systems are correct? (select all that apply)
Medium
- AEnergy can enter an ecosystem as sunlight and leave as heat
- BMatter can enter an ecosystem in the tissues of an organism that migrates into it
- CMatter can only be recycled within an ecosystem and cannot enter or leave
- DEnergy stored in an organism's tissues is removed from the ecosystem when that organism leaves
- EEcosystems are completely self-contained with no exchange of matter or energy
16.Match each term to its correct description.
Medium
- Autotroph
- Heterotroph
- Detritivore
- Saprotroph
- Synthesises its own organic molecules from simple inorganic substances
- Gains carbon compounds by ingesting the tissues of other organisms
- Breaks apart dead tissues, beginning the process of decomposition
- Releases enzymes that break down organic molecules in tissues, releasing inorganic nutrients
17.Arrange the following trophic levels in the correct order, starting from the first trophic level.
Medium
- Producers
- Primary consumers
- Secondary consumers
- Tertiary consumers
18.Which of the following are ways in which energy is lost from a food chain between trophic levels? (select all that apply)
Medium
- ANot every part of the food organism is eaten
- BConsumers are unable to digest all of the food they ingest
- CEnergy is lost as heat when consumers respire
- DEnergy is lost when organisms excrete waste products of metabolism
- EEnergy is converted into new biomass during growth
19.In a functioning ecosystem, elements such as carbon, nitrogen and phosphorus are constantly recycled.
Easy
True or false?
20.Which of the following is the main reason that food chains rarely contain more than four or five trophic levels?
Medium
- AEnergy is lost at each trophic level, so less energy is available to higher consumers
- BPredators at higher trophic levels are always larger and need less energy
- CProducers cannot support more than five consumers
- DEnergy is created at each trophic level, making longer chains unstable
21.Which of the following are carbon sinks? (select all that apply)
Medium
- AOceans
- BFossil fuels
- CPeat
- DLiving plants
- EBurning forests
22.The graph of the Keeling curve shows a zig-zag pattern that repeats every year, superimposed on a steady upward trend. Which statement best explains the repeating zig-zag pattern?
Medium
- APhotosynthesis removes carbon dioxide during spring and summer, and levels rise again in autumn and winter when respiration and decomposition exceed photosynthesis.
- BFossil fuel combustion increases every summer and decreases every winter.
- CThe Mauna Loa volcano releases carbon dioxide in regular annual pulses.
- DCarbon dioxide dissolves more readily in warm water, so ocean uptake increases every summer.
23.A sheep's energy budget shows that of the energy ingested in grass, 33% is lost in faeces, 50% is lost as heat during respiration, and 5% is lost in urine. What percentage of the ingested energy is available for production of new tissue (P)?
Medium
- A12%
- B83%
- C88%
- D17%
24.In a marine food chain, the energy present at each trophic level is measured in kJ m⁻² yr⁻¹. If the producers contain 45,000 kJ m⁻² yr⁻¹, approximately how much energy is available to the primary consumers?
Easy
- A4,500 kJ m⁻² yr⁻¹
- B450 kJ m⁻² yr⁻¹
- C40,500 kJ m⁻² yr⁻¹
- D9,000 kJ m⁻² yr⁻¹
25.A scientist measures the biomass of producers in a tropical rainforest and in a desert. Which factors explain why primary production is faster in the tropical rainforest? (select all that apply)
Medium
- AHigher levels of sunlight
- BOptimum temperatures
- CHigher levels of rainfall
- DGreater soil salinity
- ELower species diversity
26.In a functioning ecosystem, the element carbon is constantly recycled between living organisms and the abiotic environment.
Easy
True or false?
27.Match each term from the carbon cycle to its correct description.
Medium
- Carbon sink
- Carbon source
- Flux
- Pool
- A part of the carbon cycle that takes up and stores carbon
- A part of the carbon cycle that releases carbon
- A process of carbon transfer between stores
- A carbon store, such as the ocean or fossil fuels
28.Arrange the following stages of energy flow through a food chain in the correct order.
Medium
- Light energy is converted to chemical energy by producers
- Primary consumers ingest producers and gain chemical energy
- Secondary consumers ingest primary consumers
- Tertiary consumers ingest secondary consumers
29.Which statement best explains why rotating the compost container increases the rate of decomposition?
Medium
- AIt aerates the waste, providing oxygen for the respiration of decomposers.
- BIt cools the waste, slowing the respiration of decomposers.
- CIt removes carbon dioxide, which is toxic to decomposers.
- DIt adds inorganic nutrients to the compost.
30.A student sets up a sealed glass flask containing pond water, algae, and a small fish, and places it in constant light. After two weeks the fish has died even though the algae are still alive. Which is the best explanation for the fish's death?
Medium
- AThe fish had no source of inorganic nutrients
- BThe algae released no oxygen in the light
- CThe fish could not obtain carbon compounds from outside the flask
- DThe algae produced too much carbon dioxide for the fish to tolerate
31.A compost heap is turned regularly and its temperature rises to about 60 °C before falling. Which conclusion is best supported by the temperature rise?
Medium
- ASaprotrophs are releasing heat as a by-product of respiration
- BPhotosynthesis by decomposers is generating heat
- CThe compost is absorbing heat from the surrounding air
- DDecomposition has stopped because enzymes are denaturing
32.A student measures the carbon dioxide concentration in a sealed container holding a green plant. The concentration falls during the day and rises at night. Which process explains the rise at night?
Medium
- APhotosynthesis exceeds respiration
- BRespiration exceeds photosynthesis
- CCombustion of fossil fuels
- DDecomposition of the plant's tissues
33.A scientist wants to estimate the rate of primary production in a freshwater pond. Which of the following would be required to calculate the rate in g m⁻³ yr⁻¹? (select all that apply)
Hard
- AThe volume of water sampled
- BThe biomass of producers
- CThe time period over which the biomass was measured
- DThe number of secondary consumers present
- EThe temperature of the water
34.In a closed system, matter can be recycled but cannot enter or leave, while energy can enter and leave.
Easy
True or false?
35.Arrange the following stages of energy flow through a food chain in the correct order, starting from the initial energy source.
Medium
- Light energy from the sun
- Light energy converted to chemical energy in producers
- Chemical energy transferred to primary consumers
- Chemical energy transferred to secondary consumers
- Heat lost to the environment at each trophic level
36.Which process is mainly responsible for the loss in mass of the leaves?
Medium
- APhotosynthesis by the leaves
- BRespiration by saprotrophs breaking down the leaves
- CEvaporation of water from the leaves
- DCombustion of the leaves
37.Which of the following best defines an ecosystem?
Easy
- AA group of organisms interacting with each other and with the non-living parts of the environment
- BAll the organisms of the same species living in a particular area
- CThe non-living components of an environment, such as temperature and pH
- DA group of organisms that all obtain their energy in the same way
38.Which statement correctly describes an ecosystem as an open system?
Easy
- ABoth energy and matter can enter and exit the system
- BEnergy can enter and exit but matter can only be recycled within the system
- CMatter can enter and exit but energy cannot leave the system
- DNeither energy nor matter can enter or leave the system
39.Which of the following is a definition of a carbon sink?
Easy
- AA part of the carbon cycle that takes up and stores carbon
- BA part of the carbon cycle that releases carbon
- CAny process that transfers carbon between organisms
- DAn organism that obtains carbon compounds by ingesting other organisms
40.Which row correctly matches the mode of nutrition to the organism?
Medium
- APhotoautotroph — green plant
- BChemoautotroph — green plant
- CHeterotroph — cyanobacteria
- DPhotoautotroph — deep-sea vent bacterium oxidising iron(II)
41.A blackbird ate snails containing 1150 kJ of energy. Only 10% of this energy was transferred to the blackbird. Calculate the energy transferred from the snails to the blackbird, in kJ.
Medium
42.The atmospheric carbon dioxide concentration was 316 ppm in 1960 and 387 ppm in 2010. Calculate the percentage increase between 1960 and 2010. Give your answer to one decimal place.
Medium
43.Complete the sentence about energy transfer in food chains.
Medium
In a food chain, only about ____% of the energy is transferred from one trophic level to the next, while roughly ____% is lost to the environment.
44.Name the two main modes of nutrition.
Easy
The two main modes of nutrition are ____ and ____.
45.State the specific mode of nutrition used by plants.
Medium
46.State the specific mode of nutrition used by fungi.
Medium
47.State the specific mode of nutrition used by root feeding nematode worms.
Medium
48.Complete the sentence about the carbon cycle.
Medium
The process by which carbon is returned to the atmosphere from fossil fuels and organic material is called ____.
49.A tundra soil thawed considerably lost a mean of 42 g C m⁻² yr⁻¹, while soil thawed slightly lost a mean of 18 g C m⁻² yr⁻¹. Calculate the difference in mean carbon loss between the two soils. Give your answer in g C m⁻² yr⁻¹.
Medium
50.Complete the sentence about the Keeling curve.
Medium
The overall upward trend in atmospheric carbon dioxide shown on the Keeling curve is caused mainly by the ____ of fossil fuels, while the yearly fluctuations are caused by seasonal changes in the rate of ____.
51.Name the specific mode of nutrition used by a bacterium that obtains energy by oxidising iron(II) to iron(III) in a deep-sea vent.
Medium
52.In container A, the mass of leaves fell from 500 g to 125 g over 125 days. Calculate the mean rate of mass loss per day. Give your answer in g day⁻¹.
Medium
53.Explain why energy is transferred to the environment at each trophic level.
Medium
54.Outline some of the reasons that energy is lost between each trophic level of the food chain.
Hard
55.Describe the role of autotrophs within the carbon cycle.
Medium
56.List two processes in the carbon cycle that increase the levels of carbon dioxide in the atmosphere and state how they increase carbon dioxide levels.
Medium
57.Explain why tundra soils act as a carbon store.
Hard
58.A blackbird ate snails containing 1150 kJ of energy. Only 10% of this energy was transferred to the blackbird. Calculate the energy transferred from the snails to the blackbird, in kJ.
Medium
- A139 kJ
- B127 kJ
- C115 kJ
- D103 kJ
59.The atmospheric carbon dioxide concentration was 316 ppm in 1960 and 387 ppm in 2010. Calculate the percentage increase between 1960 and 2010. Give your answer to one decimal place.
Medium
- A24.8 %
- B22.5 %
- C20.2 %
- D27.1 %
60.A tundra soil thawed considerably lost a mean of 42 g C m⁻² yr⁻¹, while soil thawed slightly lost a mean of 18 g C m⁻² yr⁻¹. Calculate the difference in mean carbon loss between the two soils. Give your answer in g C m⁻² yr⁻¹.
Medium
- A26 g C m⁻² yr⁻¹
- B22 g C m⁻² yr⁻¹
- C24 g C m⁻² yr⁻¹
- D28 g C m⁻² yr⁻¹
61.In container A, the mass of leaves fell from 500 g to 125 g over 125 days. Calculate the mean rate of mass loss per day. Give your answer in g day⁻¹.
Medium
- A3 g day⁻¹
- B4 g day⁻¹
- C5 g day⁻¹
- D2 g day⁻¹

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