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 components (living organisms) and abiotic components (e.g. salinity, pH, temperature, light intensity, 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, dead plant matter washed away).
Most organisms remain in the ecosystem throughout their lives, so matter and energy are largely recycled within the system.
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

Photosynthesis converts light energy into chemical energy stored in carbon compounds such as glucose, lipids and amino acids.
When a plant is ingested, its carbon compounds and stored chemical energy pass to the primary consumer.
The primary consumer digests and absorbs the carbon compounds, using them for respiration or to build animal tissue, transferring energy to its own tissues.
When the primary consumer is eaten, its carbon compounds and stored energy pass to the secondary consumer, and so on up the food chain.
When an organism dies, the chemical energy in its tissues passes to detritivores and saprotrophs.
Food chains show feeding relationships; the arrows represent the transfer of energy (as stored chemical energy in carbon compounds) and biomass from one trophic level to the next.
Food webs show how several food chains within an ecosystem are connected, since most species have more than one food source and more than one predator.

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 known as producers.
Photoautotrophs use light energy to fix carbon dioxide into organic molecules; examples include green plants, algae and cyanobacteria.
Chemoautotrophs use energy from the oxidation of inorganic compounds (e.g. oxidising iron(II) to iron(III)) and act as producers in habitats without light, such as deep sea vents and caves.
Heterotrophs gain carbon compounds by ingesting the tissues of other organisms, then digest and assimilate them into new carbon compounds.
Types of heterotroph include consumers, detritivores and saprotrophs.
Both autotrophs and heterotrophs carry out respiration, which releases energy by the oxidation of carbon compounds and also 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 the bodies of dead organisms and the waste products of living organisms, enabling the cycling of nutrients.
Detritivores often begin decomposition by breaking apart tissues.
Saprotrophs release enzymes that break down organic molecules, releasing inorganic nutrients; they absorb some and the rest becomes available to producers.
In a functioning ecosystem, elements needed by living organisms are constantly recycled; this applies to carbon and to mineral elements such as nitrogen, calcium, phosphorus, sulfur and potassium.

Fungi as decomposers

Trophic Levels

Trophic levels describe the position of an organism 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; 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 during photosynthesis.
Energy is transferred from one trophic level to the next as each organism is ingested.
Apex predators are at the top of the food chain and have no predators; their stored energy passes to decomposers when they die.
A species may occupy different trophic levels in different food chains within a food web, e.g. sparrowhawks can be at the third, fourth or fifth trophic level.

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, with the base widest and each level decreasing in size; units are energy per unit area per year, e.g. kJ m⁻² year⁻¹.
Only about 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 (egested as faeces), heat loss during respiration, and excretion of metabolic waste such as urea.
Some organisms die without being consumed, and their bodies decompose, so their energy is lost from the food chain.
Detritivores and saprotrophs decompose uneaten parts, undigested waste and unconsumed bodies, contributing to energy loss from food chains.
Heat is lost to the environment at every trophic level by radiation during cellular respiration and other cellular processes.

Energy loss along a food chain

Primary and Secondary Production

Primary production is the accumulation of carbon compounds in the biomass of autotrophs (producers).
Primary production occurs faster in biomes with more sunlight, optimum temperatures and higher rainfall, e.g. tropical forests.
The rate of primary production is measured in units of 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 energy consumed by heterotrophs becomes new biomass; carbon is lost as carbon dioxide in respiration and energy is lost in excreted metabolic waste.
The rate of secondary production is calculated by subtracting respiratory losses from the stored energy ingested.
The rate of secondary production is always lower than the rate of primary production because of energy losses at each trophic level.

Pyramid of energy

The Carbon Cycle

The carbon cycle is the collection of processes by which carbon is transferred from one store to another.
Carbon is present in organic forms (e.g. carbohydrates and proteins in biomass) and inorganic forms (e.g. carbon dioxide in the atmosphere, hydrogen carbonate ions in oceans).
Carbon cycle diagrams show stores (pools or sinks, e.g. ocean, fossil fuels, living organisms) and fluxes (processes of transfer, e.g. dissolving, combustion, photosynthesis).
A carbon sink takes up and stores carbon, e.g. plants photosynthesising, fossil fuels and peat, and carbon dioxide dissolving in oceans.
A carbon source releases carbon, e.g. burning plant material, decay of dead matter, and respiration.
If photosynthesis exceeds respiration, there is a net uptake of carbon dioxide (carbon sink); if respiration exceeds photosynthesis, there is a net release (carbon source).
Combustion of fossil fuels (coal, oil, natural gas), peat and biomass releases carbon dioxide into the atmosphere.
The Keeling curve shows atmospheric carbon dioxide at Mauna Loa since 1958: seasonal fluctuations due to photosynthesis, and an overall rise due to human combustion of fossil fuels.

The carbon cycle

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Preguntas de práctica

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1.Which term describes an organism that synthesises its own organic molecules from simple inorganic substances in its environment?
Easy
- AAutotroph
- BHeterotroph
- CDetritivore
- DSaprotroph
2.Which organism is a photoautotroph?
Easy
- ACyanobacteria
- BA mushroom
- CA root-feeding nematode worm
- DA soil bacterium oxidising iron
3.A chemoautotroph in a deep sea volcanic vent produces ATP by oxidising iron. Which statement correctly describes this organism?
Medium
- AIt uses energy from the oxidation of inorganic compounds instead of light energy
- BIt uses light energy to split water and release electrons
- CIt gains its carbon compounds by ingesting the tissues of other organisms
- DIt releases enzymes that break down organic molecules in dead tissues
4.Which statement about ecosystems as open systems is correct?
Medium
- ABoth energy and matter can enter and exit the system
- BMatter can only be recycled within the system and cannot enter or leave
- CEnergy can enter and leave but matter cannot
- DNeither energy nor matter can enter or leave the system
5.In a closed system, matter can only be recycled within the system and cannot enter or leave.
Easy
True or false?
6.Detritivores obtain inorganic nutrients from the abiotic environment and convert them into organic molecules during photosynthesis.
Easy
True or false?
7.Which of the following are ways in which energy is lost from a food chain between trophic levels? (select all that apply)
Medium
- AHeat released to the environment during respiration
- BNot every part of the food organism is eaten
- CEgestion of undigested food as faeces
- DExcretion of metabolic waste such as urea
- EConversion of light energy into chemical energy during photosynthesis
8.Which of the following statements about pyramids of energy are correct? (select all that apply)
Medium
- AThe length of each bar represents the energy present at that trophic level
- BThey are always widest at the base and decrease in size going up
- CThe units used should be energy per unit area per year, e.g. kJ m⁻² yr⁻¹
- DThey show a smooth-sided pyramid shape
- ERoughly 10 % of energy is passed on at each trophic level

Más preguntas

9.Match each trophic level with the correct description.
Medium
- Producers
- Primary consumers
- Secondary consumers
- Tertiary consumers
- Organisms that produce their own carbon compounds
- Herbivores that feed on plant tissue
- Carnivores that are predators of primary consumers
- Carnivores that are predators of secondary consumers
10.Match each mode of nutrition or feeding type with the correct description.
Medium
- Autotroph
- Heterotroph
- Detritivore
- Saprotroph
- Synthesises its own organic molecules from inorganic substances
- Gains carbon compounds by ingesting the tissues of other organisms
- Begins decomposition by breaking apart tissues of dead organisms
- Releases enzymes that break down organic molecules in tissues
11.Place the following stages of energy transfer through a food chain into the correct order, starting with the entry of energy.
Medium
- Light energy is converted to chemical energy by producers
- Chemical energy passes to primary consumers when they ingest plants
- Chemical energy passes to secondary consumers when they are ingested
- Chemical energy passes to decomposers when organisms die
12.Which of the following processes return carbon to the atmosphere? (select all that apply)
Medium
- ARespiration
- BCombustion of fossil fuels
- CPhotosynthesis
- DDecomposition
- EDissolving of carbon dioxide in the ocean
13.Which of the following are carbon sinks? (select all that apply)
Medium
- APeat
- BFossil fuels
- CThe ocean
- DA forest fire
- EA respiring animal
14.Which of the following help to explain why food chains rarely contain more than four or five trophic levels? (select all that apply)
Medium
- AOnly around 10 % of energy is transferred to the next trophic level
- BBiomass decreases at each trophic level
- CPredators higher up the chain struggle to catch enough prey to gain sufficient energy
- DProducers contain less energy than primary consumers
- EEnergy is created at each trophic level as organisms grow
15.Which of the following are valid units for the rate of primary production? (select all that apply)
Medium
- Ag m⁻² yr⁻¹
- Bg m⁻³ yr⁻¹
- CkJ m⁻² yr⁻¹
- Dg m⁻²
- EkJ m⁻²
16.Match each process in the carbon cycle with the correct description.
Medium
- Photosynthesis
- Respiration
- Combustion
- Decomposition
- Removes carbon dioxide from the atmosphere and stores it in carbon compounds
- Releases carbon dioxide as a waste product of oxidising carbon compounds
- Releases carbon locked up in fossil fuels and biomass by burning
- Breaks down dead tissues and waste, returning carbon to the atmosphere and soil
17.Match each term with its correct definition.
Medium
- Carbon sink
- Carbon source
- Flux
- Biomass
- 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
- The mass of living material, e.g. plant matter
18.Match each stage of energy flow through a food chain with the correct description.
Medium
- Light energy
- Chemical energy in producers
- Chemical energy in consumers
- Heat energy
- The initial energy source for most food chains, captured by photosynthesis
- Stored in carbon compounds made by photosynthesis
- Transferred to the next trophic level by feeding
- Lost to the environment by radiation at every trophic level
19.Place the following stages of energy flow through a food chain into the correct order, starting with the entry of energy.
Easy
- Light energy from the sun
- Chemical energy stored in producer tissues
- Chemical energy stored in primary consumer tissues
- Chemical energy stored in secondary consumer tissues
- Heat energy lost to the environment
20.Place the following steps of decomposition into the correct order.
Medium
- An organism dies
- Detritivores break apart the tissues
- Saprotrophs release enzymes that break down organic molecules
- Inorganic nutrients are released into the soil
- Producers take up the inorganic nutrients
21.Place the following stages of an investigation into carbon release from tundra soils into the correct order.
Medium
- Collect soil samples from the tundra
- Thaw the soils to different extents
- Measure the carbon released over three years
- Calculate the difference in mean carbon loss between treatments
- Evaluate whether the results support a link to further global warming
22.Which process in the carbon cycle removes carbon dioxide from the atmosphere?
Easy
- APhotosynthesis
- BRespiration
- CCombustion
- DDecomposition
23.Which statement correctly describes a carbon sink?
Medium
- AA part of the carbon cycle that takes up and stores carbon
- BA part of the carbon cycle that releases carbon
- CA process of carbon transfer between stores
- DA part of the carbon cycle that only occurs in the ocean
24.The graph of carbon loss from tundra soils shows a mean loss of 120 g C m⁻² yr⁻¹ from considerably thawed soils and 40 g C m⁻² yr⁻¹ from slightly thawed soils. What is the difference in mean carbon loss?
Medium
- A80 g C m⁻² yr⁻¹
- B160 g C m⁻² yr⁻¹
- C3 g C m⁻² yr⁻¹
- D40 g C m⁻² yr⁻¹
25.Photosynthesis removes carbon dioxide from the atmosphere, while respiration and combustion release it.
Easy
True or false?
26.The rate of secondary production in an ecosystem is always higher than the rate of primary production.
Medium
True or false?
27.In a functioning ecosystem, the elements that living organisms need are constantly recycled.
Medium
True or false?
28.A deep-sea ecosystem is found around a volcanic vent where no sunlight penetrates. Which organism would be the producer in this ecosystem?
Medium
- AA bacterium that oxidises inorganic chemicals to produce ATP
- BA green alga that carries out photosynthesis
- CA fish that feeds on small crustaceans
- DA fungus that decomposes dead organic matter
29.
The following table shows the energy content of organisms at different trophic levels in a food chain.
Trophic level Energy / kJ m⁻² yr⁻¹
Producers 20 000
Primary consumers 2 000
Secondary consumers 200
Tertiary consumers 20
What is the approximate percentage of energy transferred from primary consumers to secondary consumers?
Medium
- A1%
- B10%
- C20%
- D90%
30.A student measures the rate of primary production in a lake. Which unit is most appropriate for the result?
Easy
- Ag m⁻² yr⁻¹
- Bg m⁻³ yr⁻¹
- CkJ m⁻²
- DkJ m⁻³
31.The graph of atmospheric carbon dioxide concentration at Mauna Loa shows a zigzag pattern superimposed on an upward trend. What causes the zigzag pattern?
Medium
- ASeasonal changes in the rate of photosynthesis
- BLong-term increase in fossil fuel combustion
- CVolcanic eruptions
- DChanges in solar radiation
32.In a compost heap, the temperature rises to about 60°C and then gradually falls. What is the most likely explanation for the rise in temperature?
Medium
- AHeat released by decomposers during respiration
- BHeat absorbed from the sun
- CHeat released by photosynthesis
- DHeat generated by physical rotation of the container
33.The diagram below shows the flow of energy through a sheep. The value for F is 100 kJ × 10⁶ yr⁻¹. What does F most likely represent?
Medium
- AEnergy lost as heat during respiration
- BEnergy stored in new tissue
- CEnergy ingested in food
- DEnergy egested in faeces
34.Which of the following statements about the carbon cycle are correct? (select all that apply)
Medium
- APhotosynthesis removes carbon dioxide from the atmosphere.
- BRespiration releases carbon dioxide into the atmosphere.
- CCombustion of fossil fuels removes carbon dioxide from the atmosphere.
- DDecomposition releases carbon dioxide into the atmosphere.
- EOceans act as a carbon sink by dissolving carbon dioxide.
35.Which of the following are reasons why energy is lost between trophic levels in a food chain? (select all that apply)
Medium
- ANot all parts of the food organism are eaten.
- BSome ingested food is not digested and is egested as faeces.
- CEnergy is lost as heat during respiration.
- DEnergy is lost through excretion of waste products such as urea.
- EEnergy is converted into matter during photosynthesis.
36.In a closed system, matter can enter and leave but energy cannot.
Easy
True or false?
37.The rate of secondary production is always lower than the rate of primary production in an ecosystem.
Easy
True or false?
38.Compare the rate of carbon release in moderately thawed soils with those in considerably thawed soils.
Medium
- AThe rate is 1.5 times higher in considerably thawed soils.
- BThe rate is 1.5 times higher in moderately thawed soils.
- CThe rate is the same in both.
- DThe rate is 2 times higher in considerably thawed soils.
39.A student wants to estimate the rate of primary production in a pond. They measure the dry mass of algae produced in a known volume of water over a set period. Which unit should they use for their result?
Medium
- Ag m⁻³ yr⁻¹
- Bg m⁻² yr⁻¹
- CkJ m⁻² yr⁻¹
- Dg m⁻³ day⁻¹
40.In an investigation into decomposition, a student places equal masses of dead leaf litter in two mesh bags. Bag A has large mesh holes (5 mm) and Bag B has small mesh holes (0.5 mm). Both are left in the same soil for 60 days. Which result is most likely?
Medium
- ABag A loses mass faster because detritivores can enter and break up the litter
- BBag B loses mass faster because saprotrophs are trapped inside and work more efficiently
- CBoth bags lose mass at exactly the same rate because decomposition is only caused by microorganisms
- DBag A loses mass slower because larger holes allow more water to drain away
41.Name the process carried out by autotrophs that converts light energy into chemical energy stored in carbon compounds.
Easy
42.Give the name of the process by which energy is released from carbon compounds by oxidation in both autotrophs and heterotrophs.
Medium
43.Complete the sentence about ecosystems using the correct terms.
Medium
Ecosystems are ____ systems, meaning that both ____ and matter can enter and exit the system.
44.Complete the sentence about autotrophs.
Medium
An autotroph synthesises its own organic molecules from simple ____ substances, while a ____ gains its carbon compounds by ingesting the tissues of other organisms.
45.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
46.The atmospheric carbon dioxide concentration was 316 ppm in 1960 and 387 ppm in 2010. Calculate the percentage increase in carbon dioxide concentration between 1960 and 2010. Give your answer to one decimal place.
Hard
47.Complete the sentence about carbon stores using the correct terms.
Easy
A part of the carbon cycle that takes up and stores carbon is called a carbon ____, while a part that releases carbon is called a carbon ____.
48.Complete the sentence about energy loss in food chains using the correct terms.
Medium
Energy is lost to the environment as ____ during respiration, and also through incomplete digestion and the ____ of waste products of metabolism.
49.Complete the sentence about the Keeling curve using the correct terms.
Medium
The seasonal fluctuations in atmospheric carbon dioxide shown on the Keeling curve are caused by changes in the rate of ____, while the overall upward trend is caused by the combustion of ____ by humans.
50.A food chain transfers 10 % of energy from one trophic level to the next. If producers contain 50 000 kJ m⁻² yr⁻¹ of energy, how much energy is transferred to the primary consumers?
Medium
51.A food chain transfers 10 % of energy from one trophic level to the next. If primary consumers contain 5000 kJ m⁻² yr⁻¹ of energy, how much energy is transferred to the secondary consumers?
Medium
52.Name the process that removes carbon dioxide from the atmosphere and stores carbon in carbon compounds in plants.
Medium
53.Explain why energy is transferred to the environment at each trophic level of a food chain.
Hard
54.Describe, with examples, the different modes of nutrition used by organisms.
Hard
55.Outline some of the reasons that energy is lost between each trophic level of a food chain.
Hard
56.Explain why the rate of secondary production is always lower than the rate of primary production in an ecosystem.
Medium
57.Explain why tundra soils act as a carbon store.
Medium
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
- A127 kJ
- B115 kJ
- C139 kJ
- D103 kJ
59.The atmospheric carbon dioxide concentration was 316 ppm in 1960 and 387 ppm in 2010. Calculate the percentage increase in carbon dioxide concentration between 1960 and 2010. Give your answer to one decimal place.
Hard
- A22.5 %
- B20.2 %
- C27.1 %
- D24.8 %
60.A food chain transfers 10 % of energy from one trophic level to the next. If producers contain 50 000 kJ m⁻² yr⁻¹ of energy, how much energy is transferred to the primary consumers?
Medium
- A5000 kJ m⁻² yr⁻¹
- B6000 kJ m⁻² yr⁻¹
- C5500 kJ m⁻² yr⁻¹
- D4500 kJ m⁻² yr⁻¹
61.A food chain transfers 10 % of energy from one trophic level to the next. If primary consumers contain 5000 kJ m⁻² yr⁻¹ of energy, how much energy is transferred to the secondary consumers?
Medium
- A550 kJ m⁻² yr⁻¹
- B600 kJ m⁻² yr⁻¹
- C450 kJ m⁻² yr⁻¹
- D500 kJ m⁻² yr⁻¹

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Trophic level	Energy / kJ m⁻² yr⁻¹
Producers	20 000
Primary consumers	2 000
Secondary consumers	200
Tertiary consumers	20