C4.2Theme C — Interaction and interdependence
Transfers of energy and matter — IB Biology HL Revision Notes & Topical Questions
10 min read 12 parts Lesson 10 of 11 2 quizzes
Lesson summary
C4.2 Transfers of energy and matter — IB BIOLOGY HL notes: Explain ecosystems as open systems, energy flow through trophic levels, production, the carbon cycle and nutrient cycling.Ecosystem = a group of organisms interacting with each other and with the non-living parts of the e…
- Closed system
- Exceptions
- Nature of science
- Food chain
- Decomposition
- Heterotroph
Part 1 of 10Ecosystems as open systems
Ecosystems as open systems
Ecosystem
Ecosystem a group of organisms interacting with each other and with the non-living parts of the environment.
- It has biotic and abiotic components, varies in size from a garden pond to an ocean, and varies in complexity from a desert to a tropical rainforest.
- Abiotic factors such as salinity, pH, temperature, light and minerals provide habitat, nutrients and resources.
Open system
- Open system energy and matter both enter and leave.
- Energy enters as sunlight and flows as stored chemical energy, and also enters and leaves in the tissues of migrating organisms.
- Matter enters and leaves with organisms or dead matter washed or cut away, such as migrating birds or removed timber.
- Most organisms stay in the ecosystem, which is largely self-contained, and recycle matter and energy when they die.
Closed system
- Closed system matter is recycled but cannot enter or leave, while energy can, and Earth is an example.
Part 2 of 10Sunlight and energy flow
1
Source
- Source the sun is the initial energy source for most food chains.
- Producers convert light energy to chemical energy by photosynthesis,
- producing glucose, lipids and amino acids.
- (used in respiration or stored as starch)
- producing glucose, lipids and amino acids.
- Primary consumers get chemical energy by ingesting plants, and secondary consumers by ingesting primary consumers.
2
Exceptions
- Exceptions deep sea volcanic vents and caves rely on bacteria that gain energy from chemical processes,
- although some caves receive energy from the surface by flowing water.
3
Nature of science
- Nature of science the statement is a useful generalisation, true for most food chains.
- Laws describe patterns without explaining them, such as the first law of thermodynamics (energy cannot be created or destroyed).
- Theories explain phenomena, such as systems theory for open and closed systems, and both can be used for predictions.
4
Flow of chemical energy
1
Plants store energy in carbon compounds.
2
A primary consumer digests the plant and absorbs these compounds.
3
They fuel respiration or build animal tissue, so energy transfers into the consumer's tissues.
4
Eating the consumer passes the compounds and energy up the chain.
5
When an organism dies its stored energy passes to detritivores and saprotrophs.
Part 3 of 10Food chains and food webs, decomposition and nutrient release, autotrophs
Food chain
Food chain the feeding relationships in an ecosystem, with arrows showing transfer of energy (as chemical energy in carbon compounds) and biomass from one trophic level to the next.
Food web
Food web connected food chains, because most species have more than one food source and more than one consumer.
Decomposition
Decomposition breaking down dead organisms, their parts and waste, which cycles nutrients because the supply of inorganic nutrients is finite.
Decomposers
- Detritivores often begin by breaking apart tissues.
- Saprotrophs release enzymes that break down organic molecules and release inorganic nutrients.
- Saprotrophs absorb some, and the rest in the soil becomes available to producers.
Autotroph
Autotroph an organism that makes its own organic molecules from simple inorganic substances, so it is a producer.
- Examples are most green plants, algae such as seaweeds and cyanobacteria.
- Building larger molecules is anabolic.
Photoautotrophs use light energy.
1
Light energy splits water by photolysis, releasing electrons, hydrogen ions and oxygen.
2
Light also excites electrons in photosynthetic pigments.
3
The electrons and hydrogen ions make ATP and reduced coenzymes.
4
ATP and reduced coenzymes make carbon compounds such as glucose in the light-independent reactions.
Food chains and food webs, decomposition and nutrient release, autotrophs
Chemoautotrophs use energy from oxidising inorganic chemicals.
- Some bacteria oxidise iron(II) (Fe2+) to iron(III) (Fe3+), and the donated electrons make ATP.
- They are the producers where light is absent, such as deep sea vents and caves.
ATP energy comes from oxidation, which is loss of electrons (OIL: oxidation is loss).
Part 4 of 10Heterotrophs and respiration
1Heterotroph
Heterotroph an organism that gets carbon compounds by ingesting the tissues of other organisms by eating plants, killing animals, consuming dead organisms or eating waste.
- Digestion can occur inside or outside the body, and the molecules are rebuilt into new proteins and nucleic acids.
- Types are consumers, detritivores and saprotrophs.
2Oxidation of carbon compounds
- Oxidation of carbon compounds glucose fuels respiration, and other compounds such as lipids can be converted to glucose first.
3
Energy from respiration supports the functions of life.
- Metabolism, reproduction, homeostasis, growth, response, excretion and nutrition.
- In growth, some chemical energy is stored in the tissues and can pass to the next trophic level.
- Heat is released as a by-product.
4
Respiration occurs in both autotrophs and heterotrophs, which differ only in how the carbon compounds are supplied.
Part 5 of 10Trophic levels and pyramids of energy
| Level | Name | Description |
|---|---|---|
| 1 | Producers | Make their own carbon compounds, for example using light |
| 2 | Primary consumers | Herbivores feeding on plants |
| 3 | Secondary consumers | Carnivores that eat primary consumers |
| 4 | Tertiary consumers | Carnivores that eat secondary consumers |
| 5 | Quaternary consumers | Carnivores that eat tertiary consumers |
Trophic level
Trophic level the position in a food chain, showing through how many organisms the energy has passed.
- Apex predators are at the top and have no predators, and their stored energy passes to decomposers after death.
Varied diet
- Varied diet a species may occupy several trophic levels, for example sparrowhawks at levels 3, 4 and 5 and robins at levels 3 and 4.
Pyramid of energy
Pyramid of energy bars showing the energy in the biomass at each trophic level.
- Bars should be drawn to scale (or as a rough sketch), widest at the base and in steps, not smooth sides.
- Levels are labelled producer, primary consumer, secondary consumer and so on.
- Units are energy per unit area per year, such as kJ m−2 year−1.
Energy decrease
- Energy decrease only about 10% passes to the next level, so biomass also decreases.
Part 6 of 10Energy losses between trophic levels
About 10% of energy is available for a consumer to store, and about 90% is lost, because
- Not every part of the food organism is eaten, such as roots, woody parts and bones.
- Not all ingested food is digested, such as cellulose and fur, which is egested as faeces.
- Heat is lost during respiration.
- Waste products of metabolism such as urea are excreted.
- Some organisms die without being consumed and decompose.
Role of decay organisms
- Role of decay organisms detritivores and saprotrophs are not in the food chain but decompose uneaten parts, undigested waste and dead bodies.
Heat loss
- Heat loss transfer is not 100% efficient,
- and heat is lost by radiation from respiration and other ATP-using processes at every level, in producers, consumers and decomposers.
Chain length
- Chain length food chains rarely exceed four or five trophic levels because too little energy remains for predators to hunt enough prey.
- Biomass falls at each level through fewer or smaller individuals, giving a pyramid of biomass.
- The energy per unit mass of biomass does not change.
- Pyramids of biomass differ from pyramids of energy.
Part 7 of 10Primary and secondary production
Primary production
Primary production accumulation of carbon compounds in the biomass of autotrophs through growth and reproduction.
- It is faster in biomes with more sunshine, optimum temperatures and more rainfall, such as tropical forest.
Measuring the rate
- Measuring the rate biomass per unit area or volume per unit time, such as g m−2 yr−1 or g m−3 yr−1 .
- (volume for aquatic habitats)
Secondary production
Secondary production accumulation of biomass in heterotrophs from ingested organisms.
- Carbon is lost as CO2 from respiration and energy is lost in excreted water and urea.
- The rate equals the stored energy ingested minus respiratory losses, so it is always lower than primary production.
Part 8 of 10Carbon cycle
1Carbon cycle
Carbon cycle the processes that transfer carbon between stores.
- Organic carbon is in living biomass, such as carbohydrates and proteins.
- Inorganic carbon is carbon dioxide in the atmosphere and hydrogen carbonate in the oceans.
2
Diagrams show stores (pools or sinks), such as oceans, fossil fuels and organisms, and fluxes, such as dissolving, combustion and photosynthesis.
- They may show terrestrial cycling, marine cycling or both, as illustrations or text boxes and arrows.
3Carbon sink
Carbon sink a part of the cycle that takes up and stores carbon.
- Plants take up carbon dioxide in photosynthesis.
- Fossil fuels and peat store carbon over very long periods.
- Oceans dissolve large amounts of carbon dioxide.
4Carbon source
Carbon source a part that releases carbon, such as burning plant material and decay.
5Net uptake
- Net uptake an organism photosynthesising faster than it respires is a net carbon sink (plants), and one respiring faster is a net source (animals).
Part 9 of 10Release of carbon dioxide
Combustion
- Combustion burning fossil fuels and organic material releases carbon dioxide and water.
- Coal, oil and natural gas formed from dead plants and animals over millions of years.
- Peat forms when plant matter does not decompose in waterlogged, acidic conditions, and releases carbon when burned or dried and decomposed.
- Biomass such as wood burns in forest or grassland fires, caused by lightning or set by humans to clear land,
- and climate change has increased wildfires.
- Biomass is also burned as fuel in wood fires or boilers.
Impact
- Impact burning biomass has less effect on atmospheric carbon dioxide than burning peat or fossil fuels because the carbon was taken from the atmosphere recently,
- while peat stored it for potentially thousands of years and fossil fuels for millions.
Part 10 of 10Keeling curve and nutrient cycling and autotroph–heterotroph interaction
Data
- Data measurements at the Mauna Loa Observatory in Hawaii began in 1958 under Charles Keeling,
- and the World Meteorological Organisation and research stations also record carbon dioxide.
Seasonal fluctuation
- Seasonal fluctuation photosynthesis lowers atmospheric CO2 in the hemisphere in spring and summer.
- In autumn and winter photosynthesis falls and respiration, decomposition and combustion exceed it, so levels rise.
Overall trend
- Overall trend combustion of fossil fuels releases carbon dioxide faster than photosynthesis removes it, so the level is a little higher each year.
1
Gas exchange link
- Gas exchange link photosynthesis takes in carbon dioxide and releases oxygen,
- and aerobic respiration by autotrophs and heterotrophs uses oxygen and releases carbon dioxide.
- (the source of atmospheric oxygen)
- Carbon fluxes from photosynthesis and respiration are huge each year.
2
Recycling of elements
- Producers take inorganic nutrients from the abiotic environment and make carbon compounds.
- Consumers get organic nutrients by eating producers and other consumers.
- Decomposers break down dead tissue and waste, returning nutrients for producers.
3
Elements cycled
- Elements cycled carbon returns to the atmosphere, and nitrogen, calcium, phosphorus, sulfur and potassium return to the soil.
Key terms
| Term | Meaning |
|---|---|
| Open system | a system in which both energy and matter can enter and leave. |
| Trophic level | the position of an organism in a food chain. |
| Primary production | accumulation of biomass in autotrophs. |
| Secondary production | accumulation of biomass in heterotrophs. |
| Chemoautotroph | an autotroph that uses energy from oxidising inorganic chemicals. |
| Carbon sink | a store that takes up and keeps carbon. |
| Carbon source | a process or store that releases carbon. |
| Decomposition | breakdown of dead organisms and waste to release nutrients. |
| Keeling curve | a record of atmospheric carbon dioxide at Mauna Loa since 1958. |
Avoid these mistakes
1
Ecosystems are closed systems — both energy and matter enter and leave, while Earth is closed for matter.
2
Energy is recycled in ecosystems — energy flows through and is lost as heat, while matter is recycled.
3
Detritivores and saprotrophs are part of the food chain — they are not, though they decompose uneaten parts and waste.
4
Pyramids of biomass and energy are the same — they measure different things.
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