Transfers of energy and matter

ecosystems

• a group of organisms interacting with each other and with non-living parts of the environment

• 2 types of system:

  • open systems: resources can enter or exit, including chemical substances and energy

  • closed system: energy can enter or exit, chemical resources cannot be removed or replaced

sunlight

• sunlight is the principal source of energy in most ecosystems and is used by producers to make carbon compounds

• some ecosystems have very little light penetration:

  • caves and oceans at depths over 200m

  • some energy may pass to these in dead organic matter or transferred form other ecosystems, which can be digested by saprotrophs

chemical energy flow through food chains

• food chain: sequence of organisms each of which feeds on the previous organism

• first organism is producer, they use external energy source to make carbon compounds

• other organisms are consumers, obtaining chemical energy from carbon compounds in the organisms they feed on

food chains and food webs

• food web: model summarising all of the possible food chains in a community

• arrows indicate the direction of transfer of energy and biomass

decomposers

• dead organic matter generated by:

  • death of whole organisms

  • defecation

  • shedding

• dead organic matter contains chemical energy in carbon compounds

• saprotrophic bacteria and fungi are decomposers, as they break down insoluble macromolecules in dead organic matter into small soluble molecules

autotrophs

• autotrophs: organisms that make carbon compounds themselves using external sources

• carbon fixation and anabolic reactions in autotrophs require an external energy source to build macromolecules

  • energy source could be inorganic chemical reactions or light

photoautotrophs and chemoautotrophs

• photoautotrophs: use sunlight to make carbon compounds by photosynthesis

• chemoautotrophs:

  • use inorganic chemical reactions

  • these are oxidation reactions, which release energy, then used to synthesise carbon compounds

  • e.g Iron oxidising bacteria absorbing Fe2+ ions from environment, energy is used to fix carbon dioxide and produce carbon compounds

heterotrophs

• heterotrophs: organisms that obtain carbon compounds from other organisms to synthesise their own carbon compounds

• digest carbon compounds (externally or internally) that were part of another organism

• they then assimilate the carbon compounds , and build their own large complex carbon compounds like proteins and nucleic acids

release of energy by cell respiration

• in both autotrophs and heterotrophs, ATP is produced by cell respiration

• carbon compounds are oxidised to release energy which is used to phosphorylate ADP into ATP

classification of organisms into trophic levels

• producers: autotrophic, 1st trophic level

• primary consumers: eat producers, 2nd trophic level

• secondary consumers: eat primary consumers, 3rd trophic level

• tertiary consumers: eat secondary consumers, 4th trophic level

• many consumers have a varied diet and occupy diff trophic levels in diff food chains

energy pyramids

• show amount of energy gained per year by each trophic level

• amounts of energy measured per unit area and per year (kJ m-2 yr-1)

• bars are labelled with the trophic level

• suitable scale should be used, the length of each bar should be proportional to the amt of energy it shows

energy lost between trophic levels

• main causes of energy loss:

  1. incomplete consumption

     • some organisms are never consumed and instead die

     • energy in dead organisms is passed to saprotrophs/detritus feeders not part of food chains

  2. incomplete digestion

     • not all substances in food are digested, instead egested in faeces and passed to saprotrophs

  3. cell respiration

     • carbon compounds oxidised in respiration can’t pass to the next trophic level, energy that they contained is lost

heat loss to environment

• energy transfers are never 100% efficient

• when energy is released by oxidising substrates during cell respiration, some energy is converted to heat

• when ATP is used within cells, more of energy is converted to heat

• both autotrophs and heterotrophs generate energy this way

limited length of food chains

• food chains are limited in length bc so much energy lost between each trophic level

• not enough energy remains to support another trophic level

• animals in higher trophic levels don’t have to eat more food to gain enough energy, their prey contains large amnt of energy per unit mass, there’s just not much prey available

primary production

• production: the accumulation of carbon compounds in biomass, produced by both autotrophs and heterotrophs by growth and reproduction

• primary production: the mass of carbon compounds synthesised from CO2 by autotrophs, in grams of carbon per square meter of eco system per year (g m-2 yr-1)

• biomes vary in their capacity to accumulate biomass

secondary production

• heterotrophs obtain carbon compounds from organisms in a lower trophic level, and use them in growth and reproduction

• secondary production: accumulation of carbon compounds in biomass by consumers

• cell respiration results in a loss of carbon compounds, therefore biomass in every trophic level

  • so, secondary production is lower than primary production for ecosystems

the carbon cycle

carbon sinks and sources

• carbon enters and exits in the form of CO2 through photosynthesis and respiration

• the rates of these processes aren’t always equal for an ecosystem:

  • if photosynthesis exceeds respiration, there is net uptake of carbon, the ecosystem is carbon sink

  • if respiration exceeds photosynthesis, there is net release, the ecosystem is carbon source

release of CO2 by combustion

• ecosystems e.g peat can act as carbon sinks by accumulating biomass, the carbon in these sinks can remain sequestered for many millions of years

• when carbon compounds burn in air, CO2 is produced and released into atmosphere

• combustion is natural in some ecosystems, ignited by lightning strikes, in recent years there’s been massive increase in rate of combustion due to human activities (burning fossil fuels)

the keeling curve

• shows atmospheric CO2 concs in Hawaii

• annual fluctuations:

  • CO2 conc increases between oct and may, and falls from may to oct due to global imbalances in rates of CO2 fixation by photosynthesis and release by respiration

  • more photosynthesis during summer, when the plants in most of earth’s land surface are in their growth season

• long term trend:

  • the increase of CO2 is not completely reversed by the decrease

  • the full Keeling curve from 1959 onwards shows CO2 conc increasing every year

  • largely due to burning of fossil fuels and other anthropogenic factors, like deforestation

interdependence of photosynthesis and respiration

• autotrophs and heterotrophs are dependent on eachother for supplies oxygen and CO2

  • autotrophs split water molecules for photosynthesis and release oxygen from them into atmosphere

  • heterotrophs absorb oxygen produced and use it to oxidise carbon compounds, producing CO2

• global carbon fluxes are extremely large, so estimate are in gigatonnes

recycling in ecosystems

• all elements of living organisms can be endlessly recycled

• they are absorbed from abiotic environment, used within living organisms and returned to abiotic environment

• autotrophs obtain all elements needed from abiotic environment as inorganic nutrients

• heterotrophs obtain these elements as part of the carbon compounds in their food

• decomposers play key role in recycling because they digest carbon compounds and return elements from them back to the abiotic environment