C4.2 Transfers of energy and matter

Definitions

Open system

• A system in which both matters and energy are exchanged across the boundaries of the system (e.g. ecosystem)

Close system 

• A system in which energy is exchanged across the boundaries but matters are not. 

Trophic level

• is the energy level of an organism.

Autotrophs

• An organism that uses external energy source to synthesize carbon compounds from simple inorganic substances

Heterotrophs

•  An organism that uses carbon compounds obtained from other organisms to synthesize carbon compounds

Consumer

• An organism that ingests other organic matter that is living or recently killed

Primary consumer → secondary consumer 

• Flow of energy / trasnfer of energy 

Decomposers 

• break down dead organisms and dead organic matter

• Detritiviours & Saprotroph 

photoautotroph: sunlight to make organic compounds via photosynthesis

chemoautotroph: uses energy from oxidation of inorganic compounds for anabolic reaction 

Trophic level: the position of an organism in a food chain

Primary production: accumulation of carbon compounds in biomass by autotrophs

Secondary production: accumulation of carbon compounds in biomass by heterotrophs

Production:  accumulation of carbon compounds in biomass. Autotrophs and heterotrophs produce biomass by growth and reproduction.

Carbon sinks in an ecosystem 

• organism that absorbs and holds more carbon than it release. (Photosynthesis > Respiration, e.g. producers)

Carbon sources in an ecosystem 

• organism that is a net producer of carbon dioxide. (Respiration > Photosynthesis, e.g. consumers)

Biomass

• Renewaable organic matter from plants, animal and microorganism -> used as verssatile energy source (*RENEWABLE, so not fossil fuels)

Ecosystem

• Ecosystem: A community and its abiotic environment

• Econsystem are

  • Open system: A system in which both matters and energy can enter and exit across the boundaries of the system (e.g. ecosystem)

  • (closed systems: energy can enter , matters cannot)

Food chain terms - definitons

• Trophic level: is the energy level of an organism.

• Autotrophs: An organism that uses external energy source to synthesize carbon compounds from simple inorganic substances

• Heterotrophs: An organism that uses carbon compounds obtained from other organisms to synthesize carbon compounds

• Consumer: An organism that ingests other organic matter that is living or recently killedx

Principal source of energy that sustains most ecosystems

Sunlight

Producers convert light energy into chemical energy

• cyanobacterium, algae, plants

Exceptions: Environments with limited/absent sunlight (caves and deep oceans)

open caves → primary energy source from dead tings that flow into cave

closed caves → chemosynthetic bacteira → harness energy from chemical reactons

Flow of chemical energy through food chains

• Producer → Primary consumer → Secondary consumer → Tertiary consumer → Quaternary consumer

• Arrow represents the flow of energy

Construction of food chains and food webs to represent feeding relationships in a community

Food webs are models that show many interconnected food chains

It is difficult to determine an organism’s trophic level in a food web because:

1. Organism eats at different trophic level.

2. The full diet of an organism is unknown

3. Diet may varies according to seasons.

 Supply of energy to decomposers as carbon compounds in organic matter coming from dead organisms

Source of energy: breakdown of dead organic matter or organic waste materials → extract energy and nutrients from decaying materials

• Products: inorganic molecules are made in the process which are returned to the environment; these molecules can be used by producers

extract energy and nutrients from decaying materials:

• dead parts of organisms

• dead whole organisms

• faeces

Two types of decomposers (dead organic matter)

Saprotrophs

• Secrete digestive enzymes, digesting dead organic matter externally, then absorb the products of digestion

Detritivores

• Directly ingest and consume dead organic matter - digested internally using digestive enzymes

Autotrophs as organisms that use external energy sources to synthesize carbon compounds from simple inorganic substances

autotroph : organism that uses texternal energy tosynthesize inorganic substances → organic compounds

• provide energy and nutrient source for other organisms

• ex. Energy is required for anabolic reactions:

  • Carbon fixation

  • Synthesis of macromolecules

two types of autotroph

1. photoautotroph : sunlight to make organic compounds via photosynthesis

2. chemoautotroph : uses energy from oxidation of inorganic compounds (from anabolic reaction) → in caves or deep ocean.

Heterotrophs as organisms that use carbon compounds abstained from other organisms to synthesize the carbon compounds that they require

Heterotrophs : use carbon compounds obtained from other organisms to synthesise their required carbon compounds

• use internal or external digestion to break down these compounds.

External digestion: release hydrolytic enzymes to digest organic molecules

Internal digestion: food is ingested, digested and broken down in specialised organs before absorption into the blood for assimilation.

Trophic levels

Trophic level: the position of an organism in a food chain

Producer: Base of food chain; provides energy and food for all other trophic levels

Primary consumer : Herbivores or ominivores that feed on producers for energy 

Secondary consumer : Feed on primary consumers as source of energy 

Tertiary : top level predators

Energy loss between trophic levels

• Respiration: Energy lost as heat

• Movement: Energy lost as muscle contracts

• Egestion: Energy lost as undigested food

• Excretion: Energy lost as metabolic waste

As the result, the pyramid of energy have a wide base and narrow top and most food chains only contain 4-5 trophic levels.

The unit for pyramid of energy kJ m^-2 Year ^-1

Flow of energy in food chain

• The initial energy is light energy from the sun. → photoautotrophs use sunlight as a principal source of energy → synthesize chemical energy → sustain the ecosystem.

  • except caves & deep ocean → chemoautotroph

• Energy is transferred through feeding

• Only about 10-20% of the energy is passed to the next trophic level

• About 80-90% of the energy is lost as respiration, excretion, egestion, and movement

 Restrictions on the number of trophic levels in ecosystems due to energy loses

Energy losses

between trophic levels restrict the length of food chains and the biomass of higher trophic levels due to inefficient energy transfer.

Primary production as accumulation of carbon compounds in biomass by autotrophs 

• Primary production: accumulation of carbon compounds in biomass by autotrophs

• Secondary production: accumulation of carbon compounds in biomass by heterotrophs

• Unit: gm^-2yr^-1

• Different biomes will have different capacity to accumulate biomass.

• Growth and Reproduction of autotrophs and heterotrophs → Biomass accumulates

  • Secondary production is lower than primary production in an ecosystem due to respiration and biomass is lost as carbon dioxide.

measure the production of food by primary producers

Production: accumulation of carbon compounds in biomass. Autotrophs and heterotrophs produce biomass by growth and reproduction.

Primary production: mass of carbon compounds by producers measured in grams of carbon accumulated per square meter of ecosystem per year

gm^-2yr^-1

• Varies by season and region (i.e precipitation, soil nutrient availability, etc)

Net Primary Production (NPP)	Gross Primary Production (GPP)	Respiration losses
Amount of biomass available to consumers	Total biomass of carbon compounds made by producers	Biomass loss due to respiration in plants

NPP = GPP - R

measure the production of food by secondary producers

Secondary production is the accumulation of biomass from carbon compounds in heterotrophs (consumers)

• Consumers obtain carbon compounds (i.e. amino acids, sugars) from organisms and use them in growth and reproduction. This increases their biomass via assimilation. 

 

Net Secondary Production (NSP)	Gross Secondary Production (GSP)	Respiration losses
Biomass that remains after accounting for respiratory losses	Total biomass assimilated by consumers (in an ecosystem)	Biomass loss due to respiration

NSP = GSP - R

lost of energy via respiration - consequence

Respiration results in loss of carbon compounds (i.e. CO₂) which decreases biomass at every trophic level.

Consequences for ecosystems:

• Secondary production < primary production

• NSP Net secondary production < GSP gross secondary production in every trophic level of consumers

• Secondary production declines with each successive trophic level

Ecosystems as carbon sinks and carbon sources

• Carbon sinks in an ecosystem is an organism that absorbs and holds more carbon than it release. (Photosynthesis > Respiration, e.g. producers)

  • ex. Forests, ocean, soil, waterlogged habitats, 

• Carbon sources in an ecosystem is an organism that is a net producer of carbon dioxide. (Respiration > Photosynthesis, e.g. consumers)

  • ex. Forest fires, respiration from organisms, volcanic eruptions

Carbon cycle

*All elements used by living organisms, are recycled by decomposers. (Detritivores, saprotroph)

Carbon being one of the element

The effect of combustion on carbon cycle

Combusion :

• the process of burning materials—such as wood, fossil fuels (coal, oil, natural gas), or biomass

• which releases stored carbon back into the atmosphere in the form of carbon dioxide and other greenhouse gases.

Natural combustion: lightning

Human combustion: combustion of different substances as source of energy; releases significant amounts of CO₂ 

• Biomass

• Peat

• Natural gas

• Oil

• Coal

Analysis of the Keeling Curve in terms of photosynthesis, respiration and combustion 

The Keeling Curve shows the concentration of CO₂ in atmosphere over time

• Annual fluctuations: 

• CO₂ increases between Oct and May (dormant season, winter where photosynthesis decreases)

• CO₂ falls from May to Oct (growing season where photosynthesis increases)

• Long- term trend:

• Although there are annual variations, by the end of each year, the CO₂ concentration is higher than beginning of each year, resulting in an upward trend.

Photosynthesis are aerobic respiration interdependent

Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis

and of photosynthesis on atmospheric carbon dioxide produced by respiration

(interdependent - need both )

• Autotrophs and heterotrophs are interdependent as well.

• Measured by gigatonnes (10¹⁵ grams)

 Recycling of all chemical elements required by living organisms in ecosystems

Living organisms contain large amounts of C, H, O, N, and P + small elements

• The quantities of these are finite

• decomposers recycle them → cycled within an ecosystem.