C4.2 Transfers of Energy and Matter

Chapter 1: Flow of energy and matter

Ecosystems as open systems

• Open systems - a system that allows for both matter and energy to be exchanged with surroundings

• closed systems - restricts the flow of matter but allows for the exchange of energy with surrounding environment.

• isolated systems - ideal systems where neither matter not energy is exchanged with surrounding environments

Energy flow in ecosystems

• Energy, which is essential for organisms to live, must be transferred among organisms to sustain life within an ecosystem

• Sunlight is the primary source of energy

• Plants and organisms (autotrophs) that convert sunlight into chemical energy are known as producers

Food chains and food webs

• food chain - diagrams that use arrows to show the flow of energy through ecosystems. Producers are always at the base.

• food web - diagrams that show the interactions of various food chains in an ecosystem. (Producers are always at the base). Food webs are used to show the interconnected food chains of an ecosystem

Trophic Levels

• Level 1 - Producers

• Level 2 - Primary Consumers

• Level 3 - Secondary Consumers

• Level 4 - Tertiary consumers

Chapter 2: Autotrophs and heterotrophs

• decomposers - organisms that break down dead organic material to extract energy and nutrients

• decomposition - secretion of enzymes that break down complex organic materials into simple molecules to gain necessary nutrients and release nutrients back into the environment

• saprotrophs - decomposers that obtain organic nutrients from dead organisms through external ingestion by secreting hydrolytic enzymes to break down the complex compounds into simple molecules.

• detritivores - decomposers that obtain their nutrients from directly ingesting the dead organic material and digesting it internally.

• autotrophs - aka primary producers. organisms that can synthesize organic molecules from inorganic sources using an external energy source. They provide organic matter to use as energy for other organisms in the ecosystem. Because the chemical reaction to make food is anabolic, autotrophs need external sources, usually sunlight, for energy

• photoautotrophs - organisms that use light as a source of energy to synthesize organic compounds from inorganic molecules. This is usually from photosynthesis.

• chemoautotrophs - organisms that obtain energy through the oxidation of inorganic compounds, like iron, sulfur, and magnesium. The reactions release energy used for carbon fixation and macromolecular synthesis

  • Usually found in hostile environments, like deep-sea hydrothermal vents and sulfur rich hot springs

• heterotrophs - aka consumers. organisms that cannot produce their own organic molecules and rely on consuming other organisms or organic matter to obtain energy and nutrients for survival

Measuring biomass

• biomass - the total dry mass of a group of organisms in a specific area or volume. inherently contains energy

• To measure the biomass of an organism, the organism must be completely dehydrated (ethical concerns)

• Measuring biomass over time helps ecologists to estimate energy availability at each trophic level, allowing for comparison of energy transfer efficiencies of different ecosystems

• In an energy pyramid, horizontal bars are used to represent the amount of energy there is at each trophic level

• “To construct an energy pyramid, begin by gathering data on the biomass or energy content of organisms at each trophic level over a specific time period within a particular ecosystem. This data can be obtained through scientific studies or ecological surveys. Once you have collected the data, organise it in a hierarchical manner to represent each trophic level as a horizontal bar in the pyramid. Ensure that the bars are drawn to scale and include appropriate units.”

• Nutrients are cycled because nutrients cannot be made by organisms. These nutrients are passed on through consumption, waste matter, and decomposition

• Sustainability - the ability of a system or process to continue indefinitely. When resources are used faster than they can be replaced, unsustainability results in resources being depleted.

Chapter 3: Energy losses

The transfer of energy between organisms up the trophic levels of a food chain is highly inefficient, as only 10% energy stored as biomass is transferred while 90% is lost.

Reasons for energy loss includes:

• Incomplete consumption: Organisms do not consume the whole organism they eat, often eating only the highly nutritious and/or easily accessible parts. This leaves uneaten biomass, like bones, tough tissues and certain organs, to be left for decomposition

• Inefficient digestion: Organisms are unable to actually digest all the energy consumed through food. This results in the energy being released as waste (like feces).

• Inefficient energy conversion and storage: Not all energy is efficiently converted and stored in an organism’s tissue

• Use in metabolic processes: Organisms use energy for their own metabolic processes like respiration, movement, and growth

• Heat Dissipation: Energy often dissipates as heat as a result of metabolic reactions like respiration as the processes are exothermic.

  • When organisms convert organic compounds into ATP (energy), some energy is lost as heat. Because organisms cannot use heat as an energy source, the energy is “lost” as it dissipates into the environment.

Because energy as biomass is lost between each trophic level, the amount of energy available eventually limits the amount of trophic levels in a food chain. This results in food chains having around 3-4 species. This energy loss also results in a decrease in the number of organisms as we move up each trophic level.

NOTE: Decomposers are not technically part of food chains but are indispensable in ecosystems as they can release simple inorganic compounds back into the environment to be used by producers.

Chapter 4: Ecological productivity

Primary productivity: the rate at which carbon compounds are accumulated by autotrophs (plants, bacteria, cyanobacteria) in an ecosystem.

Gross primary productivity: the total amount of energy captures as biomass by primary producers in an ecosystem.

• However, some of this energy is used by consumers for their own metabolic processes and is not stored as biomass, resulting in energy/respiratory losses

Net primary productivity: the energy available to consumers at higher trophic levels and supports growth, reproduction, and storage within an ecosystem.

  NPP = GPP – R

Where,

NPP – Net primary production
GPP – Gross primary production
R – Respiration losses

Secondary production: The rate at which consumers accumulate carbon compounds as part of their own biomass.

Gross secondary productivity: the total amount of biomass assimilate by heterotrophs in an ecosystem. obtained through subtracting food mass eaten by mass lost through faecal excretion.

• Some energy is lost to be used for cellular respiration.

Net secondary productivity: the energy available to sustain higher trophic levels and contributes to the overall flow of energy within an ecosystem.

In food production, feed conversion ratio is the food input in grams needed to produce a certain biomass. For example, if 150 grams of feed are needed to produce 120 grams of mass, the ratio is 1.25.

Chapter 5: The Carbon Cycle

Carbon cycle: a fundamental process that allows carbon atoms to be exchanged between the Earths’s systems.

• Allows carbon atoms to be recycled and exchanged between organisms and their surrounding environment

Carbon sources: locations or process that release more carbon into the atmosphere than they absorb (eg. fossil fuels, cellular respiration, forest fires, volcanic eruptions)

• Contribute to the increasing levels of carbon dioxide, a greenhouse gas, into the atmosphere

Carbon sinks: an environment that absorbs more carbon dioxide from the atmosphere than it releases (eg. forests, the ocean, soil)

• Help to counteract greenhouse gas emissions by storing carbon.

Carbon atoms flux between earth’s different systems: the atmosphere, the lithosphere, the hydrosphere, and the biosphere

Ecosystems can either act as carbon sinks or carbon sources

• An ecosystem becomes a carbon sink when rate of photosynthesis exceeds the rate of cell respiration

  • Forests are examples of carbon sinks as they are able to take carbon through photosynthesis and store carbon their tree trunks, branches and roots

  • Carbon can also be stored in water as dissolved gas or can combine with water to form carbonate ions.

• An ecosystem become a carbon source when the cellular respiration rates exceed photosynthesis rates, whether it is from decaying organic matter or use of fossil fuels.

  • Cut-down forest can also become carbon sources as they release the stored carbon in the atmosphere.

Saprotrophs cannot thrive in anaerobic, waterlogged soils, causing dead organic matter to not completely decompose. Over time, this creates a dark brown, acid material called peat which covers around 3% of the Earth’s land surface. It can be used in gardening and as a fuel source for heat. Over time, peat is compressed and heated over time, which creates coal

Oil and natural gas formed at the bottom of seas and lakes where decomposition is often not completed. Over time, sediments caused the organic matter to be compressed and heated. Chemical changes resulted in mixtures of liquid carbon compounds and gas that accumulated in porous rocks where they were stored.

Chapter 6:

Fossil fuels: derive from ancient organic matter that has been buried and transformed over millions of years

• The combustion of fossil fuels reintroduces ancient carbon into the carbon cycle, which can overload the cycle and the atmosphere

Combustion: when organic matter is heated in the presence of oxygen and ignites and burns.

• The products are carbon dioxide, water, and lots of heat and energy

• This can be caused by lightning strikes naturally or human activity.

Keeling Curve: a graph that shows the concentrations of carbon dioxide in Earth’s atmosphere over time.