Topic 4 Full

Paper 1 (Understandings)

Species

groups of organisms that can interbreed and produce fertile offspring

Hybrids

Cross-bred species that are sterile

Population

A group of organisms of the same species that live in the same area

Community

A group of populations living together and interacting with each other within a given area

Habitat

The environment in which a species normally lives, or the location of a living organism

Ecosystem

A community and its abiotic environment

Autotrophs

Synthesises its own organic molecules from simple inorganic substances (e.g. CO2, nitrates); also known as producers

Heterotrophs

Obtains organic molecules from other organisms (either living/recently killed or their non-living remains and detritus); also known as consumers

Mixotrophs

Certain unicellular organisms may on occasion use both forms of nutrition, depending on resource availability

Consumers

heterotrophs that feed on living or recently killed organisms by ingestion

Scavangers

heterotrophs that feed on dead or decaying matter by ingestion

Detritivores

heterotrophs that ingest organic molecules found in the non-living remnants of organisms (e.g. detritus, humus)

Saprotrophs

are heterotrophs that release digestive enzymes and then absorb the external products of digestion (decomposers)

Nutrients

materials required by an organism (nitrogen, carbon, phosphorus)

Nutrient cycle

the movement and exchange of inorganic and organic matter back into the production of matter

Main components required for ecosystem sustainability

Energy, nutrients and recycling of wastes.

Main energy source

sunlight

Trophic level

The position an organism occupies within a feeding sequence

Food chain

The linear feeding relationships in a community

Energy loss

Respiration loss 25%, Heat lost 40%, Excretion lost 10%, Stored 25%

Chemical energy converted into

Kinetic energy (e.g. muscular contractions), Electrical energy (e.g. nerve impulses), Light energy (e.g. bioluminescence)

Biomass

the total mass of a group of organisms

Limitation of potential trophic levels

energy and biomass is lost between each level of a food chain (transfers ~5-20%)

Pyramid of energy

a graph of the amount of energy at each trophic level (should be one tenth of the size of the preceding level)

Food web

a diagram that shows how food chains are linked together

Compensation point

when the net carbon dioxide assimilation in autotrophs is zero (intake \= output)

Carbon in aquatic ecosystems

present as dissolved carbon dioxide and hydrogen carbonate ions

Limestone development

corals and mollusca have hard parts made of calcium carbonate get fossilized

Methanogens

archea that produce methane in anaerobic conditions

Anaerobic conditions

Wetlands (e.g. swamps/marshes), Marine sediments (e.g. in lake mud), Digestive tract of ruminant animals (e.g. cows)

Methane in the atmosphere

oxidises to form carbon dioxide and water

Peat formation

partially decomposed organic matter in acidic and/or anaerobic conditions in waterlogged soils

Coal formation

When peat is compressed, impurities/moisture are forced out. The product has a high carbon concentration that undergoes a chemical transformation.

Carbon dioxide production

biomass and fossilised organic matter undergo combustion

Combustion sources

Fossil fuels, Biomass

Carbon fluxes

the rate of exchange of carbon between carbon sinks/reservoirs

main carbon sinks

lithosphere (earth crust), hydrosphere (oceans), atmosphere (air), biosphere (organisms)

Carbon exchange processes

Photosynthesis, Respiration, Decomposition, Gaseous dissolution, Lithification, Combustion

Causes for flux change

climate conditions, natural events and human activity

Most significant greenhouse gases

Carbon dioxide and water vapour

Gases that have less impact

methane and nitrogen oxides

Greenhouse gases

They absorb and emit long-wave (infrared) radiation, trapping heat in the atmosphere

Factors that affect atmosphere warming

The gas’ ability to absorb long wave radiation and concentration in the atmosphere

The warmed Earth

emits longer wavelength radiation (heat)

The greenhouse effect

a natural process where the atmosphere behaves like a greenhouse to trap and retain heat

How the Greenhouse Effect Works

Earth absorbs short wave radiation from the sun and re-emits it at a longer wavelength. Greenhouse gases absorb and re-radiate the longer wave radiation and hence retain the heat within the atmosphere.

Ocean Acidification

Rising levels of atmospheric carbon dioxide decrease the pH of the water

Consequences of Ocean Acidification

Disappearance of coral reefs, loss in revenue from food industries, increasing dissolved CO2 levels in oceans would cause invasive species of algae to flourish (more photosynthesis).