LifeLine

Species: groups of organism that can potentially interbreed to produce fertile offspring

• When different species cross-breed the hybrids produced are almost always infertile. 
• Members of a species may be reproductively isolated in separate populations (leads to speciation)

Population: Group of organisms of the same species, living in the same area at the same time 

• Two populations may live in different areas but still have the same species as long as they could interbreed to produce fertile offspring.
• If they never interbreed it is likely that they may develop differences.

Community: A group of different populations living together and interacting in a given area

• All species are dependent on relations with other species, which is why no population of one species can live in isolation

Habitat: The environment in which a species lives or the normal location of an organism

Ecosystem: A community and also its environment (all biotic and abiotic factors)

Autotrophs	Heterotrophs
Make their carbon compounds from carbon dioxide and other simple substances – self-feeding.E.g – PlantsRequires external energy source (e.g light)	Heterotrophs obtain carbon compounds from other organisms.Carbon compounds must be digested before they can be absorbed.
Both obtain inorganic nutrients from the abiotic environment, supply maintained by the nutrient cycle.
MixotrophsMixotrophs can have both auto/heterotrophic tendencies depending on environmental circumstances. Organisms such as Euglena gracilis can photosynthesis but also feed on detritus that they ingested by endocytosis.

Trophic Levels

• The difference level of a food chain
• Always start with an organism which can reproduce their own food (autotrophs – plants, fungus & bacteria – chemosynthetic – can produce their own food by using chemicals like methane &  H2S) 

Trophic level I – When they produce their own food – autotrophs

Trophic level II – Herbivores

Trophic level III – Carnior 

Example bear, if it feeds on plants it will be trophic level II, but if it eats flesh it will be trophic level III.

When you go up the trophic levels, the energy transfer decreases.

10% energy law, from each trophic level, only 10% of the energy is transferred, 90% will either be consumed by the organism or will be lost as heat in the ecosystem. 

This is why there are no more than 3-4 trophic levels; if there were more, there would be no energy transfer.

Food webs exist in the ecosystem. It creates a balanced energy transfer. 

Consumer

• Consumers are heterotrophs that feed on living organisms by ingestion.
• They ingest their food; take in undigested material from other organisms, digest it and absorb the products of digestion.

Detritivores

• Obtain organic nutrients by internal digestion.
• They ingest the dead matter and then absorb the products of digestion.
• Unicellular organisms ingest it into food vacuoles whilst multicellular ingest into gut.

Decomposer

• Not in any levels, they are those organisms which feed on the dead and decay matte, the consumer all trophic level but the dead part
• After consuming the dead and decay matter, they will replenish the ecosystem with minerals and nutrients. 
• Mostly bacteria

Saprotroph

• Saprotrophs are heterotrophs that obtain organic matter by external digestion.
• They secrete digestive enzymes into dead organic matter.
• Bacteria and fungi are common examples.
• Known as decomposers because they break down dead matter and release elements such as nitrogen back into the soil.