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Contents:
Topic 4.1 - Species, communities and ecosystems
Topic 4.2 - Energy flow
Topic 4.3 - Carbon cycling
Topic 4.4 - Climate change
What is a species?
➢ A species is a group of organisms that can interbreed and produce fertile offspring
➢ Members of the same species have a common gene pool
➢ A species is made up of organisms that:
○ Have similar physiological and morphological characteristics that can be
observed and measured
○ Have the ability to interbreed to produce fertile offspring
○ Are genetically distinct from other species
○ Have a common phylogeny (=family tree)
➢ Bacteria and archaeans can’t be classified into species, because the term can only
be applied to sexually reproducing organisms
Hybrids
➢ Hybrid is the infertile offspring that results after 2 different but similar species
have mated
➢ Because the offspring aren’t fertile, no new species has been created
○ Instead they’re called interspecific hybrids
■ Ex: horse + donkey = mule, horse + zebra = zorse, lion + tiger = liger
➢ Hybrids are rarely formed in nature, due to species being separated in various ways
Populations
➢ A population is all the organisms within an area that belong to the same species
➢ If a group from a species is separated from the rest of the species, it might find
itself evolving in a different way
○ Ex: they may end up with different frequencies of certain alleles for a trait
➢ A population can be geographically or reproductively isolated
○ Ex: bodies of water, mountain ranges, deep canyons, different mating calls
or different mating seasons
➢ Speciation is when a new species is formed from an old one
Autotrophs
➢ Autotrophs are organisms capable of synthesizing their organic molecules from
simple inorganic substances
○ This process involves photosynthesis
■ Light energy + inorganic molecules ⇒ organic molecules ⇒ chemical
energy
➢ These organisms are called producers because the food they make is used by other
organisms
○ Ex: algae, trees, grass, cyanobacteria
Heterotrophs
➢ Heterotrophs are organisms that can’t make their own food from inorganic matter
and therefore they get their chemical energy from autotrophs or other
heterotrophs
➢ They’re known as consumers, because they rely on other organisms for food
○ Ex: fish, sheep, insects, zooplankton
➢ Few species are both autotrophs and heterotrophs
➢ Consumers take the energy-rich carbon compounds, protein and lipids synthesized
by other organisms in order to survive
➢ Humans can synthesize vitamin D, because there are precursors in human skin that
absorb UV light waves producing vitamin D
Detritivores
➢ They feed on non-living organic matter called detritus
○ Ex: faeces, dead leaves, carcasses
○ Ex: woodlice, earthworms, dung beetles
➢ Many bottom feeders in rivers, lakes and oceans are detritivores
Saprotrophs
➢ They live on or in non-living organic matter secreting digestive enzymes and
absorbing the products of digestion
➢ They play an important role in the decay of dead organic materials
➢ The fungi and bacteria that are saprotrophs are also called decomposers , because
they break down waste material
Communities
➢ A community is a group of populations living and interacting with each other in an
area
○ Different population of species
➢ “Interacting” can mean:
○ One population feeding on another or being eaten by another
○ One species gets protection from another
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