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All the information for topic 4 IB Biology SL
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Summary document of Chapter 5 Evolution and biodiversity IB Biology
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Ecology4.1 species communities and ecosystems
Ecology is the study of relationships Essential idea:
between living organisms and between The continued survival of living organisms,
organisms and their environment including humans, depends on sustainable
communities.
Key terms:
• Species: a group of organisms that can interbreed to
produce fertile offspring.
Þ If members of two closely related species do
interbreed and produce offspring the hybrids will
be sterile e.g. mules.
Þ If they are not able to produce fertile
offspring, speciation has occurred, so
they have evolved to the point where
they are too genetically different.
• Population: a group of organisms of the same species
that live in a particular area at the same time.
Þ Organisms separated geographically or temporarily are unlikely to breed, though
the ability to do so remains. The separated organisms are regarded as being
members of different populations.
• Community: a group of populations living and interacting with each other in a particular area
Þ All organisms depend on the interaction with other species for survival e. g. a lion
depends on its prey to feed itself. To help you remember the different levels
Þ Communities also include plants and of an ecosystem, this is the order from
microbes and hence often involve bottom (smallest) to top (biggest):
Species → Population → Community →
thousands of species.
Ecosystem → Biome → Biosphere.
,• Habitat: the environment in which a species normally lives
An ecosystem is a community (group of populations that live and interact with each other in an
area) and its abiotic environment (inorganic, non-living thing)
• Abiotic factors: non-living factors, such as pH, salinity, wind speed, type of soil, etc.
• Biotic factors: living factors in an ecosystem, such as the plants and animals
Autotrophs and heterotrophs
All organisms on our planet need a supply of organic compounds
to sustain life. There are two modes of nutrition by which these organic compounds can be
obtained:
• Autotrophs: these organisms obtain carbon molecules from inorganic materials. F. ex.,
plants acquire it from CO2, synthesizing it initially with sugars like glucose and then
converting it into other organic compounds such as starch, cellulose, lipids, and amino acids.
Also called producers.
Þ Although most autotrophs fix carbon by photosynthesis, a few are
Chemoautotrophs and fix carbon by utilizing the
energy in the bonds of inorganic compounds. Exam tip
Þ The inorganic nutrient compounds, e. g. water,
In a food chain, the producers
carbon dioxide, nitrates, phosphorous, and oxygen
are always autotrophs and all
are obtained from the abiotic environment, whether consumers are heterotrophs.
it be the soil, air, or water.
• Heterotrophs: these organisms obtain organic carbon from organic substances (like
glucose or starch) produced by autotrophs. Also called consumers.
Þ ‘Hetero' means other, while 'trophic', as stated above, has to do with nutrients.
Þ Primary consumers: feed on producers (herbivores)
Þ Secondary consumers: feed on primary consumers (carnivores)
Þ Tertiary consumers: feed on primary and secondary consumers (carnivores)
Þ If they eat both producers and consumers, they’re called omnivores. Some have
specific names, like insectivores. Scavengers eat animals after they’re dead.
• Mixotrophs: organisms that use both modes of nutrition (e. g. carnivore
plants such as the algae Euglena sp. or the plant Venus Flytrap, Dionaea
muscipula, which traps insects to compensate for the nutrient-poor soil
of the wetlands)
, Consumers, detritivores and saprotrophs
Heterotrophs can be grouped according to the way they get their organic molecules from other
organisms. The most obvious way is by ingesting or eating other organisms. But that would
pose a problem for those organisms that do not have a mouth or other anatomical feature, that
would allow eating.
Consumers
Heterotrophs that ingest other organisms to obtain their organic molecules are known as
consumers. Consumers use a range of different food sources and feeding mechanisms. The
combination of food sources and feeding mechanisms can be used to classify consumers.
• Herbivores feed on producers (e.g. deer, zebra, and aphids)
• Omnivores feed on a combination of both producers and consumers (e.g. chimpanzees,
mouse)
• Carnivores feed on other consumers (e.g. lions, snakes, and ladybirds)
• Scavengers are specialized carnivores that feed mostly on dead and decaying animals (e.g.
hyenas, vultures crows)
Detritivores
A type of heterotroph that obtain nutrients by consuming non-living organic sources, such as
humus and detritus, which is waste or other organic debris, by internal digestion.
Þ Examples of detritivores include dung beetles, earthworms, woodlice, and crabs
Þ Humus is decaying leaf litter mixed with the soil
Þ Detritus is dead, particulate organic matter. This includes decaying organic material
and fecal matter
All organisms leave behind organic material called detritus (like losing hair, feathers, and skin
cells). Additionally, remains of dead decaying bodies or plants also contribute to detritus.
Detritivores are important for recycling nutrients and returning them to the soil for autotrophs
to use.
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