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Class notes Biology Oxford IB Diploma Programme: Biology Course Companion
IBDP HL Biology - 2.2 Water Notes
Summary of the entire Biology book from the IB diploma
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4.1 Species, Communities and Ecosystems
Essential idea
The continued survival of living organisms including humans depends on sustainable communities.
Objectives
Create a mesocosm.
Use your mesocosm to investigate how climate change could affect a community.
Key words: mesocosm / environment / community / ecology / climate change
Understandings
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Members of a species may be reproductively isolated in separate populations.
A community is formed by populations of different species living together and interacting with each other.
A community forms an ecosystem by its interactions with the abiotic environment.
Species have either an autotrophic or heterotrophic method of nutrition (a few species have both
methods).
Autotrophs obtain inorganic nutrients from the abiotic environment.
Consumers are heterotrophs that feed on living organisms by ingestion.
Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
The supply of inorganic nutrients is maintained by nutrient cycling.
Ecosystems have the potential to be sustainable over long periods of time.
Skills
Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
Setting up sealed mesocosms to try to establish sustainability.
Testing for association between two species using the chi-squared test with data obtained by quadrat
sampling.
Recognising and interpreting statistical significance.
,SPECIES
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Members of a species may be reproductively isolated in separate populations.
A species is a group of organisms that can potentially interbreed to produce fertile, viable offspring.
members from two different species cannot produce fertile, viable offspring.
when two different species produce hybrids by cross-breeding, hybrids are reproductively sterile.
e.g. liger, mule, tigon, wholphin.
A population is a group of organisms of the same species that are living in the same area at the same time.
different populations are reproductively isolated and unlikely to interbreed.
however they are still classified as the same species if interbreeding is functionally possible.
TERMINOLOGY
A community is formed by populations of different species living together and interacting with each other.
A community forms an ecosystem by its interactions with the abiotic environment.
Ecology: the study of the relationship between living organisms, or between living organisms and their environment.
,MODES OF NUTRITION
Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
Living organisms obtain chemical energy in one of two ways:
, Autotrophs
commonly referred to as producers.
synthesises its own organic molecules from simple inorganic substances (e.g. CO2, nitrates).
energy for this process is derived from either:
sunlight via photosynthesis.
chemosynthesis: oxidation of inorganic molecules.
Heterotrophs
commonly referred to as consumers.
cannot produce their own organic molecules.
obtains organic molecules from other organisms (living/recently killed/non-living remains/detritus).
Mixotrophs
some unicellular organisms may sometimes use both forms, depending on resource availability.
e.g. euglena gracilis possess chlorophyll for photosynthesis but may also feed on detritus.
Classification
Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
Autotrophs produce their own organic molecules by photosynthesis or chemosynthesis.
Heterotrophs obtain organic molecules from other organisms via one of three methods:
Consumers ingest organic molecules from living or recently killed organisms.
Detritivores ingest organic molecules found in the non-living remnants (e.g. detritus, humus).
Saprotrophs (decomposers) release digestive enzymes, then absorb external products of digestion.
AUTOTROPHS
Autotrophs obtain inorganic nutrients from the abiotic environment.
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