Summary Notes designed for the International Baccalaureate Diploma Programme. These notes are detailed yet concise, with all the information to achieve a 7 in IB Biology HL or SL. These notes were made using information from the IB syllabus, Oxford IB Diploma HL Biology Textbook, Bioninja and the B...
Unit 4.1
• A species is a group of organisms which can breed together and produce fertile, viable
offspring.
• A population is a group of organisms of the same species that are living in the same area and
the same time.
• A community is a group of populations living and interacting together in a given area.
• A habitat is the environment where a species normally lives.
• A community forms an ecosystem by its interaction with the abiotic environment.
• Living organisms obtain chemical energy in two ways:
• Autotrophs (producers) synthesise organic molecules by using energy obtained from:
• The sun during photosynthesis.
• The oxidation of inorganic molecules (chemosynthesis).
• Heterotrophs (consumers) obtain organic molecules from other organisms by:
• ingesting them from living or recently killed organisms (consumers)
• ingesting them from non-living organisms (detritivores)
• secreting digestive enzymes and then absorbing the products (saprotrophs)
• Mixotrophs can act as both consumers and producers
• The supply of inorganic nutrients to the earth is limited, so nutrients are recycled.
• Ecosystems are mostly self-contained and are self-sustainable for long periods of time as they
are able to gain energy and recycle nutrients and wastes.
• Mesocosms are enclosed environments that allow a small part of a natural environment to be
observed under controlled conditions. Steps to make one include:
• A bottom layer pebbles to act as drainage followed by a layer of
activated charcoal to prevent mould.
• A layer of sphagnum moss for separation and then soil on top.
• The terrarium used must be clear and able to be fully sealed.
• Species can show a positive or negative association based on
whether they are found in the same habitat or not.
• The presence of two species can be obtain using quadrat
sampling, where a quadrat (rectangular frame) is placed on the
ground and the types of species in the quadrat is recorded.
• A chi-squared test uses this data to determine if there is a
statistically significant association between the distribution of two species.
Unit 4.2
• Photosynthesis converts light energy into chemical energy.
• Chemical energy in carbon compounds flows through food chains by means of feeding.
• The position an organism occupies within a feeding sequence is known as a trophic level.
• Producers always occupy the first trophic level.
• Organisms in a food web can be part of more than 1 trophic level.
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