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 C.1
• A limiting factor is a component of an ecosystem which limits the numbers or distribution of a
population.
• They can be biotic or abiotic, such as environmental conditions or interactions between
organisms.
• According to the law of tolerance, populations
have optimal survival conditions within critical
minimal and maximal thresholds.
• Limiting factors cause rates of survival to
drop.
• The distribution of a species in response to a
limiting factor can be represented using this
type of curve:
• Plant species are highly dependent on soil
salinity.
• Plant species that are salt tolerant are called halophytes, which become stressed in freshwater
environments.
• Glycophytes are the opposite and are easily damaged by high salinity (98% of plant species).
• High salinity can be caused by cultivation of land for agriculture, making it harder for
glycophytes to extract water from soil.
• Coral species are highly dependent on oceanic temperature.
• They receive nutrition from zooxanthellae (symbiotic relationship), which cannot survive in low
temperatures.
• Therefore coral is most commonly found near the equator, in water temps between 20-30˚C.
• Quadrats can be placed at regular intervals along a transect line (which is placed along an
abiotic gradient) to generate population data and determine a pattern. The data can be applied
to the law of tolerance.
• A kite graph can be used to represent the changes in species distribution. The width of each
kite represents the abundance of each organism at a particular quadrat along the transect.
• An ecological niche consists of the conditions which determine an organisms survival, including
habitat, activity patterns, resource availability and interactions between other species.
• Two species cannot survive indefinitely in the same habitat if they share the same exact niche as
it will cause interspecific competition.
• This will cause one of two responses:
• Competitive exclusion: One species will outcompete the other.
• Resource partitioning: Both species divide resources (niche partitioning).
• A fundamental niche is the entire set of conditions under which an organism can survive and
reproduce whereas a realised niche is the set of conditions where it actually does live.
• Interactions between species in a community can be classified based on their effect on the
organisms involved.
• Herbivory is the act of eating only plant matter. Fruit eating animals spread seeds in their faeces,
promoting seed dispersal.
, • Predation is the interaction where a predator feeds on a prey species. Their populations are
intertwined, meaning they keep each others populations under control.
• There are different types of symbiotic relationships:
• Mutualism where both species benefit from the interaction (bees + flowering plants).
• Commensalism where one species benefits and the other is unaffected (barnacles + whales).
• Parasitism where one species benefits and the other is harmed (ticks + humans).
• Coral polyps secrete calcium carbonate to help build exoskeletons, protecting them and the
zooxanthellae and supplies the zooxanthellae with CO2.
• Zooxanthellae supplies the coral with oxygen, glucose and other organic molecules and helps
remove waste products from the coral.
• Lack of zooxanthellae caused by light availability, temperature increases and clean acidification
lead to coral bleaching.
• A keystone species has a disproportionately large impact on the biological community relative
to its abundance. These can be predators or the direct/indirect food source for the community.
Unit C.2
• Most species occupy different trophic levels in multiple food chains.
• A food web shows all the possible food chains in a particular community. When constructed a
food web the organisms should be positioned at their highest trophic level.
• The percentage of ingested energy converted to biomass is dependant upon the respiration
rate.
• Primary production is the production of chemical energy by producers whereas secondary
production is the generation of biomass by consumers.
• Respiration = Gross production - Net production
• Feed conversion ratios measure the efficiency of an animal in converting the food provided into
a desired output.
• FCR = mass of feed / mass of desired output.
• In closed ecosystems energy but not matter is exchanged with the surroundings.
• The type of stable ecosystem that will emerge in an area is predictable based on climate.
• Hot and humid environments
create tropic rainforests.
• Cold temperatures and little
precipitation cause taiga
biomes.
• Dry and arid environments
cause desert biomes.
• Climograph's can be used to
identify particular biomes:
• Pyramids of energy show the flow of energy between trophic levels. These
can also be used to identify particular biomes:
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