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Summary of IB Biology Topic 4 (Plant Biology)
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Summary of IB Biology Topic 4 (Plant Biology)
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Unit 4 - Ecology4.1 - Species, Communities and Ecosystems
4.1.1 - Species
Species: Group of organisms that can potentially interbreed to produce fertile, viable o spring.
Hybrids: cross-breeds between two di erent species (e.g. liger) that are sterile
Population: group of organisms of the same species living in the same area at the same time
Two populations living in di erent regions can still be classi ed as the same species if
interbreeding is functionally possible (however unlikely).
4.1.2 - Ecology Terms
Community: A group of populations living together and interacting with each other in a given area
Habitat: The environment in which a species normally lives
Ecosystem: A community and its abiotic environment/habitat
Ecology: The study of relationships between and amongst living organisms and their
environment.
4.1.3 - Modes of Nutrition
Autotrophs: organisms which synthesise their own organic molecules (food) from inorganic
substances
Types:
• Photoautotroph: uses photosynthesis
• Chemoautotroph: uses oxidation of chemicals
Commonly referred to as producers.
Heterotrophs: organisms which obtain organic molecules (food) from other organisms
Types:
• Consumers: ingest living or recently killed organisms
• Detritivores: ingest non-living remnants of organisms (e.g. detritus)
• Saprotrophs: (i.e. decomposers) release digestive enzymes on organisms and absorb the
digestive products
Mixotrophs: organisms (unicellular) which may use both forms of nutrition (depending on
resource availability).
ff ff fi ff
, 4.1.4 - Autotrophs
Inorganic molecules that autotrophs use include: carbon, nitrogen, hydrogen, oxygen and
phosphorus
They are obtained from the air, water and soil.
4.1.5 - Heterotrophs
Types of consumers:
• Herbivores: feed on plant matter
• Carnivores: feed on animal better
• Scavengers: feed on dead or decaying carcasses rather than hunting on their own
• Omnivores: feed on both
Types of detritivore food:
• Detritus: dead organic matter (e.g. decaying organic material or decal matter)
• Humus: decaying leaf litter mixed with topsoil
Detritivores include snails, worms and crabs.
Examples of saprotrophs: bacteria and fungi
4.1.6 - Nutrient Cycling
Chemical elements are constantly recycles after they are used.
4.1.7 - Mesocosm
Ecosystems are largely self-contained and can be self-sustaining for long periods of time.
Requirements of a sustainable ecosystem:
• Energy availability (e.g. sun)
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