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Summary IB Biology HL Topic 4 Ecology Notes

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Biology

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12th Grade

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Uploaded on August 7, 2024
Number of pages 11
Written in 2023/2024
Type Summary

Institution Secondary school
Education 12th Grade
Course Biology
School year 1

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UNIT 4 : ECOLOGY

4.1 - Species, communities and ecosystems

Ecology: the study of relationships between living organisms and their environment

Species: a group of organisms that can potentially interbreed to produce fertile, viable
offspring

Limitations of the biological species concept:
1. It is often impossible for individuals of different species to breed unless the species
are closely related
- If members of two closely related species do interbreed and produce offspring, the
hybrids will be sterile / infertile (eg. mules - horse and donkey) because they do not
have viable sex cells and cannot produce sperm or eggs
Hybrid: an offspring produced from a cross between parents of different species or
sub-species

2. Sometimes variation within a species might limit mating within the species. Although
capable of interbreeding, individuals do not

3. Members of the same species might be capable of interbreeding but do not because
of geographical isolation
Geographical isolation: when two populations are separated by geographical barriers like
rivers, mountains, or bodies of water

4. Asexual organisms do not interbreed

5. Interbreeding capability is unknown for extinct organisms

6. With ring species, neighboring populations of a species might be able to interbreed
but the two ends of the chain cannot interbreed
Ring species: a situation in which two populations that do not interbreed are living in the
same region and are connected by a geographic ring of populations that can interbreed

, Population: a group of organisms of the same species that are living in the same area at the
same time
Reproductive isolation: two or more populations of the same species are prevented from
interbreeding
- Organisms of the same species that live in different regions are reproductively
isolated and unlikely to breed even though they have the ability to do so
- If the populations never interbreed, gene mixing between the populations stops and
evolutionary forces like natural selection may act differently on the populations
- Over time, the populations may change to the point of not being able to interbreed
and produce viable, fertile offspring
- This leads to speciation, meaning that they would be considered separate species
Speciation: the formation of new species from an original, ancestral lineage

Community: a group of populations that are living and interacting together in the same area
eg. a forest
- All organisms are dependent on interactions with members of other species for
survival (lions prey on other animals)
- Communities involve thousands of species as they also include plants and microbes
(organisms that require a microscope to be seen)

Habitat: the environment a species normally lives in

Ecosystem: the interaction between biotic components (community) and abiotic
components (habitat)

Methods of Nutrition
Species either have an autotrophic or heterotrophic method of nutrition. A few species have
both methods (mixotrophs).

All organisms require organic molecules such as amino acids to carry out the functions of life

Autotroph: an organism that synthesises its own organic molecules from simple inorganic
substances (eg. CO2, nitrates) in the abiotic environment (soil / air / water)
- All autotrophs convert carbon dioxide from the atmosphere or dissolved in water into
organic compounds like starch, cellulose, lipids, amino acids
- Energy for this process is derived from sunlight through photosynthesis or via the
oxidation of inorganic molecules through chemosynthesis
- Autotrophs are commonly referred to as producers

Heterotroph: an organism that obtains organic molecules from other organisms (living or
dead) by ingestion
- Heterotrophs are called consumers as they obtain energy from other sources
eg. herbivores, omnivores, carnivores, scavengers
Consumers:
Herbivores - feed on producers (eg. deer, zebra)
Omnivores - feed on producers and consumers (eg. chimpanzee, mouse)
Carnivores - feed on other consumers (eg. lion, snake)
Scavengers - feed on dead and decaying remains rather than live prey (eg. hyenas, crows)

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