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Summary IB Biology Topic 4: Ecology
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  • Biology SL and HL
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  • International Baccalaureate Diploma
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  • IB Biology Course Book

Detailed objective-by-objective summary notes for Topic 4: Ecology for IB Biology SL/HL. Contains information on everything you need to know from 4.1 to 4.4, according to each understanding, application or skill. Written by a IB HL Biology student who graduated with a 45/45.

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  • March 5, 2019
  • 7
  • 2016/2017
  • Summary

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  • ib biology
  • biology
  • topic 4
  • ecology
  • species
  • ib
  • international baccalaureate
  • hl
  • sl

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  • International Baccalaureate Diploma
  • Biology SL and HL
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IB TOPIC 4 | ECOLOGY
2016 | SYJ0014


Topic 4.1: Ecology – Species, communities and ecosystem
The continued survival of living organisms including humans depends on sustainable communities.

• Understanding: Species are groups of organisms that can potentially interbreed to produce fertile offspring.

 Species: groups of organisms that can potentially interbreed to produce fertile off-springs
 Crossbreeding: interbreeding between different species with off-springs almost always infertile

• Understanding: Members of a species may be reproductively isolated in separate populations.

 Speciation: process in which one species is reproductively isolated into different populations they develop into different species where they
are unable to produce viable off-springs

Type of mechanism Description Example
Geographical isolation Population is separated as the environment Natural disasters, continental shift
imposes a geographical barrier
Ecological isolation Population is separated by occupying different Tree and mud lizards
habitats (disruptive evolution)
Temporal isolation Population is separated through reproducing at Winter and summer plants
a different season/time
Behavioural isolation Population is separated through differing in Birds of paradise
their respective mating rituals

• Understanding: Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).

 Autotrophs: organisms that synthesize their won organic molecules from simple inorganic substances
 Heterotrophs: organisms that obtain organic molecules from other organic organisms
 Mixotrophs: organisms that has both autotrophic and heterotrophic means of nutrition (e.g. Chlamodomonas or Euglena)

• Understanding: Consumers are heterotrophs that feed on living organisms by ingestion.

 Consumers: heterotrophic organisms that feed on living organisms by ingestion

• Understanding: Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.

 Detritivores: heterotrophic organisms that feed on organic nutrients from detritus (dead organic matter) by internal digestion

• Understanding: Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.

 Saprotrophs: heterotrophic organisms that feed on organic nutrients from detritus (dead organic matter) by external digestion

• Understanding: A community is formed by populations of different species living together and interacting with each other.

 Community: populations of different species living and interaction with each other
 Examples of community interactions: symbiosis (mutualism, parasitism), predation, disease agents

• Understanding: A community forms an ecosystem by its interactions with the abiotic environment.

 Ecosystem: interaction of the community with the abiotic environment
 Abiotic factors: non-living, physical components of an ecosystem (e.g. light, wind, pH, salinity, temperature)
 Biotic factors: living components of an ecosystem (e.g. symbiosis, mutualism, predation)

• Understanding: Autotrophs obtain inorganic nutrients from the abiotic environment.

 Autotrophs: obtain all nutrients from the abiotic environment (e.g. carbon, nitrogen, sodium etc.)
 Heterotrophs: obtain most nutrients from food, but they obtain many inorganic nutrients from the abiotic environment (e.g. sodium)

• Understanding: The supply of inorganic nutrients is maintained by nutrient cycling.

 Nutrient cycles: cycle process in which organisms absorb, use and return elements from and to the abiotic environment (e.g. carbon)
 Nutrients and energy: energy is able to enter and leave ecosystems while nutrients can only be cycled

• Understanding: Ecosystems have the potential to be sustainable over long periods of time.

 Requirements for ecosystem sustainability:
 Nutrient availability: enough nutrients should be present to be cycled
 Detoxification: waste products must not cumulate and needs to be cycled again
 Energy availability: energy cannot be cycled like nutrients and hence ecosystems must have a stable source




LAST EDITED 2017-03-15 | 1

, IB TOPIC 4 | ECOLOGY
2016 | SYJ0014


• Skill: Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.

Autotrophs (producers) Consumers Decomposers
Detritivores Saprotrophs
Nutrient source Abiotic; simple ions and Biotic; organisms living or has been Biotic; detritus (dead organic matter)
compounds such as CO2 dead for a short time
Process Photosynthesis Internal Internal External
(ingestion) (ingestion) (releases enzymes)
Example Plants Lions Dung beetles Fungi

• Skill: Setting up sealed mesocosms to try to establish sustainability. (Practical 5)

 Mesocosms: small, separated experimental areas set up for ecological experiments
 Usage: it can be used to test which types of ecosystems are sustainable

• Skill: Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
• Skill: Recognizing and interpreting statistical significance.

 Chi-squared test: test used to compare sets of categorical data and evaluate statistically significance
 Requirement: a contingency table of observed frequency is necessary
 Implication: if null hypothesis is rejected, the data is statistically significant (probability of getting results as extreme are small)

 Two possible hypotheses in chi-squared tests:
 H0 – two species are distributed independently (null hypothesis)
 H1 – two species associated

 Method of determining chi-squared tests:
 Outline observed frequency (fo)
𝑟𝑜𝑤 𝑡𝑜𝑡𝑎𝑙 ×𝑐𝑜𝑙𝑢𝑚𝑛 𝑡𝑜𝑡𝑎𝑙
 Determine expected frequency (fe): 𝑔𝑟𝑎𝑛𝑑 𝑡𝑜𝑡𝑎𝑙
(𝑓𝑜 −𝑓𝑒 )2
 Determine chi-squared values: 𝑥 2 = ∑ 𝑓𝑒
 Determine degree of freedom: (𝑚 − 1)(𝑛 − 1)
 m – number of rows
 n – number of columns

 Determine the valid hypothesis: if the calculated value is
below the critical region, the null hypothesis is not rejected

• Nature of science: Looking for patterns, trends and discrepancies—plants and algae are mostly autotrophic but some are not.

 Although plants and algae are mostly autotrophic, there are some that do not carry out photosynthesis
 Parasitic plants: plants that grow on other organisms, most notably plants
 Observation: only one percent of plant and algae species are parasitic
 Generalization: therefore, ecologists regard plants and algae as groups of autotrophs, with small number of parasitic species

• International mindedness: The need for sustainability in human activities could be discussed and the methods needed to promote this.
• Guidance: Mesocosm can be set up in open tanks, but sealed glass vessels are preferable because entry and exit of matter can be prevented but light
can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones.
• Guidance: To obtain data for the chi-squared test, an ecosystem should be chosen in which one or more factors affecting the distribution of the
chosen species varies. Sampling should be based on random numbers. In each quadrat the presence or absence of the chosen species should be
recorded.




LAST EDITED 2017-03-15 | 2

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