The study of relationships between living organisms and between organisms and their environment

Species: Groups of organisms that can potentietally interbreed to produce fertile offspring

If species are not closely related it is usually impossible for individuals of different species to interbreed 

If individuals of different species interbreed and produce offspring - Hybrids will be sterile [infertile don't produce sex cells because the chromosomes of parents from different species don't match] 

Example: Mule

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Population: A group of organisms of the same species living in the same area at the same time

Organisms of the SAME species are SEPARATED geographically and are UNLIKELY to breed but the ability to do so remains. The seperated organisms are part of different populations

U2: Members of a species may be reproductively isolated in seperate populations

Example: South Africans within SA and South Africans in Egypt

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Community: Group of populations of different species living together and interacting with each other in the same area

All organisms are dependent on interactions with members of other species for survival this includes plants and microbes

Example: Lions depend Zebras or Bucks 

                Finding Nemo fishbowl

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Ecosystem: A community forms an ecosystem by its interactions with the abiotic environment

Biotic: Living

Abiotic: Non-living surroundings of a community [soil, air, water] 

Ecosystem = Community + Abiotic Environment

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Energy Absorption: Autotrophs

Autotrophs: Convert Carbon Dioxide [atmosphere/dissolved in water] into Organic Compounds

Plants synthesise sugars [Glucose] then converted into organic compounds [Starch, Cellulose, Lipids, Amino Acids]

Inorganic Nutrient Compounds [Water, Carbon Dioxide, Nitrates, Phosphorous, Oxygen] obtained from Abiotic Environment [Soil, Air, Water]

Energy Source: Light


U3: Species have either heterotrophic or autoprohic method of nutrition [some species have both]

All organisms need organic molecules [Amino Acids] to carry out the functions of life [growth, motabolism and reproduction]

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Energy Absorption: Heterotrophs

Heterotrophs: Rely on other organisms for energy

Cannot make the carbon compounds needed

Obtain them from other organisms

Types of Heterotrophs:

  • Consumers
  • Detrivores
  • Saprotrophs

Mixotrophs: Plants and Algae use a combination of different modes of nutrition

Euglena will photosynthesise in suffcient light feeding as an autotroph but can also ingest particles of food by phagocytosis which it then digests

Venus flytrap photocynthesises but can also catch insects and spiders to compensate for nutrient poor soil

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Consumers: Heterotrophs that feed on organisms by ingestion to obtain their organic molecules

Ingestion: The taking in of a substance 

Consumers can be classified as:

  • Herbivores: Feed on Producers

Example: Zebras, Deer and Asphids

  • Carnivores: Feed on other Consumers

Example: Lions, Snakes and Ladybirds

  • Omnivores: Feed on both Producers and Consumers

Example: Chimpanzee and Mice

  • Scavengers: Specialized carnivores that feed mostly on dead and decaying animals

Example: Hyenas, Vultures and Crows

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Detrivores: Heterotrophs that obtain organic nutrients from non-living organic sources such as detrius and humus by internal digestion

Detrius: Dead material from living organisms [dead leaves, parts of decomposing animals and feces]

Humus: Decaying leaf litter mixed with soil

Example: Dung beetles, Earthworms, Woodlice and Crabs

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Saprotrophs: Heterotrophs that obtain organic nutrients from dead organisms by external digestion

Saprotrophs live on or live in non-living organic matter.

Secrete digestive enzymes into the organic matter [dead leaves, dead animals, wood]

Absorb the needed substances/products of digestion

Proteins, Carbs, Lipids are digested externally and absorbed

NOT Consumers - do not ingest the food

External digestion - digestive enzymes are secreted

Decomposers - breakdown organic material 

Example: Bateria and Fungi

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Nutrient Cycle

Nutrients: Elements required by an organism for growth and metabolism [carbon, nitrogen, phosphorous]

The supply of nutrients is limited so ecosystems constantly recycle the nutrients between organisms. Everyone wants organic nutrients!

  • Autotrophs: Convert nutrients from an inorganic form into organic molecules
  • Heterotrophs: Ingest other organisms to gain organic form of nutrients 
  • Saprotrophs: Breakdown organic nutrients to gain energy and in the process release nutrients back into inorganic molecules

Summary of Nutrient Cycle

Supply of nutrients is limited therefore an ecosystem recycles

Autotrophs convert inorganic into organic

Heterotrophs ingest organisms to gain organic

Saprotrophs breakdown organic and release inorganic

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Ecosystem Sustainability

There are many nutrient cycles but two of the most important are the:

Carbon Cycle

Key component of carbohydrates, fats, proteins and DNA

Nitrogen Cycle

Key component of proteins and DNA

Decomposers [detrivores and saprotrophs] recycle the resources in dead plant and animal matter for reuse

Flow of energy and nutrients in an ecosystem are between members of the biotic community. Few flows of energy and nutrients leave or enter other ecosystems

Ecosystems are therefore self-contained and self-sustaining

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Ecosystem Sustainability

To remain sustainable an ecosystem requires:

  • Continuous energy availability: Light form the sun
  • Nutrient cycling: Saprotrophs are crucial for the continuous provision of nutrients to producers
  • Recycling of waste: Certain products of metabolism are toxic [Ammonia from excretion]. Deccomposing bacteria absorb the toxic molecules as energy, breakdown and release less toxic molecules
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Mesocosms: Biological systems that contain the abiotic and biotic features of an ecosystem, but are resticted in size and under controlled conditions

Mesocosms are useful for scientific investigations because natural ecosystems prove harder to collect valid data from

  • 5 Litre clear glass jar
  • Seal to prevent entry/exit of chemical substances
  • Air containing Oxygen and Carbon Dioxide
  • Pond water containing Autotrophs, Consumers, Detrivores and Saprotrophs
  • Mud from bed of pond

Autotrophs: Produce carbon compounds and regenerate oxygen used in cell respiration by organisms in mesocosm [essential]

Saprotrophs: Decompose dead organic matter and recycle nutrients [essential]

Consumers and Detrivores: Usually included, unethical to include large organisms that cannot obtain food or enough oxygen [non-essential]

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Testing for Association between Species

  • Positive Association: Species found in the same habitat 

Example: Preditor and prey        [symbiosis]

                Herbivore and plant

  • Negative Association: Species occur separately in different habitats 

Example: Competitive exculsion as they require different nutrients 

  • No Association: Species occur as frequently when they are apart as when they are together
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Quadrat sampling can be used to:

Estimate population density/size

Measure distribution of species

Placed repeatedly in sample area to provide a reliable estimate

Placed systematically to measure changing distribution

Placed randomly to estimate popluation density [presence/absence, frequency or % coverage]

Systematic and Random Sampling are used to avoid bias in the selection of sample 

Limitation: Large and mobile animals cannot be effectively sampled.

Most suitable for plants and small slow-moving animals

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Chi-squared Test

1. Always define Hypotheses

Null Hypothesis: There is no significant difference between the distribution of two species [distribution is random]

Alternative Hypothesis: There is a significant difference between the distribution of species [species are associated]

2. Complete the contingency table of observed frequencies using the data

3. Calculate the expected values using the formula

row total x coloumn total over grand total 

Expected values: Expect to find if there is no association between the species

4. Calculate the chi-squared value

5. Determine the degrees of freedom - if species are associated df is always 1

(rows - 1) x (coloumns - 1)

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Chi-squared Test

6. Compare x squared value with the critical values and validate the hypotheses

df = 1 H0 [Null hypothesis is rejected and H1 is accepted that there is an association between the two species

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