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Edexcel Biology A Level - Core Practical 10 Summary Notes
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Summary notes on core practical 10 (Edexcel biology A). Covers control variables, measures of abundance (percentage cover, percentage frequency, local frequency, density & diversity index), data analysis, validity check and sampling techniques (frame quadrats, point quadrats, line transects and bel...

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  • June 13, 2023
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  • 2021/2022
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(10) Studying the Ecology of a Habitat
Control Variables:
• Abiotic factors: light, temperature, humidity, O2 concentration, pH

Measures:

Percentage Cover (Subjective)
• An estimate of the area within a quadrat covered by a particular species
• Qualitative description of percentage cover is taken in each quadrat; e.g. abundant, common,
frequent, occasional or rare
• Easy, but subjective

Percentage Cover (Objective)
• An estimate of the area within a quadrat covered by a particular species
• Quantitative description of percentage cover is taken in each quadrat; e.g. the number of pins that
touch a given species on a point quadrat

Percentage Frequency
• Percentage probability of a particular species occurring in a quadrat
• Measure number of presences or absences of selected species in a quadrat

Local Frequency
• The number of squares on a quadrat in which a species is found
• Reduces the possibility that rare species are not sampled, like with point sampling methods

Density
• Number per unit area
• Only applicable if it is feasible to count every individual organism in one area

Diversity Index
• Describes the relationship between the number of species in a community and the number of
individuals in each species
• Measures species richness and species evenness

Data:
• Results of investigations into the abundance and distribution of organisms can be plotted onto a kite
diagram
Abiotic factors can also be plotted onto the kite diagram
• Use statistical tests (t-test, chi-squared or correlation coefficient) to test your conclusions

Validity:
• Abiotic factors constantly change
• Organisms can change locations
• Assumes that the sampling units are representative of the population

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