BIOLOGY SPECIFICATION NOTES
Edexcel Biology Salters-Nuffield A AS/A-Level
Key:
Definitions are in turquoise
Core practicals are in orange
Equations are in green
Topic 5: On the wild side (OWS)
5.1 Understand the terms ecosystem, community, population and habitat.
Ecosystem: self-sustaining functional unit composed of both biotic and abiotic factors.
Population: Group of interbreeding individuals of the same species
Community: Various populations sharing a habitat or ecosystem
Habitat: A place with a distinct set of conditions where an organism lives
5.2 Understand that the numbers and distribution of organisms in a habitat are controlled by
biotic and abiotic factors. P.5 - 6
The numbers and distribution of organisms in a habitat are controlled by biotic and abiotic
factors.
Biotic factors include:
- Competition for resources (like food, light, water). This can be intraspecific (within
species) or interspecific (between species)
- Grazing (animals that eat plants)
- Predation
- Disease
- Parasitism
- Mutualism
Abiotic factors include:
- Solar energy input. Affected by latitude, season, cloud cover
- Climate (rainfall, wind exposure, temperature)
- Topography (altitude, slope, drainage)
- Oxygen concentration
- Edaphic (soil)
- Pollution
- Natural catastrophes
These factors are typically density dependent. This means that the effects are related to
the size of the population relative to the area available. Abiotic factors and biotic factors both
combine to produce complex interactions in a habitat. Trees for example might affect water
content, humidity and light availability for smaller plants.
, Anthropogenic factors are factors caused by humans.
5.3 Understand how the concept of niche accounts for distribution and abundance of
organisms in a habitat.
A niche is the role an organism plays in the ecosystem. Organisms have adaptations that
enable them to cope with the biotic and abiotic conditions in their niche. If two organisms
share the same niche the better adapted organism will outcompete the other.
CORE PRACTICAL 10: Carry out a study on the ecology of a habitat, such as using
quadrats and transects to determine distribution and abundance of organisms, and
measuring abiotic factors appropriate to the habitat.
Aim: use sampling techniques to study the ecology of a habitat
- Identify and explain an abiotic factor that is affecting the distribution and abundance
of organisms in a habitat
-
Equipment:
- Quadrat: used to sample non-motile organisms
- Frame quadrats are used, either 0.25m or 1m.
You can either sample systematically or randomly.
Systematically:
- Pick site that shows environmental gradient
- Lay out tape measure in a straight line across gradient, this is the transect
- Identify a species that varies in abundance
- Measure environmental gradient by measuring abiotic factors like light, soil
pH, etc
- Place quadrats at same intervals along transect
- Either measure species density or percentage cover
Percentage cover is the percentage of the area occupied by the individuals. Species
density is the number of organisms.
Random:
- Use two tape measures to measure sample area
- Use random number generator to generate coordinates
- Repeat with at least 10 quadrats
The t-test can be used to determine if there is a significant difference between two sets of
data by comparing their means.
https://www.biologyforlife.com/t-test.html
5.4 Understand the stages of succession from colonisation to a climax community.
Edexcel Biology Salters-Nuffield A AS/A-Level
Key:
Definitions are in turquoise
Core practicals are in orange
Equations are in green
Topic 5: On the wild side (OWS)
5.1 Understand the terms ecosystem, community, population and habitat.
Ecosystem: self-sustaining functional unit composed of both biotic and abiotic factors.
Population: Group of interbreeding individuals of the same species
Community: Various populations sharing a habitat or ecosystem
Habitat: A place with a distinct set of conditions where an organism lives
5.2 Understand that the numbers and distribution of organisms in a habitat are controlled by
biotic and abiotic factors. P.5 - 6
The numbers and distribution of organisms in a habitat are controlled by biotic and abiotic
factors.
Biotic factors include:
- Competition for resources (like food, light, water). This can be intraspecific (within
species) or interspecific (between species)
- Grazing (animals that eat plants)
- Predation
- Disease
- Parasitism
- Mutualism
Abiotic factors include:
- Solar energy input. Affected by latitude, season, cloud cover
- Climate (rainfall, wind exposure, temperature)
- Topography (altitude, slope, drainage)
- Oxygen concentration
- Edaphic (soil)
- Pollution
- Natural catastrophes
These factors are typically density dependent. This means that the effects are related to
the size of the population relative to the area available. Abiotic factors and biotic factors both
combine to produce complex interactions in a habitat. Trees for example might affect water
content, humidity and light availability for smaller plants.
, Anthropogenic factors are factors caused by humans.
5.3 Understand how the concept of niche accounts for distribution and abundance of
organisms in a habitat.
A niche is the role an organism plays in the ecosystem. Organisms have adaptations that
enable them to cope with the biotic and abiotic conditions in their niche. If two organisms
share the same niche the better adapted organism will outcompete the other.
CORE PRACTICAL 10: Carry out a study on the ecology of a habitat, such as using
quadrats and transects to determine distribution and abundance of organisms, and
measuring abiotic factors appropriate to the habitat.
Aim: use sampling techniques to study the ecology of a habitat
- Identify and explain an abiotic factor that is affecting the distribution and abundance
of organisms in a habitat
-
Equipment:
- Quadrat: used to sample non-motile organisms
- Frame quadrats are used, either 0.25m or 1m.
You can either sample systematically or randomly.
Systematically:
- Pick site that shows environmental gradient
- Lay out tape measure in a straight line across gradient, this is the transect
- Identify a species that varies in abundance
- Measure environmental gradient by measuring abiotic factors like light, soil
pH, etc
- Place quadrats at same intervals along transect
- Either measure species density or percentage cover
Percentage cover is the percentage of the area occupied by the individuals. Species
density is the number of organisms.
Random:
- Use two tape measures to measure sample area
- Use random number generator to generate coordinates
- Repeat with at least 10 quadrats
The t-test can be used to determine if there is a significant difference between two sets of
data by comparing their means.
https://www.biologyforlife.com/t-test.html
5.4 Understand the stages of succession from colonisation to a climax community.
