AQA A Level Biology Paper 2/3
AQA A Level Biology Paper 2/3 Exam
Study Guide Containing 249 Questions
with Definitive Solutions 2024-2025.
Ecosystem - Answer: is the community and the abiotic components of the
environment
Abiotic factors in an ecosystem - Answer: Temperature
Water availability
1
, AQA A Level Biology Paper 2/3
Humidity
Light intensity
Oxygen and carbon dioxide concentration
Wind speed
Salinity
pH of soil
Biotic factors in an ecosystem - Answer: Predators
Competition
Parasites
Symbiosis
Food availability
Disease
Community - Answer: All the populations of different species in a habitat
Population - Answer: All the individuals of one species in a habitat
Habitat - Answer: Place in which an organism lives
Ecological niche - Answer: Where an organism lives and it's role within that
habitat e.g. feeding rate,which is governed by adaptations to both biotic and
abiotic conditions.
Measuring frequency of plants or slow moving animals - Answer: Grid the area
2
, AQA A Level Biology Paper 2/3
Get coordinates from a table of random numbers and place quadrats down at
these coordinates
Record whether there is the presence or absence of a species in each quadrat
( use NE rule for any overlapping)
Repeat until there is a large sample and until a running mean has been stabilised
Calculate the percentage of organisms present in all the quadrats and scale up to
find the frequency of organisms in the given area
Evaluate measuring frequency of a species - Answer: Advantage- quick and easy in
large scale ecosystems
Disadvantage- results not detailed
Measuring percentage cover of plants or slow moving animals - Answer: Grid the
area
Get coordinates from a table of random numbers and place quadrats down at
these coordinates.
Measure the proportion of the quadrat occupied by the species and estimate the
percentage cover in each quadrat.
Repeat until there is a large sample and until a running mean has stabilised.
Calculate the mean percentage cover in all quadrats and scale up to find mean
number in given area
Measuring species density/ population of slow moving animals or plants - Answer:
Grid the area
3
, AQA A Level Biology Paper 2/3
Get coordinates from a table of random numbers and place quadrats at these
coordinates.
Count number of individuals( use NE rule for any overlapping) in a quadrat
Repeat until there is a large sample and until a running mean has stabilised
Calculate mean number of organisms in each quadrat and scale up to find mean
number in area of field.
Why do samples need to be large? - Answer: To be representative of the whole
population, allow a stats test to be carried out and avoid anomalies having a great
effect.
Evaluate measuring percentage cover of a species - Answer: Advantage -Quick
Disadvantage- subjective as estimates by different people will be different and
difficult to decide where plant starts and finishes.
Evaluate measuring species density/ population - Answer: Advantage- allows you
to calculate an estimate of the population and can calculate species diversity
Disadvantage- time consuming
When to sample systematically? - Answer: When finding out how species
distribution changes across an area use a transect.
Belt transect - Answer: Place quadrats at regular intervals ( could use more than
one quadrant at each point so the data is more representative)
Record percentage cover or frequency of each species
4
AQA A Level Biology Paper 2/3 Exam
Study Guide Containing 249 Questions
with Definitive Solutions 2024-2025.
Ecosystem - Answer: is the community and the abiotic components of the
environment
Abiotic factors in an ecosystem - Answer: Temperature
Water availability
1
, AQA A Level Biology Paper 2/3
Humidity
Light intensity
Oxygen and carbon dioxide concentration
Wind speed
Salinity
pH of soil
Biotic factors in an ecosystem - Answer: Predators
Competition
Parasites
Symbiosis
Food availability
Disease
Community - Answer: All the populations of different species in a habitat
Population - Answer: All the individuals of one species in a habitat
Habitat - Answer: Place in which an organism lives
Ecological niche - Answer: Where an organism lives and it's role within that
habitat e.g. feeding rate,which is governed by adaptations to both biotic and
abiotic conditions.
Measuring frequency of plants or slow moving animals - Answer: Grid the area
2
, AQA A Level Biology Paper 2/3
Get coordinates from a table of random numbers and place quadrats down at
these coordinates
Record whether there is the presence or absence of a species in each quadrat
( use NE rule for any overlapping)
Repeat until there is a large sample and until a running mean has been stabilised
Calculate the percentage of organisms present in all the quadrats and scale up to
find the frequency of organisms in the given area
Evaluate measuring frequency of a species - Answer: Advantage- quick and easy in
large scale ecosystems
Disadvantage- results not detailed
Measuring percentage cover of plants or slow moving animals - Answer: Grid the
area
Get coordinates from a table of random numbers and place quadrats down at
these coordinates.
Measure the proportion of the quadrat occupied by the species and estimate the
percentage cover in each quadrat.
Repeat until there is a large sample and until a running mean has stabilised.
Calculate the mean percentage cover in all quadrats and scale up to find mean
number in given area
Measuring species density/ population of slow moving animals or plants - Answer:
Grid the area
3
, AQA A Level Biology Paper 2/3
Get coordinates from a table of random numbers and place quadrats at these
coordinates.
Count number of individuals( use NE rule for any overlapping) in a quadrat
Repeat until there is a large sample and until a running mean has stabilised
Calculate mean number of organisms in each quadrat and scale up to find mean
number in area of field.
Why do samples need to be large? - Answer: To be representative of the whole
population, allow a stats test to be carried out and avoid anomalies having a great
effect.
Evaluate measuring percentage cover of a species - Answer: Advantage -Quick
Disadvantage- subjective as estimates by different people will be different and
difficult to decide where plant starts and finishes.
Evaluate measuring species density/ population - Answer: Advantage- allows you
to calculate an estimate of the population and can calculate species diversity
Disadvantage- time consuming
When to sample systematically? - Answer: When finding out how species
distribution changes across an area use a transect.
Belt transect - Answer: Place quadrats at regular intervals ( could use more than
one quadrant at each point so the data is more representative)
Record percentage cover or frequency of each species
4
