Topics to revise
Atomic structure & Radiation P1 (Physics)
Ecology P2
Required practical - Sampling ecosystems
Atomic structure is covered in both Chemistry & Physics, so there is some overlap with last week.
Checklist - Atomic structure & Radiation
Mind map
P4 Atomic structure & Radiation
Random Sampling
Use quadrats and transects to measure how organisms are distributed in an area.
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
Sampling can be carried out in two ways.
Random sampling - when you need to know how many species or number of species in an area OR want to compare two areas.
Transects - Use this when there is a gradual change in an abiotic factor, e.g. moving away from a light source, water source etc.
Independent: Type of field, e.g. sheep present, fertilizer added
Dependent: number/type of organisms or number of species counted.
Control: quadrat size, sampling method, time of day, light intensity, water availability
Independent: Abiotic factor: Light intensity (i.e moving out of a woodland), water availability, source of pollution.
Dependent: number/type of organisms or number of species counted.
Control: quadrat size, sampling method, time of day, light intensity, water availability
For both methods: Quadrat, tape measure, identification key.
Ensure enough repeats to get a representative sample (enough to get a correct idea of how many species there are).
Always at least 10 repeats
Use an appropriate size quadrat to match the sample area.
Control validity by ensuring other variables are the same.
Organisms will be most common in areas they are best adapted to. e.g. plant species that prefer shade will be in shady areas and less common in sunny areas.
Place tape measure and layout a grid
Use random number generator to identify a grid reference
Place 50cm * 50cm quadrat on floor
Use a key to identify and count species
Only record species with more than 50% of the organism inside the quadrat
Repeat for at least 10 quadrats
Repeat for 2nd area if required
Present results in bar chart.
Place tape measure across habitat (transect).
Place quadrat at intervals along line.
State the interval (about 1/10th of total length, eg every 10 m for 100m area.
Record the abiotic factor - e.g. light meter for light
Use a key to identify and count species
Only record species with more than 50% of the organism inside the quadrat
Repeat for 2 more parallel transects (3 in total)
Present results in table/graph.