Scientific Investigation Flashcards
(35 cards)
Accuracy
The closeness of a measured value to a standard or known value
Precision
The closeness of two or more measurements to each other
Representative Sample
A sample from a larger group that accurately represents the characteristics of a larger population
Random sampling
Individuals all have the same probability of being selected and are chosen randomly
e.g. using random co-ordinates for soil samples
Systematic sampling
selecting members of the population at regular intervals - every nth person
usually used along a transect
e.g. temp when climbing a hill
Stratified sampling
Dividing a population into subpopulations based on specific characteristics - must take a proportional sample (in ratio)
What is important when determining sample size?
large enough to be representative of the whole population
What is a standardised sampling method and why is it important?
a method that allows data to be collected the same way by different people at different times
controlling variables
What is a line transect?
a line or route that we stop upon and take a measurement at regular intervals
systematic sampling
How is a belt transect used?
using quadrats
can be interrupted or continuous
What is an abundance scale?
a way of applying observations to a category
DAFOR abundance scale
dominant
abundant
frequent
occasional
rare
Limitations of abundance scales
categorisation is subjective
no numbers = no statistics can be calculated
possibility of incorrect identification
Open frame quadrat
square frame
placed on top of vegetation
random/systematic sampling
count number of singular or different species
counting can be subjective an inaccurate
Grid quadrat
like an open frame but divided into squares
random/systematic sampling
used for calculating % cover - 100 squares
Point quadrat
T-shaped frame
10 long pins, plants that are hit by the pins are identified and counted
useful for tall plants and uneven ground
may damage vegetation
Kick sampling
Place net on river bed, agitate sediment, allow organisms to flow into the net
net must be downstream
used to study freshwater invertebrates
force of kicks may vary
organism may be damaged
Surber sampler
Net is directly connected to the site of disturbance, agitate sediment inside the square
net must be downstream
used to study freshwater invertebrates
unable to use if riverbed is uneven
Colonisation media
Provide an ideal habitat for the organism you want to count, wait for organism to colonise
inaccurate as only some of the population will colonise it
Pitfall trap
Dig hole, insert container (top must be ground level), cover top with slate propped on pebbles, return, count and identify
monitors terrestrial animals that live on ground surface
animals may crawl out/eat each other
if preservation fluid is used it may attract/repel specific organisms
Sweep net
Sweep net in figure of 8, set amount of times
captures organisms that live on/in vegetation
some may die when caught
organisms can fly out
Beating tray
Beat trees/vegetation and catch fallout
some organisms may not be dislodged
some species may fly away
difficult to standardise strength of beatin
Light trap
Used to catch flying organisms
identify, count, release
may escape before counting
different species are attracted to different wavelengths of light
some don’t fly in rainy conditions
Tullgren funnel
Collect soil/litter sample, place in container and turn on light (heat source), organisms move away from the light and fall through the grid into the collecting pot
heat may kill organism
some organisms may be too large for the grid
some species are not repelled by light/heat
