practicals P2 Flashcards
what is chromatography?
method to separate and identify substances
eg photosynthetic pigments
paper = used filter paper
thin- layer = uses gel eg silica
- moves faster, separates more clearly
draw line in pencil
- ink from pen will run
Rf value
distance travelled by component
over
distance travelled by solvent
how to extract pigment from leaves
remove veins
- don’t contain pigment, hard to break up
pestle and mortar
- break up cells walls releasing pigment
- may use sand to help
organic solvent added
- dissolve the pigments
filtered and centrifuged
- remove any debris from pigment
how to prepare chromatogram
draw origin line in pencil
- ink from pen will dissolve and move
add dot of pigment using capillary tube to line
- multiple dots to concentrate pigment
set up solvent with paper in below line
- not above or pigments will dissolve
mark solvent from when time up
- otherwise will dissolve
don’t move equipment
- line will not be straight and therefore inaccurate measure of distance
how to investigate taxis and kinesis
use choice chambers
(or mazes)
Petri dish with 2 different conditions
- light, humidity
places maggots or woodlice in centre
leave for set time
record conditions they are in
repeats
what is a quantitative Benedict’s test?
Benedict’s solution added
- doesn’t form brick red precipitate
instead presence of glucose measured by loss of blue colour
- colourless = high concentration
intensity measured using calorimeter
- paler = less absorbance
use same:
volume of glucose solution
sample volume of Benedicts (excess)
length of time in waterbacth
temperature of waterbacth
how to prepare dilution series of glucose
concentration decreases by same quantity between tubes
- used to compare solution with unknown concentrations to
- add set quantity of glucose solution to test tube 1 - eg 10cm3
- add half quantity of distilled water to other tubes
- use a pipette to transfer half (5) from first test tube to second
- mix
= solution half as concentrated - remove half (5) from second and move to third, mix, repeat
serial dilutions calculation
desired concentration
over
concentration of stock
x volume wanted
glucose concentration method
- prepare dilution series
- add quantitative benedicts and heat in waterbath
use same quantity in each
use calorimeter to measure absorbance
- red filter (opposite to blue)
- calibrate using distilled water at beginning and between
- plot calibrate curve
absorbance Y against concentration X
carry out benedicts on unknown concentration
- use calibration curve to find glucose concentration of it
random vs systematic sampling
random
- points chosen by chance
- no bias
= representative
right angle tapes, random coordinates
systematic
- points chosen
- may be bias, chose easiest
= unrepresentative
along straight transect
carry out many repeats
- ensure reliable estimate
how to investigate non-motile species
use quadrats and transects
quadrats
species frequency
- count number in each quadrat
or
number of quadrats with species
over
total number of quadrats
x 100
percentage cover of species
- how much of quadrat is covered
- count squares more than half covered
- quicker than counting all
transects
- how species distributed across an area, use tape measure
- quadrats at set intervals along
- calculate frequency or cover
how to investigate motile species
mark release recapture
- capture sample
- mark them, shouldn’t affect chance of survival
- release
- wait, allows them to be distributed
recapture
- count number of marked and unmarked
proportion of marked to unmarked used to estimate population size
estimate total population size
number in 1st X number in 2nd
over
number of marked in 2nd
assumptions made in MRR
- had sufficient time to disperse
- marking didn’t affect survival rate
- markings still visible
- no mass births/deaths/migration
how to assess the impact of and environmental factor on species distribution
transect:
measuring distance from somewhere
- quadrat at set intervals along
or as a grid
- use random number generator to pick coordinates
place quadrat, calculate:
- percentage cover of species
- abiotic factor
eg pH using probe, temperature with thermometer etc
plot on graph
use statistical test to determine strength of correlation between abiotic factor and cover
- eg spearmans
