PAG 5 Colorimeter and potometer Flashcards
what assumption is made when using a potometer?
that water uptake = transpiration
what precautions need to be taken when SETTING UP a potometer?
cut shoots underwater
cut shoot at slant
set up apparatus underwater
ensure apparatus is airtight
dry the leaves
remove all but one air bubbles in capillary
cut shoots underwater
prevents air bubbles from forming in the xylem vessel
why do you want to prevent air bubbles in the xylem vessel?
you do not want any blockage of the transpiration stream
needs to maintain constant water column
set up apparatus underwater
prevents apparatus from having air bubbles (such as in the capillary tubing)
cut shoots at slant
to increase the surface area for water uptake
ensure apparatus is airtight
use vaseline to cover any gaps or holes
again prevents air bubbles from forming
dry the leaves
done to ensure water potential at the leaves is lower than water potential in the leaves
to ensure humidity does not affect transpiration
what does a potometer do?
measure uptake of water
what factors need to be controlled when using a potometer?
temperature
light intensity
wind speed
humidity
if it is not the independent variable it needs to be kept constant
how to control temperature?
use room at room temperature
KEEP CONSTANT
how to control wind speed?
use same fan for all recordings
KEEP CONSTANT
how to control light intensity?
use same lamp for all recordings
KEEP CONSTANT
how to control humidity?
cover plant with a plastic bad
KEEP CONSTANT
what precautions need to be taken when using a potometer?
use the syringe to move the air bubble to stop it entering the xylem
keep supporting the shoot to prevent the seal from breaking
ENSURES VALIDITY
what is the syringe used for in a potometer?
used to move the air bubble
allows you to reset the potometer to do repeats
what is the dependent variable in a potometer experiment?
the distance travelled by the air bubble
how can the distance travelled by the air bubble be calculated?
using a ruler to measure how far it moves in the capillary
how is the rate of transpiration calculated?
using a stopwatch along with the distance travelled by the air bubble
distance/time
how can you increase the resolution in a practical?
use equipment which go to more decimal places
why is a colorimeter more useful than just using a benedict’s test?
colorimeter is QUANTITATIVE
provides a numerical value which you can interpret and compare more easily
how is a colorimeter calibrated?
using a cuvette containing distilled water
calibrates the machine to zero
why is it important to calibrate a colorimeter?
to ensure that all values are measured to the same standard making them comparable
increases validity
the more concentrated a sample
the higher the absorbance value
what is a 10-fold serial dilution?
removing 1 cm3 from 10cm3 of starting solution
then adding it to 9cm3 of distilled water
repeat for as many dilutions as you want
conc decreases by factor of 0.1 every time
what graph is made after using a colorimeter?
a calibration curve
what does a calibration curve allow you to do?
find the concentration of unknown substances
x-axis of calibration curve for Benedict’s test
concentration of glucose
y-axis of calibration curve for Benedict’s test
absorbance
