required practical 9: investigation of a named variable on the rate of respiration Flashcards
how is a respirometer used to measure rate of aerobic respiration
add yeast to set volume of glucose
add buffer to keep pH constant
add NaOH to absorb CO2
place in water of a set temperature
measure distance moved by liquid in a given time
why does the liquid move
organisms will take in oxygen when respiring, the volume of gas and pressure of container decreases. this causes the fluid to move down a pressure gradient
why is the respirometer left open before experiment begins
allows apparatus to equilibrate
allows respiration to stabilise
why is apparatus sealed
to prevent air from entering/leaving, this would affect the volume/pressure
how is rate of respiration calculated
volume of CO2 released - area of cylinder * distance moved
mass of organism / time taken
units = cm3/ min/g
how can redox indicators be used to measure rate of respiration
the indicator will change colour when accepting electrons due to reduction.
add yeast and glucose to test tube.
add buffer
add indicator
record time for colour change
what variables need to be controlled (redox indicator)
volume of yeast
volume of glucose
temperature
pH
volume of indicator
