RP 9 - The effect of temperature on the rate of respiration of cultures of yeast Flashcards
Uou were told to leave the tubes in the water bath for 5 mins.
Why?
Allow apparatus to reach equilibrium
You were told to make sure that the water bath temperature stayed at 35 degrees.
Describe how you monitored the water bath temp and kept it constant at 35 degrees
Use thermometer - take regular readings
Add hot/cold water if needed
there was no control experiment in this investigation.
describe the control experiment you would set up.
explain why this control experiment would be important?
test tube with ONLY glucose and methylene blue
OR
glucose. methylene blue and boiled yeast
ensures yeast causing colour change
you were told not to shake the tubes again.
shaking the tubes would have caused the methylene blue to go blue again.
why?
mixing with oxygen
oxygen oxidises methylene blue
respiration by yeast caused methylene blue to go colourless.
how?
accepts electrons
from glucose
the yeast cultures in the conical flasks were set up some time before you carried out your investigation.
explain why?
allows yeast to be reproduced
the conical flasks were stoppered with cotton wool.
explain why?
prevent contamination by bacteria
would compete with yeast for O2
the flasks were loosely stoppered with cotton wool rather than with rubber bungs.
why?
allow O2 through
you were instructed to add 200cm3 sterile water to yeast culture.
why?
dilutes yeast
colonies spread out enough to be able to count
you were told to stir the mixture in the beaker containing yeast culture and sterile water.
explain why you were told to do this?
distribute yeast evenly
more oxygen entered culture in 250cm3 flask than 25cm3 flask.
why?
larger surface area
for diffusion of oxygen
explain how higher conc of oxygen affects growth of population of yeast cells?
more oxygen allows more resp
produces more ATP
ATP used for growth
