Required Practical 9 Flashcards
investigation of effect of temp on respiration in yeast
you were told to leave the tubes in the water bath for 5 mins.
why?
allow apparatus to equilibriate
you were told to make sure that the water bath temp stayed at 35 degrees.
describe how you monitored the water bath temp and kept it constant at 35 degrees?
- use thermometer - take reg readings
- add hot/cold water if needed - maintain constant temp
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
