RP9 Flashcards
RP9
Independent variable
Temperature
[Could do type of sugar]
RP9
Dependent variable
Time taken for meniscus to move 1cm – demonstrating oxygen being taken in to yeast
Or time taken for methylene blue to go colourless
RP9
Controls
Volume and concentration of yeast suspension
Type
Volume and concentration glucose
Volume of methylene blue
RP9
Why does the methylene blue decolourise?
Methylene Blue accepts e- and is reduced = colourless
RP9
Why use a glass beaker as water bath rather than electric water bath?
Allows you to see colour change more easily, without removal from temperature
RP9
How do you convert time taken to rate?
1/ time
RP9
How could make your results more accurate?
Smaller intervals for temperature.
Repeat, remove anomalies
Calculate mean.
RP9
Describe a control you could set up
Methylene blue with boiled yeast and glucose. This would show that glucose alone does not cause methylene blue to go colourless and the change is a result of respiration
1 mark
Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.
So the oxygen is used/absorbed/respired
2 marks
The conical flasks were stoppered with cotton wool. Explain why the flasks were stoppered.
RP9
1 Prevent contamination by bacteria
2 Bacteria would compete with the yeast for oxygen / nutrients
3 Toxins / substances produced by bacteria might inhibit yeast growth
1 mark
The yeast cultures in the conical flasks were set up some time before you carried out your investigation. Explain why
RP9
Allow yeast to reproduce
2 marks
More oxygen entered the culture in the 250 cm3 flask than in the 25 cm3 flask.
Explain why
RP9
1 Larger surface area in 250 cm3 flask
2 For diffusion(of oxygen into the culture
1 mark
The flasks were loosely stoppered with cotton wool rather than with rubber bungs.
Explain why the flasks were loosely stoppered with cotton wool.
RP9
Allows oxygen through / is permeable to gases / carbon dioxide;
3 marks
Explain how the higher concentration of oxygen affects the growth of a population of yeast cells.
RP9
1 More oxygen allows more aerobic respiration
2 Produces more ATP
3 ATP used for growth, active transport of nutrients, cell division
OR
4 Less anaerobic respiration
5 Less ethanol produced
6 Ethanol kills/inhibits/slows
1 mark
You were told to stir the mixture in the beaker containing the yeast culture and sterile water. Explain why you were told to do this.
RP9
distribute yeast evenly
2 marks
You were instructed to add 200 cm3 sterile water to the yeast culture. Explain
why you needed to do this.
RP9
1 Reduces concentration of yeast
2 So colonies would be spread out enough to count
