Edexcel IAL Biology 7.7 Yeast respiration practical

Select a redox indicator, equilibrate identical yeast mixtures in water baths, time the same colour endpoint and compare mean rate after controlling volumes and pH.

Exam points

Identify TTC, methylene blue or DCPIP as an artificial hydrogen carrier.
Design a yeast experiment with water baths, timed colour change and repeats.

[Maximum number: 5]

Saccharomyces cerevisiae is a type of yeast. It is a single-celled organism which is widely used in brewing and baking. The photograph shows yeast cells seen through a microscope.

Figure for Question 7.7—Core Practical 15 - respiration in yeast question 1 — Edexcel A-Level Biology A2

Describe an experiment to investigate the effect of temperature on the rate of respiration in yeast, using an artificial hydrogen carrier (redox indicator).

A description that contains five of the following:

- range of five suitable temperatures used (1)

- use of thermostatic waterbath (1)

- incubate yeast and indicator separately to reach same temperature (1)

- suitable named indicator used (1)

- record time taken for colour to change (1)

- identification of one variable (1)

- repeats and calculate \{ means/SD's \} (to compare) (1)

Accept temperatures between 5 and $45^{\circ} \mathrm{C}$ (ignore additional temperatures outside the range)

Accept waterbath set at a stated temperature

Accept to equilibrate/acclimatise

Accept TTC / DCPIP / methylene blue ignore stated colours

Accept: pH

\{volume / conc/mass/strain/type\} of yeast suspension/ volume/conc of TTC Ignore species

Accept average

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7.7—Core Practical 15 - respiration in yeast question 1