# Biology Required Practical 9 (AQA)

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1. Hi Guys,
So basics I've got to plan my required practical 9, which is 'Investigation into the effect of a named variable on the rate of respiration of cultures of yeast'. I have been asked to plan an investigation of the effect of temperature on respiration in yeast. Any ideas what I should do?
Thanks 😊😊😘
2. Hi,

Think logically: Temperature is what you are changing/controlling - so temp is the independent variable (x axis: see later). rate of respiration = dependent variable (y axis later)

How are we going to (a) change temperature and (b) keep record of it?
a) we put the yeast near a boiler or, better, in a organ bath (put yeast in a small beaker, maybe, and put this beaker into a much larger beaker half full of water, and the whole thing above a bunsen burner with a square peace of gauze on a tripod.

b) of course, well done, a thermometer!

How are we going to measure rate of respiration? OK, think again! What happens in respiration? (Ask yourself six wise men: What Where Which When How AND Why?) Which products are produced in resp-n? CO2 and water. What are the substrates? glucose AND O2.
So we need to measure one of these - How? You could let the CO2 coming out be dissolved in lime water, or measure the rate of CO2 being produced by having a U-shaped capillary tube in which the level of liquid will change with amount of gas extruded.

1. Measure one of these at different temperatures -
2. Keep everything else steady = controls (in today's baby language, teachers call it "fair test" lol!) e,g, amount of O2 provided, amount of substate = glucose and pH (put in a buffer)

Then describe what you would do c results: draw a table, plot them etc.

One line on what you would expect (not asked in Q, but just for gd measure!!}

hope this helps
(A Level Biology tutor)

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