PAG 12.1

Question 1

Equipment available (per group)

Answer 1

• Computer and textbooks
• Yeast (15 g)
• 20% Sugar solutions (glucose, fructose, sucrose, lactose)
• Measuring cylinder
• Gas syringe
• Plastic syringes fitted with tubing
• Thermometer
• Flask with stopper and tubing
• Water bath
• Beaker
• Distilled water
• Ice
• Stopwatch/timer

Question 2

Method

Answer 2

1. First, conduct some research on the factors that can affect the respiration rate in yeast. Use a variety of sources of information e.g. textbooks, websites and reviews. (This information can be used later to write a short introduction to your experiment).
2. Decide on the factor you will investigate.
3. Working individually or in a small group, develop the method you will use to investigate the effect of your chosen factor on respiration rate.
4. Carry out your experiments using the apparatus available and record your data appropriately. Each student in a group should take turns to set up, measure and record readings.
5. Process and present your data appropriately.
6. Finally, write up your experiments as a short investigation. Include an introduction, aim, hypothesis, procedure, results, conclusion and evaluation. References should be clearly cited. This may be done using a word processor.

Question 3

1. Why would the factor you have chosen affect the rate of respiration in yeast?

Answer 3

1. Accurate use of theoretical knowledge about respiration including correct A Level terminology. Reference to other sources (including properly cited references here and/or in the write up) ideally including some empirical studies into the factor being considered.

Question 4

2. Would your practical procedure be reproducible?

Answer 4

2. Reproducible means that another laboratory would get similar results when following the same protocol. Students should consider whether any of the methodology, including apparatus and the way measurements are taken, is specific to your lab and this team of investigators. Are there any subjective judgements when taking measurements (e.g. using colour of an indicator to judge end points)? Is any of the apparatus non-standard and if so can it be described in sufficient detail that another lab could either adapt their equipment or allow for differences when carrying out the work?

Question 5

3. Have the variables and limitations of your experiment been considered?

Answer 5

3. Students should have a sophisticated grasp by now, as well as the ability to express their ideas, about control variables and how to deal with them. This would also be a good place to discuss ideas around validity – is there anything either in the design of the experiment or the results emerging that suggests that the investigation is not valid?

This can sound very negative but in most cases it will not be completely invalid, simply that the intended scope of the investigation was too ambitiously broad and what has actually been achieved is a valid investigation within a more limited set of conditions (e.g. students might have a goal relating to ‘yeast’ but subsequently realise that their investigation has only examined one particular strain of one particular species).