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Investigate rate of respiration CPAC 16
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- PEARSON (PEARSON)
Full CPAC 16 write up which achieved passing grade and fulfilled all necessary criteria for Biology Edexcel
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Name: Hiba Majid (P:\Science\Mr Alim\Year 12\AS Biology)(Core Practical 16)
Title Measuring the rate of oxygen uptake
HYPOTHESIS: As the mass of yeast increases, the volume of oxygen uptake, and so rate of
respiration, will increase
METHOD:
1. Carry out instructions given (or those you have produced and researched) to complete the
practical (CPAC1)
2. List apparatus below and describe techniques used when measuring quantities with a
particular piece of apparatus:
Piece of apparatus Purpose of piece of Comment on how piece of equipment Appendix
apparatus was used 5c
accurately/appropriately/safely technique
Respirometer Used to measure oxygen It was kept in the middle of the table to
uptake avoid it falling over the edge and
breaking or falling into someone’s foot
Low risk
100g dm-3 yeast The organism we used to It was measured out according to the
investigate the rate of conditions of the IV(changing mass of
respiration (aerobically), organism) using a weighing scale
as it takes in oxygen Low risk
Weighing scale Used to measure mass of It was kept in the middle of the table to
yeast and soda lime avoid it falling over the edge and
breaking or falling into someone’s foot
Low risk
Ruler To measure how much To ensure results were valid, the dye
the dye moved started at the same starting point
Low risk
2 Test tubes One as a control and one They were kept airtight to avoid any
is the experimental tube gases entering or leaving (by placing a
bung). Kept in the middle of the table to
avoid it falling over the edge and
breaking which would lead to cuts
Low risk
Soda lime Will be used to absorb Used the same mass of soda lime for
granules/powder carbon dioxide, so we each repeat. We made sure the soda
know any changes in lime was not exposed to the air too
volume are due to oxygen much or it will absorb carbon dioxide
being absorbed from the air which will interfere with
the experiment.
Medium risk
Cotton wool In order for yeast and We ensured there was a layer of thick
soda lime to be separated enough for the soda lime and yeast not
to touch but not too much as this would
lead to wastage
No risk
, Name: Hiba Majid (P:\Science\Mr Alim\Year 12\AS Biology)
Coloured liquid The movement of the We used the same amount of coloured
liquid due to pressure liquid as the distance the liquid moves
changes will help us infer may be affected by the quantity of
the intake of oxygen and liquid. We kept the liquid bottle away
help us calculate the rate from the edge of the table so that we
of respiration don’t spill it. This would lead to a slip
hazard
Low risk
Permanent marker Marks the liquid at the To ensure it was done accurately, the
pen start and end of an line was done thin enough so that we
interval of respiration could measure it by each mm but thick
enough so it was visible
Low risk
Stopwatch Used to time one minute As soon as the liquid was put inside the
intervals tube, the stopwatch began
To see how far the liquid It was managed by one person for each
moves over a set period repeat to avoid human error and
of time in order to differences between people
calculate the rate of No risk
respiration
(CPAC a2a, 2b, 2d, 3a, 3b)
3. Summarise the method used, pointing out any difficulties in carrying out the practical and
any changes that were necessary from the original plan and why they were made. Draw an
appropriate diagram as necessary (CPAC 2c)
Preliminary method:
1. Measure out 5g of soda lime on a weighing scale and place at the bottom of the test tube
2. Place a layer of cotton wool on top of the soda lime to ensure it does not touch the yeast
3. Place 3g of yeast (weighed out using a weighing scale) into the boiling tube and replace the
bung onto the test tube to seal it shut
4. Place a drop of marker fluid into the pipette using a dropping pipette.
5. Open the connection (three-way tap) to the syringe and move the fluid to a convenient place
if needed (i.e. towards the end of the ruler that is furthest from the test tube)
6. Mark the starting position of the fluid on the pipette with a fine permanent pen.
7. Isolate the respirometer by closing the connection and start the stopwatch straightaway.
8. Mark the position of the fluid on the pipette at 1 minute intervals for 5 minutes and measure
the distance travelled by the liquid during each minute (the distance from one mark to the
next on your pipette).
9. At the end of 5 minutes open the connection to the outside air by opening the 3 way tap
10. Record your results of the distance moved by the dye in a suitable table.
11. If our tube does not have volumes marked we will convert the distance moved to calculate
the volume of oxygen absorbed, using the formula: volume used = πr 2 × d, where r is the
radius of the hole of pipette. This will be recorded in a different table
12. Use 5g, 7g and 9g in order to repeat this experiment
13. Calculate the mean rate of oxygen uptake during the 5 minutes. Then we will calculate the
rate of oxygen absorbed by doing volume of oxygen absorbed/ time x mass
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