Summary
Summary Respiratometer CPAC
- Institution
- AQA
Summary of 5 pages for the course Unit 3 - Investigative and practical skills in AS Biology at AQA (Respiratometer CPAC)
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Respirometer practicalAim:
To investigate the uptake of oxygen in respiration
To measure the rate at which an organism respires
To develop practical skills
A respirometer is a piece of equipment which measures the rate of respiration and works by
the addition of red coloured liquid to a length of tubing. As the mealworms respire, the
volume of the oxygen in the tube decreases which leads to pressure decreases and
therefore the liquid moves in the direction of the organism
Independent variables - Change the time it’s measured at
(each minute it’s measured for 5
mins)
Dependent variables - Is the variable you measured, the
movement of the red liquid in the
manometer, the rate of oxygen
consumption (rate of respiration)
Control variables - Acclimatisation time (left the
mealworms to acclimatise to its new
environment, the same time
interval for each set of results, 2
mins acclimatisation time to ensure
validity of results)
- Mass of soda lime (can affect the
amount of carbon dioxide absorbed,
kept the mass of the soda lime the
same)
- Type/size mealworms (ensured they
were from the same culture and
same breed which also ensured
validity of results)
- Time intervals (used a stop clock to
measure time, measured every
minute for 5 minutes)
- Temperature of the water
(temperature can have an effect on
respiration and therefore used a
water bath at temperature of 30
degrees)
- Mass of mealworms (used 3 grams
of mealworms, can affect oxygen
uptake and respiration rate if more
mealworms are there, faster rate of
respiration)
, Apparatus:
Apparatus Why is it used?
Mealworms Measuring the respiration rate of the
organism
Manometer Used to measure the pressure difference in
column heights, the movement of the red
liquid indicated the amount of oxygen
uptake
Muslin To place the mealworms inside, ethical
implications, easier transfer of organisms
into the test tube
Soda lime Absorbs the carbon dioxide as the
experiment is measuring the oxygen not
the carbon dioxide
Respirometer Used to measure the rate of respiration of a
living organism by measuring its rate of
exchange of oxygen
A thin marker To mark the interval points of the red liquid
every minute
Stopclock To record results every minute for 5
minutes and to then calculate average
Water bath To keep at constant temperature so results
were valid
Methodology:
1. Assemble the apparatus as shown
in the figure on the left
2. Place 3g of mealworms into the
boiling tube and replace the bung,
handle live animals with care to
avoid harming them
3. Mark the starting position of the
fluid on the pipette with a fine
permanent pen
4. Isolate the respirometer by closing
the connection to the syringe and
the atmosphere and immediately
start the stopcock, mark the
position of the fluid on the pipette at 1-minute intervals for 5 minutes
5. At the end of the 5 minutes open the connection to the outside air
6. Calculate the mean rate of oxygen uptake during the 5 minutes
7. Measure the distance travelled by the liquid during each minute (the
distance from one mark to the next on your pipette)
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