CP 9 Flashcards
Describe how a respirometer works.
It is a chamber connected to a capillary
tube with a drop of dye.
As the organism in the chamber respires and uses
oxygen, the pressure decreases and the liquid moves in the capillary.
What is the control for this practical?
Replace the organism with an inert object of the same mass.
How do you find the volume of oxygen consumed
using a respirometer?
Place a fixed mass of soda lime in the respirometer with the organism.
Measure the distance moved by the dye, and use
the formula volume = distance x πr2
How can the volume of carbon dioxide produced be
found?
Perform two set-ups, one with soda lime (A) and one
without (B). Find the volume of gas used in the given
time.
Volume of carbon dioxide: volume of A - volume of B
How is the rate of respiration calculated using data
from the respirometer?
Rate =
Volume of oxygen used / mass / time
State the hazard and safety precaution involved in
the practical.
The soda lime is corrosive. Wear eye protection and handle with gloves.
IV and DV
IV: Type of Organism
DV: Rate of O2 Uptake (Volume of Gas/Min/G)
cv
● Time left for fluid to move
● temperature
● Reset fluid to
Mass of organism Time
Temperature
Mass of soda lime
Apparatus must be airtight, and replace air between each set-up
PROCEDURE
●the indicator fluid movement would move to the left
●because there is lower pressure
● because there is respiration but no photosynthesis
● therefore the pressure is reduced because the carbon dioxide produced is absorbed
● measure volume by use of {formula / three-way tap and syringe
volume = V=πr2h where h is the distance travelled by the coloured solution
EVALUATION
● No control respirometer set up and so changes in temp/atmospheric pressure can affect the results
● organisms can die in the tube especially if in contact with the soda lime
● not enough soda lime to absorb CO2
● leaks in the apparatus means that some gas will escape/ enter affecting the results
Ethical Issues and adjustments for larger organisms
- use a larger container because some organisms are bigger
- need more soda lime to ensure all CO2 is absorbed
- convert readings into volume per gram
- attach a syringe to repeat measurements
- abiotic factors i.e. light/temperature should be controlled
- do not leave the organisms in the container for too long
- have a barrier to protect the organism from soda lime
Consider your results and any differences in rates of oxygen uptake between different types of
organism. Animals usually have a higher respiration rate per gram than plants. Explain this difference
Both plants and animals respire to produce ATP for cellular processes but animals also move around and require additional ATP for muscle contraction.
Respiration rates are therefore usually higher in animals
Suggest what factors may have caused any variability seen in class results.
Some variables may not have been effectively controlled, such as temperature, amount of
movement, age or stage of development of organisms.
The low resolution of the manometer scale will also cause some uncertainty in readings.
It would have been better to have used a control respirometer alongside the experimental set-up. In the control the equipment is the same but the organisms are replaced by non-living material such as glass beads.
(a) Explain what may cause the liquid in the control tube to move towards and away from the
respirometer.
(b) Explain how you would use the control results to correct your experimental data.
A decrease in temperature or an increase in atmospheric pressure would cause movement
towards the respirometer.
An increase in temperature or a decrease in atmospheric pressure would cause movement in the opposite direction.
b) Movement towards the control respirometer would be subtracted from results; movement
away from the control respirometer would be added to results.
What is the importance of using soda lime in the respirometer? How does this affect the volume
of gas in the apparatus?
Soda lime is used to absorb any carbon dioxide produced by the respiring organisms.
The gas volume will reduce as oxygen is removed for respiration.
