Objectives
- To understand how to use a respirometer
- To be able to interpret and evaluate respirometer data
- Soda lime is corrosive. Wear eye protection, do not touch the soda lime; use a spatula to position it in the respirometer and do not inhale any dust
- Wash your hands after handling organisms
- Respirometer
- 10 live maggots
- Soda lime in muslin
- Coloured manometer fluid
- Spatula
- Stop clock
- Clamp and stand
- Dropping pipette
- Eye protection
- Ruler
Method
talk about masss etc
- Assemble the respirometer. Check that you know how to use it, especially the operation of the three way tap. Clamp the syringe and the respirometer in position when in use.
- At the bottom of the boiling tube we placed an excess of sodium hydroxide. This is used to absorb and carbon dioxide that the respiring maggots may produce.
- Place 10 maggots in the boiling tube Handle live animals with care to avoid harming them. Sodium hydroxide is toxic so extra care must be taken to ensure there is no contact between the two. Place the maggots on a gauze above the sodium hydroxide to avoid this.
- Place a drop of coloured fluid at the open end of the glass tube using the dropping pipette.
- Open the connection between the syringe and the respirometer. Use the syringe to draw the fluid onto the scale at the end furthest from the respirometer
- Mark the starting position of the fluid with a pen.
- Close the tap to isolate the respirometer from the atmosphere and the syringe and start the stop clock immediately. This is done by having the arrows point left right and up.
- Note the position of the fluid at one minute intervals for five minutes
- Work out the distance travelled by the liquid during each minute. Record your results in a suitable table.
talk about masss etc
A graph to show the average distance the fluid travelled in the respirometer in order to investigate the rate of photosynthesis:
On the y axis: the distance travelled by liquid mm per minute.
On the x axis: Temperature in degrees celsius.
On the x axis: Temperature in degrees celsius.
As can be seen by our table of results the reading obtained at the temperature of 30 degrees may be an anomalous value. This is because the reading after the 30 degree value is much higher showing that there should have been a trend of increasing result values for the distance travelled by the liquid from 17 to 40 degrees.
I believe there are several limitation of the results due to our experimental set up:
I believe there are several limitation of the results due to our experimental set up:
- We did not record the mass of the maggots we were using. Larger maggots will respire more and thus use up more oxygen than smaller maggots. Although they were roughly the same size a slightly bigger maggot from our viewing is, in proportion to the size of maggots, a large difference. This will have led to some changes in our results depending on the sizes of maggots used in each experiment.
- The respirometer may have had some air gaps. This would explain the anomaly in the results from the temperature of 30 degrees. If the boiling tube and equipment is not air tight then the maggots can draw oxygen in from the outside environment rather than from along the capillary tube.. Thus the fluid won't move/ move as far. We could have repeated all of our experiments using the same equipment to reduce this error
- Furthermore, we could have got more accurate records of the rate of respiration if we had used a log thin syringe and measured how much oxygen is removed rather than the distance the fluid had travelled.
- We could have taken our temperature readings at smaller intervals so as to analyse the optimum temperature more carefully.
- The temperature of 45 degrees killed the maggots after a period of time. This is unethical practice and thus we would not repeat this experiment at this temperature.
Analysis
The distance travelled by the fluid increases as temperature increases up to the point of 40 degrees (excluding the anomalous value)
This is because respiration is an enzyme controlled reaction. At warmer temperatures the enzymes and reactants can move faster and thus there will be more frequent collisions and thus the reactions in respiration will occur quicker. Also, more particles will have sufficient energy to overcome their activation energy and thus react.
However, the value at 45 degrees can also be explained by enzyme theory. If you increase the temperature too much then the enzyme will denature. The enzymes quartenary structure will change which alters the shape of the active site necessary in catalysing the reaction. If the active site changes then the enzyme can no longer catalyse the reactions and the substrate moleculescan no longer fit (by induced fit) into the active site. Respiration will therefore slow or stop as the enzymes responsible can no longer be used in the reaction.
The distance travelled by the fluid increases as temperature increases up to the point of 40 degrees (excluding the anomalous value)
This is because respiration is an enzyme controlled reaction. At warmer temperatures the enzymes and reactants can move faster and thus there will be more frequent collisions and thus the reactions in respiration will occur quicker. Also, more particles will have sufficient energy to overcome their activation energy and thus react.
However, the value at 45 degrees can also be explained by enzyme theory. If you increase the temperature too much then the enzyme will denature. The enzymes quartenary structure will change which alters the shape of the active site necessary in catalysing the reaction. If the active site changes then the enzyme can no longer catalyse the reactions and the substrate moleculescan no longer fit (by induced fit) into the active site. Respiration will therefore slow or stop as the enzymes responsible can no longer be used in the reaction.
1. Explain why animals usually have a higher respiration rate per gram than plants. Animals are generally more active than plants and use the ATP produced by respiration for other functions like supplying their muscles for movement which plants tend not to do. More respiration would be needed to occur for the higher demand of ATP in animals. Some animals also require energy for regulating their bodily functions like temperature. This requires energy wheres plants use diffusion and more passive processes to do this.
2 and 3 answered above
4. 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.
Explain what may cause the liquid in the control tube to move towards and away from the respirometer:
There may be some bacteria that are respiring on the inanimate object.
If the gas inside the boiling tube was to heat up then this would cause pressure to increase inside the boiling tube. This would cause the gas inside the capillary tube to be pushed back away from the boiling tube.
Explain how you would use the control results to correct your experimental data
If we found that the gas moved 1 mm an experimental temperature towards the boiling tube we would minus this value from our respiratory results as we can not account this movement to respiration.
If we found that the gas moved away 1mm at an experimental temperature then we would add 1 to our experimental value as respiration would have to have overcome this movement as well as the movement along the capillary tube.
2 and 3 answered above
4. 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.
Explain what may cause the liquid in the control tube to move towards and away from the respirometer:
There may be some bacteria that are respiring on the inanimate object.
If the gas inside the boiling tube was to heat up then this would cause pressure to increase inside the boiling tube. This would cause the gas inside the capillary tube to be pushed back away from the boiling tube.
Explain how you would use the control results to correct your experimental data
If we found that the gas moved 1 mm an experimental temperature towards the boiling tube we would minus this value from our respiratory results as we can not account this movement to respiration.
If we found that the gas moved away 1mm at an experimental temperature then we would add 1 to our experimental value as respiration would have to have overcome this movement as well as the movement along the capillary tube.