This is an experiment to investigate how temperature effects the respiration rate in maggots.

Link reaction:

Krebs cycle:

The last stage occurs in the cristae of the mitochondria and is known as oxidative phosphorylation.

Oxidative phosphorylation:

The oxygen used in the equation for aerobic respiration is used as the terminal acceptor in the electron transport chain for oxidative phosphorylation.

 So if the rate of respiration goes up, more oxygen should be consumed. This can be used using a respirometer.

Enzymes play a vital role in the process of respiration, as is shown in the diagrams of the different stages above.  Enzymes are globular protein molecules, with a tertiary structure found in all living cells. They are organic catalysts that speed up the rate of reactions. All enzymes contain an active site, a depression in the enzyme molecule, where a specific substrate molecule can collide and fit into, like a key fits a lock, to bind and form an enzyme-substrate complex. (See diagram below:)

        There are four factors that can effect the rate of an enzyme reaction:

• The pH
• The concentration of enzyme solution
• The concentration of substrate solution, and
• The temperature.

We will focus on the effect of temperature.

        If you increase the temperature, up to the optimum temperature, you increase the amount of kinetic energy, increasing random movement, allowing more collisions between the enzyme and substrate molecules to take place.  This will increase the chances of forming enzyme-substrate complexes and speed up the rate of reaction. However if the temperature increases past the optimum temperature, the enzymes will denature and no products can be formed.  The temperature coefficient Q10  =2, meaning that for every ten degree rise in temperature, the rate of the reaction is doubled.

Prediction: I predict that the respiration rate in maggots will increase if the temperature increases. Respiration takes place through a series of steps, requiring enzymes in each stage. If I increase the temperature in the experiment, the amount of kinetic energy will increase, causing the substrates and enzymes to collide more frequently, improving the chance of being more enzyme-substrate complexes, which speeding up the reaction.

        This prediction could be quantitative. If I increase the temperature by ten degrees, the rate of respiration should double, so the oxygen consumption should double.

Variables:

• My independent variable is the temperature, as I am manipulating this factor. The different temperatures I will use are: 10°C, 20°C, 30°C, 40°C. I will not go any higher as maggots are living creatures and it would not be ethical to test them at high temperatures.

• My dependant variable is oxygen consumption, as this is what I am measuring.

        I will need to control all the variables other than the independent variable to keep the experiment fair and accurate.

• I will keep the time I equilibrate constant, 5 minutes each time, using a stopwatch.  The amount of time I measure for, will also remain constant (10 minutes) using the stopwatch. However, the accuracy of this method may be limited, as times will vary slightly as reaction times may vary, even if the same person is used.
• The volume of soda lime will also remain constant, by using the same mass.
• The mass of maggots will also remain constant.
• The apparatus volume and size will remain constant by keeping the same apparatus throughout the experiment.
• The water bath will remain the same temperature, using a pre-set, pre-heated electronic water bath. The temperature of surrounding must be kept constant whilst readings are taken because changes in temperature and pressure, alter the volume of the air in the apparatus.        

Preliminary:

 Our preliminary experiment was not very successful. We tested the respiration rate of five and ten maggots in the respirometer, but found that more maggots were required as to get a significant result. We realised that twenty maggots would give a better result, but found it difficult to find maggots the same size. Instead we have decided to use the same mass of maggots. (5 grams)

Risk assessment: We will be working with living maggots so some precautions should be made. Maggots usually feed on dead or rotten flesh of meat, which carries a lot of bacteria. Therefore maggots may be carrying germs and may be infected with diseases such as salmonella, if the maggots had been into contact with infected chicken meat. Equipment will be used to handle the maggots however, if one maggot escapes, handling may be required. After the experiment all hands, surfaces and equipment should be washed to destroy any bacteria.  

Lab safety also includes no running and removing all obstacles from the floor, to avoid tripping up.

• There were two sets of apparatus I could use to create a respirometer. I could have used a capillary tube instead of a manometer, by measuring with a ruler, (see below) but decided a manometer would be easier to read, and restart again. My chosen method and apparatus also allows me to use a control tube to compensate for any environmental variables I cannot control, like atmospheric pressure changes.

Apparatus:

• Clamp
• Stand
• Boss
• Screw clip
• 5g live maggots
• Test tube x2
• Bung x2
• Soda-lime
• Stopwatch

• Control tube
• Glass beads
• 1 cm ² syringe
• Three-way tap
• Capillary U-tube containing manometer fluid and manometer
• Gauze platform
• Water bath set at 10°C, 20°C, 30°C, and 40°C.

I will use a stand, clamp and boss to hold the test tubes into place and to keep them stable throughout the experiment. It will also keep them at the same height, so the variables concerned are controlled, (for example, the temperature, or amount of light at this level.) The screw clip is left opened to allow for equilibration, and closed when we start recording the respiration rates. 5 grams of maggots will be used, as mass is more accurate than the number of maggots, as each maggot varies in size/weight, so may not be the same.  One test tube will be the experimental tube, with the maggots, and the other will be the control tube, with the beads. The same mass of soda lime will be used. it is used to absorb the carbon dioxide, which is produced in respiration. The stopwatch is fairly accurate, and will be used to tell us when to take the readings, to ensure that each reading is taken at the same time. The same person will use the stopwatch to as people have different reaction times. (This will eliminate this variable). The glass beads are used as a control, so that any

environmental changes will be compensated for. The syringe is used to ‘push’ the liquid back to zero after each reading. The three-way attaches the syringe to the bung. The capillary U-tube which will contain the manometer fluid is what we use to measure the respiration rate. The scale of the manometer allows us to do this easily. The gauze platform keeps the maggots off the soda lime, but still allows respiratory gases through. The water baths are used to investigate the respiration rate at different temperatures. They are accurate and can be kept at the same temperature for long periods of time.

Diagram of apparatus:

Method:

1. Set up apparatus as shown in diagram
2. Weigh maggots (5 grams)
3. Place maggots in test tube
4. Place test tube into water bath (10°C) for 5 minutes to allow time to equilibrate. With the screw clip open. Use a stopwatch to measure the time.
5. After the 5 minutes, set liquid to start (0), using syringe and tighten the screw clip.
6. Start stopwatch
7. At 10 minutes observe how far the liquid has moved (mm), and record data in a table.
8. Repeat two more times at the same temperature
9. Repeat at temperatures of 20°C, 30 °C, 40°C, using electronic water baths.

References:

BOOKS

• Collins, W. (1978). Collins Concise English Dictionary. William Collins Sons & Co. Ltd, Glasgow.

• Jones, M et al. (2000) Biology 1. Cambridge: CUP (Cambridge University Press)

ISBN 0 521 78719 x paperback

• Jones, M. and Gregory, J. (2001) Biology 2. Cambridge University Press, Cambridge. ISBN 0-521-79714-4

• Simpkins J and Williams, J. (1987) Advanced Human Biology. Collins educational.

WEBSITES        

•  AS & A2 Level Biology. Respiration: some basics 

        : glycolysis

        : krebs cycle        

        :electron transport chain/ oxidative phosphorylation