The rate of photosynthesis in the elodea Essay Example for Free

The rate of photosynthesis in the elodea Essay Put the boiling tube in a beaker surrounded by ice. Ensure the thermometer is standing upright in the beaker.   Note the initial temperature and maintain this throughout the experiment, either by means of adding or reducing the ice content.   Place the electric bench lamp towards the elodea specimen   Allow the elodea specimen to settle for five minutes or so.   On the fifth minute start timing for a further five minutes and count the amount of bubbles observed. Note: The same procedure must be carried out for the other two experiments, only altering the content outside the boiling tube. In order to keep the water temperature at 45o C, it is advised that cool water or some heated water (from the kettle) is added depending on the temperature observed. Prediction: I predict that when the elodea specimen is placed in ice, a few (one or two) oxygen bubbles will be observed, therefore photosynthesis will be limited. When the elodea specimen is placed in water at 45o C, more bubbles will be seen and hence the rate of photosynthesis will increase At room temperature, some bubbles will be seen but much less compared to the 45o C investigation, since the temperature is in between. Results: Ice: Time (minutes). Number of bubbles observed 1 1 2 1 3 3 4 0 5 0 Total: 5 Water maintained at 45o C: Time (minutes) Number of bubbles observed 1 3 2 10 3 12 4 3 5 1 Total: 29 Water at room temperature (tap water): Time (minutes) Number of bubbles observed 1 0 2 2 3 3 4 3 5 3 Total: 11 Discussion: From looking at my results, it appears to be that my prediction is reasonably accurate. As mentioned in my prediction, a few bubbles were observed when the elodea was placed in ice. This is because the cells within the elodea specimen eventually die. This can be explained by the concept of enzymes, which operate best at optimum temperatures. Placing the elodea in a cold environment, such as ice means that the temperature is extremely below the optimum. This inevitable leads to enzyme denaturation and only some bubbles are seen during the first two minutes prior to the denaturation. Consequently, there is some photosynthesis taking place. When the elodea cell is placed in water which is maintained at 45o C, the number of bubbles sighted increase rapidly (particularly in the second and third minutes). Notice for the fourth and the fifth minutes, the number of bubbles observed start to decline. This may well be to the fact that the temperature was not controlled as intended, and possibly exceeded 45o C, thus causing the enzyme to denature. Hence a decrease in photosynthesis is observed. When the elodea specimen is placed in water at room temperature, the number of bubbles observed are more or less the same. This is because the temperature of the water is fairly below the optimum, (which is believed to be 45o C) and therefore the rate of photosynthesis is limited. Evaluation: Despite the results fairly matching the prediction, the method used is rather unreliable. More repeats (i.e. three repeats) could have been put into practice as this would have allowed me to calculate an average and hence raising the reliability of the results. The temperature range is rather limited and so the results would have been more accurate by employing a variety of temperatures. This would have allowed me to pin-point exactly the optimum temperature of the enzyme, which is involved in photolysis. Looking at the results above, there was an incidence where the temperature was not properly controlled (the ice investigation in which 3 bubbles were noted in the third minute). I believe using a water bath would have allowed me to maintain the temperatures more precisely and save time as oppose to using a kettle. I recall whilst doing the experiment that the elodea specimen was placed somewhat close to the window. Light from the sun could have also played an important part of distorting the results because an increase in light intensity also contributes to an increase rate in photosynthesis. Therefore if this experiment is to be carried out again, it would be ideal to make use of the window blinds. Not forgetting to mention that the distance between the bench lamp and the elodea specimen was not fixed, and was varied during each investigation. This might have caused a slight degree of anomaly in the results. Having acknowledged this inconsistency has made me aware of what is required in the actual investigation. It can be argued that counting the number of bubbles can be deceiving and therefore another method should be put into consideration. An alternative way of doing the same experiment more accurately can be achieved by using a photosynthometer. A freshly cut strand of the plant is suspended upside down in a boiling tube. The healthy strand of elodea produces bubbles of oxygen gas when brightly illuminated (i. e. with a bench lamp 10 cm away from the elodea specimen) at different temperatures. The bubbles emerge from the cut end of the stem and are collected in a bulb at the base of the apparatus. From here, the oxygen gas can be drawn into the capillary tube by means of the syringe. The volume of oxygen gas collected in five minutes gives a direct measurement of the rate photosynthesis. Apparatus and Justification: Apparatus Justification of Apparatus x1 Clamp stand (with capillary tube). A lot of apparatus are involved, some of which that need to be held at a constant height above the water bath (i. e. the boiling tube with the elodea specimen). x1 Capillary tube with ruler.   Used to measure the length of the oxygen bubble(s).   Hence the volume of oxygen can be calculated. x1 Boiling tube   The use of a boiling tube is necessary as oppose to a test tube because its large enough to allow the elodea specimen to fit in with ease. x1 Elodea Canadensis specimen (10 cm long)   The elodea specimen is the basis for this investigation.   Allows the hypothesis to be tested. x1 5 ml syringe A 5 ml syringe is necessary to allow oxygen bubbles to be drawn in the capillary tube. No other apparatus can be substituted for this task. x1 30 cm Ruler   Used to measure the length of the elodea specimen, making sure that the length is constant for each investigation. To ensure a fair test. x1 Scalpel Used to cut the elodea specimen to the desired length with precision. x1 Plastic Tile   To aid in cutting the elodea specimen. To prevent any damage to the work bench. x1 Electric bench lamp with 100W filament bulb   Used to ensure a fair test as every investigation will be illuminated by a lamp at a set distance. To ensure the results are not influenced by light intensity but solely the temperature. x1 Thermometer   Used to ensure the temperature of water bath is correct, and hence to promote reliability of results. x1 Stopwatch   Used for timing the investigation for 10 minutes (five minutes for the settling of the elodea specimen and another five minutes for the investigation). x1 Beaker and ice blocks   To be used for the 0o C investigation.   To see if there is any photosynthesis evident at freezing level. Proposed Method: Diagram12: 1. Set up the clamp stand as shown above. 2. Get hold of a plastic tile and a scalpel and cut the elodea specimen at a length of 10 cm. 3. The cut end has to be inserted into the calibrated capillary tube as shown above. 4. Lower the capillary tube into the water bath, ensuring half of the boiling tube (containing the elodea specimen) is immersed in the water. 5. Place the bench lamp 10 cm away from the boiling tube. Ensure the light is directly facing the elodea specimen. 6. After setting all the apparatus up, pull the syringe on top of the capillary tube in order for the water to get into the capillary tube. This removes any air bubbles initially present in the capillary tube. 7. Place the thermometer into the water bath (or beaker in the case of the ice investigation) and turn the light on. The elodea must be allowed to settle for five minutes. 8. Time the investigation for a further five minutes by using a stopwatch. 9. On completion of the five minutes, switch the lamp off and remove the clamp stand along with the rest of the apparatus out of the water bath. 10. Pull the syringe to draw the oxygen bubbles into the capillary tube and measure the length of the bubble(s) simultaneously by making use of the ruler. 11. Note down the length of the bubble(s) on paper. 12. Repeat the same procedure three times for each temperature using the same elodea specimen. 13. Once the three trials are complete, move on to the next temperature. and carry out steps 1 -13 Ice investigation:   Get hold of the elodea specimen and place it in the boiling tube.   Put the boiling tube in a beaker surrounded by ice.   Note the initial temperature and maintain this throughout the experiment, either by means of adding or reducing the ice content.   Follow steps 5-13 above. Note: If an anomalous result is encounter during the duration of the experiment, it is advised to do that particular investigation again. Acknowledgements: 12- Diagram modified from A-Level biology Revised Edition by W D Phillips and T J Chilton, page 69. Analysis of Variables: Independent variable: The independent variable is the variable, which has to be manipulated in order to get the desired results. In this case, the independent variable is the temperature of the water baths. To obtain more accurate results, I have included temperature readings ranging from 0-65o C, in intervals of five. Three readings will be taken for each temperature and compared. Dependent variable: This is the variable which responds to the fixed conditions and which is used to test the hypothesis. In this case, the dependent variable is the volume of oxygen released by the elodea specimen. The length of the oxygen bubble(s) is going to be measured at the end of the five minute interval. This can be used to deduct the volume of oxygen produced by multiplying the length of the bubble(s) by pie, which is then multiplied by 0. 82 Fixed variables: These are variables, which have to be kept constant throughout the experiment in order to obtain accurate results. These variables cannot be manipulated at any time of the experiment. Some of the fixed variables are listed below: The light intensity (distance between the bench lamp and the elodea specimen): This can be kept constant by ensuring the elodea specimen is 10 cm away from the bench lamp. It may well be convenient reassure the distance with a ruler. The preliminary work I did have done has highlighted that 10 cm happens to be an ideal distance for sufficient photosynthesis to be followed and thus reliable results can be obtained. However if the distance between the bench lamp and elodea specimen is shorter than 10 cm, then this will have a major impact on the results. The increase in light intensity shall inevitably results in an increase in the volume of oxygen noted and thus distorting the results. Similarly if the distance is greater than 10 cm, then this decrease in light intensity shall contribute to a decrease in rate of photosynthesis and thence slowing down the rate at which the oxygen bubble(s) are released13. Therefore it is vital that this distance is kept constant throughout the experiment to ensure a fair test. * The number of leaves on the Elodea plant: The number of leaves will be kept constant throughout the whole experiment by using the same elodea specimen. The reason for keeping the same number of leaves is to ensure that the surface area provided by the leaves is the same in each investigation. Having the same number of leaves will provide the same surface area. If the number of leaves were different in each new investigation, then the number of leaves would be the independent variable. The more leaves there are the larger the surface area, and more light energy will be trapped by the leaves and a greater proportion of it will be converted into chemical energy14. Therefore more oxygen will be given off. On the other hand, a fewer amount of leaves shall results in a low yield of oxygen. In both cases, the results will be distorted if not controlled. Acknowledgements: 13- Letts Revise A2 Biology by John Parker, page 26 14- Revise A2 biology by Richard Fosbery and Jennifer Gregory; page 21 Reliability: To obtain more reliable results, three measurements would be taken in the same condition. The reason for this is that if in case, an error was made on the first attempt, the error can be amended and on the second attempt. After doing the experiment, if any of the results are anomalous then the experiment should be repeated. Results obtained can be compared to the previous results to see if there is an agreement. Light from the sun can also play an important part of distorting the results because an increase in light intensity also contributes to an increase rate in photosynthesis. Therefore it would be ideal to make use of the window blinds to promote reliability of results. Temperatures are monitored precisely by the water baths. However it is sometimes observed that the temperature of the water bath goes up or down by a degree or two. The temperature can be maintained by means of adding or removing ice to the water baths. Due to the limited number of water baths, there may well be the case of sharing a water bath to five others. This means five additional bench lamps would have an impact on my results (as light intensity increases rate of photosynthesis). The lamps may also contribute to the water baths getting hotter than required. Therefore it would be wise to carry out the investigation individually. When the apparatus are set up, the syringe (on top of the capillary tube) must be pulled to draw the water into the capillary tube. This will remove any air bubbles initially present in the capillary tube and thus leaving no ambiguity. Results: Table: showing the results I obtained during the investigation Temperature (o C) Length of Oxygen bubble (mm) Volume of Oxygen (mm) Rate of photosynthesis (mm3/min) Average rate of photosynthesis (mm3/min).