Photosynthesis Experiment

Distance from light/mm | Colorimeter reading/arbitrary units | | Algal balls solution | Hydrogen carbonate solution | | 1 | 2 | mean | 1 | 2 | mean | 0 | 0.52 | 0.52 | 0.52 | 0.50 | 0.50 | 0.50 | 250 | 0.52 | 0.45 | 0.49 | 0.59 | 0.63 | 0.61 | 500 | 0.50 | 0.49 | 0.50 | 0.52 | 0.55 | 0.54 | 750 | 0.47 | 0.55 | 0.51 | 0.54 | 0.53 | 0.54 | 1000 | 0.58 | 0.56 | 0.57 | 0.52 | 0.54 | 0.53 |
Results
Results

The results do not show the general relationship between light intensity and photosynthesis that could normally be seen had the experiment taken place without errors. The graph should show an increase in arbitrary units the further away from the light source the beaker is because the greater the distance from the light source, the lower the light intensity and so less photosynthesis would take place in the algal balls. This would result in more CO2 being present because it wouldn’t be being used up during photosynthesis. The decrease in CO2 in the solutions nearer the light source would cause the hydrogencarbonate indicator to change colour to purple/red and therefore the darker colour would produce a lower reading on the colorimeter because the blue filter would reflect the darker colour, letting less light through. In order to gain these results if the experiment were to be repeated, it must be done in a dark room where the artificial light is the only light source available to the algal ball beakers. This will enable a more reliable reading to be taken as the beakers further away from the light source will not have the light from the window to enable them to photosynthesise as much as the beakers close to the light. The trend which was expected to be seen was that the light intensity is a limiting factor in photosynthesis. The greater the intensity of light, the more the plant/algae cells photosynthesises and so takes up more carbon dioxide as the rate is increased.
The results do not show the general relationship between light intensity and photosynthesis that could normally be seen had the experiment taken place without errors. The graph should show an increase in arbitrary units the further away from the light source the beaker is because the greater the distance from the light source, the lower the light intensity and so less photosynthesis would take place in the algal balls. This would result in more CO2 being present because it wouldn’t be being used up during photosynthesis. The decrease in CO2 in the solutions nearer the light source would cause the hydrogencarbonate indicator to change colour to purple/red and therefore the darker colour would produce a lower reading on the colorimeter because the blue filter would reflect the darker colour, letting less light through. In order to gain these results if the experiment were to be repeated, it must be done in a dark room where the artificial light is the only light source available to the algal ball beakers. This will enable a more reliable reading to be taken as the beakers further away from the light source will not have the light from the window to enable them to photosynthesise as much as the beakers close to the light. The trend which was expected to be seen was that the light intensity is a limiting factor in photosynthesis. The greater the intensity of light, the more the plant/algae cells photosynthesises and so takes up more carbon dioxide as the rate is increased.
Conclusion and analysis
Conclusion and analysis
The method for the experiment allowed for error to take place, but also had advantages. The results show some anomalies – these have come about because the samples were on the counter in front of the window and so the algal balls were subject to natural light coming in from the window as well as the artificial light. This error in the method meant that the results collected were neither accurate nor reliable as at the different intervals, the algal balls could have had varying light intensities and therefore the light intensity was not a controlled factor in the experiment because the artificial light source was not the only light source. The advantage of using algal balls is that it was very easy to standardise the amount of chloroplasts in each beaker at each interval. This could then not be considered as an affecting factor because the balls were uniform in size and chlorophyll concentration in every beaker. This is an advantage also because it enables the experiment to be replicated accurately and so repeats could be taken to calculate a mean and eradicate any anomalous results which occurred due to the error. The algal balls are also cheap to grow and easy to make as hundreds can be made in a short time and they are also easy to keep alive for several weeks so they can be kept alive for further experiments. The advantage of using the hydrogencarbonate indicator as a control was that the change in colour measured by the colorimeter readings could be detected to be caused by the photosynthesising algal balls and not something which would happen anyway.

The method for the experiment allowed for error to take place, but also had advantages. The results show some anomalies – these have come about because the samples were on the counter in front of the window and so the algal balls were subject to natural light coming in from the window as well as the artificial light. This error in the method meant that the results collected were neither accurate nor reliable as at the different intervals, the algal balls could have had varying light intensities and therefore the light intensity was not a controlled factor in the experiment because the artificial light source was not the only light source. The advantage of using algal balls is that it was very easy to standardise the amount of chloroplasts in each beaker at each interval. This could then not be considered as an affecting factor because the balls were uniform in size and chlorophyll concentration in every beaker. This is an advantage also because it enables the experiment to be replicated accurately and so repeats could be taken to calculate a mean and eradicate any anomalous results which occurred due to the error. The algal balls are also cheap to grow and easy to make as hundreds can be made in a short time and they are also easy to keep alive for several weeks so they can be kept alive for further experiments. The advantage of using the hydrogencarbonate indicator as a control was that the change in colour measured by the colorimeter readings could be detected to be caused by the photosynthesising algal balls and not something which would happen anyway.

Evaluation of the method
Evaluation of the method 1. -------------------------------------------------
Obtain concentrated suspension of algae. Remove some of the liquid medium in which they are growing by centrifugation. Place 50cm3 of green algal suspension in a centrifuge and spin gently for 5 minutes. Pour off the supernatant leaving approximately 5cm3 2. -------------------------------------------------
Pour 2.5cm3 of sodium alginate solution into a small beaker 3. -------------------------------------------------
Add approximately 5cm3 of concentrated algal cells and stir the mixture with a clean cocktail stick until the algae is evenly distributed in the sodium alginate solution 4. -------------------------------------------------
Pour the mixture into an open ended syringe and attach to a clamp stand. 5. -------------------------------------------------
Pour 2% calcium chloride solution into a beaker and place under the syringe, then tighten the clamp until the algal mixture drops evenly into the calcium chloride solution in the beaker to form small balls of algae* 6. -------------------------------------------------
Leave for 10-15 minutes in the calcium chloride beaker then wash the balls in distilled water by pouring them into a small tea strainer and flushing the distilled water over them 7. -------------------------------------------------
Place 4 balls in 100ml beakers of hydrogencarbonate indicator*1 and place them at 250mm intervals along a meter stick from an artificial light source 8. -------------------------------------------------
Set up beakers of 100ml hydrogencarbonate solution by itself as a control and place at the same intervals along the meter stick 9. -------------------------------------------------
Wait 1 hour and then measure the arbitrary units of each solution using a colorimeter to detect any colour changes due to the presence of carbon dioxide. The indicator is orange/red when equilibrated with atmospheric air and it changes to yellow when more CO2 is added. Similarly, it changes through red to deep purple when CO2 is removed
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*swirl the beaker as the drops fall into the calcium chloride solution
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*1 hydrogencarbonate indicator is highly sensitive to changes in CO2 level

Method 10. -------------------------------------------------
Obtain concentrated suspension of algae. Remove some of the liquid medium in which they are growing by centrifugation. Place 50cm3 of green algal suspension in a centrifuge and spin gently for 5 minutes. Pour off the supernatant leaving approximately 5cm3 11. -------------------------------------------------
Pour 2.5cm3 of sodium alginate solution into a small beaker 12. -------------------------------------------------
Add approximately 5cm3 of concentrated algal cells and stir the mixture with a clean cocktail stick until the algae is evenly distributed in the sodium alginate solution 13. -------------------------------------------------
Pour the mixture into an open ended syringe and attach to a clamp stand. 14. -------------------------------------------------
Pour 2% calcium chloride solution into a beaker and place under the syringe, then tighten the clamp until the algal mixture drops evenly into the calcium chloride solution in the beaker to form small balls of algae* 15. -------------------------------------------------
Leave for 10-15 minutes in the calcium chloride beaker then wash the balls in distilled water by pouring them into a small tea strainer and flushing the distilled water over them 16. -------------------------------------------------
Place 4 balls in 100ml beakers of hydrogencarbonate indicator*1 and place them at 250mm intervals along a meter stick from an artificial light source 17. -------------------------------------------------
Set up beakers of 100ml hydrogencarbonate solution by itself as a control and place at the same intervals along the meter stick 18. -------------------------------------------------
Wait 1 hour and then measure the arbitrary units of each solution using a colorimeter to detect any colour changes due to the presence of carbon dioxide. The indicator is orange/red when equilibrated with atmospheric air and it changes to yellow when more CO2 is added. Similarly, it changes through red to deep purple when CO2 is removed
-------------------------------------------------
*swirl the beaker as the drops fall into the calcium chloride solution
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*1 hydrogencarbonate indicator is highly sensitive to changes in CO2 level

Method