Apparatus
1x Meter rule
1x Compass
1x Pocket book
I chose this because it is sensitive enough for this purpose, easy to use, and not too fragile
1x Quadrat
I will be using % cover count as it is more accurate than 5 cover estimate. To do this, you count the number of squares with Pleurococcus in them
Method
- Find tree 1, and use a compass to determine which side of the tree is north.
Apparatus
1x Meter rule
1x Compass
1x Pocket book
I chose this because it is sensitive enough for this purpose, easy to use, and not too fragile
1x Quadrat
I will be using % cover count as it is more accurate than 5 cover estimate. To do this, you count the number of squares with Pleurococcus in them
Method
- Find tree 1, and use a compass to determine which side of the tree is north.
- Then measure 1m up the north side of the tree, using the meter rule. Align the tope of the quadrat with the 1m mark, and count the number of squares with Pleurococcus in. Then write down this number as a percentage (because there are 100 squares in the quadrat.)
- Use the pocket book to measure the light intensity at this side if the tree. Ensure you hold it at an arms length, so as to keep it fair, and so as not to shadow the pocket book.
- Repeat this, for each of the four compass points, changing steps one and two.
- Repeat steps 1-4 with all the trees.
Results
Analysis
The graphs 1,2 and 3, and my table of averages, show that the most Pleurococcus grows on the North side of the tree. This fits with my prediction. However, I stated in my prediction that the “south side of the tree receives the most sunlight” this was not so at the time of day when I carried out my investigation. At this time of day, there was the highest light intensity in the East and West, and the lowest light intensity in the South. I think this was because during the day, as the Earth rotates about its axis, the Sun appears to move across the sky, in a curved arc. This arc leans towards the East, this means that during the period of a day, the North side receives the least sunlight. At midday, when I carried out my experiment, the range in light intensity averages between the different compass points was less than 3%, this was because I took my readings at midday, when the sun is between the East and the West, and is overhead. Therefore, at this time of the day, the different sides of the trees were receiving almost equal amounts of light. Over the period of a day, the North receives the least light.
This is necessary for the Pleurococcus to grow, because if it received a higher intensity of sunlight, the heat from this sunlight would dry out the Pleurococcus, and cause it to die. This is shown by graph 5 and my findings from Spearman’s Rank Correlation Coefficient, which were that there is a weak negative correlation between Light Intensity and amount of Pleurococcus. The higher light intensity, the less Pleurococcus. However, it is not a strong correlation, this is probably due to the time of day, at midday, there is little difference between the light intensities. As Pleurococcus is an algae, it photosynthesises. This means it needs water as is shown in the photosynthesis equation below.
Water + Carbon Dioxide Oxygen + Glucose
(aq) (g) (g) (s)
6H20 + 6CO2 6O2 + C6H12O6
(aq) (g) (g) (s)
Therefore, if it does not have enough water, it can not photosynthesise, it does not have enough energy to grow, reproduce, respire, and repair, it will, therefore, die. Another thing that Pleurococcus needs to photosynthesise, is sunlight. Even in the North, there is evidently enough sunlight for it to photosynthesise, but the heat received by the North side of the tree, from the sunlight, is not enough to dry it out, because Pleurococcus has heavy cell walls, which prevents excessive water loss. Therefore, the North side of a tree is ideal for Pleurococcus to grow on, as it is moist, but receives enough sunlight.
Evaluation
It is difficult to see if there are any major anomalies because the results are so close together. Trees 3 and 10 However, graphs 2a and 2b, show that, although there is an obvious trend, (also shown by my Spearman’s results) the results varied a lot from tree to tree. This is due to the many irregular, unpredictable variables in this experiment, for example, the individual trees may be affected by:
- Genetic factors, effecting the suitability of the tree bark
- Temperature due to outlets, from buildings
- Chemicals and moisture in the soil
- Diseases of the tree bark
- Exposure
- Shadows due to situation
- Extra chemicals on the bark due to animals and insects (e.g. dogs urinating on the bark)
- Age of tree, effecting thickness of bark
- Positioning of leaves on the tree, which will shadow the Pleurococcus.
As it would be impossible to measure all sides of all the trees at exactly the same time, other variables, such as climate, would also change. Pleurococcus is affected greatly by pollution, in some of the more exposed areas, there may have been less Pleurococcus growing due to pollution.
Due to these inaccuracies, without further more detailed investigations, although I have discovered that the most pleurococcus grows on the North, I have not really got enough data to support my hypotheses. Therefore, if I did the experiment again, I would try to eradicate some of these problems. For example, I would choose an area with larger spacing between the trees, thus ensuring that the effects of exposure etc, were more universal. I would measure all the circumferences of the tree trunks, and, using this data, select 10 of a similar size. To gather more data, I would measure more trees, and measure from all eight compass points, to give me more data. I would use a larger quadrat, with smaller squares, to ensure a higher degree of accuracy. I would also measure humidity at hourly intervals throughout the day, to investigate my theory that Pleurococcus does not grow in the lightest areas because it is too dry. I would use a sunlight hour measurers, set up at each compass point of the tree, to see how much sunlight the side of the tree received in a day. This would make my experiment more inaccurate.
Further experiments I could carry out, to research more into Pleurococcus, could include measuring:
- Different types of trees and the amount of Pleurococcus on them
- Measuring how pollution affects amount of Pleurococcus
- Testing different sites to see where the most Pleurococcus grows
- How size of tree affects amount of Pleurococcus
- What height the most Pleurococcus grows
- Investigate the other surfaces Pleurococcus grows upon
- Investigate other plants to find if other plants are affected by which compass poitn they face
