||Elodea canadensis is an aquatic plant with “whorls of mostly three leaves” . It is not native in Europe (Bromer and Jakobs 1995). Elodea canadensis also takes up nutrients fast and easily and produces much oxygen indicating high photosynthetic rates (Fröhlich 2015).
T.W. Engelmann already performed an experiment like the following. He used a prism and algae to investigate photosynthetic rates. He observed that the most photosynthesis is done under red and blue light but nearly none under green light. (Engelmann 1882).
||To what extent does photosynthesis in elodea canadensis depend on the colour of the light source?
||There will be significantly high rates of photosynthesis with red and blue light and very low rates with green light.
water bath (Julabo; Bad-/Umwälzthermostat up to +150 °C MB-5)
Elodea canadensis, one individual (length: more than 10cm; see: 4.3. Method) from school pond in Klosterneuburg, Austria (there are no concernes with taking this plant out of the ecosystem of the pond as it is available in abundance and reproduces quickly .)
a small beaker big enough to reach higher than the water level of the water bath (600ml) depending on the water bath
big supply of pond water in which the plant has grown
light source: two lamps with lightbulbs with filament of Baumax (A60, 230V ES E27, 2000h 1920 lm, order code 252262xx; Philips) with three coloured foils from Pagro (brand: LÖWE)
lux meter (Voltcraft: LM30000 0-3000 Lux)
stopwatch on my Samsung Galaxy J3 phone (android)
1. The experiment was conducted 9 times per colour resulting in 27 data points
2. The water was taken from the public pond “Silbersee” in Kritzendorf, Austria to ensure a natural environment for the plant. For every trial the same volume of water (10l) was filled into the water bath and heated to 22,2°C. The water was exchanged after every trial to ensure same chemical composition of the water in every trial.
3. The lamps were arranged around the water bath.
4. The Elodea canadensis, from the school pond (BG Klosterneuburg Austria), was cut to 10cm length using a ruler and utility knife shortly before the experiment. When performing the cutting attention should be payed to the hazard of injury. The plant was submerged and weighed down by a small paper clip on the end of the plant to keep it submerged.
5. The room was completely darkened.
6. The lamps with the coloured light were turned on for exactly 60 sec.
7. The complete darkness stayed for 15 sec to ensure photosynthesis stopped after every trial before the next one.
8. The bubbles rising were counted and noted down.
||As T.W. Engelmann observed in his study on wavelength and photosynthetic rate, the most photosynthesis is observed at red and blue light. He even coined a term for the nonexistent photosynthesis under green light: Grünlücke (engl.: “green gap”) (Engelmann 1882)
Due to the reflection of green light and due to its own colour, the plant is unable to do photosynthesis, whilst it works under blue and red light. This disproves my null hypothesis that there will be no significant difference in photosynthetic rate between the three light colours. At the same time, it supports my hypothesis that there will be a significant difference between the three light colours. The p – value indicating the probability of random correlation between the colour conditions is very low. The p – value between red and green is 0,000000552 and between blue and green is 0,0000000876, indicating very significant results.
||High School Students (Grades 9,10,11,12)
||Klosterneuburg International School