|MadSci Network: Botany|
Photosynthesis is a great topic to investigate in a high school research project; plants are easy to grow and control, and photosynthesis is perhaps the most important biological process on Earth. However, you do need to think more critically about your overall scientific method.
Familiarize yourself with
the scientific method
and ask yourself:
Is my question clear?
Do I have enough information to formulate a clear hypothesis?
What is my hypothesis (what are the expected results based on your understanding of photosynthesis)? and
Is my experiment designed properly to test this hypothesis?.
You need to be clear about the question you are testing with your experiment. By testing the effect of having an additional duration of illumination on your plants, you are essentially testing the effect of photoperiod Ė the ratio of light:darkness that a particular plant is the most adapted to (see http://en.wikipedia.org/wiki/Photoperiod, and http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Photoperiodism.html).
Plants, like animals, have entrenched circadian rhythms, meaning that they change their biological activities over a 24-hour period. These circadian rhythms will usually still occur if you place plants in constant darkness or constant light, although their ability to photosynthesize will be inhibited under dark conditions. On the other hand, if you wanted to test the effect of light intensity on the growth of your plants, then it would be better to have one group of plants under a single light and another group under two lights (or double the intensity/wattage).
Plants have a maximum photosynthetic rate that they reach when the light intensity reaches a certain level, so you could try to figure out what that level is for your particular plant species by setting up a gradient of light conditions (eg., darkness, 30 watt bulb, 60 watt bulb, 90 watt bulb, 120 watt bulb). You would expect to see an increase in growth up to a point (maybe 90 or 120 watt), at which point the rate of photosynthesis will be at itís peak.
Another possibility is to test the effect of certain wavelengths of light on the growth of plants by using different coloured light bulbs or using coloured filters in front of the bulbs. This way you could test what wavelengths of light are best for plant growth and determine those that are not especially important for plants.
Since the chlorophyll molecule contains magnesium, you could test the effect of removing magnesium from the plantsí diet (fertilizer). You could also test the effect of increased light intensity or duration on the growth of a C3 plant versus a C4 plant. C4 plants, like corn, have a more efficient mechanism to capture carbon dioxide form the atmosphere, allowing them to grow faster than C3 plants. C4 plants are also able to withstand dry conditions better since they can acquire more CO2 per unit time than C3 plants, allowing them to keep their stomata closed for longer periods of time, thus reducing water loss via transpiration.
Compare the effect of increased light duration or intensity on the growth of corn versus beans, for example. Check out this overview of C4 vs C3 plants ( http://www.biologie.uni-hamburg.de/b-online/e24/24b.htm). Remember to take the dry weight of your plants at the end of the experiment, since this will give you data specifically related to carbon acquisition and will remove variability in water retention of the plants. Also, always remember to include appropriate controls!
Check out this page from Arizona State University for great resources on all aspects of photosynthesis ( http://photoscience.la.asu.edu/photosyn/education/learn.html). Also check out this page devoted to science experiments and projects about photosynthesis ( http://www.juliantrubin.com/fairprojects/botany/photosynthesis.html).
Hope this helps you organize your research project! Good luck, and have fun with your experiment!
Try the links in the MadSci Library for more information on Botany.