Aquatic Photosynthesis of Elodea Leaves Lab


Problem: What is the effect of temperature (warm, cool, room temperature) on the rate of photosynthesis in Elodea leaves measured by the levels of dissolved oxygen in the flask solutions?

Hypothesis: If temperature is related to the rate of photosynthesis (levels of dissolved oxygen) then increasing the temperate will increase the rate of photosynthesis up to an optimal temperature.


Independent: temperature of the water bath which the Elodea plant is immersed in

Dependent: the rate of photosynthesis measured by the level of oxygen dissolved in the flask solution

Constants: Relative size of the Elodea leaf, relative surface area of the Elodea leaves, (around 3 cm each), volume of water in all beakers, amounts of light exposure to the plants, and type of light source.



Light Source
Elodea. Keep this warm and illuminated before you use it,
3 small flasks,
10g/L sodium bicarbonate (NaHCO3) solution,
oxygen sensor
Lab Quest data logger.
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Graduated cylinder
Hot Plate
3 Large beaker (1 for warm water, 1 for cool water, 1 room temp)
3 thermometers


  1. Day one: Before beginning the actual lab—Listen for teacher instructions and familiarize yourself with the LabQuest datalogger and its functions using the quick start guide.  We will devote this day to learning how to use the datalogger so that tomorrow you can quickly set up your lab and begin data collection.
  2. Get the Probe ready (Note: this may have already been done for you—if you’re not sure ask me.)
  1. Remove the blue protective ...

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Overall this is a fairly poor piece of work. The student has completed the experiment and collected data, but has made a fundamental error of understanding and so drawn the wrong conclusions. This demonstrates how important it is to pay attention to what is actually being plotted on a graph. I would also expect an undergraduate to be able to elaborate on null and alternative hypotheses.In a first year practical this write up might get 2/5, as the demonstrators should have cleared up the misunderstanding.