There are a number of variables that can affect the photosynthesis rate of Canadian water weed (Elodea). They are as follows: The amount of light: an increased light level increases the rate of photosynthesis to a certain point where at another factor limits the photosynthesis rate. The temperature: Increased temperature increases the rate of photosynthesis to a certain temperature, after which, essential enzymes are denatured, thus, in the long run, killing the plant. The CO2 levels: Increased CO2 levels also increase the rate of photosynthesis.
The variable I am going to investigate is the level of CO2, however, the addition of NaHCO3 (sodium bicarbonate) to the water may affect the osmotic ability of the water. Just 2g of sodium bicarbonate in 1000ml of water gives the equivalent salinity of seawater, and as Elodea is a fresh water plant, it cannot survive in salt water. I will need to take this into account when measuring the NaHCO3.
To work out the rate of photosynthesis I am going to count how many bubbles of O2 are given off in a minute.
I think that the more NaHCO3 there is in the solution, up to a certain point, the greater the number of O2 bubbles given off, showing a faster rate of photosynthesis.
To keep this experiment as fair as possible, the only variable I will change is the amount of NaHCO3 in the water. All other variables, i.e. the light level, will be kept the same throughout the experiment.
Large (1000ml) beaker
Piece of Elodea
NaHCO3 3x 0.2g, 3x 0.4g, 3x 0.6g, 3x 0.8g & 3x 1.0g
1. Draw up a results table. It should, ideally, resemble the table below. Amount of NaHCO3 (g)1st Attempt2nd Attempt3rd AttemptAverage number of Bubbles 0.2