To analyze the data obtained in the lentil experiment, you will need to generate a graph. The preparation of this graph is very simple - you simply plot the volume of O2 consumed by the normal and azide-treated lentils on the same graph. Be sure that you draw the best straight line and not just "connect the dots." When you are complete, the graph should look like this:
To calculate the respiration rate, simply take the slope of the lines. This will give you the rate of O2 consumption in ml/min.
1. What does the potassium hydroxide (KOH) do?
The potassium hydroxide absorbs the CO2 produced as a byproduct of aerobic respiration, forming a solid, K2CO3.
2. Why does the total volume of gas go down during this experiment?
The total volume of gas goes down because of the action of KOH. Normally, there would be roughly a 1:1 correspondence between the number of O2 molecules consumed and the number of CO2 produced by respiration. This would not cause an net change in the volume of gas in the system. However, the KOH removes the CO2 from the system (see Question 1.), thereby lowering the total pressure of the system. The surrounding air is at a higher pressure, so it pushes in on the methyl blue bubble, until the lowered volume increases the pressure inside the system to be equal to atmospheric pressure.
3. What is the cotton for?
The cotton protects the lentils from damage from the KOH. KOH is very caustic, especially when it can mix with water found on the seed coats of the lentils.