Change = environmental factors, ie temperature (keep in a water bath) , wind speed (use a fan) , light intensity (have a lamp at different distances from the plant) , and humidity (idk how you would do that actually) Organism = leafy shoot, stem cut, placed underwater Repeat = repeat, idk, 5 times? Measurement = measure how long it took for the air bubble to move a set distance (or you could measure the distance the air bubble moves in a set period of time) Same = same plant / same size of air bubble / same other conditions (ie if you change one condition then leave the others the same)
And the faster the air bubble moves, the faster the rate of transpiration!