Ascientist conducts an experiment to test the effects of light on earthworm activity. which is a variable in this experiment?
light intensity
soil conditions
temperature
earthworm activity

In executing an experiment, it is important to know the variables you are trying to manipulate and measure into. Pinpointing these variables which include the independent and dependent variables are of significance to every testing study.

earthworm activity
and 
light intensity

B.) nitrogen fixationnitrogen fixation is the process of nitrogen molecules seeping into the soil and inside plant roots and bacteria. it gives more "life" to plants