Which is the dependent variable?



Hello, trying to get some work done, and I've been given the following question:

"Consider a hypothetical study of biomass in ten different biomes. In a few sentences, describe how differences in above-ground biomass of vegetation in response to two climate variables could be analysed using multiple regression. Identify the dependent and independent variables in the regression. You do not have to give details of how to collect the data."

I am assuming that the difference in above-ground biomass is the dependent variable, and the 2 climate variables are independent - is this correct? How would they calculate the difference for all 10 biomes though? I thought I knew what I was talking about, and then I started thinking too much and have got myself in a muddle.
Any help is much appreciated!