Defining employment on grad school applications I'm not sure whether/how to include specific things on a graduate school application (biophysics) in the employment section

a) Unpaid lab work. I worked as a research assistant in a lab as an undergraduate, participated in field work, presented a poster at a conference and will be an author on a lab paper. While I will definitely include this in my application, is it misleading to not write that it was unpaid?

b) The application specifically says to include part time jobs and I wonder whether my lack of them will raise flags. Should I include the fact that I received a special stipend freshman year which had several requirements - one of which was that I not hold a job freshman year?

Some context: I was lucky enough to receive a full (need-based) scholarship all four years of university. This allowed me to focus on my academics. I began doing unpaid lab work and then stopped for a time to do paid work in a lab that ended up not being a good fit. I returned to the unpaid work which was more interesting and provided more opportunities for growth (the lab funded the fieldwork experience and conference travel/fees).
Yes, your lab work qualifies and should be listed, especially as you do not have anything else to list.  But you should indicate that it was a volunteer position.