Thus far we mostly looked at the core-lipid part (traditional biomarker) of a lipid. what is an IPL?

Intact polar lipid, forms main constituent of cell mebranes in most organsims. It is the whole molecule as it occurs in the cell with polar headgroup attached. Large sturctureal variety. they are labile compounds that degrade rapidly upan cell death (hours to days, but can be perserved better (geological time scales) in optimal and anoic conditoins).