Take this with a grain of salt as it varies by schools but generally where I'm from Bio I is organismal so like macrobio: organ systems, ecology, intro to phys. Bio II was cellular biology so like macromolecules, signal transduction, cell membrane transport, dna/rna and the big three processes, genetics implications (i.e. cell division and genetics) etc.
I HIGHLY recommend you have the cell bio version of biology under your belt before the MCAT. The MCAT has left out a lot of physiology and is now focusing on a lot of molecular things IMO. Instead of throwing tricks like what kind of blood does the pulmonary artery carry, they ask things like if a patient develops a mutation in their 20s in their eye what % of the progeny have this mutation and they ask things like what drug can be used to inhibit transcription/translation/replication etc. Genetics would be a good bet IMO but so would cell bio. If you could skip anything for now, skip the organismal bio.
With that being said, there's definitely still some physio on the MCAT but it's easier to figure out by reading the passages. Knowing stuff will help but I think molecular would be useful to learn.