You can put those tables within the same Filegroup and make backup about the latter. You can not backup on a particular transaction.
To create the filgroup in a database, execute the following script:
Use master
go
alter database MyDB add filegroup [NewFileGroupName]
go
You create a new table with this FileGroup
create table MiTabla (Columna1 int, Columna2 date) on NewFileGroupName
Then to execute the backup:
backup database MyDB Filegroup = N'NewFileGroupName' to disk = N'Ruta\archivo.bak' with notformat, noinit, name = N'Filegroupbackup', skip, norewind, nounload, stats = 10
It is important that the database in question is in recovery mode Full