UEFI HD Paritioning for Ubuntu 16.04

I have 16.04 on sda and 14.04 on sdb. These two disks have different partitioning schemes. I initially had FreeBSD on sda and installed Ubuntu 12.04(?) on sdb as a trial run. I eventually decided to stay with Ubuntu and started using sdb. I have variously had other versions of Linux on sda. Maybe that is the reason for the strange partitioning schemes.
The computer is a core i7 OC 4.2GHZ 16G RAM, mostly used for command line applications.

sda:
Number Start End Size File system Name Flags
 4 17.4kB 1049kB 1031kB bios_grub
 1 1049kB 180GB 180GB ext4
 2 180GB 200GB 20.0GB linux-swap(v1)
 3 200GB 500GB 300GB ext4
sdb:
Number Start End Size File system Name Flags
 4 17.4kB 1049kB 1031kB ext4 bios_grub
 1 1049kB 538MB 537MB fat32 boot
 2 538MB 483GB 482GB ext4
 3 483GB 500GB 17.1GB linux-swap(v1)

I plan to fix this with 16.04 on sda.

What is the bios_grub partition? This seems to be on the front of the disk in what is normally unused space, at least as far as partitioning is concerned.

1 500M FAT32 /boot/efi
2 180G ext4 /
3 300G ext4 /home
4 20G swap

Does this look OK?