Accidentally deleted my EFI partition on OS X

I accidentally deleted my EFI partition on OS X. It is completely gone. I need to fix it ASAP, so I have a few questions about this...

1) What exactly does the EFI partition do?

2) Is the EFI partition necessary?

3) How do I restore/repair/remake it?

I have a Macbook Pro (13-inch, mid 2010) 2.4 GHz running OS X Yosemite 10.10.2.

PLEASE HELP ME!!!