As i pull away from the gene bank, it says 'warning: you have an empty slot inwhich you can put another plasmid or tonic into' How do you open the extra slot to put the plasmid in?

Go to a Gene Bank and select the plasmid slot that is empty and fill it with a tonic or plasmid. You can use the Gene Bank here to shuffle your plasmids and tonics as you like. If you don't have one go to a Gatherers Garden and purchase one with some ADAM.

Gene Banks look like this

Also, the game cannot detect whether or not you actually have a tonic or plasmid to fill the slot, it just detects whether or not there are any empty slots, so don't get worried when you don't have the Adam to purchase new tonics/plasmids or have an empty slot for a while.

Cheers, got it now. I now have four plasmid slots!

I'm sure it has given me this message too but I had all of my slots filled with something. Am I missing something or does it always say that?

Yes thats the exact thing what happened to me!!!

yea same, i had that msg and i have no empty slots.

Strange...I guess it just must be something the developers missed as it happens everytime I go to one, even though I have no slots at all available.

Nah bucmuc, they're right. I definitely got that message more than a few times, even with no empty slots. I thought it was just me.