Like many B-movies, Organizm has the astonishing ability to make random scenes of nudity pop up even during monster attacks. Plus, why is our hero coating our heroine's naked body in his own blood?
Actually there's a good answer to that second question. Here's the deal. There's a secret facility with a locked room and a tank in it. So the best thing for everybody to do is open it, which reveals a body that sprouts rooty things that grow really fast and eat people. As the military people who've come in to investigate helpfully show, the best way to fight rooty things is to take your shirt off and expose your bra.
But then our hero, who it turns out is the son of the guy whose body sent out the rooty things, starts helping the military attempt to stop the crazy CGI root things from zooming all over the entire planet. The roots are - bum bum bum! - a bioweapon invented by his dad using HIS OWN CELLS! It feeds on light and nukes and whatever, and just grows and grows but there is one way to stop it. You guessed it: Our hero's blood.
And of course, in order to protect his soldier friend when they go into the heart of the big bad rooty thing to kill it, he has to smear blood all over her naked body. Yes, she has to take her shirt off and be rubbed by his bloody hands to be safe. Though he takes her pants off, he does stop short of protecting her ass with blood, which makes me wonder if there are deleted scenes where a root finds its way inside her nether spots.
Whatever. Somehow this goofy little monster movie manages to have a major blood fetish scene which is sort of awesome and sort of WTF.
Organizm via IMDB