What do you think about the addition of animations to powerpoint presentations? [...] the use of animated films to illustrate a concept (I'm in biology by the way).
There are lots of situations where animation can help much better than verbal descriptions only to show what happens. I'm chemist, so I immediately think of an animation showing (bio)chemical reaction mechanisms.
I'va been using animations of data point clouds of time series measurements: animations work most intuitively if the explained mechanism works actually in a time domain.
On the other hand, I usually avoid animation movies in a presentation.
Having a number of slides that evolve and can be played almost like a movie by going fast through the slides allows better control of where to stop in order to give explanations and also of the time taken for the whole animation: this gives degrees of freedom that help to stretch/squeeze the presentation in order to finish on time.
Bottomline: I'd recommend to think hard whether a good (static or evolving) illustration isn't more suitable for the oral presentation than a movie-like animation. But I somehow assume that you like to do one almost as much as the other.
seem less serious about the science
This won't be an issue if there's good scientific content in the animation. Particularly if meant for an oral presentation, it should be very much to the point and it should have a clear "added value" over a verbal description with the aid of a few static illustrations.
Now about the intellectual property part of the question. Obviously, this depends on your legislation (and on your actual situation).
my old supervisor seem to think that she (along with everyone else in the lab) could simply start to use my animation in their presentations
Situations exist (in my legislation: Germany) where the supervisor does have the right to do this: e.g. if you produced the animation as part of a paid full-time employment contract. In your legislation, it may even be legal to ask the student to sign over the copyright for all they produce during their thesis to the university (in Germany it is not).
On the other hand: in 3 out of 4 institues where I have been I was responsible for my presentations. If a PI wanted to use one of my slides they asked me (and I was of course happy to allow use), but there was no default unasked use. Insitute no. 4 has slides given to the suüervisors/director by default - but in practice they anyways ask for a slide being prepared for them for a particular purpose when they need something.
In any case, anyone showing your animation needs to attribute you as the author.
There is nothing wrong with asking to be paid for producing animations. But you should expect that it doesn't work out. Technically it could be done with a student employment contract which would mean that the animation is then a work made for hire (and the employer gets the copyright including the right to tell you to not have a "cornyvita's animation" line in the movie). I'd think it likely that money is scarce, though: PI usually won't have money to hire you for producing animations. Tons of other things are more urgently needed.
I therefore recommend that you make up your mind why you want to do the animations (hobby or paid work). And, if you produce them in what "currency" you'd like to be paid: citations? being known? money (hint: there may be faster and easier ways to get this. Being a professional illustrator is not generally known as the fast track to become a millionaire...)?
But: Don't underestimate the value of being known as the author of those really great scientific animations. This can translate to employment later. While super-fancy presentations won't get you hired if you suck scientifically, being a good scientist and being known to deliver good presentations is a hard to beat combination. Note that the presentations are the icing on the scientific cake: don't neglect your science for the animations. Also, this means that preferrably you are showing your animations on conferences. Second best option (in addition?): your PI attributes you explicitly as the author ("This is illustrated by cornyvita's great presentation here" ) rather than just among all those names on the acknowledgements slide at the end. Just like the PI can distinguish other important contributions "cornyvita isolated the protein, and ..." costs only few milliseconds compared to "we isolated the protein, ...)
The only situation that comes to my mind where I think there could be money for producing animations in the usual university settings are projects for producing teaching material. Some projects also have a bit of a PR budget but my guess is that a single animation will easily cost the whole PR budget for a project...