Many of the problem sets (our affectionate term for homework) at MIT are designed to be worked on in groups, and cross-department labs are very common. Many, like myself, were both.
As MIT admissions officers, our primary goal in reading these essays is to get to know you, the applicant. This type of stuff also got me into the other schools I applied to (e.g. The core of the MIT spirit is collaboration and cooperation; you can see it all over the Institute. MIT is known for its interdisciplinary research. All MIT interviewers were undergraduates at MIT, or a very few were graduate students with a lot of interaction with the undergraduates.
So don’t think they’re asking you to tell them how much you like to do research simply because you think that’s what they want to hear. It’s not to be wowed, or feel like we need to … MIT gives you plenty of opportunities to write about the deep stuff; not only is their application composed of several prompts, they also ask you to provide a list of your activities. I’m copying my resume + supplemental music resumes for MIT at the time, and a few excerpts from my Short Answer responses.