Corporate: BA specs out your tasks, it's nicely placed in task system, you have daily standups and two-week iterations / sprints and and things are generally predictable. You have dedicated people for frontend, backend, architecture, database and generally enough developers so that you can take proper leave and an HR department who you can talk to if you're not happy with things. Company typically has a culture with flashy year-end functions and developers would start at a fixed time and leave at a fixed time in the afternoons. Things tend to move slowly in corporate and typically you have to deal with lots of red tape to get anything done.
Startup (early stage): You are the BA, you are the architect, the frontend developer, the backend developer, you do everything, even take out the trash and help wash the mugs, you make coffee / tea for other developers while also running meetings and meeting directly with clients. Your computer, to save cost, is built from old server parts and the latest flashy tools aren't available, unless you're happy to pay for it out of your own pocket. HR department is a luxury the startup can't afford, if you have a problem, you have to fix it yourself or deal with it yourself. Culture typically includes working your arse off, coming in very early and leaving late, working strange hours and generally bending backwards for the company in order for it to succeed. In startups, things move very quickly, there's no red tape to protect you from doing something and if you break something, you are responsible for fixing it.