Why are there 2 drain pipes under my kitchen sink

[qchero]

When replacing my dishwasher I found there are 2 drain pipes under my kitchen sink, the one on the right is sealed just by a plastic film.

Just curious, why are there 2 drain pipes?

The previous owner remodeled it with a new sink so maybe it was sealed back then. Was it a dedicated one for dishwasher before?

And do I need to seal it with something better than a plastic film?

 

[qchero]

Photos

 

[justin_dewan90]

My guess would be it used to be for the disposer. Not the dishwasher. And yes, it needs to be sealed better. Just get a rubber cap for it just in case you want to separate the drains later down the road

 

[Mr_David]

Most likely when they replaced the disposal it would not fit to that drain because it has an all glue p-trap.

 

[qchero]

That makes sense. Thanks!