Database Design

[IrPr]

As im not such expert as well as you guys are, I've to ask some basic database designin quetions
I've to design a database for artists details, such as Biography
but just 10% of all my records have Biography data on that
there are 2 methods to me for design this table and its scripts:

1. create one table to keep all fields on that, NULL MEDIUMTEXT field for biography
   in this case my table will store one field that just used for 10% of records
   
2. create 2 tables and use one to one relationship between artists and biography
   in this case ive to use more query or use JOIN for my code

Which one is more optimized?

Another question:
I've to store two links for my tracks, low quality and high quality
Which one is more optimized?
to use one field in tracks table and use a splitter for the urls or just using serialized data
or use another table to join and use keys property?

Thanks