Questions

Nostoc is a prokaryote. Prokaryotic cells lack membrane bound organelles and well organized nucleus, that is nuclear envelope is absent in these cells.

The nuclear envelope, also known as the nuclear membrane, a bilayer membranes which surrounds the nucleus, and in eukaryotic cells it encases the genetic material.

A bug leakage results when a bug is detected which should have been detected in earlier builds/versions of the application.

A defect which exists during testing yet unfound by the tester which is eventually found by the tester/end-user is also called bug leakage.

A bug release is when a particular version of s/w is released with a set of known bug(s)/defect(s). These bugs are usually low severity and/or low priority bugs. It is done when the company can afford the existence of bug in the released s/w rather than the time/cost for fixing it in that particular version. These bugs are usually mentioned in the Release Notes.

Functional testing is a type of testing that is done against the requirements of the business application. 

Examples of functional testing are Smoke testing, Sanity testing, Regression testing, Usability testing.