Questions

A primary key is a special relational database table column or combination of columns designated to uniquely identify all table records. That is, A primary key is a column or set of columns in a table that uniquely identifies tuples (rows) in that table.

A primary key, also called a Primary Keyword.

Main Features Primary key are ::

It must contain a unique value for each row of data.

It cannot contain null values.

DNA is made of nucleotides. And these Nucleotides are made of a pentose sugar deoxyribose, a phosphate, and a nitrogen-containing bases.

Hence, the given statement 'Nucleotides are made of a pentose only' is FALSE.

Phosphorescence is a phenomenon associated with an algal division called euglenophytes. 

Phosphorescence is a phenomenon when an object is capable of releasing photons of light at a longer wavelength in response to absorbing light of a shorter wavelength. The object releasing the light only releases the light after some time has passed since it absorbed the light of a short wavelength.

Euglenophytes are single-celled plant-like protists that have no cell wall.

A protein that acts as a hormone is INSULIN.

Insulin is a peptide hormone produced by beta cells of the pancreatic islets; it is considered to be the main anabolic hormone of the body.  Insulin helps keeps your blood sugar level from getting too high or too low.