Questions

A data dictionary is a special file that contains a set of information describing the contents, format, and structure of a database and the relationship between its elements, used to control access to and manipulation of the database.

Here Homologous Means having the same relation or relative position or structure. 

Here in snakes poison is in glands and here salivary glands are in Vertebrates.

The first step in the refining of petroleum is distillation i.e,  the fractionation of crude oil in atmospheric and vacuum distillation towers.

The first process petroleum refinery is known as distillation. In this process, crude oil is heated and fed into a distillation column. As the temperature of the crude oil in the distillation column rises, the crude oil separates itself into different components, called "fractions." The fractions are then captured separately. Each fraction corresponds to a different type of petroleum product, depending on the temperature at which that fraction boils off the crude oil mixture.

Nitrogenous base: A molecule that contains nitrogen and has the chemical properties of a base.

DNA and RNA ::

The nitrogenous bases in DNA are

Adenine (A),

Guanine (G),

Thymine (T), and

Cytosine (C).

Whereas the nitrogenous bases in RNA are the same, with one exception:

Adenine (A),

Guanine (G),

Uracil (U), and

Cytosine (C).

Central Processing Unit (CPU) is the brain of any computer system.