Here's why:

* DNA structure: DNA is a complex molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known living organisms and many viruses.

* Genes: DNA is organized into units called genes. Each gene contains a specific sequence of DNA nucleotides that codes for a particular protein or functional RNA molecule. These proteins and RNA molecules are responsible for carrying out the vast majority of cellular functions.

* Inheritance: During reproduction, DNA is passed from parents to offspring. This transmission of genetic information is the basis of heredity.

While there are other molecules involved in cellular processes, like RNA, DNA holds the primary blueprint for life and is the fundamental unit of heredity.