Sigma and Pi bonds

[Amirsaman]

could you explain the biological significances of the sigma and pi
bonds within organic molecules?
It is known that Silicon-based life is not really an alternative for
Carbon-based life because it hardly forms sigma and pi  bonds within
the molecules that are formed. On the other hand, Carbon, can very
much use the sigma and pi bonds to get different arrangements and
shapes. Is there any other reason to why Sima and Pi bonds are
required in complexifying chemical reactions?