Witch substance is considered a building block for all living things

The cell is the fundamental building block for ALL living things! :) Isn't that amazing? Have a lovely day!~ <3

Hello

Cells are the building blocks of all life forms. We can delve in deeper and say that atoms are the building blocks of life because atoms are the building blocks of matter which is anything that has weight and takes up space, so everything in this case would fall under this category. 

But I believe the answer you're looking for is: Cells