What is the basic building block of all living things?

Explanation:

All the living organisms on this Earth are made up of microscopic units called cells. It is basic structural unit for all the organisms. The cells are the building block of all the living organisms. Our body is composed of trillion of cells. They carry out the functional activities of our life. A cell can be defined as a basic , structural and functional unit of life capable of independent existence. The cell was first discovered by Robert Hooke in 1665 AD. As we know that all the living organisms are made up of cells. These cells are developed as a result of a division of pre-existing cells. All the cells are same in chemical composition and metabolic processes. The function of an organism as a whole is the outcome of combined activities and interactions of the constituent cells. The cell is known as the fundamental , structural and functional unit of life.

Hope I helped!

Best regards!

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.