Which of the following are called the "building blocks" of life?

Amino acids are often referred to as the "building blocks" of life because they are the fundamental components that make up proteins. Proteins are essential macromolecules that perform a vast array of functions within biological systems, including catalyzing metabolic reactions, aiding in cell signaling, and providing structural support to cells and tissues.

The phrase "building blocks" emphasizes the idea that amino acids link together in specific sequences to form polypeptides and proteins, much like bricks are assembled to construct a building. There are 20 different amino acids that can be combined in various ways to create the diverse array of proteins found in living organisms.

Other biomolecules like carbohydrates, nucleotides, and fatty acids serve important roles in life—carbohydrates are primary energy sources, nucleotides are the building blocks of nucleic acids like DNA and RNA that carry genetic information, and fatty acids are vital components of lipids that form cell membranes and store energy. However, it is the amino acids specifically that are commonly highlighted as the direct constituents of proteins, hence their designation as the building blocks of life.