Which of the following describes atoms?

Atoms are indeed the fundamental units of matter, known as the simple building blocks that make life possible. They consist of protons, neutrons, and electrons and serve as the basic units from which everything around us is constructed. In the context of biology and chemistry, atoms combine to form molecules, which then create the various structures and functions necessary for life.

This choice highlights the essential role that atoms play as the foundation for all elements and compounds. They interact with each other through chemical bonds to form molecules that are essential for biological processes, including DNA, proteins, and carbohydrates—all crucial for living organisms.

The other options propose different concepts. Large complex structures made of molecules are more representative of compounds and cellular structures rather than atoms themselves. Products of cellular metabolism refer to the outcomes of biochemical processes within cells, rather than the basic components like atoms. Compounds formed by chemical reactions are made up of two or more atoms chemically bonded together, which again emphasizes the role of atoms rather than describing them directly. Thus, the selected answer accurately encapsulates the nature of atoms as the core building blocks of matter.