Nearly all of the body's chemical reactions, including those that produce energy and build new tissues, take place within cells.

Here's why:

* Organelles: Cells contain specialized structures called organelles, each with its own unique function. For example, mitochondria are responsible for energy production (cellular respiration), while ribosomes are responsible for protein synthesis, which is essential for building new tissues.

* Enzymes: Cells contain enzymes, which are biological catalysts that speed up chemical reactions. These enzymes are crucial for a vast array of metabolic processes.

* Compartmentalization: Cells compartmentalize different chemical reactions within specific organelles, ensuring efficiency and preventing conflicts.

While some chemical reactions might occur in the extracellular space (outside of cells), the vast majority occur within the complex and dynamic environment of a cell.