Here's why:

* Building Blocks: Proteins are made up of amino acids, which are the building blocks for all cells and tissues.

* Structural Components: Proteins provide structural support, forming the framework of cells, tissues, organs, and even the entire body.

* Enzymes: Many proteins act as enzymes, which catalyze (speed up) chemical reactions necessary for life, including those involved in growth and repair.

* Hormones: Some proteins act as hormones, signaling molecules that regulate growth and development.

* Repair Processes: Proteins are crucial for repairing damaged tissues and cells.

While other macromolecules like carbohydrates and lipids also play roles in growth and repair, proteins are the key players due to their diverse functions and structural importance.