Question

molecules that catalyze reactions in living systems by lowering the activation energy are
○ enzyme
○ steroids
○ phospholipids
○ polysaccharides

Explanation:

The question is about identifying the molecules that act as catalysts in living systems by lowering activation energy. Enzymes are biological catalysts that speed up chemical reactions in cells by reducing the activation energy required for the reaction to occur. Steroids are a type of lipid with various functions like hormone regulation, phospholipids are a major component of cell membranes, and polysaccharides are complex carbohydrates used for energy storage or structure. So the correct option is the one with enzymes.

Answer:

A. enzyme (assuming the first option with the arrow is labeled as A, the full option would be A. enzyme)