What does the symbol △ in a chemical equation mean?

Delta, or subject to change.

Explanation:

indicates that heat is applied to make the reaction proceed

plasma is the state of matter where the substance is ionized and has no definite shape or volume. the fact of being ionized makes the substance a good electrical conductor.

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.