Question

what do these two changes have in common?
saliva breaking down a piece of bread
a log decomposing in the woods
select all that apply.
both conserve mass. both are only physical changes.
both are caused by heating. both are chemical changes.

Explanation:

Step1: Analyze mass conservation

According to the law of conservation of mass, in any physical or chemical change, mass is conserved. So, both changes conserve mass.

Step2: Determine the type of change

Saliva breaking down bread involves enzymes (like amylase) reacting with starch in bread to form new substances (e.g., maltose). A log decomposing involves microorganisms breaking down complex organic compounds in the log into simpler substances (like carbon dioxide, water, and other organic molecules). These are chemical changes as new substances are formed. They are not just physical changes (where no new substances are formed) and not both caused by heating.

Answer:

Both conserve mass. Both are chemical changes.