When Mary Ann Powers deposits $25,000 into her business checking account as an investment, this transaction will have the effect of increasing owner's equity. This is because the investment represents an increase in the owner's stake in the business.
In terms of the accounting equation, which is:
Assets = Liabilities + Owner's Equity
The $25,000 deposit increases the assets (cash in the checking account) and also increases owner's equity, reflecting her ownership in the business. Therefore, the correct answer is:
Increase in owner's equity.