Why does the PPF bow outward and what does that imply about the relationship between opportunity cost

Question:

Why does the PPF bow outward and what does that imply about the relationship between and the quantity produced?
Opportunity Cost
Opportunity cost is the profit lost when one alternative is selected over another. The Opportunity Cost refers to the expected returns from the second best alternative use of resources that are foregone due to the scarcity of resources such as land,...