4.6Â Â Essay: Supply 1) What leads to a decrease in the quantity supplied of a good or service? 2) What is the difference between quantity supplied and supply? 3) List the factors that change supply and shift the supply curve. Tell what happens to supply and the supply curve when there is an increase in the factor. 4) What are substitutes in production? 5) Suppose that the number of companies selling computer software decreases. How does this change affect the supply of computer software and the supply curve of computer software?