The upward sloping orange line represents the supply of bonds, and the downv sloping blue line represents the demand for bonds. As demand for bonds increases, so do bond prices and bondholder returns.The many different kinds of bonds. The upward sloping orange line represents the supply of bonds, and the downward sloping blue line represents the demand for bonds. The demand for bonds increases, which increases the price of bonds. As bond prices increase, the interest rate decreases. Learn about the relationship between bond prices and interest rates. The response of the yield curve to changes in the demand for, or supply of, bonds will depend on the nature of the change. When interest rates are rising, you can purchase new bonds at higher yields. A fundamental principle of bond investing is that market interest rates and bond prices generally move in opposite directions.