A change in the quantity demanded is brought about by a movement along the demand curve. Quantity demanded is a phenomenon that occurs when there is a change in the price of a good, which causes movement along the demand curve. Quantity demanded is relative to the market price of the stated good. When the price changes, there will be a movement along the demand curve indicating that consumer demand requirements will change. This change is relative to changes in price, whether a reduction or an increase, and will lead to a change in the quantity demanded. On the other hand, a change in demand will be a result of other factors rather than price. These factors, such as the quantity of a good on sale, lead to a shift of the demand curve. A shift in the demand curve is an indication of a change in demand. An increase in demand increases when the quantity purchased by the consumers rises, shifting the demand curve upwards and outwards. Consequently, a reduction in demand is brought about by a reduction in the quantity the consumers purchase, thereby shifting the demand curve inwards and outwards.
A change in quantity supplied is as a result of changes in price, which lead to movements along the supply curve. The price of a commodity is the greatest determinant of customer’s purchasing power. An increase in the price causes a movement along the supply curve to the right, hence increasing the quantity supplied. When the price reduces, there will be a movement of the supply curve towards the left leading to a reduction in quantity supplied. Price is the only determinant of a movement along the supply curve, and, consequently, the quantity supplied. A change in supply is caused by factors rather than the price of a commodity. A change on the non-price determinants of supply will lead to a change in supply. This is because they shift the supply curve. It is a shift in the supply curve that leads to changes in supply. While supply defines the quantities that the sellers are able and willing to sell at a range of supply prices, quantity supplied defines the specific quantity that the seller is able and willing to sell at the prevailing market prices. Quantity supplied is represented by a point on the supply curve, whereas the supply is all points on the supply curve.