Fats are high energy molecules that assist in a growing organism. There is a lot of calories in fat that can be used for growth.When metabolising fat it produces carbon dioxide, water, and ATP. Sugars and/or starch is useful in the same method, they provide calories necessary for a seed or baby animal to grow. The starch can be cleaved into more managable sugars, and the sugars used in glycolysis and then the products of glycolysis used in the citric acid cycle. Used together an organism would have water from the fat that can be used to hydrolyze the sugars that it would consume to produce ATP.
