How does the protein that's contained in seeds or milk is useful for the plant sprouting from the seed or the baby mammal

Cows and other mammals produce milk to provide the food their babies need to grow. Seeds and milk contain proteins, fats, sugars and/or starch. 1. Explain how the fats, sugars and/or starch contained in seeds or milk are useful for the plant sprouting from the seed or the baby mammal.