The first leaves of the seedling are called cotyledons. These are not proper leaves, but nutrient stores that were present in the seed with the embryo. These nourish the plant as it develops the capacity to harvest nutrients from its environment. Some plants, called monocotyledon, have only one cotyledon while others, called dicotyledons, have two. The plant then begins to develop its first proper leaves, called primary leaves. These leaves start the process of photosynthesis or turning the energy from sunlight, water, carbon dioxide into sugars that the plant uses for food. The plant does this by using chemicals called chloroplasts.
Many plants continue to grow upwards and form new leaves at the top of the stem (meristem), as well as downwards, growing more root hairs. This growth increases the number of nutrients it can gather and helps it withstand weather, disturbance from animals, and competition from other plants.-- Reeya