Organismal development refers to the process by which a single fertilized egg, or zygote, transforms into a fully formed organism. This process involves a series of stages, including cell division, differentiation, and growth. During development, cells specialize to form various tissues and organs, guided by genetic instructions and environmental factors. Key stages of organismal development include embryonic development, where the basic body plan is established, and morphogenesis, which shapes the organism. Factors such as genes, hormones, and nutrients play crucial roles in ensuring proper development, leading to the formation of a functional adult organism.