1. Embryonic stage: The life cycle begins with the formation of a zygote, which is the result of the fusion of a male gamete (sperm) and a female gamete (egg). The zygote undergoes cell division and develops into an embryo within a protective structure, such as an egg or a uterus.
2. Juvenile stage (Hatchling/Larva): After the embryonic stage, the organism hatches from the egg as a juvenile or larva. This stage involves rapid growth and development as the juvenile acquires the necessary structures and functions for survival.
3. Adult stage: As the juvenile continues to grow and develop, it eventually reaches sexual maturity and becomes an adult. This is the reproductive phase of the organism's life, where it can produce offspring.
4. Senescence and death: As the animal ages, it enters the senescence phase characterized by a decline in physiological functions and overall health. Eventually, the organism reaches the end of its lifespan and dies.
The life span of an animal species varies widely and can range from a few days or weeks for certain insects to hundreds of years for some long-lived species like whales and tortoises. The life span is influenced by factors such as genetics, environmental conditions, diet, and predation.