Circle if Life

Life Cycle

            A life cycle is a period that involves a single generation of an organism through the means of production. In a biological life cycle, an organism undergoes a series of changes returning to the original state. It is the series of changes that it undergoes from the beginning of a certain developmental stage to the start of a similar developmental stage in the next generation. In most simple organisms such as protists and bacteria, a single generation completes a life cycle. It starts with the fission of an existing single organism, then the new individual grows to maturity and finally, it splits into two new organisms completing the life cycle. Life cycle is also a single-generation affair in higher animals. Female and male sex cells fuse to produce an individual which then grows to reproductive maturity and the process is replicated. A new cycle begins.

Life in most plants, unlike in higher animals and simple organisms, is multigenerational. For instance, one plant germinates a spore which develops into a gametophyte. It reaches maturity and forms multiple gametes that grow into sporophyte after fertilization. When they reach reproductive maturity, they produce spores and the cycle begins again.

There are three types of life cycles; haplontic, diplontic, and haplodiplontic. In the first type of life cycle, the stage is multicellular and meiosis is zygotic. An example is that of the life cycle of bacteria. In the diplontic life cycle, meiosis is gametic and multicellular. Haploid gametes are formed in this cycle. Higher animals have a diplontic life cycle. Meiosis is sporic in the last type of life cycle. Typical plants have a haplodiplontic life cycle because it includes both the gametophyte and the sporophyte.