Life cycle in biology refers to the series of changes which the members of a species undergo as they go from the beginning of a given developmental stage into the inception of the same developmental stage in the subsequent generation. In many simple organisms including bacteria and several protists, the life cycle completes within one single generation. The process in the organism begins with the fission of an existing individual and the new organism grows to maturity and then splits to two newer individuals and completes the life cycle. In the higher animals, the life cycle encompasses a single generation as well. The specific animal begins with the fusion of male and female sex cells that are called gametes. This grows to the reproductive maturity and then produces gametes, at the point when the cycle begins afresh by assuming that the fertilization takes place. In this article, we will learn about the animal life cycle, the list of life cycles, and the importance of the animal life cycle.
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A life cycle determines the series of stages which an individual organism passes through from the time it is conceived to the time it produces an offspring of its own. This series of stages is called a life cycle since an offspring passes through the same series before they can produce their own offspring. Therefore, the life cycle is repeated for each generation. The basic stages of a life cycle for all the organisms include a pre-reproductive stage in which the individuals grow and mature and pass through a reproductive stage in which the individuals produce an offspring. However, species vary a lot in their particular aspects of their own different life cycles.
Differences amongst the species in their basic life cycle often reflect adaptations to survive and produce an offspring under several different ecological conditions. Consider, for example, some plant species that live in the habitats in which they are easily able to grow, mature, and reproduce in one growing season. In the lesser fertile habitats, however, the plants may not grow enough to successfully finish their life cycles in a year. Consequently, the plant species in these habitats can have life cycles with even longer pre-reproductive stages. In addition to being affected by several environmental conditions, life cycles are influenced by the patterns of energy allocation as well. Energy which is used for the growth or the metabolism cannot be used to produce offspring. Therefore, adaptations that increase survival or reproductive success in a life cycle stage can reduce the survival or reproductive success in the other stages. This situation is called a trade-off.
One example of this trade-off is often related to the length of the reproductive stages. Some organisms, including humans and several perennial plants, have longer reproductive stages and can reproduce several times during that stage. These kinds of organisms are known to have iteroparous or repeated-births life cycles. In contrast, salmon and several annual plants are examples of the species having semelparous or single-birth life cycles. In this type of a life cycle, the individuals reproduce only once and die. Intuitively, iteroparous organisms can be expected to produce more offsprings than the semelparous species. Because of the tradeoff in the energy allocation, however, the semelparous species can, in a few cases, be more successful in producing an offspring than the iteroparous species despite the fact that they can only reproduce once. Since semelparous species cannot survive after reproducing, they can allocate all the available energy to produce an offspring. Under certain environmental conditions, the extra energy allocation might result in a large number of offsprings than the iteroparous species which must reserve enough energy for survival.
A life cycle is a period which involves one generation of an organism by means of reproduction, whether it is through the asexual reproduction or the sexual reproduction.
There are three kinds of life cycles: haplontic life cycle, diplontic life cycle, and diplobiontic life cycle.
These three types of life cycles feature an alternating haploid and diploid phases denoted by n and 2n.
The haploid organism becomes a diploid through the process of fertilization that joins the gametes. This results in a zygote that then germinates. To return to the haploid stage, the process of meiosis must occur.
The cycles differ in the product of meiosis, and if mitosis, that is, the growth occurs.
Zygotic and gametic meiosis contain one mitotic stage and form. During the n phase in the zygotic meiosis and during the 2n phase in the gametic meiosis. Hence, the zygotic and gametic meiosis are collectively termed as haplobiontic, that is, a single mitosis per phase.
The sporic meiosis, on the other hand, contains two mitosis events, which is, diplobiontic, which, in turn, means one in each phase.
1. What Are The Animal Life Cycle Stages?
The four stages of the animal life cycle are birth, growth, reproduction and lastly, death. All these animal species go through these stages, however, they manifest differently throughout the animal kingdom. Mammals are called oviparous since their embryos develop inside their mother’s wombs, while other kinds of animals are viviparous since their embryos develop in the external eggs. Some reptiles are known as ovoviviparous since their embryos develop inside the eggs which remain inside their mother’s body until they hatch.
2. What Are The Bird Life Cycle Stages In The Life Cycle Of A Bird?
Plants are the stationary organisms which sprout from one single place in the soil or ground and remain there for the rest of their lives. Although some of the plants can spread across a surface like ivies, many remain in a very small area from the germination to death or consumption. The basic life cycle of a plant begins from one seed that grows, flowers and then produces seeds of its own. Some plants complete this process in the time of weeks, while in the other plants, such as trees, they live for hundreds of years.