The Life Cycle of living organisms is defined as a series of events taking place throughout their lives which include growth, development, reproduction, and death. It is a characteristic of a particular organism and differs amongst species. This difference generally reflects a species own ways to survive, adapt and reproduce offspring in better environmental conditions. The lifespan of an individual is the time required to complete its own life cycle.
Stages of Life Cycle are −
The beginning of new life is called birth.
In this stage there is fusion of two gametes (two haploid gametes) which forms the zygote (diploid).
Example − newborns (in humans/animals), seed germination (in plants), and Egg (in insects).
This stage is known as the growth and development stage.
In this stage the various body parts of an organism develop.
The organism develops a strong immune system.
Close to end of this stage various reproductive organs develop and some start showing secondary sexual characters.
Example − childhood-puberty phase (in humans), formation of plant parts (in plants), and larvae stage (in insects).
This is known as the reproductive stage.
The reproductive structures are fully active and they are capable of giving birth to new progeny.
Haploid gametes are developed in reproductive structures through meiosis; by the process of copulation two gametes unite to give rise to a new individual.
Sex hormones are developed by organisms and they can now perform the process of mating.
Post fusion of gametes, the individual is implanted in the womb of the mother (in mammals) or are enclosed in a calcareous shell called egg ( in birds or insects) or are protected inside a fruit (in plants).
If an organism has many predators, the chance for the survival of that species is reduced. Hence, to compensate for that, those species give birth to multiple progenies.
Organisms which are Apex predators of an ecosystem, generally produce less offspring, because the energy required for reproduction is high.
Example − Adulthood between 18-50 yrs (in humans), formation of flowers and fruits (in plants), and the pupae/adult stage (in insects).
This is the final stage of the life cycle of an organism.
As this phase progresses, organisms lose their reproductive capacity and become physically weak hence are unable to conceive new progeny.
In some organisms, such as butterflies, after the process of laying eggs the female dies and the male dies post copulation.
It is an important phase as it helps in maintaining a balance of a particular species in an ecosystem.
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Life cycle of species depends on various factors, such as the environment in which they live, the energy required to reproduce, and the genetic factors.
Environment for Survival − It is an important factor which is not only responsible for a particular life cycle but also various other features a species has to adapt and survive in an environment. If the environment is conducive then those species live long, if not, then they have a short life cycle.
Energy Allocation − All life processes in an organism require energy. Hence, energy is proportionally divided into various processes. Hence, adaptations which are necessary for reproduction are only present in particular stages of life cycle. At other stages these adaptations are not useful and do not show the same success rate. This phenomenon is known as Trade-off in which energy is being traded off between stages of life cycle.
Example − Humans and Perennial plants- though they have long reproductive phases one reproduction requires lots of energy and hence they reproduce less, to preserve energy for other life processes
| Iterocarpus Life Cycle | Semelparous Life Cycle |
|---|---|
| Can perform many births during the reproductive phase. | Can perform only single birth during the reproductive phase. |
| Less offspring production. | More offspring production. |
| Occurs in long-lived individuals. | Occurs in short-lived individuals. |
| Survives after giving birth. | Dies after giving birth. |
| Energy proportionally distributed between reproduction and other life processes. | Most energy is used for the process of reproduction. |
| In plants, it is known as Polycarpy. | In plants, it is known as Monocarpy. |
| Example − Perennial plants, mammals, reptiles, birds, etc. | Example − Annual plants, invertebrate species, spiders, salmon, etc. |
Life cycle of species shows us how life runs on earth. Life cycles of some organisms are as small as a few minutes or as long as hundreds of years. Birth, Juvenile, Adult and Death are various events of a life cycle. It is a circular process of birth and death in which one organism reproduces giving rise to another individual. The new generation thus formed follows this same life cycle and in this way, various species on earth grow and evolve.
Q1. Discuss different types of life cycles found in plants
Ans. Different types of life cycle found in plants are −
Haplontic − Most of the life cycle is represented by the haploid phase except the zygote stage. Example − Various algae species.
Diplontic − Most of the life cycle is represented by diploid phase, except for a few haploid stages of gametes formation. Example − Angiosperms and Gymnosperms.
HaploDiplontic − Both haploid and diploid phases are dominant and clearly visible in the plant's life cycle. Example − Bryophytes and Pteridophytes.
Q2. Describe the life cycle of honey bees.
Ans. Life cycle of honey bees consists of the following stages −
Egg − These are small, the size of rice grain. These can be fertilized (forms female bee/queen bee) and can be unfertilized (forms male drones).
Larvae − Second stage known as the eating phase, nurse bees feed the larvae with royal jelly. Larval stage lasts for 6-7 days.
Pupa − Larva starts forming a cocoon and resembles just like the adult bee. Workers seal the pupa in the cell with beeswax. Here, all organs such as wings, skin, eyes, legs develop.
Adult − Now, the adult bee breaks open the seal and flies out .
Queen bees take 16 days, worker bees take 18-22 days and drone takes 24 days to completely develop.
Q3. Different life cycles based on reproduction.
Ans. Life cycle of organisms can be differentiated based on mode of reproduction −
Asexual reproduction − Progenies are formed without fusion of gametes and they are genetically identical to the parents.
Sexual reproduction − Progenies are formed due to fusion of two gametes male and female, and they are genetically different from parents and show variation.
Q4.Classification of crops based on life cycle.
Ans.
Annuals − Completes life cycle in 1 year since that time is conducive for their growth. Example − maize, rice, millets, etc.
Biennials − Completes life cycle in 2 years as they require two growing seasons for vegetative and reproductive stages. Example − carrots, lettuce, cabbage, etc.
Perennials − Completes their life cycle once in 3-4 years, they reproduce only when required and when conditions are favorable. Example − Mango, Citrus, etc.
Ephemeral plants − Completes life cycle every 3-4 months. Example − Tomatoes.
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