Plant Kingdom

Plant Life Cycles and Alternation of Generations

When you see a parent plant and its baby plant, do you think both resemble each other? Yes, of course! Did you know the reason? The reason lies in the fact that plants also pass on genetic information to their plant offspring. Every plant has a unique way in which this occurs. Let us understand the life cycle of a plant and what alternation of generations means.

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Alternation of Generations

( Source – Science matters)

In plants, there are two systems of reproduction. Each is called one generation. There is a rotation between these generations. So, one complete life cycle of a plant includes two generations that alternate with each other. Hence the whole mechanism is called alternation of generations.

The two generations or life cycles that occur are called the sporophyte generation and the gametophyte generation. When you speak in genetic terms, it is the rotation in between the haploid and diploid stages. This refers to the chromosomes within the plant cells.

A diploid cell has two sets of chromosomes (one each from the male parent and female parent). A haploid cell has only one set of chromosomes. The haploid generation gives birth to plants with diploid cells. This then creates a generation of haploid plants, which again give rise to a generation of diploid plants. And thus the life cycle of a plant will go on.

The whole life cycle of plants is very complex. But the greatest benefit it gives is the greater genetic control. And how does this happen? In the haploid stage, bad genes can be removed and the diploid stage allows for greater genetic diversity.

Know some terms

  • Gametophyte – A Haploid plant
  • Sporophyte – A Diploid plant
  • Mitosis – The process by which gametophytes produce haploid gametes.
  • Fertilization – Fusion of male and female gametes to form a diploid zygote.
  • Meiosis – The process by which sporophyte produces spores that are haploid.

Life Cycle of a Plant

Life Cycle of a Plant

The life cycle of plants shows some great variation. This is due to the fact that all plants are not similar. Right from simple algae and bryophytes to the complex vascular angiosperms, there is a great amount of diversity in the structure and features. Therefore, different generations are dominant in different plants. The following figure gives you an idea of the dominant and reduced stages in the life cycle of different plants.

  • The haplontic life cycle is generally exhibited by algae.  The sporophyte generation is represented only by a one-celled zygote. There are no free-living sporophytes. The gametophyte is the dominant phase.
  • The diplontic life cycle is commonly seen in gymnosperms and angiosperms with some variations. However, an Alga called Fucus also shows this kind of life cycle. In a diplontic life cycle, the diploid sporophyte is dominant, photosynthetic and is the independent phase of the plant. The gametophyte stage is characterized by a single to a few-celled haploid gametophyte.

Bryophytes and Pteridophytes show an intermediate condition called the haplo-diplontic life cycle, where phases are multicellular. But the dominant phase differs. In Bryophytes, the dominant phase is the gametophyte and in Pteridophytes, it is the sporophyte.

Solved Questions For You

Q. What generation does the flowering plants in your garden represent- Sporophyte or gametophyte?

Ans. Flowering plants represent the sporophyte generation.

Q. In Bryophytes which stage is dominant?

Ans. Gametophyte stage is dominant in Bryophytes.

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