Diplontic Life Cycle

The Diplontic life cycle refers to the life cycle of organisms, which is dominated by the diploid stage. Plants and algae show alternation of generation. All the plants showing sexual reproduction alternate between two multicellular stages, viz. Haploid gametophyte and diploid sporophytes.

The diploid stage or sporophyte is the dominant and independent stage of the plant in the diplontic life cycle. It performs photosynthesis, while the haploid phase is represented by single-cell gametes or few celled gametophytes.

At the diploid stage, meiosis is typically responsible for the production of zygotes and gametes, while mitosis is more commonly observed.

Table of Contents

Diplontic Life Cycle Examples

Types of Biological Life Cycle

Difference Between Diplontic and Haplontic Life Cycle

[Frequently Asked Questions](#Frequently Asked Questions)

Diplontic Life Cycle Examples

All phanerogams or seed-bearing plants, as well as some algae, demonstrate the Diplontic life cycle.

Brown Algae Fucus has a diplontic life cycle, which is represented by the main plant body, the thallus, being diploid. The haploid phase is formed by meiosis in reproductive cells present in the conceptacles, which produce oogonia and antheridia, respectively producing egg and sperm. These then fuse to form a diploid zygote (2n), which divides mitotically to form the thallus. Other algae which show the diplontic life cycle include Cladophora and Acetabularia, as well as diatoms.

All the seed-bearing plants, namely Gymnosperms and Angiosperms, demonstrate a diplontic life cycle.

#Types of Biological Life Cycles

Plants that undergo sexual reproduction alternate between haploid and diploid stages, known as alternation of generations. During this process, both haploid and diploid cells can divide mitotically and proliferate to produce gametophyte (n) and sporophyte (2n), respectively.

Based on the dominant stage of their life cycle, they are categorized into three types:

  1. Haplontic Life Cycle – The dominant stage is the haploid gametophyte, while the diploid sporophyte is only represented by the zygote. The zygote divides meiotically to form haploid cells, which then undergo mitosis to form multicellular haploid organisms. The diploid stage is not free-living. Examples of haplontic life cycle include: Green algae, such as Volvox, Spirogyra, Chlamydomonas, etc.

  2. Diplontic Life Cycle - The diploid sporophyte is the dominant stage, exhibiting gametic meiosis. Examples of organisms with a diplontic life cycle include: Fucus (brown algae), Gymnosperms, Angiosperms, etc.

  3. Haplodiplontic Life Cycle – Here both haploid and diploid stages are multicellular, with the gametophyte dominant and free-living, while the sporophyte is a small and short-lived phase that is dependent on the gametophyte, such as in Bryophytes.

The sporophyte is the independent and free-living dominant stage in pteridophytes, alternating with short-lived gametophyte.

Some algae such as Ulva, Polysiphonia, and Ectocarpus, as well as Kelps, have a haplodiplontic life cycle.

Also Explore:

| MCQs on Taxonomy of Angiosperms |

| MCQs on Algae |

Difference Between Diplontic and Haplontic Life Cycle

Diplontic life cycles involve two alternating generations, one of which is diploid and the other is haploid. Haplontic life cycles involve only one haploid generation, with meiosis occurring at some point to produce haploid spores or gametes.

| Diplontic Life Cycle | Haplontic Life Cycle |

| Sporophyte (2n) |

| Dominant phase: Free-living, independent, and photosynthetic | Conspicuous and represented by Zygote or few-celled sporophytes |

| Gametophyte (n) | : The haploid stage in the life cycle of a plant or alga that produces gametes and gives rise to the sporophyte. |

| Conspicuous and represented by gametes, i.e. egg cell and sperm or few-celled gametophyte | Dominant phase, which is independent, free-living and performs photosynthesis |

| Mitotic Division |

| The zygote divides mitotically to give rise to a new plant. | Haploid cells divide mitotically to produce gametes, which then fuse together to form a zygote, which then divides mitotically to give rise to a new plant. |

| Meiosis Division |

| Gametes are produced by meiosis division. | The zygote divides meiotically to form haploid cells, which proliferate by mitosis. |

| Examples |

| Angiosperms, Gymnosperms, some algae such as Fucus, Cladophora, etc. | Most of the algae such as Volvox, Spirogyra, etc. |

| Angiosperms, Gymnosperms | Most of the algae such as Fucus, Cladophora, Volvox, Spirogyra, etc. |

Frequently Asked Questions

What is a Diplontic Life Cycle?

All seed-bearing plants, the gymnosperms and angiosperms, demonstrate a diplontic life cycle, whereas bryophytes and most green algae demonstrate a haplontic life cycle.

Algae have a life cycle that includes both sexual and asexual reproduction.

The three types of the biological life cycle are haplontic, diplontic and haplodiplontic life cycle. The brown algae Fucus shows a diplontic life cycle. The haplontic life cycle is seen in most green algae. Some algae such as Ulva, Polysiphonia, Ectocarpus, Kelps have a haplodiplontic life cycle.

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