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Shrinithi Mahadevan

Life Cycle of Seedless Vascular Plants Study Guide

The life cycle of seedless vascular plants consists of alternating generations between a haploid gametophyte stage and the diploid sporophyte phase.

Introduction

The difference between vascular and non-vascular plants is that non-vascular plants do not have differentiated tissues, whilst vascular plants have differentiated tissues to transport water and other nutrients within their bodies. Unlike vascular plants, non-vascular plants do not possess roots, stems, or leaves.

Seedless vascular plants are a part of the tracheophytes. They possess vascular tissues such as xylem and phloem, but do not produce seeds or flowers for propagation. Examples of seedless vascular plants include ferns, clubmosses, whisk ferns, and horsetails.


Types of Seedless Vascular Plants

Seedless vascular plants contain vascular tissue, but they do not produce flowers or seeds. They are divided into four types: club mosses, whisk ferns, true ferns, and horsetails.

Club Mosses, or Lycopodiales, belonging to the phylum Lycphyta and order Lycopodiopsida, have a stem and microphylls, small leaves with one vein.

Club mosses Source

Whisk Ferns belong to phylum Monylophyta and class Psilotopsida. They have a stem that branches dichotomously, but they do not have roots and leaves.

Whisk Ferns Source

True Ferns belong to the phylum Monylophyta and class Polypodiopsiada and are characterized by their frond leaves with the curling tips, which are called fiddleheads.

True Ferns Source

Horsetails belong to the phylum Monylophyta and the class Equisetopsida. They have a stem made up of joints and nodes, so they are also called Arthrophyta, and their branches exist as whorls. The leaves are needle-shaped, so photosynthesis does not occur within them; rather, photosynthesis takes place within the stems of the horsetails.

Horsetails Source


Life cycle of Seedless Vascular Plants

The major difference between the life cycles of seedless and seed plants is that the seedless plants produce spores, and the seed plants produce seeds for propagation.

  • The life cycle of a seedless plant starts with the mature fern frond, which has groups of sporangia on its underside called sori. Haploid spores are produced within the sori by the process of meiosis and are released into the atmosphere.

  • Some spores which land on a suitable base germinate and form a structure called a prothallus. This is a Gametophyte and is heart-shaped in appearance. It is attached to the base with the help of thin rhizoids, which are filamentous by nature.

  • The gametophytes produce the male antheridia and the female archegonia. Haploid sperms are produced by the antheridia and are flagellated to swim towards the female archegonia. The eggs are produced by the archegonia, who also release a chemoattractant into their surroundings to attract the male sperms. The sperms swim towards the haploid eggs in wet conditions and fertilize them to form a diploid Zygote.

Life cycle of seedless vascular plant Source

  • The zygote then develops into a fern Sporophyte by mitosis. This fern sporophyte phase is the dominant phase of the entire life cycle of vascular seedless plants.

  • The new sporophyte emerges from the gametophyte prothallus and develops by mitosis into a mature diploid sporophyte of a fern with fronds. Hence, the seedless vascular plant life cycle repeats, starting with the haploid spores.

Non-vascular plants do not have a dominant sporophyte stage, and instead have a dominant gametophyte stage in their life cycle.


Functions of Seedless Vascular Plants

  • Ferns and other seedless vascular plants prevent soil erosion. They promote the weathering of rocks and thus quicken the formation of the top layer of soil.

  • Ferns harbor nitrogen-fixing cyanobacteria symbiotically and thus help in the conversion of atmospheric nitrogen into suitable nitrogen compounds, which are important nutrients for the other plants within their aquatic habitat. This is seen in the water fern called Azolla.

  • Ferns serve as food sources. Fiddleheads of the "bracken fern" Pteridium aquilinum are consumed as a popular side dish in French cuisine. They are also a traditional food of native Americans in the spring season.

  • Ferns are used medicinally. The "liquorice fern", Polypodium glycyrrhiza, has medicinal properties used by Native Americans to soothe sore throats. It also has sweet-tasting rhizomes which are utilized by the tribes of the pacific northwest coast as a sweetener.

  • Different varieties of ferns are extensively used as ornamental plants, and due to their luxurious growth even in low sunlight conditions, they are the favorites amongst house plants.


Conclusion

  • There are four types of seedless vascular plants: club mosses, whisk ferns, true ferns, and horsetails.

  • The life cycle of a seedless vascular plant begins when haploid spores are produced by the sori and released into the atmosphere. They germinate into a gametophyte called the prothallus.

  • The gametophyte makes the male antheridia which produce sperm and the female archegonia which produce eggs. The gametophyte becomes a zygote when the egg is fertilized by the sperm.

  • The zygote divides into a fern sporophyte via mitosis. The new sporophyte emerges from the prothallus and develops into a mature fern with fronds. The life cycle repeats starting with the haploid spores.

  • Ferns prevent soil erosion, assist in nitrogen fixation, are used for food and medicine, and serve as ornatmental plants.


FAQs

1. What are the differences between the life cycles of seedless and seed plants?

  • The major difference between the life cycles of seedless and seed plants is that the seedless plants produce spores, and the seed plants produce seeds for propagation.

2. How do seedless plants reproduce?

  • Seedless plants reproduce asexually by producing spores that later form gametophytes. The gametophytes reproduce sexually by producing sperms and eggs.

3. What stage is the longest part of the vascular seedless plant life cycle?

  • The sporophyte or diploid stage is the longest stage in the life cycle of seedless vascular plants.

4. How is the life cycle of seedless vascular plants different from that of non-vascular plants?

  • Seedless vascular plants have a dominant sporophyte stage in their life cycle, whilst the non-vascular plants do not have a dominant sporophyte stage. Non-vascular plants have a dominant gametophyte stage in their life cycle.

5. What are the differences between non-vascular and seedless vascular plants?

  • Non-vascular plants do not have any differentiated vascular tissues, whilst the seedless vascular plants have vascular tissues to transport water and other nutrients within their bodies. Non-vascular plants do not possess roots, stems, or leaves, but seedless vascular plants have roots, stems, and leaves.

6. What are the four types of seedless vascular plants?

  • Club mosses, whisk ferns, true ferns, and horsetails.

7. What are the functions of seedless vascular plants?

  • Soil erosion prevention, nitrogen fixation, food and medicine, ornamental plants.

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Sources

  1. Life Cycle of Seedless Vascular Plants. https://www.ck12.org/c/biology/life-cycle-of-seedless-vascular-plants/lesson/Life-Cycle-of-Seedless-Vascular-Plants-BIO/ Accessed 11 Dec, 2021.

  2. A Horsetail's Life Cycle. https://sciencing.com/horsetail-s-life-cycle-5673810.html Accessed 11 Dec, 2021.

  3. Seedless Vascular Plants. http://pressbooks-dev.oer.hawaii.edu/biology/chapter/seedless-vascular-plants/ Accessed 11 Dec, 2021.