Question

Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Answer 1

Hint: Archegonia is the female sex organ containing a large ovum or egg. In the plant kingdom, it is present in three groups- two of them do not form seeds while the third one forms seeds but not fruits.

Complete step by step answer:
Each archegonium in all the three groups is a flask- shaped structure with a lower swelled portion called venter containing egg and two or three- celled neck followed by venter canal cells. The three groups of plants that bear archegonia are bryophytes, pteridophytes, and gymnosperms. Bryophytes and pteridophytes do not bear seeds. Bryophytes are the amphibians of the plant kingdom as they live in soil but depend on water for sexual reproduction. E.g Marchantia. Gymnosperms are the plants that form seeds but not fruits. E.g. Cycas
Pteridophytes are the first terrestrial plants bearing vascular tissues for the conduction of food and water. E.g Adiantum.
Their life cycle is as follows:
- The main plant body of Pteridophyte is a sporophyte that is differentiated into true roots, stem, and leaves. Sporangia bearing leaves i.e sporophylls are present either singly or condensed in some species to form a compact structure known as strobili or cones.
- Diploid spore mother cells are present in these sporangia. They undergo meiosis one time to produce 4 haploid spores.
- The haploid spores are released from the sporangium and dispersed by wind currents to a new substratum.
- After falling on suitable soil, the germination of spores produces a green, thalloid, and free- living gametophyte known as prothallus. It represents the gametophyte stage in its life cycle.
- The prothallus bears both the type of sex organs i.e antheridium or male sex organ and archegonia or female sex organ. Antheridium produces motile sperms that require water to make its way to the mouth of archegonia.
- Their fusion produces a diploid zygote that divides repeatedly and forms an embryo. This marks the beginning of an independent sporophyte stage.

Note:
- Bryophytes and pteridophytes are cryptogams as their sex organs are hidden and seeds and flowers are absent. Gymnosperms are the phanerogams as sex organs are exposed and seeds are formed.
- In gymnosperms, after fertilization, the seeds developed from the ovule, are not covered i.e. are naked. Thus gymnosperms are fruitless plants.