Botany and Plant Science

In bryophytes like mosses and Riccia, the gametophyte is the dominant, independent, and photosynthetic phase of the life cycle. In pteridophytes (ferns), gymnosperms (Cycas), and angiosperms, the sporophyte is the dominant phase.

In Riccia, true elaters are completely absent. Instead, some of the potential spore mother cells do not undergo meiosis and instead degenerate to form sterile nurse cells, which provide nutrition to the developing spores.

In Riccia, the sex organs (antheridia and archegonia) are not exposed on the surface but are deeply embedded singly in chambers on the dorsal surface of the thallus.

Mosses are characterized by a leafy gametophore with stem-like and leaf-like structures, the complete absence of true vascular tissues, and a filamentous juvenile gametophyte stage called the protonema. Therefore, all the given statements are correct.

The sporophyte (sporogonium) of Riccia is the simplest among bryophytes, consisting solely of a capsule. It completely lacks a foot and a seta.

Since the sporophyte of Riccia consists only of a capsule and lacks a stalk (seta), it remains completely embedded within the tissue of the gametophytic thallus.

Both Riccia and Marchantia (liverworts) have unicellular, unbranched rhizoids. These can be either smooth-walled or tuberculate, but they are always single-celled and do not branch.

The peristome teeth in moss capsules are hygroscopic structures that respond to changes in humidity, aiding in the gradual and effective dispersal of spores.

When a moss spore germinates, it first produces a filamentous, branched, green, and algal-like juvenile stage called the protonema, from which the leafy gametophores later develop.

The sporophyte of Anthoceros is unique because it possesses a basal intercalary meristematic zone situated between the foot and the capsule, which allows for continuous, indeterminate growth of the sporophyte.

In Anthoceros, the ventral surface of the thallus contains slime pores (mucilage clefts) through which mucilage is secreted, and these pores also serve as entry points for symbiotic Nostoc colonies.

Stomata in mosses are restricted to the sporophyte generation, specifically on the apophysis region of the capsule. The gametophytic structures like the stem and leaves lack stomata entirely. This localization helps in gas exchange and transpiration during the development of the capsule.

The stem (axis) of the Funaria gametophyte is covered by a single-layered epidermis. This epidermis lacks both a protective cuticle and stomata, which allows for direct absorption of water and gases. Stomata in Funaria are only found on the apophysis of the sporophytic capsule.

The archegonium of Riccia is a flask-shaped structure consisting of a neck and a swollen venter. The neck contains a row of 4 neck canal cells, while the venter contains a single venter canal cell and a single large egg cell (oosphere). This cellular composition is characteristic of many primitive bryophytes.

Paraphyses are sterile, multicellular, uniseriate hair-like structures found interspersed among the sex organs in the receptacles of mosses. They help in retaining water through capillary action and protect the developing sex organs from drying out. Apophysis and hypophysis, on the other hand, refer to parts of the sporophyte capsule.