Biology BRYOPHYTES

KEY TOPICS

`star` Introduction
`star` Structure
`star` Mode of Reproduction
`star` Importance
`star` Classification
`star` Liverworts
`star` Mosses

INTRODUCTION

● These are the first group of plants to colonize the land.

● Since, these plants can live in soil but are dependent on water for sexual reproduction, they are also called Amphibians of the plant kingdom.

`color{brown}"Habitat"` :

● Thay are found commonly growing in moist shaded areas in the hills.

●They usually occur in damp, humid and shaded localities.

STRUCTURE

● The plant body of bryophytes is more differentiated than that of algae.

● It is thallus-like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids.

● They lack true roots, stem or leaves. They may possess root-like, leaf-like or stem-like structures.

LIFE CYCLE

●The main plant body or the dominant phase of the life cycle of the bryophyte is haploid. It produces gametes for sexual reproduction and is hence called a gametophyte.

●The sex organs in bryophytes are multicellular and are covered by a sterile jacket layer.

●The male sex organ is called antheridium. They produce biflagellate antherozoids.

●The female sex organ called archegonium is flask-shaped and produces a single egg.

●The antherozoids are released into water where they come in contact with archegonium where it fuses with the egg within it to produce the zygote.

●Zygotes represents the first cell of sporophyte. They do not undergo reduction division immediately. They undergo mitotic division and produce a multicellular body called a sporophyte.

●The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.

●Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores. These spores germinate to produce gametophyte. Thus spores represent the first cell of sporophyte.

IMPORTANCE

●Bryophytes in general are of little economic importance but some mosses provide food for herbaceous mammals, birds and other animals.

● Species of 𝘚𝘱𝘩𝘢𝘨𝘯𝘶𝘮, a moss, provide peat that have long been used as fuel, and because of their capacity to hold water as packing material for trans-shipment of living material.

●Mosses along with lichens are the first organisms to colonise rocks and hence, are of great ecological importance. They decompose rocks making the substrate suitable for the growth of higher plants.

●Since mosses form dense mats on the soil, they reduce the impact of falling rain and prevent soil erosion.

CLASSIFICATION

● Bryophytes are broadly divided into Liverworts and Mosses.

LIVERWORTS

●`color{maroon}"Habitat"`: They grow usually in moist, shady habitats such as banks of streams, marshy ground, damp soil, bark of trees and deep in the woods.

●`color{maroon}"Structure"`: The plant body of a liverwort is thalloid, The thallus is dorsiventral and closely appressed to the substrate. The leafy members have tiny leaf-like appendages in two rows on the stem-like structures.

●`color{maroon}"Mode of Asexual Reproduction"`: It takes place by either
`star` Fragmentation of thalli, or by
`star` The formation of specialised structures called gemmae (sing. gemma).
Gemmae are green, multicellular, asexual buds, which develop in small receptacles called gemma cups located on the thalli. The gemmae become detached from the parent body and germinate to form new individuals.

●`color{maroon}"Mode of Sexual Reproduction"`: During sexual reproduction,
`star` male (antheridium) and female (archegonium) sex organs are produced either on the same or on different thalli.
`star` The sporophyte is differentiated into a foot, seta and capsule.
`star` After meiosis, spores are produced within the capsule. These spores germinate to form free-living gametophytes.

●`color{maroon}"Example"`: 𝘔𝘢𝘳𝘤𝘩𝘢𝘯𝘵𝘪𝘢.

MOSSES

●`color{maroon}"Habitat"`: They have been found in habitats ranging from the humid tropics to the polar regions, fallen logs to lakes, rivers, and streams. In fact, they have been found just about everywhere, except in salt water.

●`color{maroon}"Dominant Structures"`: The predominant stage of the life cycle of a moss is the gametophyte which consists of two stages.
`star`The first stage is the protonema stage, which develops directly from a spore. It is a creeping, green, branched and frequently filamentous stage.
`star` The second stage is the leafy stage, which develops from the secondary protonema as a lateral bud. They consist of upright, slender axes bearing spirally arranged leaves. They are attached to the soil through multicellular and branched rhizoids. This stage bears the sex organs.


●`color{maroon}"Mode of Vegetative Reproduction"`: Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema.

●`color{maroon}"Mode of Sexual Reproduction"`:
`star` In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots.
`star` After fertilisation, the zygote develops into a sporophyte, consisting of a foot, seta and capsule.
`star` The sporophyte in mosses is more elaborate than that in liverworts. The capsule contains spores. Spores are formed after meiosis. The mosses have an elaborate mechanism of spore dispersal.

●`color{maroon}"Example"`: 𝘍𝘶𝘯𝘢𝘳𝘪𝘢, 𝘗𝘰𝘭𝘺𝘵𝘳𝘪𝘤𝘩𝘶𝘮 𝘢𝘯𝘥 𝘚𝘱𝘩𝘢𝘨𝘯𝘶𝘮

 
SiteLock