BSc 1st Year Botany Bryophytes Sample Model Practice Question Answer Papers
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- BSc 1st Year Botany Bryophytes Sample Model Practice Question Answer Papers
Index for Botany Bryophytes
The general characters of Bryophytes: Page 1
Economic importance of Bryophytes: Page 2
Important groups of Bryophytes: Page 3
Q.1. Give a brief account of the general characters of Bryophytes.
Ans.1. The term Bryophyta was coined by Robert Braun in 1864.
The Bryophytes include the simplest and most primitive members of the Embryophyta. This includes about 960 genera and 24,000 species. They occupy an important place in the plant kingdom although they have little economic value. They are cosmopolitan in distribution, mostly moist and shade-loving but terrestrial. These plants occur in abundance in temperate regions and are most common in rainy seasons. They usually grow in tufts or cushions and contribute much as a whole to the green color of mountains and forests.
With the exceptions of a few water forms, e.g., Riccia fluitans, Ricciocarpus, Riellia, and the Bryophytes are the simplest and truly land inhabiting plants, present on moist and shady places. They may be regarded as incompletely adopted to land conditions, because they require water for vegetative growth, fertilization and for other processes of life and hence are commonly called as “amphibians of plant kingdom”.
Distribution and occurrence
Bryophytes are cosmopolitan in distribution and are usually found in all places where plant can live except sea. However, Shackette in 1961 observed some bryophytes in sea. Bryophytes are of common occurrence in the moist mountain forests of tropics and subtropics as in the Arctic Tundra.
In Antarctic region the bryophytes are few. The bryophytes have been reported at 18,000 to 20,000 feet attitudes on Himalayas. In India eastern Himalayas are richest in bryophytic flora.
Usually most of bryophytes are damp loving terrestrial plants and their common and favourite habitats are:
(1) Shaded ground.
(2) Moist rocks.
(3) Barks of trees.
(4) Moist walls.
Certain bryophytes e.g., Riccia fluitans, Ricciocarpus natans, Fontnalis antipyretica and Rellia sps. are true aquatic plants. Certain bryophytes grow in bogs, e.g., Sphagnum species, Leucobryum glaucum, Drepanocladue fluitans, etc. Certain bryophytes such as Polytrichum, junipertinium occur in dry sheaths and endure drought conditions. Tortula desertorum is found in deserts.
Certain members of Jungermanniales and Musci and all species of Dendroceros are found as epiphytes on trunks and branches of trees of many tropical rain forests. (BSc 1st Year Botany Bryophytes Sample Model Practice Question Answer Papers)
Usually bryophytes are autotrophic but some may be saprophytic e.g., Buxbaumia aphylla, Cryptothallus mirabilis, etc.
Size and Form
The members of Bryophytes are smaller is size ranging from few millimeters to several centimeters. The largest known bryophyte-Dawsonia is nearly 70 cm. in length. (BSc 1st Year Botany Bryophytes Sample Model Practice Question Answer Papers)
The plant body is thalloid and liverlike in the members of Hepaticeae while it is small plant like having ‘leaf’ ‘stem’ and rhizoids in the musci.
The plants are mostly green in colour i.e., autotrophic in nutrition.
The plant represents the gametophytic generation and after gametic fusion it forms sporophyte which is normally dependent on gametophyte. The sporophyte after reduction division again forms the gametophyte. Thus, there is distinct alternation of generation.
In bryophytes, reproduction takes place by means of vegetative (asexual) and sexual methods.
Bryophytes largely multiply by means of vegetative reproduction. This takes place by death of older parts, e.g., in Riccia, Marchantia, Anthoceros, Notothylas; by branch tips as in several species of Riccia; by adventitious branches, as in several species of Riccia, Marchantia and Anthoceros; by gemmae as in the species of Marchantia, Lunularia, Funaria, etc., by tubers as in species of Riccia Anthoceros, etc., by primary and secondary protonema as in species of Funaria and other mosses.
All bryophytes are oogamous. The spermatozoids (male gametes) are motile and small while the eggs (female gametes) are large and non-motile.
The gametes (male and female) are produced within multicellular organs (antheridia and archegonia) in which there is an outer sterile layer of jacket cells.
The antheridium (male organ) consists of a central mass of androcytes enclosed by a single layer of sterile jacket cells. Each androcyte metamorphoses into a biflagellate spermatozoid.
The archegonium (female organ) is a multicellular flask-like structure. The basal swollen portion is venter and contains an egg (oosphere) in it. The elongated neck contains neck cells.
Alternation of generations
The life cycle of bryophytes consists of two distinct phases—
(i) the gametophytic phase, and
(ii) the sporophytic phase.
The two phases come one after the other in an alternating manner. The gametophytic phase is followed by sporophytic phase and the later is followed by gametophytic phase. Occurrence of these two generations one after the other in the life cycle is called alternation of generations. The plant bodies of the two generations differ in form and morphology. Thus, the bryophytes exhibit heterologous type of alternation of generations.
The Life Cycle
The life cycle of bryophytes consists of two distinct phases or generations:
(i) the gametophytic generations (the gametophyte) and
(ii) the sporophytic generation (the sporophyte).
The gametophytic phase or the gametophyte is mainly concerned with the production of gametes (or sexual reproduction). Each cell of the gametophyte has a single set of chromosome number i.e., haploid (n). It begins with the productions of haploid spores. The spores fall on suitable substratum and germinate to produce gametophytic plant body.
The gametophyte is an independent plant body which may be thalloid or leafy axis. Reaching to certain stage of maturity, it develops sex organs. The male sex organ is antheridium, which produces biflagellate motile male gametes called antherozoids. The female sex organ is archegonium, which produces non-motile female gamete called egg. The sexual reproduction is oogamous.
The haploid, motile antherozoid fuses with the haploid, non-motile egg, and forms diploid zygote. The gametophytic generation ends with the formation of diploid (2n) zygote.
The zygote is the first cell of sporophyte generation. It is retained within the archegonium and multiplies to produce the embryo, which later develops into sporophytic plant body the sporogonium. The sporophyte is dependent on gametophyte and it remains attached to it throughout its life.
The spore mother cells are produced from the sporogenous tissue in sporophyte divide by meiosis. Each diploid spore mother cell divides by meiosis and forms 4 haploid spores. The sporophytic generation ends with the formation of spores and the gametophytic generation begins.
Characteristic Features of the Bryophytes
- They usually occur on moist and shady places.
- The plant body is green in colour and have no differentiation of the leaf, root and stem. This is either thalloid in appearance (Liver worts) or may have a differentiation of ‘leaf stem and rhizoids Musci.
- The plant body is gametophyte.
- Plant remains attached to the substratum by means of rhizoids, whose function is fixation and absorption. They may be unicellular or multicellular and smooth walled or tuberculated.
- Internal structure of the thallus or plant body does not show any vascular tissue like xylem or phloem.
- The gametophytic plant body reproduces both by vegetative and sexual means. (BSc 1st Year Botany Bryophytes Sample Model Practice Question Answer Papers)
- The sexual reproduction is of oogamous type and takes place by definite male (Antheridium) and female (Archegonium) reproductive organs.
- Antherozoids are motile, biciliated structure, produced in large numbers.
- Archegonium is multicellular flask shaped organ having neck canal cell, ventral canal cell and an egg.
- Water medium is essential for fertilization.
- Fusion of antherozoid and egg results in the formation of Zygote or Oospore which is diploid (sporophyte) in nature.
- The oospore develops into the sporophyte which is usually differentiable into foot, seta and capsule.
- Spores are formed in capsule after reduction division. All spores are alike.
- Spores on germination give rise to the gametophytic plant body usually through protonema.
- There is a distinct alternation of generation.