Kingdom Plantae – The Division Bryophyta

Kingdom Plantae – The Division Bryophyta

For the sake of convenience organisms included in Plantae can be divided into two broad classifications viz. nonvascular (Bryophyta) and vascular (Tracheophyta) plants. Although this grouping is not according to any specific system of classification however it does reflect resemblances and dissimilarities amongst numerous groups of plants. Each classification (division) is divided into Subdivisions, Classes, Subclasses, and other taxonomic ranks.

In this article, you will learn about the division Bryophyta.

The very first plants to colonize land were the bryophytes. They are typically thought to have actually developed from green algae. The Bryophytes are poorly adapted to reside on land and are generally confined to damp shady locations. These plants are devoid of specialized conducting (xylem and phloem) and strengthening tissues.

Just the process of diffusion and osmosis assists in the transport of water and minerals as well as in the transport of prepared food and other substances. The plant body is with a proper cuticle or has a very thin one. The water is taken in by the basic surface of the plant. The bryophytes are stated to be the amphibians of the plant world due to the fact that they cannot live far from water. They need water for reproduction.

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Characteristics of Bryophyta
  • The bryophytes are non-vascular flowerless plants.
  • These plants show a regular alternation of heteromorphic (morphologically different) generations.
  • They have a dominant independent free-living gametophyte. This might be thalloid as in lots of liverworts or is differentiated into structures resembling to stem, leaves and absorbing and anchoring organs, rhizoids, as in mosses and some liverworts.
  • The gametophyte produces a sporophyte, which is a less conspicuous generation, partially or absolutely reliant upon the gametophyte for its nutrition.
  • The sporophyte normally includes the foot, seta, and capsule. The sporophyte is diploid (2n) which produces in sporangia one kind of haploid spores (i.e., it is homosporous) by meiosis.
  • The spores sprout and trigger gametophyte which is likewise haploid. Multicellular male and female sex organs i.e., antheridia and archegonia respectively, are born upon gametophyte either on very same or different plants. These sex organs are multicellular and protected by a sterilized covering of cells.

Gametes are produced by mitosis. Male gametes produced within antheridia are called antherozoids; antherozoids are motile and constantly produced in a great number. Female gametes formed within archegonia are called eggs. A single egg is formed in each archegonium.

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Fertilization and Development

Fertilization takes place in water. Antherozoids (n) are drawn in towards archegonia (n) chemotactically. A single antherozoid fuse with an egg (n) thus accomplishing fertilization which leads to the development of the diploid zygote (2n). The zygote is kept within the female sex organ (archegonium) for a long time. After a resting period, the zygote establishes through mitotic divisions into a diploid embryo. The embryo ultimately becomes a sporophyte which is likewise diploid.

The entire development of sporophyte thus takes place within the gametophyte plant body. Even when the sporophyte is completely developed it remains attached to the gametophyte for nourishment and protection because it does not consist of chloroplasts and is unable to perform photosynthesis.

Alternation of Generation

There is an alternation of generations in the life process of bryophytes i.e., multicellular haploid gametophytic (gamete producing) generation alternates with the multicellular diploid sporophytic (spore-producing) generation. It is a really crucial phenomenon, which supplies constant genetic variations and choice for the best genetic makeup for survival and adaptation in the changing environment(s).

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Alternation-of-Genera

Adaptation to Terrestrial Habitat

In general, bryophytes established the following adaptive characters for the terrestrial environment:

  1. The formation of a compact multicellular plant body helped in the conservation of water by reducing cell area exposed to dryland conditions. The presence of a cuticle additionally decreases the loss of water by evaporation.
  2. Development of photosynthetic tissues into special chambers for the absorption of carbon dioxide without losing much water and direct exposure to light.
  3. Development of unique structures like rhizoids for the absorption of water and anchorage.
  4. Heterogamy (production of two types of gametes) is evolved, forming nonmotile egg containing stored food and motile sperms.
  5. Gametes are produced and safeguarded by the special multicellular organs (antheridia and archegonia).
  6. The multicellular embryo is formed which is maintained and protected inside the female reproductive body throughout its development.
  7. Alternation of spore-producing generation (sporophyte) with gamete producing generation (gametophyte) enabled the plant to produce and evaluate the very best genetic recombinations for adapting to the versatile terrestrial conditions.