Pteridophytes and its Characteristics Class 11 Biology
In this article, I’ll sprinkle on an important topic of Plant kingdom, i.e., Pteridophytes of Class 11 Biology. So in this, you will get to know about What Pteridophytes are, General characteristics of Pteridophytes, the process of Reproduction in Pteridophytes and Alternation of Generation in Pteridophytes.
What are Pteridophytes?
Pteridophyte is derived from two words; Pteron, which in Greek means feather, and phyton means plant. So, this name was originally given to those groups of plants which have well developed feather like leaves. These plants do not bear any flowers or seeds. Hence, they are also called as Cryptogams, which means that their means of reproduction are hidden. A cryptogam, scientifically Cryptogamae is a plant (in the wide sense of the word) that reproduces by spores, without flowers or seeds.
“Cryptogamae” taken from Greek, i.e., kryptos which means “hidden” + gamae which means, “to marry”. The hidden reproduction refers to the fact that without seed being produced, cryptogams represent the non-seed-bearing plants. In fact, they are the first evolved plant group with a vascular tissue system for the transport of water and food. They are mostly found in damp and shady places. They include ferns and horse-tails. Mostly the ferns are grown as ornamental plants.
Read the article on KINGDOM PROTISTA for 11th class science Kingdom Protista and its Characteristics
General Characteristics of Pteridophytes
i. Pteridophytes are terrestrial plants, that grow in cool, moist and shady places e.g., ferns. Some members are aquatic (e.g., Marsileci, Azolla), xerophytic, that have the ability to survive in dry or with less water areas (e.g., Selaginellarupestris, Equisetum) or epiphytic (e.g., Lycopodium squarrosum).
ii. (An epiphyte is an organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water or from debris.)
iii. Majority of the Pteridophytes are herbs but a few are perennial and tree like (e.g., Angiopteris). Smallest Pteridophyte is Azolla (an aquatic fern) and the largest is Cyathea (tree fern).
iv. The plant body is sporophytic. A sporophyte is the diploid multicellular stage in the life cycle of a plant or alga. It develops from the zygote (formed by the fusion of haploid egg cell and a haploid sperm), so, each sporophyte cell, therefore, has a double set of chromosomes, one from each parent. The plant body is differentiated into root, stem, and leaves.
v. Roots are adventitious in nature, which means the root arises from any point other than the radicle or the root axis. In pteridophytes, roots arise at points along the stem. The stem is usually branched.
vi. Leaves are generally small, thin, scaly. Microphyllous leaves (a type of plant leaf with one single, unbranched leaf vein), are found in Equisetum. Plants with microphyll leaves occur early in the fossil records. Pteridophytes may also have simple and sessile (e.g., Selaginella) or large and pinnately compound (megaphyllous e.g., Dryopteris, Adiantum).
vii. Vascular tissue is present in stem and root. It consists of xylem and phloem. Xylem consists of tracheids only and phloem has only sieve tubes.
Reproduction in Pteridophytes
i. The dominant form of life in pteridophytes is the sporophyte, it produces spores through meiosis.
ii In the gametophyte stage of the life cycle, it forms gametes by mitosis. The spores are produced by the sporangia in the spore mother cells. These spores germinate to give rise to gametophytes.
iii. The gametophytes are free-living, multicellular and photosynthetic forms. They are called as the prothallus.
iv. The gametophytes require damp and cool places to grow, due to their dependence on water for reproduction.
v. The male sex organs are known as the antheridia and the female sex organs are called Male gametes are antherozoids, which are released by the antheridia.
vi. Antherozoids fertilizes the archegonia only in the presence of water. Once the fusion of the gametes occurs, a zygote is formed. This zygote produces the sporophyte, after cell division (mitosis).
vii. When the spores of the plants are similar then these plants are called homosporous plants, whereas, the heterosporous plants are the ones that have two different kinds of spores, the megaspores and the microspores. In these heterosporous plants, the megaspores and microspores germinate and give female and male gametophytes respectively.
Pteridophytes show a true Alternation of Generations:
There is a systematic feature of alternation of generations in pteridophytes. At the time of sporogenesis (the process of the formation of spore), the reduction division (meiosis) takes place and the haploid spores are formed. This represents the first stage of the gametophyte generation. Later on, fertilization takes place and a zygote is produced which represents the first stage of sporophyte generation. Hence, the gametophyte gives rise to the sporophyte by the process of syngamy (also called fertilization, which involves the complete and permanent fusion of two haploid gametes to form a diploid zygote). The sporophyte gives rise to the gametophyte by the process of meiosis. The gametophyte of sexual generation occurs between meiosis and syngamy while the sporophyte or asexual generation intervenes between syngamy and meiosis. The haploid phase (n) is the gametophyte and the diploid phase (2n) is the sporophyte. These two phases follow one another in the life-cycle, in regular succession.
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