Gymnosperm- Introduction, characteristics,types- for every- neet aspirants

Gymnosperm(acrogymnospermae)

Introduction

Gymnosperm are advance plant. 'Gymnosperm' word come from a Greek word that mean(naked seed), gymno means naked and sperm means seed. Main plant body is sporophyte. The seed is not enclosed by fruit or ovary Neither be before fertilization nor after fertilization. The sporangium convert into seed and integument convert into seed coat. Main period of gymnosperm nearly Jurassic period, this time does not support the gymnosperm. Gymnosperm have lowest species in algae, bryophyta, pteridophyta, gymnosperm, angiosperm. They are non flowering plant.eg: conifers cycus, ginkgo etc.











Characteristics

* They have needle like leaves.

*They found in colder areas or hilly areas but some gymnosperm found in warmer areas such as cycads and araucaria.

*They are not differentiate into style ovary and stigma.

*They do not produce flower.

*In some plant have no female cone this type of plant called unisexual plant such as cycus.

*In some plant main and female cone present in same plant this type of plant called by sexual plant such as pinus.

*Gymnosperm are more older than angiosperm on the evolutionary scale.

*Pollination direct through the wind.

*Seed have endosperm for plant growth and development of plant.

*Gymnosperm are formed directly on the surface of megasporophyll.

* They have two type of cone male cone and female cone.

Habitat

They are mostly found in colder areas where snowfall occurs such as hilly areas. 

Structure of cycus:

They are well developed plant and main plant body is sporophyte. they have an unbranched stem, pinnately compound leaf and tap root. Cycas plant have coralloid root in which present anabaena and nostoc (cyanobacteria) which fixing of nitrogen in atmosphere. Cycas is unisexual plant because they have no female cone.







 

Structure of conifers:

Conifers( pinus and cedrus) have branched stem,needle shape leafs and leaf adapted with stand( humidity, temperature, wind speed and they have sunken stomata( stomata which deep inside the leaf) which prevent the transpiration and have thick cuticle. They have tap root and present Hyphae of the fungus on the root which is known as mycorazia( fungal association with higher plant root). Pinus seed not germinate without mycorazia or hyphae of fungi because without Hyphae they cannot absorb water.pinus plant is bisexual plant because male and female cone present in same plant.

Male and female cone in gymnosperm

The spores are always produce inside the cone in gymnosperm. two type of cone in gymnosperm male cone and female cone. Male cone only form microsporangia on the microsporophyll and microspore. But In female cone form megasporangia or ovule on the megasporophyll and have spirally arrangement of leafs.





Female cone 

In female cone megasporophyll ( leaf) spirally arranged. Nucellus present inside integument in megasporangium. One cell of nucellus act as megaspore mother cell (2n). Undergo meiosis. After meiosis formed four cell known as mega spores three megaspore degenerate and one is functional cell. This functional cell develop into female gametophyte, which depend on sporophyte and Two or more archegonium form. Polen release gammat near mouth of archegonium and form zygote. If  more than one zygote is form in archegonium this stage called polyembryonic stage. Megasporangium or ovule developed into seed and integument developed into seed coat. Zygote formed multicellular embryo (2n). This embryo is sporophyte of the next generation. Endosperm (nutritive tissue) develop from female gametophyte. This seed is naked because ovary is not present.






Male cone

Main cone is smaller as compared to female cone. Microsporangium developed in many microspore through miosis. Each microspore form a multicellular structure called pollen grain. Pollen grains is a gametophyte rather than gamete, cabinet present inside the pollen grain. Punam grains direct move through the wind.















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