[Biology] Angiosperms

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WHAT IS ANGIOSPERMS?

  • Angion means Vessel, and Sperma means Seed. So, Angiosperms means seeds within vessel. The seeds of angiosperms are found in flower.
  • The Angiosperms consists of distinct group of flowering plants, and forms covered seeds.
  • Angiosperms can be said that to be the most successful group of plants.
  • Angiosperms have aroused in middle of Cretaceous period.
  • They can grow in various habitats and are known to be the most advanced group of plants with various benefits.

General Characteristics of Angiosperms:

  • The sporophyte of the Angiosperms can be differentiated into stems, leaves and roots.
  • The stamens and carpels are organized to form flower.
  • Flowers are the reproductive organs of the Angiosperm plants.
  • The root system of this group of plants is very complex; it consists of xylem, phloem, epidermis and cortex.
  • The flowers of this group undergo double fusion or triple fusion which further forms diploid zygote and triploid endosperm.
  • The seeds of the flowers get formed into fruits.
  • Flower of angiosperms is actually a modified shoot having four whorls namely:
  • Sepal
  • Petal
  • Androecium
  • Gynoecium
  • The angiosperms can either be autotrophic, parasitic, saprophytic or Insectivorous.
  • Autotrophic: Wheat, corn
  • Parasitic: Cuscutta, Santalum
  • Saprophytic: Monotrapa
  • Insectivorous: Drosera, Utricularia

Classification of Angiosperms:

  • As per the Natural system of classification, George Bentham and JD Hooker (1862-1863) classified Angiosperms into two groups,namely:
  • Monocotyledonae
  • Dicotyledonae

There are various plant family, the genera of some important plants are:

  • Ranunculaceae
  • Poacea: Paddy
  • Brassicaceae: Mustard Family plants
  • Solanacea: Potato, Tomato
  • Malvaceae: Gurhal
  • Leguminosae: Legume plants like Pea
  • Cucurbitacea: Cucurbita sp.
  • Asteraceae: Sunflower
  • Lamiaceae: Tulsi
  • Euphorbiaceae: Euphorbia sp.
  • Orchidaceae:Orchid family plants
  • Palmae: Cashewnut

Monocotyledons:

  • They monocotyledon plants have closed vascular bundle
  • The seed have single cotyledon (Mono means single)
  • The leaves of the plants are simple and generally they have parallel venation.

EXAMPLE:

  • Sugarcane
  • Banana

Dicotyledons:

  • The Dicotyledons plants have vascular bundles arranged in rings.
  • The seeds of the plants bears two cotyledons (Di means two)
  • The leaves generally have reticulate venation and the roots system is mostly tap root system.

EXAMPLE:

  • Tomato
  • Sunflower

Reproduction in Angiosperms:

  • The male sex organ in Angiopserm is stamen, and the female sex organ is Pistil/Carpel.
  • Each stamen consists of filament, and pollen grains are produced from stamen through meiosis.
  • The pistil whereas consists of one ovary where either one or many ovules are present. Female gametophytes are present in the ovules.
  • The female gametophytes are also known as embryo sac.
  • The embryo sac is formed following the Meiosis process, so the embryo sac cells are haploid.
  • Each embryo sac has three celled egg apparatus, one egg cell and two synergids along with three antipodal cells and two polar nuclei.
  • The polar nuclei fuse and forms secondary nucleus.
  • The pollen grains after its dispersal either by wind, or by animals or any other agent of pollination carried to stigma of pistil. This is known as Pollination.
  • The pollen grains germinate and the pollen tube grows through stigma and style and finally reaches the ovule.
  • The pollen tube then enters the embryo sac where two male gametes are present.
  • One of the male gametes then fuse with the egg cell and forms zygote termed as Syngamy whereas the other male gamete fuse with the diploid secondary nucleus and produces the Triploid Primary Endosperm Nucleus, also known as PEN.
  • The zygote gets developed into embryo and the Primary Endosperm Nucleus develops into endosperm which helps to give nourishment to the embryo.
  • The antipodals and synergids degenerates after the fertilisation process. During the above mentioned processes the ovules develop into seeds whereas the ovaries develop into fruits.

Life cycle and Alteration of Generation:

  • In the plants, both haploid as well as diploid cells divides by Mitosis, thus the haploid and diploid plants can be formed by this process.
  • The haploid plant body gives rise to gametes by mitosis and represents gametophyte.
  • Zygote as well follows the process of fertilization gets divided by Mitosis and helps to give rise to diploid sporophytic plants.
  • The haploid spores are produced by plant body through meiosis, then again the plant body gets divided by mitosis and forms haploid plant body.
  • During the life cycle of any sexually reproducing plant, there is alteration of generation between the gametes which produces haploid gametophyte producing gametes and diploid sporophyte producing spores.

Economic Importance of Angiosperms:

There are various economic importance’s of Angiosperms; few of them are as listed:

  • Food:
  • As grain, cereals and fruits
  • Ornamentals:
  • Angiosperms are used as Flowering plants
  • Decoration material
  • Wood:
  • Wood are obtained from Angiosperms
  • Industrial:
  • Angiosperms can be used is paper industry
  • Cosmetic industry
  • Baking industry
  • Medicines:
  • Alkaloids
  • Antibiotics
  • Environment:
  • Plants belonging to Angiosperms can be used as air purifier
  • Vegetables:
  • Plants of Angiosperms is an important food component
  • Acts as protein sources

IMPORTANT POINTS/TERMS TO REMEMBER:

  • Embryo sac
  • Egg apparatus
  • Egg cell
  • Synergids
  • Antipodal cells
  • Polar nuclei
  • Double Fertilization: The pollen tubes enter the embryo-sac where two male gametes are discharged, one of the male gametes fuses with the egg cell to form a zygote (syngamy) and the other male gamte fuses with the diploid secondary nucleus to produce the triploid primary endosperm nucleus (PEN), termed as double fertilization.

REFERENCES

  • NCERT biology; textbook for class 11. Plant Kingdom. Page no: 40-41.
  • Arihant’s handbook of Biology. Plant Kingdom. Page no: 39-41.
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