Home Plant kingdom Gymnosperms

Gymnosperms

by Ramneet Kaur
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Gymnosperms

Belong to the group Phanerogams i.e., seed bearing plants. They have naked seeds (not enclosed within a fruit). They are mainly xerophytes.

  • Have diplontic life cycle.
  • Plant body is the sporophyte & the gametophytic generation is very much reduced.
  • Sporophyte is well differentiated into root, stem & leaves.
  • Roots: Tap root system.
  • Stem: Thick, woody with scars of fallen leaves.
  • Leaves are 2 types: foliage leaves & scale leaves.
  • They are either monoecious or dioecious.
  • Secondary growth occurs.
  • They are heterosporous and bear male & female cones.
MALE REPRODUCTIVE PART:
  • Male cones are smaller in size & short lived.

They consist of spirally arranged microsporophylls.

Microsporophyll bear microsporangia inside which the microspores/pollens are produced after meiosis.

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Pollen/microspore starts dividing in the microsporangium.

They produce 1-2 prothallial cells, a generative cell & a tube cell.

Further development occurs after pollination.

The generative cell divides to form body cell & stalk cell. The body cell then produces 2 male gametes. Tube cell forms the pollen tube carrying the male gametes.

FEMALE REPRODUCTIVE PART:
  • Female cones are larger in size.

They consist of spirally arranged megasporophylls.

Megasporophyll bear megasporangia.

Megasporangia/ovule is orthotropous type.

Inside ovule develops megaspore mother cell that undergoes meiosis to form 4 megaspores, 3 of which degenerate.

The 4th functional megaspore forms the female gametophyte, that possesses 2-8 archegonia. Egg are produced in archegonia.

  • Pollination is anemophilous.
  • Fertilization occurs in archegonia.
  • Development of embryo is meroblastic.
  • The zygote divides to form the embryo having cotyledons, plumule & radicle.
  • Polyembryony occurs.
  • Ovule matures into seed & the female gametophyte forms the endosperm.

Divided into 4 classes:

Coniferopsida: e.g., Pinus, Abies, Cedrus.

Cycadopsida: e.g., Cycas, Zamia.

Ginkgopsida: e.g., Ginkgo.

Gnetopsida: e.g., Gnetum, Ephedra, Welwitschia.

PINUS:

  • Mycorrhizal roots occur.
  • Stem shows monopodial branching.
  • Simple, needle-shaped leaves.
  • Monoecious.
  • 2 microsporangia per microsporophyll.
  • Pollens possess 2 air sacs that act as wings.
  • Many cotyledons present.
  • pycnoxylic wood(densely packed).

CYCAS:

  • Coralloid roots occur.
  • Unbranched stem with a crown of leaves.
  • Leaves are pinnately compound.
  • Dioecious.
  • Microsporangia develop in groups called sori in the microsporophylls.
  • Female cone is not formed. Megasporophylls lie scattered.
  • Two cotyledons present.
  • They possess largest egg, sperm & ovule.
  • Wood is manoxylic (not compact).

Also Read Bryophyta and Alteration of generation.

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6 comments

Bhawna December 6, 2017 - 2:47 pm

Really mam it’s help me a lot .mujhe ab meri bekar ki refresher(exploring) pdne ki jrrort nhi h 😊or isse sare concept clear ho gye thnx u so much mam 🙇🙇🙇🙇🙏

Reply
Ramneet Kaur December 6, 2017 - 2:49 pm

Your welcome

Reply
Syed May 4, 2019 - 4:52 pm

Thank u mam
If u make all ur notes of clas11 and 12, chapterwise along with the helpful mnemonics and make a perfect package of covering all topics of ncert Bio, ‘Best as pdf or doc’
Then I will be the first to buy that mam
It will v useful for me and many others also mam
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Reply
Ramneet Kaur May 8, 2019 - 11:30 am

am thinking of doing that, will surely do it soon

Reply
Syed May 4, 2019 - 4:57 pm

Mam thanks for ur help

Reply
Ramneet Kaur May 8, 2019 - 11:29 am

welcome

Reply

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