Gymnosperms & Angiosperms Notes - NEET

NEET: Gymnosperms & Angiosperms Notes - NEET

The document Gymnosperms & Angiosperms Notes - NEET is a part of NEET category.
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Gymnosperm

1. Term Gymnosperm was given by Theophrastus.

2. Study of Gymnosperm known as Gymnospermology.

3. Gymnosperm & Angiosperm are collectively included under spermatophyta i.e. seed-bearing plants.

4. Gymnosperms are naked seeded plant i.e. no fruit formation takes place in these plant. i.e. in gymnosperm embryo & seed formation takes place but no fruit formation occur.

5. Gymnosperms are very limited in distribution. They are mainly found in cold regions. In India, Gymnosperms are found on Himalayan mountains. They occur on slopes of the mountain in the cold region, therefore, gymnosperms are xerophyte.

6. All gymnosperm are vascular plants. Therefore vascular tissue present i.e. xylem & phloem. Xylem lack vessels & phloem lacks companion cells.

Note :

  •  Exceptionally in xylem of Gnetum, Ephedra, Welwitschia true vessels are present.
  •  In gymnosperms vascular bundle is Conjoint-Collateral-Endarch-Open.
  •  In the vascular bundle cambium is present therefore secondary growth takes place in gymnosperms, so that Gymnosperms are woody plants.

7. Most of the gymnosperms are arborescent (woody and tree habit) - but some are present as shrub. eg. Ephedra Some Gymnosperm are liana or woody climbers. eg. Gnetumula 

 

Life Cycle Of Gymnosperm -

1. In Gymnosperms main plant body is sporophyte (diploid). All Gymnosperm are dioecious. i.e. male & female plants are separate, but exceptionally Pinus is monoecious.

 2. All Gymnosperms are heterosporus. At the time of reproduction two types of spores are formed.

  •  Microspores form – Male gametophyte
  •  Megaspores form – Female gametophyte

3. These two types of spores are formed in different sporangia.

  •  Microspores are formed in Microsporangia. Microsporangia are also termed as pollen sac.
  •  Megaspores are formed in Megasporangia. Megasporangia are also termed as ovule.

4. Both types of sporangia are formed on different sporophylls.

  •  Microsporangia are formed on Microsporophyll. It is known as stamen.
  •  Megasporangia are formed on Megasporophylls. It is known as carpel.

5. Both types of sporophylls are found in groups & form male cone (strobilus) & female cone.

  •  Gymnosperm's cone are just like flower or inflorescence of angiosperm. 
  • Carpels of Angiosperm & Gymnosperm are different to each other.

Carpel of Gymnosperm -

  •  Carpel of gymnosperm is less modified leaf it keeps its identity.
  •  Ovules of gymnosperm develop openly on carpel ovule doesnot enclosed in any structure. Therefore carpel of gymnosperm is termed as open carpel.

Carpels of Angiosperm -

  •  Angiosperm's carpel is divided into three parts ovary, style and stigma.
  •  Ovule enclosed in ovary. Therefore angiosperm's carpel termed as closed carpel. i.e. angiosperm carpel is well modified leaf. Sporophyll has lost its identity.

6. Meiosis takes place in cells of microsporangium & megasporangium and form microspore & megaspore respectively.

7. In Gymnosperm and angiosperm germination of spores is endosporic i.e. germination of spore takes place with in sporangia.

8. Male gametophyte is formed after germination of microspore. Male gametophyte is also known as pollen grain.
Male gametophyte forms male gamete.

9. In lower gymnosperm, male gametes are motile & multiciliate, but in higher gymnosperm and angiosperm male gametes are non-motile due to the absence of cilia and flagella. They (higher gymnosperm) do not require water for fertilization.

10. Female gametophyte is formed after germination of megaspore.

Female gametophyte of gymnosperm contains two type of structures

  •  Archegonia - It forms egg.
  •  Endosperm - It provides nutrition for the development of embryo.

11. Pollen grains (Male gametophyte) reach at the micropyle of ovule by wind pollination, called as onemophilly ovule by wind pollination.

Fertilization 

Two types of fertilization take place in gymnosperms

(1) Zoodio - siphonogamy & This type of fertilization occurs in lower gymnosperms. Male gametes are motile and transferred to female gamate by pollen tube.

(2) Siphonogamy & This type of fertilization occur in higher gymnosperms. Male gametes are non motile transferred to female gamete (egg) by pollen tube. After Pollination male & female gametes are fused & form a diploid zygote.

  •  In gymnosperm single fertilization takes place so that single zygote form through fertilization. In Angiosperm double fertilization takes places so that two product are formed after it (i) Zygote (ii) Endosperm.
  •  In gymnosperm endosperm form before fertilization so it is haploid but in angiosperm endosperm are formed after fertilization so endosperm of angiosperm is triploid.

Gymnosperms & Angiosperms Notes - NEET

Gymnosperms & Angiosperms Notes - NEET

Gymnosperms & Angiosperms Notes - NEET

                              Gymnosperms & Angiosperms Notes - NEET

Gymnosperms & Angiosperms Notes - NEET

 

Life Cycle Of Gymnosperm

Development Of Zygote –

1. Embryo is formed by the development of diploid zygote. After embryo formation ovule is termed as seed. (Seed = Ovule + Embryo)

  • Ovule is a sporangia. Embryo enclosed in ovule because development of spore is endosporic.
  •  Seeds are not formed in pteridophyta because germination of spore is exosporic i.e. embryo develops outside the sporangia.

2. Embryo is enclosed in seed. Seed absorbs water & bursts. Now embryo germinates and forms a new diploid plant.

Note :- Different types of polyembryony are found in gymnosperm i.e. a single seed develops many embryo.

LIFE CYCLE :

Life cycle of Gymnosperm & angiosperm is diplontic because gametophytic generation is short lived. Gametophyte is very reduced & depends on its sporophyte.

SOME IMPORTANT POINTS :

  1. Antheridia is absent in gymnosperm & angiosperm i.e. pteridophyte is last group having antheridia.
  2. But archegonia is also absent in angiosperm. So gymnosperm is last group having archegonia.

Evolution of archegonia starts form liverworts. It is well developed in moss. Gymnosperm is last group of it. So in this group it is very reduced.

Archegonia of Liverworts        – NCC = 4 - 6         VCC = 1                 Egg cell = 1

Archegonia of Moss                 – NCC = 6 - 18       VCC = 1                 Egg cell = 1

Archegonia of Pteridophyta     – NCC = 1 - 2         VCC = 1                 Egg cell = 1

Archegonia of Gymnosperm    – NCC = Absent     VCC = 1(Short lived)  Egg cell = 1

2. During evolution Gametophyte becomes reduced & sporophyte becomes well-developed.

Gametophyte               

  • Very reduced – In Angiosperm
  • Well developed – In Moss
  • Very reduced – In Thallophyta (Only zygote)

Sporophyte

Well developed – In Angiosperm

Gymnosperms are divided into two groups

(1) Cycadophyta (Lower Gymnosperm)    
(2) Coniferophyta (Higher Gymnosperm)

 

Cycadophyta

(A) The plants of this group are megaphyllous or macrophyllous with circinate vernation

(B) Presence of Ramenta.

(C) Male gamete is motile.

(D) Vascular bundles are hadrocentric in fossil members.

(E) Stem is caudex and wood is mannoxylic.

 

Cycadophyta is divided into three orders:

(i) Cycadofillicales or Pteridospermae :-

(a) This group includes seed ferns. Many characters of ferns are found in this group like megaphyllous leaves, circinate vernation, ramenta, motile gametes, hadrocentric vascular bundles.

(b) Now this group is completely extinct. eg. Lyginopteris -   Fossil plant

(ii) Benettitales :-

(a) It is also a completely extinct group. eg. Williamsonia - fossil plant

Note : Its fossils were discovered by Prof. Birbal sahani

(iii) Cycadales -

(a) Presently living cycadophytes are included in this order.

(b) All the plants of this group are living fossils.

  •  Zamia pygmea - Smallest Gymnosperm
  •  Cycas - Fern palm or Sago palm Sago is obtained from its stem.
  •  Cycas thouarsii - The diameter of its ovules is 7 cm. Its ovules, male gametes and egg are largest in plant kingdom.

CONIFEROPHYTA

Four orders are included in this group
(i) Ginkgoales :-

(a) It is the oldest order of coniferophyta. Maximum plants of this group are extinct.

(b) Only one plant of Ginkgo biloba is present in India (In Manali). Some plants are also present in China.
Ginkgo biloba -living fossil - It is also known as "Maiden hair tree".

Note : Exceptionally Ginkgo biloba belongs to higher gymnosperm but its male gametes are motile and fertilization by zoodiosiophonogamy.

(ii) Cordaitales :-(a) It is completely extinct group eg. Cordaites

(iii) Coniferales :-

(a) Conifers are included in this group.  

(b) It is the largest group of gymnosperm e.g. of Coniferales :-

(a) Pinus (Pines) :-

  •  Pinus species – A resin "turpentine" is obtained from it. Turpentine is used in varnish.
  • Pinus gerardiana – It is known as "chilgoza pine"
  • Pinus roxburghii – It is known as "chirpine".

(b) Cedrus – It is known as deodar.

(c) Taxus – It is known as Yew tree. An anticancer medicine "Taxol" is obtained from its bark.

(d) Taxodium maxicanus – The stem of this plant is thickest in the plant kingdom.

(e) Abies balsamea – A resin "Canada balsam" is obtained from it. It is used to manufacture permanent slides in biology laboratory.

(f) Juniperus virginiana – An oil is obtained from this tree - "Cedar wood oil". It is used as cleansing fluid in biology laboratory. This oil is also used in microscope to increase  the resolving power. This oil is used as nail polish remover.

(g) Araucaria species

  • Araucaria excelsa – Christmas tree
  •  Araucaria araucana – Monkey puzzle tree

(h) Sequoia species – The plants in this genus are heavy. Therefore they are called as father of forest.
Sequoia giganteum – It is called Redwood tree or Sherman tree. It is the largest gymnosperm. There is only one tree of this species and that is in California (America)

(i) Metasequoia – It is a living fossil. This plant is present in china valley.

iv) Gnetales -

(a) They are the most advanced gymnosperms.

(b) Exceptionally members of this group have vessels in xylem.

(c) Ovule of this group is bitegmic.

(d) Archegonia is absent in the members of this group. eg.

(1) Gnetum (2) Welwitschia (3) Ephedra – Exceptionally archegonia is present in Ephedra.
 

Ephedra- This gymnosperm is commonly found in Rajasthan. Ephedra is a medicinal plant. Ephedrine (Medicine) is obtained from it. It is an effective medicine in asthma. Athletes misuse it, so ephedrine is restricted for them.

Cycadofillicales were first seeded plants. First time seed habit was established in this group. In general way seed habit was originated from those pteridophytes which are now extinct.  These pteridophytes were ancestor of cycadofillicales.

Seed habit was originated from those pteridophytes which were just like Selaginella. Because Selaginella show origin of seed habit.

There is mainly two requirements for seed formation

(1) Plant should be heterosporus  
(2) Germination of mega spore should be endosporic

The document Gymnosperms & Angiosperms Notes - NEET is a part of NEET category.
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