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The latest Messages 40
2021-10-24 07:30:54
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191 views04:30
2021-10-23 09:31:33
Pteridophytes:-
Pteridophytes are primitive seedless vascular plants also called cryptogams. These have conspicuous sporophytic plant body, inconspicuous independent gametophytes with antheridia and partially embedded archegonia having 4-rowed necks.
The term Pteridophyte was coined by Haeckel (1866). There are about 13000 species of pteridophytes have been reported. They were perhaps the first land plants evolved during ordovician (450-500 million years ago) period.
The characteristic features of pteridophytes are as follow;-
Habitat:-
The pteridophytes are found in cool, damp shady places though some may flourish well in sandy-soil conditions.
Some members like Azolla, Salvinia, Marsilea species.
Plant Body:-
The size varies from a fraction of centimeter (e.g, Azolla) to 20 m in tree ferns (e.g, Angiopteris). The main plant body is a sporophyte which is differentiated into true root, stem and leaves. These organs possess well differentiated vascular tissues. The leaves are small (microphyllus) as in Selaginella or large (macrophylls) as in ferns.
Vascular Tissues:-
These are xylem and phloem present throughout the body. Xylem consists of tracheids and phloem is made up of sieve cells and albuminous cells.
Sporophylls:-
The sporophytes bear sporangia that are subtended by leaf like appendages called sporophylls. In some cases sporophylls may form distinct compact structure called strobili or cones (Selaginella and Equisetuni). The sporangia produce spores by meiosis in spore mother cells.
Spores:-
The spores germinate to give rise to inconspicuous, small but multicellular free-living, mostly photosynthetic thalloid gametophytes called prothallus. In majority of the pteridophytes, all the spores are of similar kinds; such plants are called homosporous. Genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores; such plants are called heterosporous.
145 views06:31
2021-10-23 06:54:32
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170 views03:54
2021-10-22 05:47:49
> Structural Organisation in Animals
> Class 11th Biology
> @Science_Wallah
229 views02:47
2021-10-21 16:08:57
> Morphology of Flowering Plants
> Class 11th Biology
> @Science_Wallah
268 views13:08
2021-10-21 05:26:34
> Plant Kingdom
> Class 11th Biology
> @Science_Wallah
257 viewsedited 02:26
2021-10-20 19:57:58
> The Living World
> Class 11th Biology
> @Science_Wallah
283 views16:57
2021-10-18 07:00:05
Natural System of Classification:-
It is also known as phenetic system of classification. The natural system of classification is based on natural affinities among the organisms. It considers both external and internal features like structure, anatomy, embryology and phytochemistry.
Advantages:-
Advantages of natural system are given below:-
(i) Only related organisms are kept in a group.
(ii) Unrelated organisms are kept in separate groups.
(iii) It shows natural relationships among the organisms.
(iv) It shows possible origin of different taxa.
Disadvantages:-
Disadvantages of natural system are given below:-
(i) There is more emphasis given on natural character.
(ii) In this system several related families are separated and unrelated families are put together.
(iii) Evolutionary basis is neglected.
3. Phylogenetic System of Classification:-
The phylogenetic system of classification indicates the evolutionary as well as genetic relationships among organisms. This system is based on fossil records of biochemical, anatomical, morphological, physiological, embryological and genetical.
The system was initiated by Engler and PrantI (1887-1899) in Die Naturalichen Pflanzefamilien. In phylogenetic system, flowering plants are placed in ascending series related to complexity of floral morphology.
The phylogenetic system of classification are mainly the rearrangement of taxonomic characters in addition to the phylogenetic information.
Advantages:-
Advantages of phylogenetic system are given below:-
(i) Families and order in this system are of small size.
(ii) This system is in conformation with the modern views of phylogeny.
(iii) They use information from various sources to solve problems of classification. Such informations become more important in the absence of supporting fossil evidences.
Disadvantages:-
Disadvantages of phylogenetic system are given below:-
(i) This is not helpful in plant identification.
(ii) The classification is outdated as the habit is used as . main basis of classification.
378 views04:00
2021-10-18 06:01:12
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292 views03:01
2021-10-17 10:44:10
GUYS HERE WE START PLANT KINGDOM SO BE UP TO DATE:-
Types of Classification System:-
These includes artificial system, natural system and phylogenetic system of classification.
The various systems used in classification ofiplants are being discussed here:-
1. Artificial System of Classification
This system is based on comparison of one or a few superficial characteristics, which are helpful in easy identification of organisms.
This system remained in use for about two thousand years.
Aristotle is known as father of Zoology.
Carolus Linnaeus is known as father of Taxonomy.
Advantages:-
Advantages of artificial system as below:-
(i) Artificial system is easy to remember as only one or few characters are used.
(ii) The traits used are of interest to humans.
Disadvantages:-
Disadvantages of artificial system are given below:-
(i) This system use only few superficial characters (i.e., habits, numbers, colours and shapes of leaves, etc) which leads to many organisms grouped together,
(ii) They considered mainly the vegetative characters or the androecium characters as given by linnaeus.
(iii) It does not demonstrate natural and phylogenetic relationships.
(iv) This gave equal weightage to vegetative and reproductive/sexual characters this is not acceptable, as vegetative characters are more easily influenced by the environmental factors.
(v) They sparated the closely related species.
337 views07:44
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