Wednesday, May 6, 2020

Biology - Kingdom Plantae - Explanation

Kingdom plantae : 

Kingdom Plantae is further classified on the basis of characteristics like absence or presence of seeds, vascular tissues, differentiation of plant body, etc.

• Phanerogams are commonly called seed producing plants. They produce special reproductive structures that are visible (Phaneros – visible)

• Cryptogams are spore producing plants and do not produce seeds and flowers. They reproduce sexually by gametes but sex organs are concealed (kryptos : hidden, gamos : marriage). 

Classification of Kingdom Plantae is represented as follows :

Classification of Kingdom Plantae

Salient features of major plant groups under Cryptogams : 

A. Division : Thallophyta - 

Members are mostly aquatic, few grow on other plants as epiphytes. Some grow symbiotically and epizoic i.e. growing or living non-parasitically on the exterior of living organisms. Aquatic algae grow in marine or fresh water. Most of them are free living while some are symbiotic. Plant body is thalloid i.e. undifferentiated into root, stem and leaves. They may be small, unicellular, microscopic like Chlorella (non￾motile), Chlamydomonas (motile). They can be multicellular, unbranched, filamentous like Spirogyra or branched, filamentous like Chara. Sargassum, a huge macroscopic sea weed which measures more than 60 meters in length is also an alga.

The algal cell wall contains either polysacchrides like cellulose / glucose or a verity of proteins or both. Reserve food is in the form of starch and its other forms. Reprocuction takes place by vegetative asexual and sexual way. The life cycle shows phenomenon of alternation of generation, dominant haploid and reduced diploid phases. Algae are classified as per its pigments like chlorophyll, xanthophylls and phycobilin.

a. Chlorophyceae (green algae) :

These are mostly fresh water (few brackish water and marine). Plant body is unicellular, colonial, filamentous. Cell wall contains cellulose. Chloroplasts are of various shapes like discoid, plate-like, reticulate, cup-shaped, ribbon-shaped or spiral with chlorophyll a and
b. The stored food is in the form of starch.
Pyrenoids are located on Chloroplast. Members are rich in protein, so used as food; used even by space travellers. e.g. Chlorella. Chlamydomonas, Spirogyra, Chara, V olvox, U lothrix etc.

b. Phaeophyceae (Brown algae) :

Plant body : Mostly marine, rarely fresh water. Simple branched / filamentous (e.g. Ectocarpus) / profusely branched (Petalonia).Cell wall has cellulose, fucans and algin. Photosynthetic pigments like chlorophyll-a, -c and fucoxanthin are present. Mannitol, laminarin and starch are stored food materials. Body is usually differentiated into holdfast, stalk called stipe and leaf-like photosynthetic organ called frond. Many species of marine algae are used as food. e.g. Porphyra, L aminaria, Sargassum. Some species are used for production of hydrocolloids. e.g. Ectocarpus, Foucus, etc.

c. Rhodophyceae (Red algae) :

Plant body These are found in marine as well as fresh water on the surface, deep sea and brakish water. Plant body is thalloid. Cells contain chlorophyll a, d and phycoerythrin. Cell wall is made up of cellulose and pectin glued with other carbohydrates. Stored food is in the form of Floridean starch. Commercially important agar-agar which is used as solidifying agent in tissue culture medium is obtained from red algae. e.g. Chondrus, Batrachospermum Porphyra, Gelidium , Gracillaria, Polysiphonia, etc.

B. Bryophyta (Bryon : moss ; phyton : plant) :

Bryophytes are mostly terrestrial plants. They are found in moist shady places. But they need water for fertilization and completion of their life cycle. Hence they are called ‘amphibious plants’. They include approximately 960 genera and about 25,000 species. Life cycle of Bryophytes shows sporophytic and gametophytic stages. Vegetative plant body is thalloid or leafy which represents gametophytic generation. Spore producing capsule represents sporophytic generation. Bryophytes have root-like structures called rhizoids. Rhizoids are unicellular in liverworts while multicellular in mosses. Rhizoids absorb water and minerals and also help in fixation of thallus on the substratum. Bryophytes are divided into two groups : liverworts and mosses.

a. Liverworts (Hepaticeae) : 

These are lower members of Bryophyta. These are primitive group of Bryophytes. Gametophyte possesses flat plant body called thallus. The thallus is green, dorsiventral, prostrate with unicellular rhizoids. e.g. Riccia, Marchantia.

Hornworts (Anthocerotae) -
These member possess flattened thallus. The thallus produces horny structures which are called sporophytes hence the name hornworts. e.g. Anthoceros.

b. Mosses (Musci) :

These are advanced members of Bryophyta which possess erect plant body. Gametophytic phase of the life cycle includes two stages namely; protonema stage and leafy stage. The protonema is prostrate green, branched and filamentous (it is also called juvenile gametophyte). It bears many buds. Leafy stage is produced from each bud. Thus protonema helps in the vegetative propagation. The leafy stage has erect, slender stem like (Cauloid) main axis bearing spiral leaf like structures (Phylloid). It is fixed in soil by multicellular branched rhizoids. This stage bears sex organs. Vegetative reproduction takes place by fragmentation and budding in secondary protonema.
e.g. F unaria, P olytrichum, Sphagnum , etc.

C. Pteridophyta (Pteron : feather, phyton : plant) :

Evolutionarily, Pteridophytes are the first vascular and true land plants. Hence considered as the first successful terrestrial plants with true roots, stem and leaves. These plants have a primitive conducting system and they are the only Cryptogams with vascular tissues. The late Paleozoic era is regarded as the age of Pteridophytes. The group has about 400 genera and 11,000 species. The plants consist of pinnate (feather like) leaves. Leaves may be small called microphylls (e.g. Selaginella) or large called macrophylls (e.g. N ephrolepis / fern).
Nephrolepis (Fern)

Pteridophytes grow in moist and shady places. Pteridophytes show sporophytic and gametophytic stages in life cycle. e.g. Ferns, Horsetail. Some are aquatic (Az olla, Marsilea), xerophytic (Equisetum) and epiphytic (L ycopodium). Pteriodphytes show heteromorphic alternation of generations in which the sporophyte is diploid, dominant, autotrophic and independent. It is differentiated into root, stem and leaves. The primary root is short lived and soon replaced by adventitious roots while the stem may be aerial or underground. Leaves may be scaly (Equisetum) simple and sessile (L ycopodium) or large and pinnately compound (N ephrolepis / Ferns). In these members Xylem consists of only tracheids and Phloem consists of only sieve cells. Secondary growth is not seen in Pteridophytes due to absence of cambium.  Pteridophytes are classified as -Psilopsida- (Psilotum), Lycopsida - (Selaginella and L ycopodium), Sphenopsida - (Equiesetum) and Pteropsida - (Dryopteris, Pteris and Adiantum)


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