what are Distinguishing features of phaeophyceae(marks_5)
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1. Plant body is immobile, multicellular and highly differentiated both externally and internally. [Unicellular, colonial (motile and non-motile) and unbranched filamentous forms are completely absent).
2. They range from simple microscopic heterotrichous filament (Ectocarpus) to largest alga (Macrocystis pyrifera), which attains a length of 60-90 meters. (The largest forms are known as kelps or rockweeds. Lessonia davicans reachs a length of 4 meters and looks like a miniature tree. Nereocystis luelkeana, the bladder kelp which attains a length of 25-30 meters. Postelsia palmae- formis appears like a palm tree and commonly known as Sea Palm)
3. Commonly the plant body is differentiated into hold fast, a short or elongated stipe and an expanded blade. The blade performs photosynthesis and bears reproductive structures. Many species remain afloat by having air bladder
4. The photosynthetic pigments include chlorophyll a, chlorophyll c, β-carotene and xanthophylls like lutein, fucoxanthin, flavoxanthin and violaxanthin. The fucoxanthin is however present sufficiently which partially mask the chlorophyll and carotenoid, thereby giving the characteristic brown colouration.
5. The growth of the plant body may be apical (Fucales, Dictyotales), intercalary (Laminariales) or trichothallic (Ectocarpales).
6. The cell wall is differentiated into outer and inner layers. The outer mucilaginous layer has fucinic and alginic acid, but the inner layer is mainly cellulosic. [The alginic acid is used to manufacture artificial silk and adhesive, obtained commercially from Sargassum, Laminaria etc].
7. The cells usually have many small vesicles and white granules. The granules are called fucosan vesicles.
8. Pyrenoides are usually absent, but, if present, is of single stalk type.
9. Motile structures (zoospores and gametes) have two laterally inserted unequal flagella, of which larger one is tinsel or pantonema- tic and the smaller one is whiplash or acronematic type.
10. The reserve foods are commonly laminarin and mannitol. Sucrose and glycerol are also present in some members.
11. They reproduce by all the three means: vegetative, asexual and sexual.
a. Vegetative reproduction takes place by fragmentation. Special reproductive branches, the propagules, are developed in some members of Sphacelariales; those develop to new plants after detachment.
b. Asexual reproduction takes place by zoospores except Tilopteridales, Dictyotales and Fucales. The zoospores produced in unilocular sporangia are haploid, while in pleurilocular sporangia they are diploid.
c. Sexual reproduction ranges from isogamy (Ectocarpales and Sphacelariales) to oogamy (Fucales, Dictyotales and Laminariales) through anisogamy (Cutleriales and Tilopteridales).
12. In most of the members fertilisation is external. Zygote does not undergo meiotic division and on germination it develops diploid thallus.
13. The members show various types of alternation of generations i.e., isomorphic (Ectocarpus), heteromorphic (Laminaria) or diplontic (Sargassum).
2. They range from simple microscopic heterotrichous filament (Ectocarpus) to largest alga (Macrocystis pyrifera), which attains a length of 60-90 meters. (The largest forms are known as kelps or rockweeds. Lessonia davicans reachs a length of 4 meters and looks like a miniature tree. Nereocystis luelkeana, the bladder kelp which attains a length of 25-30 meters. Postelsia palmae- formis appears like a palm tree and commonly known as Sea Palm)
3. Commonly the plant body is differentiated into hold fast, a short or elongated stipe and an expanded blade. The blade performs photosynthesis and bears reproductive structures. Many species remain afloat by having air bladder
4. The photosynthetic pigments include chlorophyll a, chlorophyll c, β-carotene and xanthophylls like lutein, fucoxanthin, flavoxanthin and violaxanthin. The fucoxanthin is however present sufficiently which partially mask the chlorophyll and carotenoid, thereby giving the characteristic brown colouration.
5. The growth of the plant body may be apical (Fucales, Dictyotales), intercalary (Laminariales) or trichothallic (Ectocarpales).
6. The cell wall is differentiated into outer and inner layers. The outer mucilaginous layer has fucinic and alginic acid, but the inner layer is mainly cellulosic. [The alginic acid is used to manufacture artificial silk and adhesive, obtained commercially from Sargassum, Laminaria etc].
7. The cells usually have many small vesicles and white granules. The granules are called fucosan vesicles.
8. Pyrenoides are usually absent, but, if present, is of single stalk type.
9. Motile structures (zoospores and gametes) have two laterally inserted unequal flagella, of which larger one is tinsel or pantonema- tic and the smaller one is whiplash or acronematic type.
10. The reserve foods are commonly laminarin and mannitol. Sucrose and glycerol are also present in some members.
11. They reproduce by all the three means: vegetative, asexual and sexual.
a. Vegetative reproduction takes place by fragmentation. Special reproductive branches, the propagules, are developed in some members of Sphacelariales; those develop to new plants after detachment.
b. Asexual reproduction takes place by zoospores except Tilopteridales, Dictyotales and Fucales. The zoospores produced in unilocular sporangia are haploid, while in pleurilocular sporangia they are diploid.
c. Sexual reproduction ranges from isogamy (Ectocarpales and Sphacelariales) to oogamy (Fucales, Dictyotales and Laminariales) through anisogamy (Cutleriales and Tilopteridales).
12. In most of the members fertilisation is external. Zygote does not undergo meiotic division and on germination it develops diploid thallus.
13. The members show various types of alternation of generations i.e., isomorphic (Ectocarpus), heteromorphic (Laminaria) or diplontic (Sargassum).
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