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Essay on non-flowering plants (Cryptogams)

Non-flowering plants (Cryptogams)

Non-flowering plants belong to three groups of the plant kingdom: Thallophyta, Bryophyta and Pteridophyta.

I. Thallophyta:

Plants belonging to this group are the simplest and most primitive ones. Their bodies are not differentiated into organs like root, stem and leaf.

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In fact, the body is an undifferentiated mass of cells known as thallus. The thalloid body may be unicellular or a colony of cells which does not exhibit any division.

The sex organs are usually unicellular. Thallophytes may further be divided into (a) bacteria (b) algae (c) fungi (d) lichens (e) viruses, (f) mycoplasmas and (g) rickettsia. (a) Bacteria

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Bacteria are the smallest and simplest in structure of all living organisms. Majority of them are devoid of chloroplast (chlorophyll) and are unable to manufacture their own food material, so they depend on organic products for their existence. They were first discovered by Leeuwenhoek in 1683. Bacterial cells are procaryotic with simple nucleus and devoid of nucleolus and nuclear membrane. They generally reproduce by transverse ordinary fission.

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Economic Importance of Bacteria

1. Beneficial Bacteria

Some of the beneficial activities of bacteria are:

(i) Soil-fertility:

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Some of the soil-fertile bacteria are Nitromonas, Nitrobacter, Azotobacter, Clostridium and Rhizobium. They are involved in the decomposition of nitrogenous organic compounds of both plant and animal bodies in the soil and thereby maintain the soil fertility. Azotobacter, Rhizobium and Clostridium are able to fix atmospheric nitrogen in the soil.

(ii) Source of Antibiotics:

Prominent antibiotics produced by bacteria are bacitracin and polymyxin.

(iii) Fermentation:

The bacteria used in fermentation are Clostridium acetobutylicum which ferment carbohydrates into acetone, methyl alcohol and n-butyl alcohol. Acetobacter acetic oxidizes alcohol to acetic acid which is responsible for characteristic odour and flavour of vinegar. Lactobacillus, Leuconostoc and Streptococcus ferment milk to lactic acid.

(iv) Retting of Fibres:

Clostridium butyric um and Clostridium felsineum are used in retting of jute, flax and hemp fibres.

2. Harmful Bacteria

The harmful results of bacterial activity are:

(i) Spoilage of Foodstuffs:

Putrefaction of meat is caused by B. subtilis, B. cereus, and E. coli and Proteus vulgaris. Spoilage of fish is caused largely by Achromobacter, Flavobacterium, Micrococcus and Pseudomonas. Food poisoning bacteria are Clostridium botulinum, Salmonella enteritidis and Salmonella typhimurium.

(ii) Animal Diseases:

Bacteria cause tuberculosis in cattle, anthrax in sheep, chicken cholera, and glanders in horses, sheep and goats. Anthrax is caused by B. anthracis.

(iii) Human Diseases:

Many of the serious human diseases are caused by bacteria, e.g.. Tuberculosis (Mycobacterium tuberculosis varhominis), diphtheria (Cornebacterium diphtheriae), leprosy (Mycobacterium leprae) and tetanus (Clostridium tetani)

(iv) Plant Diseases:

Bacteria cause various plant diseases, e.g., leaf spot (Pseudomonas angulata), Extensive blight (Erwinia amylovora), and soft rot (Erwinia aroideae). Vascu­lar diseases (Bacterium stewartii) bacterial galls and canker (Cornebacterium michiganense)

Bacteriophage (Bacteria-Eating Agents):

Bacteriophage or bacterial viruses are obligate parasites which are dependent upon living bacteria. They are composed of protein and DNA. They reproduce only in the presence of living cells. They are formed by (i) absorption of virus particles by bacterial cells (ii) increase of virus particles in bacterial cells (iii) liberation of virus particles due to bursting of bacterial cells.

(b) Algae:

Algae are chlorophyll-bearing lower group of plants in which the body is not differentiated into roots, stems and leaves. They are found in fresh water of ponds, lakes, rivers and swamps. A great majority of these types growing in the sea are called seaweeds or marine algae. They show a great diversity in their mode of reproduction.

The lower forms reproduce vegetatively by cell division, but higher forms reproduce asexually by spores (zoospores, aplanospores, hormospores, endospores and hypnospores) and sexually by gametes (antherozoids and oosphere). Algae may be divided into the following groups on the basis of pigments found in them:

(i) Cyanophyta (Blue-green algae):

True nucleus and chromatophores are lacking. The pigmentation is characterized by chlo­rophyll-a, P-carotene and phycoerythrin, e.g., Nostoc, Anabaena and Rivularia.

(ii) Chlorophyta (Green algae):

The pigment present in this group is chlorophyll. Starch is the principal storage food, e.g., Volvox, Chlorella, Spirogyra, Ulothrix and Chlamydomonas.

(iii) Euglenophyta:

The pigment is chlorophyll and stored food is paramylum, e.g., Euglena.

(iv) Xanthophyta (Yellow-green algae):

There is excess of xanthophyll pigment and reserve food is fat or leucosin, e.g., Vaucheria and Botrydium.

(v) Diatoms:

The pigment is golden-brown diatom which masks the chlorophyll. Reserve foods are fats and volutin, e.g., Cymbella and Navicula.

(vi) Pyrrophyta (Fire algae):

Chromatophores are yellowish green due to the presence of dinoxanthin and peridinin. The reserve food is starch.

(vii) Phaeophyta (Brown algae):

The chloro­plasts contain photosynthetic pigments which are masked by another pigment called fucoxanthin. The reserve foods are starch (sugar), alcohol mannitol and polysaccha­rides as laminarin, e.g., Laminaria, Sargas- sum and Fucus.

(viii) Rhodophyta (Red algae):

Chlorophyll is associated with a red pigment known as phycoerythrin and a blue pigment, phycocyanin. Food reserves are alcohol in the form of polysaccharides known as floridean starch, e.g., Compsopogon, Cenimium and Callithamnion. Economic Importance

Algae are rich in vitamin A, C, D and E, therefore, are taken by man as delicious food. Some of the sea­weeds contain iodine so; goiter is unknown among the people who eat seaweeds. They are the chief source of food for fish. Farmers, along the coasts of the oceans, use them to increase the fertility of soil. Agar-agar is a product of algae which is used as a culture medium for the growth of bacteria and fungi in laboratories,

(c) Fungi:

Fungi are the largest group of thallophyta characterized by the absence of chlorophyll, however, a distinct cell wall and well organised nucleus is present. Due to the absence of chlorophyll, they cannot manufacture carbohydrates and have to lead a parasitic or saprophytic mode of life. The vegetative body of fungus is mycelium formed of numerous, slender, thread like colourless filaments called hyphae. The reserve food materials of fungi are glycogen and oils.

Fungi reproduce asexually by means of gonidia or spores (zoospores, conidia and sporangiospores). Sexual reproduction involves fusion of two nuclei of different parentage (antheridium, the male organ and oogonium or ascogonium, the female organ). Fungi are divided into three groups:

(i) Phycomycetes:

Algal fungi, e.g., Phytophthora, Pythium, Mucor and Plasmopara.

(ii) Ascomyceles:

Sac-fungi, e.g, Morchella, Peziza, Claviceps, Neurospora and Saccharomyces (Yeasts).

(iii) Basidioinycetes:

Basidial fungi, e.g, Puccinia, Uromyces, Ustilago and Agaricus.

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