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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Fertilizers Pesticides and Biological Methods of Pest Control Know More

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  • Plants grown as green manure in India are sunn-hemp (Crotolaria juncea), dhaincha (Sesbania aculeata), cowpea (Vigna sinensis).
  • Farmyard manure consists of a mixture of cattle dung and crop residue. FYM increases the aeration in the soil, makes the soil loose and permits easy penetration of soil.
  • Rhizobium is a Gram -ve bacterium. The protein lecithin present on the root surfaces of a particular leguminous plant acts as a recognition chemical between the plant and Rhizobium to form nodules. Nitrogen fixation by Rhizobium is better in the presence of phosphorus. Nitrogen fixation by Rhizobium takes place in the presence of leghaemoglobin, which is a pigment.
  • Anabaena azollae is a cyanobacterium present in the leaf cavities of Azolla. An appreciable increase by 50% is observed in the yield of rice by the use of Azolla.
  • Azotobacter is a Gram -ve, aerobic, free living bacterium. Clostridium and Chlorobium are anaerobic nitrogen fixing bacteria. Rhodospirillum is an example of photosynthetic and nitrogen fixing bacteria. The presence of Azospirillum lipoferum was reported in Brazil. This nitrogen fixing bacterium forms a loose association with the roots of maize, grass, etc.
  • In the filamentous forms of cyanobacteria like Nostoc, Anabaena, etc, there is a special, thick-walled cell called heterocyst, which is a site of nitrogen fixation.
  • The fungal hyphae in mycorrhiza increase the absorption of water and some nutrients like nitrogen, phosphorus, potassium and calcium.
  • According to their chemical composition, pesticides are classified into different groups such as organochlorines, organophosphates, carbamates, pyrethroids, triazines.
  • DDT, BHC, aldrin are the examples of organochlorines. These are chlorinated organic compounds, which get deposited in the fatty tissues of animals and are called lipophilic. These are contact poisons.
  • Malathion, parathions, diazinon and fenitrothion are organophosphates. Constituent of 'Flit' is malathion. They have a strong effect on the nervous system, and thus, act as neurotoxins.
  • Carbamates are the pesticides that interfere with the nervous system functions. 'Baygon' is chemically a carbamate called propoxur.
  • Pyrethroids are the synthetic derivatives of pyrethrin. They are obtained from the inflorescence of Chrysanthemum cinerarifolium. They act as insect repellents.
  • Triazines are derived from urea. They inhibit the Hill reaction of photosynthesis in weeds, and thus, control them.
  • The growth of milk weed vine in citrus plantation can be controlled by a mycoherbicide developed from a fungus Phytophthora palmivora.
  • Lady bird beetles are used to control a common pest called fluted scale insect on citrus trees.
  • Gambusia fish feeds on the larvae of mosquito, thus, controlling the mosquito population.
  • Azadirachtin from neem and nicotine from tobacco are effective insecticides.
  • Protein toxins called thuriosides are produced by some bacteria like Bacillus thuringinesis. These are highly toxic to certain insects.
  • Rotenone is a bioinsecticide extracted from the roots of Derris elliptica.
  • DDT is dichloro diphenyl trichloroethane. It was discovered by Paul Muller.
  • Bordeaux mixture consists of lime (calcium hydroxide) and copper sulphate dissolved in water.
  • 'Devine' and 'Collego' are the fungal spore products recently introduced to control weeds.

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