Tag: zoology

BGA and Azolla have known to be used for the rice cultivation and they are very good for increasing the crop yield and productivity as they supply the soil and the plant with enough nitrogen. They are known used together as the biofertilizers.

Cyanobacteria also known as Cyanophyta, are a phylum of bacteria that obtain their energy through photosynthesis, and are the only photosynthetic prokaryotes able to produce oxygen. The name "cyanobacteria" comes from the color of the bacteria. Cyanobacteria, which are prokaryotes, are also called "blue-green algae", though the term "algae" in modern usage is restricted to eukaryotes. Phototrophic eukaryotes perform photosynthesis by plastids that may have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis. These endosymbiotic cyanobacteria in eukaryotes may have evolved or differentiated into specialized organelles such as chloroplasts, etioplasts and leucoplasts. By producing and releasing oxygen (as a byproduct of photosynthesis), cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxygenation Event and the "rusting of the Earth", which dramatically changed the composition of the Earth's life forms and led to the near-extinction of anaerobic organisms.

Nostoc belongs to cyanobacteria genus, and it can be used as biofertilizer. It is also called the blue-green algae. Nostoc converts atmospheric nitrogen into ammonia, which can be further converted to a suitable form for plant growth. Biofertilizers enhance the quality of plants and soil.

Myxomycetes, also called as mycetozoa, phylum of fungus-like organisms within the kingdom protista, commonly known as true slime molds. They exhibit characteristics of both protozoans (one-celled microorganisms) and fungi. Myxomycetes is a class of slime molds, formerly regarded as animals (Mycetozoa), but now generally thought to be plants and often separated as a distinct phylum (Myxophyta); equivalent to the division Myxomycota. They are found on damp earth and decaying vegetable matter and consist of naked masses of protoplasm, which creep very slowly over the surface and ingest solid food.

Biofertilizers are the suspension of microorganism which mainly increases the growth of the plants. These secrete the growth promoting substances. The microorganisms in bio-fertilizers restore the soil's natural nutrient cycle and build soil organic matter. Bio-fertilizers such as Rhizobium, Azotobacter, Azospirilium and blue-green algae (BGA) are used. Anabaena in association with water fern Azolla contributes nitrogen up to 60 kg/ha/season and also enriches soils with organic matter.

Mycorrhiza is the symbiotic relationship between fungi and plant roots in which both gets benefit from each other. Fungus acts as the plant's root hairs and acts as an extension of the root system for more absorption of nutrients and in turn receives carbohydrates (sugars) and growth factors from the plant, Plants with thick roots, poorly branched and with few root hairs, are usually more dependent on mycorrhizae for normal growth and development. Thus, the correct answer is option C.

Blue Green Algae (BGA) is a good alternative source of nitrogen in rice fields to increase the soil fertility. Various BGA like Nostoc, Anabaena, Aulosira Scytonema are used to increase rice production. Out of all these, Aulosira fertilissima are most commonly used in rice fields.

Rhizobium is an important symbiont for legumes but it plays an important role with nonlegumes by producing growth hormones. When wheat is inoculated with Rhizobium, no effects are observed in terms of growth and yield, which indicates that uptake of soil nitrogen is not seen as in legumes.

Heterocyst is a specialized nitrogen=fixing cell found in some filamentous cyanobacteria like Nostoc, Anabaena. It has cell wall which is made up of three layers. It carries carries out nitrogen fixation. It is formed due to lack of fixed nitrogen. It fixes nitrogen under aerobic conditions. It contains nif gens and synthesize nitrogenase enzyme. Apart from nitrogenase enzymes, it also contains other enzymes required for nitrogen fixation. It promotes vegetative reproduction by filament fragmentation. It does not possesses PS II and hence cannot produce oxygen.