Biofertilizers are available commercially in our country for farmers.

Azolla pinnate is a small free-floating freshwater fern which is widely used as a biofertiliser in Indian rice fields. So, the correct answer is D.

Several fungi are known to form symbiotic associations with plants, i.e., mycorrhiza. The most common fungal partners of mycorrhiza are Glomus species.

Photosynthesis is the process by which light energy from the sun is used to synthesise sugars from carbon dioxide, releasing oxygen as a waste product. In primitive days, cyanobacteria were only the primary producers because the redox structure of oceans favoured them to fix nitrogen and also they had the capacity to use water as the source of electrons in photosynthesis. They made the atmosphere oxygen rich and allowed the appearance of aerobic organisms. 

Cyanobacteria are unicellular prokaryotes that photosynthesise. They form huge colonies that appear as algal bloom in polluted waters. They can fix nitrogen from the atmosphere by means of specialised structures called as heterocysts.

Cow dung is available in plenty in India. It is used as manure or pattings for fuel. The cow dung solution has antifungal and insecticide properties. The application of cow dung also improves soil salinity and alkalinity. The presence of this manure helps in better nitrogen fixation through rhizobia.

Blue green algae or cyanobacteria synthesize a gelatinous mass around themselves, enclosing multiple filaments. This causes the surface area on which they thrive to be slippery

Cyanobacteria are algae, which contains phycocyanin pigment and because of this pigment they are of blue-green colour and known as blue green algae.

Biofertilizers are used because they increase soil fertility, crop productivity, and production. Use of biofertilizers is both economical as well as environment-friendly. They remain symbiotically associated with the roots while some are free living. They solubilize the undissolved minerals.

Prokaryotes are unicellular organisms. They lack membrane-bound organelles like mitochondria, golgi apparatus. They also lack true nucleus. Instead, they have nucleoid or incipient nucleus. Nucleoid is an undifferetiated, unorganised, fibrillar nucleus without any limiting membrane. They have ribosomes in the cytoplasm. Examples include bacteria, Cyanophyceae. 

Prokaryotes are unicellular organisms without membrane-bound organelles like mitochondria, golgi complex. They lack true nucleus. Instead, they have nucleoid, genetic material without nuclear envelope. The examples of prokaryotes include bacteria, Cyanobacteria (Blue green algae). Blue green algae are photosynthetic bacteria.

Biofertilizers are organisms that enrich the nutrient quality of the soil. The main source of biofertilizers are bacteria, fungus, and cyanobacteria. Symbiotic cyanobacteria Anabaena azollae fixes nitrogen in the leaves of Azolla ( aquatic fern ). Azolla pinnata ( a pteridophyte ) is used as an excellent biofertilizer in the rice field. 

Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen. In paddy fields, cyanobacteria serve as an important biofertilizer. 

In paddy fields,biological nitrogen fixation is brought about by Cyanobacteria(Nostoc, Anabaena).

Nostoc and legumes help in increasing soil fertility by nitrogen fixation in the soil.

Some cyanobacteria can fix atmospheric nitrogen in anaerobic conditions by means of specialized cells called heterocysts. These heterocyst forming species are specialized for nitrogen fixation, and are able to fix nitrogen gas into ammonia, nitrites, or nitrates, which can be absorbed by plants and converted to proteins and nucleic acids as nitrogen cannot be directly absorbed by plants. Therefore, some of the cyanobacterial species are used as biofertilizers. 

A biofertilizer is a substance which contains nutrient rich living microorganisms which colonize the rhizosphere or the interior of the plant and promotes the growth of the plant or the seed by increasing the availability of primary nutrients to the plant.

The cyanobacteria fix atmospheric nitrogen through the help of enzyme nitrogenase and are oxygenic photosynthetic also.

Phycocyanin Antioxidant. Phycocyanin is the main component in Linablue Spirulina Extract. It is a blue pigment that is important in the photosynthesis (food production) of cyanobacteria. It assists the function of chlorophyll, especially during low light conditions. So, the correct option is "C" (Phycocyanin).

Nostoc is a genus of blue green algae. It is photosynthetic cyanobacteria. It contains chlorophyll pigment and carries out photosynthesis. It also has ability to fix atmospheric nitrogen and make it available to the plants. It is a non-symbiotic nitrogen fixer.

The cyanobacteria or the blue-green bacteria represent a group of photosynthetic, mostly photolysis-mediated oxygen-evolving monerans (prokaryotes). These are the only organisms able to perform oxygenic photosynthesis that can also fix nitrogen. So, the correct option is 'Cyanobacteria'.

Probiotics are also called good bacterias. These are beneficial in nature. Eg.,  Lactobacillus is a probiotic found in the human gut. 

Stromatolites are layered bio-chemical structures formed in shallow water by the trapping, binding and cementation of sediments by microorganisms, especially cyanobacteria. Stromatolites provide ancient records of life on earth by fossil remains, which might date from more than 3.5 billion years ago.

Since, BGA is a prokaryotic organism, they lack true nucleus and membrane bound organelles which means that chloroplast (double membrane bound chlorophyll containing plastids) is absent in them. Thus, option B is incorrect. Chromatophores are light reflecting, pigment containing cells. The peripheral region of BGA protoplast contains thylakoids and is termed as chromoplast. Thylakoids contain photosynthetic pigments (chrolophyll a, xanthophylls, phycobilin) in their membranes and serve as site for photosynthesis. Thus, option C is correct and D is incorrect.

• Certain bacteria, which grow anaerobically on cellulosic material, produce a large amount of methane along with $CO _2$ and $H _2$. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. 
• These bacteria are present in the rumen (a part of the stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In the rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. 
• Hence Methanobacterium feed cellulose in the anaerobic condition is a true statement.
• So, the correct answer is 'Methanobacterium feed cellulose in anaerobic condition'.

On the basis of their energy source, organisms are classified as organotrophic and lithotrophs. Most prokaryotes and all non-phototrophic eukaryotes use organic compounds as their energy source and thus, are referred to as organotrophs. They oxidise organic compounds during cellular respiration and the produced oxygen as a byproduct. But some Cyanobacteria and Archaea use inorganic compounds as an electron donor in electron transport chain and are referred to as lithotrophs, none of the eukaryotes falls in this category. Virus act as non-living outside the cell. It becomes active when it enters the host cell and derives the cellular protein from the host.

Biofertilizers are the suspension of microorganism which is formed by ploughing in legumes. They enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi, and cyanobacteria (blue-green algae). Biofertilizers will help solve such problems as increased salinity of the soil and chemical run-offs from the agricultural fields.

Nitrogen is the important nutrient for plant growth. Plant obtains nitrogen from the atmosphere with the help of symbiotic and free nitrogen-fixing microorganisms. Azotobacter  is aerobic free living nitrogen fixing organism and fixes atmospheric nitrogen non-symbiotically. Therefore, all plants, trees, vegetables get benefited. Whereas VAM, Anabaena and Rhizobium are the symbiotic organisms. 

Blue-green alga like Nostoc, Anabaena fix atmospheric nitrogen and hence enhance soil fertility. Hence, these organisms are used as biofertilizers. Blue-green alga has special thick-walled cells, called as heterocysts, which carry on the process of fixation of atmospheric nitrogen.

Green manure acts mainly as soil acidifying matter to decrease the alkalinity/pH of alkali soils by generating humic acid and acetic acid. The root systems of some varieties of green manure grow deep in the soil and bring up nutrient resources unavailable to shallower-rooted crops. Erosion control is often also taken into account when selecting which green manure cover crop to plant.

Water bloom is a dense aquatic population of microscopic photosynthetic organisms produced by an abundance of nutrient salts in surface water, coupled with adequate sunlight for photosynthesis. The microorganisms or the toxic substances that they release may discolour the water, deplete its oxygen content, poison aquatic animals and waterfowl, and irritate the skin and respiratory tract of humans. It majorly caused because of Cyanobacteria and dinoflagellates. 

Azolla pinnata is an aquatic fern, which contains a nitrogen-fixing cyanobacteria. It contains Anabaena azollae in its leaf cavities. It is an excellent biofertilizer for paddy fields because they can fix nitrogen in moist condition also.

The pink color, typical of healthy and effective nodules, is due to the presence of a protein called leghemoglobin. This special protein contains Iron (Fe) and molybdenum (Mo) and is responsible for binding oxygen. This provides sufficient oxygen for the metabolic functions of the bacteroids but prevents the accumulation of free oxygen that would destroy the activity of nitrogenase.

Bacillus thuringiensis (Bt) is commonly used as a biopesticide. It is sporulating, a gram-positive facultative-aerobic soil bacterium. It synthesizes the proteins known as delta endotoxins or cry proteins which infect the insects by paralyzing the digestive tract and makes it porous.

Anabaena is a cyanobacteria. It has ability to fix atmospheric nitrogen. It converts nitrogen into ammonia. The heterocysts present in it are specialized cyanobacterial cells for nitrogen fixation. It contains enzyme nitrogenase. Nitrogenase is inactivated by oxygen. Hence, the heterocyst creates a micro anaerobic environment.

A membranous coiled semicircular structure attached to plasma membrane and found in blue-green algae is called as Lamellasome. It is approximately 200 mμ in diameter. Mesosome is folded invagination found in the plasma membrane of bacteria that increases the surface area. They are the site of respiration. Microsome is a fragment of endoplasmic reticulum. It is an artificial structure and is not present in living cell.

Blue-green algae are also called as cyanobacteria. The blue colour of blue-green algae is due to presence of pigments phycocyanin and allophycocyanin. The green colour is due to presence of chlorophyll pigment. Phycoerythrin pigment results in the red colour. Anthocyanins pigment gives red, purple and blue colours in many fruits and vegetables. Anthoxanthin pigment gives white or colorless to a creamy to yellow color to petals of flowers.

Cyanobacteria are also called as Blue green algae. They are prokaryotic bacteria. They are nitrogen fixing bacteria. They are capable of fixing atmospheric nitrogen into ammonium compounds and making it available to the plants. They are useful bifertilizers in fields of rice for cultivation. They are used either free-living and in symbiotic association.

There are many similarities between cyanobacterium and bacterium. They both posses saparophytic mode of life. They both lack true cell organelles. They both posses nucleoid instead of true nucleus. 

The red sea is the saltiest sea and connects to the ocean without any river meeting the sea. It is named so because of the abundant occurrence of red coloured planktonic cyanophyceae called Trichodesmium erythraeum. This cyanophyceae imparts red colour to red sea. This results in the algal bloom or red bloom.

Cyanobacteria are also called as Blue green algae. They are unicellular, colonial, filamentous prokaryotes. They are found in marine and terrestrial habitats. The colonies are surrounded by a gelatinous sheath. They are photosynthetic bacteria. They often form blooms in water bodies and results in eutrophication. Some Cyanobacteria like Nostoc can fix atmospheric nitrogen in specialized cells called heterocysts and make it available to plants.

BGA is chefly used as fertilizer in paddy fields for paddy crops.

Azolla forms a symbiotic association with Anabaena for nitrogen fixation.

Green manures are fertilizers consisting of growing plants that are ploughed back into the soil.All the above are good examples of green manure.

Sesbania rostrate is mainly used as green manure to improve the fertility of the soil due to its fast growth, high biomass production and the ability to convert atmospheric nitrogen into a usable form for plants.

Fertilizers provide three main macronutrients: potassium, nitrogen and phosphorous which are consumed in larger quantities and are present in plant tissue, in quantities from 0.15% to 6.0% of a dry matter (DM) (0% moisture) basis. Iron is a micronutrient for plant growth which is not available in fertilizers.

The apogeotropic or positively geotropic roots appear in Cycas sporophyte are called Corolloid roots or Corollorhiza. These roots looks like anthozoans or coelenterates. They contain Blue green algae or cyanobacteria like Nostoc and Anabaena, and perform symbiotic nitrogen fixation. They show mutual association with plant body.

So, the correct option is ‘Cyanobacteria’.

The kingdom monera is comprised of the prokaryotic organisms. The blue-green algae are included under the kingdom monera. These are the primitive form of prokaryotic organisms. They are unicellular or multicellular forming filamentous structures. They do not have well-developed cellular components such as a nuclear membrane, nucleus, mitochondria, etc. 

The cyanobacteria (also referred to as blue-green algae) have chlorophyll a similar to green plants and are photosynthetic autotrophs. The cyanobacteria are unicellular, colonial or filamentous, fresh-water marine or terrestrial algae. The colonies are generally surrounded by a gelatinous sheath. They often form blooms in polluted water bodies. Some of these organisms can fix atmospheric nitrogen in specialized cells called heterocysts, e.g, Nostoc and Anabaena.

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.