NEET Practice Questions (MCQs) with Answers & Solutions

Archaebacteria are the most primitive form of bacteria. These live in diverse habitat, e.g. extreme hot temperature, saline condition, variable pH, etc. Saline bacteria are called Halophiles (e.g., Halobacterium, Halococcus).

Concept Enhancer: The ability of archaebacteria to survive in harsh conditions is due to the presence of branched lipid chain in their membrane, which reduces the fluidity of their membrane.

Viroids are infectious agents composed solely of a small, single-stranded, circular RNA molecule without a protein coat. They are the smallest known infectious pathogens, smaller than viruses, and can cause plant diseases.

Methanogens are group of obligate anaerobic ancient and primitive bacteria. They are involved in methanogenesis and produce methane gas in ruminant of cattles.

Chitin is the major component of the cell walls of most fungi. It is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose. Chitin provides structural integrity and rigidity to the fungal cell wall.

Viroids are infectious, non-protein-coding, highly structured with samll circular RNA's, which have the ability ot replicate autonomously. These contain RNA of low molecular weight and induce diseases in higher plants.

Heterotrophic bacteria are the most abundant prokaryotes helpful to humans in making curd from milk (like Lactobacillus) and in the production of antibiotics (like Streptomyces).

Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria that are capable of performing oxygenic photosynthesis. They are prokaryotic organisms and are often found in aquatic environments.

Yeast or saccharomyces cerevisiae is a fungus of class-Ascomycetes. Saccharomyces sp. are widely used in baking and brewing industries. Paramecium and Plasmodium belong to kingdom-Protista, Penicillium belongs to kingdom-fungi. Lichen is a composite organism formed from the symbiotic association of algae and fungi.

Nostoc and Anabaena are examples of cyanobacteria or blue-green algae.

Methanogens are present in the gut of several ruminants animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals. Thus, they are most abundant in a cattle yard.

Thermophiles live in very hot places, typically form 60º to 80ºC. Many thermophiles (some eubacteria and archaebacteria) are autotrophs and have metabolisms based on sulphur. Some thermophilic archaebacteria form the basis of food webs around deep-sea thermal vents, where they must withstand extreme temperature and pressures. Archaebacteria can grow in higly acidic (pH = 0.7) and very basic (pH = 11) environments.