General Q&A for Class 12 · Page 233
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
How can growth of weeds be controlled?
Growth of weeds can be controlled through multiple methods that are often used in combination for effective management. Mechanical and physical control involves manual removal by hand-pulling or uprooting weeds before they flower and set seeds, which is effective for small areas but labor-intensive for large fields. Farmers also use tools like hoes, weeders, and harrows to remove weeds and loosen soil, or employ inter-cultivation—tilling between crop rows to uproot weeds while aerating
- GeneralClass 12All
Which microorganisms are not affected by antibiotics?
. Viruses are the primary group of microorganisms that are completely unaffected by antibiotics. Unlike bacteria, viruses lack the cellular machinery and metabolic processes that antibiotics target—they cannot build cell walls, synthesize proteins independently, or carry out metabolic functions on their own. Instead, viruses hijack the living cells of host organisms to reproduce, making them fundamentally different from bacteria in structure and function. This is why ant
- GeneralClass 12All
What are pathogens?
Pathogens are disease-causing microorganisms or biological agents that invade host organisms and disrupt normal physiological functions, leading to illness or infection. They include bacteria, viruses, fungi, protozoa, and parasitic worms, each capable of causing a wide range of diseases in humans, animals, and plants. Pathogens spread through various routes including air, water, food, direct contact, insect vectors, and contaminated surfaces. The severity of diseases caused by pathog
- GeneralClass 12All
What will you observe if you keep moist bread outside in open for few days?
If you leave moist bread exposed to open air for several days, you will observe the growth of fuzzy, cotton-like structures in various colors—typically white, green, black, or blue—covering the bread's surface. This visible growth consists of fungal colonies, primarily bread mold species like Rhizopus (black mold), Penicillium (blue-green mold), and Aspergillus, which reproduce by releasing microscopic spores into the air. The moisture and nutrients in b
- GeneralClass 12All
Which group of microorganisms cause malaria?
Malaria is caused by protozoa, specifically parasitic protozoans belonging to the genus Plasmodium. Among the several species that infect humans, Plasmodium falciparum, P. vivax, P. ovale, and P. malariae are the most common, with P. falciparum being the deadliest. These single-celled parasites have a complex life cycle involving both human hosts and female Anopheles mosquitoes, which transmit the parasite through blood-feeding.</
- GeneralClass 12All
Name the instrument (or device) which is needed to see the microorganisms.
A microscope is the essential instrument required to observe microorganisms, as most are far too small to be seen with the naked eye. The compound light microscope, most commonly used in schools and basic laboratories, uses visible light and multiple glass lenses to magnify specimens between 40 to 1000 times their actual size, making bacteria, protozoa, fungi, and algae visible. More advanced microscopes like electron microscopes can magnify objects up to millions of times, revealing even vir
- GeneralClass 12All
Which microorganisms are used in agriculture and why?
Nitrogen-fixing bacteria, particularly Rhizobium species and free-living bacteria like Azotobacter, are extensively used in agriculture as biofertilizers because they convert atmospheric nitrogen into plant-usable forms, reducing or eliminating the need for expensive and environmentally harmful synthetic fertilizers. Rhizobium bacteria form symbiotic relationships with leguminous crops (beans, peas, clover, soybeans), colonizing root nodules and supplying nitrogen d
- GeneralClass 12All
Name two diseases caused by protozoa.
Malaria and amoebic dysentery are two significant diseases caused by protozoa that affect millions of people globally. Malaria is caused by Plasmodium species (particularly P. falciparum and P. vivax), parasitic protozoa transmitted to humans through the bite of infected female Anopheles mosquitoes. The parasites invade red blood cells, causing recurring cycles of high fever, chills, sweating, fatigue, and anemia. Malaria remains one of the deadliest infect
- GeneralClass 12All
Which microorganisms produce alcohol? Name the group to which these microorganisms belong?
Yeast microorganisms produce alcohol through the fermentation process, and they belong to the fungi group. The most commercially important species is Saccharomyces cerevisiae, commonly called brewer's yeast or baker's yeast, which has been used for thousands of years to produce alcoholic beverages and ferment bread dough. These single-celled fungi metabolize sugars under anaerobic conditions (without oxygen), converting glucose into ethanol (alcohol) and carbon dioxide as waste produ
- GeneralClass 12All
Microbes help us to keep our environment clean, how?
Microbes act as nature's recyclers by decomposing dead organic matter—plant debris, animal carcasses, fallen leaves, and waste materials—breaking them down into simpler inorganic substances that return nutrients to soil and water ecosystems. Bacteria and fungi are the primary decomposers that secrete enzymes to digest complex organic molecules like cellulose, proteins, and fats, converting them into carbon dioxide, water, minerals, and humus. Without microbial decomposition, dead
- GeneralClass 12All
Some microorganisms live in the roots of leguminous plants. Are they harmful or useful to plants and why?
Microorganisms living in the roots of leguminous plants are extremely useful and establish a mutually beneficial symbiotic relationship with their host plants. The bacteria Rhizobium and related species colonize root nodules of legumes like peas, beans, lentils, clover, and alfalfa, where they perform biological nitrogen fixation—converting atmospheric nitrogen gas into ammonia and other nitrogen compounds that plants can absorb and use for growth. This process is invaluable be
- GeneralClass 12All
How can we prevent mosquitoes from breeding?
Preventing mosquito breeding focuses on eliminating stagnant water sources where mosquitoes lay eggs and larvae develop, since mosquitoes require standing water to complete their life cycle. Remove all sources of standing water around homes and communities—empty containers, flower pots, old tires, buckets, bird baths, clogged gutters, and discarded bottles should be regularly emptied or disposed of. For water storage containers that cannot be eliminated, keep them tightly covered with l
- GeneralClass 12All
Name three substances that are used for commercial production of alcohol and wine by fermentation.
Grapes, grains (particularly malted barley), and sugarcane or molasses are the three primary raw materials used for commercial alcohol and wine production through fermentation. Grapes contain natural sugars (glucose and fructose) and are the traditional and predominant raw material for wine production—red, white, rosé, and sparkling wines all begin with crushed grapes fermented by naturally present or added yeast strains. Different grape varieties, growing regions, and fermentati
- GeneralClass 12All
Why Yeast is used in baking industry?
Yeast is indispensable in the baking industry because it produces carbon dioxide gas through fermentation, which causes bread dough to rise and develop its characteristic light, airy, and fluffy texture. When yeast (Saccharomyces cerevisiae) is mixed with flour, water, and sugar, it metabolizes the sugars present in the dough and releases carbon dioxide bubbles that become trapped in the gluten network formed by wheat proteins. This process, called leavening, creates thousands of tin
- GeneralClass 12All
What is fermentation and who discovered this process?
Fermentation is a metabolic process in which microorganisms, particularly yeast and certain bacteria, break down sugars in the absence of oxygen to produce energy, releasing alcohol, carbon dioxide, or organic acids as byproducts. This anaerobic process has been exploited by humans for thousands of years to produce bread, beer, wine, yogurt, cheese, and pickled foods, though the underlying science was not understood until the 19th century. Different microorganisms produce different fermentati
- GeneralClass 12All
Name two common insects which act as carriers of disease-causing microorganisms.
Mosquitoes and houseflies are two extremely common insects that act as carriers (vectors) of disease-causing microorganisms, transmitting pathogens from infected hosts to healthy individuals. Female Anopheles mosquitoes transmit malaria-causing Plasmodium parasites, while Aedes mosquitoes spread dengue, chikungunya, Zika virus, and yellow fever through their blood-feeding behavior. Mosquitoes inject pathogens directly into the bloodstream when they pierce skin to fe
- GeneralClass 12All
Name an antibiotic extracted from fungus (mould). Name the fungus.
Penicillin is the famous antibiotic extracted from fungus, and it is derived from the mold Penicillium notatum (also Penicillium chrysogenum). Scottish bacteriologist Alexander Fleming accidentally discovered penicillin in 1928 when he noticed that a Penicillium mold contaminating his bacterial culture plates had killed the surrounding Staphylococcus bacteria. This serendipitous observation led to the development of the world's first widely used antibiotic,
- GeneralClass 12All
Name the micro-organism which is used for the large scale production of alcohol.
Yeast, specifically the species Saccharomyces cerevisiae, is the microorganism used extensively for large-scale commercial alcohol production. This single-celled fungus carries out alcoholic fermentation, a metabolic process where it breaks down sugars (glucose, fructose, or sucrose) in the absence of oxygen, producing ethanol (alcohol) and carbon dioxide as byproducts. Breweries, distilleries, and wineries rely on controlled yeast fermentation to produce beer, wine, whiskey, vodka,
- GeneralClass 12All
What are the major groups of microorganisms?
The major groups of microorganisms include bacteria, viruses, fungi, protozoa, and algae, each with distinct characteristics, structures, and ecological roles. Bacteria are single-celled prokaryotic organisms without a defined nucleus, found virtually everywhere and playing crucial roles in nutrient cycling, digestion, and decomposition, though some cause diseases. Viruses are non-cellular infectious agents that require living host cells to reproduce, causing numerous plant, animal, and human
- GeneralClass 12All
What is the name of the microorganisms which reproduce only inside the living cells of other organisms?
Viruses are the microorganisms that can reproduce only inside the living cells of host organisms. Unlike bacteria, fungi, or protozoa, viruses are not technically considered fully "alive" because they lack cellular structure, cannot carry out metabolic processes independently, and possess no machinery for self-replication. A virus consists simply of genetic material (DNA or RNA) enclosed in a protein coat, and sometimes an outer lipid envelope. Once a virus invades a host cell, it hij