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Q1. Which of these is a disease-causing microorganism in plants?
The virus causing yellow vein mosaic of bhindi (okra) is a disease-causing microorganism in plants. It is transmitted by insects like whiteflies and causes yellowing and vein clearing in leaves. Rhizobium and Lactobacillus are beneficial bacteria, and yeast is used in baking and fermentation.
Q2. What is the process of converting atmospheric nitrogen into usable nitrogen compounds called?
Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into usable nitrogen compounds like ammonia and nitrates. This can be done by bacteria like Rhizobium, blue-green algae, or through atmospheric fixation by lightning. The nitrogen cycle is the larger cycle, pasteurisation is heat treatment, and fermentation is microbial conversion of sugars.
Q3. What is the name of the natural process that recycles nitrogen in various forms between the atmosphere, soil, plants, and animals?
The nitrogen cycle is the natural process that recycles nitrogen in different forms between the atmosphere, soil, plants, and animals. It includes nitrogen fixation, nitrification, assimilation, ammonification, and denitrification. The water, carbon, and oxygen cycles are different biogeochemical cycles.
Q4. Which of these is an example of algae?
Spirogyra is a filamentous green alga found in freshwater. It contains chlorophyll and performs photosynthesis. Mushroom is a fungus, Amoeba is a protozoan, and Rhizobium is a bacterium. Spirogyra is a classic example of algae.
Q5. What are the proteins produced by the body’s immune system to fight pathogens called?
Antibodies are Y-shaped proteins produced by the body’s immune system (specifically B cells) in response to antigens. They bind specifically to pathogens and neutralize them. Antigens are foreign substances that trigger antibody production. Antibiotics kill bacteria, and antiseptics are used on wounds.
Q6. Which microorganism is used in the fermentation process to make bread and alcohol?
Yeast (Saccharomyces cerevisiae) is used in fermentation to produce bread (carbon dioxide makes dough rise) and alcohol (ethanol). Lactobacillus makes curd, Rhizobium fixes nitrogen, and Penicillium produces antibiotics. Yeast is the main organism for these processes.
Q7. What do we call the bacteria commonly found in curd and beneficial for digestion?
Lactobacillus is a beneficial bacterium found in curd (yogurt). It ferments lactose into lactic acid, giving curd its sour taste, and is beneficial for gut health. Rhizobium fixes nitrogen, Streptococcus can be harmful, and Acetobacter produces vinegar.
Q8. What is the general term for an organism that carries a disease-causing microbe without getting sick itself?
A vector or carrier is an organism that transmits a disease-causing microbe from one host to another without itself being affected. For example, mosquitoes carry malaria parasites, and houseflies carry cholera bacteria. A host is the organism in which the pathogen lives, and a pathogen is the disease-causing agent.
Q9. Diseases that can spread from one person to another are called?
Communicable diseases are those that can spread from an infected person to a healthy person through air, water, food, vectors, or physical contact. Examples include the common cold, tuberculosis, and cholera. Deficiency diseases are caused by lack of nutrients, non-communicable diseases do not spread, and genetic diseases are inherited.
Q10. Which process involves the conversion of sugar into alcohol or acids by microorganisms?
Fermentation is the process by which microorganisms like yeast and bacteria convert sugars into alcohol or acids. Yeast produces alcohol and carbon dioxide, while Lactobacillus produces lactic acid. Nitrogen fixation, pasteurization, and preservation are different processes.
Q11. Ringworm in humans is caused by which type of microorganism?
Ringworm is a fungal skin infection caused by dermatophytes. It appears as ring-shaped rashes on the skin. It is not caused by bacteria, viruses, or protozoa. Typhoid and cholera are bacterial diseases, and malaria is protozoan.
Q12. What do we call a living organism that is visible only under a microscope?
Microorganisms are living organisms that are too small to be seen with the naked eye and require a microscope for observation. They include bacteria, viruses, fungi, algae, and protozoa. Insects, mammals, and reptiles are all visible without a microscope.
Q13. Which bacteria live in the root nodules of leguminous plants and fix atmospheric nitrogen?
Rhizobium bacteria live in the root nodules of leguminous plants (like peas, beans, and groundnuts). They fix atmospheric nitrogen into ammonia, which is then used by the plants. Lactobacillus is used in curd, E. coli is found in the intestine, and Salmonella causes food poisoning.
Q14. What is the process of heating milk to a high temperature to kill harmful bacteria called?
Pasteurization is the process of heating milk to about 72°C for 15 seconds and then quickly cooling it to kill harmful bacteria without affecting its nutritional value. It was developed by Louis Pasteur. Fermentation uses microbes, nitrogen fixation is for soil, and preservation is a broader term.
Q15. What is the term for a disease-causing microorganism?
A pathogen is a disease-causing microorganism such as bacteria, viruses, fungi, or protozoa. Examples include Salmonella (bacteria), HIV (virus), and Plasmodium (protozoa). Antibodies fight pathogens, antibiotics kill bacteria, and carriers spread pathogens.
Q16. Which method involves treating food to prevent spoilage by microorganisms?
Fermentation, pasteurization, and preservation are all methods used to prevent food spoilage by microorganisms. Fermentation produces acids/alcohol, pasteurization uses heat, and preservation includes methods like salting, sugaring, and refrigeration. All are effective ways to protect food from microbial growth.
Q17. Amoeba is an example of which group of microorganisms?
Amoeba is a single-celled protozoan that moves using pseudopodia. It is a consumer that feeds on bacteria and other organic matter. Protozoa are unicellular eukaryotic organisms. Bacteria are prokaryotic, fungi are multicellular (except yeast), and algae are photosynthetic.
Q18. What is the name of the bacterial vaccine that prevents tuberculosis?
BCG (Bacillus Calmette-Guérin) is a vaccine given to prevent tuberculosis (TB), caused by Mycobacterium tuberculosis. OPV is the oral polio vaccine, MMR is for measles, mumps, and rubella, and DTP is for diphtheria, tetanus, and pertussis.
Q19. Which microorganism is considered non-living outside a host cell and causes diseases like the common cold?
Viruses are considered non-living outside a host cell because they cannot reproduce or carry out metabolic functions on their own. They become active only inside a host cell. The common cold is caused by rhinovirus. Bacteria, fungi, and protozoa are living organisms.
Q20. What have you learnt about the size of microorganisms?
Microorganisms are very small and cannot be seen without a microscope. Their size ranges from nanometres (viruses) to micrometres (bacteria, fungi, protozoa). They are not all the same size, and they are not visible as dots without magnification.
Q21. Where can microorganisms live?
Microorganisms are found everywhere—in air, water, soil, hot springs, deserts, marshy lands, and inside living organisms. They are adapted to survive in extreme environments as well. They are not limited to any single habitat.
Q22. Microorganisms are found in:
Microorganisms are found in air, water, soil, and inside the bodies of plants and animals. They are ubiquitous and can survive in diverse conditions. They are not confined to spoiled food or any one environment.
Q23. Microorganisms can be:
Microorganisms can be unicellular (e.g., bacteria, amoeba, yeast) or multicellular (e.g., moulds, some algae). Viruses are acellular. So, microorganisms include both unicellular and multicellular forms.
Q24. Which groups are included under microorganisms?
Microorganisms include bacteria, fungi, protozoa, and some algae. Viruses are also included, though they are acellular. The correct group includes these four major categories. Not all microorganisms are pathogenic; many are beneficial.
Q25. How are viruses different from other microorganisms?
Viruses are unique because they can only reproduce inside a host cell. Outside the host, they are inert and non-living. They do not carry out metabolic processes and are much smaller than other microorganisms. They are not the largest microbes and do not make their own food.
Q26. Some microorganisms are useful for the commercial production of:
Microorganisms are used commercially to produce medicines (like antibiotics from Penicillium) and alcohol (through fermentation by yeast). They are also used to produce biofuels, but the broad correct answer includes medicines and alcohol. They are not used to produce plastics or metals.
Q27. Which protozoan causes serious diseases like dysentery and malaria?
Entamoeba histolytica causes amoebic dysentery, and Plasmodium causes malaria. Rhizobium and Lactobacillus are bacteria, Penicillium and Aspergillus are fungi, and yeast is a fungus. These protozoan parasites are responsible for serious diseases.
Q28. What can cause food poisoning?
Food poisoning is caused by consuming food contaminated with harmful microorganisms (bacteria like Salmonella, E. coli) or their toxins. Salt and refrigeration preserve food, and cooking kills microbes. Spoilage by pathogens leads to poisoning.
Q29. Where do nitrogen-fixing microorganisms reside in leguminous plants?
Nitrogen-fixing bacteria like Rhizobium reside in the root nodules of leguminous plants. These nodules provide an oxygen-limited environment where the bacteria can convert atmospheric nitrogen into ammonia, which is then used by the plant.
Q30. What is the role of these bacteria in root nodules?
The bacteria in root nodules (Rhizobium) fix atmospheric nitrogen into usable ammonia. This enriches the soil with nitrogen compounds, which are essential for plant growth. This process increases soil fertility without the need for chemical fertilizers.
Q31. Which organisms, present in soil, can fix atmospheric nitrogen?
Some bacteria (like Rhizobium and Azotobacter) and blue-green algae (cyanobacteria) can fix atmospheric nitrogen in the soil. Earthworms improve soil structure but do not fix nitrogen. Fungi decompose organic matter, and viruses do not fix nitrogen.
Q32. What is the role of decomposer microorganisms?
Decomposer microorganisms (like bacteria and fungi) break down dead plants and animals and organic waste into simpler substances, recycling nutrients back into the soil. This is essential for maintaining soil fertility and cleaning the environment.
Q33. What do certain bacteria do to nitrogen compounds in the soil?
Certain bacteria perform denitrification, converting nitrates in the soil back into nitrogen gas (N₂), which is released into the atmosphere. This completes the nitrogen cycle. They do not produce oxygen or store nitrogen compounds permanently.
Q34. Which plant disease is caused by a fungus?
Rust of wheat is a fungal disease caused by Puccinia species. Citrus canker is bacterial, and yellow vein mosaic of bhindi is viral. Rust of wheat is the only fungal disease among the options.
Q35. In the nitrogen cycle, plants absorb nitrogen from the soil in the form of:
Plants absorb nitrogen from the soil in the form of nitrates (NO₃⁻) and nitrites (NO₂⁻). Nitrogen gas cannot be absorbed directly. Ammonia is converted to nitrates by nitrifying bacteria. Proteins are made by plants, not absorbed.
Q36. Which of these is not a part of the nitrogen cycle?
Photosynthesis is not a part of the nitrogen cycle; it is part of the carbon and oxygen cycles. Nitrogen fixation, nitrification, and denitrification are all steps in the nitrogen cycle, which involves the conversion of nitrogen between different forms.
Q37. Algae are important because they:
Algae are important because they produce oxygen through photosynthesis and are used as food (e.g., spirulina, seaweed). They do not cause human diseases (some algae can be harmful, but not as pathogens), fix nitrogen (cyanobacteria do), or make antibiotics (fungi do).
Q38. Antibodies are produced by:
Antibodies are produced by white blood cells (specifically B lymphocytes) in response to antigens. They are proteins that help neutralise pathogens. Pathogens trigger antibody production, vaccines stimulate it, and antibiotics are medicines that kill bacteria.
Q39. Fermentation by yeast is used in making:
Yeast fermentation is used to make bread (carbon dioxide makes it rise) and beer (alcohol production). Cheese and yogurt are made by bacteria (Lactobacillus), pickles use salt and vinegar, and compost is made by decomposers.
Q40. The process of preservation by adding salt or sugar works by:
Salt and sugar preserve food by creating a hypertonic environment. This draws water out of microbial cells, causing them to dehydrate and die. This prevents spoilage. It does not kill microbes instantly but inhibits their growth.
Q41. Which of these is a communicable disease?
Influenza (flu) is a communicable disease caused by the influenza virus. It spreads through droplets from coughs and sneezes. Diabetes, heart disease, and cancer are non-communicable diseases caused by metabolic, lifestyle, or genetic factors.
Q42. A mosquito carrying malaria parasites is an example of a:
A mosquito is a vector or carrier that transmits the malaria parasite (Plasmodium) without getting sick itself. It spreads the pathogen from one host to another. The pathogen is the parasite, and the host is the organism infected.
Q43. Penicillin, an antibiotic, is obtained from:
Penicillin is an antibiotic obtained from the fungus Penicillium. It was discovered by Alexander Fleming in 1928. It kills bacteria and is used to treat bacterial infections. It is not obtained from bacteria, viruses, or protozoa.
Q44. The virus that causes polio primarily affects the:
The poliovirus primarily affects the nervous system, particularly the spinal cord and brainstem. It can cause paralysis. It is transmitted through contaminated water and food. The polio vaccine (OPV/IPV) prevents this disease.
Q45. Which microorganism helps in the formation of curd?
Lactobacillus bacteria convert milk sugar (lactose) into lactic acid, which coagulates milk proteins to form curd (yogurt). Yeast is used in baking, Rhizobium fixes nitrogen, and Acetobacter produces vinegar. Lactobacillus is the key organism for curd formation.
Q46. Blue-green algae are now classified as:
Blue-green algae are now classified as cyanobacteria. They are prokaryotic bacteria capable of photosynthesis. They are not true algae (which are eukaryotic). They also fix atmospheric nitrogen and are important in the nitrogen cycle.
Q47. In the nitrogen cycle, the conversion of ammonia to nitrites and nitrates is called:
Nitrification is the biological oxidation of ammonia to nitrites (by Nitrosomonas) and then to nitrates (by Nitrobacter). This makes nitrogen available to plants. Nitrogen fixation is the conversion of N₂ to ammonia, denitrification is the reverse, and assimilation is uptake by plants.
Q48. Vaccines work by:
Vaccines contain antigens (weakened or dead pathogens) that stimulate the body’s immune system to produce antibodies and memory cells. This provides immunity without causing the disease. They do not directly kill pathogens or weaken the immune system.
Q49. Which of these is a method of food preservation that uses low temperature?
Refrigeration is a method of food preservation that uses low temperature. It slows down microbial growth and enzyme activity, keeping food fresh for longer. Salting uses salt, canning uses heat and sealing, and smoking uses smoke.
Q50. Microorganisms that thrive in extreme environments like hot springs are called:
Extremophiles are microorganisms that thrive in extreme environments such as hot springs, high salt, high acidity, or high pressure. Thermophiles (heat-loving) are a type of extremophile. Pathogens cause diseases, decomposers break down matter, and carriers spread diseases.
Q51. The causative agent of citrus canker in plants is a:
Citrus canker is caused by the bacterium Xanthomonas citri. It affects citrus plants, causing lesions on leaves, stems, and fruits. Rust of wheat is fungal, yellow vein mosaic is viral, and nematodes cause root-knot diseases. The correct causative agent is a bacterium.
Q52. Which step in the nitrogen cycle is performed by rhizobium bacteria?
Rhizobium bacteria perform nitrogen fixation—the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃). This occurs in root nodules of leguminous plants. Denitrification, nitrification, and ammonification are performed by other bacteria.
Q53. Antibodies are specific, meaning:
Antibodies are specific in that each type of antibody binds to a specific antigen (like a lock and key). They are produced by the immune system in response to particular pathogens. They are not broad-spectrum or produced at night, and they are highly useful.
Q54. The process where bacteria convert dead organic matter into ammonia is called:
Ammonification is the process where decomposer bacteria convert organic nitrogen from dead plants and animals into ammonia (NH₃). This makes nitrogen available for nitrification. Nitrogen fixation is from N₂, nitrification is ammonia to nitrates, and denitrification is nitrates to N₂.
Q55. A person who has recovered from measles will not get it again because their body now has:
After recovering from measles, the body develops memory cells that “remember” the pathogen. If the same virus enters again, these cells trigger a rapid and strong antibody response, preventing reinfection. This is called acquired immunity. Antibiotics are not involved.
Q56. Which of these is a free-living nitrogen-fixing bacterium in soil?
Azotobacter is a free-living nitrogen-fixing bacterium found in soil. It fixes atmospheric nitrogen without requiring a host plant. Rhizobium requires root nodules, Lactobacillus is used in curd, and Salmonella is a pathogen.
Q57. Malaria is caused by a protozoan, but it is spread by:
Malaria is spread by the bite of an infected female Anopheles mosquito, which is a vector. The protozoan parasite (Plasmodium) is transmitted through the mosquito’s bite. It is not waterborne, airborne, or spread by direct contact.
Q58. The ‘active immunity’ provided by a vaccine is:
Active immunity from vaccination is generally long-lasting or permanent because the body produces its own antibodies and memory cells. Booster doses may be needed for some vaccines, but the immunity is not temporary. It is effective in humans and animals.
Q59. Which gas makes up about 78% of the atmosphere but is unusable by most organisms in that form?
Nitrogen (N₂) makes up about 78% of the atmosphere. Most organisms cannot use it directly in this form. It must be fixed into usable compounds like ammonia or nitrates through nitrogen fixation. Oxygen is about 21%, carbon dioxide is less than 1%, and hydrogen is very scarce.
Q60. What is the primary reason for adding yeast to bread dough?
Yeast is added to bread dough primarily to produce carbon dioxide gas through fermentation. The gas gets trapped in the dough, causing it to rise and become light and fluffy. Flavor is a secondary effect, and yeast does not add color or kill bacteria.