General Science/Everyday Science MCQs
Topic Notes: General Science/Everyday Science
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
331
Nitrogen-fixing bacteria exist mainly in which part of plants?
Answer:
Roots
Symbiotic bacteria like Rhizobium inhabit root nodules of legumes. They fix atmospheric nitrogen into ammonia, enriching soil fertility. Free-living nitrogen-fixers also exist, but roots are the most common site for symbiosis.
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332
The conversion of ammonium to nitrate (NO₃⁻) by chemical oxidation is called:
Answer:
onversion of ammonium to nitrate (NO₃⁻) by chemical oxidation is called:
Nitrification is carried out by specialized bacteria like Nitrosomonas and Nitrobacter. They oxidize ammonium into nitrite and then nitrate. This makes nitrogen more available to plants but also more prone to leaching.
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333
Plants can take up nitrogen in which forms?
Answer:
NH₄⁺ and NO₃⁻
Plants primarily absorb nitrogen as ammonium (NH₄⁺) and nitrate (NO₃⁻). Atmospheric N₂ cannot be directly absorbed and requires fixation. This bioavailable nitrogen supports plant growth and productivity.
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334
Earth’s atmosphere contains about how much nitrogen?
Answer:
78%
Nitrogen makes up nearly 78% of Earth’s atmosphere, oxygen about 21%, and trace gases the rest. This stable nitrogen reservoir is essential for the nitrogen cycle, though atmospheric N₂ is unusable to most organisms without fixation.
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335
The depletion of trees is causing accumulation of which gas?
Answer:
Carbon dioxide (CO₂)
Trees absorb CO₂ during photosynthesis. Deforestation reduces this uptake, causing more CO₂ to remain in the atmosphere. Rising CO₂ is the main driver of global warming.
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336
The movement of carbon between Earth’s spheres is called the carbon cycle. Which spheres are involved?
Answer:
Biosphere, atmosphere, hydrosphere, and geosphere
The carbon cycle spans all four spheres of Earth. Carbon moves through photosynthesis, respiration, ocean absorption, fossil fuel burning, and rock formation. This interconnected exchange regulates climate and supports life.
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337
Which of the following is a **nonpoint source** of water pollution?
Answer:
Urban and suburban lands
Nonpoint sources are diffuse and cannot be traced to a single discharge location, such as runoff from streets, lawns, and farms. Factories and sewage plants are **point sources** because they discharge from identifiable outlets. Nonpoint sources are harder to regulate and often carry fertilizers, oils, and chemicals into water bodies.
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338
Nitrogen-fixing blue-green alga is:
Answer:
Nostoc
Nostoc, a cyanobacterium, fixes atmospheric nitrogen into ammonia, enriching soils. Rhizobium associates with legume roots, while Clostridium and Nitrosomonas have other roles in the nitrogen cycle. Nostoc thrives in waterlogged soils and paddy fields.
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✅ That completes **Q139–Q172** in the same structured style.
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339
Which is a sedimentary biogeochemical cycle?
Answer:
Phosphorus cycle
The phosphorus cycle is sedimentary because it does not involve a gaseous phase. Phosphates move through rocks, soil, water, and living organisms. In contrast, nitrogen, carbon, and oxygen cycles involve the atmosphere.
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340
Excess fluoride in drinking water leads to:
Answer:
Fluorosis
Chronic fluoride exposure causes dental and skeletal fluorosis. Teeth develop mottling, and bones become brittle. This is a major public health issue in areas with naturally high groundwater fluoride.
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