जीव विज्ञान – Biology MCQ
जीव विज्ञान – कृषि/वन प्रवेश
Biology · Agriculture, Veterinary & Forestry Entrance · ८४० प्रश्न
८४० प्रश्न उपलब्ध। मोड छान्नुहोस्:
जीव विज्ञान: प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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Oxidation of ammonia to nitrite in soil is carried out by:
सही उत्तर: घ) Nitrosomonas
Nitrosomonas converts ammonia to nitrite in the first step of nitrification. Nitrobacter carries out the second step, converting nitrite to nitrate.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Which of the following is a free-living aerobic nitrogen-fixing bacterium?
सही उत्तर: ख) Azotobacter
Azotobacter fixes atmospheric nitrogen without a host and is used as a biofertilizer. Nitrosomonas does not fix nitrogen; it oxidises ammonia to nitrite.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Leghaemoglobin in legume root nodules functions to:
सही उत्तर: क) Protect nitrogenase from oxygen
Leghaemoglobin binds oxygen and keeps its free concentration low, because nitrogenase is inactivated by O2. It gives active nodules their pink colour.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The enzyme nitrogenase requires which metal for its activity?
सही उत्तर: ख) Molybdenum
Nitrogenase contains a molybdenum-iron (MoFe) cofactor that reduces N2 to ammonia. This is why molybdenum is important for legume crops.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Opening of stomata is mainly associated with the influx of which ion into guard cells?
सही उत्तर: क) K+
Accumulation of potassium ions lowers the water potential of guard cells, water enters, and they become turgid, opening the pore. Ca2+ is rather involved in signalling for closure.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Guttation in plants takes place through:
सही उत्तर: ख) Hydathodes
Guttation is the loss of water as liquid droplets through hydathodes, usually in early morning when root pressure is high. Stomata release water as vapour in transpiration.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Lenticels in woody stems help in:
सही उत्तर: ख) Gaseous exchange
Lenticels are lens-shaped openings in the bark that allow exchange of gases. Guttation occurs through hydathodes at leaf margins.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The central, dark-coloured, non-conducting wood of an old tree trunk is called:
सही उत्तर: क) Heartwood
Heartwood (duramen) is dark because of deposits like tannins and resins, and it is durable. Sapwood (alburnum) is the outer, lighter, water-conducting wood.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Estimating the age of a tree by counting its annual rings is called:
सही उत्तर: ग) Dendrochronology
Dendrochronology is the study of annual growth rings to date trees and past climate. Palynology is the study of pollen grains.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Annual rings in a woody stem are formed by the activity of the:
सही उत्तर: ग) Vascular cambium
Each year the vascular cambium forms wide springwood and narrow autumnwood, producing one annual ring. Cork cambium produces bark, not annual rings.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
यी अभ्यास प्रश्न हुन्, आधिकारिक प्रश्न होइनन्। पाठ्यक्रम, विज्ञापन र नतिजाका लागि सम्बन्धित निकायको आधिकारिक वेबसाइट हेर्नुहोस्। उत्तरमा गल्ती भेटे प्रश्नमुनिको "टिप्पणी / गल्ती रिपोर्ट" मा लेख्नुहोस्।
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