Class 12 Biology – Daily Revision MCQ (English Medium)
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Which is the only gaseous plant growth regulator?
Chapter 7: Plant Growth and Mineral Nutrition
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Answer: C. Ethylene
Ethylene is a gaseous growth regulator; it is known especially for ripening fruits.Bolting — sudden elongation of internodes just before flowering in rosette plants such as cabbage and beet — is promoted by:
Chapter 7: Plant Growth and Mineral Nutrition
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Answer: A. gibberellins
Gibberellins cause stem/internode elongation and promote bolting in rosette plants.Which glial cells produce the myelin sheath around medullated nerve fibres of the peripheral nervous system (PNS)?
Chapter 9: Control and Co-ordination
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Answer: D. Schwann cells
Schwann cells, the most abundant glial cells of the PNS, form the myelin sheath around medullated nerves.During an action potential, the membrane potential of a nerve fibre changes from about −70 mV to about:
Chapter 9: Control and Co-ordination
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Answer: B. +30 mV
Na⁺ ions rush into the axon, so the inside becomes positive and the potential rises from −70 mV to about +30 mV.The nitrogen-fixing cyanobacterium Anabaena lives in association with which water fern that is used as a biofertilizer?
Chapter 11: Enhancement of Food Production
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Answer: C. Azolla
Anabaena lives in the dorsal lobe of Azolla leaves and fixes nitrogen, so Azolla is used as a biofertilizer in paddy fields.Gause's competitive exclusion principle states that two closely related species competing for the same resources:
Chapter 13: Organisms and Populations
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Answer: B. cannot co-exist indefinitely
Two closely related species competing for the same resources cannot co-exist indefinitely; the competitively inferior one is eliminated.A population growing in a habitat with limited resources shows which type of growth curve?
Chapter 13: Organisms and Populations
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Answer: D. Sigmoid (S-shaped, logistic)
With limited resources there is a lag phase, then rapid growth, then levelling off at the carrying capacity — a logistic or sigmoid curve.An inverted pyramid of biomass is typically seen in which ecosystem?
Chapter 14: Ecosystems and Energy Flow
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Answer: A. Ocean (aquatic)
In the ocean the biomass of tiny phytoplankton at any moment is less than that of the consumers feeding on them, so the biomass pyramid is inverted.Down's syndrome is caused by:
Chapter 3: Inheritance and Variation
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Answer: B. an extra copy of chromosome 21 (trisomy 21)
Failure of chromosome 21 to separate (non-disjunction) gives three copies of it, so the person has 47 chromosomes instead of 46.Which one of these codons does not code for any amino acid and stops the growth of the polypeptide chain?
Chapter 4: Molecular Basis of Inheritance
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Answer: D. UGA
Of the 64 codons, UAA, UAG and UGA are termination (stop) codons; AUG codes for methionine.
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All questions are written by PadhaiNotes in our own words from the chapters of the official Maharashtra State Board Balbharati textbook (ebalbharati.in). Each question shows its chapter.