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Biology MCQs

Practice complete Biology MCQs covering Introduction to Biology, Cell Biology, Cell Structure, Cell Division, Biomolecules, Plant Physiology, Human Physiology, Genetics, Evolution, Biotechnology, Ecology, Classification of Living Organisms, Plant Kingdom, Animal Kingdom, Microbiology, Human Diseases, Nutrition, Reproduction, Environmental Biology, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Page 26 of 103
Question #501
The technique of growing plants in a nutrient solution without soil is called:
A. Vermiculture
B. Hydroponics
C. Tissue culture
D. Aquaculture
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Correct Answer: Option B

Explanation:
Hydroponics involves growing plants with their roots in a mineral nutrient solution in water, without soil. This allows precise control of nutrients and is used in research and commercial production. Aquaculture is fish farming, tissue culture is in vitro plant propagation, vermiculture is earthworm composting.
This question belongs to: Science Biology
Question #502
The disorder caused by an extra X chromosome in males (XXY) is:
A. Klinefelter syndrome
B. Cri du chat syndrome
C. Down syndrome
D. Turner syndrome
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Correct Answer: Option A

Explanation:
Klinefelter syndrome (47,XXY) is a sex chromosome aneuploidy causing male hypogonadism, tall stature, gynecomastia, and infertility. Turner syndrome (45,X) affects females. Down syndrome is trisomy 21. Cri du chat is deletion in chromosome 5. Nondisjunction during meiosis leads to these aneuploidies.
This question belongs to: Science Biology
Question #503
The biodegradable plastic PHB (polyhydroxybutyrate) is produced by:
A. Saccharomyces cerevisiae
B. Escherichia coli
C. Bacillus megaterium
D. Lactobacillus
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Correct Answer: Option C

Explanation:
Certain bacteria, like Bacillus megaterium and Alcaligenes eutrophus, accumulate polyhydroxyalkanoates (PHA) such as PHB as intracellular carbon and energy storage under nutrient stress. These are used to make biodegradable plastics. E. coli is engineered for some bioplastics, but natural producers include Bacillus.
This question belongs to: Science Biology
Question #504
The organ that is responsible for the detoxification of ammonia to urea in humans is the:
A. Liver
B. Kidney
C. Spleen
D. Pancreas
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Correct Answer: Option A

Explanation:
The liver converts toxic ammonia (from amino acid deamination) into less toxic urea via the urea cycle (ornithine cycle) in hepatocytes. Urea is then excreted by the kidneys. The kidneys filter urea but do not produce it. Pancreas produces enzymes/hormones, spleen filters blood.
This question belongs to: Science Biology
Question #505
The phenomenon of a plant bending toward a light source is called:
A. Thigmotropism
B. Hydrotropism
C. Phototropism
D. Geotropism
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Correct Answer: Option C

Explanation:
Phototropism is the directional growth of a plant in response to light; shoots exhibit positive phototropism (grow towards light), roots negative. Auxin redistribution causes differential growth. Geotropism is gravity response, hydrotropism water, thigmotropism touch. Phototropism optimizes light capture for photosynthesis.
This question belongs to: Science Biology
Question #506
The method of separating proteins based on their size using an electric field is:
A. DNA sequencing
B. PCR
C. SDS-PAGE
D. ELISA
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Correct Answer: Option C

Explanation:
SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) denatures proteins and coats them with negative charge, allowing separation by molecular weight in an electric field. PCR amplifies DNA, sequencing determines base order, ELISA detects antigens/antibodies. SDS-PAGE is a fundamental biochemistry technique.
This question belongs to: Science Biology
Question #507
The part of the plant embryo that develops into the root is the:
A. Radicle
B. Hypocotyl
C. Plumule
D. Epicotyl
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Correct Answer: Option A

Explanation:
The radicle is the embryonic root, emerging first during germination, and develops into the primary root system. The plumule develops into the shoot, hypocotyl is below cotyledons, epicotyl above cotyledons. The radicle grows downward (positively geotropic) to anchor and absorb water.
This question belongs to: Science Biology
Question #508
The antibiotic that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit is:
A. Vancomycin
B. Penicillin
C. Tetracycline
D. Cephalosporin
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Correct Answer: Option C

Explanation:
Tetracycline binds to the 30S ribosomal subunit, blocking attachment of aminoacyl-tRNA, thus inhibiting protein synthesis. Penicillin and cephalosporins inhibit cell wall synthesis, vancomycin also inhibits cell wall synthesis. Aminoglycosides like streptomycin also target 30S. Protein synthesis inhibitors exploit the difference between bacterial and human ribosomes.
This question belongs to: Science Biology
Question #509
The disease caused by the poliovirus primarily affects the:
A. Liver
B. Nervous system
C. Kidney
D. Lungs
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Correct Answer: Option B

Explanation:
Poliovirus attacks motor neurons in the spinal cord and brainstem, causing paralysis. It spreads via the fecal-oral route. Vaccination (IPV/OPV) has almost eradicated it globally. The virus replicates in the intestine and then invades the nervous system. Polio survivors may suffer post-polio syndrome later.
This question belongs to: Science Biology
Question #510
The mineral that is a component of the hormone insulin is:
A. Calcium
B. Zinc
C. Sulfur
D. Iron
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Correct Answer: Option B

Explanation:
Zinc is a component of the insulin hexamer stored in pancreatic beta cells; it stabilizes the insulin structure. Iron is in hemoglobin, calcium in bones/signaling, sulfur in some amino acids. Zinc deficiency impairs insulin secretion. Many enzymes require zinc as a cofactor.
This question belongs to: Science Biology
Question #511
The type of plant tissue that has thin walls and functions in photosynthesis and storage is:
A. Collenchyma
B. Parenchyma
C. Sclerenchyma
D. Xylem
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Correct Answer: Option B

Explanation:
Parenchyma cells are living, thin-walled, and isodiametric, making up the ground tissue of plants. They are involved in photosynthesis (chlorenchyma), storage, and secretion. Collenchyma provides support with uneven thickening, sclerenchyma has lignified walls and is often dead, xylem conducts water.
This question belongs to: Science Biology
Question #512
The molecule that carries the genetic code from the nucleus to the cytoplasm is:
A. tRNA
B. rRNA
C. DNA
D. mRNA
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Correct Answer: Option D

Explanation:
Messenger RNA (mRNA) is transcribed from DNA in the nucleus and carries the codon sequence to ribosomes in the cytoplasm for translation into protein. tRNA brings amino acids, rRNA forms ribosomes, DNA stays in the nucleus. mRNA is the template for protein synthesis.
This question belongs to: Science Biology
Question #513
The scientist who proposed the theory of evolution by natural selection is:
A. Jean-Baptiste Lamarck
B. Gregor Mendel
C. Louis Pasteur
D. Charles Darwin
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Correct Answer: Option D

Explanation:
Charles Darwin, in 'On the Origin of Species' (1859), proposed natural selection as the mechanism for evolution, based on variation, inheritance, and differential survival. Mendel discovered genetics, Pasteur disproved spontaneous generation, Lamarck proposed inheritance of acquired characters. Wallace independently arrived at natural selection.
This question belongs to: Science Biology
Question #514
The type of joint that allows the head to rotate from side to side is:
A. Ball and socket joint
B. Pivot joint
C. Hinge joint
D. Gliding joint
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Correct Answer: Option B

Explanation:
The atlantoaxial joint (between atlas and axis vertebrae) is a pivot joint, allowing rotation of the head ('no' motion). Hinge allows flexion/extension, ball and socket multiaxial, gliding sliding. The odontoid process of the axis acts as a pivot.
This question belongs to: Science Biology
Question #515
The process of removing waste products from the blood using a machine is called:
A. Transfusion
B. Bypass
C. Dialysis
D. Endoscopy
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Correct Answer: Option C

Explanation:
Dialysis artificially filters waste products (urea, creatinine) and excess fluid from the blood when kidneys fail, using a semipermeable membrane. Hemodialysis uses an external dialyzer, peritoneal dialysis uses the peritoneal membrane. Bypass is a surgical procedure, transfusion is blood transfer, endoscopy is visualization.
This question belongs to: Science Biology
Question #516
The term 'transgenic' refers to an organism that:
A. Contains genes from another species introduced by genetic engineering
B. Is a clone
C. Has undergone natural mutation
D. Is produced by cross-breeding
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Correct Answer: Option A

Explanation:
Transgenic organisms carry a foreign gene (transgene) deliberately inserted into their genome using recombinant DNA technology. Example: transgenic mice with human genes for disease modeling. GMO is broader, but transgenic specifically involves genes from different species. Cloning copies genome, cross-breeding is within species.
This question belongs to: Science Biology
Question #517
The pollen tube enters the ovule through the:
A. Hilum
B. Chalaza
C. Micropyle
D. Funicle
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Correct Answer: Option C

Explanation:
The pollen tube typically enters the ovule through the micropyle, a small opening in the integuments. This is called porogamy. Occasionally, entry through the chalaza (chalazogamy) or integuments (mesogamy) occurs. The micropyle also allows water entry during seed germination.
This question belongs to: Science Biology
Question #518
The protein that gives red blood cells their flexibility and shape is:
A. Hemoglobin
B. Myosin
C. Spectrin
D. Keratin
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Correct Answer: Option C

Explanation:
Spectrin is a cytoskeletal protein that lines the inner surface of the RBC membrane, maintaining its biconcave shape and providing elasticity to squeeze through capillaries. Hemoglobin carries oxygen, myosin is a motor protein, keratin is structural in skin/hair. Defects in spectrin cause spherocytosis.
This question belongs to: Science Biology
Question #519
The kingdom that contains prokaryotic organisms is:
A. Plantae
B. Monera
C. Fungi
D. Protista
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Correct Answer: Option B

Explanation:
Whittaker's five-kingdom system places all prokaryotes (bacteria, cyanobacteria, archaea) in Monera. They lack a true nucleus and membrane-bound organelles. Protista has unicellular eukaryotes, Fungi and Plantae are multicellular eukaryotes (except yeast). Monera reproduces asexually mainly by binary fission.
This question belongs to: Science Biology
Question #520
The molecule that binds to the operator region of the lac operon to inhibit transcription is:
A. RNA polymerase
B. Inducer
C. CAP protein
D. Repressor protein
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Correct Answer: Option D

Explanation:
The lac repressor protein (product of lacI gene) binds to the operator sequence, preventing RNA polymerase from transcribing the structural genes. When lactose is present, allolactose (inducer) binds the repressor, causing it to release the operator, allowing transcription. This is negative regulation.
This question belongs to: Science Biology

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