Biology MCQs

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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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Question #581
The functional unit of the human kidney is the:
A. Nephron
B. Neuron
C. Hepatocyte
D. Alveolus
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Correct Answer: Option A

Explanation:
The nephron is the microscopic structural and functional unit that filters blood and forms urine. It consists of the renal corpuscle (glomerulus + Bowman's capsule) and tubules. Alveoli are lung units, neurons are nerve cells, hepatocytes are liver cells. Each kidney contains about one million nephrons.
This question belongs to: Science Biology
Question #582
The part of the brain that coordinates voluntary muscle movements and maintains balance is the:
A. Thalamus
B. Cerebrum
C. Cerebellum
D. Medulla oblongata
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Correct Answer: Option C

Explanation:
The cerebellum, located at the back of the brain, integrates sensory input and fine-tunes motor activity, posture, and equilibrium. The cerebrum handles conscious thought and voluntary actions, the thalamus relays sensory information, the medulla controls vital autonomic functions like breathing and heart rate.
This question belongs to: Science Biology
Question #583
Which hormone is produced by the anterior pituitary to stimulate growth of bones and muscles?
A. Thyroxine
B. Growth hormone
C. Cortisol
D. Adrenaline
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Correct Answer: Option B

Explanation:
Growth hormone (somatotropin) stimulates protein synthesis, cell division, and growth of bones and muscles, especially during childhood. Thyroxine regulates metabolism, cortisol is a stress hormone from the adrenal cortex, adrenaline is from the adrenal medulla. GH deficiency leads to dwarfism; excess causes gigantism or acromegaly.
This question belongs to: Science Biology
Question #584
The site of fertilization in the human female reproductive tract is usually the:
A. Cervix
B. Uterus
C. Ampulla of the fallopian tube
D. Ovary
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Correct Answer: Option C

Explanation:
Fertilization typically occurs in the ampulla, the widest region of the fallopian tube, where the sperm meets the secondary oocyte. The zygote then travels to the uterus for implantation. The ovary releases the egg, the uterus supports embryo development, the cervix is the lower portion opening into the vagina.
This question belongs to: Science Biology
Question #585
Which pathogen causes tuberculosis in humans?
A. Streptococcus pneumoniae
B. Plasmodium vivax
C. Mycobacterium tuberculosis
D. Salmonella typhi
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Correct Answer: Option C

Explanation:
Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis, typically affecting the lungs. It is spread through airborne droplets. S. pneumoniae causes pneumonia, S. typhi typhoid, P. vivax malaria. TB is treated with a multi-drug regimen including isoniazid and rifampicin.
This question belongs to: Science Biology
Question #586
The vaccine for tuberculosis is known as:
A. OPV
B. DPT
C. MMR
D. BCG
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Correct Answer: Option D

Explanation:
BCG (Bacille Calmette-Guérin) is a live attenuated vaccine derived from Mycobacterium bovis, used to protect against tuberculosis, especially in children. DPT is for diphtheria, pertussis, tetanus; MMR for measles, mumps, rubella; OPV is oral polio vaccine. BCG is often administered at birth in endemic regions.
This question belongs to: Science Biology
Question #587
Deficiency of which vitamin causes night blindness?
A. Vitamin D
B. Vitamin B₁
C. Vitamin A
D. Vitamin C
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Correct Answer: Option C

Explanation:
Vitamin A (retinol) is essential for the synthesis of rhodopsin, the visual pigment in rod cells responsible for low-light vision. Deficiency leads to night blindness (nyctalopia) and, if severe, xerophthalmia and permanent blindness. Vitamin B₁ deficiency causes beriberi, C scurvy, D rickets.
This question belongs to: Science Biology
Question #588
Which of the following is a water-soluble vitamin that acts as a coenzyme in carboxylation reactions?
A. Vitamin K
B. Vitamin B₁
C. Vitamin B₇ (Biotin)
D. Vitamin A
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Correct Answer: Option C

Explanation:
Biotin (vitamin B₇) is a water-soluble B vitamin that functions as a coenzyme for carboxylase enzymes, important in fatty acid synthesis and gluconeogenesis. Vitamin B₁ acts in decarboxylation, A and K are fat-soluble. Biotin is widely distributed in foods and also synthesized by gut bacteria.
This question belongs to: Science Biology
Question #589
The genetic material in humans is organized as:
A. RNA molecules
B. Multiple linear chromosomes in the nucleus
C. A single circular chromosome
D. Only mitochondrial DNA
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Correct Answer: Option B

Explanation:
Human cells have 46 linear chromosomes in the nucleus (22 pairs of autosomes and one pair of sex chromosomes), made of DNA and histone proteins. Mitochondria also contain small circular DNA. Prokaryotes have a single circular chromosome. RNA is not the primary genetic material in humans.
This question belongs to: Science Biology
Question #590
In a cross between a homozygous dominant plant (TT) and a heterozygous plant (Tt), what proportion of the offspring will show the recessive phenotype?
A. 0%
B. 25%
C. 50%
D. 100%
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Correct Answer: Option A

Explanation:
Cross: TT × Tt. Gametes: T (from TT) and T or t (from Tt). Offspring genotypes: TT and Tt. Both express the dominant phenotype because the recessive allele t is masked by T. No tt offspring are produced, so 0% show the recessive trait.
This question belongs to: Science Biology
Question #591
The scientist who published 'On the Origin of Species' is:
A. Gregor Mendel
B. Alfred Wallace
C. Charles Darwin
D. Jean-Baptiste Lamarck
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Correct Answer: Option C

Explanation:
Charles Darwin's 1859 book 'On the Origin of Species by Means of Natural Selection' laid out the theory of evolution by natural selection. Mendel's work on heredity was published later, Wallace independently conceived natural selection but Darwin's book detailed the evidence comprehensively. Lamarck proposed earlier theories.
This question belongs to: Science Biology
Question #592
The type of fossil formed when minerals replace organic material, preserving the original structure, is called:
A. Cast fossil
B. Trace fossil
C. Mold fossil
D. Petrified fossil
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Correct Answer: Option D

Explanation:
Petrified fossils (permineralization) form when dissolved minerals infiltrate the porous tissues of dead organisms and harden, turning the remains into stone while preserving internal structure. Mold and cast fossils are impressions, trace fossils are tracks or burrows. Petrified wood is a common example.
This question belongs to: Science Biology
Question #593
The trophic level in a food chain that contains organisms that feed on primary consumers is the:
A. Producer
B. Primary consumer
C. Secondary consumer
D. Decomposer
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Correct Answer: Option C

Explanation:
Secondary consumers are carnivores or omnivores that eat primary consumers (herbivores). Example: frog eating grasshopper. Producers are autotrophs, primary consumers are herbivores, decomposers break down dead matter. Trophic levels represent energy transfer steps. Energy decreases at each higher level.
This question belongs to: Science Biology
Question #594
The major greenhouse gas emitted from agricultural rice paddies is:
A. Chlorofluorocarbons
B. Nitrous oxide
C. Carbon dioxide
D. Methane
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Correct Answer: Option D

Explanation:
Methane (CH₄) is produced by methanogenic bacteria in anaerobic conditions of flooded rice paddies. It is a potent greenhouse gas, with a global warming potential many times that of CO₂. Nitrous oxide comes from fertilizers, CO₂ from fossil fuels, CFCs from refrigerants. Methane also comes from livestock.
This question belongs to: Science Biology
Question #595
Which of the following is an example of a mutualistic symbiosis?
A. Tapeworm in human gut
B. Barnacles on whale skin
C. Lichen (algae and fungus)
D. Mosquito sucking blood
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Correct Answer: Option C

Explanation:
Lichens are a mutualistic association between an alga (or cyanobacterium) and a fungus. The alga photosynthesizes, providing food; the fungus provides shelter, water, and minerals. Both benefit. Tapeworm is parasitism, barnacles on whales commensalism (or sometimes parasitism depending on effect), mosquito blood-sucking is parasitism.
This question belongs to: Science Biology
Question #596
The shape of a bacterial chromosome is typically:
A. Fragmented
B. Triangular
C. Linear
D. Circular
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Correct Answer: Option D

Explanation:
Most bacteria possess a single circular double-stranded DNA molecule located in the nucleoid region. Some bacteria may also have linear chromosomes or multiple chromosomes, but the typical prokaryotic chromosome is circular. Eukaryotes have linear chromosomes. Plasmids are small, circular extra-chromosomal DNA in bacteria.
This question belongs to: Science Biology
Question #597
The technique used to separate proteins based on their isoelectric point is:
A. Isoelectric focusing
B. Western blotting
C. PCR
D. SDS-PAGE
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Correct Answer: Option A

Explanation:
Isoelectric focusing (IEF) separates proteins in a pH gradient according to their isoelectric point (pI), the pH at which a protein has no net charge and stops migrating. SDS-PAGE separates by size, Western blotting detects specific proteins after separation, PCR amplifies DNA. IEF is often used in 2D gel electrophoresis.
This question belongs to: Science Biology
Question #598
The vector used for introducing foreign genes into monocot plants is often:
A. Bacteriophage lambda
B. Ti plasmid
C. Cosmid
D. Particle bombardment (gene gun)
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Correct Answer: Option D

Explanation:
Monocots are less susceptible to Agrobacterium-mediated transformation using Ti plasmid. Therefore, direct gene transfer methods like particle bombardment (biolistics) are commonly used. The gene gun shoots DNA-coated gold or tungsten particles into plant cells. Ti plasmid works well for dicots. Bacteriophage and cosmids are for bacterial cloning.
This question belongs to: Science Biology
Question #599
In animal husbandry, the crossbreeding of superior males of one breed with superior females of another breed is called:
A. Grading up
B. Outcrossing
C. Inbreeding
D. Crossbreeding
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Correct Answer: Option D

Explanation:
Crossbreeding involves mating individuals of different breeds to combine desirable traits and exploit hybrid vigor (heterosis). Inbreeding is within the same breed, outcrossing is within breed but unrelated, grading up is repeated crossing with a superior breed. Crossbreeding improves productivity in dairy and meat animals.
This question belongs to: Science Biology
Question #600
The silkworm disease caused by the protozoan Nosema bombycis is called:
A. Pebrine
B. Muscardine
C. Flacherie
D. Grasserie
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Correct Answer: Option A

Explanation:
Pebrine is a serious disease of silkworms caused by the microsporidian Nosema bombycis, transmitted transovarially. It was identified by Louis Pasteur. Flacherie is bacterial, muscardine is fungal, grasserie is viral. Pebrine control involves screening mother moths and destroying infected eggs.
This question belongs to: Science Biology

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