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 #1981
The disease caused by deficiency of niacin is:
A. Pellagra
B. Goiter
C. Beriberi
D. Anemia
Discuss
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Correct Answer: Option A

Explanation:
Pellagra, with symptoms of dermatitis, diarrhea, and dementia, is due to niacin (B₃) deficiency. Beriberi is B₁ deficiency, anemia can be iron/B₁₂/folate, goiter iodine.
This question belongs to: Science Biology
Question #1982
Which of the following is a communicable disease?
A. Hypertension
B. Tuberculosis
C. Diabetes
D. Cancer
Discuss
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Correct Answer: Option B

Explanation:
Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis, spreading through airborne droplets. Cancer, diabetes, and hypertension are non-communicable.
This question belongs to: Science Biology
Question #1983
The genetic material in most bacteria is:
A. Circular DNA
B. Single-stranded RNA
C. Double-stranded RNA
D. Linear DNA
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Correct Answer: Option A

Explanation:
Bacteria typically have a single circular double-stranded DNA chromosome located in the nucleoid. They may also have plasmids.
This question belongs to: Science Biology
Question #1984
In humans, the number of autosomal chromosomes in a sperm is:
A. 44
B. 22
C. 46
D. 23
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Correct Answer: Option B

Explanation:
Human sperm is haploid (n=23) containing 22 autosomes and one sex chromosome (X or Y). Somatic cells have 44 autosomes + XY or XX.
This question belongs to: Science Biology
Question #1985
Mendel's law of segregation is based on the separation of:
A. Centromeres
B. Non-homologous chromosomes
C. Homologous chromosomes during meiosis I
D. Sister chromatids
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Correct Answer: Option C

Explanation:
The law of segregation states that two alleles of a gene segregate during gamete formation, which corresponds to the separation of homologous chromosomes in anaphase I.
This question belongs to: Science Biology
Question #1986
In a dihybrid cross, the F₂ phenotypic ratio is:
A. 1:1
B. 1:2:1
C. 9:3:3:1
D. 3:1
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Correct Answer: Option C

Explanation:
Mendel's dihybrid cross (e.g., yellow round × green wrinkled) gave a 9:3:3:1 phenotypic ratio in the F₂ generation, illustrating independent assortment.
This question belongs to: Science Biology
Question #1987
Which of the following is an X-linked recessive disorder?
A. Hemophilia
B. Turner syndrome
C. Down syndrome
D. Klinefelter syndrome
Discuss
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Correct Answer: Option A

Explanation:
Hemophilia A and B are X-linked recessive, affecting mostly males. Down syndrome is trisomy 21, Turner is XO, Klinefelter is XXY.
This question belongs to: Science Biology
Question #1988
The base that pairs with adenine in RNA is:
A. Cytosine
B. Thymine
C. Guanine
D. Uracil
Discuss
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Correct Answer: Option D

Explanation:
In RNA, uracil replaces thymine and pairs with adenine (A-U). In DNA, adenine pairs with thymine. Guanine always pairs with cytosine.
This question belongs to: Science Biology
Question #1989
The process of mRNA synthesis from DNA is called:
A. Transcription
B. Translation
C. Transformation
D. Replication
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Correct Answer: Option A

Explanation:
Transcription, catalyzed by RNA polymerase, copies the genetic information from a DNA template into a complementary mRNA strand. Translation is protein synthesis.
This question belongs to: Science Biology
Question #1990
The human chromosome number (2n) is:
A. 48
B. 44
C. 46
D. 23
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Correct Answer: Option C

Explanation:
Humans have 46 chromosomes in somatic cells (22 pairs of autosomes and one pair of sex chromosomes). Gametes have 23 chromosomes.
This question belongs to: Science Biology
Question #1991
Which of the following is a vestigial organ in humans?
A. Appendix
B. Liver
C. Lungs
D. Heart
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Correct Answer: Option A

Explanation:
The vermiform appendix is a remnant of the cecum in herbivorous ancestors, now with minor immune function, thus considered vestigial.
This question belongs to: Science Biology
Question #1992
The theory of natural selection was proposed by:
A. Lamarck
B. De Vries
C. Mendel
D. Darwin
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Correct Answer: Option D

Explanation:
Charles Darwin and Alfred Wallace independently proposed natural selection as the mechanism for evolution. Darwin published 'On the Origin of Species' in 1859.
This question belongs to: Science Biology
Question #1993
Which of the following provides direct evidence of evolution?
A. Fossils
B. Analogous organs
C. Embryology
D. Molecular biology
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Correct Answer: Option A

Explanation:
Fossils are the preserved remains or impressions of past organisms, showing transitional forms and evolutionary change over geological time.
This question belongs to: Science Biology
Question #1994
The 'Urey-Miller experiment' synthesized which organic molecules?
A. Proteins
B. Amino acids
C. DNA
D. Lipids
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Correct Answer: Option B

Explanation:
Stanley Miller and Harold Urey simulated early Earth conditions and obtained amino acids (like glycine and alanine) by applying electric discharge to a mixture of gases.
This question belongs to: Science Biology
Question #1995
Homologous organs indicate:
A. Natural selection
B. Divergent evolution
C. Convergent evolution
D. Adaptive radiation
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Correct Answer: Option B

Explanation:
Homologous organs share a common ancestral origin but may have different functions (e.g., forelimbs of vertebrates), indicating divergent evolution.
This question belongs to: Science Biology
Question #1996
The plant cell wall is mainly composed of:
A. Chitin
B. Lignin
C. Cellulose
D. Peptidoglycan
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Correct Answer: Option C

Explanation:
The primary cell wall of plants consists of cellulose microfibrils embedded in a matrix of hemicellulose and pectin. Secondary walls may contain lignin.
This question belongs to: Science Biology
Question #1997
Which organelle is the site of photosynthesis?
A. Endoplasmic reticulum
B. Chloroplast
C. Mitochondria
D. Golgi body
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Correct Answer: Option B

Explanation:
Chloroplasts contain chlorophyll and thylakoids, where light reactions occur, and stroma for the Calvin cycle. They convert light energy to chemical energy.
This question belongs to: Science Biology
Question #1998
The 'powerhouse of the cell' is the:
A. Nucleus
B. Ribosome
C. Lysosome
D. Mitochondria
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Correct Answer: Option D

Explanation:
Mitochondria generate most of the cell's ATP through oxidative phosphorylation. They have a double membrane and their own DNA.
This question belongs to: Science Biology
Question #1999
Which cell organelle is involved in the synthesis of lipids?
A. Lysosome
B. Rough ER
C. Golgi apparatus
D. Smooth ER
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Correct Answer: Option D

Explanation:
Smooth endoplasmic reticulum (SER) lacks ribosomes and synthesizes lipids, steroid hormones, and detoxifies drugs. Rough ER synthesizes proteins.
This question belongs to: Science Biology
Question #2000
The fluid mosaic model describes the structure of:
A. Cell wall
B. Cytoplasm
C. Nucleus
D. Plasma membrane
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Correct Answer: Option D

Explanation:
The fluid mosaic model (Singer-Nicolson) depicts the cell membrane as a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol, giving it fluidity.
This question belongs to: Science Biology

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