Biology MCQs

Question #221

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Which of the following diseases is transmitted through the bite of a rabid animal?

A. Tetanus

B. Malaria

C. Typhoid

D. Rabies

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Correct Answer: Option D

Explanation:
Rabies is a viral zoonotic disease caused by the rabies virus, transmitted through the saliva of infected animals (dogs, bats, raccoons) via bites or scratches. It affects the central nervous system and is almost always fatal once symptoms appear. Post-exposure prophylaxis (wound cleaning, rabies immunoglobulin, and vaccine) is effective if given promptly.

This question belongs to: Science Biology

Question #222

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Which of the following is a fungal disease of plants?

A. Citrus canker

B. Crown gall

C. Late blight of potato

D. Tobacco mosaic

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Correct Answer: Option C

Explanation:
Late blight of potato is caused by the oomycete Phytophthora infestans (historically considered a fungus). It caused the Irish Potato Famine. Tobacco mosaic is viral, citrus canker is bacterial (Xanthomonas), crown gall is bacterial (Agrobacterium tumefaciens). Fungal plant diseases also include rust, smut, and powdery mildew. Oomycetes are now classified under Chromista but traditionally studied in mycology.

This question belongs to: Science Biology

Question #223

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Which vitamin is essential for the absorption of calcium from the intestine?

A. Vitamin B₁

B. Vitamin D

C. Vitamin C

D. Vitamin A

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Correct Answer: Option B

Explanation:
Vitamin D (calciferol) promotes the absorption of calcium and phosphorus from the small intestine by inducing synthesis of calcium-binding proteins. It is synthesized in the skin upon exposure to UV light and then activated in the liver and kidneys. Deficiency leads to rickets in children and osteomalacia in adults. Vitamin A is for vision, C for collagen, B₁ for energy metabolism.

This question belongs to: Science Biology

Question #224

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The deficiency of vitamin B₁₂ leads to which type of anemia?

A. Iron-deficiency anemia

B. Aplastic anemia

C. Sickle cell anemia

D. Pernicious anemia

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Correct Answer: Option D

Explanation:
Pernicious anemia is a megaloblastic anemia resulting from vitamin B₁₂ (cobalamin) deficiency, often due to lack of intrinsic factor (produced by stomach parietal cells) needed for its absorption. It is characterized by large, immature red blood cells and neurological symptoms. Iron deficiency causes microcytic anemia. Sickle cell is genetic, aplastic is bone marrow failure.

This question belongs to: Science Biology

Question #225

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Which of the following is an example of a monounsaturated fatty acid?

A. Stearic acid

B. Linolenic acid

C. Oleic acid

D. Linoleic acid

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Correct Answer: Option C

Explanation:
Oleic acid is a monounsaturated fatty acid (one double bond), found in olive oil. Stearic acid is saturated, linoleic acid is polyunsaturated (two double bonds), linolenic acid is polyunsaturated (three double bonds). Unsaturated fats are generally liquid at room temperature and healthier for the heart. Oleic acid is an omega-9 fatty acid.

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Question #226

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The sugar present in DNA nucleotides is:

A. Fructose

B. Ribose

C. Glucose

D. Deoxyribose

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Correct Answer: Option D

Explanation:
DNA contains the pentose sugar 2'-deoxyribose, which lacks an oxygen atom on the 2' carbon compared to ribose in RNA. This structural difference makes DNA more chemically stable and suitable for long-term genetic storage. Nucleotides consist of a nitrogenous base, a pentose sugar, and a phosphate group. Ribose is present in RNA.

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Question #227

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In a double-stranded DNA molecule, if adenine constitutes 30%, what is the percentage of guanine?

A. 70%

B. 20%

C. 30%

D. 40%

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Correct Answer: Option B

Explanation:
According to Chargaff's rule, A = T and G = C. If A = 30%, then T = 30%. The total for A+T is 60%. The remaining 40% is G+C, so G = 20% and C = 20%. This base pairing is due to specific hydrogen bonding: A-T (2 bonds), G-C (3 bonds). This question applies the concept of base composition.

This question belongs to: Science Biology

Question #228

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Mendel's law of independent assortment applies to genes located on:

A. Mitochondrial DNA

B. Different non-homologous chromosomes

C. Sex chromosomes only

D. The same chromosome

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Correct Answer: Option B

Explanation:
The law of independent assortment states that alleles of different genes segregate independently of each other during gamete formation, provided the genes are on different non-homologous chromosomes. If genes are linked (on the same chromosome), they tend to be inherited together unless crossing over occurs. This law was derived from Mendel's dihybrid crosses, yielding the 9:3:3:1 ratio.

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Question #229

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The theory of natural selection was proposed jointly by Charles Darwin and:

A. Gregor Mendel

B. Alfred Russel Wallace

C. Jean-Baptiste Lamarck

D. Thomas Malthus

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Correct Answer: Option B

Explanation:
Alfred Russel Wallace independently conceived the theory of natural selection and sent his manuscript to Darwin. In 1858, both presented their papers jointly at the Linnean Society. Darwin's 'On the Origin of Species' (1859) elaborated the theory. Mendel discovered genetics, Lamarck proposed inheritance of acquired traits, Malthus influenced Darwin with his ideas on population growth.

This question belongs to: Science Biology

Question #230

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The forelimbs of humans, whales, and bats exhibit similarity in basic structure due to common ancestry. This is an example of:

A. Vestigial organs

B. Adaptive radiation

C. Analogous organs

D. Homologous organs

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Correct Answer: Option D

Explanation:
Homologous organs share a common ancestral origin and structural plan but may have different functions (e.g., human arm, whale flipper, bat wing). This indicates divergent evolution. Analogous organs have different origins but similar functions (e.g., wings of birds and insects) due to convergent evolution. Vestigial organs are reduced and non-functional, like the human appendix.

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Question #231

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Which of the following eras is known as the 'Age of Reptiles'?

A. Cenozoic

B. Paleozoic

C. Mesozoic

D. Proterozoic

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Correct Answer: Option C

Explanation:
The Mesozoic era (about 250-65 million years ago) is called the 'Age of Reptiles' or 'Age of Dinosaurs' because reptiles, especially dinosaurs, dominated terrestrial ecosystems. It is divided into Triassic, Jurassic, and Cretaceous periods. The Cenozoic is the 'Age of Mammals', the Paleozoic saw the rise of fishes and amphibians, and the Proterozoic is earlier.

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Question #232

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The pyramid of energy in an ecosystem is always:

A. Inverted

B. Variable

C. Spindle-shaped

D. Upright

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Correct Answer: Option D

Explanation:
The pyramid of energy shows the flow of energy at successive trophic levels. Energy decreases as it moves up (about 10% transfer), so the pyramid is always upright. Pyramids of number and biomass may be inverted in some ecosystems (e.g., parasitic food chains, pond ecosystem), but the energy pyramid never is, according to the second law of thermodynamics.

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Question #233

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The Chipko movement is associated with the conservation of:

A. Wildlife

B. Forests

C. Water bodies

D. Soil

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Correct Answer: Option B

Explanation:
The Chipko movement, initiated in the 1970s in Uttarakhand (India), involved villagers (mainly women) hugging trees to prevent them from being cut down by contractors. It was a non-violent protest for forest conservation and sustainable use. Sunderlal Bahuguna was a prominent leader. It raised awareness about deforestation and environmental protection.

This question belongs to: Science Biology

Question #234

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Which of the following microorganisms is used in the production of curd from milk?

A. Clostridium botulinum

B. Salmonella typhi

C. Lactobacillus

D. Streptococcus pneumoniae

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Correct Answer: Option C

Explanation:
Lactobacillus species convert lactose (milk sugar) into lactic acid, which lowers the pH and causes milk protein casein to coagulate, forming curd. This fermentation process also gives curd its characteristic sour taste. S. pneumoniae causes pneumonia, Salmonella typhi typhoid, Clostridium botulinum botulism. Lactobacillus is also a probiotic.

This question belongs to: Science Biology

Question #235

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Which process is used to make plants disease-free using meristem culture?

A. Hybridization

B. Tissue culture

C. Mutagenesis

D. Cloning

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Correct Answer: Option B

Explanation:
Meristem culture, a type of tissue culture, involves excising the virus-free apical meristem (shoot tip) and growing it on a nutrient medium to produce a whole plant free of viruses. This is because meristematic cells lack vascular connections through which viruses spread. Cloning produces identical copies, hybridization crosses varieties, mutagenesis uses mutagens.

This question belongs to: Science Biology

Question #236

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The Ti plasmid used in plant genetic engineering is derived from:

A. Pseudomonas putida

B. Agrobacterium tumefaciens

C. Escherichia coli

D. Bacillus subtilis

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Correct Answer: Option B

Explanation:
Agrobacterium tumefaciens is a soil bacterium that naturally transfers part of its Ti (tumor-inducing) plasmid DNA (T-DNA) into the plant genome, causing crown gall disease. Scientists have harnessed this capability by replacing the tumor-causing genes with desirable genes, making it a vector for creating transgenic plants. E. coli vectors are used for bacterial transformation.

This question belongs to: Science Biology

Question #237

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The technique used to amplify small quantities of DNA in vitro is:

A. Polymerase chain reaction (PCR)

B. DNA sequencing

C. Gel electrophoresis

D. Southern blotting

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Correct Answer: Option A

Explanation:
PCR, invented by Kary Mullis, allows exponential amplification of a specific DNA segment using a thermostable DNA polymerase (Taq polymerase), primers, and thermal cycling. Gel electrophoresis separates DNA fragments, Southern blotting detects specific sequences, DNA sequencing determines the order of bases. PCR is widely used in diagnostics, forensics, and research.

This question belongs to: Science Biology

Question #238

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Which of the following is an example of a biofertilizer containing a free-living nitrogen-fixing bacterium?

A. Rhizobium

B. Azotobacter

C. Nostoc

D. Mycorrhiza

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Correct Answer: Option B

Explanation:
Azotobacter is a free-living, aerobic, nitrogen-fixing soil bacterium used as a biofertilizer for non-legume crops like wheat, maize, and cotton. Rhizobium is symbiotic, Nostoc is a cyanobacterium (algal biofertilizer), and mycorrhiza is a fungal symbiont that enhances phosphorus uptake. Biofertilizers reduce the need for chemical nitrogen fertilizers and are eco-friendly.

This question belongs to: Science Biology

Question #239

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The rearing of silkworms for silk production is known as:

A. Sericulture

B. Vermiculture

C. Pisciculture

D. Apiculture

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Correct Answer: Option A

Explanation:
Sericulture involves the cultivation of mulberry plants (Morus alba) and rearing of the silkworm Bombyx mori to produce raw silk. Apiculture is beekeeping, pisciculture is fish farming, vermiculture is earthworm rearing for compost. India is the second-largest producer of silk after China, producing mulberry, tasar, eri, and muga silk.

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Question #240

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Which scientist is credited with disproving the theory of spontaneous generation?

A. Edward Jenner

B. Louis Pasteur

C. Alexander Fleming

D. Robert Koch

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Correct Answer: Option B

Explanation:
Louis Pasteur, through his famous swan-neck flask experiment (1861), demonstrated that life does not arise spontaneously from non-living matter. Sterilized broth in flasks remained sterile unless exposed to airborne microorganisms. Fleming discovered penicillin, Koch established postulates for microbial disease, Jenner developed smallpox vaccine. Pasteur's work was foundational for microbiology.

This question belongs to: Science Biology

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