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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Page 69 of 103
Question #1361
In the ABO blood group system, the 'I' gene has three alleles: IA, IB, and i. When a person has the genotype IAIB, they express both A and B antigens. This is an example of:
A. Incomplete dominance
B. Multiple allelism only
C. Pleiotropy
D. Codominance
Discuss
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Correct Answer: Option D

Explanation:
Codominance occurs when two different alleles of a gene are fully and equally expressed in the heterozygous condition. In the ABO blood group, the IA and IB alleles are codominant. An individual with the genotype IAIB produces both A and B antigens on the surface of their red blood cells, resulting in the AB blood type. While the ABO system also involves multiple alleles (IA, IB, i), the specific expression of both antigens is codominance.
This question belongs to: Science Biology
Question #1362
The genetic code is said to be 'degenerate' because:
A. More than one codon can code for the same amino acid
B. The code is not universal
C. Some codons code for more than one amino acid
D. One amino acid is coded by only one codon
Discuss
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Correct Answer: Option A

Explanation:
The degeneracy of the genetic code refers to the fact that most amino acids are specified by more than one codon. For example, leucine is coded by six different codons (UUA, UUG, CUU, CUC, CUA, CUG). This redundancy is primarily due to the 'wobble' hypothesis, where the third base of the codon can have non-standard base pairing with the first base of the anticodon, allowing a single tRNA to recognize multiple codons.
This question belongs to: Science Biology
Question #1363
The enzyme responsible for joining the Okazaki fragments on the lagging strand during DNA replication is:
A. DNA polymerase III
B. DNA helicase
C. DNA ligase
D. DNA primase
Discuss
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Correct Answer: Option C

Explanation:
During DNA replication, the lagging strand is synthesized discontinuously in short segments called Okazaki fragments. After the RNA primers are removed and replaced with DNA by DNA polymerase I, the fragments remain separated by nicks in the sugar-phosphate backbone. DNA ligase is the enzyme that catalyzes the formation of phosphodiester bonds between these fragments, sealing the nicks and creating a continuous DNA strand.
This question belongs to: Science Biology
Question #1364
In the lac operon of E. coli, the 'i' gene codes for a repressor protein. In the absence of lactose, the repressor binds to the:
A. Operator region
B. Promoter region
C. RNA polymerase
D. Structural genes (z, y, a)
Discuss
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Correct Answer: Option A

Explanation:
In the lac operon, the 'i' gene (regulatory gene) constitutively produces a repressor protein. In the absence of lactose (the inducer), this active repressor binds specifically to the operator region of the operon. The operator overlaps with the promoter, physically blocking RNA polymerase from binding to the promoter or moving forward to transcribe the structural genes (z, y, a). When lactose is present, it binds to the repressor, inactivating it and allowing transcription.
This question belongs to: Science Biology
Question #1365
Which of the following chromosomal disorders in humans is characterized by a karyotype of 47, XXY?
A. Klinefelter syndrome
B. Down syndrome
C. Turner syndrome
D. Patau syndrome
Discuss
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Correct Answer: Option A

Explanation:
Klinefelter syndrome is a sex chromosomal aneuploidy in males characterized by the karyotype 47, XXY. Individuals are phenotypically male but often exhibit feminine characteristics such as gynecomastia (development of breasts), sparse body hair, and are typically sterile due to underdeveloped testes. Down syndrome is trisomy 21 (47, +21), Turner syndrome is 45, X0, and Patau syndrome is trisomy 13.
This question belongs to: Science Biology
Question #1366
The Miller-Urey experiment simulated the primitive Earth's atmosphere. The mixture of gases used in the experiment was:
A. CO2, NH3, H2O, and O2
B. CH4, NH3, H2, and H2O (vapor)
C. CH4, CO2, N2, and H2O
D. CO2, N2, H2O, and O2
Discuss
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Correct Answer: Option B

Explanation:
In 1953, Stanley Miller and Harold Urey conducted an experiment to test the Oparin-Haldane hypothesis of chemical evolution. They simulated the reducing atmosphere of primitive Earth, which they believed lacked free oxygen. The gas mixture used was methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor (H2O). By applying electrical sparks (simulating lightning), they successfully synthesized amino acids and other organic compounds.
This question belongs to: Science Biology
Question #1367
The evolutionary process where two unrelated species evolve similar traits independently, often due to adapting to similar environments, is called:
A. Coevolution
B. Parallel evolution
C. Convergent evolution
D. Divergent evolution
Discuss
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Correct Answer: Option C

Explanation:
Convergent evolution occurs when distantly related organisms independently evolve similar traits or structures to adapt to similar ecological niches or environmental pressures. The resulting structures are called analogous organs (e.g., wings of birds and insects, eyes of octopuses and mammals). Divergent evolution is when related species evolve different traits (homologous organs). Coevolution is when two species evolve in response to each other.
This question belongs to: Science Biology
Question #1368
The Hardy-Weinberg equation p^2 + 2pq + q^2 = 1 is used to calculate:
A. The carrying capacity of an ecosystem
B. The rate of mutation in a population
C. The expected genotype frequencies in a population
D. The energy transfer between trophic levels
Discuss
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Correct Answer: Option C

Explanation:
The Hardy-Weinberg equation is a fundamental principle in population genetics used to calculate the expected frequencies of genotypes in a population that is not evolving (in genetic equilibrium). 'p' represents the frequency of the dominant allele, and 'q' represents the frequency of the recessive allele. p^2 is the frequency of the homozygous dominant genotype, 2pq is the heterozygous genotype, and q^2 is the homozygous recessive genotype.
This question belongs to: Science Biology
Question #1369
In an ecological food chain, the 10% law of energy transfer implies that if producers fix 10,000 kcal of energy, the energy available to the tertiary consumers will be:
A. 1 kcal
B. 1,000 kcal
C. 10 kcal
D. 100 kcal
Discuss
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Correct Answer: Option C

Explanation:
According to Lindeman's 10% law, only about 10% of the energy from one trophic level is transferred to the next; the rest is lost as heat through respiration. Producers (Trophic Level 1) have 10,000 kcal. Primary consumers (Level 2) get 10% of 10,000 = 1,000 kcal. Secondary consumers (Level 3) get 10% of 1,000 = 100 kcal. Tertiary consumers (Level 4) get 10% of 100 = 10 kcal.
This question belongs to: Science Biology
Question #1370
In primary ecological succession on a bare rock (xerarch), the first organisms to colonize the rock are typically:
A. Mosses
B. Shrubs
C. Lichens
D. Grasses
Discuss
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Correct Answer: Option C

Explanation:
In primary succession on a bare, lifeless rock (xerosere), the pioneer species are usually lichens (a symbiotic association of fungi and algae or cyanobacteria). Lichens can survive in harsh, dry conditions and secrete acids that slowly weather the rock, contributing to soil formation. Once a thin layer of soil is formed, mosses can colonize, followed by herbs, grasses, shrubs, and eventually a climax forest community.
This question belongs to: Science Biology
Question #1371
The term 'biological magnification' refers to:
A. The rapid growth of algae in nutrient-rich water bodies
B. The increasing concentration of non-biodegradable toxic substances in organisms at higher trophic levels
C. The increase in the number of organisms at higher trophic levels
D. The increase in biodiversity in a climax community
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Correct Answer: Option B

Explanation:
Biological magnification (or biomagnification) is the process where the concentration of persistent, non-biodegradable toxic substances (like DDT, mercury, or PCBs) increases progressively at each successive trophic level in a food chain. Because these substances are not metabolized or excreted, they accumulate in the tissues of organisms. Top predators end up with the highest, often lethal, concentrations of these toxins.
This question belongs to: Science Biology
Question #1372
Which of the following is an example of a mutualistic relationship where a fungus and an alga live together?
A. Cuscuta on a host plant
B. Mycorrhiza
C. Lichen
D. Rhizobium in root nodules
Discuss
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Correct Answer: Option C

Explanation:
A lichen is a classic example of mutualism between a fungus (mycobiont) and an alga or cyanobacterium (phycobiont). The algal partner performs photosynthesis and provides organic food to the fungus. In return, the fungal partner provides a protective environment, absorbs water and minerals, and anchors the lichen to the substrate. Mycorrhiza is a mutualism between fungi and plant roots, and Rhizobium is a mutualism between bacteria and legume roots.
This question belongs to: Science Biology
Question #1373
The restriction enzyme EcoRI recognizes the palindromic DNA sequence 5'-GAATTC-3' and cuts the DNA between the:
A. C and G
B. T and C
C. A and T
D. G and A
Discuss
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Correct Answer: Option D

Explanation:
Restriction enzymes are molecular scissors that cut DNA at specific recognition sites. EcoRI, isolated from Escherichia coli strain RY13, recognizes the 6-base pair palindromic sequence 5'-GAATTC-3'. It cuts the phosphodiester bond between the G and the A on both strands, leaving single-stranded overhangs called 'sticky ends' (5'-AATT-3'). These sticky ends are crucial for joining DNA fragments from different sources using DNA ligase.
This question belongs to: Science Biology
Question #1374
In the recombinant plasmid pBR322, the 'rop' gene codes for a protein that:
A. Helps in the replication of the plasmid
B. Produces proteins that restrict the growth of the host cell
C. Confers resistance to ampicillin
D. Confers resistance to tetracycline
Discuss
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Correct Answer: Option A

Explanation:
pBR322 is a widely used cloning vector. The 'rop' gene (Repressor Of Primer) codes for a small polypeptide that regulates and helps in the replication of the plasmid by inhibiting the synthesis of the RNA primer required for plasmid DNA replication. The 'ampR' and 'tetR' genes confer resistance to ampicillin and tetracycline, respectively, serving as selectable markers. Exam tip: 'rop' = replication control; 'R' = resistance.
This question belongs to: Science Biology
Question #1375
Golden Rice is a genetically modified crop developed primarily to combat the deficiency of:
A. Protein
B. Vitamin C
C. Vitamin A
D. Iron
Discuss
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Correct Answer: Option C

Explanation:
Golden Rice is a transgenic variety of rice (Oryza sativa) engineered to produce beta-carotene, a precursor of Vitamin A, in the edible endosperm. The beta-carotene gives the rice grains a characteristic golden-yellow color. It was developed to address Vitamin A deficiency (VAD), a major public health issue in developing countries that causes blindness and increases susceptibility to infectious diseases in children.
This question belongs to: Science Biology
Question #1376
RNA interference (RNAi) is a technique used in genetic engineering to silence specific genes. In the development of nematode-resistant transgenic tobacco plants, the source of the silencing RNA was:
A. The nematode itself (Agrobacterium-mediated delivery of nematode genes)
B. A virus
C. A bacterium
D. The plant's own genome
Discuss
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Correct Answer: Option A

Explanation:
RNAi is a cellular defense mechanism in eukaryotes that silences specific mRNA. To create nematode-resistant tobacco, scientists used Agrobacterium as a vector to introduce nematode-specific genes into the host plant. The plant then produced both sense and anti-sense RNA for these genes. The double-stranded RNA (dsRNA) formed triggered the RNAi pathway, degrading the nematide's mRNA when it tried to express those essential genes inside the plant roots, killing the nematode.
This question belongs to: Science Biology
Question #1377
In animal husbandry, the 'Murrah' breed is highly valued for its high milk yield and is a breed of:
A. Buffalo
B. Goat
C. Cattle
D. Sheep
Discuss
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Correct Answer: Option A

Explanation:
The Murrah is a premier breed of water buffalo (Bubalus bubalis) originating from the Haryana and Punjab regions of India. It is renowned for its high milk yield, high fat content in milk, and adaptability to local conditions. It is one of the most important dairy breeds in India and has been exported worldwide for dairy improvement. Sahiwal and Holstein are cattle breeds.
This question belongs to: Science Biology
Question #1378
In apiculture, the 'Apis mellifera' is preferred over the indigenous 'Apis cerana indica' primarily because:
A. It has a higher honey collection capacity and stays in the hive for longer periods
B. It is more aggressive and defends the hive better
C. It does not sting
D. It requires less floral nectar to produce honey
Discuss
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Correct Answer: Option A

Explanation:
Apis mellifera (the Italian or European honeybee) is widely preferred in commercial apiculture over the indigenous Apis cerana indica because it has a significantly higher honey collection capacity, yields more honey per hive, has a higher reproduction rate, and tends to stay in the hive for longer periods without swarming (absconding). While it can be more aggressive, its superior productivity makes it the choice for commercial beekeeping.
This question belongs to: Science Biology
Question #1379
The silkworm, Bombyx mori, feeds exclusively on the leaves of which plant during its larval stage?
A. Teak
B. Eucalyptus
C. Castor
D. Mulberry (Morus alba)
Discuss
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Correct Answer: Option D

Explanation:
The domesticated silkworm, Bombyx mori, is a monophagous insect, meaning it feeds almost exclusively on the fresh leaves of the mulberry plant (primarily Morus alba). The quality and quantity of silk produced are directly dependent on the quality of the mulberry leaves consumed by the larvae. While tasar silkworms feed on oak and castor, the common mulberry silkworm requires Morus alba.
This question belongs to: Science Biology
Question #1380
Robert Koch is famous for establishing 'Koch's postulates', which are a set of criteria used to:
A. Classify bacteria based on Gram staining
B. Develop vaccines against viral diseases
C. Establish a causal relationship between a specific microbe and a specific disease
D. Discover the structure of DNA
Discuss
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Correct Answer: Option C

Explanation:
Robert Koch, a German physician and microbiologist, formulated Koch's postulates in the late 19th century. These four criteria are designed to establish a causal relationship between a specific microbe and a specific disease. The postulates require that the microbe must be found in all cases of the disease, isolated and grown in pure culture, cause the disease when inoculated into a healthy susceptible host, and be re-isolated from the experimentally infected host.
This question belongs to: Science Biology

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