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 #841
In snapdragon (Antirrhinum), a cross between red and white flowers produces pink flowers. This is an example of:
A. Epistasis
B. Incomplete dominance
C. Codominance
D. Complete dominance
Discuss
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Correct Answer: Option B

Explanation:
Incomplete dominance occurs when the phenotype of the heterozygote is an intermediate blend of the two homozygous phenotypes. In snapdragons, a cross between a homozygous red (RR) and homozygous white (rr) flower produces heterozygous pink (Rr) flowers. Neither allele is completely dominant over the other, resulting in a blended phenotype.
This question belongs to: Science Biology
Question #842
The AB blood group in the ABO system is an example of:
A. Multiple allelism only
B. Codominance
C. Incomplete dominance
D. Pleiotropy
Discuss
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Correct Answer: Option B

Explanation:
Codominance occurs when both alleles in a heterozygote are fully and equally expressed. In the ABO blood group system, the IA and IB alleles are codominant. An individual with the genotype IAIB will have both A and B antigens on the surface of their red blood cells, resulting in the AB blood type. It also involves multiple alleles (IA, IB, i).
This question belongs to: Science Biology
Question #843
Phenylketonuria (PKU) is an example of:
A. Sex-linked inheritance
B. Pleiotropy
C. Epistasis
D. Polygenic inheritance
Discuss
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Correct Answer: Option B

Explanation:
Pleiotropy is a phenomenon where a single gene influences multiple, seemingly unrelated phenotypic traits. Phenylketonuria (PKU) is an autosomal recessive metabolic disorder caused by a mutation in a single gene (PAH) that codes for the enzyme phenylalanine hydroxylase. This single mutation leads to multiple effects: intellectual disability, reduced hair and skin pigmentation, and musty odor.
This question belongs to: Science Biology
Question #844
Human skin color is a classic example of:
A. Pleiotropy
B. Polygenic inheritance
C. Linkage
D. Mendelian inheritance
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Correct Answer: Option B

Explanation:
Polygenic inheritance occurs when a single phenotypic trait is controlled by two or more different genes at different loci, each having an additive effect. Human skin color, height, and eye color are controlled by multiple genes (e.g., at least three genes for skin color). This results in a continuous range of phenotypes, forming a bell-shaped curve in a population.
This question belongs to: Science Biology
Question #845
In the XX-XY system of sex determination, the male is:
A. Heterogametic (XY)
B. Haploid (X)
C. Diploid (XX)
D. Homogametic (XX)
Discuss
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Correct Answer: Option A

Explanation:
In the XX-XY system of sex determination, found in humans and most mammals, females have two identical sex chromosomes (XX) and are homogametic, producing only X-bearing eggs. Males have two different sex chromosomes (XY) and are heterogametic, producing two types of sperm: 50% with X and 50% with Y. The sperm determines the sex of the offspring.
This question belongs to: Science Biology
Question #846
Color blindness is an example of which type of inheritance?
A. X-linked recessive
B. Autosomal recessive
C. Autosomal dominant
D. Y-linked
Discuss
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Correct Answer: Option A

Explanation:
Color blindness (specifically red-green color blindness) is an X-linked recessive disorder. The gene responsible is located on the X chromosome. Males (XY) are more frequently affected because they only have one X chromosome; a single recessive allele will cause the disorder. Females (XX) need two recessive alleles to be affected, making them more likely to be carriers.
This question belongs to: Science Biology
Question #847
A mutation that involves the change of a single nucleotide base in the DNA sequence is called a:
A. Point mutation
B. Chromosomal deletion
C. Frameshift mutation
D. Inversion
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Correct Answer: Option A

Explanation:
A point mutation is a genetic mutation where a single nucleotide base is changed, inserted, or deleted from a sequence of DNA or RNA. The classic example is sickle cell anemia, caused by a single point mutation in the beta-globin gene, where adenine is replaced by thymine, changing the amino acid from glutamic acid to valine.
This question belongs to: Science Biology
Question #848
DNA fingerprinting relies on the variation in which type of DNA sequences?
A. Mitochondrial DNA
B. Exons
C. Variable Number Tandem Repeats (VNTRs)
D. Introns
Discuss
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Correct Answer: Option C

Explanation:
DNA fingerprinting (DNA profiling) is a technique used to identify individuals based on their unique DNA patterns. It primarily relies on the analysis of Variable Number Tandem Repeats (VNTRs) or Short Tandem Repeats (STRs), which are highly polymorphic, non-coding, repetitive DNA sequences that vary greatly in length and number between individuals.
This question belongs to: Science Biology
Question #849
The theory of chemical evolution of life was proposed by:
A. Stanley Miller
B. Oparin and Haldane
C. Charles Darwin
D. Louis Pasteur
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Correct Answer: Option B

Explanation:
The chemical evolution theory, also known as the biochemical theory of the origin of life, was proposed independently by Alexander Oparin (1924) and J.B.S. Haldane (1929). They proposed that life originated from pre-existing non-living organic molecules (like RNA, proteins, lipids) through a series of complex chemical reactions in the primitive reducing atmosphere of Earth.
This question belongs to: Science Biology
Question #850
In the Miller-Urey experiment, which of the following was synthesized?
A. Living cells
B. Amino acids
C. Complex proteins
D. Nucleic acids
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Correct Answer: Option B

Explanation:
The Miller-Urey experiment (1953) simulated the conditions of the primitive Earth's atmosphere (methane, ammonia, hydrogen, and water vapor) in a closed system and applied electrical sparks to simulate lightning. After a week, they found that several organic compounds, including amino acids (the building blocks of proteins), had been synthesized, supporting the theory of chemical evolution.
This question belongs to: Science Biology
Question #851
Darwin's theory of evolution is primarily based on the concept of:
A. Natural selection and branching descent
B. Sudden large mutations
C. Use and disuse of organs
D. Inheritance of acquired characters
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Correct Answer: Option A

Explanation:
Charles Darwin's theory of evolution, presented in 'On the Origin of Species' (1859), is based on two main concepts: branching descent (all organisms are related through common ancestry) and natural selection (survival of the fittest). Natural selection states that individuals with traits better suited to their environment are more likely to survive and reproduce, passing those traits to the next generation.
This question belongs to: Science Biology
Question #852
Industrial melanism in the peppered moth (Biston betularia) is a classic example of:
A. Artificial selection
B. Gene flow
C. Genetic drift
D. Natural selection
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Correct Answer: Option D

Explanation:
Industrial melanism is a classic example of natural selection in action. Before the industrial revolution, light-colored moths were more common as they blended with lichen-covered trees, avoiding predators. Pollution killed the lichen and darkened the trees, making dark-colored (melanic) moths better camouflaged. The population shifted to predominantly dark moths, demonstrating survival of the fittest.
This question belongs to: Science Biology
Question #853
The Hardy-Weinberg principle describes:
A. The process of speciation
B. The origin of life
C. The genetic equilibrium in a non-evolving population
D. The mechanism of natural selection
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Correct Answer: Option C

Explanation:
The Hardy-Weinberg principle states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences (like mutation, selection, gene flow, genetic drift, and non-random mating). It describes a theoretical, non-evolving population (genetic equilibrium) and provides a mathematical baseline (p2 + 2pq + q2 = 1) to measure evolutionary change.
This question belongs to: Science Biology
Question #854
The forelimbs of humans, whales, bats, and cats are examples of:
A. Homologous organs
B. Analogous organs
C. Connecting links
D. Vestigial organs
Discuss
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Correct Answer: Option A

Explanation:
Homologous organs are structures that have a similar fundamental anatomical plan and evolutionary origin but may perform different functions. The forelimbs of humans (for grasping), whales (for swimming), bats (for flying), and cats (for running) all have the same basic bone structure (humerus, radius, ulna, carpals, metacarpals, phalanges), indicating divergent evolution from a common ancestor.
This question belongs to: Science Biology
Question #855
The wings of a bird and the wings of an insect are examples of:
A. Vestigial organs
B. Atavisms
C. Analogous organs
D. Homologous organs
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Correct Answer: Option C

Explanation:
Analogous organs are structures that perform similar functions but have different anatomical structures and evolutionary origins. The wings of a bird (modified forelimbs with bones and feathers) and the wings of an insect (membranous extensions of the exoskeleton) both evolved for flight but are not derived from a common winged ancestor. This is an example of convergent evolution.
This question belongs to: Science Biology
Question #856
Which radioactive isotope is commonly used for dating relatively recent fossils (up to about 50,000 years old)?
A. Potassium-40
B. Uranium-238
C. Rubidium-87
D. Carbon-14
Discuss
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Correct Answer: Option D

Explanation:
Carbon-14 (radiocarbon) dating is used to determine the age of organic materials up to about 50,000 to 60,000 years old. Living organisms absorb Carbon-14 from the atmosphere. When they die, absorption stops, and the Carbon-14 decays at a known rate (half-life of 5,730 years). By measuring the remaining Carbon-14, the age of the fossil can be calculated.
This question belongs to: Science Biology
Question #857
Which of the following is considered a direct ancestor of modern humans (Homo sapiens)?
A. Ramapithecus
B. Dryopithecus
C. Neanderthal man
D. Australopithecus
Discuss
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Correct Answer: Option D

Explanation:
Australopithecus (e.g., 'Lucy') is considered one of the earliest direct ancestors or a very close relative of the genus Homo. They were bipedal hominins who lived in Africa about 4 to 2 million years ago. Dryopithecus and Ramapithecus are earlier ape-like ancestors. Homo neanderthalensis was a close relative but is generally considered a separate species that went extinct, though some interbreeding occurred.
This question belongs to: Science Biology
Question #858
Archaeopteryx is considered a connecting link between:
A. Reptiles and birds
B. Fish and amphibians
C. Birds and mammals
D. Reptiles and mammals
Discuss
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Correct Answer: Option A

Explanation:
Archaeopteryx is a famous fossil that exhibits characteristics of both reptiles and birds, making it a classic connecting link. It had reptilian features like teeth, a long bony tail, and clawed fingers, but also avian features like feathers, wings, and a bird-like beak. It provides strong evidence for the evolutionary theory that birds evolved from theropod dinosaurs.
This question belongs to: Science Biology
Question #859
In a food chain, the first trophic level is always occupied by:
A. Carnivores
B. Decomposers
C. Producers (Green plants)
D. Herbivores
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Correct Answer: Option C

Explanation:
A food chain represents the flow of energy and nutrients. The first trophic level is always occupied by producers (autotrophs), primarily green plants and algae, which convert solar energy into chemical energy via photosynthesis. The second level is primary consumers (herbivores), the third is secondary consumers (carnivores), and so on.
This question belongs to: Science Biology
Question #860
Which ecological pyramid is always upright and never inverted?
A. Pyramid of species
B. Pyramid of number
C. Pyramid of biomass
D. Pyramid of energy
Discuss
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Correct Answer: Option D

Explanation:
The pyramid of energy is always upright because of the 10% law of energy transfer. As energy flows from one trophic level to the next, a large portion (about 90%) is lost as heat due to metabolic processes (respiration). Only about 10% is transferred to the next level. Therefore, the total energy content always decreases at higher trophic levels, making an inverted pyramid of energy impossible.
This question belongs to: Science Biology

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