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 95 of 103
Question #1881
Consider statements about evolution: 1. Natural selection leads to adaptation. 2. Mutations are the ultimate source of genetic variation. 3. Evolution occurs at the individual level. Which are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option B

Explanation:
Natural selection is the process where organisms with traits better suited to their environment are more likely to survive and reproduce, leading to adaptation of the population over time. Mutations, which are random changes in the DNA sequence, are the ultimate source of all new genetic variation upon which evolutionary forces act. Evolution is a population-level phenomenon, defined as a change in allele frequencies over generations; it does not occur within a single individual's lifetime. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1882
Consider statements about ecology: 1. Producers form the base of the food chain. 2. Decomposers recycle nutrients back into the ecosystem. 3. Energy flows bidirectionally in a food chain. Which are correct?
A. 1, 2 and 3
B. 2 and 3 only
C. 1 and 2 only
D. 1 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
Producers (autotrophs like green plants) form the first trophic level and the base of all food chains, converting solar energy into chemical energy. Decomposers (bacteria and fungi) break down dead organic matter and waste, releasing essential inorganic nutrients back into the soil for producers to use, thus completing the nutrient cycle. Energy flow in an ecosystem is strictly unidirectional, moving from the sun to producers and then to consumers, and is eventually lost as heat; it does not flow bidirectionally. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1883
Consider statements about environment: 1. The ozone layer protects Earth from UV radiation. 2. Greenhouse gases trap heat in the atmosphere. 3. Acid rain is beneficial for soil fertility. Which are correct?
A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option B

Explanation:
The stratospheric ozone layer acts as a vital shield, absorbing the majority of the sun's harmful ultraviolet (UV-B and UV-C) radiation, protecting life on Earth. Greenhouse gases (like CO2, methane, water vapor) absorb and re-emit infrared radiation, trapping heat in the troposphere and maintaining Earth's temperature (the greenhouse effect). Acid rain, containing sulfuric and nitric acids, is highly detrimental; it leaches essential nutrients from the soil, releases toxic aluminum, and damages plant life, reducing soil fertility. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1884
Consider statements about microorganisms: 1. Bacteria are prokaryotic organisms. 2. Fungi are eukaryotic organisms. 3. Viruses have a cellular structure. Which are correct?
A. 1 and 2 only
B. 1 and 3 only
C. 1, 2 and 3
D. 2 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
Bacteria are unicellular prokaryotic organisms, characterized by the absence of a true nucleus and membrane-bound organelles. Fungi are eukaryotic organisms, possessing a true nucleus and membrane-bound organelles, and can be unicellular (yeasts) or multicellular (molds, mushrooms). Viruses are acellular, non-cellular entities; they consist of genetic material (DNA or RNA) enclosed in a protein coat (capsid) and lack any cellular structure or metabolic machinery. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1885
Consider statements about biotechnology: 1. Restriction enzymes cut DNA at specific sequences. 2. DNA ligase joins DNA fragments together. 3. PCR is used to sequence DNA. Which are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1, 2 and 3
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
Restriction endonucleases are molecular scissors that recognize and cut DNA at specific, highly specific palindromic nucleotide sequences, creating fragments with sticky or blunt ends. DNA ligase is an enzyme that catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, effectively joining or 'pasting' them together, crucial in recombinant DNA technology. PCR (Polymerase Chain Reaction) is used to exponentially amplify specific DNA segments, not to sequence them; DNA sequencing is a separate technique. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1886
Consider statements about animal husbandry: 1. Artificial insemination is used in cattle breeding. 2. Multiple ovulation embryo transfer increases herd quality. 3. Crossbreeding reduces genetic diversity. Which are correct?
A. 1 and 3 only
B. 1, 2 and 3
C. 1 and 2 only
D. 2 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
Artificial insemination (AI) is a widely used reproductive technology in cattle breeding, allowing the use of superior bull semen to improve the genetic merit of the herd without keeping the bull. Multiple Ovulation Embryo Transfer (MOET) involves stimulating a superior female to produce multiple eggs, fertilizing them, and transferring the embryos to surrogate mothers, rapidly increasing the number of high-quality offspring. Crossbreeding involves mating animals of different breeds to combine desirable traits and increase heterozygosity, thereby increasing, not reducing, genetic diversity. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1887
Consider statements about scientists: 1. Edward Jenner developed the smallpox vaccine. 2. Alexander Fleming discovered penicillin. 3. Louis Pasteur discovered the structure of DNA. Which are correct?
A. 1 and 3 only
B. 2 and 3 only
C. 1, 2 and 3
D. 1 and 2 only
Discuss
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Correct Answer: Option D

Explanation:
Edward Jenner, an English physician, is credited with developing the world's first successful vaccine against smallpox in 1796, using material from cowpox lesions. Alexander Fleming, a Scottish bacteriologist, discovered the first true antibiotic, penicillin, in 1928, from the fungus Penicillium notatum. Louis Pasteur made immense contributions to microbiology and immunology, but the double helix structure of DNA was discovered by James Watson and Francis Crick in 1953. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1888
Consider statements about cell biology: 1. The cell membrane is selectively permeable. 2. The cell wall is present in animal cells. 3. The nucleus controls cell activities. Which are correct?
A. 1, 2 and 3
B. 1 and 3 only
C. 1 and 2 only
D. 2 and 3 only
Discuss
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Correct Answer: Option B

Explanation:
The cell membrane (plasma membrane) is selectively permeable, meaning it allows certain substances to pass through while restricting others, maintaining cellular homeostasis. The nucleus is the control center of the eukaryotic cell, housing the DNA and directing cellular activities like growth, metabolism, and reproduction. The cell wall is a rigid outer layer present in plant cells, fungi, and bacteria, but it is completely absent in animal cells, which only have a flexible cell membrane. Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1889
Consider statements about plant biology: 1. Photosynthesis occurs in chloroplasts. 2. Respiration occurs in mitochondria. 3. Transpiration occurs only through roots. Which are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option B

Explanation:
Photosynthesis, the process of converting light energy into chemical energy (glucose), occurs in the chloroplasts of plant cells, specifically involving the thylakoid membranes and stroma. Cellular respiration, the process of breaking down glucose to release ATP for cellular work, occurs primarily in the mitochondria of both plant and animal cells. Transpiration is the loss of water vapor from the aerial parts of the plant, primarily through the stomata on the leaves, not through the roots (which absorb water). Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1890
Consider statements about human anatomy: 1. The heart pumps blood throughout the body. 2. The lungs exchange oxygen and carbon dioxide. 3. The kidneys produce urine. Which are correct?
A. 1, 2 and 3
B. 1 and 3 only
C. 1 and 2 only
D. 2 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
The heart is a muscular pump that circulates blood through the cardiovascular system, delivering oxygen and nutrients to tissues and removing waste. The lungs are the primary organs of the respiratory system, where gas exchange occurs: oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli to be exhaled. The kidneys are the primary excretory organs, filtering blood to remove metabolic waste, excess water, and ions, producing urine. All statements are correct.
This question belongs to: Science Biology
Question #1891
Consider statements about human physiology: 1. The stomach digests proteins. 2. The small intestine absorbs nutrients. 3. The large intestine absorbs water. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option B

Explanation:
The stomach secretes gastric juice containing hydrochloric acid and the enzyme pepsin, which initiates the digestion of proteins into smaller peptides. The small intestine is the primary site for the final digestion of food and the absorption of most nutrients (amino acids, simple sugars, fatty acids, vitamins) into the bloodstream through its villi. The large intestine (colon) primarily absorbs water, electrolytes, and some vitamins produced by gut bacteria, forming solid feces. All statements are correct.
This question belongs to: Science Biology
Question #1892
Consider statements about human diseases: 1. Typhoid is caused by a bacterium. 2. Malaria is caused by a protozoan. 3. Dengue is caused by a virus. Which are correct?
A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option D

Explanation:
Typhoid fever is a systemic bacterial infection caused by Salmonella enterica serotype Typhi, transmitted through contaminated food and water. Malaria is a life-threatening disease caused by protozoan parasites of the genus Plasmodium (like P. falciparum), transmitted by Anopheles mosquitoes. Dengue fever is a viral infection caused by the Dengue virus (a flavivirus), transmitted by Aedes mosquitoes. All three statements correctly identify the causative agents of these major diseases.
This question belongs to: Science Biology
Question #1893
Consider statements about human immunity: 1. Innate immunity is present from birth. 2. Acquired immunity develops after exposure to an antigen. 3. Vaccines provide natural immunity. Which are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1, 2 and 3
D. 1 and 3 only
Discuss
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Correct Answer: Option B

Explanation:
Innate (natural) immunity is the non-specific defense mechanism present from birth, including physical barriers like skin and chemical barriers like stomach acid. Acquired (adaptive) immunity is highly specific and develops after the body is exposed to a specific pathogen or antigen, involving the production of antibodies and memory cells. Vaccines provide artificial immunity (specifically, artificial active immunity), not natural immunity, which is acquired through actual infection or from mother to child. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1894
Consider statements about human nutrition: 1. A balanced diet provides all essential nutrients. 2. Malnutrition only refers to undernutrition. 3. Water is essential for life. Which are correct?
A. 1, 2 and 3
B. 1 and 2 only
C. 2 and 3 only
D. 1 and 3 only
Discuss
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Correct Answer: Option D

Explanation:
A balanced diet contains all the essential macronutrients (carbohydrates, proteins, fats) and micronutrients (vitamins, minerals) in the correct proportions required for optimal health, growth, and maintenance. Malnutrition is a broad term that refers to deficiencies, excesses, or imbalances in a person's intake of energy and/or nutrients; it includes both undernutrition (wasting, stunting) and overnutrition (overweight, obesity). Water is an essential nutrient, crucial for hydration, transport, and all biochemical reactions. Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1895
Consider statements about vitamins: 1. Vitamin A is fat-soluble. 2. Vitamin C is water-soluble. 3. Vitamin D is synthesized in the skin. Which are correct?
A. 1, 2 and 3
B. 2 and 3 only
C. 1 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option A

Explanation:
Vitamins are classified by their solubility. Vitamins A, D, E, and K are fat-soluble, meaning they are absorbed with dietary fats and can be stored in the body's liver and fatty tissues. Vitamins B-complex and C are water-soluble, meaning they dissolve in water and are generally not stored in significant amounts. Vitamin D (cholecalciferol) is unique because it can be synthesized endogenously in the skin when exposed to ultraviolet B (UVB) radiation from sunlight. All statements are correct.
This question belongs to: Science Biology
Question #1896
Consider statements about genetics: 1. DNA is double-stranded. 2. RNA is single-stranded. 3. DNA contains uracil. Which are correct?
A. 1 and 3 only
B. 1, 2 and 3
C. 1 and 2 only
D. 2 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
DNA (deoxyribonucleic acid) typically exists as a double-stranded helical molecule, with two complementary strands held together by hydrogen bonds between base pairs. RNA (ribonucleic acid) is generally single-stranded, allowing it to fold into complex three-dimensional shapes necessary for its various functions (mRNA, tRNA, rRNA). DNA contains the nitrogenous bases adenine, guanine, cytosine, and thymine; it does not contain uracil, which is found in RNA instead of thymine. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1897
Consider statements about evolution: 1. Fossils provide evidence of past life. 2. Homologous organs indicate common ancestry. 3. Analogous organs indicate common ancestry. Which are correct?
A. 1 and 3 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option D

Explanation:
Fossils are the preserved remains or traces of ancient organisms, providing direct, chronological evidence of evolutionary changes and past life forms over millions of years. Homologous organs (like the forelimbs of humans, whales, and bats) share a common structural plan and evolutionary origin, indicating divergent evolution from a common ancestor. Analogous organs (like the wings of birds and insects) perform similar functions but have different structural plans and evolutionary origins, indicating convergent evolution, not common ancestry. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1898
Consider statements about ecology: 1. A food chain shows energy flow. 2. A food web shows interconnected food chains. 3. The pyramid of energy is always inverted. Which are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1, 2 and 3
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
A food chain is a linear sequence illustrating the transfer of energy and matter from one organism to another through consumption. A food web is a complex, interconnected network of multiple food chains, representing the realistic, multiple feeding relationships in an ecosystem. The pyramid of energy, which shows the amount of energy available at each trophic level, is always upright, never inverted, because energy is lost as heat at each transfer according to the 10% law. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1899
Consider statements about environment: 1. The ozone layer is in the stratosphere. 2. CFCs deplete the ozone layer. 3. Global warming is caused by a decrease in CO2. Which are correct?
A. 1, 2 and 3
B. 2 and 3 only
C. 1 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option D

Explanation:
The ozone layer, a region of high ozone concentration, is located in the stratosphere, approximately 15 to 35 kilometers above Earth's surface, where it absorbs harmful UV radiation. Chlorofluorocarbons (CFCs), once widely used in refrigerants and aerosols, release chlorine atoms in the stratosphere that catalytically destroy ozone molecules, leading to ozone depletion. Global warming is primarily caused by an increase, not a decrease, in atmospheric greenhouse gases like carbon dioxide (CO2), which trap more heat. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1900
Consider statements about microorganisms: 1. Bacteria can be beneficial or harmful. 2. Fungi are used in food production. 3. Viruses are living outside a host. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
Bacteria exhibit diverse roles; many are beneficial (e.g., gut flora, nitrogen fixers, decomposers), while some are pathogenic and cause diseases. Fungi are extensively used in food production, such as yeast (Saccharomyces) in baking and brewing, and molds (Penicillium) in cheese making (e.g., Roquefort, Camembert). Viruses are considered non-living outside a host cell because they lack metabolic machinery and cannot replicate independently; they only exhibit living characteristics when inside a host. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology

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