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 45 of 103
Question #881
The first antibiotic, Penicillin, was extracted from which microorganism?
A. Fungus (Penicillium notatum)
B. Bacterium
C. Actinomycete
D. Virus
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Correct Answer: Option A

Explanation:
Penicillin, the first true antibiotic, was discovered by Alexander Fleming in 1928. He observed that a mold contaminating a Staphylococcus culture plate was inhibiting bacterial growth. The mold was identified as Penicillium notatum (now P. chrysogenum). Penicillin is extracted from this fungus and is effective against many Gram-positive bacteria.
This question belongs to: Science Biology
Question #882
In recombinant DNA technology, restriction enzymes are used to:
A. Cut DNA at specific recognition sequences
B. Join DNA fragments together
C. Insert DNA into a host cell
D. Amplify DNA
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Correct Answer: Option A

Explanation:
Restriction enzymes (restriction endonucleases) are molecular 'scissors' that cut DNA at specific, highly specific recognition sequences (palindromic sequences). They are essential tools in genetic engineering for cutting both the source DNA (gene of interest) and the vector DNA at specific sites, creating compatible ends for ligation. DNA ligase is used to join the fragments.
This question belongs to: Science Biology
Question #883
The enzyme Taq polymerase, used in PCR, is obtained from:
A. Escherichia coli
B. Salmonella typhimurium
C. Agrobacterium tumefaciens
D. Thermus aquaticus
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Correct Answer: Option D

Explanation:
Taq polymerase is a thermostable DNA polymerase enzyme isolated from the thermophilic bacterium Thermus aquaticus, found in hot springs. It is used in the Polymerase Chain Reaction (PCR) because it can withstand the high temperatures (around 94°C) required for the denaturation step of PCR without being destroyed, unlike normal DNA polymerases.
This question belongs to: Science Biology
Question #884
Gel electrophoresis is a technique used to separate:
A. Proteins based on charge only
B. Cells based on density
C. Lipids based on solubility
D. DNA fragments based on size
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Correct Answer: Option D

Explanation:
Gel electrophoresis is a widely used technique to separate charged molecules, primarily DNA, RNA, or proteins, in an electric field through a gel matrix (usually agarose for DNA). DNA fragments are separated based on their size (length in base pairs). Smaller fragments move faster and further through the gel than larger ones. The separated DNA bands are visualized using ethidium bromide and UV light.
This question belongs to: Science Biology
Question #885
A plasmid used as a cloning vector must have:
A. A single restriction site only
B. A large size to hold more DNA
C. No antibiotic resistance genes
D. An origin of replication and a selectable marker
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Correct Answer: Option D

Explanation:
A plasmid used as a cloning vector in genetic engineering must have certain essential features: an Origin of Replication (ori) to ensure its replication within the host cell, a Selectable Marker (like an antibiotic resistance gene) to identify and eliminate non-transformants, and at least one unique Restriction Site (cloning site) for the insertion of the foreign DNA.
This question belongs to: Science Biology
Question #886
Bt cotton is a genetically modified crop that contains a gene from:
A. Pseudomonas fluorescens
B. Bacillus thuringiensis
C. Escherichia coli
D. Agrobacterium tumefaciens
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Correct Answer: Option B

Explanation:
Bt cotton is a transgenic crop developed by inserting cry genes (e.g., cryIAc, cryIIAb) from the soil bacterium Bacillus thuringiensis (Bt). These genes code for crystal proteins (Cry proteins) that are toxic to certain insect pests, particularly the cotton bollworm. When the insect ingests the protein, it is activated in its alkaline gut, creating pores in the gut lining, leading to the insect's death.
This question belongs to: Science Biology
Question #887
Gene therapy was first attempted to treat a patient with which genetic disorder?
A. Sickle cell anemia
B. Hemophilia
C. Cystic fibrosis
D. Adenosine Deaminase (ADA) deficiency
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Correct Answer: Option D

Explanation:
Gene therapy involves correcting a genetic defect by introducing a functional gene into a patient's cells. The first clinical gene therapy was given in 1990 to a 4-year-old girl with Adenosine Deaminase (ADA) deficiency, a severe combined immunodeficiency (SCID) caused by a mutation in the ADA gene. The functional ADA gene was introduced into her lymphocytes using a retroviral vector.
This question belongs to: Science Biology
Question #888
The property of a plant cell that allows it to generate a whole new plant from a single cell or tissue is called:
A. Totipotency
B. Somatic hybridization
C. Protoplast fusion
D. Micropropagation
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Correct Answer: Option A

Explanation:
Totipotency is the genetic ability of a single plant cell to divide and differentiate into all the cell types of the plant, ultimately generating an entire new plant. This property is the fundamental basis of plant tissue culture. Micropropagation is the technique used to rapidly multiply plants using this totipotency, often through the formation of callus and somatic embryos.
This question belongs to: Science Biology
Question #889
Rhizobium is used as a biofertilizer primarily for:
A. Decomposing organic matter
B. Producing auxins
C. Fixing atmospheric nitrogen in legume root nodules
D. Solubilizing phosphates
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Correct Answer: Option C

Explanation:
Rhizobium is a symbiotic nitrogen-fixing bacterium that forms root nodules in the roots of leguminous plants (like peas, beans, clover). Inside these nodules, the bacterium converts atmospheric nitrogen (N2) into ammonia (NH3), which the plant can use. In return, the plant provides the bacteria with carbohydrates and a protected environment. It significantly reduces the need for chemical nitrogen fertilizers.
This question belongs to: Science Biology
Question #890
Bacillus thuringiensis (Bt) is widely used as a:
A. Biofertilizer
B. Bioremediation agent
C. Biopesticide (Bioinsecticide)
D. Bioherbicide
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Correct Answer: Option C

Explanation:
Bacillus thuringiensis (Bt) is widely used as a biopesticide, specifically a bioinsecticide. The spores of Bt contain crystalline proteins (Cry toxins) that are toxic to the larvae of many insects, particularly Lepidoptera (caterpillars), Diptera (flies), and Coleoptera (beetles). When sprayed on crops or ingested by transgenic plants, these toxins kill the pests without harming humans, animals, or beneficial insects.
This question belongs to: Science Biology
Question #891
Rosie, the first transgenic cow, was engineered to produce human:
A. Growth hormone
B. Interferon
C. Insulin
D. Alpha-lactalbumin
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Correct Answer: Option D

Explanation:
Rosie, the first transgenic cow, was created in 2000. She was genetically modified to produce milk that contained human alpha-lactalbumin, a protein found in human breast milk. Her milk was nutritionally more balanced for human babies than normal cow's milk, containing about 2.4 grams per liter of this human protein. This demonstrated the potential of transgenic animals for producing pharmaceutical or nutritional products.
This question belongs to: Science Biology
Question #892
Which of the following is a high-yielding exotic breed of cattle used in dairy farming?
A. Sahiwal
B. Gir
C. Holstein-Friesian
D. Red Sindhi
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Correct Answer: Option C

Explanation:
Holstein-Friesian (often just called Holstein) is a high-yielding exotic breed of dairy cattle originating from the Netherlands. They are known for their high milk production, although the milk has a lower fat content compared to some indigenous breeds. Sahiwal, Gir, and Red Sindhi are important indigenous (Indian) cattle breeds known for their disease resistance and heat tolerance.
This question belongs to: Science Biology
Question #893
The most common species of honeybee used for commercial apiculture in India is:
A. Apis mellifera
B. Apis dorsata
C. Apis cerana indica
D. Apis florea
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Correct Answer: Option C

Explanation:
Apis cerana indica (the Indian honeybee) is the most commonly domesticated species for commercial apiculture (beekeeping) in India. It is well-adapted to the local climate and is less aggressive than Apis dorsata (the rock bee). Apis mellifera (the Italian bee) is also widely used globally and in India for its high honey yield and gentle nature. Apis florea is the little bee, which is not suitable for commercial beekeeping.
This question belongs to: Science Biology
Question #894
Sericulture is the rearing of which insect for the production of silk?
A. Lac insect
B. Honeybee
C. Silkworm (Bombyx mori)
D. Prawn
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Correct Answer: Option C

Explanation:
Sericulture is the process of rearing silkworms (primarily Bombyx mori) for the production of silk. The silkworm feeds on mulberry leaves (Morus alba) and spins a continuous filament of silk protein (fibroin) to form a cocoon around itself during its pupal stage. The cocoons are then boiled to kill the pupa and unwind the silk filament for textile production.
This question belongs to: Science Biology
Question #895
Which of the following is a major activity in fisheries (aquaculture)?
A. Breeding and rearing of fish and other aquatic organisms
B. Cultivation of mulberry plants
C. Rearing of silkworms
D. Management of dairy cattle
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Correct Answer: Option A

Explanation:
Fisheries, or aquaculture, involves the breeding, rearing, and harvesting of fish, shellfish, algae, and other aquatic organisms in various water environments for food, commercial, and recreational purposes. It includes both inland fisheries (freshwater like ponds, rivers) and marine fisheries (saltwater like oceans). It is a major source of protein and livelihood globally.
This question belongs to: Science Biology
Question #896
Robert Hooke is credited with the discovery of:
A. Bacteria
B. Cells (in dead cork tissue)
C. Living cells
D. Nucleus
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Correct Answer: Option B

Explanation:
Robert Hooke, an English scientist, is credited with the discovery of cells in 1665. He observed a thin slice of dead cork tissue from an oak tree under a primitive compound microscope. He saw a honeycomb-like structure of small compartments, which he called 'cells' (from the Latin 'cella', meaning small room). He was actually observing the non-living cell walls of dead plant cells.
This question belongs to: Science Biology
Question #897
Antonie van Leeuwenhoek is known for being the first to observe:
A. Mitochondria
B. Chromosomes
C. Cell division
D. Living cells (animalcules)
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Correct Answer: Option D

Explanation:
Antonie van Leeuwenhoek, a Dutch linen merchant and amateur scientist, is known as the 'father of microbiology'. Using his own handcrafted, high-quality single-lens microscopes, he was the first person to observe and describe living, single-celled organisms, which he called 'animalcules' (little animals). These included bacteria, protozoa, and sperm cells, in the late 17th century.
This question belongs to: Science Biology
Question #898
Louis Pasteur is famous for his work on:
A. Pasteurization and disproving spontaneous generation
B. Theory of evolution
C. Laws of inheritance
D. Discovery of penicillin
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Correct Answer: Option A

Explanation:
Louis Pasteur, a French microbiologist, is famous for several groundbreaking contributions. He developed the process of pasteurization (heating liquids to kill harmful microbes). He also conclusively disproved the theory of spontaneous generation using his famous swan-neck flask experiment, demonstrating that life only arises from pre-existing life (biogenesis). He also developed vaccines for rabies and anthrax.
This question belongs to: Science Biology
Question #899
Edward Jenner is credited with developing the first vaccine against:
A. Polio
B. Rabies
C. Tuberculosis
D. Smallpox
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Correct Answer: Option D

Explanation:
Edward Jenner, an English physician, is known as the 'father of immunology'. In 1796, he developed the world's first successful vaccine against smallpox. He observed that milkmaids who had contracted cowpox (a mild disease) were immune to smallpox. He inoculated a boy with material from a cowpox blister, successfully conferring immunity to smallpox, thus pioneering the concept of vaccination.
This question belongs to: Science Biology
Question #900
Alexander Fleming discovered the first antibiotic, Penicillin, from:
A. Penicillium notatum
B. Streptomyces griseus
C. Escherichia coli
D. Bacillus subtilis
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Correct Answer: Option A

Explanation:
Alexander Fleming, a Scottish bacteriologist, discovered penicillin in 1928. He returned from a vacation to find that a Petri dish containing Staphylococcus bacteria had been accidentally contaminated by a mold. He noticed a clear zone around the mold where the bacteria had been killed. The mold was identified as Penicillium notatum, and the antibacterial substance was named penicillin.
This question belongs to: Science Biology

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