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 #801
Thyroxine, secreted by the thyroid gland, primarily regulates:
A. Blood calcium levels
B. Basal metabolic rate (BMR)
C. Water balance in the body
D. Blood sugar levels
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Correct Answer: Option B

Explanation:
Thyroxine (T4) and Triiodothyronine (T3) are the main hormones secreted by the thyroid gland. They play a crucial role in regulating the basal metabolic rate (BMR), which is the rate at which the body uses energy at rest. They also influence growth, development, and body temperature. Calcitonin, also from the thyroid, regulates blood calcium.
This question belongs to: Science Biology
Question #802
Which hormone is responsible for lowering blood glucose levels by promoting cellular uptake of glucose?
A. Glucagon
B. Cortisol
C. Thyroxine
D. Insulin
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Correct Answer: Option D

Explanation:
Insulin is a peptide hormone secreted by the beta cells of the Islets of Langerhans in the pancreas. Its primary function is to lower blood glucose levels (hypoglycemic effect) by promoting the cellular uptake of glucose, particularly in muscle and fat cells, and its conversion to glycogen (glycogenesis) in the liver. Glucagon has the opposite effect.
This question belongs to: Science Biology
Question #803
Spermatogenesis occurs in which part of the male reproductive system?
A. Seminiferous tubules
B. Vas deferens
C. Epididymis
D. Prostate gland
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Correct Answer: Option A

Explanation:
Spermatogenesis is the process of formation of sperm cells (spermatozoa) from undifferentiated spermatogonia. This process occurs exclusively in the seminiferous tubules, which are highly coiled tubes located within the testes. The epididymis is where sperm mature and are stored, and the vas deferens transports them.
This question belongs to: Science Biology
Question #804
The release of a mature egg from the ovary is called:
A. Menstruation
B. Implantation
C. Fertilization
D. Ovulation
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Correct Answer: Option D

Explanation:
Ovulation is the process in the female menstrual cycle where a mature ovarian follicle ruptures and discharges an ovum (secondary oocyte) into the fallopian tube, where it can potentially be fertilized. It typically occurs around the 14th day of a 28-day cycle, triggered by a surge in Luteinizing Hormone (LH).
This question belongs to: Science Biology
Question #805
Typhoid fever is caused by which bacterium?
A. Vibrio cholerae
B. Streptococcus pneumoniae
C. Salmonella typhi
D. Mycobacterium leprae
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Correct Answer: Option C

Explanation:
Typhoid fever is a life-threatening systemic infection caused by the bacterium Salmonella typhi. It is transmitted through contaminated food and water. Symptoms include sustained high fever, headache, abdominal pain, and sometimes a rash. The Widal test is a common diagnostic test for typhoid. S. pneumoniae causes pneumonia, and V. cholerae causes cholera.
This question belongs to: Science Biology
Question #806
Diphtheria is a bacterial disease caused by:
A. Corynebacterium diphtheriae
B. Clostridium tetani
C. Haemophilus influenzae
D. Bacillus anthracis
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Correct Answer: Option A

Explanation:
Diphtheria is a highly contagious bacterial infection caused by Corynebacterium diphtheriae. It primarily affects the mucous membranes of the nose and throat, producing a thick gray pseudomembrane. The bacteria also produce a potent exotoxin that can damage the heart, kidneys, and nervous system. It is preventable by the DPT vaccine.
This question belongs to: Science Biology
Question #807
The common cold is primarily caused by which virus?
A. Coronavirus
B. Rhinovirus
C. Influenza virus
D. Adenovirus
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Correct Answer: Option B

Explanation:
The common cold is a viral infectious disease of the upper respiratory tract. While many viruses can cause it, Rhinoviruses are the most common causative agents, responsible for 30-50% of cases. Coronaviruses and adenoviruses can also cause colds. Influenza virus causes the flu, which is a more severe respiratory illness.
This question belongs to: Science Biology
Question #808
Dengue fever is transmitted by the bite of an infected:
A. Aedes mosquito
B. Tsetse fly
C. Anopheles mosquito
D. Culex mosquito
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Correct Answer: Option A

Explanation:
Dengue fever is a mosquito-borne viral infection caused by the Dengue virus (four serotypes). It is primarily transmitted by the bite of an infected female Aedes aegypti mosquito (and Aedes albopictus). These mosquitoes typically bite during the day. Anopheles transmits malaria, and Culex transmits filariasis and Japanese encephalitis.
This question belongs to: Science Biology
Question #809
Ringworm is a fungal infection caused by which of the following genera?
A. Microsporum
B. Saccharomyces
C. Penicillium
D. Aspergillus
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Correct Answer: Option A

Explanation:
Ringworm (dermatophytosis) is a superficial fungal infection of the skin, hair, or nails. It is caused by dermatophyte fungi, primarily from the genera Microsporum, Trichophyton, and Epidermophyton. Despite the name, it is not caused by a worm. Aspergillus can cause aspergillosis, and Saccharomyces is yeast used in baking and brewing.
This question belongs to: Science Biology
Question #810
Malaria is caused by a protozoan parasite of the genus:
A. Entamoeba
B. Plasmodium
C. Trypanosoma
D. Leishmania
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Correct Answer: Option B

Explanation:
Malaria is a life-threatening mosquito-borne infectious disease caused by protozoan parasites of the genus Plasmodium. Four species infect humans: P. falciparum (most severe), P. vivax, P. ovale, and P. malariae. The parasite undergoes a complex life cycle in both humans (asexual phase) and the female Anopheles mosquito (sexual phase).
This question belongs to: Science Biology
Question #811
Amoebiasis is caused by which protozoan?
A. Plasmodium vivax
B. Entamoeba histolytica
C. Trypanosoma brucei
D. Giardia lamblia
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Correct Answer: Option B

Explanation:
Amoebiasis, also known as amoebic dysentery, is an intestinal infection caused by the protozoan parasite Entamoeba histolytica. It is transmitted through ingestion of cysts in contaminated food or water. Symptoms include abdominal pain, diarrhea, and dysentery (bloody stools). It can also spread to the liver, causing amoebic liver abscesses.
This question belongs to: Science Biology
Question #812
Ascariasis is a common helminthic disease caused by:
A. Wuchereria bancrofti
B. Ascaris lumbricoides
C. Ancylostoma duodenale
D. Taenia solium
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Correct Answer: Option B

Explanation:
Ascariasis is caused by the large roundworm Ascaris lumbricoides, which is the most common human helminth infection globally. Infection occurs through the ingestion of embryonated eggs from contaminated soil, food, or water. The worms reside in the small intestine and can cause malnutrition, intestinal blockage, and other complications.
This question belongs to: Science Biology
Question #813
Filariasis, leading to elephantiasis, is caused by:
A. Trichinella spiralis
B. Ascaris lumbricoides
C. Wuchereria bancrofti
D. Fasciola hepatica
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Correct Answer: Option C

Explanation:
Filariasis, commonly known as elephantiasis due to the severe swelling of limbs and genitals, is caused by filarial worms like Wuchereria bancrofti and Wuchereria malayi. These thread-like nematodes are transmitted by the bite of infected Culex mosquitoes. The adult worms lodge in the lymphatic vessels, causing chronic inflammation and blockage.
This question belongs to: Science Biology
Question #814
Which of the following is an example of innate immunity?
A. Passive immunity from mother's milk
B. Antibodies produced after vaccination
C. Physical barriers like skin and mucous membranes
D. Memory T cells
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Correct Answer: Option C

Explanation:
Innate immunity is the non-specific, inborn defense mechanism present from birth. It includes physical barriers (skin, mucous membranes), physiological barriers (stomach acid, tears), cellular barriers (neutrophils, macrophages), and cytokine barriers (interferons). Antibodies and memory cells are part of acquired (adaptive) immunity.
This question belongs to: Science Biology
Question #815
Vaccination provides which type of immunity?
A. Artificial passive immunity
B. Natural passive immunity
C. Natural active immunity
D. Artificial active immunity
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Correct Answer: Option D

Explanation:
Vaccination involves the introduction of a weakened, killed, or partial pathogen (antigen) into the body. This stimulates the immune system to produce its own antibodies and memory cells without causing the disease. Since the body actively produces the immune response due to an artificial stimulus, it is called artificial active immunity.
This question belongs to: Science Biology
Question #816
Antibodies transferred from mother to fetus through the placenta is an example of:
A. Natural active immunity
B. Artificial active immunity
C. Natural passive immunity
D. Artificial passive immunity
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Correct Answer: Option C

Explanation:
Natural passive immunity occurs when pre-formed antibodies are transferred naturally from one individual to another. During pregnancy, maternal antibodies (primarily IgG) cross the placenta to the fetus, providing temporary protection against diseases the mother is immune to. Colostrum (mother's milk) also provides IgA antibodies to the newborn.
This question belongs to: Science Biology
Question #817
Which class of antibody is the most abundant in human blood plasma?
A. IgA
B. IgM
C. IgE
D. IgG
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Correct Answer: Option D

Explanation:
Immunoglobulin G (IgG) is the most abundant antibody in human blood plasma, constituting about 75-80% of all antibodies. It is the only antibody that can cross the placenta, providing passive immunity to the fetus. IgG is crucial for long-term immunity, neutralizing toxins, viruses, and bacteria, and activating the complement system.
This question belongs to: Science Biology
Question #818
Which antibody is primarily responsible for allergic reactions?
A. IgG
B. IgA
C. IgE
D. IgM
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Correct Answer: Option C

Explanation:
Immunoglobulin E (IgE) is present in very low concentrations in the blood but plays a central role in Type I hypersensitivity (allergic) reactions. When an allergen binds to IgE antibodies attached to mast cells and basophils, it triggers the release of inflammatory mediators like histamine, causing symptoms like itching, swelling, and anaphylaxis.
This question belongs to: Science Biology
Question #819
Rheumatoid arthritis is an example of which type of disorder?
A. Infectious disease
B. Immunodeficiency
C. Allergy
D. Autoimmune disease
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Correct Answer: Option D

Explanation:
Rheumatoid arthritis is a chronic inflammatory autoimmune disease where the immune system mistakenly attacks the body's own healthy tissues, specifically the synovial membranes of joints. This leads to painful swelling, bone erosion, and joint deformity. Other examples of autoimmune diseases include Type 1 diabetes, multiple sclerosis, and systemic lupus erythematosus.
This question belongs to: Science Biology
Question #820
Glycogen is a polysaccharide primarily stored in:
A. Animal liver and muscle cells
B. Bacterial cell membranes
C. Plant cells
D. Fungal cell walls
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Correct Answer: Option A

Explanation:
Glycogen is a highly branched polysaccharide of glucose, often referred to as 'animal starch'. It is the primary storage form of carbohydrates in animals and fungi. It is mainly stored in the liver and muscle cells. When blood glucose levels drop, glycogen is broken down (glycogenolysis) to release glucose for energy.
This question belongs to: Science Biology

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