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 #1261
The disorder caused by the deficiency of the enzyme phenylalanine hydroxylase is:
A. Homocystinuria
B. Maple syrup urine disease
C. Albinism
D. Phenylketonuria
Discuss
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Correct Answer: Option D

Explanation:
PKU leads to accumulation of phenylalanine, causing mental retardation. Albinism is tyrosinase defect, MSUD branched-chain ketoacid dehydrogenase, homocystinuria methionine metabolism.
This question belongs to: Science Biology
Question #1262
The scientist who discovered the blood groups (ABO system) was:
A. Charles Drew
B. Paul Ehrlich
C. Alexander Fleming
D. Karl Landsteiner
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Correct Answer: Option D

Explanation:
Karl Landsteiner discovered the ABO blood group system in 1901, for which he received the Nobel Prize. He also discovered the Rh factor with others.
This question belongs to: Science Biology
Question #1263
The structure that connects the pharynx to the middle ear and equalizes pressure is the:
A. Eustachian tube
B. Auditory canal
C. Cochlea
D. Semicircular canals
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Correct Answer: Option A

Explanation:
The Eustachian (auditory) tube connects the nasopharynx to the middle ear, allowing pressure equalization across the eardrum. The cochlea is for hearing, semicircular canals for balance.
This question belongs to: Science Biology
Question #1264
The vitamin that is required for the synthesis of melanin is:
A. Vitamin B₆
B. Vitamin D
C. Vitamin A
D. Vitamin C
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Correct Answer: Option D

Explanation:
Vitamin C is a cofactor for the enzyme tyrosinase, which is involved in melanin synthesis. Vitamin A is for vision, B₆ for amino acid metabolism, D for calcium.
This question belongs to: Science Biology
Question #1265
The enzyme that catalyzes the synthesis of cAMP from ATP is:
A. Guanylyl cyclase
B. Adenylyl cyclase
C. Phospholipase C
D. Protein kinase A
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Correct Answer: Option B

Explanation:
Adenylyl cyclase converts ATP to cyclic AMP, a second messenger. Guanylyl cyclase makes cGMP, phospholipase C produces IP₃/DAG, PKA is activated by cAMP.
This question belongs to: Science Biology
Question #1266
The disease caused by the protozoan Trypanosoma cruzi is:
A. Sleeping sickness
B. Chagas disease
C. Leishmaniasis
D. Malaria
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Correct Answer: Option B

Explanation:
Chagas disease is caused by T. cruzi, transmitted by triatomine bugs. Sleeping sickness is T. brucei, malaria Plasmodium, leishmaniasis Leishmania.
This question belongs to: Science Biology
Question #1267
The hormone that stimulates the secretion of cortisol from the adrenal cortex is:
A. FSH
B. ACTH
C. Prolactin
D. TSH
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Correct Answer: Option B

Explanation:
Adrenocorticotropic hormone (ACTH) from the anterior pituitary stimulates the adrenal cortex to produce cortisol and androgens. TSH stimulates thyroid, FSH gonads.
This question belongs to: Science Biology
Question #1268
The pigment that is present in the fovea centralis of the retina for high acuity color vision is:
A. Rhodopsin
B. Iodopsin (cone pigments)
C. Lutein
D. Melanin
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Correct Answer: Option B

Explanation:
The fovea contains tightly packed cones with photopsins (iodopsins) sensitive to red, green, blue. Rhodopsin is in rods for dim light.
This question belongs to: Science Biology
Question #1269
The structure that prevents the backflow of urine from the bladder to the ureters is the:
A. Ureterovesical valve
B. Detrusor muscle
C. Renal pelvis
D. Urethral sphincter
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Correct Answer: Option A

Explanation:
The oblique entry of the ureters into the bladder creates a valve-like effect, preventing reflux. The urethral sphincter controls urination.
This question belongs to: Science Biology
Question #1270
The vitamin that is a component of the coenzyme NAD⁺ and NADP⁺ is:
A. Thiamine
B. Riboflavin
C. Niacin
D. Biotin
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Correct Answer: Option C

Explanation:
Niacin (vitamin B₃) is the precursor of NAD⁺ and NADP⁺, essential electron carriers in redox reactions. Thiamine is TPP, riboflavin FAD, biotin for carboxylation.
This question belongs to: Science Biology
Question #1271
The scientist who developed the first successful heart-lung machine was:
A. Willem Kolff
B. Michael DeBakey
C. John Gibbon
D. Christiaan Barnard
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Correct Answer: Option C

Explanation:
John Gibbon developed the heart-lung machine and performed the first successful open-heart surgery using it in 1953. Barnard did first heart transplant.
This question belongs to: Science Biology
Question #1272
The process of protein folding that is assisted by chaperone proteins occurs in the:
A. Lysosome
B. Endoplasmic reticulum
C. Nucleus
D. Golgi apparatus
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Correct Answer: Option B

Explanation:
Chaperone proteins like BiP assist in proper protein folding in the rough ER. Misfolded proteins are degraded. Golgi modifies, lysosome digests.
This question belongs to: Science Biology
Question #1273
The disease caused by the tapeworm Taenia solium is:
A. Ascariasis
B. Filariasis
C. Trichinosis
D. Taeniasis
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Correct Answer: Option D

Explanation:
Taeniasis is intestinal infection with adult Taenia solium (pork tapeworm). Cysticercosis is when larvae infect tissues. Ascariasis is roundworm, filariasis nematode, trichinosis Trichinella.
This question belongs to: Science Biology
Question #1274
The hormone that induces sleep and is secreted by the pineal gland is:
A. Melatonin
B. Acetylcholine
C. Dopamine
D. Serotonin
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Correct Answer: Option A

Explanation:
Melatonin, synthesized from serotonin, is released in darkness, regulating circadian rhythms and promoting sleep. Serotonin is a neurotransmitter, dopamine reward, acetylcholine muscle contraction.
This question belongs to: Science Biology
Question #1275
The organelle that is involved in the formation of the acrosome in sperm cells is the:
A. Mitochondria
B. Lysosome
C. Endoplasmic reticulum
D. Golgi apparatus
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Correct Answer: Option D

Explanation:
The Golgi apparatus forms the acrosomal vesicle, which contains hydrolytic enzymes for penetrating the egg during fertilization.
This question belongs to: Science Biology
Question #1276
The technique used to measure the electrical activity of the brain is:
A. EMG
B. ECG
C. EchoCG
D. EEG
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Correct Answer: Option D

Explanation:
Electroencephalography (EEG) records electrical activity of the brain via scalp electrodes. ECG is for heart, EMG for muscles, EchoCG ultrasound of heart.
This question belongs to: Science Biology
Question #1277
The pigment that gives the characteristic yellow color to egg yolk is:
A. Anthocyanin
B. Beta-carotene
C. Lycopene
D. Xanthophyll
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Correct Answer: Option D

Explanation:
Xanthophylls, oxygenated carotenoids, are responsible for the yellow color of egg yolk, autumn leaves, and corn. Beta-carotene is orange, lycopene red.
This question belongs to: Science Biology
Question #1278
The disease caused by the nematode Wuchereria bancrofti is transmitted by:
A. Culex mosquito
B. Anopheles mosquito
C. Sandfly
D. Aedes mosquito
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Correct Answer: Option A

Explanation:
Lymphatic filariasis (elephantiasis) is caused by Wuchereria bancrofti and transmitted by Culex mosquito. Malaria is Anopheles, dengue Aedes, leishmaniasis sandfly.
This question belongs to: Science Biology
Question #1279
The hormone that promotes the absorption of glucose into cells is:
A. Epinephrine
B. Glucagon
C. Cortisol
D. Insulin
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Correct Answer: Option D

Explanation:
Insulin stimulates GLUT4 transporters to move to the cell membrane, increasing glucose uptake in muscle and adipose tissue. Glucagon raises blood glucose.
This question belongs to: Science Biology
Question #1280
The scientist who discovered the bacterium that causes leprosy was:
A. Louis Pasteur
B. Robert Koch
C. Gerhard Armauer Hansen
D. Albert Neisser
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Correct Answer: Option C

Explanation:
G.H.A. Hansen discovered Mycobacterium leprae in 1873, the first bacterium identified as causing a human disease. Koch later discovered TB.
This question belongs to: Science Biology

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