Biology MCQs

Science

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.

2054
Total Questions

Practice Questions

Page 70 of 103
Question #1381
The discovery of the enzyme 'restriction endonuclease' was a milestone in biotechnology. The first such enzyme was isolated by:
A. Watson and Crick
B. Hamilton O. Smith, Kent W. Wilcox, and Thomas J. Kelly
C. Kary Mullis
D. Paul Berg
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
While restriction enzymes were first observed by Linn and Arber, the first Type II restriction endonuclease (HindII), which is the type used in genetic engineering because it cuts at specific recognition sites, was isolated and characterized by Hamilton O. Smith, Kent W. Wilcox, and Thomas J. Kelly in 1970 from Haemophilus influenzae. For this discovery, Smith shared the Nobel Prize in Physiology or Medicine in 1978. Kary Mullis invented PCR.
This question belongs to: Science Biology
Question #1382
Which of the following scientists is credited with the discovery of the 'Krebs cycle' (Citric Acid Cycle)?
A. Hans Adolf Krebs
B. Otto Warburg
C. Arthur Kornberg
D. Melvin Calvin
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The Krebs cycle, also known as the citric acid cycle or TCA cycle, is the central metabolic pathway for the oxidation of acetyl-CoA to produce energy (ATP, NADH, FADH2). It was discovered by the British-German biochemist Sir Hans Adolf Krebs in 1937. He was awarded the Nobel Prize in Physiology or Medicine in 1953 for this discovery. Melvin Calvin elucidated the carbon pathway in photosynthesis.
This question belongs to: Science Biology
Question #1383
In the human digestive system, the 'Peyer's patches' are aggregated lymphoid nodules found primarily in the mucosa and submucosa of the:
A. Esophagus
B. Ileum (small intestine)
C. Large intestine
D. Stomach
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Peyer's patches are organized lymphoid follicles (aggregated lymphoid nodules) located in the mucosa and submucosa of the small intestine, most abundantly in the ileum (the distal part). They are a crucial component of the gut-associated lymphoid tissue (GALT) and play a vital role in monitoring intestinal bacteria populations, preventing the growth of pathogenic bacteria, and training the immune system to recognize antigens.
This question belongs to: Science Biology
Question #1384
The 'Foramen of Panizza' is a small opening found in the heart of which animal, allowing blood to bypass the pulmonary circuit?
A. Frog
B. Shark
C. Rabbit
D. Crocodile
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
The Foramen of Panizza is a small opening located between the left and right aortic arches at the base of the heart in crocodilians (crocodiles, alligators). It allows blood to flow between the two systemic arches. During diving, when pulmonary resistance increases, this foramen allows deoxygenated blood to bypass the lungs and enter the systemic circulation, conserving oxygen for vital organs. Frogs have a three-chambered heart without this specific foramen.
This question belongs to: Science Biology
Question #1385
In the human eye, the 'macula lutea' and its central depression, the 'fovea centralis', are significant because the fovea contains:
A. Only cones, providing the sharpest central vision and color discrimination
B. An equal number of rods and cones
C. Only rods, providing high sensitivity to dim light
D. The blind spot where the optic nerve exits
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The macula lutea is a yellowish spot near the center of the retina. Its central depression, the fovea centralis, is the point of sharpest vision. The fovea is packed exclusively with cone cells and lacks blood vessels and rods. This high density of cones, combined with the displacement of overlying retinal layers, allows for maximum visual acuity and color discrimination in bright light. The blind spot is the optic disc.
This question belongs to: Science Biology
Question #1386
The 'Haversian system' or 'osteon' is the fundamental functional unit of compact bone in:
A. Cartilage
B. Mammalian bone
C. Fish bone
D. Bird bone
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
The Haversian system (osteon) is the characteristic structural unit of compact (cortical) bone in mammals. It consists of a central Haversian canal (containing blood vessels and nerves) surrounded by concentric layers of calcified matrix called lamellae. Between the lamellae are small spaces called lacunae, which house osteocytes (bone cells). Canaliculi connect the lacunae. Bird bones are pneumatic (hollow), and cartilage lacks Haversian systems.
This question belongs to: Science Biology
Question #1387
In the process of blood clotting, the enzyme 'thrombin' is formed from its inactive precursor 'prothrombin' in the presence of:
A. Plasmin and sodium
B. Heparin and potassium
C. Thromboplastin and calcium ions
D. Fibrinogen and calcium
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Blood clotting (coagulation) is a cascade of enzymatic reactions. When tissue is damaged, it releases thromboplastin (tissue factor). In the presence of calcium ions (Ca2+), thromboplastin activates the conversion of the inactive plasma protein prothrombin (synthesized in the liver with the help of Vitamin K) into the active enzyme thrombin. Thrombin then catalyzes the conversion of soluble fibrinogen into insoluble fibrin threads, forming the clot mesh.
This question belongs to: Science Biology
Question #1388
The 'Sinoatrial (SA) node' is known as the natural pacemaker of the heart because:
A. It is located in the ventricles
B. It receives signals from the brain first
C. It generates action potentials spontaneously at the highest intrinsic rate
D. It has the highest threshold for stimulation
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
The Sinoatrial (SA) node, located in the right atrium, is the natural pacemaker because its cells are autorhythmic; they can spontaneously generate action potentials without external neural input. Crucially, the SA node has the highest intrinsic rate of depolarization (about 70-80 beats per minute) compared to other autorhythmic tissues like the AV node or Purkinje fibers. Therefore, it sets the pace for the entire heart, overriding slower pacemakers.
This question belongs to: Science Biology
Question #1389
In the nephron, the 'Loop of Henle' is primarily responsible for:
A. Reabsorption of glucose and amino acids
B. Secretion of hydrogen and potassium ions
C. Filtration of blood plasma
D. Concentration of urine by creating a medullary osmotic gradient
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
The Loop of Henle is a U-shaped tube extending into the renal medulla. Its primary function is to concentrate the urine by creating a hyperosmotic gradient in the medullary interstitium through the counter-current multiplier mechanism. The descending limb is permeable to water but not salts, while the ascending limb is impermeable to water but actively transports salts out. This gradient allows the collecting duct to reabsorb water under the influence of ADH.
This question belongs to: Science Biology
Question #1390
The 'Blood-Brain Barrier' (BBB) is formed primarily by the tight junctions between the endothelial cells of capillaries in the brain and the surrounding:
A. Ependymal cells
B. Microglia
C. Oligodendrocytes
D. Astrocytes
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
The Blood-Brain Barrier (BBB) is a highly selective semipermeable border that protects the brain from many substances in the blood. It is primarily formed by the tight junctions between the endothelial cells of the brain's capillaries. These endothelial cells are closely associated with the foot processes of astrocytes (a type of glial cell), which induce and maintain the tight junctions, restricting the passage of large molecules, toxins, and pathogens into the brain tissue.
This question belongs to: Science Biology
Question #1391
In the endocrine system, the hormone 'Oxytocin' is synthesized in the hypothalamus but is stored and released by the:
A. Thyroid gland
B. Anterior pituitary
C. Posterior pituitary (Neurohypophysis)
D. Adrenal medulla
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Oxytocin (and ADH/vasopressin) are peptide hormones synthesized by the neurosecretory cells of the hypothalamus (supraoptic and paraventricular nuclei). They are transported down the axons of these neurons and stored in the nerve terminals of the posterior pituitary (neurohypophysis). Upon neural stimulation, they are released directly into the bloodstream from the posterior pituitary. The anterior pituitary synthesizes its own hormones.
This question belongs to: Science Biology
Question #1392
The 'corpus luteum' in the ovary secretes large amounts of progesterone primarily to:
A. Initiate menstruation
B. Trigger the LH surge for ovulation
C. Maintain the uterine endometrium for potential implantation of a fertilized egg
D. Stimulate the growth of ovarian follicles
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
After ovulation, the ruptured Graafian follicle transforms into a temporary endocrine structure called the corpus luteum. Its primary function is to secrete large amounts of progesterone (and some estrogen). Progesterone is crucial for maintaining the thickened, highly vascularized uterine endometrium (secretory phase), making it receptive for the implantation of a blastocyst. If fertilization does not occur, the corpus luteum degenerates, progesterone levels drop, and menstruation begins.
This question belongs to: Science Biology
Question #1393
Which of the following is a viral disease that primarily attacks the immune system, specifically the CD4+ T helper cells?
A. Influenza
B. Hepatitis B
C. HIV (AIDS)
D. Herpes Simplex
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Human Immunodeficiency Virus (HIV), the causative agent of Acquired Immunodeficiency Syndrome (AIDS), is a retrovirus that specifically targets and destroys CD4+ T helper cells, which are crucial for coordinating the adaptive immune response. As the CD4+ count drops, the immune system becomes severely compromised, leading to opportunistic infections and certain cancers. Hepatitis B targets the liver, Herpes causes lesions, and Influenza targets the respiratory tract.
This question belongs to: Science Biology
Question #1394
The 'Widal test' is a diagnostic test used to detect the presence of antibodies against the causative agent of:
A. Typhoid fever
B. Malaria
C. Tuberculosis
D. Dengue
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The Widal test is a serological agglutination test used to diagnose enteric (typhoid) fever, caused by Salmonella enterica serotype Typhi. It detects the presence of specific antibodies (O and H antigens) in the patient's serum against the O (somatic) and H (flagellar) antigens of the Salmonella typhi bacteria. A significant rise in antibody titer indicates an active or recent infection. It is not used for TB (Mantoux test), malaria (blood smear), or dengue (NS1/IgM).
This question belongs to: Science Biology
Question #1395
In human nutrition, the 'Glycemic Index' (GI) of a food measures:
A. The rate at which the food raises blood glucose levels after consumption
B. The total carbohydrate content per 100 grams
C. The amount of dietary fiber present in the food
D. The caloric value of the food
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The Glycemic Index (GI) is a numerical scale (from 0 to 100) that measures how quickly a carbohydrate-containing food raises blood glucose levels compared to a reference food (usually pure glucose or white bread). Foods with a high GI (like white bread, sugary drinks) cause a rapid spike in blood sugar, while low GI foods (like whole grains, legumes) cause a slower, more gradual rise. It does not measure total carbohydrate amount.
This question belongs to: Science Biology
Question #1396
The vitamin that acts as a hormone in the body and is synthesized in the skin upon exposure to ultraviolet (UV) sunlight is:
A. Vitamin E
B. Vitamin D
C. Vitamin C
D. Vitamin A
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Vitamin D (specifically cholecalciferol, Vitamin D3) is unique because it can be synthesized endogenously in the human skin. When 7-dehydrocholesterol in the skin is exposed to ultraviolet B (UVB) radiation from sunlight, it is converted to previtamin D3, which then isomerizes to Vitamin D3. It is subsequently hydroxylated in the liver and kidneys to its active hormonal form, calcitriol, which regulates calcium and phosphorus metabolism.
This question belongs to: Science Biology
Question #1397
In genetics, the phenomenon where the expression of one gene is masked or modified by the expression of another non-allelic gene is called:
A. Pleiotropy
B. Penetrance
C. Linkage
D. Epistasis
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Epistasis is a form of gene interaction where the expression of one gene (the epistatic gene) masks, suppresses, or modifies the expression of another non-allelic gene (the hypostatic gene). This alters the expected Mendelian dihybrid ratio (9:3:3:1) into modified ratios like 9:7 (complementary), 9:3:4 (recessive epistasis), or 12:3:1 (dominant epistasis). Pleiotropy is one gene affecting multiple traits, and linkage is genes being on the same chromosome.
This question belongs to: Science Biology
Question #1398
The 'Philadelphia chromosome', associated with Chronic Myelogenous Leukemia (CML), is the result of a reciprocal translocation between chromosomes:
A. 14 and 21
B. 9 and 22
C. 11 and 14
D. 8 and 14
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
The Philadelphia chromosome is a specific genetic abnormality found in the bone marrow cells of most patients with Chronic Myelogenous Leukemia (CML). It is formed by a reciprocal translocation between the long arms of chromosome 9 and chromosome 22, denoted as t(9;22). This translocation fuses the BCR gene on chromosome 22 with the ABL1 gene on chromosome 9, creating a mutant BCR-ABL1 fusion protein with constitutive tyrosine kinase activity, driving uncontrolled cell division.
This question belongs to: Science Biology
Question #1399
In molecular biology, the 'Wobble hypothesis' explains the flexibility in base pairing between the:
A. Third base of the codon and the first base of the anticodon
B. Second base of the codon and the second base of the anticodon
C. First base of the codon and the first base of the anticodon
D. DNA template and the newly synthesized mRNA
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The Wobble hypothesis, proposed by Francis Crick, explains the degeneracy of the genetic code. It states that the base pairing rules (A-U, G-C) are strictly followed for the first two bases of the mRNA codon, but the third base of the codon (the 3' end) can form non-standard or 'wobble' base pairs with the first base of the tRNA anticodon (the 5' end). This allows a single tRNA molecule to recognize and bind to more than one synonymous codon.
This question belongs to: Science Biology
Question #1400
The process of 'Southern blotting' is a technique used in molecular biology to detect:
A. Specific proteins in a sample
B. Specific RNA sequences in a sample
C. Lipids in a cell membrane
D. Specific DNA sequences in a sample
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Southern blotting, named after its inventor Edwin Southern, is a laboratory method used to detect specific DNA sequences in a complex DNA sample. The process involves digesting DNA with restriction enzymes, separating the fragments by gel electrophoresis, transferring (blotting) them onto a nylon or nitrocellulose membrane, and then hybridizing the membrane with a labeled, complementary DNA or RNA probe. Northern blotting detects RNA, and Western blotting detects proteins.
This question belongs to: Science Biology

More Science Topics

chemistry MCQs
Physics MCQs
Today's Top Topics
Physics 1287 chemistry 1089 Biology 2054
Explore Subjects
Computer 5279 History GK 3374 English 15164 Static General Knowledge 6362 Reasoning 1120
Practice Mix
The term 'Deuce' is used when the score is tied in tennis. What specific score does it denote?
The 'Vittala Temple' is known for its:
Two stations A and B are 450 km apart. A train leaves station A at 4:00 PM at 60 km/h. Another train leaves station B at 5:00 PM at 70 km/h traveling towards A. At what time will they meet?
Which of the following is a characteristic of a distributed operating system?
Select the correct passive voice of: 'She gave me a book.'