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 #1441
The 'Central Dogma' of molecular biology, which describes the flow of genetic information, was proposed by:
A. Severo Ochoa
B. Francis Crick
C. James Watson
D. Marshall Nirenberg
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Correct Answer: Option B

Explanation:
The Central Dogma of molecular biology was proposed by Francis Crick in 1958. It describes the fundamental flow of genetic information within a biological system: DNA is transcribed into RNA, and RNA is translated into protein. The flow is typically unidirectional: DNA -> RNA -> Protein. While exceptions exist (like reverse transcription in retroviruses, where RNA -> DNA), the central dogma remains the core principle of gene expression.
This question belongs to: Science Biology
Question #1442
In the human digestive system, the 'Villi' of the small intestine are covered with even smaller, microscopic projections on the epithelial cells called:
A. Stereocilia
B. Cilia
C. Flagella
D. Microvilli
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Correct Answer: Option D

Explanation:
The inner surface of the small intestine is lined with finger-like projections called villi, which increase the surface area for absorption. The epithelial cells (enterocytes) covering these villi have their own microscopic, finger-like projections on their apical surface, called microvilli. Collectively, these microvilli form a 'brush border'. This further massively increases the surface area, maximizing the efficiency of nutrient absorption. Cilia are motile, and stereocilia are found in the inner ear and epididymis.
This question belongs to: Science Biology
Question #1443
The 'Bohr effect' and the 'Haldane effect' are both phenomena related to the transport of gases in the blood. The Bohr effect facilitates the loading of oxygen in the:
A. Kidneys
B. Tissues
C. Lungs
D. Liver
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Correct Answer: Option C

Explanation:
The Bohr effect describes how an increase in pCO2 or a decrease in pH (increase in H+) reduces hemoglobin's affinity for oxygen, shifting the oxygen dissociation curve to the right and promoting oxygen unloading. Conversely, in the lungs, where pCO2 is low and pH is relatively higher (more alkaline), the Bohr effect works in reverse: hemoglobin's affinity for oxygen increases, facilitating the loading (binding) of oxygen to hemoglobin. The Haldane effect describes the reciprocal relationship for CO2 transport.
This question belongs to: Science Biology
Question #1444
In plant reproduction, the phenomenon where the pollen tube enters the ovule through the micropyle is called:
A. Mesogamy
B. Apogamy
C. Porogamy
D. Chalazogamy
Discuss
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Correct Answer: Option C

Explanation:
In angiosperms, the pollen tube must enter the ovule to deliver the male gametes to the embryo sac. The most common and typical pathway is through the micropyle (the small opening at the tip of the integuments), which is called porogamy. In some plants (like Casuarina, Juglans), the pollen tube enters through the chalaza (the base of the nucellus), which is called chalazogamy. Entry through the integuments is called mesogamy. Apogamy is the formation of a sporophyte without fertilization.
This question belongs to: Science Biology
Question #1445
The 'Hormone Gastrin' is secreted by the 'G cells' of the stomach and primarily stimulates:
A. The pancreas to secrete bicarbonate
B. The liver to produce bile
C. The gastric glands to secrete hydrochloric acid (HCl) and pepsinogen
D. The gall bladder to contract
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Correct Answer: Option C

Explanation:
Gastrin is a peptide hormone produced by the G cells (gastrin cells) located in the pyloric antrum of the stomach. Its primary function is to stimulate the parietal cells of the gastric glands to secrete hydrochloric acid (HCl) and the chief cells to secrete pepsinogen. This prepares the stomach for the digestion of food. Gastrin also stimulates gastric motility and growth of the gastric mucosa. Secretin and CCK stimulate the pancreas and gall bladder.
This question belongs to: Science Biology
Question #1446
In the context of human diseases, 'Elephantiasis' is a chronic condition characterized by the severe swelling of limbs and genitals. It is caused by the filarial worm:
A. Ascaris lumbricoides
B. Ancylostoma duodenale
C. Wuchereria bancrofti
D. Taenia solium
Discuss
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Correct Answer: Option C

Explanation:
Elephantiasis, or lymphatic filariasis, is caused by parasitic nematode worms, primarily Wuchereria bancrofti (responsible for about 90% of cases), Wuchereria malayi, and Brugia timori. These worms are transmitted by mosquitoes (like Culex). The adult worms lodge in the lymphatic vessels, causing severe inflammation, blockage, and damage to the lymphatic system. This leads to the accumulation of lymph fluid and massive, disfiguring swelling (edema) of the limbs, genitals, and breasts, resembling an elephant's skin and legs.
This question belongs to: Science Biology
Question #1447
The 'Restriction enzyme EcoRI' was isolated from the bacterium Escherichia coli strain RY13. The 'RI' in EcoRI stands for:
A. The specific strain (RY13) and the order of discovery
B. Restriction Isoform
C. Recombinant Insertion
D. Ribosomal Inhibitor
Discuss
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Correct Answer: Option A

Explanation:
The nomenclature for restriction enzymes is based on the genus, species, strain, and order of discovery of the source bacterium. In EcoRI: 'E' stands for the genus Escherichia, 'co' stands for the species coli, 'R' stands for the strain RY13, and 'I' indicates that it was the first restriction enzyme isolated from this particular strain. This systematic naming convention helps scientists identify the exact source of the enzyme.
This question belongs to: Science Biology
Question #1448
In the human body, the 'Sinoatrial (SA) node' is located in the wall of the:
A. Left atrium
B. Right atrium
C. Left ventricle
D. Right ventricle
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Correct Answer: Option B

Explanation:
The Sinoatrial (SA) node, the natural pacemaker of the heart, is a small, specialized mass of autorhythmic cardiac muscle cells located in the upper wall of the right atrium, just below the opening of the superior vena cava. It spontaneously generates electrical impulses at a regular rate, which spread through the atrial myocardium, causing the atria to contract and push blood into the ventricles. The impulse then reaches the AV node.
This question belongs to: Science Biology
Question #1449
The 'Hormone Erythropoietin' (EPO), which stimulates the production of red blood cells in the bone marrow, is primarily secreted by the:
A. Spleen
B. Liver
C. Bone marrow itself
D. Kidneys
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Correct Answer: Option D

Explanation:
Erythropoietin (EPO) is a glycoprotein hormone that is the primary regulator of red blood cell production (erythropoiesis). It is primarily produced and secreted by the interstitial fibroblasts in the kidneys (specifically in the peritubular capillary bed) in response to cellular hypoxia (low oxygen levels). A small amount is also produced by the liver. EPO travels to the bone marrow, where it stimulates the proliferation and differentiation of erythroid progenitor cells into mature red blood cells.
This question belongs to: Science Biology
Question #1450
In plant anatomy, the 'Bundle sheath' cells in C4 plants are characterized by having:
A. Only amyloplasts
B. No chloroplasts
C. Small chloroplasts with well-developed grana
D. Large, agranal (lacking grana) chloroplasts
Discuss
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Correct Answer: Option D

Explanation:
In C4 plants, the leaves exhibit Kranz anatomy, where the vascular bundles are surrounded by a distinct layer of bundle sheath cells. These bundle sheath cells are large and contain numerous, large chloroplasts that lack grana (agranal). Because they lack grana, they cannot perform the light-dependent reactions (which require PSII, located in the grana) but are highly efficient at performing the Calvin cycle (light-independent reactions) in a high CO2 environment, minimizing photorespiration.
This question belongs to: Science Biology
Question #1451
The 'Hormone Atrial Natriuretic Peptide' (ANP) is secreted by the heart in response to high blood pressure and primarily acts to:
A. Increase heart rate and contractility
B. Decrease blood pressure by promoting sodium and water excretion by the kidneys
C. Constrict blood vessels
D. Increase blood volume by promoting sodium reabsorption
Discuss
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Correct Answer: Option B

Explanation:
Atrial Natriuretic Peptide (ANP) is a hormone secreted by the atrial myocytes (muscle cells) of the heart in response to excessive stretching of the atrial walls, which occurs when blood volume and pressure are high. ANP acts to lower blood pressure and volume by promoting vasodilation and increasing the excretion of sodium (natriuresis) and water by the kidneys. It also inhibits the renin-angiotensin-aldosterone system (RAAS) and the release of ADH.
This question belongs to: Science Biology
Question #1452
In the context of human reproduction, the 'Placenta' is fully formed and functional by the end of which trimester of pregnancy?
A. First trimester (end of 12 weeks)
B. Second trimester (end of 24 weeks)
C. At the time of birth
D. Third trimester (end of 36 weeks)
Discuss
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Correct Answer: Option A

Explanation:
The placenta begins to form immediately after implantation of the blastocyst. By the end of the first trimester (around 12 weeks of gestation), the placenta is fully formed and takes over the primary role of hormone production (progesterone and estrogen) from the corpus luteum. It is fully functional in providing oxygen, nutrients, and waste removal for the developing fetus for the remainder of the pregnancy. It is not fully formed at conception, nor does it wait until the second or third trimester.
This question belongs to: Science Biology
Question #1453
The 'Hormone Leptin' is primarily secreted by adipose (fat) tissue and acts on the hypothalamus to:
A. Stimulate appetite
B. Increase fat storage
C. Suppress appetite and increase energy expenditure
D. Lower blood glucose levels
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Correct Answer: Option C

Explanation:
Leptin is a peptide hormone produced primarily by adipocytes (fat cells). Its concentration in the blood is proportional to the amount of body fat. Leptin acts as a satiety signal, crossing the blood-brain barrier to act on receptors in the hypothalamus. It suppresses appetite (anorexigenic effect) and increases energy expenditure, thereby regulating long-term food intake and body weight. It is often called the 'satiety hormone' or 'fat hormone'.
This question belongs to: Science Biology
Question #1454
In genetics, the 'Hardy-Weinberg equilibrium' can be disrupted by several evolutionary forces. Which of the following is NOT a factor that disrupts this equilibrium?
A. Mutation
B. Genetic drift
C. Random mating
D. Gene flow (migration)
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Correct Answer: Option C

Explanation:
The Hardy-Weinberg principle states that allele and genotype frequencies in a population will remain constant (in equilibrium) from generation to generation in the absence of evolutionary influences. The conditions required for this equilibrium are: no mutation, random mating, no gene flow (migration), very large population size (no genetic drift), and no natural selection. Therefore, random mating is a condition that MAINTAINS the equilibrium, not a factor that disrupts it. Non-random mating would disrupt it.
This question belongs to: Science Biology
Question #1455
The 'Hormone Ghrelin' is often called the 'hunger hormone' because it is secreted primarily by the stomach and acts on the hypothalamus to:
A. Promote fat breakdown
B. Stimulate appetite and food intake
C. Suppress appetite
D. Increase metabolism
Discuss
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Correct Answer: Option B

Explanation:
Ghrelin is a peptide hormone produced mainly by the endocrine cells of the stomach, especially when it is empty. It is often called the 'hunger hormone' because it acts on the arcuate nucleus of the hypothalamus to stimulate appetite (orexigenic effect) and promote food intake. Ghrelin levels rise before meals and fall after eating. It has the opposite effect of leptin, which suppresses appetite.
This question belongs to: Science Biology
Question #1456
In the human body, the 'Corpus callosum' is a large band of nerve fibers that connects the:
A. Left and right cerebral hemispheres
B. Cerebrum and cerebellum
C. Thalamus and hypothalamus
D. Brain and spinal cord
Discuss
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Correct Answer: Option A

Explanation:
The corpus callosum is the largest white matter structure in the brain, consisting of over 200 million axons. It forms a broad, flat band located deep in the longitudinal fissure (the cleft between the two hemispheres). Its primary function is to serve as the main communication pathway, allowing the left and right cerebral hemispheres to share information, coordinate activities, and integrate sensory, motor, and cognitive functions.
This question belongs to: Science Biology
Question #1457
The 'Hormone Inhibin' is secreted by the Sertoli cells in males and the granulosa cells in females, and its primary function is to:
A. Inhibit the secretion of Follicle Stimulating Hormone (FSH) from the anterior pituitary
B. Stimulate the production of testosterone
C. Promote the development of secondary sexual characteristics
D. Stimulate the secretion of Luteinizing Hormone (LH)
Discuss
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Correct Answer: Option A

Explanation:
Inhibin is a peptide hormone that is part of the negative feedback loop regulating the reproductive system. In males, it is secreted by the Sertoli cells of the testes in response to high levels of testosterone and spermatogenesis. In females, it is secreted by the granulosa cells of the ovarian follicles and the corpus luteum. Its primary function is to selectively inhibit the secretion of Follicle Stimulating Hormone (FSH) from the anterior pituitary gland, without affecting LH secretion.
This question belongs to: Science Biology
Question #1458
In plant physiology, the 'Photoperiodism' refers to the response of plants to:
A. The direction of light
B. The wavelength of light
C. The relative lengths of day and night (light and dark periods)
D. The intensity of light
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Correct Answer: Option C

Explanation:
Photoperiodism is the physiological reaction of organisms, particularly plants, to the length of the day or a dark period. It is the mechanism by which plants measure the relative lengths of light and dark periods to regulate developmental processes, most notably the timing of flowering. Plants are classified as short-day plants, long-day plants, or day-neutral plants based on their flowering response to photoperiod. The photoreceptor pigment phytochrome is crucial in perceiving these light/dark signals.
This question belongs to: Science Biology
Question #1459
The 'Hormone Calcitonin' is secreted by the parafollicular cells (C cells) of the thyroid gland and primarily acts to:
A. Decrease blood glucose levels
B. Decrease blood calcium levels
C. Increase blood glucose levels
D. Increase blood calcium levels
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Correct Answer: Option B

Explanation:
Calcitonin is a peptide hormone secreted by the parafollicular cells (also known as C cells) of the thyroid gland. Its primary function is to lower (decrease) the level of calcium in the blood (hypocalcemic effect) when it becomes too high. It achieves this by inhibiting osteoclast activity in bones (reducing bone resorption) and stimulating calcium excretion by the kidneys. It has the opposite effect of parathyroid hormone (PTH), which increases blood calcium.
This question belongs to: Science Biology
Question #1460
In the human body, the 'Hypothalamus' is a small but crucial region of the brain that links the nervous system to the endocrine system via the:
A. Adrenal gland
B. Pituitary gland
C. Thyroid gland
D. Spinal cord
Discuss
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Correct Answer: Option B

Explanation:
The hypothalamus is a small, highly complex region located at the base of the brain, near the pituitary gland. It is the primary link between the nervous and endocrine systems. It controls the pituitary gland (the 'master gland') both neurally (via the posterior pituitary, where it stores and releases ADH and oxytocin) and hormonally (via the anterior pituitary, by secreting releasing and inhibiting hormones that regulate the production of anterior pituitary hormones). Through the pituitary, the hypothalamus regulates a vast array of bodily functions.
This question belongs to: Science Biology

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