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 27 of 103
Question #521
The functional unit of the liver is the:
A. Nephron
B. Alveolus
C. Islet of Langerhans
D. Hepatic lobule
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Correct Answer: Option D

Explanation:
The hepatic lobule is the basic structural and functional unit of the liver, consisting of plates of hepatocytes radiating from a central vein. Bile canaliculi, sinusoids, and portal triads are key features. Nephrons are kidney units, alveoli lung units, islets pancreatic endocrine units.
This question belongs to: Science Biology
Question #522
The chemical reaction that links amino acids together is a:
A. Hydrolysis
B. Dehydration synthesis
C. Oxidation
D. Reduction
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Correct Answer: Option B

Explanation:
Peptide bond formation is a condensation (dehydration synthesis) reaction where the carboxyl group of one amino acid reacts with the amino group of another, releasing a water molecule. Hydrolysis breaks bonds by adding water. Oxidation/reduction involve electron transfer. Dehydration synthesis builds polymers.
This question belongs to: Science Biology
Question #523
The protein-digesting enzyme in the small intestine that is activated by enterokinase is:
A. Rennin
B. Pepsin
C. Trypsin
D. Amylase
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Correct Answer: Option C

Explanation:
Trypsinogen, secreted by the pancreas, is activated to trypsin by enterokinase (intestinal enzyme). Trypsin then activates other zymogens. Pepsin is active in the stomach, rennin in infants, amylase digests starch. This cascade prevents premature protein digestion in the pancreas.
This question belongs to: Science Biology
Question #524
The blood vessel that carries deoxygenated blood from the upper body to the right atrium is the:
A. Aorta
B. Pulmonary vein
C. Superior vena cava
D. Inferior vena cava
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Correct Answer: Option C

Explanation:
The superior vena cava drains deoxygenated blood from the head, neck, arms, and upper thorax into the right atrium. The inferior vena cava drains the lower body. Pulmonary veins carry oxygenated blood, aorta carries oxygenated blood from left ventricle to body.
This question belongs to: Science Biology
Question #525
The condition caused by the accumulation of uric acid crystals in joints is:
A. Rheumatoid arthritis
B. Osteoarthritis
C. Gout
D. Osteoporosis
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Correct Answer: Option C

Explanation:
Gout is a form of arthritis resulting from hyperuricemia and deposition of monosodium urate crystals in joints, causing intense pain and inflammation. It is often diet-related. Rheumatoid arthritis is autoimmune, osteoarthritis is degenerative, osteoporosis is loss of bone mass.
This question belongs to: Science Biology
Question #526
The process of transferring pollen grains from the anther to the stigma of another flower of a different plant of the same species is:
A. Fertilization
B. Dispersal
C. Self-pollination
D. Cross-pollination
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Correct Answer: Option D

Explanation:
Cross-pollination (allogamy) involves transfer between genetically different plants of the same species, promoting genetic variation. Self-pollination occurs within the same flower or plant. Fertilization is gamete fusion, dispersal is seed/fruit spread. Agents of cross-pollination include wind, insects, water, birds.
This question belongs to: Science Biology
Question #527
The human enzyme that breaks down hydrogen peroxide in the body is found in which organelle?
A. Golgi body
B. Lysosome
C. Nucleus
D. Peroxisome
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Correct Answer: Option D

Explanation:
Peroxisomes contain catalase and other oxidases that detoxify hydrogen peroxide and other harmful substances. They also play a role in lipid metabolism. Lysosomes contain hydrolytic enzymes, Golgi modifies proteins, nucleus houses DNA. Peroxisomes are abundant in liver and kidney cells.
This question belongs to: Science Biology
Question #528
Which of the following is a characteristic of monocotyledonous plants?
A. Taproot system
B. Two cotyledons
C. Trimerous flowers
D. Reticulate venation
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Correct Answer: Option C

Explanation:
Monocots typically have trimerous flowers (floral parts in multiples of three), parallel venation, fibrous roots, and one cotyledon. Dicots have reticulate venation, taproots, tetramerous/pentamerous flowers, and two cotyledons. Examples: grasses, lilies, orchids. These features are key in plant classification.
This question belongs to: Science Biology
Question #529
The instrument used to measure blood pressure is a:
A. Sphygmomanometer
B. Electrocardiograph
C. Thermometer
D. Stethoscope
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Correct Answer: Option A

Explanation:
A sphygmomanometer, often used with a stethoscope, measures arterial blood pressure (systolic/diastolic) in mmHg. A stethoscope listens to heart/lung sounds, thermometer measures temperature, ECG records heart electrical activity. Normal blood pressure is about 120/80 mmHg.
This question belongs to: Science Biology
Question #530
The type of asexual reproduction in yeast where a small outgrowth develops into a new individual is:
A. Fragmentation
B. Spore formation
C. Budding
D. Binary fission
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Correct Answer: Option C

Explanation:
Budding is an asymmetric division where a new yeast cell forms as a small bud on the parent, eventually pinching off. Binary fission is symmetric splitting (bacteria), fragmentation is breaking into pieces, spore formation involves spores. Budding can occur in some hydra as well.
This question belongs to: Science Biology
Question #531
The technique used to produce a large number of identical copies of a specific DNA fragment is:
A. Microarray
B. DNA sequencing
C. PCR
D. Gel electrophoresis
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Correct Answer: Option C

Explanation:
Polymerase chain reaction (PCR) amplifies a specific DNA segment exponentially using primers, DNA polymerase (Taq), and thermal cycling. Gel electrophoresis separates DNA by size, sequencing determines base order, microarray analyzes gene expression. PCR is crucial in cloning, diagnostics, and forensics.
This question belongs to: Science Biology
Question #532
The lymphatic system returns leaked fluid from tissues back to the:
A. Bloodstream
B. Heart
C. Kidneys
D. Lungs
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Correct Answer: Option A

Explanation:
Lymphatic vessels collect interstitial fluid (lymph) and return it to the venous circulation (subclavian veins). This maintains fluid balance. Along the way, lymph nodes filter pathogens. The heart pumps blood, kidneys filter blood, lungs exchange gases. The lymphatic system is unidirectional.
This question belongs to: Science Biology
Question #533
The structure that produces cerebrospinal fluid in the brain is the:
A. Meninges
B. Corpus callosum
C. Pineal gland
D. Choroid plexus
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Correct Answer: Option D

Explanation:
The choroid plexus, located in the ventricles of the brain, is a network of capillaries and ependymal cells that secretes cerebrospinal fluid (CSF). CSF cushions the brain, removes waste, and maintains chemical environment. Meninges are protective coverings, corpus callosum connects hemispheres, pineal secretes melatonin.
This question belongs to: Science Biology
Question #534
The polysaccharide that serves as the main energy storage in animals is:
A. Cellulose
B. Chitin
C. Glycogen
D. Starch
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Correct Answer: Option C

Explanation:
Glycogen is a highly branched polysaccharide of glucose, stored primarily in the liver and muscles. Starch is the plant equivalent. Cellulose is a structural polysaccharide in plants, chitin in arthropods and fungi. Glycogen can be rapidly mobilized to maintain blood glucose.
This question belongs to: Science Biology
Question #535
The disease caused by the deficiency of thiamine (vitamin B₁) is:
A. Rickets
B. Beriberi
C. Scurvy
D. Pellagra
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Correct Answer: Option B

Explanation:
Beriberi results from lack of thiamine (B₁), affecting the nervous and cardiovascular systems. It manifests as dry beriberi (peripheral neuropathy) or wet beriberi (heart failure). Pellagra is niacin deficiency, scurvy vitamin C, rickets vitamin D. Thiamine is a coenzyme in carbohydrate metabolism.
This question belongs to: Science Biology
Question #536
The plant response to touch, such as the closing of Mimosa pudica leaves, is:
A. Geotropism
B. Thigmonasty
C. Thigmotropism
D. Phototropism
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Correct Answer: Option B

Explanation:
Thigmonasty (seismonasty) is a non-directional, rapid response to touch or vibration, exemplified by the drooping of Mimosa pudica leaves. Thigmotropism is directional growth towards/away from touch (e.g., tendrils). Phototropism is light-directed growth, geotropism gravity-directed.
This question belongs to: Science Biology
Question #537
The hormone that stimulates the kidney to reabsorb sodium and water, increasing blood pressure, is:
A. Aldosterone
B. Renin
C. ANP
D. ADH
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Correct Answer: Option A

Explanation:
Aldosterone, from the adrenal cortex, acts on the distal tubule and collecting duct to increase sodium reabsorption (and water follows) and potassium secretion, raising blood volume and pressure. ADH increases water reabsorption, ANP reduces sodium reabsorption, renin is an enzyme initiating the RAAS.
This question belongs to: Science Biology
Question #538
The type of stem modification found in ginger is:
A. Corm
B. Bulb
C. Rhizome
D. Tuber
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Correct Answer: Option C

Explanation:
Ginger is a rhizome, an underground modified stem growing horizontally, bearing nodes, internodes, scale leaves, and buds. Potato is a tuber, gladiolus a corm, onion a bulb (modified stem with fleshy leaf bases). Rhizomes store food and aid vegetative propagation.
This question belongs to: Science Biology
Question #539
The organ that stores and concentrates bile is the:
A. Duodenum
B. Pancreas
C. Gall bladder
D. Liver
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Correct Answer: Option C

Explanation:
The gall bladder, a small pear-shaped sac under the liver, stores and concentrates bile produced by the liver, releasing it into the duodenum in response to cholecystokinin (CCK). The liver makes bile, pancreas secretes enzymes, duodenum is the entry point.
This question belongs to: Science Biology
Question #540
The enzyme that adds nucleotides to the growing DNA strand during replication is:
A. Primase
B. Helicase
C. DNA polymerase
D. Ligase
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Correct Answer: Option C

Explanation:
DNA polymerase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, extending the new strand complementary to the template. Helicase unwinds DNA, ligase joins fragments, primase synthesizes RNA primer. In prokaryotes, DNA polymerase III is the main replicative enzyme.
This question belongs to: Science Biology

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