Biology MCQs

Question #61

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Which of the following animals belongs to the phylum Annelida?

A. Earthworm

B. Planaria

C. Tapeworm

D. Roundworm

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Correct Answer: Option A

Explanation:
Earthworm (Pheretima) belongs to phylum Annelida, characterized by metameric segmentation (body divided into segments), a closed circulatory system, and setae for locomotion. Tapeworm is a platyhelminth (flatworm), roundworm is nematode (Ascaris), Planaria is a free-living platyhelminth. Annelids include polychaetes (Nereis), oligochaetes (earthworm), and hirudinea (leech).

This question belongs to: Science Biology

Question #62

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What is the botanical name of the common mango plant?

A. Ficus benghalensis

B. Musa paradisiaca

C. Citrus sinensis

D. Mangifera indica

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Correct Answer: Option D

Explanation:
Mangifera indica is the scientific name of mango. Musa paradisiaca is banana, Citrus sinensis is orange, Ficus benghalensis is banyan tree. The genus Mangifera refers to mango, 'indica' indicates its origin in India. It belongs to the family Anacardiaceae. Mango is the national fruit of India. Scientific naming follows binomial nomenclature, with genus and species epithet.

This question belongs to: Science Biology

Question #63

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Which plant tissue is responsible for the transport of organic nutrients?

A. Xylem

B. Sclerenchyma

C. Collenchyma

D. Phloem

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Correct Answer: Option D

Explanation:
Phloem transports organic solutes (mainly sucrose) from source (leaves) to sink (roots, fruits) in a process called translocation, using sieve tubes and companion cells. Xylem transports water and minerals from roots upwards. Collenchyma and sclerenchyma are mechanical tissues providing support. Phloem is alive at maturity, while xylem vessels are dead. Companion cells regulate sieve tube activity.

This question belongs to: Science Biology

Question #64

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The opening and closing of stomata is regulated by the:

A. Guard cells

B. Xylem vessels

C. Epidermal hairs

D. Phloem cells

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Correct Answer: Option A

Explanation:
Stomata are surrounded by two kidney-shaped guard cells in dicots (dumb-bell-shaped in grasses) that control pore opening/closing via turgor pressure changes. When guard cells absorb water and become turgid, the stomatal pore opens; when flaccid, it closes. This process is influenced by light, CO₂ concentration, and abscisic acid (ABA). Stomata are critical for gas exchange and transpiration.

This question belongs to: Science Biology

Question #65

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Which of the following is NOT a plant hormone?

A. Auxin

B. Thyroxine

C. Gibberellin

D. Cytokinin

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Correct Answer: Option B

Explanation:
Thyroxine is an animal hormone secreted by the thyroid gland, regulating metabolism. Auxin, gibberellin, cytokinin, abscisic acid, and ethylene are plant hormones (phytohormones). Plant hormones control growth, development, and responses to environment. Thyroxine contains iodine and affects basal metabolic rate. Thus, thyroxine is unrelated to plant physiology.

This question belongs to: Science Biology

Question #66

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In human digestive system, the enzyme that digests fats is:

A. Sucrase

B. Amylase

C. Lipase

D. Pepsin

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Correct Answer: Option C

Explanation:
Lipase is the fat-digesting enzyme, produced mainly by the pancreas (pancreatic lipase) and also by lingual and gastric glands. It hydrolyzes triglycerides into monoglycerides and free fatty acids. Bile salts emulsify fats, increasing surface area for lipase action. Amylase digests starch, pepsin digests proteins, sucrase hydrolyzes sucrose. Lipase requires colipase for optimal activity.

This question belongs to: Science Biology

Question #67

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The enzyme produced in the small intestine that converts trypsinogen into trypsin is:

A. Carboxypeptidase

B. Pepsin

C. Enterokinase

D. Renin

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Correct Answer: Option C

Explanation:
Enterokinase (enteropeptidase) is secreted by the intestinal mucosa and activates the pancreatic proenzyme trypsinogen to trypsin, which then activates other zymogens. Pepsin is active in the stomach, renin is a milk-curdling enzyme (chymosin), carboxypeptidase is a pancreatic protease. This cascade ensures that protein-digesting enzymes are activated only in the appropriate location to prevent autodigestion.

This question belongs to: Science Biology

Question #68

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The volume of air inspired or expired during normal breathing is called:

A. Residual volume

B. Total lung capacity

C. Tidal volume

D. Vital capacity

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Correct Answer: Option C

Explanation:
Tidal volume (TV) is the amount of air breathed in or out in one normal respiratory cycle, about 500 mL in a healthy adult. Vital capacity is the maximum air exhaled after a maximum inspiration. Total lung capacity is the total volume of air lungs can hold. Residual volume is the air remaining in lungs after maximum expiration to prevent alveolar collapse.

This question belongs to: Science Biology

Question #69

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Oxygen transport in the blood is primarily by:

A. Conversion to bicarbonate

B. Binding to plasma proteins

C. Plasma as dissolved gas

D. Binding to hemoglobin in RBCs

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Correct Answer: Option D

Explanation:
Approximately 97% of O₂ is transported bound to hemoglobin (as oxyhemoglobin), while only 3% is dissolved in plasma. Each hemoglobin molecule can bind four O₂ molecules cooperatively. CO₂ is mainly transported as bicarbonate (70%), carbaminohemoglobin (23%), and dissolved (7%). The affinity of hemoglobin for O₂ is influenced by pH, CO₂, and temperature (Bohr effect).

This question belongs to: Science Biology

Question #70

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Which blood vessel carries blood away from the heart?

A. Venule

B. Artery

C. Capillary

D. Vein

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Correct Answer: Option B

Explanation:
Arteries (except pulmonary arteries) carry oxygenated blood away from the heart to body tissues. Pulmonary arteries carry deoxygenated blood from heart to lungs. Veins return blood to the heart. Capillaries are exchange vessels. Arteries have thick elastic walls to withstand high pressure. The aorta is the largest artery. Remember: 'A' for Artery = Away from heart.

This question belongs to: Science Biology

Question #71

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The S-A node (sinoatrial node) is located in the:

A. Aorta

B. Left ventricle

C. Interventricular septum

D. Right atrium

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Correct Answer: Option D

Explanation:
The sinoatrial (SA) node is a specialized cluster of cells in the right atrium near the opening of the superior vena cava. It generates electrical impulses spontaneously, setting the pace of the heartbeat, hence called the pacemaker. The impulse spreads to the atrioventricular (AV) node, then to bundle of His and Purkinje fibers. Normal SA node firing rate is 60-100/min.

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Question #72

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The glomerular filtration rate (GFR) in a healthy adult is approximately:

A. 50 mL/min

B. 250 mL/min

C. 500 mL/min

D. 125 mL/min

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Correct Answer: Option D

Explanation:
Glomerular filtration rate (GFR) is the volume of filtrate formed per minute by both kidneys, normally about 125 mL/min (180 L/day). Nearly 99% of the filtrate is reabsorbed, leaving about 1-2 liters of urine per day. GFR is regulated by the juxtaglomerular apparatus. It's an important clinical indicator of kidney function, estimated from serum creatinine.

This question belongs to: Science Biology

Question #73

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Which part of the brain regulates body temperature, hunger, and thirst?

A. Pons

B. Hypothalamus

C. Cerebellum

D. Medulla oblongata

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Correct Answer: Option B

Explanation:
The hypothalamus is a small region in the forebrain that maintains homeostasis by regulating body temperature, hunger, thirst, sleep, and emotions. It also controls pituitary gland secretions. The cerebellum coordinates movement, medulla controls respiration and heart rate, pons relays signals. Hypothalamus acts as the body's thermostat and the link between nervous and endocrine systems.

This question belongs to: Science Biology

Question #74

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A person having prolonged bleeding after an injury might be deficient in vitamin:

A. Vitamin C

B. Vitamin D

C. Vitamin K

D. Vitamin A

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Correct Answer: Option C

Explanation:
Vitamin K is essential for the synthesis of clotting factors (II, VII, IX, X) in the liver. Deficiency leads to prolonged clotting time and excessive bleeding. Vitamin A is for vision, C for collagen (scurvy causes bleeding gums but not clotting defect), D for bones. Newborns receive vitamin K injection to prevent hemorrhagic disease. Green leafy vegetables are rich sources.

This question belongs to: Science Biology

Question #75

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The genetic disorder due to the presence of an extra copy of chromosome 21 is:

A. Down syndrome

B. Phenylketonuria

C. Turner's syndrome

D. Klinefelter's syndrome

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Correct Answer: Option A

Explanation:
Down syndrome (trisomy 21) is an autosomal aneuploidy caused by nondisjunction resulting in three copies of chromosome 21. It is characterized by intellectual disability, flat facial profile, protruding tongue, and simian crease. Turner's syndrome is monosomy X (45, X). Klinefelter's is 47, XXY. Phenylketonuria is an inborn error of metabolism (autosomal recessive) due to deficiency of phenylalanine hydroxylase.

This question belongs to: Science Biology

Question #76

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In a monohybrid cross between two heterozygous pea plants (Tt), the phenotypic ratio of tall to dwarf in the offspring is expected to be:

A. 9:3:3:1

B. 1:2:1

C. 3:1

D. 1:1

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Correct Answer: Option C

Explanation:
When both parents are heterozygous (Tt × Tt), the offspring genotypes are TT (25%), Tt (50%), and tt (25%). Since tall (T) is dominant over dwarf (t), both TT and Tt are tall, resulting in 3 tall : 1 dwarf phenotypic ratio. The genotypic ratio is 1:2:1. 9:3:3:1 is the dihybrid phenotypic ratio. 1:1 ratio is seen in test cross (Tt × tt).

This question belongs to: Science Biology

Question #77

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The concept of 'survival of the fittest' was proposed by:

A. De Vries

B. Lamarck

C. Mendel

D. Darwin

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Correct Answer: Option D

Explanation:
'Survival of the fittest' was a phrase used by Herbert Spencer but adopted by Darwin to describe natural selection—organisms best adapted to the environment survive and reproduce. Lamarck proposed inheritance of acquired characters, Mendel discovered laws of heredity, De Vries proposed mutation theory. Darwin's theory emphasizes differential reproductive success of variants.

This question belongs to: Science Biology

Question #78

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Which of the following gases is mainly responsible for the greenhouse effect?

A. Hydrogen

B. Nitrogen

C. Carbon dioxide

D. Oxygen

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Correct Answer: Option C

Explanation:
Carbon dioxide (CO₂) is the primary greenhouse gas, along with methane (CH₄), nitrous oxide (N₂O), water vapor, and CFCs. These trap heat in the atmosphere, leading to global warming and climate change. CO₂ levels have risen due to fossil fuel burning and deforestation. The greenhouse effect is natural and essential, but enhanced levels cause global temperature rise.

This question belongs to: Science Biology

Question #79

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Which of the following represents a correct food chain?

A. Grass → Grasshopper → Frog → Snake

B. Frog → Grasshopper → Grass → Snake

C. Grasshopper → Grass → Frog → Snake

D. Grass → Frog → Grasshopper → Snake

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Correct Answer: Option A

Explanation:
A food chain shows the flow of energy from producer to consumers. Grass (producer) → Grasshopper (primary consumer/herbivore) → Frog (secondary consumer/carnivore) → Snake (tertiary consumer). Arrows point in the direction of energy flow. Option A has incorrect order, C and D start with consumer. Typically, energy decreases at each trophic level. This illustrates the correct trophic sequence.

This question belongs to: Science Biology

Question #80

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The biodiversity hotspot concept was introduced by:

A. Norman Myers

B. E.O. Wilson

C. Charles Darwin

D. Alexander von Humboldt

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Correct Answer: Option A

Explanation:
Norman Myers introduced the concept of biodiversity hotspots in 1988—regions with high endemic species and significant habitat loss (≥70% original vegetation lost). Examples: Western Ghats, Indo-Burma. Conservation efforts prioritize these areas. Darwin contributed evolution, Humboldt to biogeography, E.O. Wilson is known for sociobiology and biodiversity studies. Hotspots cover only 2.4% of Earth's land but hold >50% of plant species.

This question belongs to: Science Biology

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