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 #141
Which of the following hormones is responsible for the closure of stomata during water stress?
A. Cytokinin
B. Gibberellin
C. Auxin
D. Abscisic acid (ABA)
Discuss
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Correct Answer: Option D

Explanation:
Abscisic acid (ABA) is a stress hormone that induces stomatal closure by causing efflux of K⁺ ions from guard cells, leading to loss of turgor, thereby reducing water loss during drought. Auxin and cytokinin promote growth, gibberellin stimulates stem elongation and seed germination. ABA also promotes seed dormancy and leaf senescence.
This question belongs to: Science Biology
Question #142
The double fertilization characteristic of angiosperms results in the formation of:
A. Zygote and embryo sac
B. Two embryos
C. Two zygotes
D. Zygote and endosperm
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Correct Answer: Option D

Explanation:
Double fertilization involves one male gamete fusing with the egg cell to form a diploid zygote, and the second male gamete fusing with the two polar nuclei (central cell) to form a triploid primary endosperm nucleus. The endosperm provides nutrition to the developing embryo. This unique feature ensures efficient nutrient supply and is typical of angiosperms.
This question belongs to: Science Biology
Question #143
Which of the following is a respiratory disease caused by a coronavirus?
A. COVID-19
B. Influenza
C. Pneumonia caused by Streptococcus
D. Tuberculosis
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Correct Answer: Option A

Explanation:
COVID-19 is caused by SARS-CoV-2, a novel coronavirus. Tuberculosis is bacterial (Mycobacterium). Influenza is caused by influenza viruses (Orthomyxoviridae), not coronavirus. Pneumonia can be bacterial or viral, but the question specifies Streptococcus which is bacterial. COVID-19 emerged in 2019, causing a global pandemic, primarily affecting the respiratory system.
This question belongs to: Science Biology
Question #144
The organelle responsible for the synthesis of lipids and detoxification of drugs in liver cells is:
A. Lysosome
B. Rough endoplasmic reticulum
C. Golgi apparatus
D. Smooth endoplasmic reticulum
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Correct Answer: Option D

Explanation:
Smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in lipid and steroid hormone synthesis, carbohydrate metabolism, and detoxification of drugs and poisons (via cytochrome P450 enzymes). Rough ER synthesizes proteins. Golgi modifies/packages. Lysosomes digest. Liver cells have abundant SER. SER also sequesters Ca²⁺ ions in muscle cells (sarcoplasmic reticulum).
This question belongs to: Science Biology
Question #145
The process by which white blood cells engulf pathogens is called:
A. Dialysis
B. Exocytosis
C. Phagocytosis
D. Pinocytosis
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Correct Answer: Option C

Explanation:
Phagocytosis ('cell eating') is the process by which cells like macrophages and neutrophils engulf solid particles, including pathogens, by extending pseudopodia to form a phagosome, which fuses with lysosomes for degradation. Pinocytosis is 'cell drinking', uptake of fluid. Exocytosis is secretion. Dialysis is artificial separation. Phagocytosis is a key innate immune defense.
This question belongs to: Science Biology
Question #146
Which of the following conditions is characterized by the presence of ketone bodies in urine, often associated with diabetes mellitus?
A. Hematuria
B. Glycosuria
C. Ketonuria
D. Proteinuria
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Correct Answer: Option C

Explanation:
Ketonuria is the presence of ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) in urine, resulting from increased fat metabolism due to carbohydrate unavailability in uncontrolled diabetes mellitus. Glycosuria is glucose in urine, proteinuria is protein, hematuria is blood. Ketonuria indicates diabetic ketoacidosis, a medical emergency requiring immediate treatment.
This question belongs to: Science Biology
Question #147
The specific region where the exchange of gases occurs between air and blood in the lungs is the:
A. Bronchioles
B. Trachea
C. Bronchi
D. Alveoli
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Correct Answer: Option D

Explanation:
Alveoli are tiny, thin-walled air sacs surrounded by a network of pulmonary capillaries. Oxygen diffuses from alveolar air into blood, and CO₂ diffuses from blood into alveolar air. Bronchi and bronchioles are air passages, trachea is the windpipe. The large surface area of alveoli (about 70 m²) facilitates efficient gas exchange.
This question belongs to: Science Biology
Question #148
Which of the following is responsible for the 'lub-dub' sound of the heart?
A. Contraction of ventricles
B. Opening of heart valves
C. Blood flow turbulence
D. Closing of heart valves
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Correct Answer: Option D

Explanation:
The first heart sound 'lub' is caused by the closure of the atrioventricular valves (mitral and tricuspid) at the beginning of ventricular systole. The second sound 'dub' is due to closure of semilunar valves (aortic and pulmonary) at the end of systole. Abnormal sounds (murmurs) indicate valve defects. This is due to turbulence, but the sound specifically is produced by valve closure.
This question belongs to: Science Biology
Question #149
The hormone that stimulates the contraction of the uterus during childbirth is:
A. Progesterone
B. Oxytocin
C. Prolactin
D. Estrogen
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Correct Answer: Option B

Explanation:
Oxytocin, released from the posterior pituitary, stimulates uterine smooth muscle contractions during parturition (childbirth) and milk ejection during lactation. Prolactin stimulates milk production. Estrogen and progesterone regulate reproductive cycle and maintain pregnancy. Oxytocin is also known as the 'love hormone' and functions through positive feedback during labor.
This question belongs to: Science Biology
Question #150
Which of the following organisms is a prokaryote?
A. Paramecium
B. Cyanobacteria
C. Yeast
D. Amoeba
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Correct Answer: Option B

Explanation:
Cyanobacteria (blue-green algae) are prokaryotes, possessing a nucleoid region but no true nucleus or membrane-bound organelles. Amoeba, yeast (fungus), and Paramecium are eukaryotes. Cyanobacteria perform oxygenic photosynthesis and some fix nitrogen, having chlorophyll a and phycobilins. They are classified under Kingdom Monera. Examples: Nostoc, Anabaena.
This question belongs to: Science Biology
Question #151
Assertion (A): Human blood is a connective tissue. Reason (R): Blood cells are embedded in a liquid extracellular matrix called plasma.
A. Both A and R are true, but R is not the correct explanation.
B. A true, R false.
C. A false, R true.
D. Both A and R are true, and R is the correct explanation.
Discuss
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Correct Answer: Option D

Explanation:
Blood is classified as a specialized connective tissue because it has cells (RBCs, WBCs, platelets) suspended in a fluid matrix (plasma) and connects different body parts by transporting substances. Connective tissues have cells separated by extracellular matrix. Thus, the reason correctly justifies the assertion. Bone, cartilage, lymph are other connective tissues.
This question belongs to: Science Biology
Question #152
Which of the following is a correct statement about prokaryotic DNA?
A. It is linear and associated with histones.
B. It is enclosed within a nuclear membrane.
C. It is circular and located in the nucleoid region.
D. It consists of multiple linear chromosomes.
Discuss
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Correct Answer: Option C

Explanation:
Prokaryotic DNA is typically circular, double-stranded, and found in a nucleoid region without a nuclear membrane. It is not associated with histones (though some Archaea have histone-like proteins). Plasmids are extra-chromosomal DNA. Eukaryotic DNA is linear and complexed with histones. This difference is fundamental in cell classification.
This question belongs to: Science Biology
Question #153
The term 'plasmolysis' refers to:
A. Shrinking of the protoplasm away from the cell wall in a hypertonic solution
B. Bursting of an animal cell in hypotonic solution
C. Equal movement of water across membrane
D. Swelling of a plant cell in hypotonic solution
Discuss
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Correct Answer: Option A

Explanation:
Plasmolysis occurs when a plant cell is placed in a hypertonic solution, causing water to leave the cell by exosmosis, leading to shrinkage of the protoplasm and its detachment from the cell wall. Incipient plasmolysis is when protoplast just starts to pull away. Opposite is deplasmolysis (when placed in hypotonic solution). Swelling is turgidity. Animal cells undergo crenation or lysis.
This question belongs to: Science Biology
Question #154
Which of the following is a characteristic feature of mammals?
A. Lay eggs only
B. Presence of feathers
C. Presence of mammary glands
D. Cold-blooded metabolism
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Correct Answer: Option C

Explanation:
Mammals are distinguished by the presence of mammary glands in females that secrete milk for nourishing young. They are warm-blooded, have hair/fur, and most give birth to live young (viviparous), though monotremes like platypus lay eggs. Feathers are characteristic of birds. Cold-blooded refers to ectotherms (reptiles, amphibians, fish). Mammals are endotherms.
This question belongs to: Science Biology
Question #155
The functional unit of striated muscle contraction from one Z-line to the next is the:
A. Sarcolemma
B. Myofibril
C. Sarcomere
D. Sarcoplasm
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Correct Answer: Option C

Explanation:
A sarcomere is the segment between two Z-lines (Z-discs) and is the basic contractile unit of skeletal and cardiac muscle. It contains actin (thin) and myosin (thick) filaments. Sarcolemma is the plasma membrane, sarcoplasm is cytoplasm, myofibril is a bundle of contractile filaments. Shortening of sarcomeres leads to muscle contraction per sliding filament theory.
This question belongs to: Science Biology
Question #156
Which of the following is a correct statement about the circulation of blood in humans?
A. The right ventricle pumps blood to the lungs.
B. Pulmonary vein carries deoxygenated blood.
C. Pulmonary artery carries oxygenated blood.
D. The left atrium receives deoxygenated blood from the body.
Discuss
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Correct Answer: Option A

Explanation:
The right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs for oxygenation. The pulmonary artery is the only artery carrying deoxygenated blood. Pulmonary veins carry oxygenated blood from lungs to the left atrium. The left atrium receives oxygenated blood, not deoxygenated. The right atrium receives deoxygenated blood from the body. Thus, C is correct.
This question belongs to: Science Biology
Question #157
Deficiency of vitamin A primarily affects:
A. Bone development
B. Energy metabolism
C. Blood clotting
D. Vision
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Correct Answer: Option D

Explanation:
Vitamin A (retinol) is essential for the synthesis of rhodopsin (visual pigment in rod cells) and maintenance of epithelial tissues. Deficiency causes night blindness (nyctalopia), xerophthalmia, and ultimately permanent blindness. Bone development is related to vitamin D and calcium. Blood clotting is vitamin K, energy metabolism involves B vitamins. Thus, vision is primarily affected.
This question belongs to: Science Biology
Question #158
In the process of urine formation, the step that involves selective reabsorption of glucose, amino acids, and water from the filtrate back into the blood is:
A. Tubular reabsorption
B. Glomerular filtration
C. Tubular secretion
D. Ultrafiltration
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Correct Answer: Option A

Explanation:
Tubular reabsorption occurs mainly in the proximal convoluted tubule, where essential substances like glucose, amino acids, and most water are reabsorbed into peritubular capillaries via active and passive transport. Glomerular filtration/ultrafiltration is the initial passive filtration of blood. Tubular secretion adds substances like H⁺ and K⁺ to filtrate.
This question belongs to: Science Biology
Question #159
Which of the following is an example of a connective tissue?
A. Smooth muscle
B. Epidermis
C. Neuron
D. Blood
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Correct Answer: Option D

Explanation:
Blood is a fluid connective tissue. Epidermis is epithelial tissue, neuron is part of nervous tissue, smooth muscle is muscle tissue. Connective tissues include bone, cartilage, blood, adipose tissue, and areolar tissue, characterized by cells embedded in a matrix. They provide support, protection, and transport.
This question belongs to: Science Biology
Question #160
Which part of the flower is responsible for producing pollen grains?
A. Style
B. Ovary
C. Anther
D. Stigma
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Correct Answer: Option C

Explanation:
The anther is the terminal part of the stamen (male reproductive organ) where pollen grains are produced through microsporogenesis. Stigma is the receptive surface for pollen, style connects stigma to ovary. Ovary contains ovules, which develop into seeds after fertilization. The anther has four microsporangia (pollen sacs).
This question belongs to: Science Biology

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