Biology: Practice Questions with Answers
Human body, plants, diseases, and ecology. Try each question first: tap an option to check it, and the explanation appears below.
Question 1Easy
Which human endocrine gland is responsible for secreting the hormone melatonin, which regulates circadian rhythms and sleep-wake cycles?
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✅ C. Pineal gland
The pineal gland is a small endocrine gland located near the center of the brain that synthesizes and secretes melatonin in response to darkness, modulating biological sleep rhythms. The thyroid gland produces hormones regulating basal metabolic rates, while adrenal glands secrete cortisol and adrenaline responding to stress. The thymus gland plays an essential role in T-lymphocyte maturation during immune development. Melatonin synthesis is stimulated by darkness and inhibited by light exposure.
Question page →Question 2Medium
Which plant tissue consists of dead, hollow, thick-walled lignified cells that provide structural strength and conduct water?
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✅ B. Xylem vessels
Xylem vessels consist of dead, hollow, thick-walled lignified cells that jointly facilitate the upward transport of water and dissolved minerals while providing mechanical support to the plant body. Other tissues such as phloem specialize in the translocation of organic nutrients, whereas parenchyma cells remain living and perform storage functions. This specialized vascular tissue is a hallmark of tracheophytes or vascular plants.
Question page →Question 3Hard
During the light-dependent reactions of photosynthesis, what is the source of electrons that replenish those lost by chlorophyll P680 in Photosystem II?
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✅ B. Photolysis of water molecules
The photolysis, or light-driven splitting, of water molecules releases oxygen, protons, and electrons that replenish the electron vacancy in the reaction center chlorophyll P680 of Photosystem II. Carbon dioxide is utilized in the Calvin cycle within the stroma, NADP+ acts as the terminal electron acceptor in Photosystem I, and oxidative phosphorylation occurs during cellular respiration. This photolytic release of oxygen sustains aerobic life on Earth.
Question page →Question 4Easy
Deficiency of which fat-soluble vitamin causes night blindness (Nyctalopia)?
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✅ A. Vitamin A
Vitamin A, also known as retinol, is a fat-soluble nutrient crucial for the formation of rhodopsin, a light-sensitive pigment in the retinal rod cells required for night vision. A lack of this vitamin leads directly to night blindness and xerophthalmia.
Question page →Question 5Medium
In human genetics, what causes Turner syndrome, characterized by monosomy of the sex chromosomes?
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✅ B. Complete absence of one X chromosome resulting in 45,X0 karyotype
Turner syndrome is a genetic chromosomal disorder caused by monosomy of the sex chromosomes, where affected females possess only a single X chromosome leading to a 45,X0 karyotype. Klinefelter syndrome involves an extra X chromosome producing XXY, Down syndrome results from trisomy twenty-one, and Cri-du-chat syndrome stems from a deletion on chromosome five. Individuals with Turner syndrome typically exhibit short stature and gonadal dysgenesis.
Question page →Question 6Hard
Which specific chromosomal abnormality causes Turner syndrome in human females, characterized by sexual infantilism and short stature?
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✅ B. Monosomy X
Turner syndrome results from monosomy X, where affected phenotypic females possess only a single X chromosome instead of the normal pair due to meiotic nondisjunction. Trisomy 13 causes Patau syndrome, marked by severe neurological and structural malformations. Trisomy 18 leads to Edwards syndrome with characteristic clenched fists and overlapping fingers. An XXY genotype produces Klinefelter syndrome in phenotypic males, featuring hypogonadism and tall stature.
Question page →Question 7Easy
Which human blood group lacks both A and B antigens on the surface of its red blood cells?
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✅ D. Blood Group O
Individuals with blood group O lack both A and B surface antigens on their red blood cells, which prevents immune attack when their blood is transfused into recipients of various other blood groups. Conversely, blood group AB possesses both surface antigens while lacking corresponding antibodies in the plasma. A vital practical corollary is that individuals with blood group AB are recognized as universal plasma donors, whereas O-negative individuals are universal red blood cell donors.
Question page →Question 8Medium
Which human blood cells are responsible for phagocytosis and act as primary phagocytic cells of the innate immune system?
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✅ B. Neutrophils and Monocytes
Neutrophils and monocytes act as the primary professional phagocytes of the innate immune system, actively migrating toward infection sites to engulf, digest, and destroy foreign pathogens through phagocytosis. Erythrocytes, or red blood cells, are specialized exclusively for oxygen transport across the body, while thrombocytes, or platelets, are vital for blood clotting. B-lymphocytes belong to the adaptive immune system and function primarily by producing specific antibodies rather than direct cellular phagocytosis. Questions examining the functional roles of formed elements in human blood regularly appear in general science sections.
Question page →Question 9Hard
Consider the following statements regarding human respiratory pigments: 1. Hemoglobin is an iron-containing conjugated protein found inside red blood cells. 2. Hemocyanin is a copper-containing respiratory pigment found in the blood of many molluscs and arthropods. Which of the statements given above is/are correct?
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✅ C. Both 1 and 2
Hemoglobin is the primary respiratory pigment in vertebrates, utilizing an iron porphyrin heme group to transport oxygen efficiently. Hemocyanin utilizes copper atoms instead of iron and appears blue when oxygenated, serving respiratory functions in various invertebrates like molluscs and crustaceans. Both statements accurately describe biochemical adaptations for oxygen transport across diverse animal phyla. Oxygen binding affinity is influenced by physiological factors such as pH, carbon dioxide concentration, and temperature.
Question page →Question 10Medium
Which plant cell organelle contains its own circular DNA and 70S ribosomes, allowing it to synthesize some of its own proteins independently?
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✅ A. Chloroplast
Chloroplasts possess their own circular DNA and 70S ribosomes, allowing them to synthesize specific proteins independently as semi-autonomous cellular organelles. Endoplasmic reticulum and vacuoles lack independent genetic material for protein synthesis. Mitochondria share this endosymbiotic origin and also contain circular DNA.
Question page →Question 11Medium
Which specialized respiratory organs are present for gaseous exchange in arachnids such as spiders and scorpions?
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✅ B. Book lungs
Arachnids such as spiders and scorpions possess specialized respiratory structures known as book lungs for gas exchange in terrestrial environments. These internal organs consist of stacked, blood-filled lamellae enclosed in a chamber, which resemble the pages of a book to maximize surface area for oxygen absorption. Insects utilize tracheal tubes, whereas aquatic arthropods typically rely on gills.
Question page →Question 12Medium
Which nucleic acid component consists of a nitrogenous base, a pentose sugar, and at least one phosphate group?
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✅ B. Nucleotide
A nucleotide comprises a nitrogenous base, a pentose sugar, and one or more phosphate groups, serving as the repeating monomer unit of nucleic acids like DNA and RNA. A nucleoside lacks the phosphate group entirely. Fundamental biochemical definitions are frequently featured in competitive biology questions.
Question page →Question 13Easy
Which of the following diseases is caused by a bacterial infection?
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✅ B. Tuberculosis
Tuberculosis is a contagious bacterial infection caused by Mycobacterium tuberculosis, primarily affecting the pulmonary system. Malaria is caused by protozoan parasites, influenza by viral pathogens, and dengue by a mosquito-borne flavivirus. Antibiotics are effective treatments for bacterial infections but have no effect against viral agents.
Question page →Question 14Easy
Which human organ is primarily responsible for filtering metabolic wastes from the blood and forming urine?
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✅ C. Kidney
The kidneys are paired bean-shaped organs that filter waste products, excess ions, and water from the blood to produce urine, maintaining systemic osmoregulation. The liver processes nutrients and detoxifies metabolic byproducts, while the heart pumps blood and lungs facilitate gas exchange. Nephrons serve as the functional structural units inside each kidney.
Question page →Question 15Hard
During the contraction cycle of a mammalian skeletal muscle fiber, the binding of calcium ions to which regulatory protein triggers the exposure of myosin-binding sites on actin filaments?
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✅ A. Troponin
Calcium ions released from the sarcoplasmic reticulum bind to troponin, causing a conformational shift in tropomyosin that uncovers the myosin-binding sites on actin filaments, allowing cross-bridge formation. Sliding filament theory explains muscular contraction mechanics. ATP provides energy for the power stroke.
Question page →Question 16Medium
Which vascular bundle type is commonly found in the roots of dicotyledonous plants?
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✅ C. Radial arrangement
Dicotyledonous roots characteristically display a radial vascular bundle layout where separate patches of xylem and phloem alternate along different radii, facilitating efficient water and nutrient transport. Alternative options like conjoint collateral bundles are predominantly found in stems and leaves rather than roots.
Question page →Question 17Hard
Which of the following phenomena describes the mechanism by which C4 plants minimize photorespiration compared to C3 plants under high temperature and drought conditions?
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✅ A. Spatial separation of carbon dioxide fixation and the Calvin cycle between mesophyll and bundle sheath cells
C4 plants minimize wasteful photorespiration by employing spatial separation, where initial carbon dioxide fixation occurs in mesophyll cells via PEP carboxylase to form a four-carbon acid, which is then transported into bundle sheath cells to release carbon dioxide for the Calvin cycle. Rubisco operates in the interior bundle sheath cells surrounded by high local concentrations of carbon dioxide. This physiological adaptation enhances photosynthetic efficiency in tropical and arid environments where temperatures promote high rates of photorespiration in C3 plants.
Question page →Question 18Easy
What is the site of gaseous exchange in human lungs?
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✅ C. Alveoli
Alveoli are tiny, balloon-like air sacs located at the terminal ends of the respiratory tree where the actual exchange of oxygen and carbon dioxide occurs via simple diffusion. Bronchi and the trachea act merely as conducting pathways for airflow, while the larynx houses the vocal cords. The immense surface area of millions of alveoli ensures efficient pulmonary gas exchange.
Question page →Question 19Medium
What is the chromosomal constitution of an individual with Turner syndrome?
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✅ B. 45, XO
Turner syndrome is a genetic disorder affecting females characterized by the complete or partial absence of one X chromosome, resulting in a monosomy constitution denoted as 45, XO. Conditions involving extra chromosomes such as 47, XXY correspond to Klinefelter syndrome rather than Turner syndrome. Affected individuals exhibit short stature, gonadal dysgenesis, and webbed neck characteristics.
Question page →Question 20Medium
Which autoimmune disorder is characterized by the destruction of acetylcholine receptors at the neuromuscular junction, leading to extreme skeletal muscle fatigue?
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✅ A. Myasthenia gravis
Myasthenia gravis is an autoimmune condition where antibodies target and destroy acetylcholine receptors at neuromuscular junctions, causing progressive muscle weakness. Multiple sclerosis affects the central nervous system myelin sheath rather than motor endplates. Medical conditions involving autoimmune responses are important for general science.
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