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 67 of 103
Question #1321
The edible part of a pine seed is:
A. Cotyledons
B. Endosperm
C. Perisperm
D. Female gametophyte (haploid tissue)
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Correct Answer: Option D

Explanation:
In gymnosperms like Pinus, the female gametophyte develops within the ovule and serves as the nutritive tissue for the developing embryo. Unlike angiosperms, where the nutritive tissue is the triploid endosperm formed after double fertilization, the gymnosperm nutritive tissue is haploid and forms before fertilization. Therefore, the edible part of a pine seed is the haploid female gametophyte.
This question belongs to: Science Biology
Question #1322
Which of the following animals belongs to the class Chondrichthyes?
A. Labeo rohita
B. Pristis (Sawfish)
C. Hippocampus
D. Catla catla
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Correct Answer: Option B

Explanation:
Chondrichthyes are cartilaginous fishes with a skeleton made entirely of cartilage, a ventral mouth, and lack operculum. Pristis (sawfish), Scoliodon (dogfish), and Carcharodon (great white shark) belong to this class. Labeo rohita (Rohu) and Catla catla are Osteichthyes (bony fishes). Hippocampus (seahorse) is also a bony fish. Exam tip: Chondrichthyes = cartilaginous; Osteichthyes = bony.
This question belongs to: Science Biology
Question #1323
The water vascular system, tube feet, and radial symmetry are characteristic features of the phylum:
A. Echinodermata
B. Mollusca
C. Hemichordata
D. Arthropoda
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Correct Answer: Option A

Explanation:
The phylum Echinodermata (spiny-skinned animals like starfish, sea urchins, sea cucumbers) is uniquely characterized by a water vascular system used for locomotion, capture and transport of food, and respiration. The tube feet are the terminal effectors of this system. They exhibit secondary radial symmetry in adults, though their larvae are bilaterally symmetrical. Mollusks have a muscular foot, and arthropods have jointed appendages.
This question belongs to: Science Biology
Question #1324
Which of the following is a connecting link between Annelida and Arthropoda?
A. Balanoglossus
B. Peripatus
C. Neopilina
D. Archaeopteryx
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Correct Answer: Option B

Explanation:
Peripatus (velvet worm) is a classic connecting link between the phyla Annelida and Arthropoda. It possesses annelid-like features such as a soft body, segmental arrangement of nephridia, and circular muscles, alongside arthropod-like features such as tracheal respiration, an open circulatory system, and clawed legs. Balanoglossus links Hemichordata and Chordata, and Archaeopteryx links reptiles and birds.
This question belongs to: Science Biology
Question #1325
Pneumatophores, specialized roots that grow vertically upwards to facilitate gas exchange in swampy areas, are found in:
A. Cuscuta
B. Orchids
C. Nepenthes
D. Rhizophora
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Correct Answer: Option D

Explanation:
Pneumatophores are negative geotropic, spongy roots that grow upwards out of the water or mud to obtain oxygen in anaerobic, waterlogged soils. They are a characteristic adaptation of mangrove plants like Rhizophora (mangrove). Orchids have epiphytic aerial roots, Cuscuta has parasitic haustoria, and Nepenthes has modified pitcher leaves for insectivory.
This question belongs to: Science Biology
Question #1326
The phenomenon where the primary root is short-lived and is replaced by a cluster of roots arising from the base of the stem is seen in:
A. Peepal tree
B. Carrot
C. Grasses
D. Mustard
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Correct Answer: Option C

Explanation:
In monocotyledonous plants like grasses, the primary tap root formed from the radicle is short-lived and aborts early. It is subsequently replaced by a large number of fibrous roots that arise adventitiously from the base of the stem. This forms a fibrous root system. Mustard, peepal, and carrot exhibit a tap root system derived from the primary root.
This question belongs to: Science Biology
Question #1327
In a cymose inflorescence, the growth of the main axis is:
A. Continuous and terminates in a flower
B. Limited, ending in a flower, with lateral branches continuing growth
C. Always forming a raceme
D. Restricted to the base of the plant
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Correct Answer: Option B

Explanation:
In cymose inflorescence, the main floral axis has limited growth and terminates in a flower. Subsequent flowers are produced by lateral branches, which also terminate in flowers, creating a sympodial growth pattern. This is in contrast to racemose inflorescence, where the main axis continues to grow indefinitely (monopodial) and flowers are arranged in an acropetal or basipetal order.
This question belongs to: Science Biology
Question #1328
The transfer of pollen grains from the anther of one plant to the stigma of a genetically different plant is known as:
A. Geitonogamy
B. Cleistogamy
C. Xenogamy
D. Autogamy
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Correct Answer: Option C

Explanation:
Xenogamy is the type of cross-pollination where pollen grains are transferred from the anther of one plant to the stigma of a genetically different plant. This promotes genetic diversity. Autogamy is self-pollination within the same flower. Geitonogamy is the transfer of pollen between different flowers on the same plant (functionally cross-pollination but genetically self-pollination). Cleistogamy is closed, self-pollinating flowers.
This question belongs to: Science Biology
Question #1329
In angiosperms, the functional megaspore undergoes mitotic divisions to form the embryo sac, which typically contains:
A. 7 cells, 8 nuclei
B. 8 cells, 8 nuclei
C. 4 cells, 4 nuclei
D. 7 cells, 7 nuclei
Discuss
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Correct Answer: Option A

Explanation:
The female gametophyte (embryo sac) in angiosperms is typically monosporic (develops from one functional megaspore). The megaspore undergoes three successive mitotic divisions to form an 8-nucleate, 7-celled structure. This includes 3 antipodal cells, 2 synergids, 1 egg cell, and 1 central cell containing 2 polar nuclei. Exam tip: Remember '8 nuclei, 7 cells' because the central cell has 2 nuclei but is 1 cell.
This question belongs to: Science Biology
Question #1330
Which plant hormone is widely used as a synthetic herbicide to kill broadleaf weeds in lawns and cereal crops?
A. Naphthaleneacetic acid (NAA)
B. Gibberellic acid
C. 2,4-Dichlorophenoxyacetic acid (2,4-D)
D. Kinetin
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Correct Answer: Option C

Explanation:
2,4-D is a synthetic auxin widely used as a selective herbicide. It kills broadleaf dicot weeds without harming monocot crops like wheat, rice, and lawn grasses, as dicots are more sensitive to auxin overdoses, which cause uncontrolled growth and eventual death. NAA and gibberellic acid are used for rooting and growth promotion, and kinetin is a cytokinin.
This question belongs to: Science Biology
Question #1331
The process of separation of leaf, flower, or fruit from the plant body is called abscission. It is primarily controlled by:
A. Auxin
B. Ethylene and Abscisic Acid
C. Gibberellin
D. Cytokinin
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Correct Answer: Option B

Explanation:
Abscission is the natural shedding of plant parts. It is primarily promoted by ethylene and abscisic acid (ABA), which stimulate the formation of an abscission zone at the base of the petiole or pedicel. This zone consists of weak-walled cells that break down, causing the part to fall. Auxin, conversely, delays abscission. Exam tip: Ethylene is the 'ripening and shedding' hormone.
This question belongs to: Science Biology
Question #1332
Which of the following plant tissues consists of dead cells with highly thickened, lignified walls and provides the main mechanical support in mature plants?
A. Chlorenchyma
B. Sclerenchyma
C. Collenchyma
D. Parenchyma
Discuss
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Correct Answer: Option B

Explanation:
Sclerenchyma is a simple permanent tissue composed of dead cells with extremely thick, lignified, and pitted cell walls. These cells (fibers and sclereids) are narrow, elongated, and provide rigid mechanical strength, allowing plant parts to withstand bending and pressure. Collenchyma provides flexible support in growing parts, and parenchyma is for storage and photosynthesis (chlorenchyma).
This question belongs to: Science Biology
Question #1333
The specific type of xylem element that is dead, lacks protoplast at maturity, and has perforated end walls (sieve plates) is NOT found in xylem, but rather in:
A. Phloem
B. Xylem tracheids
C. Xylem parenchyma
D. Xylem vessels
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Correct Answer: Option A

Explanation:
The question describes sieve elements, which are the conducting cells of the phloem, not xylem. Sieve tube elements are living but lack a nucleus at maturity and have perforated end walls called sieve plates. Xylem vessels and tracheids are dead, hollow, and lack perforated end walls (vessels have perforation plates, but they are not called sieve plates). Xylem parenchyma is living.
This question belongs to: Science Biology
Question #1334
In the C4 photosynthetic pathway, the primary CO2 acceptor is:
A. Oxaloacetate (OAA)
B. Phosphoenolpyruvate (PEP)
C. Ribulose-1,5-bisphosphate (RuBP)
D. Malate
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Correct Answer: Option B

Explanation:
In C4 plants, the initial fixation of CO2 occurs in the mesophyll cells. The primary CO2 acceptor is a 3-carbon compound, phosphoenolpyruvate (PEP). The enzyme PEP carboxylase catalyzes the reaction, forming a 4-carbon compound, oxaloacetate (OAA). In C3 plants, the primary acceptor is RuBP, a 5-carbon compound, and the enzyme is RuBisCO.
This question belongs to: Science Biology
Question #1335
Photorespiration in C3 plants occurs when RuBisCO acts as an oxygenase instead of a carboxylase. This process primarily takes place in which organelles?
A. Peroxisome and Lysosome
B. Chloroplast and Nucleus
C. Chloroplast, Mitochondria, and Peroxisome
D. Mitochondria and Golgi apparatus
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Correct Answer: Option C

Explanation:
Photorespiration is a wasteful pathway that occurs when RuBisCO fixes O2 instead of CO2, producing phosphoglycolate. This 2-carbon compound is metabolized through a complex pathway involving three organelles: it is processed in the peroxisome, then the mitochondria, and finally returns to the chloroplast. This process consumes ATP and releases CO2 without producing any sugar.
This question belongs to: Science Biology
Question #1336
The theory of 'Munch Hypothesis' explains the mechanism of:
A. Guttation
B. Ascent of sap
C. Transpiration pull
D. Translocation of food in phloem
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Correct Answer: Option D

Explanation:
The Munch hypothesis, or mass flow hypothesis, explains the translocation of organic solutes (primarily sucrose) through the phloem. It proposes that the movement is driven by a turgor pressure gradient between the source (where sugars are loaded into the phloem, increasing osmotic pressure) and the sink (where sugars are unloaded, decreasing osmotic pressure). Water flows from xylem to phloem and back, driving the bulk flow.
This question belongs to: Science Biology
Question #1337
Which of the following human digestive enzymes is secreted in an inactive form and is activated by the enzyme enterokinase?
A. Pepsinogen
B. Trypsinogen
C. Amylase
D. Procarboxypeptidase
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Correct Answer: Option B

Explanation:
Trypsinogen is an inactive proenzyme secreted by the pancreatic acinar cells. Upon entering the small intestine (duodenum), it is specifically activated into the active enzyme trypsin by the enzyme enterokinase (also known as enteropeptidase), which is secreted by the intestinal mucosa. Trypsin then activates other pancreatic proenzymes like chymotrypsinogen and procarboxypeptidase. Pepsinogen is activated by HCl.
This question belongs to: Science Biology
Question #1338
The hormone secretin, released by the duodenal mucosa, primarily stimulates the pancreas to secrete:
A. Digestive enzymes
B. Water and bicarbonate ions
C. Glucagon
D. Insulin
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Correct Answer: Option B

Explanation:
Secretin is a peptide hormone released by the S cells of the duodenal mucosa in response to acidic chyme entering from the stomach. Its primary action is to stimulate the pancreatic ductal cells to secrete a large volume of water and bicarbonate ions. This alkaline juice neutralizes the acidic chyme, providing the optimal pH for pancreatic digestive enzymes to function. Cholecystokinin (CCK) stimulates enzyme secretion.
This question belongs to: Science Biology
Question #1339
The 'Bohr effect' in human physiology describes the shift in the oxygen dissociation curve of hemoglobin due to changes in:
A. Partial pressure of CO2 and H+ concentration (pH)
B. Temperature only
C. Partial pressure of O2 only
D. Concentration of 2,3-BPG only
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Correct Answer: Option A

Explanation:
The Bohr effect describes how an increase in the partial pressure of CO2 (pCO2) or a decrease in pH (increase in H+ concentration) reduces hemoglobin's affinity for oxygen, shifting the oxygen dissociation curve to the right. This facilitates the unloading of oxygen in metabolically active tissues where CO2 and acid levels are high. The reverse occurs in the lungs, enhancing oxygen loading.
This question belongs to: Science Biology
Question #1340
In the human respiratory system, the Haldane effect refers to:
A. The diffusion of oxygen across the alveolar membrane
B. The regulation of breathing rate by the medulla
C. The effect of oxygenation of hemoglobin on CO2 transport
D. The effect of CO2 on oxygen binding to hemoglobin
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Correct Answer: Option C

Explanation:
The Haldane effect describes how the oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of CO2. Conversely, deoxygenated blood in the tissues has an increased capacity to carry CO2. This is complementary to the Bohr effect. Exam tip: Bohr = CO2 affects O2; Haldane = O2 affects CO2.
This question belongs to: Science Biology

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