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 38 of 103
Question #741
The nucleolus within the nucleus is the site of synthesis for which cellular component?
A. mRNA
B. rRNA and ribosome assembly
C. DNA
D. Lipids
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Correct Answer: Option B

Explanation:
The nucleolus is a prominent, non-membrane-bound structure within the nucleus. It is the site of active ribosomal RNA (rRNA) synthesis and the assembly of ribosomal subunits. These subunits then exit the nucleus through nuclear pores to combine in the cytoplasm and form functional ribosomes for protein synthesis.
This question belongs to: Science Biology
Question #742
In which stage of mitosis do chromosomes align at the cell equator?
A. Telophase
B. Anaphase
C. Prophase
D. Metaphase
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Correct Answer: Option D

Explanation:
During metaphase, the nuclear envelope has completely disappeared, and the chromosomes, attached to spindle fibers at their kinetochores, are moved to the center of the cell. This alignment of chromosomes at the cell equator is called the metaphase plate. This stage is crucial for the equal distribution of genetic material to daughter cells.
This question belongs to: Science Biology
Question #743
Crossing over between homologous chromosomes occurs during which sub-stage of Prophase I in meiosis?
A. Zygotene
B. Leptotene
C. Diplotene
D. Pachytene
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Correct Answer: Option D

Explanation:
Prophase I of meiosis is divided into five sub-stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs specifically during the pachytene stage at structures called recombination nodules.
This question belongs to: Science Biology
Question #744
What is the structural arrangement of microtubules in a centriole?
A. 9+0
B. 9+2
C. 9+1
D. 6+6
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Correct Answer: Option A

Explanation:
Centrioles are cylindrical structures composed of nine evenly spaced peripheral fibrils of tubulin, arranged in a 9+0 pattern. Each fibril is a triplet of microtubules. The central part is non-branched and lacks microtubules. Centrioles are involved in forming the spindle apparatus in animal cells and basal bodies of cilia and flagella.
This question belongs to: Science Biology
Question #745
The Fluid Mosaic Model of the cell membrane was proposed by which scientists?
A. Watson and Crick
B. Singer and Nicolson
C. Schleiden and Schwann
D. Robertson and Danielli
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Correct Answer: Option B

Explanation:
The Fluid Mosaic Model of the plasma membrane was proposed by S. Jonathan Singer and Garth Nicolson in 1972. It describes the cell membrane as a dynamic, fluid structure composed of a phospholipid bilayer with globular proteins embedded or attached, moving laterally within the lipid matrix.
This question belongs to: Science Biology
Question #746
Which of the following is an example of active transport across the cell membrane?
A. Osmosis
B. Sodium-Potassium Pump
C. Facilitated diffusion
D. Diffusion
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Correct Answer: Option B

Explanation:
Active transport requires energy (ATP) to move molecules against their concentration gradient. The Sodium-Potassium pump (Na+/K+ ATPase) is a classic example, moving 3 Na+ ions out of the cell and 2 K+ ions into the cell per ATP hydrolyzed. Osmosis, diffusion, and facilitated diffusion are passive processes.
This question belongs to: Science Biology
Question #747
Phagocytosis is a type of which cellular process?
A. Endocytosis
B. Plasmolysis
C. Osmosis
D. Exocytosis
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Correct Answer: Option A

Explanation:
Phagocytosis, or 'cell eating', is a type of endocytosis where the cell membrane engulfs large solid particles, such as bacteria or cellular debris, forming a vesicle called a phagosome. This phagosome then fuses with a lysosome for digestion. It is primarily performed by specialized cells like macrophages and neutrophils.
This question belongs to: Science Biology
Question #748
Which cell junction in plant cells allows for cytoplasmic continuity between adjacent cells?
A. Desmosomes
B. Plasmodesmata
C. Tight junctions
D. Gap junctions
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Correct Answer: Option B

Explanation:
Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, enabling the transport of water, ions, molecules, and even some viruses between them, thus ensuring cytoplasmic continuity. Gap junctions perform a similar function in animal cells, while tight junctions and desmosomes are for sealing and adhesion, respectively.
This question belongs to: Science Biology
Question #749
Apoptosis is best described as:
A. Uncontrolled cell division
B. Programmed cell death
C. Accidental cell death due to injury
D. Cell swelling and bursting
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Correct Answer: Option B

Explanation:
Apoptosis is a highly regulated and organized process of programmed cell death that occurs in multicellular organisms. It is crucial for development, maintaining tissue homeostasis, and eliminating damaged or infected cells. Unlike necrosis (accidental cell death), apoptosis does not cause inflammation and involves cell shrinkage and fragmentation.
This question belongs to: Science Biology
Question #750
Which of the following organisms is included in the Kingdom Monera?
A. Cyanobacteria
B. Yeast
C. Amoeba
D. Mushroom
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Correct Answer: Option A

Explanation:
Kingdom Monera includes all prokaryotic organisms, which lack a true nucleus and membrane-bound organelles. Cyanobacteria (blue-green algae) are prokaryotes and thus belong to Monera. Amoeba is a protist, while yeast and mushrooms are fungi, which belong to the Kingdom Fungi and are eukaryotic.
This question belongs to: Science Biology
Question #751
Euglenoids are placed in which kingdom of the five-kingdom classification?
A. Fungi
B. Monera
C. Plantae
D. Protista
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Correct Answer: Option D

Explanation:
Euglenoids are unicellular eukaryotic organisms that possess characteristics of both plants (chloroplasts for photosynthesis) and animals (lack of a cell wall and presence of a flagellum for movement). Due to their unique features and unicellular nature, they are classified under the Kingdom Protista.
This question belongs to: Science Biology
Question #752
The cell wall of fungi is primarily composed of:
A. Silica
B. Cellulose
C. Peptidoglycan
D. Chitin
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Correct Answer: Option D

Explanation:
The cell wall of fungi is primarily composed of chitin, a tough, complex polysaccharide also known as fungal cellulose. This distinguishes them from plants, whose cell walls are made of cellulose, and bacteria, whose cell walls contain peptidoglycan. Chitin provides structural support and protection to fungal cells.
This question belongs to: Science Biology
Question #753
Which of the following is an example of a Bryophyte?
A. Funaria
B. Spirogyra
C. Pinus
D. Fern
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Correct Answer: Option A

Explanation:
Bryophytes are non-vascular land plants that include mosses, liverworts, and hornworts. Funaria is a common moss and a classic example of a bryophyte. Spirogyra is a green alga, ferns are pteridophytes (vascular cryptogams), and Pinus is a gymnosperm.
This question belongs to: Science Biology
Question #754
Pteridophytes are also known as:
A. Vascular cryptogams
B. Flowering plants
C. Naked seeded plants
D. Amphibians of the plant kingdom
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Correct Answer: Option A

Explanation:
Pteridophytes (ferns and their relatives) are the first terrestrial plants to possess vascular tissues (xylem and phloem) for water and nutrient transport. However, they do not produce seeds or flowers and reproduce via spores. Hence, they are called 'vascular cryptogams'. Bryophytes are called 'amphibians of the plant kingdom'.
This question belongs to: Science Biology
Question #755
Which of the following is a characteristic feature of the phylum Porifera?
A. Jointed appendages
B. Nematocysts
C. Water canal system
D. Radial symmetry
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Correct Answer: Option C

Explanation:
Porifera (sponges) are characterized by the presence of a complex water canal system (canal system) used for food gathering, respiratory exchange, and waste removal. Water enters through numerous small pores called ostia and exits through a large opening called the osculum. They are mostly marine and asymmetrical.
This question belongs to: Science Biology
Question #756
Jointed appendages are the defining characteristic of which phylum?
A. Annelida
B. Arthropoda
C. Mollusca
D. Echinodermata
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Correct Answer: Option B

Explanation:
Arthropoda is the largest phylum of the animal kingdom, and its defining characteristic is the presence of jointed appendages (legs, antennae, etc.). The word 'Arthropoda' literally means 'jointed legs'. They also have a chitinous exoskeleton and a hemocoel (blood-filled body cavity). Examples include insects, spiders, and crustaceans.
This question belongs to: Science Biology
Question #757
The water vascular system is a unique feature of which phylum?
A. Chordata
B. Echinodermata
C. Mollusca
D. Hemichordata
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Correct Answer: Option B

Explanation:
The water vascular system is a unique network of fluid-filled canals found exclusively in Echinodermata (e.g., starfish, sea urchins). It is primarily used for locomotion (via tube feet), capturing and handling food, and respiration. Adult echinoderms exhibit radial symmetry, while their larvae are bilaterally symmetrical.
This question belongs to: Science Biology
Question #758
Which of the following is a defining characteristic of all Chordates?
A. Ventral nerve cord
B. Exoskeleton made of chitin
C. Open circulatory system
D. Presence of a notochord at some stage of life
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Correct Answer: Option D

Explanation:
All chordates, at some point during their larval or adult stages, possess three key features: a dorsal hollow nerve cord, a notochord (a flexible rod supporting the body), and pharyngeal slits. The notochord may be replaced by a vertebral column in vertebrates. Arthropods have a ventral nerve cord and open circulatory system.
This question belongs to: Science Biology
Question #759
Animals that can live both in water and on land, having moist skin for respiration, belong to which class?
A. Mammalia
B. Pisces
C. Amphibia
D. Reptilia
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Correct Answer: Option C

Explanation:
Amphibia (e.g., frogs, toads, salamanders) are characterized by their dual habitat (amphi = both, bios = life). They can live in water and on land. They have moist, glandular skin without scales, which aids in respiration. They typically have a larval stage (tadpole) that undergoes metamorphosis to become an adult.
This question belongs to: Science Biology
Question #760
Which of the following is a unique characteristic of birds (Class Aves)?
A. Presence of mammary glands
B. Presence of external pinnae
C. Poikilothermic nature
D. Body covered with feathers
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Correct Answer: Option D

Explanation:
The most unique and defining characteristic of Class Aves (birds) is the presence of feathers, which are modified scales used for flight and insulation. Birds are warm-blooded (homeothermic), have a four-chambered heart, and possess a beak instead of jaws. Mammary glands and external pinnae are features of mammals.
This question belongs to: Science Biology

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