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 10 of 103
Question #181
The scientific name of the common frog is:
A. Rana tigrina
B. Crocodylus palustris
C. Felis domestica
D. Homo sapiens
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Correct Answer: Option A

Explanation:
Rana tigrina is the scientific name of the Indian bullfrog. Homo sapiens refers to humans, Felis domestica is the domestic cat, and Crocodylus palustris is the marsh crocodile. Binomial nomenclature gives each organism a unique genus and species name. Rana is the genus, tigrina the species, both italicized when printed.
This question belongs to: Science Biology
Question #182
Which branch of biology deals with the study of heredity and variation?
A. Paleontology
B. Embryology
C. Genetics
D. Ecology
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Correct Answer: Option C

Explanation:
Genetics is the science of heredity and variation, explaining how traits are passed from parents to offspring and why individuals differ. Ecology studies organisms and environment, embryology deals with development, paleontology with fossils. Gregor Mendel is the father of genetics. The term 'genetics' was coined by William Bateson.
This question belongs to: Science Biology
Question #183
Which of the following is NOT a characteristic of prokaryotic cells?
A. Presence of membrane-bound organelles
B. Circular DNA
C. Presence of 70S ribosomes
D. Cell wall generally present
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Correct Answer: Option A

Explanation:
Prokaryotes lack membrane-bound organelles like mitochondria, Golgi apparatus, and endoplasmic reticulum. They have 70S ribosomes, a single circular chromosome in a nucleoid, and typically a cell wall (except Mycoplasma). Eukaryotes possess membrane-bound organelles. This fundamental difference defines the two major cell types in the living world.
This question belongs to: Science Biology
Question #184
The fluid mosaic model describes the structure of which cellular component?
A. Plasma membrane
B. Cell wall
C. Nucleus
D. Ribosome
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Correct Answer: Option A

Explanation:
The fluid mosaic model, proposed by Singer and Nicolson (1972), describes the plasma membrane as a phospholipid bilayer with proteins floating like icebergs in a sea of lipids. It accounts for membrane fluidity and selective permeability. The cell wall is rigid, nucleus has a double membrane, ribosome is a ribonucleoprotein complex.
This question belongs to: Science Biology
Question #185
Which organelle is known as the 'suicide bag' of the cell?
A. Lysosome
B. Golgi apparatus
C. Peroxisome
D. Ribosome
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Correct Answer: Option A

Explanation:
Lysosomes contain hydrolytic enzymes that can digest cellular components and even the whole cell if they burst, a process called autolysis. Hence, they are called suicide bags. They also perform autophagy and phagocytosis. Peroxisomes detoxify peroxides, Golgi modifies proteins, ribosomes synthesize proteins. Lysosomes are formed from the Golgi apparatus.
This question belongs to: Science Biology
Question #186
The centriole is involved in which cellular process?
A. Cell division
B. Lipid synthesis
C. Protein synthesis
D. Photosynthesis
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Correct Answer: Option A

Explanation:
Centrioles are cylindrical microtubular structures found near the nucleus in animal cells, forming the centrosome. They organize spindle fibers during cell division (mitosis and meiosis) and are also the basal bodies of cilia and flagella. They are absent in higher plant cells. Centrioles duplicate during S phase and migrate to poles during prophase.
This question belongs to: Science Biology
Question #187
The smallest cell in the human body is:
A. Neuron
B. Red blood cell
C. Sperm cell
D. Ovum
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Correct Answer: Option C

Explanation:
The sperm cell is the smallest cell in the human body, about 5 µm in length (head). The ovum is the largest (about 100 µm diameter). RBCs are about 7-8 µm, neurons can be up to a meter long. Sperm cells are highly specialized for motility and genetic material delivery.
This question belongs to: Science Biology
Question #188
In a eukaryotic cell, the site of ribosomal RNA synthesis is the:
A. Golgi body
B. Nucleolus
C. Mitochondria
D. Cytoplasm
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Correct Answer: Option B

Explanation:
The nucleolus is a dense spherical structure within the nucleus where ribosomal RNA (rRNA) is transcribed and ribosomal subunits are assembled. They then exit to the cytoplasm. The cytoplasm is the site of translation. Mitochondria have their own 70S ribosomes but their rRNA is synthesized within the organelle. Golgi modifies proteins.
This question belongs to: Science Biology
Question #189
Which type of plastid stores starch?
A. Etioplast
B. Chloroplast
C. Leucoplast
D. Chromoplast
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Correct Answer: Option C

Explanation:
Leucoplasts are colourless plastids that store nutrients: amyloplasts store starch, elaioplasts store lipids, aleuroplasts store proteins. Chloroplasts contain chlorophyll for photosynthesis, chromoplasts give yellow/orange colour (carotenoids), etioplasts are undeveloped chloroplasts in dark-grown plants. Amyloplasts are abundant in roots and tubers like potato.
This question belongs to: Science Biology
Question #190
The crossing over that causes genetic recombination occurs during which substage of meiosis?
A. Zygotene
B. Leptotene
C. Pachytene
D. Diplotene
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Correct Answer: Option C

Explanation:
Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs during the pachytene stage of prophase I. The synaptonemal complex facilitates this. Chiasmata become visible in diplotene when the synaptonemal complex dissolves. Leptotene is chromosome condensation, zygotene is synapsis. This process is crucial for genetic variation.
This question belongs to: Science Biology
Question #191
Which of the following is an example of an animal cell that lacks a nucleus in its mature form?
A. Neuron
B. Leukocyte
C. Erythrocyte (human RBC)
D. Hepatocyte
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Correct Answer: Option C

Explanation:
Mature mammalian red blood cells (erythrocytes) lose their nucleus and other organelles during development to maximize space for hemoglobin. Thus they are anucleate. They cannot divide or repair themselves and have a lifespan of about 120 days. Neurons, leukocytes, and hepatocytes are nucleated. RBCs obtain energy through anaerobic glycolysis.
This question belongs to: Science Biology
Question #192
Which of the following organisms belongs to Kingdom Monera?
A. Agaricus
B. Euglena
C. Bacillus
D. Paramecium
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Correct Answer: Option C

Explanation:
Bacillus is a genus of rod-shaped bacteria, placed in Kingdom Monera because they are prokaryotic. Euglena and Paramecium are unicellular eukaryotes in Kingdom Protista. Agaricus (mushroom) belongs to Kingdom Fungi. Monera includes all prokaryotes like bacteria, cyanobacteria, and archaea. They are characterized by absence of true nucleus and membrane-bound organelles.
This question belongs to: Science Biology
Question #193
Which vertebrate class is characterized by a three-chambered heart (except crocodiles)?
A. Mammals
B. Amphibians
C. Reptiles
D. Birds
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Correct Answer: Option C

Explanation:
Reptiles generally have a three-chambered heart with two atria and one partially divided ventricle; crocodiles are an exception with a four-chambered heart. Amphibians have a three-chambered heart with two atria and one undivided ventricle. Mammals and birds have four-chambered hearts. This adaptation reflects their metabolic demands and evolutionary advancement.
This question belongs to: Science Biology
Question #194
Which of the following is a cartilaginous fish?
A. Catla
B. Scoliodon (dogfish)
C. Rohu
D. Hippocampus (seahorse)
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Correct Answer: Option B

Explanation:
Scoliodon is a cartilaginous fish (Chondrichthyes), possessing a cartilaginous endoskeleton, placoid scales, and ventral mouth. Rohu and Catla are bony fishes (Osteichthyes). Hippocampus is also a bony fish. Chondrichthyes include sharks, rays, and skates. They lack an air bladder and have to swim constantly to avoid sinking.
This question belongs to: Science Biology
Question #195
The process of conversion of atmospheric nitrogen into nitrates by microorganisms is called:
A. Nitrification
B. Nitrogen fixation
C. Denitrification
D. Ammonification
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Correct Answer: Option B

Explanation:
Nitrogen fixation is the process by which atmospheric N₂ is reduced to ammonia, which is then converted into nitrates that plants can absorb. This can be biological (by bacteria like Rhizobium, Azotobacter), physical (lightning), or industrial (Haber-Bosch process). Nitrification is the oxidation of ammonia to nitrates. Ammonification releases ammonia from organic matter. Denitrification converts nitrates back to N₂.
This question belongs to: Science Biology
Question #196
Which of the following is an example of a parasitic plant?
A. Cuscuta
B. Mimosa pudica
C. Nepenthes
D. Aloe vera
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Correct Answer: Option A

Explanation:
Cuscuta (dodder) is a total stem parasite that wraps around the host plant and absorbs nutrients through haustoria. It lacks chlorophyll and leaves. Mimosa is sensitive plant, Nepenthes is insectivorous, Aloe vera is a succulent. Parasitic plants derive some or all of their nutrition from other living plants. Cuscuta is economically important as a weed.
This question belongs to: Science Biology
Question #197
The primary xylem in roots is:
A. Endarch
B. Mesarch
C. Centrarch
D. Exarch
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Correct Answer: Option D

Explanation:
In roots, the protoxylem (first formed xylem) lies towards the periphery and metaxylem towards the centre; this arrangement is called exarch. In stems, protoxylem is towards the centre, called endarch. Exarch condition is typical of roots. Mesarch is found in ferns. This arrangement aids in understanding anatomical differences between root and stem.
This question belongs to: Science Biology
Question #198
The vascular bundles in monocot stems are:
A. Arranged in a ring
B. Scattered and closed
C. Radial
D. Open and collateral
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Correct Answer: Option B

Explanation:
Monocot stems have numerous vascular bundles scattered in the ground tissue. They are closed (lack cambium), collateral, and hence do not undergo secondary growth. Dicot stems have vascular bundles arranged in a ring, open (with cambium) allowing secondary growth. Radial vascular bundles are characteristic of roots. Scattered bundles are a key identifying feature of monocots.
This question belongs to: Science Biology
Question #199
The pores present in the bark of woody stems for gaseous exchange are called:
A. Lenticels
B. Sclereids
C. Stomata
D. Hydathodes
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Correct Answer: Option A

Explanation:
Lenticels are small, raised pores in the bark (periderm) of woody stems and roots that permit gas exchange between internal tissues and the atmosphere. Stomata are on leaves, hydathodes are for guttation, sclereids are sclerenchyma cells. Lenticels are filled with loosely arranged complementary cells and are visible as small dots on the surface of bark.
This question belongs to: Science Biology
Question #200
Which of the following is the correct sequence of events in the Calvin cycle?
A. Reduction → Carboxylation → Regeneration
B. Carboxylation → Regeneration → Reduction
C. Carboxylation → Reduction → Regeneration
D. Regeneration → Carboxylation → Reduction
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Correct Answer: Option C

Explanation:
The Calvin cycle (C3 cycle) consists of three phases: carboxylation (fixation of CO₂ by RuBisCO to 3-PGA), reduction (conversion of 3-PGA to G3P using ATP and NADPH), and regeneration (regeneration of RuBP). This cycle occurs in the stroma of chloroplasts and is the light-independent reaction of photosynthesis.
This question belongs to: Science Biology

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