Free Topic-Wise General Studies MCQs
Dive into cellular biology with high-yield questions on mitochondria, ribosomes, nucleus, and more. A definitive guide to understanding cell structure and function for UPSC.
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Explanation: Endosomes are sorting vesicles formed by endocytosis. Late endosomes frequently fuse with primary lysosomes to form secondary lysosomes for the degradation of internalized molecules.
Explanation: While most Krebs cycle enzymes float freely in the matrix, succinate dehydrogenase is anchored in the inner membrane, also functioning directly as Complex II of the electron transport chain.
Explanation: The intermembrane space holds the proton gradient pumped by the electron transport chain before the protons flow back into the matrix through ATP synthase.
Explanation: Mitochondria contain their own genetic material, which exists as circular, double-stranded DNA (mtDNA), heavily supporting their evolutionary origin from ancient bacteria.
Explanation: Cardiolipin is a double-phospholipid characteristic of bacterial and mitochondrial inner membranes. It tightly seals the membrane to maintain the essential proton motive force.
Explanation: While the F0 portion is embedded in the inner membrane, the F1 'knob' projects into the matrix, where it catalyzes the phosphorylation of ADP into ATP as protons flow through.
Explanation: Pompe disease is a lysosomal storage disorder caused by a deficiency in acid alpha-glucosidase, leading to a toxic, cell-destroying buildup of glycogen in muscle tissues.
Explanation: After digestion is complete, the remaining lysosomal vesicle containing undegradable waste is called a residual body. These can either be expelled or accumulate in aging cells as lipofuscin.
Explanation: Stroma lamellae (or unstacked thylakoids) connect the grana stacks, allowing for a shared internal lumen and efficient distribution of photosynthetic products.
Explanation: The thylakoid membrane houses the photosystems (chlorophyll), electron transport chain, and ATP synthase required to harvest light energy and convert it into ATP and NADPH.
Explanation: Cytochrome c oxidase (Complex IV) is the final transmembrane enzyme complex in the ETC. It transfers electrons to oxygen while pumping protons across the membrane.
Explanation: Porins are integral membrane proteins that form large, open aqueous channels in the outer mitochondrial membrane, allowing free passage of molecules under 5000 Daltons.
Explanation: When a cell receives an apoptotic signal, the outer mitochondrial membrane becomes permeable, releasing Cytochrome C into the cytosol, which triggers the caspase cascade.
Explanation: The stroma is the protein-rich aqueous fluid surrounding the thylakoids. It houses RuBisCO and other enzymes necessary for synthesizing sugars during the dark reactions.
Explanation: In I-cell disease, the Golgi fails to add the mannose-6-phosphate tag. As a result, hydrolytic enzymes are secreted outside the cell instead of being routed to lysosomes.
Explanation: Dense granules in platelets are classified as lysosome-related organelles. They store serotonin, ADP, and calcium, which are released during blood coagulation.
Explanation: Unlike the 80S ribosomes found in the eukaryotic cytoplasm, mitochondria possess 70S ribosomes, structurally mirroring those found in prokaryotic organisms.
Explanation: An autophagosome is a transient, double-membrane structure that engulfs cellular debris or damaged organelles. It subsequently fuses with a lysosome to degrade its contents.
Explanation: Tay-Sachs is a lysosomal storage disorder where the absence of the enzyme hexosaminidase A leads to a toxic accumulation of lipids (gangliosides) in nerve cells.
Explanation: The acrosome is essentially a giant, specialized lysosome that contains hydrolytic enzymes (like hyaluronidase) designed to digest the outer protective layers of the ovum.
Explanation: Chlorophyll and other photosynthetic pigments are anchored within the thylakoid membranes, forming the photosystems required for the light-dependent reactions.
Explanation: Nuclear DNA is tightly wrapped around histone proteins to form nucleosomes. Mitochondrial DNA is circular and naked, lacking histones, which makes it highly susceptible to mutation.
Explanation: Osteoclasts attach to the bone matrix and undergo exocytosis, releasing acid and lysosomal hydrolases directly into the extracellular space to dissolve the bone minerals and collagen.
Explanation: Mitochondria divide independently of the host cell's nuclear division cycle through a process highly similar to bacterial binary fission.
Explanation: Cardiac muscle cells require a continuous, massive supply of ATP to sustain endless rhythmic contractions, resulting in mitochondrial volumes comprising up to 40% of the cell space.
Explanation: Cardiolipin is a unique double-phospholipid found almost exclusively in the inner mitochondrial membrane (and bacterial membranes), crucial for maintaining the proton motive force.
Explanation: Proplastids are immature, unpigmented plastids that divide rapidly and subsequently differentiate into all other specialized plastid types (chloroplasts, chromoplasts, etc.) based on cellular needs.
Explanation: Chromoplasts synthesize and store fat-soluble carotenoid pigments (like carotenes and xanthophylls), providing vibrant colors to attract pollinators and seed dispersers.
Explanation: Lysosomal enzymes (specifically cathepsins) are massively upregulated during amphibian metamorphosis to digest and absorb the tadpole's tail, recycling the nutrients for the growing frog.
Explanation: The stroma contains chloroplast DNA, ribosomes, and all the enzymes necessary for the Calvin cycle (dark reactions), including the highly abundant enzyme RuBisCO.
Explanation: Chromoplasts contain high concentrations of carotenoids, giving flowers and fruits their distinct yellow, orange, and red hues to visually attract pollinators and seed-dispersing animals.
Explanation: Oxygen sits at the end of the electron transport chain (at Complex IV) where it accepts depleted electrons and hydrogen ions to form metabolic water.
Explanation: Thermogenin (UCP1) is found in the inner mitochondrial membrane of brown fat cells. It allows protons to leak back into the matrix, generating heat instead of ATP.
Explanation: Enzymes synthesized in the rough ER are transported to the Golgi apparatus, where they are processed, sorted, and pinched off as primary lysosomes.
Explanation: Acid phosphatase is a highly conserved hydrolase. Because it is universally present in lysosomes, it serves as the standard marker enzyme for locating them via cytochemical staining.
Explanation: Pyrenoids are specialized structures within the chloroplasts of many algae and hornworts that help concentrate CO2 around RuBisCO and often serve as centers for starch formation.
Explanation: Autophagy (self-eating) is a highly regulated mechanism where cells sequester old or damaged organelles in autophagosomes, which then fuse with lysosomes for recycling.
Explanation: Leucoplasts are non-pigmented plastids. Depending on the plant tissue, they differentiate to store bulk nutrients like starch (amyloplasts), oils (elaioplasts), or proteins (aleuroplasts).
Explanation: When lung macrophages phagocytose silica dust, the sharp particles physically rupture the lysosomal membrane, spilling acid hydrolases into the cytosol, killing the cell and causing fibrosis.
Explanation: Mitochondrial inheritance is strictly maternal. The ovum provides the cytoplasm and its organelles to the zygote, while paternal mitochondria in the sperm are systematically degraded.
Explanation: The Golgi apparatus modifies proteins synthesized in the rough ER. The addition of a mannose-6-phosphate tag acts as a specific shipping label directing the vesicle to become a lysosome.
Explanation: The F0-F1 particles represent the ATP synthase complex. They utilize the proton gradient generated across the inner membrane to convert ADP into cellular ATP.
Explanation: Cristae are deep invaginations of the inner mitochondrial membrane that significantly increase the surface area available for housing the electron transport chain and ATP synthase complexes.
Explanation: Amyloplasts are a category of leucoplasts that synthesize and store starch (amylose) granules, predominantly found in tubers like potatoes and seeds.
Explanation: Lysosomal enzymes are acid hydrolases that require a mildly acidic environment (pH around 5.0) to function, preventing accidental digestion of the neutral cytosol if they leak.
Explanation: The mitochondrial matrix contains all the soluble enzymes required for the Krebs cycle (except succinate dehydrogenase, which is on the inner membrane).
Explanation: Mammalian red blood cells (erythrocytes) expel their nucleus, mitochondria, and lysosomes during maturation to prevent the cells from consuming the oxygen they are meant to transport.
Explanation: A secondary lysosome, or phagolysosome, is the active digestive stage formed when a primary lysosome merges with a vesicle containing material destined for degradation.
Explanation: The structural and genetic similarities between modern chloroplasts and free-living cyanobacteria (blue-green algae) strongly indicate that chloroplasts originated from an ancestral cyanobacterial endosymbiont.
Explanation: Chloroplasts (and mitochondria) contain 70S ribosomes, identical to those found in bacteria, providing strong evidence for the endosymbiotic theory of organelle evolution.
Explanation: Stroma lamellae are flat, membranous tubules that interconnect the grana stacks inside a chloroplast, ensuring efficient distribution of photosynthetic materials.
Explanation: Elaioplasts are specialized colorless plastids responsible for the synthesis and storage of lipids and oils, commonly found in the seeds of monocots and dicots.
Explanation: Etioplasts are plastids that develop in the dark. They lack active chlorophyll and possess prolamellar bodies, quickly reverting to chloroplasts upon light exposure.
Explanation: The large central vacuole of a mature plant cell functions as a lytic compartment, containing acid hydrolases and maintaining a low internal pH to digest and recycle cellular waste.
Explanation: A specialized vacuolar-type H+-ATPase (V-ATPase) in the lysosomal membrane constantly pumps hydrogen ions (protons) from the cytosol into the lysosome, keeping the pH around 5.0.
Explanation: Elaioplasts are colorless plastids dedicated to storing fats, oils, and lipids. They are particularly abundant in the seeds of oil-producing plants like mustard and sunflower.
Explanation: Beta oxidation is the process of breaking down fatty acids into acetyl-CoA, which then directly enters the Krebs cycle within the mitochondrial matrix.
Explanation: Chloroplasts share significant structural and genetic similarities with cyanobacteria (blue-green algae), indicating they originated when an ancient eukaryote engulfed a photosynthetic bacterium.
Explanation: Autolysis is the destruction of a cell through the uncontrolled action of its own lysosomal enzymes, earning lysosomes the nickname 'suicide bags'.
Explanation: While chlorophyll and carotenoids are fat-soluble pigments located in chloroplasts and chromoplasts, anthocyanins are water-soluble and stored in the central vacuole.