Cell

Cell is part of Biology. Below are notes on 14 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Cell Division: Mitosis and Meiosis (Stages and Significance)

• Cell division in eukaryotes occurs via Mitosis (somatic cells) or Meiosis (germ cells).
• Prokaryotes divide by Amitosis (binary fission).
• The human somatic cell contains 46 chromosomes (23 pairs), making it diploid (2n).
• Cell Cycle:
• Interphase is the preparatory phase before cell division (M-phase).
• Interphase consists of G1, S, and G2 phases.
• S-phase (Synthesis phase): DNA synthesis (replication) occurs, doubling the DNA content (e.g., from 2C to 4C) but keeping the chromosome number constant.
• DNA replication takes place when chromatin is opened up.
• G0 phase: Quiescent stage for cells that exit the cell cycle and do not divide further.
• Chromatin organizes itself into rodshaped chromosomes before cell division.
• Mitosis (Equational Division):
• Occurs in somatic cells for growth, repair, and asexual reproduction.
• Stem cells self-renew via mitotic cell division.
• Results in two diploid (2n) daughter cells genetically identical to the parent cell.
• Uncontrolled mitosis leads to cancer (tumors) due to a breakdown of regulatory mechanisms.
• Metaphase: Chromosomes align at the equatorial plate; morphology of chromosomes is best studied during this stage.
• Meiosis (Reductional Division):
• Occurs in germ cells to form gametes (sperm/egg).
• Results in four haploid (n) daughter cells, genetically different.
• Meiosis I (Prophase I):
• Zygotene: Homologous chromosomes pair (synapsis) and the synaptonemal complex forms.
• Pachytene: Crossing over (exchange of genetic material) occurs between non-sister chromatids of homologous chromosomes.
• Diplotene: Chiasmata (visible points of crossing over) are formed and visible as homologous chromosomes begin to separate.
• Cell Differentiation: The process by which meristematic cells transform into specific permanent tissues.
• Meristematic tissues in plants (e.g., cambium) are regions of continuous cell division.
• Apoptosis: The cellular and molecular control of programmed cell death.

Cell Theory and its Postulates

• Robert Hooke discovered cells in 1665 by observing cork cells.
• The cell is the fundamental organizational and functional unit of life.
• Cells are the smallest units exhibiting the properties of life, including metabolism, response to the environment, growth, and reproduction.
• Cell Theory (proposed by Matthias Schleiden & Theodor Schwann, 1838-1839):
• All living organisms are composed of one or more cells.
• The cell is the basic structural and functional unit of all living organisms.
• Rudolf Virchow (1855) extended the cell theory with the dictum "Omnis cellula e cellula" (All cells arise from pre-existing cells).
• T.H. Huxley described protoplasm as the physical basis of life.

Cell Wall: Structure and Functions (in plants, fungi, and bacteria)

• Cell wall is an outer, rigid protective layer present in plant cells, fungal cells, and bacterial cells.
• Cell wall is absent in animal cells (e.g., humans, tapeworms).
• Animal cells have a cell membrane and an extracellular matrix (ECM) made of sugars and proteins, but lack a cell wall.
• Plant cells possess both a cell wall and a cell membrane.
• Composition based on organism:
• Plants: Primarily Cellulose (a polysaccharide). Also contains hemicellulose, pectin, and lignin (in secondary walls).
• Fungi: Chitin (a nitrogen-containing polysaccharide). Fungal cell walls are not made of cellulose.
• Bacteria: Peptidoglycan (also known as Murein).
• The repeating disaccharide unit in cellulose is Cellobiose.
• A plant cell from which the cell wall has been removed is termed a Protoplast.
• The substance present in the cells of cork which makes them impervious to gases and water is Suberin.
• Functions: Provides structural support, maintains cell shape, protects against mechanical stress, prevents excessive water uptake (osmotic lysis), and acts as a barrier against pathogens.

Chloroplasts: Structure and Photosynthesis (in plant cells)

• Chloroplasts are the primary sites of photosynthesis in plant cells.
• Structure: Double-membraned organelle (outer and inner membranes form the envelope).
• The inner space (stroma) contains flattened membranous sacs called thylakoids, enzymes for carbohydrate synthesis (Calvin cycle), small circular DNA, ribosomes (70S type), and various RNAs.
• Thylakoids are often stacked into grana (singular: granum); stroma lamellae (intergranal thylakoids) connect thylakoids of different grana.
• Photosynthesis: Light-dependent reactions occur in the thylakoid membranes (chlorophyll absorbs light); Light-independent reactions (Calvin cycle) occur in the stroma.
• Semi-autonomous Nature: Chloroplasts possess their own DNA, ribosomes, and RNA, enabling them to self-replicate and synthesize some of their own proteins.
• Protein Transport: A protein targeting the inner thylakoid space must pass through 3 distinct phospholipid bilayer membranes: the outer chloroplast membrane, the inner chloroplast membrane, and the thylakoid membrane.
• Plastid Types (based on pigment and function):
• Chloroplasts: Green plastids containing chlorophyll and other photosynthetic pigments, site of photosynthesis.
• Chromoplasts: Non-green pigmented plastids (contain carotenoids, xanthophylls) providing yellow, orange, or red colors to flowers and fruits.
• Leucoplasts: Colorless plastids primarily involved in storage.
• Amyloplasts: Store starch.
• Elaioplasts (Oleoplasts): Store oils and fats.
• Proteinoplasts (Aleuroplasts): Store proteins.
• Key Cell Organelle Functions:
• Chloroplast: Photosynthesis.
• Mitochondria: Cellular Respiration.
• Nucleus: Contains genetic material, controls cell activities (not primarily secretion).
• Ribosomes: Protein synthesis.
• Chromatophores: Pigment-containing and light-reflecting cells, primarily found in animals (e.g., for camouflage), not a type of plant plastid.

Cytoplasm and Cytosol: Composition and Functions

• Cytoplasm: The living content of a cell, excluding the nucleus, enclosed by the cell membrane. It comprises the cytosol and cellular organelles.
• Cytosol: The jelly-like fluid portion of the cytoplasm (cytoplasmic matrix), excluding organelles and insoluble suspended particles. It is the site of many metabolic reactions.
• Protoplasm: The entire living content of a cell, including cytoplasm (cytosol + organelles) and nucleoplasm (the living material within the nucleus).
• Composition of Cytosol/Cytoplasm:
• Water: Constitutes approximately 80% of the living material in most organisms.
• Macromolecules: Proteins, carbohydrates, lipids, and nucleic acids.
• Small molecules: Ions, amino acids, nucleotides, and simple sugars.
• Ergastic Substances: Metabolically inactive cell inclusions found in cytoplasm, such as reserve materials (e.g., starch granules, glycogen, fat droplets), crystals, and pigments.
• Key Organic Molecules:
• Cellulose: A carbohydrate made up of (+)-glucose units. It is the most abundantly found organic substance in nature.
• Starch: A carbohydrate also made up of (+)-glucose units, serving as a plant's energy reserve material.
• RNA (Ribonucleic Acid): Mainly found in the cytoplasm, generally singlestranded with 100-5000 bases. Unlike DNA, RNA is alkali sensitive.
• Functions and Metabolic Processes:
• Metabolism: The complete set of chemical reactions that occur within cells, encompassing both the synthesis (anabolism) and breakdown (catabolism) of biomolecules.
• Glycolysis: The breakdown of glucose into pyruvate and energy. This process occurs in the cytoplasm/cytosol.
• Enzymes: Biological catalysts that increase the rate of biochemical reactions by decreasing the activation energy. Most enzymes perform their action at the site where they are produced.
• Enzyme Inhibition (Reversible Competitive): In this type of inhibition, the inhibitor structurally resembles the substrate, binds to the enzyme's active site, and increases the Km (Michaelis constant) while leaving the Vmax (maximum reaction rate) unchanged.

Endoplasmic Reticulum (Rough and Smooth): Structure and Functions

• Endoplasmic Reticulum (ER) is a network of tiny tubular structures and flattened sacs (cisternae).
• ER serves as an intracellular transport system, moving materials to different parts of the cytoplasm and nucleus.
• Rough Endoplasmic Reticulum (RER):
• Characterized by the presence of ribosomes attached to its surface, giving it a rough appearance.
• Primary function: Protein synthesis (by ribosomes) for secretion or integration into membranes.
• Smooth Endoplasmic Reticulum (SER):
• Lacks ribosomes on its surface, appearing smooth.
• Key functions: Synthesis of lipids, synthesis of steroid hormones.
• Additional functions: Detoxification of drugs and toxic substances (especially in liver cells), metabolism of carbohydrates, and storage of calcium ions (e.g., sarcoplasmic reticulum in muscle cells).
• A defective Smooth Endoplasmic Reticulum would result in the inability to synthesize lipids.

Golgi Apparatus: Structure and Functions (Modification, Packaging, Transport)

• Golgi apparatus (Golgi complex/body) consists of flattened, membrane-bound sacs called cisternae, stacked parallel.
• It has distinct cis (forming) face towards ER and trans (maturing) face towards the cell membrane.
• Main functions include modification, packaging, and transport of proteins and lipids.
• Modification: Glycosylation of proteins and lipids, forming glycoproteins and glycolipids.
• Packaging: Packages modified substances into vesicles for secretion or delivery to other cellular destinations.
• Transport: Acts as a processing and packaging station for cellular secretions.
• Involved in the formation of lysosomes.
• Essential for the formation of the acrosome in the spermatozoa of animals.
• In plants, aids in the formation of the cell plate during cell division and synthesis of cell wall components.

Lysosomes and Peroxisomes: Roles in Intracellular Digestion and Detoxification

• Lysosomes:
• Membrane-bound organelles, primarily formed by budding from the Golgi apparatus (derived from ER).
• Contain various powerful hydrolytic enzymes (acid hydrolases) such as lipases, proteases, nucleases, and carbohydrases.
• These digestive enzymes are synthesized by the Rough Endoplasmic Reticulum (RER) and then processed by the Golgi bodies.
• Function optimally in an acidic environment (pH ~5).
• Known as the 'suicide bags' of the cell because they can digest the cell's own components (autolysis) if the membrane ruptures.
• Act as the cell's waste disposal system, breaking down old, worn-out cell organelles (autophagy) and foreign materials (e.g., bacteria, viruses) ingested by the cell (heterophagy/phagocytosis).
• Are rich in hydrolytic enzymes, functioning as the storehouse for these digestive enzymes.
• Digest organic materials like proteins, lipids, carbohydrates, and nucleic acids. They do not break down inorganic materials nor do they stop the entry of foreign materials; rather, they digest them.
• Peroxisomes (Microbodies):
• Small, single-membrane-bound organelles found in both plant and animal cells.
• Contain oxidative enzymes, notably catalase and oxidases.
• Involved in metabolic reactions that produce hydrogen peroxide (H2O2) as a byproduct.
• Catalase enzyme rapidly converts the toxic hydrogen peroxide into water and oxygen, thus playing a key role in detoxification.
• Participate in the breakdown of long-chain fatty acids (beta-oxidation) and detoxification of harmful substances (e.g., alcohol in liver cells).

Mitochondria: Structure, Cellular Respiration, and ATP Synthesis

• Mitochondria: Known as the "powerhouse of the cell."
• Function: Primary site of aerobic cellular respiration, responsible for ATP (Adenosine Triphosphate) formation.
• ATP is the "energy currency" for cellular processes.
• Structure: Double-membraned organelle; the inner membrane is folded into cristae, increasing surface area for reactions.
• ATP synthesis in mitochondria occurs on the inner mitochondrial membrane.
• Genetic Material: Mitochondria contain their own circular DNA and ribosomes, enabling them to synthesize some of their own proteins (semi-autonomous).
• Mitochondria and Chloroplasts are the only eukaryotic cell organelles containing their own DNA and ribosomes.
• Origin: Believed to have evolved from freeliving bacteria engulfed by ancestral eukaryotic cells (Endosymbiotic theory).
• Cellular Respiration: The metabolic process by which cells obtain energy (ATP) by breaking down glucose and other organic molecules.
• Aerobic Respiration: Requires oxygen, results in the complete breakdown of glucose into CO₂ and H₂O.
• End products of aerobic respiration: CO₂ + H₂O.
• Oxygen's role in aerobic respiration: Acts as the final electron acceptor in the Electron Transport Chain.
• ATP yield from aerobic oxidation of one glucose molecule: Approximately 30-32 or 36-38 ATP. (For sucrose, typically double that of glucose).
• Stages of Respiration:
• 1. Glycolysis:
• Location: Cytoplasm.
• Process: Breaks down one Glucose (6-carbon) molecule into two Pyruvate (3-carbon) molecules.
• Key intermediates: Glucose-6phosphate, Fructose-6-phosphate, Fructose 1,6-bisphosphate.
• Does not directly consume oxygen.
• 2. Pyruvate Oxidation (Link Reaction):
• Location: Pyruvate moves from cytoplasm into the mitochondrial matrix.
• Process: Pyruvate Dehydrogenase enzyme converts Pyruvate to Acetyl-CoA (2-carbon), releasing CO₂.
• 3. Krebs Cycle (Citric Acid Cycle):
• Location: Mitochondrial matrix.
• Process: Acetyl-CoA enters the cycle, generating CO₂, ATP/ GTP, NADH, and FADH₂.
• 4. Electron Transport Chain (ETC) & Oxidative Phosphorylation:
• Location: Inner mitochondrial membrane.
• Process: Electrons from NADH and FADH₂ are passed along protein complexes, creating a proton gradient that drives ATP synthase.
• Oxygen directly participates here as the final electron acceptor, forming H₂O.
• Anaerobic Respiration / Fermentation: Occurs in the absence or lack of oxygen, producing much less ATP.
• In yeast: Pyruvate is converted to Ethanol + CO₂ + ATP (alcoholic fermentation).
• In muscle cells (due to lack of oxygen): Pyruvate is converted to Lactic Acid + ATP (lactic acid fermentation).
• Methanol is not a breakdown product of glucose during respiration.
• Fatty acids are oxidized via alpha (α) and beta (β) oxidation, with beta-oxidation primarily occurring in mitochondria.
• Chemosynthetic bacteria obtain energy by oxidizing inorganic chemical compounds.

Nucleus: Nuclear Envelope, Chromatin, Nucleolus, and Functions

• Nucleus: General
• Discovered by Robert Brown (1831).
• Controls cell activities and plays a vital role in cellular reproduction.
• Largest organelle in eukaryotic cells, generally.
• Absent in mature mammalian Red Blood Cells (RBCs) and Platelets.
• In plant cells, both nucleus and chloroplasts are separately surrounded by their own membranes.
• Nuclear Envelope
• Double-membraned structure with nuclear pores.
• Separates the nucleus from the cytoplasm.
• Chromatin & Chromosomes
• Eukaryotic chromatin is composed of DNA and proteins (histones and nonhistone proteins).
• DNA (Deoxyribonucleic Acid):
• Hereditary material of all living organisms.
• Double helical structure described by Watson and Crick.
• Nuclear DNA consists of two anti-parallel nucleotide chains.
• One turn of B-form DNA helix measures 3.4 nm (34 Å) and contains ~10 base pairs. Z-form DNA has 12 base pairs per turn.
• Subunits are nucleotides.
• A nucleotide contains a nitrogenous base, deoxyribose sugar, and a phosphate group.
• Purine bases in DNA: Adenine (A) and Guanine (G).
• Functional segments of DNA are called genes.
• DNA is also found in mitochondria and chloroplasts.
• Not all segments of DNA code for synthesis of proteins.
• Histone Proteins:
• Small, basic proteins associated with chromosomal DNA in eukaryotic cells.
• Rich in basic amino acids: Arginine and Lysine.
• Lack Tryptophan.
• DNA wraps around histone octamers to form nucleosomes.
• Chromonema:
• A coiled chromatin fiber.
• Paranemic coils allow easy separation of sister chromatids.
• Chromosomes contain information for inheritance.
• Nucleolus
• Dense, spherical structure within the nucleus, not membrane-bound.
• Primary site of ribosomal RNA (rRNA) synthesis and ribosome biogenesis.
• RNA (Ribonucleic Acid)
• Present in nuclei, cytoplasm, mitochondria, chloroplasts, and ribosomes (in plant cells). In animal cells, also in nucleus, mitochondria, and ribosomes.
• mRNA (messenger RNA) carries genetic information copied from DNA.
• The presence of nucleic acids (DNA and RNA) is a feature common to the nucleus, chloroplasts, and mitochondria.

Plasma Membrane: Fluid Mosaic Model, Structure, and Functions

• Plasma membrane (cell membrane) is essential for all living cells, regulating substance movement.
• Fluid Mosaic Model (Singer & Nicolson, 1972): Describes the membrane as a "sea" of phospholipids with "icebergs" of proteins floating in it, highlighting the quasi-fluid nature of lipids.
• Structure/Composition:
• Phospholipid Bilayer: Forms the fundamental structure; amphipathic (hydrophilic heads face outwards, hydrophobic tails face inwards).
• Proteins:
• Integral (intrinsic) proteins: Embedded within or span the entire lipid bilayer (transmembrane).
• Peripheral (extrinsic) proteins: Loosely associated with the surface.
• Cholesterol: Embedded in animal cell membranes; regulates membrane fluidity. Absent in plant cells (Ergosterol in fungi).
• Carbohydrates: Oligosaccharides attached to lipids (glycolipids) or proteins (glycoproteins) on the outer surface, forming the Glycocalyx (cell coat) for cell recognition and protection (e.g., from phagocytes).
• Properties:
• Flexible: Enables cell to change shape and engulf materials (e.g., endocytosis).
• Selectively Permeable (Semi-permeable): Allows certain substances (e.g., water, O2, CO2) to pass through more easily than others, maintaining cell homeostasis.
• Functions:
• Transport of Substances:
• Passive Transport: Movement down a concentration gradient, no energy required.
• Diffusion: Movement of particles/molecules from higher to lower concentration (e.g., O2, CO2).
• Osmosis: Specific diffusion of water molecules from higher water concentration (lower solute) to lower water concentration (higher solute) through a semi-permeable membrane.
• Cell in hypotonic solution (lower solute outside): Gains water, swells.
• Cell in hypertonic solution (higher solute outside): Loses water, shrinks (e.g., salt on cucumber, raisins in water).
• Facilitated Diffusion: Uses carrier or channel proteins to move substances down gradient, no energy.
• Active Transport: Movement of substances against a concentration gradient (from lower to higher), requires energy (ATP) from respiration, and specific carrier proteins (e.g., Na+/K+ pump).
• Cell Recognition and Adhesion: Mediated by glycocalyx and specific membrane proteins.
• Cell Communication: Via receptor proteins and junctions (e.g., gap junctions, absent in sperm cells).
• Endocytosis: Engulfing larger particles or liquids (phagocytosis for solids, pinocytosis for liquids).
• Plasma membrane is NOT made of cellulose (cellulose forms plant cell walls).
• Plasma membrane is a bilayer, not singlelayered.

Prokaryotic and Eukaryotic Cells: Structural Organization and Differences

• Prokaryotic cells lack a true nucleus and membrane-bound organelles.
• The undefined nuclear region in prokaryotes is called a nucleoid, lacking a nuclear membrane and histone proteins.
• Prokaryotic genetic material (DNA) is "naked," meaning it is not associated with histone proteins.
• Most prokaryotes have a single, circular chromosome.
• Bacterial genetic material is found in the cytoplasm, specifically the nucleoid region.
• Prokaryotic cells possess a cell wall (except Mycoplasmas), plasma membrane, and 70S ribosomes.
• Typical size of prokaryotic cells is 1-10 micrometers (µm); for example, E.coli is approx. 2 µm (2000 nm).
• Examples of prokaryotes include Bacteria (e.g., E.coli) and Archaea.
• Eukaryotic cells possess a true nucleus with a nuclear membrane and various membranebound organelles (e.g., mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus).
• Eukaryotic genetic material is organized as chromatin within the nucleus, associated with histone proteins.
• Eukaryotic cells have 80S ribosomes.
• Mitochondria are membrane-bound organelles found exclusively in eukaryotic cells, responsible for cellular respiration.
• Examples of eukaryotes include yeast, plants, human beings, Monocytes, Chondrocytes, Basophils, and Lymphocytes (all animal cell types).
• All life forms contain essential "molecules of life": carbohydrates, proteins, nucleic acids, and lipids.
• Nucleic acids (DNA and RNA) contain Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus, but not Sulfur.
• Purine bases in nucleic acids are Adenine (A) and Guanine (G).
• DNA primarily functions to encode genetic information (genes).
• The enzyme Helicase unwinds the DNA double helix.
• Zymase is an enzyme that converts glucose to ethyl alcohol (fermentation).
• Viruses are acellular and lack their own metabolic enzymes; they depend on host cell machinery for replication.
• Viroids are infectious agents composed of a single-stranded RNA molecule without a protein coat.
• Mycoplasmas are bacteria that lack a cell wall.
• Mature xylem fibres in plants are dead and non-nucleated. Mammalian red blood cells also lack nuclei at maturity.
• Single-celled organisms perform all life processes (food uptake, respiration, excretion) within their single cell; they do not possess specialized organs and are in direct contact with the external environment.
• Phospholipids are primary components of cell membranes.
• Cellulose is a structural component of plant cell walls.
• Starch is the primary energy storage polysaccharide in plants.

Ribosomes: Structure and Role in Protein Synthesis

• Ribosomes are the primary sites of protein synthesis (translation) in both prokaryotic and eukaryotic cells.
• They are non-membranous organelles.
• Composed of ribosomal RNA (rRNA) and ribosomal proteins.
• Found freely in the cytoplasm or attached to the surface of the Rough Endoplasmic Reticulum (RER), giving RER its "rough" appearance.
• During protein synthesis, ribosomes decode messenger RNA (mRNA), and transfer RNA (tRNA) carries specific amino acids.
• tRNA carries activated amino acids at its 3'CCA terminal.
• Proteins are polymers assembled from αamino acids; their specific amino acid sequence dictates the final 3-D folded structure.
• Examples of proteins include Keratin (structural protein) and Insulin (a hormone with 51 amino acid residues).
• Most enzymes are proteins, functioning as macromolecular biological catalysts that speed up chemical reactions without being consumed.
• Enzyme activity is regulated and influenced by factors like temperature (e.g., optimal at ~37°C for many mammalian enzymes) and pH.
• Zymogens are inactive precursors of enzymes.
• Ribozymes are RNA molecules that exhibit catalytic activity.
• While ribosomes contain rRNA (a type of nucleic acid), they do not possess their own genetic material (DNA or encoding RNA) in the sense of a cell's nucleus, mitochondria, or chloroplasts.
• Venkatraman Ramakrishnan (along with Thomas A. Steitz and Ada E. Yonath) received the 2009 Nobel Prize in Chemistry for structural studies of the ribosome, notably using the organism Thermus thermophilus.

Vacuoles: Types and Functions (Storage, Turgor)

• Vacuoles are membrane-bound sacs found in the cytoplasm.
• Plant Cells:
• Typically possess a large, central vacuole, which can occupy up to 90% of the cell volume.
• The membrane enclosing the plant vacuole is called tonoplast.
• Contains cell sap, a mixture of water, sugars, amino acids, proteins, mineral salts, and waste products (including pigments like anthocyanins).
• Functions:
• Storage: Stores water, nutrients, waste products, and pigments.
• Turgor and Rigidity: Maintains turgor pressure against the cell wall, providing turgidity and structural rigidity to the plant cell.
• Animal Cells: Generally have smaller, fewer, and temporary vacuoles, involved in storage, transport, and waste removal. Vacuoles are present, not absent.
• Unicellular Organisms (e.g., Amoeba):
• Food Vacuoles: Formed by engulfing food particles (phagocytosis), playing a role in nutrition and digestion.
• Contractile Vacuoles: Crucial for osmoregulation, expelling excess water and some waste products from the cell.
• Meristematic Cells (in plants): Characterized by small or absent vacuoles, dense cytoplasm, thin cell walls, and large nuclei.
• Storage Polysaccharides (Cellular Location):
• Starch: The primary storage polysaccharide found in plant cells.
• Glycogen: The primary storage polysaccharide found in animal cells (e.g., liver, muscle).

5. Heredity

Practice MCQs: Cell

Cell Division: Mitosis and Meiosis (Stages and Significance)

1. In human body, the cell growth and differentiation are highly controlled and regulated, but in cancer cells

   Asked in: UPSC CDS 1 2017 · Asst. Fisheries Development Officer 2024

   1. there is breakdown of these regulatory mech‐ anisms leading to formation of benign and malignant tumors
   2. controlled cell division and over-production of genetic material occur
   3. RNA is mutated and produced in less amount
   4. DNA is mutated and produced in less amount
   Show answer

   Answer: A. there is breakdown of these regulatory mech‐ anisms leading to formation of benign and malignant tumors

   The fundamental characteristic of cancer cells is the loss of control over cell growth and division, contrasting sharply with the tightly regulated processes in normal cells. Reevving and stapling, along with marling and norselling, are methods used to attach netting to ropes in fishing gear construction.

2. The National Bureau of Plant Genetic Resources is located at

   Asked in: Assistant Conservator of Forest (ACF) 2012

   1. Bangalore
   2. Jammu
   3. New Delhi
   4. Shillong
   Show answer

   Answer: C. New Delhi

   NBPGR plays a vital role in ensuring food security and agricultural sustainability by maintaining a diverse collection of germplasm of crops and their wild relatives.

3. What is the number of chromosomes found in human somatic cell?

   Asked in: UPSC Geoscientist 2023

   1. 48
   2. 56
   3. 46
   4. 42
   Show answer

   Answer: C. 46

   Human somatic (body) cells are diploid, meaning they contain two sets of chromosomes. Humans have 23 pairs of chromosomes, with one set of 23 chromosomes inherited from each parent. Thus, the total number of chromosomes in a human somatic cell is 23 2 = 46.

4. Transformation of meristematic cells into specific permanent tissues occurs by the process of

   Asked in: UPSC NDA 1 2021

   1. Cell differentiation.
   2. Cell division.
   3. Cell multiplication.
   4. Cell regeneration.
   Show answer

   Answer: A. Cell differentiation.

   - Meristematic cells are undifferentiated plant cells capable of active division. - Permanent tissues are composed of cells that have undergone differentiation and often lose the ability to divide or divide slowly, performing specific functions. - Differentiation involves changes in cell structure and function leading to specialization.

5. Consider the following statements: DNA replication takes place when chromatin is opened up. Chromatin organises itself into rod- shaped chromosomes before cell division. Both prokaryotes and eukaryotes have the same process for cell division. Which of the statements given above is/are correct ?

   Asked in: UPSC NDA 1 2024

   1. 1 only
   2. 1 and 2 only
   3. 1, 2 and 3
   4. 3 only
   Show answer

   Answer: B. 1 and 2 only

   Statement 1 is correct: DNA replication happens during the S phase when chromatin is relatively decondensed ('opened up') to allow access for replication enzymes. Statement 2 is correct: Before eukaryotic cell division (mitosis or meiosis), the diffuse chromatin fibers condense and coil tightly to form discrete, visible chromosomes. Statement 3 is incorrect: Prokaryotic cell division (binary fission) is a simpler process than eukaryotic cell division (mitosis and meiosis), which involves complex stages, spindle formation, and chromosome segregation mechanisms not found in prokaryotes.

6. Consider the following statements about stem cells : 1. Stem cells have the potential for self- renewal via mitotic cell division. 2. In 1908, James Thomas and his colleagues first derived human embryonic stem cells from donated blastocysts through in vitro fertilization. Which of the statements given above is/are correct?

   Asked in: UPSC CISF AC EXE 2024

   1. 1 only
   2. 2 only
   3. Both 1 and 2
   4. Neither 1 nor 2
   Show answer

   Answer: A. 1 only

   Statement 1 is correct: Stem cells possess the unique ability to divide and renew themselves through mitotic cell division, maintaining the stem cell population. Statement 2 is incorrect: Human embryonic stem cells were first successfully derived in 1998 by James Thomson and his colleagues at the University of Wisconsin-Madison, not in 1908 by James Thomas.

7. During cell division, DNA synthesis takes place in

   Asked in: WBPSC CS Prelims 2015

   1. Interphase
   2. Anaphase
   3. Prophase
   4. Telophase
   Show answer

   Answer: A. Interphase

   Interphase is the stage of the cell cycle that precedes cell division (mitosis or meiosis). It is during the 'S' (Synthesis) phase of Interphase that the cell replicates its DNA, ensuring that each daughter cell receives a complete set of chromosomes.

Cell Theory and its Postulates

8. The biologist who discovered the scientific function of cells in 1665 was :

   Asked in: HAS Prelims 2019

   1. Robert Hooke
   2. Andreas Vesalius
   3. William Harvey
   4. John Hunter
   Show answer

   Answer: A. Robert Hooke

   - In 1665, Robert Hooke published his book "Micrographia", which contained detailed drawings of observations made with a microscope. - While observing a thin slice of cork, Hooke saw small, box- like structures that reminded him of the cells where monks lived in a monastery, and he coined the term "cell" to describe these structures. - Although Hooke primarily observed and described the structure of cells (specifically dead plant cells), his work in 1665 marks the first observation and naming of cells, laying the foundation for cell biology. The question's phrasing "discovered the scientific function of cells" is perhaps imprecise, as understanding cell function came much later, but 1665 is definitively linked to Hooke's discovery of the cell structure. - The other options are incorrect: Andreas Vesalius was a 16th-century anatomist, William Harvey discovered blood circulation in the 17th century (early 1600s), and John Hunter was an 18th-century surgeon.

9. The cell was first time described by ______.

   Asked in: MPSC CS Prelims 2020

   1. Lamarck
   2. Schwann
   3. Robert Hooke
   4. Rudolf Virchow
   Show answer

   Answer: C. Robert Hooke

   - Robert Hooke used a primitive microscope to observe cork. - He coined the term "cell" based on the appearance of cork tissue. - His work was published in his book Micrographia.

10. Which one of the following is the smallest unit showing the properties of life such as capacity for metabolism, response to the environment, growth and reproduction ?

    Asked in: UPSC NDA 1 2015

    1. Gene
    2. Chromosome
    3. Nucleus
    4. Cell
    Show answer

    Answer: D. Cell

    Understanding the concept of the cell as the basic unit of life.

11. Who among the following first discovered cell ?

    Asked in: UPSC NDA 1 2018

    1. Robert Brown
    2. Robert Hooke
    3. Leeuwenhoek
    4. Rudolf Virchow
    Show answer

    Answer: B. Robert Hooke

    In 1665, Robert Hooke published his book "Micrographia", where he described his observations using a microscope. He examined a thin slice of cork and observed small, box-like compartments, which he called "cells" because they reminded him of the rooms (cells) in a monastery.

12. The fundamental organisational unit of life is

    Asked in: WBCS Main Paper 4 2021

    1. protein
    2. cell
    3. DNA
    4. RNA
    Show answer

    Answer: B. cell

    The cell theory states that all living organisms are composed of cells and products of cells, and that all cells come from pre-existing cells.

13. Cell was discovered by

    Asked in: WBCS Main Paper 4 2021

    1. Charles Darwin
    2. Robert Hooke
    3. Gregor Mendel
    4. Robert Brown
    Show answer

    Answer: B. Robert Hooke

    Robert Hooke observed cells in cork in 1665. He coined the term "cell".

14. Cells were first discovered by - (1) Robert Hooke (2) Schleiden and Schwann (3) Purkinje (4) Robert Brown

    Asked in: Head Master Praveshika School (Sanskrit Edu.) 2021

    1. (1)
    2. (2)
    3. (3)
    4. (4)
    Show answer

    Answer: A. (1)

    Robert Hooke discovered cells.

Cell Wall: Structure and Functions (in plants, fungi, and bacteria)

15. Cell wall is not present in cells of

    Asked in: UPSC CDS 1 2021

    1. Bacteria
    2. Plants
    3. Fungi
    4. Humans
    Show answer

    Answer: D. Humans

    Animal cells, including human cells, are characterized by the absence of a cell wall. They are surrounded only by a cell membrane.

16. Which one of the following is not found in animal cells ?

    Asked in: UPSC CDS 2 2019 · UPSC CAPF 2021

    1. Free ribosomes
    2. Mitochondria
    3. Nucleolus
    4. Cell wall
    Show answer

    Answer: D. Cell wall

    A cell wall is a rigid outer layer that provides structural support and protection to the cell. It is a characteristic feature of plant cells (made primarily of cellulose), fungi, algae, and bacteria, but it is not found in animal cells. Animal cells are enclosed only by a cell membrane.

17. Cell wall is absent in which one of the following organisms ?

    Asked in: UPSC CDS 2 2023

    1. Bacteria
    2. Diatom
    3. Mushroom
    4. Tapeworm
    Show answer

    Answer: D. Tapeworm

    Let's check the presence of cell walls in the given organisms: A) Bacteria have cell walls typically made of peptidoglycan. B) Diatoms are a type of algae belonging to Protista; they have unique cell walls made of silica, called frustules. C) Mushrooms are fungi; fungal cells have cell walls made primarily of chitin. D) Tapeworms are multicellular animals (Platyhelminthes). Animal cells characteristically lack cell walls.

18. Cell wall of any fungus is different from plants in having

    Asked in: UPSC NDA 1 2017

    1. cellulose
    2. chitin
    3. cholesterol
    4. glycogen
    Show answer

    Answer: B. chitin

    Fungal cell walls contain chitin, whereas plant cell walls contain cellulose.

19. Consider the following statements regarding cell wall composition : Bacterial cell wall is made of peptidoglycan. Fungal cell wall is made of cellulose. Animals lack cell wall and have extracellular matrix made up of sugar and proteins. Select the correct answer using the code given below :

    Asked in: UPSC NDA 1 2023

    1. 2 only
    2. 1 and 2
    3. 1 and 3
    4. 1, 2 and 3
    Show answer

    Answer: C. 1 and 3

    Statement 1 is correct. The cell wall of most bacteria is primarily composed of peptidoglycan, a polymer consisting of sugars and amino acids, which provides structural support and protection. Statement 2 is incorrect. Fungal cell walls are mainly composed of chitin, a tough polysaccharide, although other components like glucans are also present. Plant cell walls are made of cellulose. Statement 3 is correct. Animal cells do not possess a rigid cell wall. Instead, animal tissues have an extracellular matrix (ECM) which is a complex network of secreted molecules, including various proteins (like collagen, elastin) and glycoproteins (like proteoglycans, which are composed of protein and carbohydrate chains), providing support, adhesion, and signaling functions.

20. Which one of the following statements about animal cells and plant cells is correct?

    Asked in: UPSC NDA 2 2022

    1. Animal cells have only cell membrane not cell wall, whereas plant cells have only cell wall not cell membrane.
    2. Animal cells have only cell membrane not cell wall, but plant cells have both.
    3. Both animal and plant cells have cell membrane and cell wall.
    4. Only some cells of animals have cell wall and all plant cells have cell membrane.
    Show answer

    Answer: B. Animal cells have only cell membrane not cell wall, but plant cells have both.

    The presence of a cell wall is a defining characteristic of plant cells (and fungal, algal, and bacterial cells) that is absent in animal cells. Both plant and animal cells have a cell membrane.

21. Animal cell wall is essentially made of :

    Asked in: UPSC CAPF 2014

    1. Protein
    2. Carbohydrate
    3. Lipid bilayer
    4. Cellulose
    Show answer

    Answer: C. Lipid bilayer

    Biologically, animal cells fundamentally lack a cell wall. Cell walls are found in plant cells (cellulose), fungal cells (chitin), bacterial cells (peptidoglycan), etc., providing structural support outside the cell membrane. Animal cells only have a cell membrane as their outer boundary. The cell membrane is primarily composed of a lipid bilayer with embedded proteins and associated carbohydrates. Given the options, "Lipid bilayer" is the most accurate description of the essential structural component of the animal cell membrane. The question is likely flawed in its phrasing, using "cell wall" instead of "cell membrane", or is designed to test the knowledge that animal cells lack a cell wall, with the options representing components of structures found in other organisms or other parts of the animal cell. Assuming the most probable intent of the test setter asking about the main structural component at the cell periphery among the options, Lipid bilayer (the core of the cell membrane) is the closest fit, although technically it's the membrane, not a wall.

Chloroplasts: Structure and Photosynthesis (in plant cells)

22. Which among the following is a character of chloroplast which makes them qualified to self- replication?

    Asked in: BPSC Prelims Exam 68th

    1. Presence of DNA only
    2. Absence of RNA
    3. Presence of both DNA and RNA
    4. More than one of the above
    Show answer

    Answer: C. Presence of both DNA and RNA

    Chloroplasts (and mitochondria) are semi-autonomous organelles containing their own DNA and ribosomes.

23. A protein is synthesized in the endoplasmic reticulum bound ribosomes and it targets to the inner thylakoid space of chloroplast. How many double-layered membrane layers it has to pass to reach its destination?

    Asked in: UPSC CDS 1 2018

    1. 2
    2. 3
    3. 4
    4. 5
    Show answer

    Answer: C. 4

    Reaching the inner thylakoid space from the cytoplasm requires crossing the chloroplast outer membrane, inner membrane, and thylakoid membrane (3 layers). Starting from the ER lumen adds the step of exiting the ER, which requires crossing the ER membrane.

24. Plastids, in which materials such as starch, oils and protein granules are stored, are called:

    Asked in: UPSC Geoscientist 2020

    1. Leucoplasts
    2. Chromoplasts
    3. Chloroplasts
    4. Chromatophores
    Show answer

    Answer: A. Leucoplasts

    Plastids are a type of organelle found in plant cells and some eukaryotic algae. They are broadly classified based on the pigments they contain. Leucoplasts are non-pigmented plastids primarily involved in the storage of food substances like starch (amyloplasts), lipids/oils (elaioplasts), and proteins (aleuroplasts).

25. Pigment containing and light reflecting cells are :

    Asked in: HAS Prelims 2019

    1. Leucoplasts
    2. Chloroplasts
    3. Chromatophore
    4. Chromatoplasts
    Show answer

    Answer: C. Chromatophore

    Chromatophores are cells in animals (like fish, amphibians, reptiles, and cephalopods) that contain pigment and are responsible for producing color through either pigments or light reflection/scattering (structural coloration). They allow animals to change color rapidly for camouflage, thermoregulation, or communication.

26. Consider the following plant cell organelles and their specific functions. Organelle Function 1. Chloroplast : Photosynthesis 2. Mitochondria : Respiration 3. Nucleus : Secretion 4. Ribosomes : Protein synthesis Which of the above pairs is/are correctly matched?

    Asked in: KPSC KAS Prelims 2014

    1. 2 only
    2. 1 and 3 only
    3. 1, 2 and 4 only
    4. 1, 2, 3 and 4
    Show answer

    Answer: C. 1, 2 and 4 only

    Understanding the specific functions of key plant cell organelles like chloroplasts, mitochondria, nucleus, and ribosomes is essential.

27. Which one of the following plant plastids stores starch, oil and protein granules?

    Asked in: UPSC NDA 1 2022

    1. Chloroplast
    2. Leucoplast
    3. Chromoplast
    4. Xanthoplast
    Show answer

    Answer: B. Leucoplast

    Leucoplasts are storage plastids in plant cells, specialized for storing starch, oils, and proteins.

28. Which one of the following cell organelles synthesizes its own proteins involving genes present in its DNA?

    Asked in: UPSC CISF AC EXE 2019

    1. Endoplasmic reticulum
    2. Plasma membrane
    3. Plastid
    4. Lysosome
    Show answer

    Answer: C. Plastid

    Mitochondria and plastids are unique among eukaryotic organelles because they possess their own circular DNA (similar to bacterial DNA) and ribosomes (70S type). This allows them to synthesize some of the proteins required for their function, independently of the cell's nucleus and cytoplasmic ribosomes.

Cytoplasm and Cytosol: Composition and Functions

29. The living content of a cell is called protoplasm. It is composed of :

    Asked in: UPSC CDS 1 2016

    1. Cytoplasm only
    2. Cytoplasm and nucleoplasm
    3. Nucleoplasm only
    4. Cytoplasm, nucleoplasm and other organelles
    Show answer

    Answer: D. Cytoplasm, nucleoplasm and other organelles

    - Protoplasm refers to all the living substance within a cell membrane. - In eukaryotic cells, protoplasm includes the cytoplasm (the material within the cell membrane but outside the nucleus) and the nucleoplasm (the substance within the nucleus). - Cytoplasm itself consists of the cytosol (the jelly-like substance) and the organelles suspended within it. Nucleoplasm contains the genetic material (DNA) and other components of the nucleus.

30. The breakdown of glucose in cytoplasm results in the formation of

    Asked in: UPSC NDA 2 2022

    1. pyruvate and energy
    2. pyruvate and carbon dioxide
    3. pyruvate and oxygen
    4. pyruvate and nitrogen
    Show answer

    Answer: A. pyruvate and energy

    Glycolysis occurs in the cytoplasm and converts glucose into pyruvate, yielding energy (ATP).

31. Metabolically inactive cell inclusions remaining in the cytoplasm is called

    Asked in: TNPSC CS Prelims 2017

    1. Reserve materials
    2. Ergastic substances
    3. Secretory substances
    4. Crystals
    Show answer

    Answer: B. Ergastic substances

    Ergastic substances are non-living cellular products or inclusions found within the cytoplasm or vacuoles of cells. They include reserve food materials (like starch grains, glycogen), secretory materials, excretory products, pigments, and crystals. They are distinct from the metabolically active components of the cytoplasm.

32. Cellulose and starch both are made up of

    Asked in: UKPSC CS Prelims 2016

    1. (+) – glucose
    2. (–) – fructose
    3. Both (a) and (b) given above
    4. (+) – galactose
    Show answer

    Answer: A. (+) – glucose

    - Cellulose and starch are polysaccharides. - The monomer unit for both is glucose. - Natural glucose is (+)-glucose (D-glucose).

33. To which of the following chemical groups – Cellulose belongs?

    Asked in: UKPSC CS Prelims 2021

    1. Carbohydrates
    2. Proteins
    3. Lipids
    4. Nucleic acids
    Show answer

    Answer: A. Carbohydrates

    - Cellulose is a polysaccharide. - Polysaccharides are a major class of carbohydrates. - Cellulose forms the cell walls of plants.

34. Which of the following statements about enzymes is/are correct? 1. They are biocatalysts. 2. They perform their action on the site where they are produced Select the correct answer from the codes given below:

    Asked in: UPPCS Prelims 2019

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Show answer

    Answer: A. 1 only

    Statement 1: They are biocatalysts. This is correct. Enzymes are proteins (with a few exceptions being catalytic RNA molecules called ribozymes) that speed up biochemical reactions in living organisms without being consumed in the process. This fits the definition of a biocatalyst. Statement 2: They perform their action on the site where they are produced. This statement is incorrect as a general rule. Some enzymes do act where they are produced (e.g., metabolic enzymes within a cell), but many others are synthesized in one location and then secreted to act in a different location. For example, digestive enzymes are produced in organs like the pancreas, stomach, and small intestine but act in the lumen of the digestive tract. Enzymes involved in blood clotting are produced in the liver but circulate in the blood and act at the site of injury.

35. In which part of the cell, the glucose is converted into pyruvate ?

    Asked in: UPSC CAPF 2020

    1. Mitochondria
    2. Nucleus
    3. Cytoplasm
    4. Endoplasmic reticulum
    Show answer

    Answer: C. Cytoplasm

    Glycolysis is the first stage of cellular respiration and occurs in the cytoplasm. It breaks down a molecule of glucose (a 6-carbon sugar) into two molecules of pyruvate (a 3-carbon molecule), producing a net gain of ATP and NADH.

Endoplasmic Reticulum (Rough and Smooth): Structure and Functions

36. Which one of the following functions is not carried out by smooth endoplasmic reticulum?

    Asked in: UPSC CDS 1 2019

    1. Transport of materials
    2. Synthesis of lipid
    3. Synthesis of protein
    4. Synthesis of steroid hormone
    Show answer

    Answer: C. Synthesis of protein

    The endoplasmic reticulum (ER) is involved in various cellular functions. The rough endoplasmic reticulum (RER) is characterized by the presence of ribosomes on its surface and is primarily responsible for the synthesis and modification of proteins destined for secretion, insertion into membranes, or delivery to other organelles. The smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in lipid synthesis, steroid hormone synthesis, detoxification, and calcium storage. Protein synthesis is mainly carried out by ribosomes, either free in the cytoplasm or attached to the RER. Therefore, synthesis of protein is not a primary function of the smooth endoplasmic reticulum.

37. Which one of the following correctly represents RER?

    Asked in: UPSC Geoscientist 2020

    1. Endoplasmic reticulum having no ribosomes attached to its surface
    2. Endoplasmic reticulum having ribosomes attached to its surface
    3. Endoplasmic reticulum with rounded vesicles
    4. Endoplasmic reticulum with Golgi appears on its surface
    Show answer

    Answer: B. Endoplasmic reticulum having ribosomes attached to its surface

    The endoplasmic reticulum (ER) is a network of membranes throughout the cytoplasm of eukaryotic cells. It exists in two forms: rough ER (RER) and smooth ER (SER). The presence of ribosomes on the outer surface of the membrane distinguishes RER from SER. These ribosomes are involved in the synthesis of proteins, particularly those destined for secretion or insertion into membranes.

38. Match the cell organelles listed in Column 'A' with their functions given in Column 'B' and choose the correct option: Column - A Column - B i. Golgi Body

    Asked in: HAS Prelims 2021

    1. Digestion ii. Smooth Endoplasmic
    2. Formation of Reticulum Lysosome iii. Ribosome
    3. Protein Synthesis iv. Lysosome
    4. Lipid Synthesis Code: A. i-A, ii-B, iii-C, iv-D B. i-B, ii-D, iii-A, iv-C C. i-B, ii-D, iii-C, iv-A D. i-D, ii-C, iii-A, iv-B
    Show answer

    Answer: C. Protein Synthesis iv. Lysosome

    - Golgi Body (or Golgi apparatus) modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. It also plays a role in the synthesis of some polysaccharides and is involved in the formation of lysosomes. - Smooth Endoplasmic Reticulum (SER) is involved in the synthesis of lipids (including steroids), detoxification of drugs and poisons, and storage of calcium ions. - Ribosomes are the sites where protein synthesis occurs. They can be free in the cytoplasm or attached to the rough endoplasmic reticulum. - Lysosomes are membrane-bound organelles containing hydrolytic enzymes that digest waste materials and cellular debris. They are often referred to as the "suicide bags" of the cell due to their role in autolysis.

39. Match the cell organelle listed in Column - 'A' with their function in Column - 'B' and select the correct option. Column - A Column - B i. Golgi body

    Asked in: HAS Prelims 2021

    1. Digestion ii. Smooth endoplasmic
    2. Formation of reticulum lysosome iii. Ribosome
    3. Protein Synthesis iv. Lysosome
    4. Lipid Synthesis Code : A. i-A, ii-B, iii-C, iv-D B. i-B, ii-D, iii-A, iv-C C. i-B, ii-D, iii-C, iv-A D. i-D, ii-C, iii-A, iv-B
    Show answer

    Answer: C. Protein Synthesis iv. Lysosome

    - Golgi body: Processes, packages, and modifies proteins and lipids, forms secretory vesicles and lysosomes. - Smooth endoplasmic reticulum: Synthesizes lipids, steroids, and phospholipids; detoxifies drugs and poisons; stores calcium ions. - Ribosomes: Translate mRNA into proteins. - Lysosomes: Membrane-bound organelles containing digestive enzymes that break down waste materials and cellular debris.

40. Movement of materials to different parts of cytoplasm and nucleus is generally carried out by

    Asked in: UPSC NDA 1 2021

    1. Ribosomes.
    2. Mitochondria.
    3. Lysosomes.
    4. Endoplasmic reticulum.
    Show answer

    Answer: D. Endoplasmic reticulum.

    The endoplasmic reticulum (ER) is a vast network of interconnected membranes extending throughout the cytoplasm of eukaryotic cells. It forms a continuous network with the outer membrane of the nuclear envelope, providing channels and pathways for the transport of molecules within the cell. Proteins synthesized on ribosomes attached to the rough ER are often transported within the ER lumen, and lipids synthesized in the smooth ER can also move through the ER network. The ER system is crucial for intracellular transport.

41. A cell is unable to synthesize lipids. Which of its cell organelles might be defective?

    Asked in: UPSC NDA 1 2022

    1. Smooth endoplasmic reticulum
    2. Golgi bodies
    3. Lysosomes
    4. Mitochondria
    Show answer

    Answer: A. Smooth endoplasmic reticulum

    The smooth endoplasmic reticulum (SER) is a major site for lipid synthesis in eukaryotic cells.

42. One of the additional functions of Smooth Endoplasmic Reticulum (SER) is

    Asked in: UPSC NDA 2 2018

    1. protein synthesis
    2. lipid synthesis
    3. storage of biomolecules
    4. detoxification of toxic substances
    Show answer

    Answer: D. detoxification of toxic substances

    - RER has ribosomes on its surface and is involved in synthesizing and modifying proteins destined for secretion or insertion into membranes. - SER lacks ribosomes and is involved in metabolic processes. - Key functions of SER include lipid synthesis, detoxification, carbohydrate metabolism, and calcium storage.

Golgi Apparatus: Structure and Functions (Modification, Packaging, Transport)

43. Which cytoplasmic organelle is associated with 'acrosome' formation in the spermatozoa of animals?

    Asked in: TNPSC CS Prelims 2017

    1. Lysosome
    2. Chloroplast
    3. Golgi complex
    4. Chromosome
    Show answer

    Answer: C. Golgi complex

    The acrosome is a cap-like structure covering the head of a sperm, derived from the Golgi apparatus, containing enzymes essential for penetrating the egg cell.

Lysosomes and Peroxisomes: Roles in Intracellular Digestion and Detoxification

44. Lysosome is formed from which of the following cell organelles?

    Asked in: UPSC CDS 1 2018

    1. Nucleus
    2. Endoplasmic reticulum
    3. Golgi bodies
    4. Ribosomes
    Show answer

    Answer: C. Golgi bodies

    Lysosomes are part of the endomembrane system and originate from the Golgi apparatus.

45. Which one of the following cell organelles mainly functions as storehouse of digestive enzymes?

    Asked in: UPSC CDS 1 2019

    1. Desmosome
    2. Ribosome
    3. Lysosome
    4. Vacuoles
    Show answer

    Answer: C. Lysosome

    Lysosomes are responsible for cellular digestion and waste breakdown.

46. Microbodies found to be present in plant and animal cells contain

    Asked in: UPSC CDS 1 2024

    1. broken down membranes
    2. enzymes
    3. acidic fluids
    4. waste metabolites
    Show answer

    Answer: B. enzymes

    Microbodies are known for containing enzymes involved in specific metabolic pathways.

47. Which one of the following cell organelles is known as 'suicide bags' of a cell ?

    Asked in: UPSC CDS 2 2019

    1. Lysosomes
    2. Plastids
    3. Endoplasmic reticulum
    4. Mitochondria
    Show answer

    Answer: A. Lysosomes

    Lysosomes contain digestive enzymes that can break down cellular components, leading to cell self-destruction under specific circumstances.

48. Which organelle in animal cells can digest foreign materials ?

    Asked in: UPSC CDS 2 2024

    1. Endoplasmic reticulum
    2. Lysosome
    3. Golgi body
    4. Mitochondria
    Show answer

    Answer: B. Lysosome

    - Lysosomes contain powerful digestive enzymes. - They are involved in phagocytosis (digestion of foreign particles) and autophagy (digestion of cellular components).

49. Which one of the following organelles of mammalian cell is rich in hydrolytic enzymes ?

    Asked in: UPSC NDA 1 2019

    1. Mitochondria
    2. Ribosomes
    3. Lysosome
    4. Nucleus
    Show answer

    Answer: C. Lysosome

    Lysosomes contain enzymes like proteases, lipases, nucleases, and glycosidases, which work optimally

50. If human blood is placed in a 2% detergent solution, what will happen to the RBC?

    Asked in: UPSC NDA 1 2021

    1. The RBC will shrink.
    2. The RBC will swell and become turgid.
    3. The RBC will swell and burst.
    4. The RBC will lyse.
    Show answer

    Answer: D. The RBC will lyse.

    Detergents are surfactants that disrupt cell membranes, which are primarily composed of lipid bilayers and proteins. Placing red blood cells (RBCs) in a detergent solution causes the detergent molecules to interact with and solubilize the lipids and proteins of the cell membrane. This disruption leads to the breakdown and disintegration of the cell membrane, a process called lysis.

Mitochondria: Structure, Cellular Respiration, and ATP Synthesis

51. The powerhouse of cell is

    Asked in: BPSC Prelims Exam 64th WBPSC CS Prelims 2022

    1. cell wall
    2. mitochondrion
    3. ribosome
    4. nucleus
    Show answer

    Answer: B. mitochondrion

    Mitochondria are often referred to as the "powerhouses" of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.

52. Which one of the following is the 'energy currency' for cellular processes?

    Asked in: UPSC CDS 1 2020

    1. Glucose
    2. ATP
    3. ADP
    4. Pyruvic acid
    Show answer

    Answer: B. ATP

    - ATP is a molecule that stores and releases energy in cells. - Energy from metabolic processes (like glucose breakdown) is stored in ATP. - Cells directly use the energy released from the hydrolysis of ATP for their activities.

53. Which one of the following cell organelles contains DNA?

    Asked in: UPSC CDS 1 2020

    1. Golgi apparatus
    2. Mitochondrion
    3. Lysosome
    4. Endoplasmic reticulum
    Show answer

    Answer: B. Mitochondrion

    Out of the options provided, only the mitochondrion contains its own DNA (mtDNA). The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids. Lysosomes contain digestive enzymes. The Endoplasmic reticulum is involved in protein and lipid synthesis and transport. None of these latter organelles contain DNA.

54. Which cell organelles have their own DNA and Ribosomes ?

    Asked in: UPSC CDS 1 2021

    1. Golgi body and Endoplasmic Reticulum
    2. Mitochondria and Plastids
    3. Lysosome and Golgi body
    4. Vacuole and Plastids
    Show answer

    Answer: B. Mitochondria and Plastids

    - Both mitochondria and plastids are believed to have originated through endosymbiosis, a process where prokaryotic cells were engulfed by early eukaryotic cells. - This evolutionary history explains why they retain their own DNA (circular, similar to bacterial DNA) and ribosomes (70S type, similar to bacterial ribosomes), separate from the nuclear DNA and cytoplasmic ribosomes (80S type) of the host cell.

55. Match List-I with List-II and select the correct answer using the code given below the Lists : List-I List-II (Cell Organelle) (Function)

    Asked in: UPSC CDS 2 2017

    1. Mitochondria 1. Photosynthesis
    2. Chloroplast 2. Protein synthesis
    3. Ribosomes 3. Intracellular digestion
    4. Lysosomes 4. ATP formation Code : A. A-3, B-1, C-2, D-4 B. A-2, B-1, C-4, D-3 C. A-4, B-1, C-2, D-3 D. A-4, B-2, C-1, D-3
    Show answer

    Answer: C. Ribosomes 3. Intracellular digestion

    Mitochondria are known as the powerhouses of the cell because they are the primary sites of cellular respiration, generating ATP. Chloroplasts are organelles found in plant cells and algae where photosynthesis takes place. Ribosomes are responsible for protein synthesis. Lysosomes contain hydrolytic enzymes that break down waste materials and cellular debris through intracellular digestion.

56. Which one of the following is the correct combination of organelles and their functions ?

    Asked in: UPSC CDS 2 2023

    1. Mitochondria – Respiration; Chloroplast – Photosynthesis; Ribosome – Protein Synthesis; Rough endoplasmic reticulum – Transport of pro‐ teins
    2. Mitochondria – Respiration; Chloroplast – Photosynthesis; Ribosome – Transport of pro‐ teins; Rough endoplasmic reticulum – Protein synthesis
    3. Mitochondria – Respiration; Chloroplast – Protein synthesis; Ribosome – Photosynthesis; Rough endoplasmic reticulum – Transport of pro‐ teins
    4. Mitochondria – Photosynthesis; Chloroplast – Respiration; Ribosome – Protein synthesis; Rough endoplasmic reticulum – Transport of pro‐ teins
    Show answer

    Answer: A. Mitochondria – Respiration; Chloroplast – Photosynthesis; Ribosome – Protein Synthesis; Rough endoplasmic reticulum – Transport of pro‐ teins

    Mitochondria are often called the "powerhouses" of the cell because they are the primary sites of cellular respiration, the process that generates ATP (energy) by breaking down glucose and other fuel molecules. Chloroplasts (found in plant cells and algae) are the sites of photosynthesis, where light energy is converted into chemical energy in the form of glucose. Ribosomes are responsible for protein synthesis, translating messenger RNA (mRNA) into polypeptide chains. The endoplasmic reticulum (ER) is a network of membranes involved in protein and lipid synthesis. The Rough ER is studded with ribosomes and is particularly involved in synthesizing proteins that are destined for secretion, insertion into membranes, or transport to other organelles. It also plays a role in folding and transporting these proteins.

57. Which of the following statements is/are true in reference to break-down of glucose? (i) In cytoplasm, glucose breaks down into pyruvate which has four carbon molecules (ii) Due to lack of oxygen, pyruvate gets converted to lactic acid (iii) In absence of oxygen, pyruvate gets converted to carbon dioxide and ethanol

    Asked in: CGPSC Prelims Exam 2021

    1. (i), (ii) and (iii)
    2. (i) and (iii)
    3. (ii) and (iii)
    4. Only (iii)
    Show answer

    Answer: C. (ii) and (iii)

    Statement (i) is incorrect. Glucose is a 6-carbon molecule, and during glycolysis in the cytoplasm, it breaks down into two molecules of pyruvate, each of which is a 3-carbon molecule. Statement (ii) is correct. In the absence of oxygen (anaerobic conditions), pyruvate can be converted to lactic acid through lactic acid fermentation, as seen in muscle cells during strenuous exercise or in some bacteria. Statement (iii) is correct. Also in the absence of oxygen, pyruvate can be converted to carbon dioxide and ethanol through alcoholic fermentation, as seen in yeast. Therefore, statements (ii) and (iii) are true.

Nucleus: Nuclear Envelope, Chromatin, Nucleolus, and Functions

58. Polynucleotide chain of DNA contains

    Asked in: UPSC CDS 1 2017

    1. a nitrogenous base, deoxyribose sugar and phosphate group
    2. a nitrogenous base, ribose sugar and phosphate group
    3. deoxyribose sugar, ribose sugar and phosphate group
    4. a nitrogenous base and phosphate group only
    Show answer

    Answer: A. a nitrogenous base, deoxyribose sugar and phosphate group

    Understanding the basic building blocks of DNA (nucleotides) and their components is fundamental to molecular biology.

59. Which one of the following statements regarding histone proteins is correct?

    Asked in: UPSC CDS 1 2019

    1. Histones are proteins that are present in mitochondrial membrane.
    2. Histones are proteins that are present in nucleus in association with DNA.
    3. Histones are proteins associated with lipids in the cytosol.
    4. Histones are proteins associated with carbo‐ hydrates in the cytosol.
    Show answer

    Answer: B. Histones are proteins that are present in nucleus in association with DNA.

    Histone proteins are primarily located in the nucleus where they bind to DNA to help package it into chromatin.

60. In plant cells, RNA is present in

    Asked in: UPSC CDS 1 2023

    1. cytoplasm only
    2. nuclei and cytoplasm only
    3. nuclei, cytoplasm, mitochondria, chloroplast and endoplasmic reticulum
    4. nuclei, cytoplasm, mitochondria, chloroplast and ribosomes
    Show answer

    Answer: D. nuclei, cytoplasm, mitochondria, chloroplast and ribosomes

    RNA's presence in mitochondria and chloroplasts reflects their endosymbiotic origin and semi- autonomous nature, possessing their own genetic systems.

61. Which cells in human body have no nucleus?

    Asked in: UPSC CDS 1 2024

    1. Muscle cells
    2. Phagocytic cells
    3. Red blood cells
    4. Ciliated cells
    Show answer

    Answer: C. Red blood cells

    Mature mammalian red blood cells (erythrocytes) are unique among human cells in that they extrude their nucleus during development. This anucleated state, along with the absence of other organelles like mitochondria, maximizes the space available within the cell for hemoglobin, which is essential for oxygen transport.

62. Which of the following cells do not contain nucleus? 1. Root hair cells 2. Red blood cells 3. Platelets 4. Monocytes Select the correct answer using the code given below.

    Asked in: UPSC CDS 2 2016

    1. 1 only
    2. 2 and 3 only
    3. 1, 2 and 4
    4. 2, 3 and 4
    Show answer

    Answer: B. 2 and 3 only

    - Statement 1: Root hair cells are specialized epidermal cells of plant roots involved in water and nutrient absorption. They are eukaryotic cells and do contain a nucleus, cytoplasm, and other organelles. - Statement 2: Mature mammalian red blood cells (erythrocytes) are anucleated, meaning they lose their nucleus during maturation. This allows them to maximize the space available for hemoglobin, increasing oxygen-carrying capacity. - Statement 3: Platelets (thrombocytes) are not complete cells but are small, irregular fragments of cytoplasm derived from megakaryocytes found in bone marrow. They lack a nucleus. They play a crucial role in blood clotting. - Statement 4: Monocytes are a type of white blood cell (leukocyte) and are part of the immune system. They are large, mononuclear cells, meaning they do contain a prominent, often kidney-shaped or lobed nucleus. - Therefore, among the given options, only red blood cells and platelets lack a nucleus.

63. In plant cells

    Asked in: UPSC CDS 2 2022

    1. Nucleus does not need a membrane but chloroplasts are surrounded by their own mem‐ brane.
    2. Nucleus and chloroplasts are surrounded sep‐ arately by their own membrane.
    3. Nucleus is surrounded by membrane but chloroplasts do not need membrane.
    4. Both nucleus and chloroplasts are not surrounded by any membrane.
    Show answer

    Answer: B. Nucleus and chloroplasts are surrounded sep‐ arately by their own membrane.

    - The nucleus in plant cells is a prominent organelle enclosed by a double membrane known as the nuclear envelope. - Chloroplasts, the sites of photosynthesis in plant cells, are also enclosed by a double membrane. Therefore, both the nucleus and chloroplasts are surrounded separately by their own membranes.

64. Chromosomes are composed of DNA and :

    Asked in: UPSC CDS 2 2023

    1. lipids
    2. vitamins
    3. proteins
    4. carbohydrates
    Show answer

    Answer: C. proteins

    The DNA carries the genetic information, while the proteins, especially histones, play a crucial role in packaging and organizing the DNA within the limited space of the nucleus. This DNA-protein complex is known as chromatin.

Plasma Membrane: Fluid Mosaic Model, Structure, and Functions

65. Osmosis is the process of movement of water molecules from its

    Asked in: UPSC CDS 1 2021

    1. higher concentration to its lower concentration through a cell wall.
    2. lower concentration to its higher concentration through a fully permeable membrane.
    3. higher concentration to its lower concentration through a fully permeable membrane.
    4. higher concentration to its lower concentration through a semi-permeable membrane.
    Show answer

    Answer: D. higher concentration to its lower concentration through a semi-permeable membrane.

    - The key components of osmosis are the movement of solvent (water), the direction from higher to lower water concentration/potential, and the presence of a semi-permeable membrane. - A semi- permeable membrane allows solvent molecules to pass through but restricts the passage of solute molecules.

66. Which one of the following statements is correct about the cell membrane ?

    Asked in: UPSC CDS 1 2022

    1. It is made up of cellulose.
    2. It is a permeable structure for all substances.
    3. It is flexible and enables the cell to engulf many materials.
    4. It does not allow diffusion of gases like oxygen and carbon dioxide.
    Show answer

    Answer: C. It is flexible and enables the cell to engulf many materials.

    The cell membrane is primarily composed of a lipid bilayer with embedded proteins (fluid mosaic model). This structure is flexible and allows the cell to change shape and engulf substances from the external environment through processes like endocytosis (e.g., phagocytosis and pinocytosis), which is essential for functions like nutrition or defence.

67. Which one of the following is active transport ?

    Asked in: UPSC CDS 2 2019

    1. It is the movement of a substance against a diffusion gradient with the use of energy from respiration.
    2. It is the movement of a substance against a diffusion gradient without the use of energy.
    3. It is the movement of a substance against a diffusion gradient with the use of energy from photosynthesis.
    4. It is the movement of a substance along a diffusion gradient with the use of energy from respiration.
    Show answer

    Answer: A. It is the movement of a substance against a diffusion gradient with the use of energy from respiration.

    Active transport is characterized by the movement against a concentration gradient and the requirement of energy expenditure by the cell.

68. Which one of the following is a feature of Membrane ?

    Asked in: UPSC CDS 2 2022

    1. Bilayer of phospholipid molecule in which proteins and cholesterol are embedded
    2. Bilayer of proteins molecule in which lipid and cholesterol are embedded
    3. Bilayer of neutral lipid in which proteins and cholesterol are embedded
    4. Bilayer of neutral lipid lacking cholesterol and proteins
    Show answer

    Answer: A. Bilayer of phospholipid molecule in which proteins and cholesterol are embedded

    - The fluid mosaic model describes the structure of the cell membrane. - It consists of a double layer (bilayer) of phospholipid molecules, with their hydrophilic heads facing outwards and inwards, and hydrophobic tails facing each other in the interior. - Various proteins are embedded within, associated with, or spanning this lipid bilayer, performing functions like transport, signaling, and enzymatic activity. - Cholesterol molecules are also interspersed within the phospholipid bilayer in animal cells, helping to regulate membrane fluidity.

69. In the following simplified diagram of a plant cell, five parts/organelles are marked from 1 to 5 : [Image of a plant cell diagram with labels 1-5] Which one of the following correctly represents the above parts/organelles ?

    Asked in: UPSC CDS 2 2023

    1. 1 – cell membrane; 2 – cell wall; 3 – vacuole; 4 – endoplasmic reticulum; 5 – nucleus
    2. 1 – cell wall; 2 – cell membrane; 3 – endoplas‐ mic reticulum; 4 – nucleus; 5 – vacuole
    3. 1 – cell wall; 2 – cell membrane; 3 – endoplas‐ mic reticulum; 4 – vacuole; 5 – nucleus
    4. 1 – cell wall; 2 – cell membrane; 3 – vacuole; 4 – endoplasmic reticulum; 5 – nucleus
    Show answer

    Answer: D. 1 – cell wall; 2 – cell membrane; 3 – vacuole; 4 – endoplasmic reticulum; 5 – nucleus

    Identifying key features of plant cells, such as the presence of a cell wall outside the cell membrane and a large central vacuole, is crucial for interpreting such diagrams. The relative position and appearance of organelles like the nucleus and endoplasmic reticulum within the cytoplasm should also be considered.

70. Which of the following features are found in cells of meristematic tissues in plants?

    Asked in: UPSC Geoscientist 2020

    1. Cells active with thick cellulose walls
    2. Cells active with little cytoplasm and thin cellulose walls
    3. Cells active with dense cytoplasm, thick cellulose walls, and no nuclei
    4. Cell active with dense cytoplasm, thin cellu‐ lose walls and prominent nuclei
    Show answer

    Answer: D. Cell active with dense cytoplasm, thin cellu‐ lose walls and prominent nuclei

    Meristematic tissue consists of actively dividing cells responsible for growth in plants. These cells are characterized by dense cytoplasm, thin cellulose cell walls, and prominent nuclei, which are features necessary for high metabolic activity and rapid cell division.

71. Which one of the following processes describes the movement of particles or molecules from a region of higher concentration to a region of lower concentration ?

    Asked in: UPSC Geoscientist 2024

    1. Diffusion
    2. Osmosis
    3. Plasmolysis
    4. Deplasmolysis
    Show answer

    Answer: A. Diffusion

    Diffusion is the movement of particles from high to low concentration.

Prokaryotic and Eukaryotic Cells: Structural Organization and Differences

72. Which of the following does not have any enzyme in its cells?

    Asked in: BPSC Prelims Exam 65th

    1. Lichen
    2. Virus
    3. Bacteria
    4. Algae
    Show answer

    Answer: B. Virus

    Viruses are acellular and lack their own metabolic enzymes, relying on the host cell's machinery.

73. Glucose is converted to ethyl alcohol by the enzyme

    Asked in: BPSC Prelims Exam 66th

    1. maltase
    2. invertase
    3. zymase
    4. diastase
    Show answer

    Answer: C. zymase

    Alcoholic fermentation is the process by which sugars like glucose are converted into ethanol and carbon dioxide. This complex biochemical pathway is carried out by microorganisms, typically yeast, and involves a series of enzymatic reactions. The collective enzymatic system responsible for the conversion of simple sugars (like glucose or fructose) to ethanol is historically known as zymase. Zymase is not a single enzyme but rather a complex of enzymes found in yeast cells, including enzymes from glycolysis and alcohol dehydrogenase.

74. Bacteria have an undefined nuclear region which lacks a nuclear membrane and contains only DNA without proteins. Such a region is called :

    Asked in: UPSC CDS 2 2023

    1. Nucleosome
    2. Nucleus
    3. Nucleoprotein
    4. Nucleoid
    Show answer

    Answer: D. Nucleoid

    The nucleoid contains the genomic DNA and associated proteins in a prokaryotic cell, but it is not enclosed by a nuclear membrane, distinguishing it from the true nucleus found in eukaryotic cells.

75. Which one of the following has non- nucleated cells at maturity?

    Asked in: UPSC Geoscientist 2023

    1. Xylem parenchyma
    2. Xylem fibre
    3. Palisade parenchyma
    4. Companion cell
    Show answer

    Answer: B. Xylem fibre

    Different types of plant cells have varying structures and functions, and their state at maturity (living or dead, presence or absence of organelles like nucleus) differs.

76. All life forms contain “molecules of life”.

    Asked in: UPSC NDA 1 2015

    1. Carbohydrates
    2. Proteins
    3. Nucleic acids
    4. All of the above
    Show answer

    Answer: D. All of the above

    These are These three types of molecules play crucial roles: Carbohydrates are primary energy sources and structural components; Proteins perform a vast array of functions including enzymes, structural support, and transport; Nucleic acids carry genetic information (DNA) and are involved in protein synthesis (RNA). Lipids are also often considered a fourth major class of biomolecules.

77. Which one of the following is an organelle that is NOT found in prokaryotic cells?

    Asked in: UPSC NDA 1 2018

    1. Cell wall
    2. Mitochondria
    3. Plasma membrane
    4. Ribosome
    Show answer

    Answer: B. Mitochondria

    Prokaryotic cells (like bacteria and archaea) are structurally simpler than eukaryotic cells. A key difference is the absence of membrane-bound organelles in prokaryotes. A) Cell wall: Many prokaryotes have a cell wall (though different in composition from eukaryotic cell walls like those in plants or fungi). B) Mitochondria: Mitochondria are membrane-bound organelles responsible for cellular respiration and ATP production in eukaryotic cells. They are not found in prokaryotic cells. In prokaryotes, respiration occurs in the cytoplasm and across the cell membrane. C) Plasma membrane: The plasma membrane (cell membrane) surrounds the cytoplasm and is present in all cells, both prokaryotic and eukaryotic. D) Ribosome: Ribosomes are responsible for protein synthesis and are found in the cytoplasm of all cells, both prokaryotic and eukaryotic (though prokaryotic ribosomes are 70S, and eukaryotic ribosomes are 80S).

78. Which one of the following structures is not present in a prokaryotic cell ?

    Asked in: UPSC NDA 1 2023

    1. Cell wall
    2. Ribosomes
    3. Nucleus
    4. Plasma membrane
    Show answer

    Answer: C. Nucleus

    Prokaryotic cells (like bacteria and archaea) are characterized by the absence of membrane-bound organelles. The nucleus is a membrane-bound organelle that houses the genetic material in eukaryotic cells. In prokaryotic cells, the genetic material (usually a single circular chromosome) is located in a region called the nucleoid, but it is not enclosed within a membrane. Cell walls are typically present in most prokaryotes, providing structural support. Ribosomes are present in prokaryotic cells and are essential for protein synthesis (prokaryotic ribosomes are smaller, 70S, compared to eukaryotic 80S). The plasma membrane (cell membrane) is a fundamental component present in all types of cells, both prokaryotic and eukaryotic, enclosing the cytoplasm.

Ribosomes: Structure and Role in Protein Synthesis

79. Most of the enzymes are

    Asked in: BPSC Prelims Exam 67th Re Exam

    1. lipids
    2. acids
    3. alkalis
    4. proteins
    Show answer

    Answer: D. proteins

    Most enzymes are biological catalysts that are protein molecules.

80. Biological catalysts are protein molecules which 1. speed up a chemical reaction 2. remain unchanged after reaction 3. function optimally at 37 °C 4. do not have an enzymatic activity Select the correct answer using the code given below.

    Asked in: UPSC CDS 2 2016

    1. 1 only
    2. 1, 2 and 3
    3. 2 and 3 only
    4. 1, 3 and 4
    Show answer

    Answer: B. 1, 2 and 3

    - Biological catalysts are enzymes, which are indeed protein molecules (with a few exceptions like catalytic RNA). - Statement 1 is correct: Enzymes are catalysts, meaning they increase the rate of a chemical reaction without being consumed in the process. - Statement 2 is correct: Like all catalysts, enzymes are not permanently altered or used up during the reaction and can be reused. - Statement 3 is generally correct in the context of human enzymes: Many enzymes in the human body function optimally at physiological temperature, which is around 37 °C. However, the optimal temperature varies greatly among enzymes from different organisms (e.g., enzymes from thermophilic bacteria function at much higher temperatures). Assuming the question refers to typical biological contexts like the human body, this statement is considered correct. - Statement 4 is incorrect: Biological catalysts are enzymes, and their activity is enzymatic activity. This statement directly contradicts the definition. - Based on the statements, 1 and 2 are universally true for catalysts. Statement 3 is true for a common subset of biological catalysts (human enzymes). Statement 4 is false. The option including 1, 2, and 3 is the most fitting choice.

81. In a mammalian cell, protein is synthesized on:

    Asked in: UPSC Geoscientist 2021

    1. Golgi apparatus
    2. Plasma membrane
    3. Lysosomes
    4. Rough endoplasmic reticulum
    Show answer

    Answer: D. Rough endoplasmic reticulum

    Ribosomes are the sites of protein synthesis, and they are associated with the RER for specific types of proteins.

82. Ribozymes are

    Asked in: JPSC CS Prelims 2016

    1. DNA
    2. RNA
    3. Proteins
    4. None of these
    Show answer

    Answer: B. RNA

    Ribozymes are RNA molecules that possess catalytic activity. While most biological enzymes are proteins, some RNA molecules can also catalyze biochemical reactions. This catalytic RNA is called a ribozyme.

83. Venkataram Ramakrishnan and his co- worker got the Nobel Prize in 2009. There investigation was on the structural characterization of Ribosomes and they used the experimental organism viz.

    Asked in: KPSC KAS Prelims 2014

    1. Pyrolobtus fumarli
    2. Sulfobolus thurbers
    3. Methanopyrus Kandiers
    4. Thermus thermophilus
    Show answer

    Answer: D. Thermus thermophilus

    - The 2009 Nobel Prize in Chemistry was awarded for structural studies of the ribosome. - Thermus thermophilus is a thermophilic bacterium commonly used in structural biology due to the stability of its macromolecules. - Ramakrishnan, Steitz, and Yonath utilized ribosomal components from various organisms, including Thermus thermophilus and Haloarcula marismortui, for their prize-winning work.

84. Which of the following statements is/are correct? (1) mRNA (2) (3) (4) mRNA

    Asked in: KPSC KAS Prelims 2024

    1. (1)
    2. (2)
    3. (3)
    4. (4)
    Show answer

    Answer: D. (4)

    The question tests the understanding of the central dogma of molecular biology and the roles of different types of RNA (mRNA, tRNA, rRNA) in gene expression. Each statement accurately describes a fundamental function of these molecules.

85. The molecule acting as a second messenger in the biological system is

    Asked in: KPSC KAS Prelims 2024

    1. cDNA
    2. cAMP
    3. tRNA
    4. hnRNA
    Show answer

    Answer: B. cAMP

    cAMP (cyclic adenosine monophosphate) is a crucial second messenger involved in many signal transduction pathways within cells. It relays signals from many hormones and neurotransmitters that bind to G protein-coupled receptors on the cell surface.

Vacuoles: Types and Functions (Storage, Turgor)

86. Which one of the following statements about starch and glycogen is correct ?

    Asked in: UPSC CDS 2 2022

    1. Both starch and glycogen are found in plant cells.
    2. Both starch and glycogen are found in animal cells.
    3. Starch is present in plant cells and glycogen is present in animal cells.
    4. Both starch and glycogen are present in plant cells as well as animal cells.
    Show answer

    Answer: C. Starch is present in plant cells and glycogen is present in animal cells.

    - Starch is the primary storage carbohydrate in plants. It is stored in plastids (like chloroplasts and amyloplasts) and is the main form of carbohydrate consumed by humans from plant sources (e.g., grains, potatoes). - Glycogen is the primary storage carbohydrate in animals and fungi. In animals, it is primarily stored in the liver and muscles, where it can be quickly mobilized to provide glucose for energy. Therefore, starch is characteristic of plant cells, while glycogen is characteristic of animal cells.

87. Which one of the following statements about 'vacuoles' is not correct?

    Asked in: UPSC NDA 1 2022

    1. In plants, there is a large central vacuole that may occupy 90% of total cell volume.
    2. In plant cells, vacuoles provide turgidity and rigidity.
    3. In Amoeba, vacuoles have role in nutrition.
    4. Vacuoles are absent in animal cells.
    Show answer

    Answer: D. Vacuoles are absent in animal cells.

    Vacuoles are present in both plant and animal cells, but their size and primary functions differ significantly.

88. Which one of the following cell organelles may play a role in expelling excess water and wastes in case of unicellular organisms ?

    Asked in: UPSC NDA 2 2020

    1. Lysosome
    2. Vacuole
    3. Golgi body
    4. Endoplasmic reticulum
    Show answer

    Answer: B. Vacuole

    - Vacuoles in unicellular organisms can include contractile vacuoles, which are vital for maintaining osmotic balance by expelling excess water. - Lysosomes are involved in intracellular digestion. - Golgi body (or Golgi apparatus) is involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. - Endoplasmic reticulum is involved in protein and lipid synthesis.

89. In plant cells, the turgidity and rigidity is provided by

    Asked in: UPSC CAPF 2019

    1. ribosomes
    2. mitochondria
    3. golgi apparatus
    4. vacuoles full of cell sap
    Show answer

    Answer: D. vacuoles full of cell sap

    - Turgor pressure is the pressure exerted by the cell contents (driven by the vacuole) against the cell wall. - The cell wall provides structural support and prevents bursting. - Together, turgor pressure and the cell wall make the plant cell turgid and rigid.

90. Which of the following best represents the cells of a meristem of plant?

    Asked in: UPSC CAPF 2022

    1. Dense cytoplasm, thin cell wall, large nuclei and absence of vacuoles
    2. Dense cytoplasm, thin cell wall, large nuclei and large vacuoles
    3. Dense cytoplasm, thin cell wall, small nuclei and absence of vacuoles
    4. Dense cytoplasm, thick cell wall, small nuclei and large vacuoles
    Show answer

    Answer: A. Dense cytoplasm, thin cell wall, large nuclei and absence of vacuoles

    Meristematic cells are undifferentiated plant cells that are actively undergoing cell division. Characteristics of these cells include dense cytoplasm, thin primary cell walls (as they are rapidly growing and dividing), relatively large and prominent nuclei (controlling the cell cycle), and usually small or absent vacuoles, which would otherwise occupy significant volume and potentially hinder rapid division.