Part 1 — Cell Theory, Cell as Unit of Life; Prokaryotic vs Eukaryotic Cells (Q1–25)

Part 1 — Cell Theory, Cell as Unit of Life; Prokaryotic vs Eukaryotic Cells; Cell Envelope; Basic Organelles & Endomembrane System (Q1–25)

Q1.

Who proposed the Cell Theory that “All living organisms are composed of cells and cell products”?
A. Antonie van Leeuwenhoek
B. Matthias Schleiden and Theodor Schwann ✅
C. Robert Hooke
D. Louis Pasteur

Explanation:

• A. Antonie van Leeuwenhoek: Pioneering microscopist who observed microbes but did not formulate the general cell theory.

• B. Matthias Schleiden and Theodor Schwann (Correct): Schleiden (plants) and Schwann (animals) formulated the classical cell theory (1838–1839) that all living things are made of cells.

• C. Robert Hooke: Coined the term “cell” after observing cork (1665), but did not articulate the full cell theory.

• D. Louis Pasteur: Famous for germ theory and disproving spontaneous generation, not for cell theory formulation.

Q2.

Which statement best describes the modern cell theory?
A. Cells arise only from pre-existing cells ✅
B. All organisms are made of one cell only
C. Cells have no biochemical processes
D. Cells are static and unchanging

Explanation:

• A. Cells arise only from pre-existing cells (Correct): Modern cell theory includes (1) all organisms are composed of cells, (2) cell is the basic unit of life, and (3) cells arise by division of pre-existing cells (Virchow).

• B. All organisms are made of one cell only: False; organisms can be unicellular or multicellular.

• C. Cells have no biochemical processes: False; cells carry out metabolism and all biochemical reactions.

• D. Cells are static and unchanging: False; cells grow, divide, differentiate, and respond to stimuli.

Q3.

Which of the following is a true distinction between prokaryotic and eukaryotic cells?
A. Prokaryotes have membrane-bound nucleus; eukaryotes lack it
B. Prokaryotes have 80S ribosomes; eukaryotes have 70S ribosomes
C. Prokaryotes lack membrane-bound organelles; eukaryotes have membrane-bound organelles ✅
D. Prokaryotes have linear DNA; eukaryotes have circular DNA

Explanation:

• A. Reversed and incorrect — prokaryotes lack membrane-bound nucleus, eukaryotes have it.

• B. Wrong — prokaryotes have 70S ribosomes; eukaryotes have 80S ribosomes (except mitochondria/chloroplasts).

• C. Correct — hallmark difference: prokaryotes lack membrane-bound organelles (no ER, Golgi, mitochondria), while eukaryotes possess them.

• D. Incorrect generalization — prokaryotes typically have circular DNA; eukaryotes have linear chromosomes in nucleus.

Q4.

Which structure is characteristic of prokaryotic cells but not eukaryotic cells?
A. Mitochondrion
B. Plasmid ✅
C. Endoplasmic reticulum
D. Golgi apparatus

Explanation:

• A. Mitochondrion: Membrane-bound organelle found in eukaryotes, absent in prokaryotes.

• B. Plasmid (Correct): Small, circular extrachromosomal DNA commonly present in bacteria (prokaryotes); rare in eukaryotes (though plasmids can be used experimentally).

• C. Endoplasmic reticulum: Eukaryotic membrane-bound organelle; absent in prokaryotes.

• D. Golgi apparatus: Eukaryotic only.

Q5.

Which pair correctly matches cell wall composition with the organism?
A. Bacteria — Cellulose, Plants — Peptidoglycan
B. Bacteria — Peptidoglycan, Fungi — Chitin ✅
C. Plants — Chitin, Fungi — Cellulose
D. Animals — Peptidoglycan, Bacteria — Cellulose

Explanation:

• A. Incorrect — bacteria do not have cellulose walls; plants do.

• B. Correct — bacterial walls are primarily peptidoglycan (murein); fungal walls are mainly chitin. Plant walls are cellulose.

• C. Incorrect swap.

• D. Wrong — animals lack cell walls.

Q6.

The fluid mosaic model of membrane structure was proposed by:
A. Davson and Danielli
B. Singer and Nicolson ✅
C. Robertson
D. Singer and Robertson

Explanation:

• A. Davson and Danielli: Proposed an earlier “protein-lipid sandwich” model (static proteins), later replaced.

• B. Singer and Nicolson (Correct): Introduced the fluid mosaic model (1972) describing proteins embedded in a fluid phospholipid bilayer that can move laterally.

• C. Robertson: Proposed unit membrane concept but not the modern fluid mosaic model.

• D. Singer and Robertson: Not correct pairing.

Q7.

Which of the following is NOT part of the endomembrane system?
A. Nuclear envelope
B. Endoplasmic reticulum
C. Golgi apparatus
D. Mitochondrion ✅

Explanation:

• A. Nuclear envelope: Yes — continuous with ER, so included.

• B. ER: Central component of endomembrane system.

• C. Golgi apparatus: Yes — processes and ships proteins/lipids within system.

• D. Mitochondrion (Correct): Not part of endomembrane system; mitochondria are semi-autonomous organelles with separate origin and membranes.

Q8.

Which organelle is primarily responsible for protein synthesis?
A. Mitochondrion
B. Ribosome ✅
C. Lysosome
D. Golgi body

Explanation:

• A. Mitochondrion: Produces ATP and houses some of its own protein synthesis machinery, but general protein synthesis occurs on ribosomes.

• B. Ribosome (Correct): Sites of translation — synthesize polypeptides; found free in cytosol or attached to rough ER.

• C. Lysosome: Digestive organelle with hydrolytic enzymes.

• D. Golgi body: Modifies, sorts, and packages proteins, not primary site of synthesis.

Q9.

Which of the following statements about rough endoplasmic reticulum (RER) is true?
A. RER lacks ribosomes and synthesizes lipids
B. RER has ribosomes and synthesizes secretory and membrane proteins ✅
C. RER is the site of ATP production
D. RER digests cellular waste

Explanation:

• A. False — RER has ribosomes and synthesizes proteins; smooth ER lacks ribosomes.

• B. Correct — ribosomes on RER synthesize proteins destined for secretion, membrane insertion, or lysosomes.

• C. False — mitochondria produce ATP.

• D. False — lysosomes digest waste.

Q10.

Which cellular structure modifies, sorts and packages proteins for secretion?
A. Endoplasmic reticulum
B. Golgi apparatus ✅
C. Mitochondrion
D. Ribosome

Explanation:

• A. ER: Synthesizes proteins and lipids; initial folding and glycosylation occur here but final processing occurs in Golgi.

• B. Golgi apparatus (Correct): Cis→trans polarity; modifies (e.g., glycosylation), sorts, packages proteins into vesicles for secretion or delivery.

• C. Mitochondrion: Energy production.

• D. Ribosome: Protein synthesis, not post-translational processing and sorting.

Q11.

Which organelle contains hydrolytic enzymes and functions in intracellular digestion?
A. Lysosome ✅
B. Peroxisome
C. Vacuole
D. Golgi body

Explanation:

• A. Lysosome (Correct): Membrane-bound organelle with acid hydrolases for digestion, autophagy, and phagosome digestion.

• B. Peroxisome: Contains oxidases/catalase for detoxifying peroxides, not general hydrolytic digestion.

• C. Vacuole: In plants, central vacuole stores substances and can be lytic in some cases, but classical lysosomes are the primary digesters.

• D. Golgi body: Processes proteins and makes lysosomal enzymes but not the digestive action itself.

Q12.

Which statement about mitochondria is CORRECT?
A. Mitochondria are single-membraned and lack DNA
B. Mitochondria have inner membrane folded into cristae and contain their own DNA ✅
C. Mitochondria are part of the endomembrane system
D. Mitochondria produce proteins for secretion

Explanation:

• A. Incorrect — mitochondria are double-membraned and contain circular DNA.

• B. Correct — inner membrane cristae increase surface area for oxidative phosphorylation; mitochondria have their own 70S ribosomes and mtDNA.

• C. Incorrect — mitochondria are not part of the endomembrane system.

• D. Incorrect — while mitochondria synthesize some of their own proteins, they do not produce secretory proteins.

Q13.

Which plastid is specialized for photosynthesis?
A. Leucoplast
B. Chromoplast
C. Chloroplast ✅
D. Peroxisome

Explanation:

• A. Leucoplast: Non-pigmented plastids for storage (starch, oil).

• B. Chromoplast: Pigmented plastids (carotenoids) for color, not photosynthesis primarily.

• C. Chloroplast (Correct): Contain chlorophyll and thylakoid membranes (grana) where photosynthesis occurs.

• D. Peroxisome: Microbody for oxidation reactions, not a plastid.

Q14.

Which cellular components form the cytoskeleton?
A. Cellulose and lignin
B. Microfilaments (actin), microtubules (tubulin) and intermediate filaments ✅
C. Phospholipids and proteins of membrane
D. Ribosomes and proteasomes

Explanation:

• A. Components of plant cell wall, not cytoskeleton.

• B. Correct — cytoskeleton is a network of microfilaments (actin), microtubules (tubulin), and intermediate filaments (in many eukaryotes) that provide structure, transport tracks, and motility.

• C. Membrane components but not the cytoskeleton.

• D. Ribosomes/proteasomes are not structural cytoskeletal elements.

Q15.

The typical axoneme structure of eukaryotic cilia and flagella is:
A. 9 + 2 microtubule arrangement ✅
B. 9 + 0 triplets
C. 3 + 3 microfilament array
D. Random microtubule arrangement

Explanation:

• A. 9 + 2 (Correct): Nine peripheral doublet microtubules surrounding a central pair — characteristic of motile eukaryotic cilia/flagella.

• B. 9 + 0 triplets: Describes centriole/ basal body (9 triplet microtubules, no central pair).

• C. 3 + 3: Not a valid structural motif.

• D. Random: Incorrect — highly ordered structure.

Q16.

Which structure is involved in formation of microtubules and organization of mitotic spindle in animal cells?
A. Nucleolus
B. Centriole (centrosome) ✅
C. Lysosome
D. Golgi body

Explanation:

• A. Nucleolus: Site of rRNA synthesis, not microtubule organization.

• B. Centriole/centrosome (Correct): Centrosome contains a pair of centrioles (9 triplets) and organizes microtubules and spindle poles in animal cells; centrioles are generally absent in higher plant cells.

• C. Lysosome: Digestive organelle.

• D. Golgi body: Protein processing/packaging.

Q17.

Which of the following is a function of the plasma membrane?
A. Protein synthesis only
B. Selective permeability and cell signalling ✅
C. DNA replication only
D. Photosynthesis

Explanation:

• A. Plasma membrane is not the site of protein synthesis (ribosomes are).

• B. Correct — the membrane controls movement of substances (selective permeability), has receptors for signalling, and supports cell adhesion.

• C. DNA replication occurs in nucleus/organelles.

• D. Photosynthesis occurs in chloroplasts in plants.

Q18.

Which transport process requires ATP directly?
A. Simple diffusion
B. Facilitated diffusion
C. Primary active transport (e.g., Na⁺/K⁺ pump) ✅
D. Osmosis

Explanation:

• A. Simple diffusion: Passive, no energy.

• B. Facilitated diffusion: Passive via carriers or channels, no ATP.

• C. Primary active transport (Correct): Uses ATP hydrolysis to transport ions/molecules against gradients (e.g., Na⁺/K⁺ ATPase).

• D. Osmosis: Passive movement of water down its gradient.

Q19.

Which of these best describes endocytosis?
A. Export of large molecules from cell
B. Uptake of substances by invagination of plasma membrane into vesicles ✅
C. Movement of gases across membrane
D. Synthesis of vesicles in Golgi body only

Explanation:

• A. Export is exocytosis, not endocytosis.

• B. Correct — endocytosis involves plasma membrane folding in to form vesicles (phagocytosis, pinocytosis, receptor-mediated endocytosis).

• C. Gas movement is diffusion, not endocytosis.

• D. Vesicle formation also occurs at the plasma membrane and ER, not exclusively Golgi.

Q20.

Which statement about ribosomes is CORRECT?
A. Eukaryotic cytosolic ribosomes are 70S
B. Prokaryotic ribosomes are 80S
C. Ribosomes are composed of rRNA and proteins and are sites of translation ✅
D. Ribosomes are membrane-bound organelles with double membranes

Explanation:

• A. Incorrect — eukaryotic cytosolic ribosomes are 80S (60S + 40S).

• B. Incorrect — prokaryotic ribosomes are 70S (50S + 30S).

• C. Correct — ribosomes consist of rRNA and proteins and synthesize polypeptides by translating mRNA.

• D. Incorrect — ribosomes are non-membranous.

Q21.

Which microbody contains catalase and functions in detoxification of hydrogen peroxide?
A. Lysosome
B. Peroxisome ✅
C. Glyoxysome
D. Vacuole

Explanation:

• A. Lysosome: Digestive hydrolytic enzymes, not primarily catalase.

• B. Peroxisome (Correct): Microbody with oxidases and catalase for detoxifying H₂O₂; important in lipid metabolism.

• C. Glyoxysome: Specialized microbody in plants (germinating seeds) converting fats to carbohydrates.

• D. Vacuole: Storage, osmotic balance.

Q22.

Which of the following statements is TRUE about the nuclear envelope?
A. It is single-membraned and impermeable
B. It is double-membraned and continuous with rough ER ✅
C. It has no pores and isolates nucleus completely
D. It is absent in eukaryotes

Explanation:

• A. Incorrect — it is a double membrane (inner & outer).

• B. Correct — outer membrane is continuous with rough ER; nuclear pores allow selective transport of molecules.

• C. Incorrect — nuclear pores exist to allow RNA/protein traffic.

• D. Incorrect — nuclear envelope defines eukaryotic nucleus.

Q23.

Which organelle is the principal site for lipid synthesis and detoxification of drugs?
A. Rough ER
B. Smooth ER ✅
C. Golgi apparatus
D. Lysosome

Explanation:

• A. RER: Associated with protein synthesis due to ribosomes.

• B. Smooth ER (Correct): Lacks ribosomes; synthesizes lipids, steroids, and detoxifies xenobiotics; stores Ca²⁺ in muscle (sarcoplasmic reticulum).

• C. Golgi: Protein modification and sorting.

• D. Lysosome: Digestion.

Q24.

Which structure is primarily responsible for maintaining turgor pressure in plant cells?
A. Cell membrane
B. Vacuole ✅
C. Chloroplast
D. Mitochondrion

Explanation:

• A. Cell membrane: Controls exchange but turgor maintained by internal osmotic pressure.

• B. Vacuole (Correct): Large central vacuole stores water and solutes; osmotic pressure pushes cytoplasm against cell wall (turgor).

• C. Chloroplast: Photosynthesis.

• D. Mitochondrion: Energy production.

Q25.

Which statement about chromatin is correct?
A. Chromatin = DNA + histone proteins; condenses into chromosomes during cell division ✅
B. Chromatin is only RNA and never DNA
C. Chromatin is found in prokaryotic nucleus
D. Chromatin lacks any proteins

Explanation:

• A. Correct: Chromatin is the complex of DNA packaged with histone (and non-histone) proteins; it condenses into visible chromosomes during mitosis/meiosis in eukaryotes.

• **B. Incorrect — chromatin is primarily DNA + proteins, not only RNA.

• **C. Incorrect — prokaryotes lack a true nucleus; DNA exists as nucleoid but not chromatin in same histone-bound form (though some prokaryotes have histone-like proteins).

• **D. Incorrect — chromatin includes histones and other proteins essential for packaging and regulation.

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