Part 4 — Cell Envelope, Cell Membrane, Cell Wall, Membrane Transport, Endomembrane System (Q76–100)

Q76.

Which model of the plasma membrane is widely accepted today?
A. Unit membrane model
B. Protein-lipid sandwich model
C. Fluid mosaic model ✅
D. Lamellar model

Explanation:

A. Unit membrane model: Robertson (1959), outdated.
B. Protein-lipid sandwich: Davson & Danielli, rigid & incorrect.
C. Fluid mosaic model (Correct): Singer & Nicolson (1972); dynamic phospholipid bilayer with proteins.
D. Lamellar model: Not valid.

Q77.

Which is the major structural component of biological membranes?
A. DNA
B. Phospholipids ✅
C. Proteins only
D. Steroids only

Explanation:

A. DNA: Not part of membranes.
B. Phospholipids (Correct): Form bilayer with hydrophobic tails and hydrophilic heads.
C. Proteins: Integral/peripheral proteins embedded, but not the base framework.
D. Steroids (cholesterol): Important regulators of fluidity, not primary structure.

Q78.

Cholesterol in animal cell membranes functions to:
A. Increase fluidity only
B. Decrease fluidity only
C. Buffer membrane fluidity (maintain stability) ✅
D. Facilitate DNA synthesis

Explanation:

A. Increase only: Partial.
B. Decrease only: Partial.
**C. Correct — cholesterol reduces fluidity at high temperatures and prevents rigidity at low temperatures.
**D. DNA synthesis unrelated.

Q79.

Which is NOT a function of cell membrane proteins?
A. Enzymatic activity
B. Transport
C. DNA replication ✅
D. Signal transduction

Explanation:

**A. Enzymes in membrane: yes.
**B. Transport proteins/channels: yes.
C. DNA replication (Correct): Occurs in nucleus/mitochondria, not membrane.
**D. Signal transduction: receptors in membranes.

Q80.

Which structure is absent in animal cell envelope but present in plants?
A. Cell wall ✅
B. Cell membrane
C. Glycocalyx
D. Nuclear envelope

Explanation:

A. Cell wall (Correct): Absent in animals, present in plants (cellulose).
B. Cell membrane: Present in both.
C. Glycocalyx: Found in animal cells too.
D. Nuclear envelope: Present in both.

Q81.

Plant cell wall middle lamella is rich in:
A. Cellulose
B. Pectin ✅
C. Lignin
D. Hemicellulose

Explanation:

A. Cellulose: Structural polysaccharide in primary/secondary wall.
B. Pectin (Correct): Glue-like, cements adjacent cells.
C. Lignin: Secondary wall thickening.
D. Hemicellulose: Present, not major in lamella.

Q82.

What is the main function of plasmodesmata?
A. Protein synthesis
B. Intercellular communication ✅
C. Secretion
D. ATP synthesis

Explanation:

A. Protein synthesis: Ribosomes do this.
B. Intercellular communication (Correct): Plasmodesmata connect cytoplasm of adjacent cells.
C. Secretion: Golgi-mediated.
D. ATP synthesis: Mitochondria.

Q83.

Which type of transport does NOT require energy?
A. Facilitated diffusion ✅
B. Active transport
C. Endocytosis
D. Sodium-potassium pump

Explanation:

A. Facilitated diffusion (Correct): Passive via carrier/channel proteins.
B. Active transport: Needs ATP.
C. Endocytosis: ATP-dependent.
D. Na⁺/K⁺ pump: ATPase.

Q84.

Osmosis involves:
A. Active transport of solute
B. Passive diffusion of water across semipermeable membrane ✅
C. Bulk transport
D. Protein synthesis

Explanation:

A. Active transport: Not osmosis.
**B. Correct — osmosis = water diffusion down gradient through membrane.
**C. Bulk transport = endo/exocytosis.
**D. Not relevant.

Q85.

Plasmolysis in plant cells occurs when:
A. Cell is placed in hypotonic solution
B. Cell is placed in hypertonic solution ✅
C. Cell is placed in isotonic solution
D. Turgor pressure increases

Explanation:

A. Hypotonic: Cell swells (turgid).
B. Hypertonic (Correct): Water leaves cell, membrane shrinks away from wall.
C. Isotonic: No net change.
**D. Turgor increases in hypotonic, not plasmolysis.

Q86.

Reverse osmosis is used in:
A. Blood circulation
B. Water purification ✅
C. Respiration
D. Photosynthesis

Explanation:

**A. Circulation = pumping by heart.
B. Reverse osmosis (Correct): Pressure-driven purification of water.
**C. Respiration/Photosynthesis: not relevant.

Q87.

Which process exports vesicles out of the cell?
A. Endocytosis
B. Exocytosis ✅
C. Diffusion
D. Osmosis

Explanation:

A. Endocytosis: Import.
B. Exocytosis (Correct): Vesicles fuse with membrane → release contents.
C. Diffusion: Passive molecular movement.
D. Osmosis: Water diffusion.

Q88.

Pinocytosis refers to:
A. Cell drinking (uptake of fluid) ✅
B. Cell eating (solids)
C. Exocytosis
D. Simple diffusion

Explanation:

A. Pinocytosis (Correct): Ingestion of liquid via vesicles.
**B. Phagocytosis = solid ingestion.
**C. Exocytosis = secretion.
**D. Diffusion = passive.

Q89.

Which organelles form the endomembrane system?
A. ER, Golgi, lysosomes, vacuoles ✅
B. Nucleus, mitochondria, chloroplasts
C. Ribosomes, nucleolus, centrosome
D. Cell wall, membrane, cytoskeleton

Explanation:

**A. Correct — endomembrane system = interconnected transport/secretion network.
**B. Semi-autonomous organelles, not part.
**C. Non-membranous structures.
**D. Not endomembrane.

Q90.

Proteins synthesized in RER are sent to Golgi via:
A. Lysosomes
B. Transport vesicles ✅
C. Cytoskeleton
D. Peroxisomes

Explanation:

A. Lysosomes: Not transport, but final product.
B. Transport vesicles (Correct): Carry proteins RER → cis-Golgi.
**C. Cytoskeleton provides tracks but not vesicles.
**D. Peroxisomes are metabolic organelles.

Q91.

Which part of Golgi receives vesicles from ER?
A. Trans face
B. Cis face ✅
C. Medial cisternae
D. None

Explanation:

A. Trans face: Shipping end.
B. Cis face (Correct): Receiving end from ER.
C. Medial cisternae: Processing zone.
**D. Wrong.

Q92.

The trans face of Golgi is responsible for:
A. Receiving vesicles
B. Secreting vesicles out ✅
C. DNA synthesis
D. ATP synthesis

Explanation:

**A. Receiving = cis face.
B. Trans face (Correct): Packaging and dispatch.
**C. DNA synthesis: nucleus.
**D. ATP: mitochondria.

Q93.

Which organelle originates lysosomes?
A. Rough ER
B. Golgi apparatus ✅
C. Mitochondria
D. Ribosome

Explanation:

A. RER: Makes hydrolytic enzymes.
B. Golgi (Correct): Packages enzymes into lysosomes.
C. Mitochondria: Energy.
D. Ribosome: Protein synthesis.

Q94.

Which organelle is rich in hydrolytic enzymes?
A. Peroxisome
B. Lysosome ✅
C. Mitochondria
D. Golgi

Explanation:

A. Peroxisome: Oxidases, catalase.
B. Lysosome (Correct): 40+ hydrolytic enzymes.
C. Mitochondria: Krebs cycle.
**D. Golgi: modification.

Q95.

What is common between mitochondria and chloroplast?
A. Both single-membraned
B. Both lack DNA
C. Both semi-autonomous with 70S ribosomes ✅
D. Both part of endomembrane system

Explanation:

**A. Both are double-membraned.
**B. Both have DNA.
**C. Correct — semi-autonomous, with circular DNA & 70S ribosomes.
**D. Not part of endomembrane.

Q96.

Which statement about bacterial glycocalyx is correct?
A. Made of cellulose
B. Provides protection & adhesion ✅
C. Site of photosynthesis
D. Provides energy

Explanation:

**A. Not cellulose, but polysaccharides/proteins.
**B. Correct — capsule/slime layer aids protection, adhesion.
**C. Photosynthesis occurs in thylakoid membranes (cyanobacteria).
**D. Not energy source.

Q97.

Fluidity of plasma membrane increases with:
A. More saturated fatty acids
B. More unsaturated fatty acids ✅
C. More cholesterol only
D. More proteins

Explanation:

**A. Saturated = rigid.
B. Unsaturated (Correct): Kinks prevent tight packing → fluid.
**C. Cholesterol regulates but does not increase always.
**D. Proteins don’t dictate fluidity.

Q98.

Aquaporins are specialized for:
A. Glucose transport
B. Water transport ✅
C. Ion transport
D. DNA replication

Explanation:

**A. Glucose: glucose transporters (GLUT).
B. Aquaporins (Correct): Water channel proteins.
**C. Ion transport = ion channels.
**D. DNA replication = nuclear enzymes.

Q99.

Which of the following is NOT part of plant cell wall?
A. Cellulose
B. Pectin
C. Chitin ✅
D. Hemicellulose

Explanation:

**A. Cellulose: main structure.
**B. Pectin: middle lamella.
C. Chitin (Correct): Fungal walls, not plant.
**D. Hemicellulose: true component.

Q100.

Which best describes the endomembrane system’s role?
A. Energy production
B. Protein & lipid transport, processing and secretion ✅
C. Genetic material replication
D. ATP hydrolysis

Explanation:

**A. Energy = mitochondria.
**B. Correct — ER, Golgi, lysosomes, vacuoles coordinate synthesis, modification, and secretion.
**C. Genetic = nucleus.
**D. ATP hydrolysis = energy use, not system function.

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Part 4 — Cell Envelope, Cell Membrane, Cell Wall, Membrane Transport, Endomembrane System (Q76–100)