Part 3 — Nucleus, Ribosomes, Plastids, Microbodies, Cytoskeleton, Cilia, Flagella & Centrioles (Q51–75)

Q51.

The nuclear envelope is continuous with which organelle?
A. Golgi apparatus
B. Endoplasmic reticulum ✅
C. Lysosome
D. Ribosome

Explanation:

A. Golgi apparatus: Not directly continuous.
B. ER (Correct): Outer nuclear membrane is continuous with rough ER.
C. Lysosome: Not connected to nucleus.
D. Ribosome: Free or bound to ER, not continuous.

Q52.

The dense structure in the nucleus responsible for rRNA synthesis is:
A. Chromatin
B. Nucleolus ✅
C. Nuclear pore
D. Centrosome

Explanation:

A. Chromatin: DNA + proteins, not rRNA synthesis.
B. Nucleolus (Correct): Synthesizes rRNA and assembles ribosomal subunits.
C. Nuclear pore: Transport structure.
D. Centrosome: Outside nucleus, organizes microtubules.

Q53.

Euchromatin differs from heterochromatin because:
A. Euchromatin is transcriptionally active, heterochromatin is inactive ✅
B. Euchromatin is condensed, heterochromatin is relaxed
C. Euchromatin stains dark, heterochromatin stains light
D. Euchromatin is DNA-free

Explanation:

A. Correct: Euchromatin = loosely packed, active; heterochromatin = tightly packed, inactive.
**B. Reversed statement.
**C. Opposite: heterochromatin stains dark; euchromatin stains light.
**D. DNA-free is false, both contain DNA.

Q54.

What is the function of nuclear pores?
A. ATP synthesis
B. Transport of RNA and proteins between nucleus and cytoplasm ✅
C. DNA replication
D. Ribosome assembly

Explanation:

A. ATP synthesis: In mitochondria.
**B. Correct — nuclear pores selectively allow mRNA, tRNA, proteins, and ribosomal subunits to pass.
C. DNA replication: Occurs inside nucleus but not pore’s role.
D. Ribosome assembly: In nucleolus.

Q55.

Which ribosome type is present in eukaryotic cytoplasm?
A. 70S
B. 80S ✅
C. 50S
D. 30S

Explanation:

A. 70S: Found in prokaryotes, mitochondria, and chloroplasts.
B. 80S (Correct): Eukaryotic cytosolic ribosomes (40S + 60S).
C. 50S: Large subunit of 70S ribosome.
D. 30S: Small subunit of 70S ribosome.

Q56.

The Svedberg (S) unit refers to:
A. Protein concentration
B. Sedimentation coefficient ✅
C. ATP content
D. RNA sequence

Explanation:

A. Protein concentration: Wrong.
B. Sedimentation coefficient (Correct): Measure of ribosome subunit sedimentation in centrifugation; not additive (e.g., 50S + 30S = 70S).
C. ATP content: Irrelevant.
D. RNA sequence: Unrelated.

Q57.

Which plastid is colorless and stores starch in roots?
A. Chromoplast
B. Leucoplast ✅
C. Chloroplast
D. Etioplast

Explanation:

A. Chromoplast: Colored, carotenoids.
B. Leucoplast (Correct): Colorless plastids, storage of starch, oils, proteins.
C. Chloroplast: Green, photosynthesis.
D. Etioplast: Semi-developed chloroplast in dark.

Q58.

Grana in chloroplast are stacks of:
A. Cristae
B. Thylakoids ✅
C. Stroma
D. Cisternae

Explanation:

A. Cristae: In mitochondria.
B. Thylakoids (Correct): Grana = stacks of thylakoid discs containing chlorophyll.
C. Stroma: Fluid around grana.
D. Cisternae: Flattened sacs of ER/Golgi.

Q59.

Which plastid contains carotenoid pigments (orange/yellow/red)?
A. Chloroplast
B. Chromoplast ✅
C. Leucoplast
D. Etioplast

Explanation:

A. Chloroplast: Green pigment chlorophyll.
B. Chromoplast (Correct): Pigments for flower/fruit coloration.
C. Leucoplast: Storage, colorless.
D. Etioplast: Pre-chloroplast stage.

Q60.

Which plastid type is specialized in oil and fat storage?
A. Amyloplast
B. Elaioplast ✅
C. Proteinoplast
D. Chromoplast

Explanation:

A. Amyloplast: Starch storage.
B. Elaioplast (Correct): Oil/fat storage.
C. Proteinoplast: Protein storage.
D. Chromoplast: Pigment storage.

Q61.

Glyoxysomes are specialized microbodies found in:
A. Animal liver
B. Plant germinating seeds ✅
C. Bacteria
D. Amoeba

Explanation:

A. Animal liver: Peroxisomes, not glyoxysomes.
B. Plant germinating seeds (Correct): Convert stored lipids into carbohydrates during germination.
C. Bacteria: Lack glyoxysomes.
D. Amoeba: Absent.

Q62.

Which enzyme is abundant in peroxisomes?
A. DNA polymerase
B. Catalase ✅
C. Rubisco
D. RNA polymerase

Explanation:

A. DNA polymerase: Nuclear replication.
B. Catalase (Correct): Breaks down H₂O₂ → water + oxygen.
C. Rubisco: In chloroplasts.
D. RNA polymerase: In transcription.

Q63.

Which cytoskeletal element is made of tubulin proteins?
A. Microtubules ✅
B. Actin filaments
C. Intermediate filaments
D. Collagen fibers

Explanation:

A. Microtubules (Correct): Tubulin-based hollow tubes.
B. Actin filaments: Microfilaments.
C. Intermediate filaments: Keratin, vimentin, etc.
D. Collagen fibers: Extracellular, not cytoskeletal.

Q64.

The contractile ring during cytokinesis in animal cells is formed by:
A. Microtubules
B. Actin microfilaments ✅
C. Intermediate filaments
D. Centrioles

Explanation:

A. Microtubules: Spindle fibers, not contractile ring.
B. Actin filaments (Correct): Actin + myosin form contractile ring.
C. Intermediate filaments: Structural support, no contraction.
D. Centrioles: Organize spindle, not contractile ring.

Q65.

The typical axoneme structure of eukaryotic cilia and flagella is:
A. 9 + 2 arrangement ✅
B. 9 + 0 triplets
C. 7 + 1
D. Random arrangement

Explanation:

A. 9 + 2 (Correct): 9 outer doublets + 2 central singlets.
B. 9 + 0 triplets: Centrioles/basal bodies.
C. 7 + 1: Not found.
D. Random: False.

Q66.

Which motor protein powers ciliary/flagellar movement?
A. Dynein ✅
B. Kinesin
C. Myosin
D. Tubulin

Explanation:

A. Dynein (Correct): ATPase motor in microtubules; drives sliding of doublets.
B. Kinesin: Moves cargo along microtubules in cytoplasm.
C. Myosin: Motor for actin filaments.
D. Tubulin: Structural protein, not motor.

Q67.

Centrioles are absent in:
A. Animal cells
B. Plant cells ✅
C. Protozoa
D. Algae

Explanation:

A. Animal cells: Have centrioles.
B. Plant cells (Correct): Higher plants lack centrioles; spindle formed differently.
C. Protozoa: Many have centrioles (basal bodies).
D. Algae: Centrioles may be present in flagellated types.

Q68.

Centrioles are made of:
A. 9 triplet microtubules with central pair
B. 9 triplet microtubules without central pair ✅
C. 9 doublet microtubules with central pair
D. Random filaments

Explanation:

A. 9 + 2 = cilia/flagella.
B. 9 triplets without central (Correct): Centriole = 9 triplets arranged in cylinder.
C. That’s cilia/flagella, not centriole.
D. Wrong.

Q69.

Which structure organizes spindle fibers during cell division in animals?
A. Nucleolus
B. Centrosome ✅
C. Lysosome
D. Golgi

Explanation:

A. Nucleolus: Ribosome assembly.
B. Centrosome (Correct): Pair of centrioles act as MTOC (microtubule organizing center).
C. Lysosome: Digestion.
D. Golgi: Packaging.

Q70.

Which is NOT a function of cytoskeleton?
A. Intracellular transport
B. Maintenance of cell shape
C. ATP synthesis ✅
D. Cell motility

Explanation:

A. Transport: Microtubules serve as tracks.
B. Shape maintenance: True.
C. ATP synthesis (Correct): Done in mitochondria, not cytoskeleton.
D. Motility: Actin + microtubules involved.

Q71.

Which plastid type develops from proplastids when exposed to light?
A. Etioplast
B. Chromoplast
C. Chloroplast ✅
D. Leucoplast

Explanation:

A. Etioplast: Intermediate stage in dark, but develops into chloroplast upon light.
B. Chromoplast: Develops from chloroplast sometimes, not directly from proplastid.
C. Chloroplast (Correct): Proplastids develop into chloroplasts under light.
D. Leucoplast: Develops in storage tissues.

Q72.

Which of the following is double-membraned and semi-autonomous?
A. Lysosome
B. Chloroplast ✅
C. Golgi
D. Ribosome

Explanation:

A. Lysosome: Single membrane.
B. Chloroplast (Correct): Double membrane, own DNA, ribosomes.
C. Golgi: Single membrane.
D. Ribosome: Non-membranous.

Q73.

Which plastid stores proteins?
A. Amyloplast
B. Elaioplast
C. Proteinoplast ✅
D. Chromoplast

Explanation:

A. Amyloplast: Starch storage.
B. Elaioplast: Lipids/oil.
C. Proteinoplast (Correct): Stores proteins.
D. Chromoplast: Pigments.

Q74.

The stroma of chloroplast is functionally similar to:
A. Cytoplasm ✅
B. Matrix of mitochondria
C. Tonoplast
D. Nucleolus

Explanation:

A. Cytoplasm (Correct): Semi-fluid medium where enzymes of Calvin cycle work.
B. Mitochondrial matrix: Analogy possible, but question asks functional similarity to general cytoplasm.
C. Tonoplast: Vacuolar membrane.
D. Nucleolus: rRNA synthesis.

Q75.

Which ribosomes are present inside mitochondria and chloroplasts?
A. 70S ✅
B. 80S
C. 60S
D. 40S

Explanation:

A. 70S (Correct): Same as prokaryotes, supports endosymbiotic theory.
B. 80S: Cytoplasmic ribosomes of eukaryotes.
C. 60S: Large subunit of 80S.
D. 40S: Small subunit of 80S.

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Part 3 — Nucleus, Ribosomes, Plastids, Microbodies, Cytoskeleton, Cilia, Flagella & Centrioles (Q51–75)