Biology

Cell Structure & Function

🔬 Chapter 4 · MDCAT Biology
📅 Updated Jan 2026 ⏱️ 30 min read 🎯 High-yield

Cell Structure and Function — Complete MDCAT Notes & MCQs

Full MDCAT Biology Chapter 4 on cell structure: prokaryotic vs eukaryotic cells, plant vs animal cells, organelles (nucleus, ER, Golgi, mitochondria, lysosomes, peroxisomes), plasma membrane, cytoskeleton, chromosomes, and cell junctions. Includes 199 solved MCQs with explanations and year-wise past papers.

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⚡Quick Answers to Common Searches

Direct, snippet-optimized answers to the top questions students search about Cell Structure and Function.

What is cell structure and function?

Cell structure and function studies the parts of a cell (organelles, membranes, chromosomes) and their roles. Covers prokaryotic vs eukaryotic, plant vs animal, organelles, and chromosomes.

Prokaryotic vs eukaryotic?

Prokaryotes: no nucleus, 70S ribosomes, circular DNA, peptidoglycan wall. Eukaryotes: true nucleus, 80S ribosomes, linear histone-bound DNA, membrane-bound organelles.

Plant vs animal cell?

Plant exclusive: cellulose cell wall, large central vacuole, chloroplasts, plasmodesmata. Animal exclusive: centrioles, cholesterol in membrane.

What is the fluid mosaic model?

The plasma membrane is a fluid phospholipid bilayer with embedded proteins. Fluidity depends on fatty acid saturation, chain length, and cholesterol.

What does the nucleus do?

The nucleus stores DNA, coordinates cell activities, and controls protein synthesis. It contains the nucleolus (rRNA synthesis) and is bounded by a double membrane with pores.

Rough ER vs smooth ER?

Rough ER (ribosomes) — protein synthesis. Smooth ER — lipid/steroid synthesis, detoxification, Ca²⁺ storage.

What does the Golgi apparatus do?

Golgi modifies, sorts, and packages proteins and lipids. Cis face receives, trans face ships. Produces lysosomes.

Why are mitochondria the powerhouse?

Mitochondria produce ATP via oxidative phosphorylation on the cristae. They have their own DNA and 70S ribosomes — semi-autonomous.

What is a nucleosome?

A nucleosome = 147 bp DNA wrapped 1.65 times around a histone octamer (2× H2A, H2B, H3, H4). H1 is the linker histone.

Euchromatin vs heterochromatin?

Euchromatin — loose, active, light (transcribed). Heterochromatin — dense, inactive, dark (centromeres, telomeres).

How many chromosomes in humans?

46 chromosomes (2n) — 44 autosomes + 2 sex chromosomes (XX/XY). Gametes are haploid with 23.

Types of chromosomes?

Metacentric (central), sub-metacentric (off-center), acrocentric (near end), telocentric (at tip — absent in humans).

Function of lysosome?

Lysosomes contain acid hydrolases (pH~5) for intracellular digestion, autophagy, phagocytosis, and autolysis. Marker: acid phosphatase.

What is a peroxisome?

Peroxisomes contain catalase to break down H₂O₂ and oxidize fatty acids. Glyoxysomes (plants) convert fats → carbohydrates.

How many MCQs from Cell Structure?

Cell Structure typically contributes 4–6 MCQs out of 81 Biology MCQs in MDCAT.

❓People Also Ask — Cell Structure & Function

Questions students most frequently search about this chapter. Answers are direct and exam-focused.

QWhat are the 3 main differences between prokaryotes and eukaryotes?
(1) Nucleus: prokaryotes lack one (nucleoid); eukaryotes have a double-membrane nucleus. (2) Ribosomes: 70S vs 80S. (3) Organelles: prokaryotes lack membrane-bound organelles; eukaryotes have ER, Golgi, mitochondria, etc.
QWhat is the difference between rough and smooth ER?
Rough ER has ribosomes and synthesizes secretory/membrane proteins. Smooth ER lacks ribosomes — synthesizes lipids and steroids, detoxifies drugs, and stores Ca²⁺.
QWhat are the functions of the Golgi apparatus?
The Golgi modifies, sorts, and packages proteins and lipids, produces lysosomes, forms the cell plate in plants, and participates in glycosylation.
QWhat is the structure of mitochondria?
Mitochondria have a double membrane — outer smooth, inner folded into cristae. Inside is the matrix (Krebs enzymes, mtDNA, 70S ribosomes). Cristae contain ATP synthase (F₀F₁).
QWhat are the differences between plant and animal cells?
Plant: cellulose wall, large central vacuole, chloroplasts, plasmodesmata. Animal: centrioles, cholesterol. Both have nucleus, mitochondria, ER, Golgi, ribosomes.
QWhat is a chromosome?
A chromosome is a thread-like structure of DNA and histones. It has a centromere, telomeres, and two arms (p short, q long). Humans have 46 chromosomes.
QWhat are the 4 types of chromosomes by centromere?
Metacentric (middle, V-shape), sub-metacentric (L-shape), acrocentric (J-shape, near end), telocentric (I-shape, at tip — not in humans).
QWhat is the chemical composition of chromosomes?
Chromosomes = DNA + histones + non-histone proteins. Histones (H1, H2A, H2B, H3, H4) are basic proteins rich in lysine and arginine.
QWhat is a nucleosome?
A nucleosome is DNA (147 bp) wrapped 1.65 times around a histone octamer — "beads on a string" unit of chromatin.
QWhat is the endosymbiotic theory?
Mitochondria and chloroplasts evolved from engulfed bacteria. Evidence: own circular DNA, 70S ribosomes, double membrane, binary fission.
QWhat are the functions of the lysosome?
Lysosomes perform autophagy (digest own organelles), phagocytosis (digest engulfed material), and autolysis (self-digestion). Enzyme marker: acid phosphatase.
QWhat is the 9+2 arrangement?
9+2 = eukaryotic cilia/flagella (9 microtubule doublets + 2 singlets). Centrioles and basal bodies have 9+0 triplets.
QWhat are desmosomes, tight junctions, and gap junctions?
Tight junctions seal cells (occludins/claudins). Desmosomes adhere via cadherins. Gap junctions allow communication via connexins.
QWhat is the function of the nucleolus?
The nucleolus is the site of rRNA transcription and ribosome subunit assembly. It forms around the Nucleolar Organizer Regions (NORs).
QWhat are the functions of the plasma membrane?
The plasma membrane provides selective permeability, mediates transport (active/passive), signaling (receptors), and cell recognition (glycocalyx).
QWhat is the difference between euchromatin and heterochromatin?
Euchromatin: loosely packed, active, light under EM. Heterochromatin: densely packed, inactive, dark (centromeres, telomeres — constitutive).
QWhat are the types of cell junctions in plants?
Plants have plasmodesmata — cytoplasmic channels through the cell wall for intercellular transport and communication.
QWhy do prokaryotes have 70S ribosomes?
70S ribosomes (50S + 30S) are smaller than eukaryotic 80S (60S + 40S). This is a key difference exploited by antibiotics like chloramphenicol.
QWhat is the function of the cytoskeleton?
The cytoskeleton (microtubules, microfilaments, intermediate filaments) provides shape, movement, and internal transport. Microtubules: tubulin. Microfilaments: actin. Intermediate: keratin.
QWhich organelles are semi-autonomous?
Mitochondria and chloroplasts — they have their own circular DNA, 70S ribosomes, and can divide by binary fission (endosymbiotic theory).

📋Syllabus & Learning Outcomes

According to PMDC/PMC MDCAT syllabus, Cell Structure and Function covers:

📝Full Notes — Cell Structure & Function

🔬 Cell Structure – Schematic Notes

⚡ Prokaryotic vs Eukaryotic

FeatureProkaryoticEukaryotic
NucleusAbsent (nucleoid)Present (double membrane)
DNACircular, nakedLinear, histone‑bound
Ribosomes70S (50S+30S)80S (60S+40S)
Membranous organellesAbsentPresent (ER, Golgi, etc.)
Cell wallPeptidoglycan (murein)Plants: cellulose; Fungi: chitin; Animals: absent
Size0.5–5 µm10–100 µm

🌱 Plant vs Animal Cell

  • Plant exclusive: cell wall (cellulose), large central vacuole, plastids (chloroplasts), plasmodesmata.
  • Animal exclusive: centrioles, cholesterol in membrane.
  • Shared: nucleus, mitochondria, ER, Golgi, ribosomes, plasma membrane.

🧫 Fluid Mosaic Model

  • Phospholipid bilayer + proteins (integral/peripheral).
  • Asymmetry: outer leaflet rich in phosphatidylcholine, inner in phosphatidylserine.
  • Fluidity depends on fatty acid saturation (unsaturated → fluid), chain length, cholesterol (buffer).
  • Functions: selective permeability, transport, signaling, recognition.

🧬 Nucleus & Chromosomes

  • Nuclear envelope (double membrane) with pores; nucleolus – rRNA synthesis.
  • Chromatin: DNA + histones (H2A, H2B, H3, H4)₂ + H1 linker.
  • Nucleosome = DNA wrapped around histone octamer.
  • Euchromatin (active) vs Heterochromatin (inactive, e.g., centromeres).
  • Human: 46 chromosomes (44 autosomes + XX/XY); centromere & telomeres.
  • Chromosome shapes: metacentric, sub‑metacentric, acrocentric (telocentric in other species).

⚙️ Endomembrane System

  • Rough ER: ribosomes, protein folding & secretion.
  • Smooth ER: lipid synthesis, detoxification, Ca²⁺ storage (sarcoplasmic reticulum).
  • Golgi: cis (receiving) → trans (shipping); modifies, sorts, packages.
  • Lysosomes: pH ~5, acid hydrolases; autophagy, phagocytosis, autolysis.
  • Peroxisomes: catalase, H₂O₂ breakdown; glyoxysomes (plants) convert fats → carbs.

⚡ Mitochondria

  • Double membrane; inner folded into cristae (F₀F₁ ATP synthase).
  • Matrix: Krebs enzymes, mtDNA, 70S ribosomes → semi‑autonomous.
  • Maternal inheritance; cardiolipin in inner membrane.

🧪 Other Structures

  • Ribosomes: 70S (prokaryotes, organelles) / 80S (cytoplasm).
  • Cytoskeleton: microtubules (tubulin, 9+2 axoneme), microfilaments (actin), intermediate filaments (keratin).
  • Centrioles: 9+0 triplets; form basal bodies of cilia/flagella.
  • Cilia/Flagella: 9+2 arrangement; motor protein dynein.

🔗 Junctions

  • Plant: plasmodesmata (cytoplasmic bridges).
  • Animal: tight junctions (seal), desmosomes (adhesion, cadherins), gap junctions (connexins – communication).

🔑 High‑Yield MCQs & Traps

  • Prokaryotic ribosome = 70S; eukaryotic cytoplasm ribosome = 80S.
  • Plant cell has cell wall of cellulose; fungi = chitin; bacteria = peptidoglycan.
  • Inner mitochondrial membrane contains cardiolipin and F₀F₁ particles.
  • Nucleosome: DNA + histone octamer; linker H1 not part of core.
  • Centriole = 9+0; cilia/flagella = 9+2 arrangement.
  • Lysosome pH ~5; enzyme marker = acid phosphatase.
  • Peroxisome marker = catalase; glyoxysome in plants.
  • Euchromatin (light, active) ↔ heterochromatin (dark, silent).
  • Golgi cis face receives from ER; trans face dispatches vesicles.
  • ⚠️ Trap: Animal cells lack cell wall, but have cholesterol in membrane for fluidity.
  • ⚠️ Trap: Mitochondria and chloroplasts have 70S ribosomes and circular DNA (endosymbiont theory).

💡 Key MDCAT focus: organelle-specific markers (catalase→peroxisome, cardiolipin→mitochondria), differences in ribosome sizes, and plant vs animal cell features.

✅Practice MCQs — Test 1

🧪 Basic Concepts

50 MCQs
1Which structure is present in a typical plant cell but absent in a typical animal cell?
  • A. Mitochondria
  • B. Large central vacuole
  • C. Ribosomes
  • D. Centrioles
Answer: B. Large central vacuole
Plant cells have a large central vacuole for storage and turgor; animal cells have smaller vacuoles.
2The primary component of the plant cell wall that provides structural support is:
  • A. Chitin
  • B. Peptidoglycan
  • C. Cellulose
  • D. Glycogen
Answer: C. Cellulose
Cellulose is a polysaccharide that forms microfibrils, providing strength to the plant cell wall.
3In plant cells, the middle lamella is primarily composed of:
  • A. Cellulose
  • B. Hemicellulose
  • C. Magnesium and calcium pectates
  • D. Lignin
Answer: C
Pectates (calcium/magnesium pectate) act as a cementing layer between adjacent plant cells.
4Centrioles are typically found in:
  • A. Higher plants
  • B. Most animal cells
  • C. Prokaryotic cells
  • D. All of the above
Answer: B. Most animal cells
Centrioles are present in animal cells and some lower plants, but absent in higher plants and prokaryotes.
5Which of the following is responsible for the turgor pressure in plant cells?
  • A. Nucleus
  • B. Chloroplast
  • C. Central vacuole
  • D. Smooth ER
Answer: C. Central vacuole
The central vacuole stores water; when full, it pushes against the cell wall, creating turgor pressure.
6The cell wall of bacteria is made of a unique polymer called:
  • A. Cellulose
  • B. Chitin
  • C. Peptidoglycan
  • D. Amylopectin
Answer: C. Peptidoglycan
Peptidoglycan (murein) is a mesh of sugar chains cross-linked by peptides, providing structural integrity.
7Prokaryotic cells lack which of the following?
  • A. Plasma membrane
  • B. Ribosomes
  • C. Membrane-bound organelles
  • D. DNA
Answer: C
Prokaryotes have no nucleus or other membrane-bound organelles; they have a nucleoid region.
8Eukaryotic ribosomes are 80S, consisting of subunits:
  • A. 50S and 30S
  • B. 60S and 40S
  • C. 70S and 10S
  • D. 60S and 20S
Answer: B
80S ribosomes are composed of a 60S large subunit and a 40S small subunit.
9The genetic material of a prokaryote is located in the:
  • A. Nucleus
  • B. Nucleolus
  • C. Nucleoid
  • D. Mesosome
Answer: C. Nucleoid
Prokaryotes lack a true nucleus; their circular DNA is concentrated in the nucleoid region.
10Mesosomes in prokaryotes are involved in:
  • A. Protein synthesis
  • B. Cell wall formation and respiration
  • C. Lipid storage
  • D. Movement
Answer: B
Mesosomes are infoldings of the plasma membrane that aid in cell division and respiration.
11Which of the following is true for both prokaryotes and eukaryotes?
  • A. Presence of mitochondria
  • B. Presence of a nuclear envelope
  • C. Presence of a plasma membrane
  • D. Presence of a cytoskeleton
Answer: C
Both cell types have a plasma membrane that regulates transport and maintains homeostasis.
12The size of a typical eukaryotic cell is roughly:
  • A. 1–10 µm
  • B. 10–100 µm
  • C. 100–500 µm
  • D. 1–5 nm
Answer: B
Eukaryotic cells are generally 10–100 µm in diameter, much larger than prokaryotes (0.5–5 µm).
13Which organelle in eukaryotes supports the endosymbiotic theory by having its own 70S ribosomes?
  • A. Golgi apparatus
  • B. Mitochondria
  • C. Lysosomes
  • D. Endoplasmic reticulum
Answer: B. Mitochondria
Mitochondria and chloroplasts have their own 70S ribosomes, supporting their bacterial origin.
14Prokaryotic DNA is characterized as being:
  • A. Linear and associated with histones
  • B. Circular and naked
  • C. Contained within a double membrane
  • D. Single-stranded only
Answer: B
Prokaryotic DNA is circular, not bound by a nuclear envelope, and lacks histones.
15The 'Powerhouse of the cell' refers to the:
  • A. Nucleus
  • B. Golgi body
  • C. Mitochondria
  • D. Ribosome
Answer: C. Mitochondria
Mitochondria produce ATP via cellular respiration, supplying energy for cellular activities.
16Rough Endoplasmic Reticulum (RER) is primarily involved in:
  • A. Lipid synthesis
  • B. Detoxification of drugs
  • C. Protein synthesis
  • D. Calcium storage
Answer: C. Protein synthesis
RER is studded with ribosomes that synthesize proteins destined for secretion or membranes.
17The Smooth Endoplasmic Reticulum (SER) is abundant in cells that synthesize:
  • A. Enzymes
  • B. Steroid hormones
  • C. Structural proteins
  • D. RNA
Answer: B. Steroid hormones
SER is involved in lipid and steroid hormone synthesis, as well as detoxification.
18The stacks of flattened membrane-bound sacs in the Golgi apparatus are called:
  • A. Cristae
  • B. Cisternae
  • C. Thylakoids
  • D. Vesicles
Answer: B. Cisternae
Cisternae are the flattened, stacked membrane compartments of the Golgi apparatus.
19The 'cis' face of the Golgi apparatus is also known as the:
  • A. Shipping face
  • B. Maturing face
  • C. Forming face
  • D. Secretory face
Answer: C. Forming face
The cis face receives vesicles from the ER; it is the forming/entry face.
20Lysosomes are produced by the:
  • A. Mitochondria
  • B. Golgi apparatus
  • C. Nucleus
  • D. Smooth ER
Answer: B. Golgi apparatus
Lysosomal enzymes are packaged by the Golgi into vesicles that become primary lysosomes.
21The inner folds of the mitochondrial membrane are called:
  • A. Matrix
  • B. Cristae
  • C. Cisternae
  • D. Grana
Answer: B. Cristae
Cristae increase surface area for electron transport chain complexes.
22Which organelle contains enzymes for the Krebs cycle?
  • A. Mitochondrial cristae
  • B. Mitochondrial matrix
  • C. Cytosol
  • D. Nucleoplasm
Answer: B
The Krebs cycle enzymes are located in the mitochondrial matrix.
23Autolysis (self-digestion) of a cell is performed by:
  • A. Peroxisomes
  • B. Lysosomes
  • C. Glyoxysomes
  • D. Vacuoles
Answer: B. Lysosomes
Lysosomes contain hydrolytic enzymes that can digest cellular components when ruptured.
24The function of the nucleolus is the synthesis of:
  • A. DNA
  • B. mRNA
  • C. rRNA
  • D. tRNA
Answer: C. rRNA
The nucleolus is the site of rRNA transcription and ribosome subunit assembly.
25Which organelle is continuous with the outer nuclear membrane?
  • A. Golgi body
  • B. Endoplasmic reticulum
  • C. Lysosome
  • D. Mitochondria
Answer: B. Endoplasmic reticulum
The outer nuclear membrane is continuous with the rough ER.
26Detoxification of harmful drugs in the liver is a function of:
  • A. RER
  • B. SER
  • C. Golgi apparatus
  • D. Nucleolus
Answer: B. SER
Smooth ER in hepatocytes contains cytochrome P450 enzymes that detoxify drugs.
27The fluid mosaic model describes the structure of the:
  • A. Cell wall
  • B. Nuclear envelope
  • C. Plasma membrane
  • D. Mitochondrial membrane
Answer: C. Plasma membrane
The plasma membrane is a fluid bilayer of phospholipids with embedded proteins.
28Which organelle is involved in the formation of the cell plate in plants?
  • A. Mitochondria
  • B. Golgi apparatus
  • C. Centrioles
  • D. Lysosomes
Answer: B. Golgi apparatus
Golgi-derived vesicles fuse to form the cell plate during plant cytokinesis.
29Ribosomes are chemically composed of:
  • A. DNA and Protein
  • B. RNA and Protein
  • C. Lipid and Protein
  • D. RNA and Carbohydrate
Answer: B. RNA and Protein
Ribosomes consist of rRNA (ribosomal RNA) and ribosomal proteins.
30The pH inside a lysosome is typically:
  • A. Neutral
  • B. Highly alkaline
  • C. Acidic
  • D. Slightly basic
Answer: C. Acidic
Lysosomal pH is about 4.5–5.0, optimal for hydrolytic enzyme activity.
31Chromosomes are most clearly visible during which phase of cell division?
  • A. Prophase
  • B. Metaphase
  • C. Anaphase
  • D. Telophase
Answer: A. Prophase
Chromosomes condense and become visible under light microscopy during prophase.
32A chromosome with the centromere in the middle, dividing it into two equal arms, is:
  • A. Metacentric
  • B. Sub-metacentric
  • C. Acrocentric
  • D. Telocentric
Answer: A. Metacentric
Metacentric chromosomes have equal p and q arms.
33The chemical composition of a eukaryotic chromosome is:
  • A. 100% DNA
  • B. DNA and Histone proteins
  • C. RNA and Non-histone proteins
  • D. DNA and Lipids
Answer: B
Chromatin is composed of DNA, histones, and non-histone proteins.
34The basic structural unit of chromatin, consisting of DNA wrapped around histones, is the:
  • A. Nucleolus
  • B. Nucleosome
  • C. Centromere
  • D. Chromatid
Answer: B. Nucleosome
Nucleosomes are beads of DNA wrapped around histone octamers.
35A human somatic cell contains how many chromosomes?
  • A. 23
  • B. 44
  • C. 46
  • D. 48
Answer: C. 46
Humans have 46 chromosomes (22 pairs of autosomes + 2 sex chromosomes).
36The point where two sister chromatids are attached is the:
  • A. Telomere
  • B. Centromere
  • C. Chromomere
  • D. Kinetochore
Answer: B. Centromere
Sister chromatids are joined at the centromere.
37How many histone proteins make up the core of a nucleosome?
  • A. 4
  • B. 6
  • C. 8
  • D. 10
Answer: C. 8
The core octamer consists of two each of H2A, H2B, H3, and H4.
38The region at the end of a chromosome that prevents it from sticking to others is the:
  • A. Centromere
  • B. Telomere
  • C. Secondary constriction
  • D. Sat-body
Answer: B. Telomere
Telomeres protect chromosome ends from degradation and fusion.
39Transcriptionally active, loosely packed chromatin is called:
  • A. Heterochromatin
  • B. Euchromatin
  • C. Pro-chromatin
  • D. Pseudo-chromatin
Answer: B. Euchromatin
Euchromatin is less condensed and contains actively transcribed genes.
40Chromosomes that are identical in shape and carry the same genes are called:
  • A. Heterologous
  • B. Homologous
  • C. Analogous
  • D. Vestigial
Answer: B. Homologous
Homologous chromosomes are pairs (one from each parent) with same gene loci.
41Which organelle is responsible for the 'glycation' (addition of carbohydrates) of proteins?
  • A. Ribosome
  • B. Golgi apparatus
  • C. Mitochondria
  • D. Lysosome
Answer: B. Golgi apparatus
Golgi apparatus modifies proteins by adding carbohydrate groups (glycosylation).
42The protein present in eukaryotic flagella is:
  • A. Flagellin
  • B. Tubulin
  • C. Actin
  • D. Keratin
Answer: B. Tubulin
Eukaryotic flagella are made of microtubules composed of α- and β-tubulin.
43Which of the following is NOT part of the endomembrane system?
  • A. Nuclear envelope
  • B. Golgi apparatus
  • C. Peroxisome
  • D. Endoplasmic reticulum
Answer: C. Peroxisome
Peroxisomes are not derived from the ER/Golgi and are not part of the endomembrane system.
44The number of chromosomes in a human egg cell is:
  • A. 46
  • B. 22
  • C. 23
  • D. 44
Answer: C. 23
Gametes are haploid (n=23).
45An acrocentric chromosome has the centromere:
  • A. At the very tip
  • B. In the center
  • C. Near one end
  • D. Slightly off-center
Answer: C. Near one end
Acrocentric centromeres are near one end, producing a very short p arm.
46Mitochondria divide by:
  • A. Mitosis
  • B. Meiosis
  • C. Fission-like process
  • D. Budding
Answer: C. Fission-like process
Mitochondria replicate via binary fission, similar to bacteria.
47The space between the two membranes of the nuclear envelope is called:
  • A. Perinuclear space
  • B. Nucleoplasm
  • C. Cytosol
  • D. Cisternal space
Answer: A. Perinuclear space
The perinuclear space is continuous with the ER lumen.
48Which protein is found in the bacterial cell wall?
  • A. Keratin
  • B. Collagen
  • C. Murein
  • D. Albumin
Answer: C. Murein
Murein is another name for peptidoglycan, the bacterial cell wall polymer.
49Histones are rich in which basic amino acids?
  • A. Glycine and Alanine
  • B. Lysine and Arginine
  • C. Valine and Leucine
  • D. Proline and Serine
Answer: B. Lysine and Arginine
Lysine and arginine are positively charged, allowing histones to bind negatively charged DNA.
50What is the approximate size of a bacterial ribosome?
  • A. 50S
  • B. 70S
  • C. 80S
  • D. 100S
Answer: B. 70S
Prokaryotic ribosomes are 70S (50S + 30S subunits).

✅Practice MCQs — Test 2

🧪 Advanced Concepts

50 MCQs
1During the transition from a primary to a secondary cell wall in specialized plant cells, which of the following is true?
  • A. The secondary wall is deposited outside the primary wall.
  • B. Lignification occurs primarily in the middle lamella during this stage.
  • C. The secondary wall is thicker and contains more cellulose and lignin than the primary wall.
  • D. The primary wall disappears to allow for expansion.
Answer: C
Secondary wall is deposited inside the primary wall and is thickened with lignin and more cellulose.
2Which statement regarding the 'Extracellular Matrix (ECM)' of animal cells is most accurate compared to the plant cell wall?
  • A. The ECM is primarily composed of cellulose and hemicellulose.
  • B. The ECM consists of glycoproteins like collagen and fibronectin, lacking in plant walls.
  • C. Animal cells possess a middle lamella to adhere to adjacent cells.
  • D. Both structures are equally permeable to large globular proteins.
Answer: B
Animal ECM contains collagen, fibronectin, and proteoglycans; plant walls have cellulose, hemicellulose, pectin.
3In the 'Fluid Mosaic Model,' the degree of membrane fluidity is inversely proportional to:
  • A. The concentration of unsaturated fatty acid tails.
  • B. The temperature of the environment.
  • C. The concentration of cholesterol at high temperatures in animal membranes.
  • D. The length of the phospholipid hydrocarbon chains.
Answer: D
Longer hydrocarbon chains increase van der Waals interactions, decreasing fluidity.
4Which of the following organelles is structurally and functionally linked to the 'Glyoxylate Cycle' in germinating fatty seeds?
  • A. Peroxisomes
  • B. Glyoxysomes
  • C. Lysosomes
  • D. Mitochondria
Answer: B. Glyoxysomes
Glyoxysomes (specialized peroxisomes) house the glyoxylate cycle to convert fats to carbohydrates.
5The presence of 'Plasmodesmata' is a unique feature of plant cells; the functional equivalent in animal cells for direct chemical communication is:
  • A. Tight junctions
  • B. Desmosomes
  • C. Gap junctions
  • D. Adherens junctions
Answer: C. Gap junctions
Gap junctions are channels that allow direct cytoplasmic communication between animal cells.
6The antibiotic Penicillin targets the cross-linking of peptidoglycan. This would be least effective against:
  • A. Staphylococcus aureus
  • B. Escherichia coli
  • C. Mycoplasma pneumoniae
  • D. Bacillus subtilis
Answer: C. Mycoplasma pneumoniae
Mycoplasma lacks a cell wall entirely, so penicillin has no effect.
7Which of the following is a characteristic of the prokaryotic 'Nucleoid' that differentiates it from eukaryotic 'Chromatin'?
  • A. It is associated with non-histone polyamines and topoisomerases for folding.
  • B. It contains introns and exons in equal proportions.
  • C. It is replicated only during a specific S-phase of the cell cycle.
  • D. It is physically separated from the ribosomes by a thin proteinaceous layer.
Answer: A
Nucleoid DNA is folded by polyamines and topoisomerases, not histones.
8In eukaryotic cells, the 80S ribosome dissociates into 60S and 40S subunits. The 60S subunit itself contains which rRNA components?
  • A. 16S rRNA
  • B. 5S, 5.8S, and 28S rRNA
  • C. 23S and 5S rRNA
  • D. 18S rRNA only
Answer: B
The 60S subunit contains 28S, 5.8S, and 5S rRNAs.
9The prokaryotic flagellum is powered by a proton motive force. Which part of the flagellum acts as the 'motor' embedded in the cell envelope?
  • A. The Filament
  • B. The Hook
  • C. The Basal Body
  • D. The Pilus
Answer: C. Basal Body
The basal body (rotor) uses proton flow to rotate the flagellum.
10Which molecular feature is shared by both Archaebacteria and Eukaryotes, but not Eubacteria?
  • A. Peptidoglycan in the cell wall
  • B. Ester-linked membrane lipids
  • C. Methionine as the initiator amino acid for translation
  • D. 70S ribosomes
Answer: C
Archaea and eukaryotes both use methionine as the start codon; bacteria use formylmethionine.
11The 'Signal Hypothesis' explains how proteins are directed to the Rough ER. The Signal Recognition Particle (SRP) binds to:
  • A. The 3' end of the mRNA
  • B. The hydrophobic signal sequence at the N-terminus of the growing polypeptide
  • C. The Golgi cisternae receptors
  • D. The nuclear pore complex
Answer: B
SRP recognizes the N-terminal signal peptide emerging from the ribosome.
12A cell treated with a drug that inhibits the 'cis-Golgi' enzymes would primarily fail to:
  • A. Produce ATP
  • B. Modify N-linked oligosaccharides on newly synthesized proteins
  • C. Synthesize phospholipids for the plasma membrane
  • D. Replicate mitochondrial DNA
Answer: B
Initial processing of N-linked glycans occurs in the cis-Golgi.
13Which of the following is NOT a function of the Smooth Endoplasmic Reticulum (SER) in specialized cells?
  • A. Sarcoplasmic reticulum in muscles storing Ca²⁺ ions.
  • B. Hydroxylating drugs to make them more water-soluble for excretion.
  • C. Synthesis of hydrolytic enzymes for the primary lysosome.
  • D. Conversion of glucose-6-phosphate to glucose in the liver.
Answer: C
Hydrolytic enzymes for lysosomes are synthesized on RER, not SER.
14The 'Chemiosmotic Theory' of ATP synthesis in mitochondria depends on the accumulation of protons in the:
  • A. Mitochondrial matrix
  • B. Inner mitochondrial membrane
  • C. Intermembrane space
  • D. Outer membrane pores
Answer: C
Protons are pumped into the intermembrane space, creating a gradient.
15Primary lysosomes become secondary lysosomes when they:
  • A. Bud off from the trans-Golgi network.
  • B. Fuse with a phagosome or endosome.
  • C. Accumulate lipofuscin pigments.
  • D. Decrease their internal pH to 7.0.
Answer: B
After fusing with a phagosome (containing material to digest), they become secondary lysosomes.
16The 'F₀-F₁ Particle' (ATP Synthase) is located on the cristae. The F₁ component specifically functions as:
  • A. A proton channel
  • B. A catalytic head that synthesizes ATP from ADP and Pi
  • C. An electron carrier in the respiratory chain
  • D. A lipid-anchoring protein
Answer: B
F₁ is the catalytic subunit that synthesizes ATP.
17Pompe's Disease is a clinical condition resulting from the failure of which organelle to break down glycogen?
  • A. Peroxisome
  • B. Lysosome
  • C. Smooth ER
  • D. Mitochondria
Answer: B. Lysosome
Pompe disease is caused by deficiency of lysosomal acid α-glucosidase.
18Which organelle is responsible for the 'photorespiration' pathway in plants, working in conjunction with chloroplasts and mitochondria?
  • A. Glyoxysome
  • B. Peroxisome
  • C. Ribosome
  • D. Golgi body
Answer: B. Peroxisome
Peroxisomes in leaves carry out the glycolate pathway of photorespiration.
19The 'Nuclear Pore Complex (NPC)' is highly selective. Proteins destined for the nucleus must possess a specific:
  • A. KDEL sequence
  • B. Nuclear Localization Signal (NLS)
  • C. Signal peptide
  • D. Carbohydrate tag
Answer: B. Nuclear Localization Signal (NLS)
NLS (e.g., PKKKRKV) binds importins for nuclear import.
20In the endomembrane system, 'Retrograde Transport' refers to the movement of vesicles from:
  • A. ER to Golgi
  • B. Golgi to ER
  • C. Golgi to Plasma Membrane
  • D. Nucleus to Cytoplasm
Answer: B. Golgi to ER
Retrograde transport returns proteins from Golgi back to ER (e.g., KDEL receptors).
21During the formation of a 'Nucleosome,' the DNA wraps around the histone octamer approximately:
  • A. 1 time
  • B. 1.65 to 2 times
  • C. 5 times
  • D. 10 times
Answer: B
DNA wraps ~1.65 turns (147 bp) around the histone core.
22Which histone protein acts as a 'linker' to stabilize the entry and exit of DNA around the nucleosome core?
  • A. H2A
  • B. H2B
  • C. H3
  • D. H1
Answer: D. H1
Histone H1 binds linker DNA between nucleosomes, promoting higher-order folding.
23'Heterochromatin' remains condensed throughout the cell cycle. Which of the following is an example of constitutive heterochromatin?
  • A. Active insulin gene in pancreas cells
  • B. Centromeric regions of chromosomes
  • C. The entire X-chromosome in a male
  • D. Ribosomal RNA genes
Answer: B
Centromeres and telomeres are permanently condensed (constitutive heterochromatin).
24A 'Karyotype' is an organized profile of a person's chromosomes. It is traditionally prepared using cells arrested in:
  • A. Prophase
  • B. Metaphase
  • C. Anaphase
  • D. Interphase
Answer: B. Metaphase
Metaphase chromosomes are maximally condensed and distinct.
25If a diploid organism has 2n = 12, how many DNA molecules (chromatids) are present in a cell at the end of G2 phase?
  • A. 6
  • B. 12
  • C. 24
  • D. 48
Answer: C. 24
After S phase, each chromosome has two sister chromatids, so 12 chromosomes × 2 = 24 DNA molecules.
26The 'Kinetochore' is a complex protein structure that forms on the:
  • A. Telomere
  • B. Centromere
  • C. Nucleolar Organizer Region (NOR)
  • D. Chromatid arms
Answer: B. Centromere
Kinetochores assemble at the centromere and attach to spindle microtubules.
27'Acrocentric' chromosomes in humans include which of the following pairs?
  • A. 1, 2, 3
  • B. 13, 14, 15
  • C. 19, 20
  • D. X and Y only
Answer: B
Human acrocentric chromosomes are 13, 14, 15, 21, and 22.
28The chemical 'Colchicine' is used in chromosome studies because it:
  • A. Stimulates DNA replication
  • B. Inhibits spindle formation, arresting cells in metaphase
  • C. Dissolves the nuclear envelope
  • D. Promotes cytokinesis
Answer: B
Colchicine binds tubulin, preventing spindle polymerization and arresting cells at metaphase.
29Which part of the chromosome is responsible for maintaining the stability and integrity of the linear DNA molecule after multiple replications?
  • A. Centromere
  • B. Telomere
  • C. Secondary constriction
  • D. Chromomere
Answer: B. Telomere
Telomeres prevent progressive shortening and end-to-end fusion.
30The 'Nucleolar Organizer Region (NOR)' is associated with the formation of the nucleolus and is usually found at the:
  • A. Primary constriction
  • B. Secondary constriction (Satellite)
  • C. Telomere
  • D. Centromere
Answer: B
NORs are secondary constrictions containing rRNA genes.
31In the 'Endosymbiotic Theory,' the fact that mitochondria have their own circular DNA and lack histones suggests they evolved from:
  • A. Ancient cyanobacteria
  • B. Ancient aerobic Proteobacteria
  • C. Primitive fungi
  • D. Viral particles
Answer: B
Mitochondria likely descended from aerobic α-proteobacteria.
32Which of the following lipids is unique to the inner mitochondrial membrane and is essential for the function of ETC complexes?
  • A. Cholesterol
  • B. Phosphatidylcholine
  • C. Cardiolipin
  • D. Sphingomyelin
Answer: C. Cardiolipin
Cardiolipin is a diphosphatidylglycerol that stabilizes respiratory supercomplexes.
33'Zellweger Syndrome' is a rare disorder characterized by the absence of functional:
  • A. Lysosomes
  • B. Peroxisomes
  • C. Mitochondria
  • D. Ribosomes
Answer: B. Peroxisomes
Zellweger syndrome is a peroxisome biogenesis disorder.
34The 'Svedberg Unit (S)' depends on which physical properties of a particle?
  • A. Mass and density only
  • B. Mass, density, and shape
  • C. Mass and volume only
  • D. Charge and mass
Answer: B
Svedberg coefficient depends on mass, density, and shape (frictional coefficient).
35Which of the following describes 'Autophagy'?
  • A. A cell eating another cell.
  • B. An organelle (like a mitochondrion) being digested by the cell's own lysosomes.
  • C. The synthesis of new organelles by the ER.
  • D. Secretion of enzymes outside the cell.
Answer: B
Autophagy is the lysosomal degradation of damaged organelles or cellular components.
36Eukaryotic cilia and flagella exhibit a '9+2' arrangement of microtubules. These microtubules are composed of:
  • A. Actin and Myosin
  • B. Alpha and Beta Tubulin
  • C. Keratin and Desmin
  • D. Flagellin subunits
Answer: B
Microtubules are polymers of α- and β-tubulin dimers.
37The 'Basal Body' of a cilium is structurally identical to a:
  • A. Centromere
  • B. Centriole
  • C. Nucleosome
  • D. Ribosome
Answer: B. Centriole
Basal bodies are modified centrioles that organize ciliary microtubules.
38Which enzyme is specifically used as a marker for identifying the 'Mitochondrial Matrix'?
  • A. Cytochrome oxidase
  • B. ATP synthase
  • C. Malate dehydrogenase (Krebs cycle enzyme)
  • D. Acid phosphatase
Answer: C
Malate dehydrogenase is a soluble matrix enzyme; others are membrane-bound or lysosomal.
39In a 'Metacentric' chromosome, the ratio of the p-arm (short arm) to the q-arm (long arm) is approximately:
  • A. 1:1
  • B. 1:2
  • C. 1:10
  • D. 0:1
Answer: A. 1:1
Metacentric chromosomes have arms of roughly equal length.
40High concentrations of 'Calcium ions' are stored in the SER of muscle cells. Upon a nerve impulse, these ions are released into the:
  • A. Mitochondrial matrix
  • B. Sarcoplasm (Cytoplasm)
  • C. T-tubules
  • D. Nucleoplasm
Answer: B
Ca²⁺ is released from sarcoplasmic reticulum into the sarcoplasm to trigger contraction.
41The total number of kinetochores in a human somatic cell during Mitotic Metaphase is:
  • A. 23
  • B. 46
  • C. 92
  • D. 184
Answer: C. 92
Each chromosome has two kinetochores (one per sister chromatid); 46 chromosomes × 2 = 92.
42Which of the following proteins is responsible for the 'pinching off' of vesicles from the plasma membrane during endocytosis?
  • A. Clathrin
  • B. Dynamin
  • C. Tubulin
  • D. Actin
Answer: B. Dynamin
Dynamin forms a collar around the vesicle neck and hydrolyzes GTP to pinch off the vesicle.
43The 'Nuclear Lamina' is a network of intermediate filaments that supports the nuclear envelope. It is composed of:
  • A. Lamins
  • B. Keratins
  • C. Vimentins
  • D. Tubulins
Answer: A. Lamins
Lamins are type V intermediate filaments.
44'Tay-Sachs disease' is caused by the accumulation of lipids (gangliosides) in the brain due to the deficiency of a specific enzyme in:
  • A. Mitochondria
  • B. Smooth ER
  • C. Lysosomes
  • D. Peroxisomes
Answer: C. Lysosomes
Tay-Sachs results from deficient hexosaminidase A in lysosomes.
45Which form of DNA replication occurs in both the Nucleus and the Mitochondria?
  • A. Semiconservative replication
  • B. Conservative replication
  • C. Dispersive replication
  • D. Only mitochondria use rolling circle replication
Answer: A. Semiconservative replication
Both nuclear and mitochondrial DNA replicate semiconservatively.
46A 'Satellite Chromosome' is one that possesses a:
  • A. Centromere at the very end
  • B. Secondary constriction
  • C. Lack of DNA
  • D. Circular shape
Answer: B. Secondary constriction
Satellite chromosomes have a secondary constriction (NOR) separating a small distal segment.
47'Stroma' is to Chloroplast as ________ is to Mitochondria.
  • A. Cristae
  • B. Matrix
  • C. Inner membrane
  • D. Intermembrane space
Answer: B. Matrix
Stroma (chloroplast) and matrix (mitochondria) are the soluble phases of these organelles.
48In prokaryotes, the 'pili' are primarily used for:
  • A. Locomotion
  • B. Attachment and conjugation (DNA transfer)
  • C. Protein synthesis
  • D. Protection against antibiotics
Answer: B
Pili (fimbriae) mediate attachment; sex pili transfer DNA during conjugation.
49The pH of the cytosol is approximately 7.2. The pH of the lysosomal lumen is maintained at approximately 5.0 by:
  • A. Passive diffusion of H⁺ ions
  • B. Active transport of H⁺ ions via proton pumps (V-type ATPase)
  • C. Production of organic acids
  • D. Release of OH⁻ ions
Answer: B
V-ATPases actively pump H⁺ into the lysosome, acidifying its lumen.
50During 'Apoptosis' (Programmed Cell Death), which organelle releases Cytochrome C into the cytoplasm?
  • A. Golgi apparatus
  • B. Lysosome
  • C. Mitochondria
  • D. Endoplasmic reticulum
Answer: C. Mitochondria
Cytochrome c release from mitochondria triggers caspase activation.

✅Practice MCQs — Test 3

🧪 Exam-Level Questions

50 MCQs
1The 'Transition Temperature (T_m)' of a biological membrane is the temperature at which it switches from a gel-like to a fluid state. Which of the following modifications would most effectively increase the T_m of a membrane?
  • A. Increasing the proportion of cis-unsaturated fatty acids.
  • B. Shortening the fatty acid chain lengths.
  • C. Increasing the ratio of saturated to unsaturated phospholipids.
  • D. Introducing more double bonds in the 'kink' position of the tails.
Answer: C
Saturated fatty acids pack more tightly, increasing the transition temperature.
2Which of the following best describes the 'Asymmetry' of the plasma membrane maintained by flippases and floppases?
  • A. Phosphatidylserine is primarily found on the outer leaflet to signal apoptosis.
  • B. Glycolipids are found exclusively on the cytosolic leaflet.
  • C. Phosphatidylcholine and sphingomyelin are concentrated in the exoplasmic leaflet.
  • D. Peripheral proteins are always glycosylated on the cytosolic side.
Answer: C
Flippases maintain asymmetric distribution; phosphatidylcholine and sphingomyelin are enriched in the outer leaflet.
3In the Mitochondrial Electron Transport Chain, 'Cyanide' toxicity occurs because it binds to the iron within which complex, preventing the final transfer of electrons to Oxygen?
  • A. Complex I (NADH Dehydrogenase)
  • B. Complex II (Succinate Dehydrogenase)
  • C. Complex III (Cytochrome bc₁ complex)
  • D. Complex IV (Cytochrome c oxidase)
Answer: D. Complex IV
Cyanide inhibits cytochrome c oxidase (Complex IV) by binding to heme a₃.
4The 'V-type ATPase' located on the lysosomal membrane is responsible for acidification. This process is 'electrogenic,' meaning it would create a positive charge inside the lysosome unless balanced by:
  • A. The efflux of H⁺ ions.
  • B. The influx of Cl⁻ ions through specific channels.
  • C. The active transport of Na⁺ out of the lysosome.
  • D. The breakdown of ATP into cAMP.
Answer: B
Cl⁻ influx (via CLC channels) neutralizes the positive charge from H⁺ pumping.
5Which of the following is the primary reason why 'Mycoplasma' species are naturally resistant to Vancomycin and Beta-lactams?
  • A. They possess a highly thick layer of Peptidoglycan.
  • B. They lack a cell wall entirely and incorporate sterols into their membranes.
  • C. They produce enzymes that cleave the beta-lactam ring.
  • D. Their cell wall contains D-amino acids that the drugs cannot recognize.
Answer: B
Mycoplasma has no cell wall, so drugs targeting cell wall synthesis are ineffective.
6The 'KDEL' retrieval sequence is found on soluble proteins that belong in the ER. If a protein accidentally reaches the Golgi, it is captured by KDEL receptors and sent back to the ER via:
  • A. COPII-coated vesicles
  • B. COPI-coated vesicles
  • C. Clathrin-coated vesicles
  • D. Caveolae
Answer: B. COPI-coated vesicles
COPI vesicles mediate retrograde transport from Golgi to ER.
7During 'Nuclear Import,' the small GTPase 'Ran' exists in two states. Where is the concentration of 'Ran-GTP' highest, and what is its role?
  • A. Highest in the cytoplasm; helps Importin bind to the cargo.
  • B. Highest in the nucleus; causes the dissociation of cargo from Importin.
  • C. Highest in the cytoplasm; promotes the movement of cargo through the NPC.
  • D. Highest in the nucleus; helps Exportin bind to the cargo for export.
Answer: B
Ran-GTP in the nucleus triggers cargo release from importins.
8'I-Cell Disease' (Inclusion Cell Disease) is a severe lysosomal storage disorder caused by a deficiency in the enzyme that 'tags' lysosomal enzymes with:
  • A. Glucose-6-Phosphate
  • B. Mannose-6-Phosphate
  • C. Galactose-1-Phosphate
  • D. Sialic acid
Answer: B. Mannose-6-Phosphate
Lysosomal enzymes require mannose-6-phosphate for proper targeting; deficiency causes I-cell disease.
9Which of the following proteins acts as the 'molecular motor' for 'Retrograde' transport (moving from the periphery toward the nucleus) along microtubules?
  • A. Kinesin-1
  • B. Cytoplasmic Dynein
  • C. Myosin V
  • D. Tropomyosin
Answer: B. Cytoplasmic Dynein
Dynein moves toward the minus end of microtubules (retrograde).
10The 'Signal Peptidase' enzyme performs its function in the:
  • A. Cytosol, before the protein enters the ER.
  • B. Lumen of the ER, by cleaving the signal sequence.
  • C. Golgi apparatus, during post-translational modification.
  • D. Nucleoplasm, before mRNA export.
Answer: B
Signal peptidase in the ER lumen removes the signal peptide from nascent proteins.
11The '30 nm Chromatin Fiber' is formed by the folding of the nucleosome chain. Which model suggests a 'fluid' and 'disordered' folding rather than a perfect solenoid?
  • A. Solenoid Model
  • B. Zig-zag Model
  • C. Interdigitated Model
  • D. Fractal Globule Model
Answer: B. Zig-zag Model
The zig-zag model describes a more irregular, dynamic folding pattern.
12'Telomerase' is a specialized DNA polymerase that carries its own internal template. This template is composed of:
  • A. Short sequences of DNA
  • B. RNA
  • C. Basic proteins
  • D. Zinc-finger motifs
Answer: B. RNA
Telomerase uses an RNA template (TERC) to add telomeric repeats.
13Which 'Epigenetic' modification is generally associated with 'Gene Silencing' and the formation of Heterochromatin?
  • A. Acetylation of Lysine on Histone H3
  • B. Methylation of DNA at CpG islands
  • C. Phosphorylation of Serine on Histone H2A
  • D. Ubiquitination of Histone H2B
Answer: B
DNA methylation at CpG islands and histone deacetylation promote heterochromatin formation.
14In a 'Robertsonian Translocation,' which type of chromosomes are involved in the fusion of their long arms?
  • A. Two Metacentric chromosomes
  • B. One Metacentric and one Telocentric chromosome
  • C. Two Acrocentric chromosomes
  • D. Two Sub-metacentric chromosomes
Answer: C
Robertsonian translocations involve two acrocentric chromosomes fusing at the centromere.
15'Nondisjunction' during Meiosis I results in which of the following gamete distributions?
  • A. Two normal gametes, one with n+1, and one with n-1.
  • B. Two gametes with n+1 and two gametes with n-1.
  • C. Four gametes with n+1.
  • D. All gametes are perfectly normal.
Answer: A
Meiosis I nondisjunction yields two n+1 and two n-1 gametes.
16The 'Single-Strand Binding Proteins (SSBs)' in prokaryotic replication prevent re-annealing. What is the eukaryotic functional homolog?
  • A. PCNA
  • B. RPA (Replication Protein A)
  • C. MCM Complex
  • D. FEN1
Answer: B. RPA
RPA is the eukaryotic single-strand binding protein.
17'Barr Bodies' represent inactivated X-chromosomes in females. This inactivation is mediated by a long non-coding RNA known as:
  • A. SRY
  • B. XIST
  • C. TIX
  • D. miRNA-21
Answer: B. XIST
XIST RNA coats the inactive X chromosome, leading to silencing.
18A 'Dicentric Bridge' is a chromosomal abnormality that typically occurs during anaphase due to:
  • A. Paracentric inversion crossover
  • B. Pericentric inversion crossover
  • C. Reciprocal translocation
  • D. Simple deletion
Answer: A
Paracentric inversion heterozygosity can produce a dicentric chromatid, forming a bridge in anaphase.
19Which histone variant is specifically found at the 'Centromere' and is essential for assembly of the Kinetochore?
  • A. H3.3
  • B. CENP-A (a variant of H3)
  • C. H2A.X
  • D. H2A.Z
Answer: B. CENP-A
CENP-A replaces canonical H3 at centromeres, defining kinetochore attachment sites.
20The 'Hayflick Limit' refers to the number of times a normal human cell population will divide before cell division stops. This is primarily dictated by:
  • A. Mitochondrial decay
  • B. Accumulation of lipofuscin
  • C. Telomere shortening
  • D. Smooth ER stress
Answer: C
Telomeres shorten with each division; when critically short, cells enter senescence.
21'Cardiolipin' is a unique phospholipid found almost exclusively in the inner mitochondrial membrane. Its primary function is to:
  • A. Act as a secondary messenger for cAMP.
  • B. Stabilize the 'respiratory supercomplexes' of the ETC.
  • C. Facilitate the transport of glucose into the matrix.
  • D. Anchor the ribosomes to the outer membrane.
Answer: B
Cardiolipin organizes and stabilizes electron transport chain supercomplexes.
22Which enzyme in the 'Peroxisome' is responsible for the α-oxidation of branched-chain fatty acids (like Phytanic acid)?
  • A. Catalase
  • B. Superoxide Dismutase
  • C. Phytanoyl-CoA hydroxylase
  • D. Urate Oxidase
Answer: C
Phytanoyl-CoA hydroxylase catalyzes the first step of α-oxidation of phytanic acid.
23'Molecular Chaperones' like Hsp70 assist in protein folding. They prevent misfolding by:
  • A. Adding carbohydrate chains to the protein.
  • B. Binding to exposed hydrophobic patches on the polypeptide.
  • C. Cleaving incorrect disulfide bonds.
  • D. Degenerating the protein in the proteasome.
Answer: B
Hsp70 binds hydrophobic regions to prevent aggregation and assist proper folding.
24The 'Endoplasmic Reticulum-Associated Degradation (ERAD)' pathway targets misfolded proteins for destruction in the:
  • A. Lysosome
  • B. Peroxisome
  • C. Proteasome
  • D. Nucleolus
Answer: C. Proteasome
ERAD retrotranslocates misfolded proteins to the cytosol for proteasomal degradation.
25'Mitochondrial Eve' refers to the concept that all living humans inherited their mitochondrial DNA from a single woman. This is possible because:
  • A. Sperm mitochondria are destroyed by autophagy (mitophagy) upon fertilization.
  • B. Paternal mitochondria do not contain DNA.
  • C. The egg cell lacks a nucleus.
  • D. Mitochondrial DNA is only replicated in females.
Answer: A
Paternal mitochondria are selectively degraded after fertilization, leading to maternal inheritance.
26If a cell is treated with 'Brefeldin A,' which inhibits the activation of ADP-ribosylation factors (ARFs), the most immediate result is:
  • A. Inhibition of DNA replication.
  • B. Collapse of the Golgi apparatus into the ER.
  • C. Failure of the mitochondria to produce ATP.
  • D. Permanent condensation of chromosomes.
Answer: B
Brefeldin A disrupts COPI vesicle formation, causing Golgi to merge with ER.
27In 'Oxidative Phosphorylation,' the 'Chemiosmotic Coupling' is uncoupled by 'Thermogenin' (UCP1) in brown fat. The result of this uncoupling is:
  • A. Increased ATP production.
  • B. Generation of heat instead of ATP.
  • C. Cessation of Oxygen consumption.
  • D. Accumulation of NADH in the cytosol.
Answer: B
UCP1 allows proton leak, generating heat (non-shivering thermogenesis) instead of ATP.
28Which of the following statements regarding 'Archaeal' membranes is TRUE, distinguishing them from both Bacteria and Eukaryotes?
  • A. They use fatty acids linked by ester bonds.
  • B. They use isoprenoid chains linked to glycerol by ether bonds.
  • C. They lack any form of glycerol backbone.
  • D. They contain high amounts of cholesterol.
Answer: B
Archaeal membranes have ether-linked isoprenoid chains, providing stability in extreme environments.
29The 'Nuclear Lamina' disassembles during prophase of mitosis due to the:
  • A. Acetylation of Histones.
  • B. Phosphorylation of Lamins by Cyclin-dependent kinases (CDKs).
  • C. Cleavage of DNA by endonucleases.
  • D. Dephosphorylation of the nuclear envelope.
Answer: B
CDK-mediated phosphorylation of lamins causes nuclear lamina disassembly.
30Which organelle plays a central role in 'Stress-Induced Apoptosis' by sensing the accumulation of misfolded proteins?
  • A. Lysosome
  • B. Endoplasmic Reticulum
  • C. Golgi Body
  • D. Centriole
Answer: B. Endoplasmic Reticulum
ER stress activates the unfolded protein response (UPR), which can trigger apoptosis.
31The 'Base Excision Repair (BER)' pathway in the nucleus specifically corrects:
  • A. Thymine dimers caused by UV light.
  • B. Mismatched base pairs after replication.
  • C. Chemically modified bases like uracil in DNA.
  • D. Double-strand breaks.
Answer: C
BER repairs small base modifications (e.g., deamination, oxidation).
32'Chloramphenicol' inhibits 70S ribosomes. Why can this antibiotic be toxic to human cells at high doses?
  • A. Human cytosolic ribosomes are 70S.
  • B. It inhibits mitochondrial ribosomes, which are 70S-like.
  • C. It prevents mRNA export from the nucleus.
  • D. It binds to the 80S ribosome's 40S subunit.
Answer: B
Mitochondria have 70S ribosomes; chloramphenicol can impair mitochondrial protein synthesis.
33The 'Porins' found in the outer mitochondrial membrane are structurally most similar to those found in:
  • A. The plasma membrane of Red Blood Cells.
  • B. The outer membrane of Gram-negative bacteria.
  • C. The nuclear envelope.
  • D. The endoplasmic reticulum.
Answer: B
Porins are β-barrel proteins, similar to bacterial outer membrane porins.
34In the 'Golgi Cisternal Maturation Model,' which of the following happens?
  • A. Cargo moves through static cisternae via vesicles.
  • B. The cisternae themselves move and change from cis to trans over time.
  • C. Proteins are synthesized directly in the Golgi lumen.
  • D. The Golgi remains physically attached to the RER at all times.
Answer: B
Cisternae mature from cis to trans as they acquire enzymes.
35Which of the following is the 'Rate-limiting' step of microtubule assembly?
  • A. Elongation
  • B. Nucleation (formation of the dimer core)
  • C. Treadmilling
  • D. Hydrolysis of GTP
Answer: B
Nucleation (formation of a short oligomer) is slow and rate-limiting.
36'Laminopathies' (like Hutchinson-Gilford Progeria) are caused by mutations in genes encoding:
  • A. Mitochondrial enzymes
  • B. Nuclear structural proteins
  • C. Lysosomal hydrolases
  • D. Ribosomal RNA
Answer: B
Progeria results from a mutation in LMNA, encoding lamin A.
37Which 'Intermediate Filament' is used by pathologists as a marker for tumors of epithelial origin (Carcinomas)?
  • A. Vimentin
  • B. Desmin
  • C. Keratin
  • D. Neurofilament
Answer: C. Keratin
Keratin intermediate filaments are specific to epithelial cells.
38The 'Tight Junction' (Zonula occludens) is primarily composed of which proteins?
  • A. Cadherins and Catenins
  • B. Occludins and Claudins
  • C. Integrins and Fibronectins
  • D. Connexins
Answer: B
Occludins and claudins are the main transmembrane proteins of tight junctions.
39'P-type ATPases' are a class of transporters that are autophosphorylated during the transport cycle. An example is:
  • A. The H⁺ pump in the lysosome.
  • B. The Na⁺/K⁺ ATPase in the plasma membrane.
  • C. The ABC transporters in the Golgi.
  • D. The Porins in the mitochondria.
Answer: B
Na⁺/K⁺ ATPase is a P-type ATPase that forms a phosphorylated intermediate.
40During 'Autophagy,' the double-membrane structure that engulfs the target organelle is the:
  • A. Phagosome
  • B. Autophagosome
  • C. Residual Body
  • D. Primary Lysosome
Answer: B. Autophagosome
The autophagosome is a double-membrane vesicle that sequesters cytoplasmic material for degradation.
41'Heteroplasmy' in mitochondrial genetics refers to:
  • A. The presence of both normal and mutated mtDNA within a single cell.
  • B. The presence of different types of nuclei in one cell.
  • C. The variation of lipid types in the membrane.
  • D. The ability of mitochondria to change shape.
Answer: A
Heteroplasmy is a mixture of wild-type and mutant mtDNA in a cell.
42Which 'Centromere' position is NOT found in the standard human karyotype?
  • A. Metacentric
  • B. Sub-metacentric
  • C. Acrocentric
  • D. Telocentric
Answer: D. Telocentric
Humans do not have telocentric chromosomes; centromeres are not at the absolute tip.
43The 'Signal Recognition Particle (SRP)' consists of:
  • A. Only protein
  • B. Only RNA
  • C. 7S RNA and six different polypeptides
  • D. DNA and Lipids
Answer: C
SRP is a ribonucleoprotein complex with 7S RNA and six protein subunits.
44'Microtubule-Associated Proteins (MAPs)' like Tau are critical for stabilizing axons. Hyperphosphorylation of Tau leads to:
  • A. Increased nerve conduction.
  • B. Formation of Neurofibrillary Tangles (Alzheimer's Disease).
  • C. Enhanced ATP production.
  • D. Rapid muscle contraction.
Answer: B
Hyperphosphorylated Tau aggregates into neurofibrillary tangles, a hallmark of Alzheimer's.
45Which of the following ions is kept at a very low concentration in the cytosol (10⁻⁷ M) but high in the ER lumen?
  • A. Na⁺
  • B. K⁺
  • C. Ca²⁺
  • D. Mg²⁺
Answer: C. Ca²⁺
ER lumen has high Ca²⁺ concentration (∼mM), while cytosolic Ca²⁺ is kept very low (∼100 nM).
46The 'Glycocalyx' of an animal cell, involved in cell-to-cell recognition and immune response, is chemically composed of:
  • A. Pure phospholipids
  • B. Glycoproteins and glycolipids
  • C. Integral membrane proteins only
  • D. Peripheral cholesterol molecules
Answer: B
Glycocalyx is the carbohydrate-rich coat of glycoproteins and glycolipids.
47Which of the following molecules can cross the lipid bilayer via simple diffusion without the aid of a membrane protein?
  • A. Na⁺ and K⁺ ions
  • B. Glucose
  • C. O₂ and CO₂
  • D. ATP
Answer: C. O₂ and CO₂
Small nonpolar gases (O₂, CO₂) diffuse freely across the lipid bilayer.
48In the 'Fluid Mosaic Model,' which factor most significantly prevents the membrane from becoming too rigid at low temperatures?
  • A. Increasing the concentration of saturated fatty acids
  • B. The presence of cholesterol acting as a temperature buffer
  • C. The presence of long-chain hydrocarbons
  • D. Tight packing of integral proteins
Answer: B
Cholesterol modulates fluidity; at low T, it prevents packing.
49'Active Transport' is distinguished from 'Facilitated Diffusion' by which of the following requirements?
  • A. The use of a carrier protein
  • B. Movement along a concentration gradient
  • C. The direct or indirect consumption of metabolic energy (ATP)
  • D. The involvement of the Golgi apparatus
Answer: C
Active transport requires energy (ATP or ion gradient) to move against gradient.
50Which of the following junctional complexes in animal cells provides the strongest mechanical attachment between adjacent cells?
  • A. Tight junctions
  • B. Desmosomes (Anchoring junctions)
  • C. Gap junctions
  • D. Plasmodesmata
Answer: B. Desmosomes
Desmosomes use cadherins and intermediate filaments to provide strong adhesion.

📄Past Paper MCQs

📅 Actual MDCAT / NUMS Questions

49 MCQs
1Which of the following is the outermost boundary in most plant cells?
MDCAT 2016
  • A. Plasma membrane
  • B. Glycocalyx
  • C. Cell wall
  • D. Cytoplasm
Answer: C. Cell wall
Plant cells have a rigid cell wall outside the plasma membrane.
2The cell wall is absent in:
NUMS 2017
  • A. Bacteria
  • B. Yeast
  • C. Mycoplasma
  • D. Algae
Answer: C. Mycoplasma
Mycoplasma lacks a cell wall; it has a flexible plasma membrane with sterols.
3The primary wall of the plant cell is composed of:
MDCAT 2019
  • A. Chitin
  • B. Pectin and Cellulose
  • C. Lignin
  • D. Glycoproteins
Answer: B. Pectin and Cellulose
Primary wall contains cellulose microfibrils embedded in pectin and hemicellulose.
4Which structure is responsible for the movement of materials between adjacent plant cells?
NUMS 2020
  • A. Tight junctions
  • B. Gap junctions
  • C. Plasmodesmata
  • D. Desmosomes
Answer: C. Plasmodesmata
Plasmodesmata are channels for intercellular transport in plants.
5In a typical animal cell, the cell membrane contains ________, which is absent in plant cell membranes.
MDCAT 2022
  • A. Phospholipids
  • B. Proteins
  • C. Cholesterol
  • D. Glycolipids
Answer: C. Cholesterol
Animal cell membranes contain cholesterol for fluidity; plant membranes have little cholesterol.
6Which of the following is absent in a prokaryotic cell?
MDCAT 2017
  • A. DNA
  • B. Ribosomes
  • C. Mitochondria
  • D. Plasma membrane
Answer: C. Mitochondria
Prokaryotes lack membrane-bound organelles like mitochondria.
7The size of ribosomes in a prokaryotic cell is:
NUMS 2018
  • A. 80S
  • B. 70S
  • C. 60S
  • D. 40S
Answer: B. 70S
Prokaryotic ribosomes are 70S.
8The cell wall of Archaebacteria differs from Eubacteria by lacking:
MDCAT 2021
  • A. Proteins
  • B. Polysaccharides
  • C. Peptidoglycan
  • D. Lipids
Answer: C. Peptidoglycan
Archaea lack peptidoglycan; their cell walls contain pseudopeptidoglycan or other polymers.
9Which of the following is a membrane-bound organelle found in eukaryotes but not in prokaryotes?
NUMS 2023
  • A. Ribosome
  • B. Lysosome
  • C. Cytoplasm
  • D. Plasma membrane
Answer: B. Lysosome
Lysosomes are membrane-bound organelles absent in prokaryotes.
10The hereditary material in prokaryotes is:
MDCAT 2024
  • A. Enclosed in a nuclear envelope
  • B. Linear DNA
  • C. Circular DNA floating in the cytoplasm
  • D. Only RNA
Answer: C. Circular DNA floating in the cytoplasm
Prokaryotes have a single circular DNA in the nucleoid region.
11Prokaryotes divide by a process called:
MDCAT 2018
  • A. Mitosis
  • B. Meiosis
  • C. Binary fission
  • D. Schizogony
Answer: C. Binary fission
Binary fission is the simple division method of prokaryotes.
12The photosynthetic prokaryotes lack:
NUMS 2019
  • A. Chlorophyll
  • B. Ribosomes
  • C. Chloroplasts
  • D. Cell wall
Answer: C. Chloroplasts
Prokaryotes have chlorophyll but no chloroplasts; photosynthesis occurs on infolded membranes.
13Subunits of 80S ribosomes are:
MDCAT 2020
  • A. 50S and 30S
  • B. 60S and 40S
  • C. 70S and 10S
  • D. 60S and 30S
Answer: B. 60S and 40S
Eukaryotic 80S ribosomes consist of 60S and 40S subunits.
14Peptidoglycan is also known as:
NUMS 2021
  • A. Cellulose
  • B. Murein
  • C. Chitin
  • D. Lignin
Answer: B. Murein
Peptidoglycan is also called murein.
15Mesosomes are the internal extensions of the:
MDCAT 2025
  • A. Cell wall
  • B. Nuclear membrane
  • C. Plasma membrane
  • D. ER
Answer: C. Plasma membrane
Mesosomes are infoldings of the plasma membrane in bacteria.
16Which organelle is known as the 'suicide bag' of the cell?
MDCAT 2016
  • A. Mitochondria
  • B. Lysosome
  • C. Golgi body
  • D. Ribosome
Answer: B. Lysosome
Lysosomes contain digestive enzymes that can destroy the cell if ruptured.
17The major site for lipid synthesis in the cell is:
NUMS 2017
  • A. Rough ER
  • B. Smooth ER
  • C. Golgi apparatus
  • D. Nucleolus
Answer: B. Smooth ER
Smooth ER synthesizes lipids, steroids, and detoxifies drugs.
18Cristae are found in which organelle?
MDCAT 2017
  • A. Chloroplast
  • B. Mitochondria
  • C. Golgi apparatus
  • D. Endoplasmic reticulum
Answer: B. Mitochondria
Cristae are folds of the inner mitochondrial membrane.
19The receiving face of the Golgi apparatus is called:
NUMS 2018
  • A. Trans face
  • B. Cis face
  • C. Shipping face
  • D. Maturing face
Answer: B. Cis face
The cis face receives vesicles from the ER.
20Which organelle is involved in the detoxification of drugs and poisons?
MDCAT 2019
  • A. RER
  • B. SER
  • C. Mitochondria
  • D. Lysosomes
Answer: B. SER
Smooth ER in liver cells contains cytochrome P450 for detoxification.
21Ribosomes are synthesized in the:
NUMS 2020
  • A. Cytoplasm
  • B. Golgi body
  • C. Nucleolus
  • D. Rough ER
Answer: C. Nucleolus
The nucleolus is the site of ribosome biogenesis.
22The fluid-filled space inside the mitochondria is called:
MDCAT 2021
  • A. Stroma
  • B. Matrix
  • C. Lumen
  • D. Cisternae
Answer: B. Matrix
The matrix is the inner compartment of mitochondria.
23Which organelle is responsible for the glycosylation of proteins?
NUMS 2022
  • A. Golgi apparatus
  • B. Mitochondria
  • C. Lysosome
  • D. Ribosome
Answer: A. Golgi apparatus
Golgi modifies proteins by adding carbohydrate groups.
24Enzymes for the Krebs cycle are located in the:
MDCAT 2023
  • A. Mitochondrial inner membrane
  • B. Mitochondrial matrix
  • C. Cytosol
  • D. Intermembrane space
Answer: B. Mitochondrial matrix
Krebs cycle enzymes are in the mitochondrial matrix.
25The function of the Rough Endoplasmic Reticulum is:
NUMS 2024
  • A. Lipid synthesis
  • B. Protein synthesis
  • C. Detoxification
  • D. Storage of Calcium
Answer: B. Protein synthesis
RER synthesizes and processes secretory and membrane proteins.
26Lysosomes contain ________ enzymes.
MDCAT 2018
  • A. Oxidative
  • B. Hydrolytic
  • C. Synthetic
  • D. Reductive
Answer: B. Hydrolytic
Lysosomes contain hydrolytic enzymes (acid hydrolases).
27The stack of cisternae in a plant cell is specifically called:
NUMS 2016
  • A. Grana
  • B. Dictyosome
  • C. Mesosome
  • D. Lysosome
Answer: B. Dictyosome
In plants, the Golgi stack is called a dictyosome.
28ATP synthesis occurs in the ________ of mitochondria.
MDCAT 2020
  • A. Outer membrane
  • B. F₀-F₁ particles (ATP synthase)
  • C. Intermembrane space
  • D. Outer chamber
Answer: B. F₀-F₁ particles (ATP synthase)
ATP synthase (F₀F₁) is located on the inner membrane/cristae.
29Which of the following organelle is semi-autonomous?
NUMS 2025
  • A. Golgi complex
  • B. Mitochondria
  • C. Endoplasmic reticulum
  • D. Lysosome
Answer: B. Mitochondria
Mitochondria have their own DNA and ribosomes, making them semi-autonomous.
30Nuclear pores allow the transport of:
MDCAT 2022
  • A. DNA
  • B. Chromosomes
  • C. RNA and Proteins
  • D. Mitochondria
Answer: C. RNA and Proteins
Nuclear pores facilitate bidirectional transport of RNA and proteins.
31Chromosomes are composed of:
MDCAT 2017
  • A. DNA and RNA
  • B. DNA and Protein
  • C. DNA and Lipids
  • D. RNA and Protein
Answer: B. DNA and Protein
Chromatin consists of DNA, histones, and non-histone proteins.
32The number of chromosomes in a human somatic cell is:
NUMS 2018
  • A. 23
  • B. 46
  • C. 44
  • D. 48
Answer: B. 46
Human somatic cells are diploid (2n=46).
33A chromosome with a centromere at the very end is called:
MDCAT 2019
  • A. Metacentric
  • B. Sub-metacentric
  • C. Telocentric
  • D. Acrocentric
Answer: C. Telocentric
Telocentric centromeres are at the chromosome tip (not found in humans).
34The basic structural unit of a chromosome is:
NUMS 2020
  • A. Nucleotide
  • B. Nucleoid
  • C. Nucleosome
  • D. Nucleolus
Answer: C. Nucleosome
Nucleosomes are the repeating units of chromatin.
35The protein involved in the packaging of DNA in eukaryotes is:
MDCAT 2021
  • A. Actin
  • B. Tubulin
  • C. Histone
  • D. Keratin
Answer: C. Histone
Histones are basic proteins that package DNA.
36Sister chromatids are joined at the:
NUMS 2022
  • A. Telomere
  • B. Centromere
  • C. Kinetochore
  • D. Chiasmata
Answer: B. Centromere
Sister chromatids are held together by the centromere.
37Chromatin that is loosely packed and transcriptionally active is:
MDCAT 2023
  • A. Heterochromatin
  • B. Euchromatin
  • C. Pro-chromatin
  • D. Meta-chromatin
Answer: B. Euchromatin
Euchromatin is decondensed and transcriptionally active.
38The 'p' arm of a chromosome refers to the:
NUMS 2024
  • A. Long arm
  • B. Short arm
  • C. Satellite arm
  • D. Centromere
Answer: B. Short arm
p arm is the short arm (petit).
39In a nucleosome, DNA is wrapped around ________ histone molecules.
MDCAT 2020
  • A. 4
  • B. 6
  • C. 8
  • D. 10
Answer: C. 8
The core histone octamer contains 8 histone molecules.
40How many autosomes are present in a human sperm?
NUMS 2019
  • A. 44
  • B. 22
  • C. 23
  • D. 46
Answer: B. 22
Human sperm has 22 autosomes (plus one sex chromosome).
41Secondary constriction on a chromosome is also known as:
MDCAT 2024
  • A. Centromere
  • B. Telomere
  • C. Nucleolar organizer
  • D. Kinetochore
Answer: C. Nucleolar organizer
Secondary constriction (NOR) contains rRNA genes.
42Chromosomes are most condensed and visible during:
NUMS 2021
  • A. Prophase
  • B. Metaphase
  • C. Anaphase
  • D. Telophase
Answer: A. Prophase
Prophase chromosomes condense and become visible.
43Metacentric chromosomes have a ________ shape during anaphase.
MDCAT 2016
  • A. J-shape
  • B. L-shape
  • C. V-shape
  • D. I-shape
Answer: C. V-shape
Metacentric chromosomes appear V-shaped during anaphase.
44The ends of chromosomes are called:
NUMS 2023
  • A. Centromeres
  • B. Telomeres
  • C. Satellites
  • D. Chromatids
Answer: B. Telomeres
Telomeres protect chromosome ends.
45Histones are rich in basic amino acids like:
MDCAT 2025
  • A. Valine and Leucine
  • B. Lysine and Arginine
  • C. Glycine and Alanine
  • D. Serine and Threonine
Answer: B. Lysine and Arginine
Lysine and arginine are positively charged, binding DNA.
46Karyotyping involves the study of chromosomes during:
NUMS 2017
  • A. Interphase
  • B. Metaphase
  • C. Prophase
  • D. G1 phase
Answer: B. Metaphase
Metaphase chromosomes are easiest to visualize and classify.
47A chromosome with a very short 'p' arm and a long 'q' arm is:
MDCAT 2018
  • A. Metacentric
  • B. Acrocentric
  • C. Telocentric
  • D. Sub-metacentric
Answer: B. Acrocentric
Acrocentric chromosomes have a very short p arm.
48In human females, the sex chromosomes are:
NUMS 2020
  • A. XY
  • B. XX
  • C. XO
  • D. XXY
Answer: B. XX
Females have two X chromosomes.
49The DNA content of a cell doubles during:
MDCAT 2019
  • A. G1 phase
  • B. G2 phase
  • C. S phase
  • D. M phase
Answer: C. S phase
DNA replication occurs during S phase.

🔍Direct Search Queries — Cell Structure & Function

Exact search terms students use on Google for this chapter. Click any to jump to the relevant section:

cell structure and function MDCAT notes prokaryotic vs eukaryotic cells plant vs animal cell differences cell organelles and their functions fluid mosaic model of plasma membrane nucleus structure and function rough ER vs smooth ER Golgi apparatus function mitochondria structure and function lysosome function and structure peroxisome vs glyoxysome nucleosome structure chromosome types by centromere euchromatin vs heterochromatin 9+2 arrangement cilia flagella tight junctions desmosomes gap junctions what is cell structure difference prokaryote eukaryote why mitochondria is powerhouse what are histones what is 70S vs 80S ribosome cell wall composition cell structure MCQs with answers cell structure MCQs pdf organelles MCQs MDCAT past papers cell structure UHS MDCAT biology MCQs NUMS biology past papers cell structure chapter 4 class 11 notes cell organelles notes class 11 biology chromosome structure class 11 notes endosymbiotic theory evidence

❔Frequently Asked Questions

What is cell structure and function?
Cell structure and function studies the parts of a cell (organelles, membranes, chromosomes) and the roles they play. This chapter covers prokaryotic vs eukaryotic cells, plant vs animal cells, nucleus, ER, Golgi, mitochondria, and chromosomes.
What is the difference between prokaryotic and eukaryotic cells?
Prokaryotes lack a membrane-bound nucleus and organelles, have 70S ribosomes, circular DNA, and peptidoglycan cell walls. Eukaryotes have a true nucleus, 80S ribosomes, linear histone-bound DNA, membrane-bound organelles, and are 10-100 µm in size.
What are the main differences between plant and animal cells?
Plant cells have a cellulose cell wall, large central vacuole, plastids (chloroplasts), and plasmodesmata. Animal cells have centrioles and cholesterol in the membrane. Both share a nucleus, mitochondria, ER, Golgi, and ribosomes.
What is the fluid mosaic model?
The fluid mosaic model describes the plasma membrane as a fluid phospholipid bilayer with embedded proteins that can move laterally. Fluidity depends on fatty acid saturation, chain length, and cholesterol.
What are the functions of the nucleus?
The nucleus stores genetic material (DNA), coordinates cell activities, and controls protein synthesis via transcription. It contains the nucleolus (rRNA synthesis) and is bounded by a double-membrane envelope with pores.
What is the function of the rough and smooth ER?
Rough ER (with ribosomes) synthesizes and processes proteins for secretion and membranes. Smooth ER synthesizes lipids, steroids, detoxifies drugs, and stores Ca²⁺ (in muscle as sarcoplasmic reticulum).
What does the Golgi apparatus do?
The Golgi modifies, sorts, and packages proteins and lipids. It has a cis (receiving) face and a trans (shipping) face, and produces lysosomes and vesicles.
Why are mitochondria called the powerhouse of the cell?
Mitochondria produce ATP via oxidative phosphorylation in the cristae of the inner membrane. They have their own DNA and 70S ribosomes, and are semi-autonomous.
What is a nucleosome?
A nucleosome is the basic unit of chromatin — 147 base pairs of DNA wrapped 1.65 times around a histone octamer (2 each of H2A, H2B, H3, H4). Histone H1 is the linker.
What is the difference between euchromatin and heterochromatin?
Euchromatin is loosely packed and transcriptionally active (light under EM). Heterochromatin is densely packed and inactive (dark), including centromeres and telomeres (constitutive).
How many chromosomes do humans have?
Humans have 46 chromosomes (2n) — 44 autosomes (22 pairs) plus 2 sex chromosomes (XX female, XY male). Gametes are haploid with 23 chromosomes.
What are the types of chromosomes by centromere position?
Metacentric (central), sub-metacentric (slightly off-center), acrocentric (near the end), and telocentric (at the tip). Humans lack telocentric chromosomes; human acrocentrics are 13, 14, 15, 21, 22.
What is the function of the lysosome?
Lysosomes contain acid hydrolases (pH ~5) for intracellular digestion, autophagy, phagocytosis, and autolysis. Marker enzyme: acid phosphatase.
What is a peroxisome?
Peroxisomes contain catalase and oxidase enzymes to break down H₂O₂ and fatty acids. Glyoxysomes are specialized peroxisomes in plants that convert fats to carbohydrates.
How many MCQs come from Cell Structure in MDCAT?
Cell Structure and Function typically contributes 4–6 MCQs out of 81 Biology MCQs in MDCAT.
Which topics from Cell Structure are most frequently asked in MDCAT?
Prokaryotic vs eukaryotic differences, 70S vs 80S ribosomes, plant vs animal cell features, fluid mosaic model, nucleus function, ER/Golgi/mitochondria functions, nucleosome structure, and chromosome types.
What is the 9+2 arrangement?
The 9+2 arrangement describes eukaryotic cilia and flagella — 9 microtubule doublets surrounding 2 central singlets. Centrioles and basal bodies have 9+0 triplets.
What are desmosomes, tight junctions, and gap junctions?
Tight junctions seal adjacent cells (occludins, claudins), desmosomes adhere via cadherins to intermediate filaments, and gap junctions allow communication via connexins.
What is the endosymbiotic theory?
The endosymbiotic theory states that mitochondria and chloroplasts originated from engulfed bacteria. Evidence: own circular DNA, 70S ribosomes, double membrane, and binary fission.
Which organelles are semi-autonomous?
Mitochondria and chloroplasts are semi-autonomous — they have their own DNA, ribosomes (70S), and can divide by binary fission.

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Biodiversity
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