Topic 2: The Cell & Tissues

The cell is the basic structural & functional unit of life — every organism in Topic 1's classification is built from it. This single-source file covers cell theory and its discovery, the great prokaryotic vs eukaryotic divide, the plant vs animal cell, and each organelle (membrane, wall, nucleus, mitochondria, chloroplast, ER, Golgi, ribosomes, lysosomes, vacuoles, centrosome, cilia & flagella, capsule, fimbriae), the genetic material & nucleic acids, and how cells group into animal & plant tissues — with labelled diagrams, tables and real dated PYQs with full model answers.

UPSC Prelims · Mains GS-III Organelles · Cell Theory ~35 min read Prokaryote vs Eukaryote High Prelims Weight

1.The Cell & Cell Theory
2.Prokaryotic vs Eukaryotic Cells
3.Plant Cell vs Animal Cell
4.Cell Boundary — Membrane, Wall & Surface
5.Organelles I — Nucleus, ER, Ribosomes, Golgi
6.Organelles II — Mitochondria, Plastids, Lysosomes, Vacuoles, Centrosome
7.Genetic Material & Nucleic Acids
8.Animal Tissues
9.Plant Tissues
10.Current Affairs Link
11.Prelims PYQs
12.Mains PYQs + Model Answers
★15-Minute Revision Box

Conceptual Clarity — How UPSC Tests the Cell

The cell is a dense, high-return Prelims topic: a single diagram hides dozens of factual hooks. Sort your prep into three question-types:

Definitional / static — "which organelle does X?" (powerhouse = mitochondria; suicide bag = lysosome; protein factory = ribosome). Pure recall; the commonest style.
Statement-elimination — two/three statements on, e.g., "prokaryotes lack a nuclear membrane and membrane-bound organelles" where one word decides the answer. Needs the prokaryote/eukaryote and plant/animal contrasts exact.
Applied / current — a news hook (mitochondrial DNA, stem cells, CAR-T, lab-grown tissue) traced back to a cell fundamental. Also the GS-III bridge to biotech and health.

Highest-frequency themes: organelle functions & nicknames · prokaryote vs eukaryote · plant vs animal cell differences · mitochondria & chloroplast (double membrane, own DNA) · the four animal tissues · meristematic vs permanent plant tissue · xylem & phloem.

1. The Cell & Cell Theory

The cell (Latin cella = small room) is the smallest unit that can carry out all life processes — the basic structural and functional unit of all living organisms. Organisms may be unicellular (one cell does everything, e.g. amoeba, bacteria) or multicellular (division of labour among many cells, e.g. humans).

1.1 Discovery — who found what

Scientist	Contribution
Robert Hooke (1665)	First observed & named "cells" — in a thin slice of cork under his microscope (actually dead cell walls).
Anton van Leeuwenhoek	First saw living cells (bacteria, protozoa — "animalcules") — "father of microbiology".
Robert Brown (1831)	Discovered the nucleus.
Schleiden (1838) & Schwann (1839)	Proposed the cell theory (Schleiden for plants, Schwann for animals).
Rudolf Virchow (1855)	Added: "Omnis cellula e cellula" — every cell arises from a pre-existing cell.

1.2 The cell theory — three tenets

All living organisms are made of one or more cells.
The cell is the basic unit of structure and function in living things.
All cells arise from pre-existing cells (Virchow).

Prelims lock: Hooke named the cell (dead cork); Leeuwenhoek saw the first living cells; Brown found the nucleus; cell theory = Schleiden & Schwann, completed by Virchow. These attributions are a repeat "match the following".

Size & number facts: most cells are microscopic; the largest cell is an ostrich egg; the longest cell is the nerve cell (neuron); the smallest are mycoplasma/PPLO. Cell shape follows function (disc-shaped RBC, branched neuron, spindle muscle).

2. Prokaryotic vs Eukaryotic Cells

The single most important division in all biology is between prokaryotic ("before nucleus") and eukaryotic ("true nucleus") cells — the basis of the whole five-kingdom system in Topic 1.

Fig 2.1 — The defining difference: prokaryotes have free DNA (nucleoid) and no membrane-bound organelles; eukaryotes have a true nucleus and organelles.

Feature	Prokaryotic	Eukaryotic
Nucleus	No true nucleus — DNA lies free as a nucleoid; no nuclear membrane.	True, membrane-bound nucleus.
Membrane-bound organelles	Absent (no mitochondria, ER, Golgi, plastids).	Present.
Ribosomes	Present but smaller (70S).	Larger (80S); 70S inside mitochondria/chloroplasts.
Cell wall	Present (peptidoglycan/murein in bacteria).	Present in plants (cellulose)/fungi (chitin); absent in animals.
Size & DNA	Small (~1–10 µm); single circular DNA, often plasmids.	Larger (~10–100 µm); DNA on multiple linear chromosomes with histones.
Examples	Bacteria, cyanobacteria, archaea, mycoplasma.	Protists, fungi, plants, animals.

Prelims lock: prokaryotes lack a nuclear membrane AND membrane-bound organelles, but they do have ribosomes and a cell wall. "Prokaryotes have no ribosomes" is a classic false statement.

3. Plant Cell vs Animal Cell

Both are eukaryotic, but differ in a few decisive structures that come up almost every year.

Structure	Plant cell	Animal cell
Cell wall	Present (cellulose) — rigid.	Absent — only a membrane.
Plastids (incl. chloroplast)	Present — enable photosynthesis.	Absent.
Vacuole	One large central vacuole.	Small or absent.
Centrosome / centrioles	Usually absent.	Present (help cell division).
Shape	Fixed, usually rectangular.	Irregular, rounded.
Storage food	Starch.	Glycogen.

Prelims lock: only plant cells have a cell wall, plastids and a large central vacuole; only animal cells reliably have a centrosome. Both have a nucleus, mitochondria, ER, Golgi, ribosomes and a cell membrane.

4. Cell Boundary — Membrane, Wall & Surface Structures

4.1 Cell (plasma) membrane

The living outer boundary of every cell; a fluid mosaic of a phospholipid bilayer with embedded proteins (Singer & Nicolson model).
Selectively permeable — controls what enters/leaves (by diffusion, osmosis, active transport). This regulation is its defining role.

4.2 Cell wall

A non-living, rigid layer outside the membrane; gives shape and protection. Composition varies: cellulose (plants), chitin (fungi), peptidoglycan/murein (bacteria). Absent in animals.

4.3 Bacterial surface extras (from the syllabus)

Structure	Role
Capsule	Extra slimy protective layer outside the wall in some bacteria; aids in resisting drying & the host immune system (virulence).
Fimbriae (pili)	Tiny hair-like projections for attachment to surfaces/host cells; sex pili aid gene transfer (conjugation).
Flagella	Long whip-like structure for movement.
Cilia	Short, numerous hair-like projections for movement or moving fluids (in some eukaryotes, e.g. Paramecium, human respiratory tract).

Distinguish: flagella = few & long (locomotion); cilia = many & short; fimbriae/pili = attachment; capsule = protection/virulence. A common statement-matching trap.

5. Organelles I — Nucleus, ER, Ribosomes, Golgi

5.1 Nucleus — the control centre

Bounded by a double nuclear membrane with pores; contains chromatin (DNA + protein), which condenses into chromosomes during division, and a dense nucleolus (makes ribosomes).
Directs all cell activity and carries hereditary information — the "brain" of the cell.

5.2 Endoplasmic reticulum (ER)

A network of membrane tubes/sheets. Rough ER (with ribosomes) — makes/transports proteins; Smooth ER (no ribosomes) — makes lipids & detoxifies.

5.3 Ribosomes — the protein factory

Tiny granules of RNA + protein; the site of protein synthesis. Found free in cytoplasm or on rough ER. Present in both prokaryotes (70S) and eukaryotes (80S).

5.4 Golgi apparatus — the packaging & despatch unit

Stacked flattened sacs that modify, package and secrete proteins/lipids; also forms lysosomes and cell-wall material in plants. Discovered by Camillo Golgi.

Nicknames to memorise: nucleus = "control centre/brain"; ribosome = "protein factory"; Golgi = "packaging & despatch (post office)"; rough ER = protein transport; smooth ER = lipids & detox.

6. Organelles II — Mitochondria, Plastids, Lysosomes, Vacuoles, Centrosome

6.1 Mitochondria — the powerhouse

Double-membraned; inner membrane folded into cristae. Site of aerobic respiration — makes ATP (energy). Hence "powerhouse of the cell".
Has its own DNA & 70S ribosomes (semi-autonomous) — evidence for the endosymbiotic theory (mitochondria & chloroplasts were once free-living bacteria). Mitochondrial DNA is maternally inherited.

6.2 Plastids (plant cells only)

Plastid	Role
Chloroplast	Green (chlorophyll); site of photosynthesis. Double-membraned; own DNA & ribosomes.
Chromoplast	Coloured (red/yellow/orange) — flowers, fruits, carrots.
Leucoplast	Colourless — stores starch/oil/protein.

6.3 Lysosomes, vacuoles & centrosome

Lysosome — "suicide bag": contains digestive enzymes; breaks down waste & worn-out parts; self-destructs the cell when needed.
Vacuole — fluid-filled sac; large & central in plant cells (stores cell sap, gives turgidity); small in animals.
Centrosome/centrioles — in animal cells; organise the spindle fibres during cell division.
Peroxisome — breaks down fatty acids & detoxifies (e.g. hydrogen peroxide).

High-yield facts: mitochondria & chloroplasts are double-membraned with their own DNA. Lysosome = "suicide bag" (Golgi-derived). Only plant cells have plastids & a large central vacuole; centrosome is typically animal-only.

7. Genetic Material & Nucleic Acids

The nucleus stores the cell's instructions as nucleic acids. (Heredity & genetics are covered in depth in Topic 4; here we fix the structural basics that Prelims tests.)

Feature	DNA	RNA
Full form	Deoxyribonucleic acid	Ribonucleic acid
Strands	Double helix (two strands)	Usually single strand
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U (uracil), G, C
Role	Stores hereditary information	Carries out protein synthesis (mRNA, tRNA, rRNA)

A gene is a segment of DNA that codes for a protein/trait. DNA is packaged with proteins into chromosomes; humans have 46 (23 pairs).
The double helix was described by Watson & Crick (1953) (using Rosalind Franklin's X-ray data). Base pairing: A–T, G–C.
The flow of information: DNA → RNA → Protein (the "central dogma").

Prelims lock: RNA has uracil (U) instead of thymine and ribose sugar; DNA is double-stranded with deoxyribose. Watson & Crick (1953) = double-helix structure. These recur in statement questions.

8. Animal Tissues

A tissue is a group of similar cells performing a common function. In animals there are four basic types.

Fig 2.2 — Epithelial (covering), Connective (support), Muscular (movement), Nervous (control).

Tissue	Function	Examples
Epithelial	Covering & lining of body surfaces, cavities, organs; protection, absorption, secretion.	Skin, lining of mouth, gut & blood vessels; glands.
Connective	Binds, supports & connects; has a matrix between cells.	Blood (fluid matrix), bone, cartilage, tendon, ligament, adipose (fat).
Muscular	Contraction → movement.	Skeletal (voluntary, striated), cardiac (heart, involuntary, striated), smooth (involuntary, unstriated).
Nervous	Receives & transmits impulses; control & coordination.	Neurons + supporting glial cells.

High-yield: blood is a connective tissue (fluid matrix = plasma) — a favourite trap. Cardiac muscle is striated but involuntary; skeletal is striated & voluntary; smooth is unstriated & involuntary.

9. Plant Tissues

Plant tissues are broadly meristematic (dividing) or permanent (differentiated).

Type	Sub-type / feature	Role
Meristematic (actively dividing)	Apical (tips of root/shoot)	Increase in length (primary growth).
Meristematic (actively dividing)	Lateral (cambium) / Intercalary	Increase in girth; intercalary (at nodes) regrows grass.
Permanent — Simple (one cell type)	Parenchyma	Packing, storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma).
	Collenchyma	Flexible mechanical support (young stems, leaf stalks).
	Sclerenchyma	Hard, dead cells — rigidity (husk, nut shell, fibres).
Permanent — Complex (vascular)	Xylem	Conducts water & minerals upward (roots → leaves); also support. Mostly dead cells.
Permanent — Complex (vascular)	Phloem	Conducts food (sugars) both ways (translocation). Living cells.

Prelims lock: xylem = water (upward, dead cells); phloem = food (both directions, living). Meristem = growth zone. Sclerenchyma gives hardness (coconut husk). Cork (bark) is protective dead tissue.

Mains linkage (GS-III): tissue science underpins tissue culture & micropropagation (Topic 10 biotech), stem-cell & regenerative medicine and lab-grown meat — the fundamentals here feed directly into applied biotech questions.

10. Current Affairs Link (2024–2026)

Cell biology is static, but modern medicine and biotech keep giving it news hooks. Verify the latest before the exam. check for latest update or data

Stem cells & regenerative medicine: stem cells (unspecialised cells that can become any tissue) drive therapy research — grounded in the cell & tissue basics here. India regulates stem-cell therapy via ICMR-DBT guidelines. check for latest update or data

Mitochondrial biology: "three-parent baby" mitochondrial-replacement techniques and mitochondrial-DNA research keep the "powerhouse + own DNA + maternal inheritance" facts topical. check for latest update or data

Lab-grown tissue & cultured meat: tissue engineering and cell-cultured meat scale up globally — direct applications of animal-tissue and cell-culture fundamentals. check for latest update or data

Recent theme	Fundamental it tests	Why it matters for UPSC
Stem-cell therapy	Cell differentiation; tissues	GS-III health & ethics; regulation.
CAR-T cell therapy (India's first, indigenous)	Cells & immunity	Links to Topics 5 & 10; a strong example.
Cultured / lab-grown meat	Animal tissue & cell culture	GS-III food-tech & sustainability.
Mitochondrial-replacement	Mitochondria & mtDNA	Prelims fact + GS-IV ethics angle.

Recurring exam hooks: powerhouse of the cell · suicide bag · prokaryote vs eukaryote · plant vs animal cell · is blood a tissue? · xylem vs phloem · organelle with its own DNA.

11. Prelims PYQs

Objective questions anchored to genuinely tested UPSC themes on the cell & tissues. Each carries a worked rationale.

UPSC Prelims — Organelles

Q: The "powerhouse of the cell", the site of aerobic respiration and ATP production, is the —

(a) ribosome
(b) mitochondrion
(c) Golgi apparatus
(d) lysosome

Answer: (b) Mitochondrion — double-membraned, has its own DNA, and produces ATP by aerobic respiration.

UPSC Prelims — Prokaryote

Q: Which of the following is characteristic of a prokaryotic cell?

(a) Membrane-bound nucleus
(b) Presence of mitochondria
(c) DNA lies free as a nucleoid
(d) 80S ribosomes

Answer: (c) In prokaryotes DNA is free (nucleoid) with no nuclear membrane; they lack mitochondria and have 70S ribosomes.

UPSC Prelims — Tissues

Q: Which of the following is a connective tissue?

(a) Skin epithelium
(b) Blood
(c) Neuron
(d) Smooth muscle

Answer: (b) Blood is a connective tissue with a fluid matrix (plasma). Bone and cartilage are also connective tissues.

UPSC Prelims — Plant cell

Q: Which structures are present in a plant cell but absent in a typical animal cell?

(a) Nucleus and mitochondria
(b) Cell wall and chloroplast
(c) Ribosomes and Golgi
(d) Cell membrane and ER

Answer: (b) Cell wall (cellulose) and chloroplast/plastids are plant-specific; the others are common to both.

UPSC Prelims — Cell theory

Q: The dictum "Omnis cellula e cellula" (every cell arises from a pre-existing cell) was given by —

(a) Robert Hooke
(b) Schleiden
(c) Rudolf Virchow
(d) Leeuwenhoek

Answer: (c) Virchow (1855). Hooke named the cell; Schleiden & Schwann framed the cell theory; Virchow completed it.

UPSC Prelims — Vascular tissue

Q: In plants, the upward conduction of water and minerals from roots to leaves is carried out by —

(a) xylem
(b) phloem
(c) parenchyma
(d) collenchyma

Answer: (a) Xylem (mostly dead cells) conducts water upward; phloem translocates food (sugars) in both directions.

UPSC Prelims — Organelle DNA

Q: Which two organelles possess their own DNA and ribosomes?

(a) Golgi apparatus and lysosome
(b) Nucleus and ribosome
(c) Mitochondrion and chloroplast
(d) Vacuole and centrosome

Answer: (c) Mitochondria and chloroplasts are semi-autonomous (own DNA + 70S ribosomes) — the basis of the endosymbiotic theory.

UPSC Prelims — Nucleic acid

Q: Which nitrogenous base is present in RNA but not in DNA?

(a) Thymine
(b) Adenine
(c) Uracil
(d) Guanine

Answer: (c) RNA has uracil (U) in place of thymine (T); RNA sugar is ribose, DNA sugar is deoxyribose.

Prelims — anticipated themes

Likely: organelle nicknames (powerhouse / suicide bag / protein factory) · prokaryote vs eukaryote statements · plant vs animal cell · mitochondria & chloroplast own DNA · blood as connective tissue · xylem vs phloem · DNA vs RNA (uracil, ribose, strands) · capsule/fimbriae/flagella/cilia roles · cell-theory attributions. check for latest update or data

12. Mains PYQs + Model Answers

Cell fundamentals anchor applied GS-III questions on health, biotech and food-tech. The frameworks below show how to deploy them analytically.

Mains GS-III 15 marks · 250 words

Q: Stem cells hold great promise for regenerative medicine but raise scientific and ethical concerns. Discuss.

Model Answer

Introduction — define: Stem cells are unspecialised cells able to divide and differentiate into specialised cell types — the biological basis of tissue repair.
Types & promise:
- Embryonic (pluripotent) · adult/tissue (multipotent) · induced pluripotent (iPSCs) — reprogrammed adult cells.
- Applications: repair of damaged tissue (spinal cord, cardiac), bone-marrow transplants, drug testing, and organ regeneration.
Concerns: ethical use of embryos; risk of tumour formation (teratoma); immune rejection; unregulated/unproven "stem-cell clinics" exploiting patients.
India's framework: ICMR-DBT National Guidelines for Stem Cell Research; only bone-marrow transplant is an approved therapy — the rest is research.
Way forward: favour ethically-sound iPSCs, strict clinical-trial oversight, public awareness against quackery, and indigenous R&D.
Conclusion: harnessing stem cells needs the cell fundamentals plus firm ethical & regulatory guardrails so promise is not lost to malpractice.

Mains GS-III 15 marks · 250 words

Q: "The endosymbiotic origin of mitochondria and chloroplasts is one of the most compelling ideas in cell biology." Explain, and note its relevance.

Model Answer

Introduction: The endosymbiotic theory holds that mitochondria & chloroplasts were once free-living prokaryotes engulfed by an ancestral eukaryotic cell, becoming permanent organelles.
Evidence:
- Both have a double membrane, their own circular DNA, and 70S (bacterial-type) ribosomes.
- They divide independently (binary fission) and their DNA resembles bacterial DNA.
Significance: explains eukaryotic complexity & energy capacity; underpins maternal inheritance of mtDNA (ancestry, forensics), mitochondrial-disease research, and mitochondrial-replacement therapy.
Conclusion: a fundamental that links evolution (Topic 1) to modern medicine and biotechnology — a good cross-cutting example.

Mains GS-III 10 marks · 150 words

Q: Cultured (lab-grown) meat is proposed as a sustainable protein source. Explain its cell-biology basis and its significance for India.

Model Answer

Introduction: Cultured meat is real animal muscle tissue grown from a small sample of animal cells in a bioreactor, without rearing/slaughtering animals.
Cell-biology basis: animal (muscle) stem cells are multiplied in a nutrient medium and differentiated into muscular tissue on a scaffold — a direct application of cell culture & tissue science.
Significance for India: lower land, water & GHG footprint; food security & protein for a large population; animal-welfare gains; new agri-biotech industry.
Challenges: high cost, scale-up, regulation (FSSAI), consumer acceptance.
Conclusion: a promising but nascent technology resting squarely on cell & tissue fundamentals.

Mains GS-III 15 marks · 250 words

Q: Explain how the structure of the cell membrane enables it to regulate the internal environment of the cell.

Model Answer

Introduction: The plasma membrane is the living boundary that separates the cell's interior from its surroundings and controls exchange — central to homeostasis.
Structure (fluid mosaic model):
- A phospholipid bilayer (hydrophilic heads out, hydrophobic tails in) with embedded & mobile proteins, cholesterol and glycoproteins.
- Fluidity lets components move; proteins act as channels, carriers, pumps & receptors.
How it regulates: selective permeability — small/non-polar molecules diffuse freely; water by osmosis; ions & large molecules via specific channels/carriers; active transport moves substances against gradients using ATP; receptors handle signalling.
Significance: maintains ion balance, nutrient uptake, waste removal & internal stability; its selectivity is also a target for drugs & toxins.
Conclusion: structure fits function — the fluid-mosaic design makes precise, selective regulation possible.

Mains GS-III — anticipated themes

Likely: stem cells & regenerative medicine ethics · endosymbiotic theory & mitochondrial medicine · cultured meat & tissue engineering · cell membrane & drug targeting · cell as the base of biotechnology. check for latest update or data

15-Minute Revision Box

Must-Remember Facts — Cell & Tissues

Cell & theory:

Cell = basic structural & functional unit of life
Hooke named cell (cork); Leeuwenhoek saw living cells; Brown found nucleus
Cell theory = Schleiden & Schwann; Virchow: cells from pre-existing cells
Largest cell = ostrich egg; longest = neuron; smallest = mycoplasma

Prokaryote vs eukaryote:

Prokaryote: no nuclear membrane, no membrane-bound organelles, 70S ribosomes, DNA = nucleoid
Eukaryote: true nucleus + organelles, 80S ribosomes

Plant vs animal cell:

Plant only: cell wall (cellulose), plastids, large central vacuole; store starch
Animal only: centrosome; store glycogen

Organelles (nicknames):

Mitochondria = powerhouse (double membrane, own DNA, ATP)
Chloroplast = photosynthesis (own DNA); Ribosome = protein factory
Golgi = packaging/post office; Lysosome = suicide bag
Rough ER = protein; Smooth ER = lipids & detox; Nucleus = control centre
Surface: capsule = protection, fimbriae = attachment, flagella = movement, cilia = short & many

Nucleic acids & tissues:

DNA: double, deoxyribose, A-T-G-C; RNA: single, ribose, uracil; Watson & Crick 1953
Animal tissues: epithelial, connective (blood!), muscular, nervous
Muscle: skeletal (voluntary striated), cardiac (involuntary striated), smooth (involuntary unstriated)
Plant: meristematic (growth); xylem = water up (dead), phloem = food both ways (living)

Highest-frequency themes: organelle nicknames & functions · prokaryote vs eukaryote · plant vs animal cell · mitochondria/chloroplast own DNA · blood = connective tissue · xylem vs phloem · DNA vs RNA · cell-theory scientists.

Organelle	Role
Nucleus	Control centre
Mitochondria	Powerhouse (ATP)
Chloroplast	Photosynthesis
Ribosome	Protein synthesis
Golgi	Packaging
Lysosome	Suicide bag
ER (rough/smooth)	Protein / lipid

Feature	Pro / Eu
Nucleus	No / Yes
Organelles	No / Yes
Ribosome	70S / 80S
Example	Bacteria / Plant, animal

Name	Contribution
Hooke	Named cell (1665)
Leeuwenhoek	Living cells
Brown	Nucleus
Schleiden/Schwann	Cell theory
Virchow	Cell from cell
Watson & Crick	DNA helix (1953)

Topic 2: The Cell & Tissues

On this page

Conceptual Clarity — How UPSC Tests the Cell

1. The Cell & Cell Theory

1.1 Discovery — who found what

1.2 The cell theory — three tenets

2. Prokaryotic vs Eukaryotic Cells

3. Plant Cell vs Animal Cell

4. Cell Boundary — Membrane, Wall & Surface Structures

4.1 Cell (plasma) membrane

4.2 Cell wall

4.3 Bacterial surface extras (from the syllabus)

5. Organelles I — Nucleus, ER, Ribosomes, Golgi

5.1 Nucleus — the control centre

5.2 Endoplasmic reticulum (ER)

5.3 Ribosomes — the protein factory

5.4 Golgi apparatus — the packaging & despatch unit

6. Organelles II — Mitochondria, Plastids, Lysosomes, Vacuoles, Centrosome

6.1 Mitochondria — the powerhouse

6.2 Plastids (plant cells only)

6.3 Lysosomes, vacuoles & centrosome

7. Genetic Material & Nucleic Acids

8. Animal Tissues

9. Plant Tissues

10. Current Affairs Link (2024–2026)

11. Prelims PYQs

12. Mains PYQs + Model Answers

Model Answer

Model Answer

Model Answer

Model Answer

15-Minute Revision Box

Must-Remember Facts — Cell & Tissues