Chapter Overview & Weightage
Structural Organisation in Animals covers animal tissues and the morphology/anatomy of three organisms: earthworm, cockroach, and frog. NEET questions are highly factual — straight from NCERT diagrams and text.
This chapter carries 3-4% weightage in NEET with 2-3 questions. Tissue types and cockroach anatomy are the most tested areas.
| Year | NEET Q Count | Key Topics Tested |
|---|---|---|
| 2025 | 2 | Epithelial tissue, cockroach |
| 2024 | 3 | Connective tissue, earthworm |
| 2023 | 2 | Muscular tissue, frog |
| 2022 | 2 | Cockroach excretion, tissue types |
| 2021 | 3 | Earthworm circulation, epithelial types |
graph TD
A[Animal Organisation] --> B[Animal Tissues]
A --> C[Earthworm]
A --> D[Cockroach]
A --> E[Frog]
B --> F[Epithelial]
B --> G[Connective]
B --> H[Muscular]
B --> I[Neural]
F --> J[Simple: Squamous, Cuboidal, Columnar]
F --> K[Stratified, Pseudostratified]
G --> L[Loose, Dense, Cartilage, Bone, Blood]Key Concepts You Must Know
Tier 1 (Always asked)
- Four types of animal tissues and their subtypes
- Epithelial tissue: types, locations, functions
- Connective tissue: classification (loose, dense, specialized)
- Cockroach: excretory system (Malpighian tubules), blood (haemolymph, no haemoglobin)
Tier 2 (Frequently asked)
- Earthworm: closed circulatory system, nephridia for excretion
- Frog: three-chambered heart, cutaneous + pulmonary respiration
- Difference between striated, unstriated, and cardiac muscle
- Blood as a connective tissue (liquid matrix)
Tier 3 (Occasional)
- Earthworm: clitellum function, typhlosole
- Cockroach: compound eyes, mosaic vision
- Frog: sexual dimorphism, hibernation/aestivation
Important Formulas
| Tissue Type | Subtypes | Key Feature |
|---|---|---|
| Epithelial | Squamous, cuboidal, columnar, ciliated, glandular | No blood supply (avascular), covers surfaces |
| Connective | Loose (areolar, adipose), Dense (tendons, ligaments), Specialized (cartilage, bone, blood) | Most abundant, has matrix |
| Muscular | Striated (skeletal), Unstriated (smooth), Cardiac | Contractile |
| Neural | Neurons, neuroglia | Electrical impulses |
| Feature | Earthworm | Cockroach | Frog |
|---|---|---|---|
| Phylum | Annelida | Arthropoda | Chordata (Amphibia) |
| Circulation | Closed | Open (haemolymph) | Closed, 3-chambered heart |
| Respiration | Cutaneous | Tracheal | Cutaneous + Pulmonary |
| Excretion | Nephridia | Malpighian tubules | Kidneys (mesonephric) |
| Blood pigment | Haemoglobin (dissolved in plasma) | No respiratory pigment | Haemoglobin (in RBC) |
Cockroach blood (haemolymph) does NOT carry oxygen because it has no respiratory pigment. Gas exchange occurs directly via the tracheal system. This is why insects can be extremely active despite having “open” circulation — oxygen delivery does not depend on blood.
Solved Previous Year Questions
PYQ 1 — NEET 2024
Problem: Malpighian tubules are the excretory organs of: (a) Earthworm (b) Cockroach (c) Frog (d) Hydra
Solution:
Answer: (b) Cockroach
Malpighian tubules are thin, tubular structures attached to the junction of midgut and hindgut in insects. They absorb waste from haemolymph and convert it to uric acid (uricotelic excretion).
PYQ 2 — NEET 2023
Problem: Which type of muscle shows intercalated discs?
Solution:
Answer: Cardiac muscle
Intercalated discs are specialized cell junctions unique to cardiac muscle. They allow rapid transmission of electrical impulses between adjacent cells, enabling the heart to contract as a coordinated unit (syncytium).
Difficulty Distribution
| Difficulty | % of Questions | What to Expect |
|---|---|---|
| Easy | 45% | Tissue identification, organism features |
| Medium | 40% | Comparative questions between organisms |
| Hard | 15% | Detailed anatomy (specific structures) |
Expert Strategy
Week 1: Animal tissues — master all types with locations and functions. Make a visual comparison table. Focus on epithelial and connective tissue subtypes.
Week 2: Cockroach anatomy (most tested organism). Know: Malpighian tubules, tracheal system, compound eyes, haemolymph, hepatic caeca.
Week 3: Earthworm and frog. Focus on excretory and circulatory system differences. Earthworm has closed circulation; cockroach has open; frog has closed with a 3-chambered heart.
For tissue identification, remember the key diagnostic features: epithelial = cells tightly packed, no matrix; connective = cells in a matrix; muscular = elongated, contractile; neural = long processes (axons). This helps in diagram-based NEET questions.
Common Traps
Trap 1 — Blood is a connective tissue. Despite being liquid, blood fits the definition of connective tissue (cells dispersed in an extracellular matrix — plasma). Students often classify it separately.
Trap 2 — Earthworm haemoglobin is dissolved in plasma, not in RBCs. Earthworm blood has haemoglobin, but it is dissolved directly in the plasma (no RBCs). This is different from vertebrates where Hb is inside red blood cells.
Trap 3 — Cockroach has mosaic vision, not image vision. Compound eyes form multiple images that overlap to create a mosaic pattern. The image is less detailed but excellent for detecting movement. This is distinct from the single-image vision of vertebrate eyes.
Trap 4 — Frog uses both lungs and skin for respiration. During hibernation (winter), skin is the primary respiratory surface since the frog is underwater. During active periods, both lungs and skin contribute. Buccal cavity also helps in respiration.