Structural Organisation in Animals
NCERT Line-by-Line Breakdown for NEET 2026
Unit 2: Structural Organisation in Plants and AnimalsIn multicellular animals, a group of similar cells along with intercellular substances perform a specific function. Such an organization is called Tissue. This chapter covers the four basic tissue types and the detailed morphology and anatomy of the Frog.
1. Animal Tissues
A. Epithelial Tissue (Covering)
Has a free surface (facing body fluid or outside environment). Cells are compactly packed with little intercellular matrix.
| Type | Structure | Location (NEET Gems) | Function |
|---|---|---|---|
| Squamous | Flattened cells, irregular boundaries. (Pavement epithelium). | Air sacs of lungs, Walls of blood vessels. | Diffusion boundary. |
| Cuboidal | Cube-like cells. | Ducts of glands, Tubular parts of nephron (PCT). | Secretion and absorption. |
| Columnar | Tall, slender cells. Nuclei at base. | Lining of Stomach and Intestine. | Secretion and absorption. |
| Ciliated | Cuboidal or Columnar bearing cilia. | Bronchioles, Fallopian tubes. | Move particles/mucus. |
- Tight Junctions: Stop substances from leaking.
- Adhering Junctions: Cementing to keep cells together.
- Gap Junctions: Facilitate communication (ions/molecules transfer).
B. Connective Tissue
Most abundant. Links and supports other tissues.
- Loose CT:
- Areolar: Beneath skin (support framework).
- Adipose: Fat storage.
- Dense CT:
- Dense Regular: Tendons (Muscle to Bone) & Ligaments (Bone to Bone).
- Dense Irregular: Skin.
- Specialized CT: Cartilage (Chondrocytes), Bone (Osteocytes), Blood (Fluid CT).
C. Muscular & Neural Tissue
Striated, Voluntary, Multinucleated (Syncytial). Attached to bones.
Non-striated, Involuntary, Fusiform (tapering). Blood vessels, Stomach.
Striated, Involuntary, Branched. Intercalated discs (Communication junctions).
2. The Frog (Rana tigrina)
The 2026 Syllabus specifically mentions “an insect (Frog)”. We must focus on the Frog as the model organism. Frogs are Amphibians, Poikilotherms (Cold-blooded), and show Camouflage/Mimicry.
🐸 Morphology
- Skin: Moist, slippery (mucus). No scales. Respiration through skin (Cutaneous).
- Body Division: Head and Trunk. Neck and Tail are absent.
- Eyes: Bulged, covered by nictitating membrane (protection in water).
- Ears: Tympanum (membranous) receives sound signals.
- Sexual Dimorphism: Males have Vocal Sacs and Copulatory (Nuptial) pads on the first digit of forelimbs.
🐸 Anatomy
1. Digestive System
Short alimentary canal (carnivores = short gut). Mouth → Buccal Cavity → Oesophagus → Stomach → Intestine → Rectum → Cloaca.
Note: Cloaca is the common opening for digestive, excretory, and reproductive systems.
2. Circulatory System
Heart: 3-Chambered (2 Atria, 1 Ventricle). Covered by Pericardium.
- Sinus Venosus: Triangular structure joining the Right Atrium (receives blood).
- Conus Arteriosus: Ventricle opens into this sac on the ventral side.
- Portal Systems: Hepatic Portal System (Liver-Intestine) & Renal Portal System (Kidney-Lower body).
3. Excretory System
Ureotelic (Excretes Urea). Main organs: Pair of Kidneys, Ureters, Cloaca, Urinary bladder.
Male Frogs: Ureters act as Urogenital duct (carry sperm + urine).
Female Frogs: Ureters and Oviduct open separately into cloaca.
4. Nervous System
- CNS: Brain + Spinal Cord.
- PNS: Cranial Nerves (10 Pairs) + Spinal Nerves.
- Brain: Olfactory lobes, Paired Cerebral hemispheres, Optic lobes (Midbrain), Cerebellum & Medulla oblongata (Hindbrain). Medulla passes through Foramen Magnum.
📝 Rapid Fire MCQs
Q1. Which of the following cells help in maintaining the current of water in Sponges?
- A) Choanocytes
- B) Pinacocytes
- C) Porocytes
- D) Amoebocytes
Click to check Answer
Answer: A) Choanocytes (Collar cells).
Q2. In male frogs, the ureters act as:
- A) Urinary duct only
- B) Spermatic duct only
- C) Urogenital duct
- D) None of these
Click to check Answer
Answer: C) Urogenital duct.