class 11 notes

Class 11 Biology Notes Chapter 7 (Chapter 7) – Examplar Problems (English) Book

Philoid

Philoid

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Examplar Problems (English)
Alright class, let's delve into Chapter 7: Structural Organisation in Animals from your NCERT Exemplar. This chapter is crucial not just for your Class 11 understanding but forms a strong foundation for many questions in competitive government exams. We'll cover the different types of animal tissues and then look at the morphology and anatomy of an invertebrate (Earthworm, Cockroach) and a vertebrate (Frog) as representative examples. Pay close attention to the specific details and comparative aspects.

Chapter 7: Structural Organisation in Animals - Detailed Notes

I. Animal Tissues

A group of similar cells along with intercellular substances performing a specific function is called a tissue. Tissues are organized in specific proportions and patterns to form organs like the stomach, lung, heart, etc. When organs associate to perform a common function, they form an organ system (e.g., digestive system).

There are four basic types of animal tissues:

  1. Epithelial Tissue
  2. Connective Tissue
  3. Muscular Tissue
  4. Neural Tissue

1. Epithelial Tissue (Epithelium)

  • Function: Provides covering or lining for some part of the body. Acts as a barrier, involved in secretion, absorption, excretion, sensation.
  • Structure: Cells are compactly packed with little intercellular matrix. One surface is free (facing body fluid or outside environment), the other attached to underlying tissue by a non-cellular basement membrane.
  • Types:
    • Simple Epithelium: Single layer of cells.
      • Squamous: Thin, flattened cells with irregular boundaries.
        • Location: Walls of blood vessels (endothelium), air sacs of lungs (alveoli).
        • Function: Diffusion boundary.
      • Cuboidal: Cube-like cells.
        • Location: Ducts of glands, tubular parts of nephrons (e.g., PCT - Proximal Convoluted Tubule, often with microvilli), germinal epithelium.
        • Function: Secretion, absorption.
      • Columnar: Tall, slender cells; nuclei usually near the base. Free surface may have microvilli or cilia.
        • Location: Lining of stomach and intestine (microvilli increase surface area for absorption). Lining of bronchioles, fallopian tubes (ciliated - moves particles/mucus/ova).
        • Function: Secretion, absorption, movement.
      • Pseudostratified: Appears multilayered but is single-layered as all cells touch the basement membrane; nuclei at different levels. Often ciliated.
        • Location: Lining of trachea, upper respiratory tract.
        • Function: Protection, secretion, mucus movement.
    • Compound (Stratified) Epithelium: More than one layer of cells.
      • Function: Protection against chemical and mechanical stresses. Limited role in secretion/absorption.
      • Location: Dry surface of the skin (keratinized stratified squamous), moist surface of buccal cavity, pharynx, inner lining of salivary gland ducts, pancreatic ducts (non-keratinized stratified squamous). Transitional epithelium (ureters, urinary bladder - stretchable).
  • Glandular Epithelium: Specialized columnar or cuboidal cells for secretion.
    • Unicellular: Isolated glandular cells (e.g., Goblet cells of alimentary canal - secrete mucus).
    • Multicellular: Cluster of cells (e.g., Salivary glands).
    • Exocrine glands: Secrete products (mucus, saliva, earwax, oil, milk, digestive enzymes) through ducts or tubes onto a surface.
    • Endocrine glands: Ductless glands; secrete hormones directly into the fluid bathing the gland (blood).
  • Cell Junctions: Provide structural and functional links between cells.
    • Tight Junctions: Prevent substance leakage across a tissue.
    • Adhering Junctions: Cement neighbouring cells together.
    • Gap Junctions: Facilitate communication by connecting cytoplasm of adjoining cells for rapid transfer of ions, small molecules, sometimes big molecules.

2. Connective Tissue

  • Function: Linking and supporting other tissues/organs. Most abundant and widely distributed tissue.
  • Structure: Cells are loosely spaced and embedded in an intercellular matrix. The matrix can be jelly-like, fluid, dense, or rigid. Contains protein fibres (collagen, elastin).
  • Components: Cells (fibroblasts, macrophages, mast cells, adipocytes, plasma cells), Fibres (collagen - strength; elastin - flexibility), Matrix (ground substance - modified polysaccharides).
  • Types:
    • Loose Connective Tissue: Cells and fibres loosely arranged in a semi-fluid matrix.
      • Areolar Tissue: Beneath the skin. Support framework for epithelium. Contains fibroblasts, macrophages, mast cells.
      • Adipose Tissue: Mainly beneath the skin. Specialized to store fat (adipocytes). Acts as insulator, shock absorber.
    • Dense Connective Tissue: Fibres and fibroblasts compactly packed.
      • Dense Regular: Collagen fibres parallel between bundles of fibres. High tensile strength.
        • Tendons: Attach skeletal muscle to bone.
        • Ligaments: Attach bone to bone (more elastic fibres).
      • Dense Irregular: Fibroblasts and fibres (mostly collagen) oriented differently. Present in the skin (dermis).
    • Specialized Connective Tissue:
      • Cartilage: Solid, pliable matrix resists compression. Cells (chondrocytes) enclosed in small cavities (lacunae) within the matrix produced by them. Mostly avascular.
        • Locations: Tip of nose, outer ear joints, between vertebral bones, limbs and hands in adults, embryonic skeleton.
      • Bone: Hard, non-pliable matrix rich in calcium salts and collagen fibres (gives strength). Main tissue providing structural frame. Supports/protects softer tissues. Site of blood cell production (bone marrow). Cells (osteocytes) present in lacunae. Haversian canals present in mammalian bone.
      • Blood: Fluid connective tissue. Contains plasma (matrix), Red Blood Cells (RBCs/erythrocytes), White Blood Cells (WBCs/leukocytes), and Platelets (thrombocytes).
        • Plasma: Straw-coloured fluid (approx. 55% of blood). Contains water, proteins (fibrinogen, globulins, albumins), nutrients, hormones, salts etc.
        • RBCs: Biconcave, anucleated in mammals. Contain haemoglobin for O2 transport.
        • WBCs: Nucleated, involved in defense. Types: Granulocytes (Neutrophils, Eosinophils, Basophils) and Agranulocytes (Lymphocytes, Monocytes).
        • Platelets: Cell fragments from megakaryocytes. Involved in blood clotting.
        • Function: Transport of gases, nutrients, hormones, waste products; defense; clotting.

3. Muscle Tissue

  • Function: Movement of the body and internal organs. Property of contractility.
  • Structure: Composed of long, cylindrical fibres arranged in parallel arrays, composed of fine myofibrils. Contract (shorten) in response to stimulation, then relax (lengthen).
  • Types:
    • Skeletal Muscle: Attached to bones. Striated (striped appearance due to actin/myosin arrangement). Voluntary control. Fibres are multinucleated (syncytium) and unbranched.
    • Smooth Muscle: Walls of internal organs (blood vessels, stomach, intestine). Non-striated (smooth). Involuntary control. Cells are fusiform (spindle-shaped), uninucleated, and tapered at ends.
    • Cardiac Muscle: Only in the heart wall. Striated. Involuntary control. Cells are cylindrical, branched, uninucleated. Contain intercalated discs (communication junctions/gap junctions) allowing cells to contract as a unit.

4. Neural Tissue

  • Function: Exerts greatest control over body's responsiveness to changing conditions. Specialized for conductivity.
  • Components:
    • Neurons (Nerve cells): Unit of neural system. Excitable cells. Structure: Cell body (cyton) with nucleus and cytoplasm, Dendrites (short processes receiving impulses), Axon (long process transmitting impulses away).
    • Neuroglia: Make up more than half the volume of neural tissue. Protect and support neurons. Non-excitable. (e.g., Schwann cells, Oligodendrocytes, Astrocytes, Microglia).

II. Morphology and Anatomy of Earthworm (Pheretima)

  • Phylum: Annelida
  • Habitat: Moist soil. Nocturnal.
  • Morphology:
    • Long, cylindrical body, reddish-brown.
    • Segmented (metamerism) - 100-120 segments (metameres).
    • Dorsal surface: Dark median line (dorsal blood vessel). Ventral surface: Genital openings.
    • Anterior end: Mouth, prostomium (sensory lobe).
    • Clitellum: Prominent dark band of glandular tissue (segments 14-16). Secretes cocoon. Body divisible into pre-clitellar, clitellar, post-clitellar regions.
    • Setae: S-shaped chitinous structures in epidermal pits (except 1st, last, clitellum). Help in locomotion.
    • Apertures: Mouth, anus, spermathecal openings (ventro-lateral, intersegmental grooves 5-9), female genital pore (ventral, 14th), male genital pores (ventro-lateral, 18th), nephridiopores.
  • Anatomy:
    • Body Wall: Cuticle (non-cellular), Epidermis (columnar), Muscular layers (circular, longitudinal), Coelomic epithelium.
    • Alimentary Canal: Straight tube. Mouth (1-3) -> Buccal cavity -> Pharynx -> Oesophagus (5-7) -> Gizzard (8-9, muscular, grinds soil) -> Stomach (9-14, calciferous glands neutralize humic acid) -> Intestine (15-last) -> Anus.
    • Typhlosole: Internal median fold of dorsal wall in intestine (after 26th segment, except last 23-25 segments). Increases absorptive surface area.
    • Circulatory System: Closed type. Blood glands (4, 5, 6 segments) produce blood cells & haemoglobin (dissolved in plasma). Dorsal vessel, ventral vessel, sub-neural vessel, lateral-oesophageal vessels. Hearts (lateral hearts, lateral-oesophageal hearts).
    • Respiratory System: No specialized organs. Gas exchange via moist body surface (cutaneous respiration).
    • Excretory System: Segmentally arranged coiled tubules - Nephridia.
      • Septal Nephridia: Both sides of intersegmental septa (15-last), open into intestine.
      • Integumentary Nephridia: Attached to lining of body wall (3-last), open on body surface.
      • Pharyngeal Nephridia: 3 paired tufts (4, 5, 6 segments), open into pharynx/buccal cavity.
      • Function: Regulate volume/composition of body fluids. Excretion is ureotelic (primarily urea).
    • Nervous System: Segmentally arranged ganglia on ventral paired nerve cord. Anteriorly (3rd-4th seg), nerve cord bifurcates, encircles pharynx, joins cerebral ganglia dorsally to form nerve ring. Sensory receptors for light, touch, chemical stimuli.
    • Reproductive System: Hermaphrodite (bisexual). Testes (2 pairs, 10th & 11th seg), seminal vesicles, vasa deferentia, prostate duct, male genital pore (18th). Ovaries (1 pair, 12-13th intersegmental septum), oviducts, female genital pore (14th). Spermathecae (4 pairs, 6th-9th seg, receive sperm during copulation).
    • Reproduction: Cross-fertilization (exchange of sperm during copulation). Mature sperm, egg cells, nutritive fluid deposited in cocoon secreted by clitellum. Fertilization and development occur within cocoon deposited in soil. Direct development (no larva).

III. Morphology and Anatomy of Cockroach (Periplaneta americana)

  • Phylum: Arthropoda, Class Insecta
  • Habitat: Damp, warm places. Nocturnal omnivores. Pests, vectors of diseases.
  • Morphology:
    • Brown/black, flattened, segmented body (approx. 34-53 mm long). Wings extend beyond abdomen in males.
    • Exoskeleton: Hard, chitinous plates called sclerites (dorsal tergites, ventral sternites, lateral pleurites). Joined by flexible arthrodial membrane.
    • Body Divisions: Head, Thorax, Abdomen.
      • Head: Triangular, formed by fusion of 6 segments. Lies at right angle to body axis (hypognathous). Bears compound eyes (pair), antennae (thread-like, sensory), mouthparts (biting & chewing type: labrum, mandibles, maxillae, labium, hypopharynx/tongue).
      • Thorax: 3 parts - Prothorax, Mesothorax, Metathorax. Bears 3 pairs of walking legs (coxa, trochanter, femur, tibia, tarsus-5 segments, claw). Bears 2 pairs of wings: Forewings (tegmina, mesothoracic, opaque, leathery, protective), Hindwings (metathoracic, transparent, membranous, used in flight).
      • Abdomen: 10 segments. 7th sternum (female) boat-shaped, forms brood pouch with 8th & 9th sterna. 10th segment has anal cerci (paired, jointed sensory structures) in both sexes. Males have anal styles (paired, unjointed, ventral, 9th segment).
  • Anatomy:
    • Alimentary Canal: Foregut (mouth -> pharynx -> oesophagus -> crop (stores food) -> gizzard/proventriculus (grinding)), Midgut/Mesenteron (site of digestion/absorption; 6-8 blind tubules hepatic/gastric caeca at foregut-midgut junction secrete digestive juice), Hindgut (ileum, colon, rectum -> anus; broader than midgut; Malpighian tubules at midgut-hindgut junction for excretion).
    • Circulatory System: Open type. Poorly developed blood vessels opening into space (haemocoel). Visceral organs bathed in blood (haemolymph - colourless plasma + haemocytes). Heart is elongated tube along mid-dorsal line, differentiated into 13 funnel-shaped chambers with ostia (pores) on either side. Blood flows anteriorly.
    • Respiratory System: Network of trachea opening through 10 pairs of small holes called spiracles (lateral side; 2 thoracic, 8 abdominal). Trachea subdivide into tracheoles carrying oxygen directly to cells. No respiratory pigment.
    • Excretory System: Malpighian tubules (100-150 yellow, thin filaments) at midgut-hindgut junction. Absorb nitrogenous wastes from haemolymph, convert to uric acid (uricotelism), excreted through hindgut. Fat body, nephrocytes, uricose glands also help.
    • Nervous System: Series of fused, segmentally arranged ganglia joined by paired longitudinal connectives (ventral side). Supra-oesophageal ganglion ('brain') supplies nerves to antennae, compound eyes. Sub-oesophageal ganglion. Double ventral nerve cord. Sense organs: Antennae, eyes (compound - mosaic vision; many ommatidia), maxillary palps, labial palps, anal cerci.
    • Reproductive System: Dioecious (separate sexes).
      • Male: Testes (pair, 4th-6th abdominal segments), vas deferens, ejaculatory duct, seminal vesicles (store sperm bundles - spermatophores), male gonopore (ventral to anus), accessory reproductive gland (mushroom gland, phallic gland). External genitalia (male gonapophysis / phallomere) - chitinous asymmetrical structures around male gonopore.
      • Female: Ovaries (pair, 2nd-6th abdominal segments; each with 8 ovarioles containing developing ova), oviducts unite to form common oviduct/vagina opening into genital chamber. Spermathecae (pair, 6th segment, open into genital chamber). Collaterial glands secrete hard case (ootheca) around eggs.
    • Reproduction: Fertilization internal. Fertilized eggs encased in ootheca (dark reddish/black capsule, ~8mm long). Ootheca dropped/glued in suitable place. Each ootheca contains 14-16 eggs. Development is paurometabolous (gradual metamorphosis through nymphal stages). Nymph resembles adult, moults ~13 times to reach adult form.

IV. Morphology and Anatomy of Frog (Rana tigrina)

  • Phylum: Chordata, Class Amphibia
  • Habitat: Freshwater, land. Poikilotherms (cold-blooded). Exhibit camouflage (mimicry) and aestivation (summer sleep), hibernation (winter sleep).
  • Morphology:
    • Skin: Smooth, slippery due to mucus (mucous glands). Always moist. Dorsal side olive green with dark spots, ventral side pale yellow. Water absorbed through skin.
    • Body Divisions: Head, Trunk. (Neck, tail absent).
    • Head: Snout, nostrils (pair), bulging eyes (covered by nictitating membrane in water), tympanum (ear, behind eyes).
    • Trunk: Forelimbs (4 digits, smaller), Hindlimbs (5 digits, larger, muscular, webbed - swimming).
    • Sexual dimorphism: Males have sound-producing vocal sacs and copulatory/nuptial pad on first digit of forelimb (absent in females).
  • Anatomy:
    • Body Cavity (Coelom): Accommodates well-developed organs/systems.
    • Digestive System: Short alimentary canal (carnivorous). Mouth -> Buccal cavity -> Pharynx -> Oesophagus -> Stomach -> Intestine (Duodenum, Ileum) -> Rectum -> Cloaca -> Cloacal aperture. Liver secretes bile (stored in gall bladder). Pancreas secretes pancreatic juice. Digestion by HCl/pepsin (stomach), pancreatic juice/bile/intestinal juice (intestine). Absorption by villi/microvilli in intestine. Undigested waste passes to rectum, eliminated through cloaca.
    • Respiratory System:
      • Cutaneous Respiration: Skin (in water and on land).
      • Buccal Respiration: Lining of buccal cavity (on land).
      • Pulmonary Respiration: Lungs (pair, elongated, pink sacs in upper thorax) (on land). Air enters through nostrils -> buccal cavity -> lungs.
    • Circulatory System: Closed type. Well-developed blood vascular system and lymphatic system.
      • Heart: 3-chambered (2 atria, 1 ventricle). Covered by pericardium. Receives blood from body via vena cava (into right atrium), from lungs via pulmonary vein (into left atrium). Ventricle pumps mixed blood (oxygenated + deoxygenated) into conus arteriosus / truncus arteriosus. Incomplete double circulation.
      • Blood: Plasma, RBCs (nucleated, biconvex, contain haemoglobin), WBCs, Platelets.
      • Vascular System: Arteries, Veins. Hepatic portal system (veins from intestine to liver), Renal portal system (veins from lower body to kidney).
      • Lymphatic System: Lymph, lymph channels, lymph nodes.
    • Excretory System: Pair of compact, dark red, bean-shaped kidneys (posteriorly located). Functional unit is nephron/uriniferous tubule. Ureters emerge from kidneys (male: act as urinogenital duct opening into cloaca; female: open separately into cloaca). Urinary bladder (thin-walled, ventral to rectum, opens into cloaca). Excretes urea (ureotelic). Waste eliminated through cloaca.
    • Control & Coordination: Endocrine glands (pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals, gonads) secrete hormones. Nervous system well-organized.
      • Central Nervous System (CNS): Brain, Spinal cord. Brain enclosed in cranium (brain box). Divided into Forebrain (olfactory lobes, cerebral hemispheres, diencephalon), Midbrain (optic lobes - pair), Hindbrain (cerebellum, medulla oblongata - passes into spinal cord through foramen magnum).
      • Peripheral Nervous System (PNS): Cranial nerves (10 pairs), Spinal nerves (10 pairs).
      • Autonomic Nervous System (ANS): Sympathetic, Parasympathetic.
      • Sense Organs: Touch (sensory papillae), Taste (taste buds), Smell (nasal epithelium), Vision (eyes - simple), Hearing (tympanum, internal ear).
    • Reproductive System: Dioecious. Well-organized systems.
      • Male: Testes (pair, yellowish, ovoid; attached to kidney by mesorchium). Vasa efferentia (10-12) arise from testes, enter kidney, open into Bidder's canal, finally communicate with urinogenital duct -> cloaca.
      • Female: Ovaries (pair, near kidneys; no functional connection). Oviduct (pair) separate from kidney, opens into cloaca separately. Mature female produces 2500-3000 ova at a time.
    • Reproduction: External fertilization (in water). Female lays eggs (spawn), male deposits sperm over them. Development is indirect, involves larval stage (tadpole). Tadpole undergoes metamorphosis (controlled by thyroxine) to form adult frog.

Multiple Choice Questions (MCQs)

  1. Which type of epithelial tissue forms the lining of blood vessels and air sacs of lungs?
    a) Simple Cuboidal Epithelium
    b) Simple Columnar Epithelium
    c) Simple Squamous Epithelium
    d) Stratified Squamous Epithelium

  2. Tendons and ligaments are examples of:
    a) Loose Connective Tissue
    b) Dense Regular Connective Tissue
    c) Dense Irregular Connective Tissue
    d) Specialized Connective Tissue

  3. Intercalated discs are characteristic features found in:
    a) Skeletal muscle fibres
    b) Smooth muscle fibres
    c) Cardiac muscle fibres
    d) Neurons

  4. In Earthworm (Pheretima), the prominent dark band of glandular tissue called clitellum is found in segments:
    a) 5-9
    b) 9-14
    c) 14-16
    d) 18-20

  5. The function of the gizzard in the digestive system of Cockroach is primarily:
    a) Storage of food
    b) Secretion of digestive enzymes
    c) Grinding of food particles
    d) Absorption of nutrients

  6. Which of the following structures helps in excretion in Cockroach?
    a) Nephridia
    b) Malpighian tubules
    c) Flame cells
    d) Green glands

  7. In Frog, respiration occurs through:
    a) Lungs only
    b) Skin and Lungs only
    c) Skin, Buccal cavity, and Lungs
    d) Gills, Skin and Lungs

  8. Which type of connective tissue is characterized by chondrocytes found within lacunae?
    a) Bone
    b) Blood
    c) Cartilage
    d) Areolar tissue

  9. Haemoglobin in Earthworm is found dissolved in:
    a) Red Blood Cells
    b) White Blood Cells
    c) Blood Plasma
    d) Coelomic Fluid

  10. Paurometabolous development, involving nymphal stages, is observed in:
    a) Earthworm
    b) Frog
    c) Cockroach
    d) Humans

Answer Key:

  1. c) Simple Squamous Epithelium
  2. b) Dense Regular Connective Tissue
  3. c) Cardiac muscle fibres
  4. c) 14-16
  5. c) Grinding of food particles
  6. b) Malpighian tubules
  7. c) Skin, Buccal cavity, and Lungs
  8. c) Cartilage
  9. c) Blood Plasma
  10. c) Cockroach

Make sure you revise these notes thoroughly. Focus on the locations and functions of different tissues, and the specific anatomical features and physiological processes of the earthworm, cockroach, and frog. Understanding the comparative aspects will be very beneficial for your exams. Good luck!

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