Class 11 Biology Notes Chapter 7 (Structural organisation in animals) – Biology Book

Detailed Notes with MCQs of Chapter 7: Structural Organisation in Animals. This chapter is fundamental because it explains how cells group together to form tissues, tissues organize into organs, and organs into organ systems, creating a functional organism. Understanding this hierarchy and the specific structures, especially in the example animals, is crucial for many competitive government exams.

Chapter 7: Structural Organisation in Animals - Detailed Notes

I. Levels of Organisation:

• Cellular Level: Cells are loosely aggregated, show some division of labour (e.g., Sponges).
• Tissue Level: Cells performing similar functions are grouped into tissues (e.g., Coelenterates).
• Organ Level: Tissues are grouped to form organs, each specialised for a particular function (e.g., Platyhelminthes).
• Organ System Level: Organs associate to form functional systems, each concerned with a specific physiological function (e.g., Annelids, Arthropods, Molluscs, Echinoderms, Chordates).

II. Animal Tissues:
Tissues are groups of similar cells along with intercellular substances performing a specific function. There are four basic types:

A. Epithelial Tissue (Epithelium):

• Characteristics: Forms covering or lining for body parts. Cells are compactly packed with little intercellular matrix. Rests on a non-cellular basement membrane. Avascular (gets nutrients by diffusion from underlying connective tissue). Has a free surface facing body fluid or the outside environment.
• Functions: Protection, secretion, absorption, filtration, excretion, sensory reception.
• Types:
  • 1. Simple Epithelium: Single layer of cells.
    • a) Simple Squamous: Thin, flattened cells with irregular boundaries.
      • Location: Walls of blood vessels (endothelium), air sacs (alveoli) of lungs, lining of coelom.
      • Function: Diffusion boundary, filtration.
    • b) Simple Cuboidal: Cube-like cells.
      • Location: Ducts of glands, tubular parts of nephrons in kidneys, ovary, testes.
      • Function: Secretion, absorption. (Epithelium of PCT of nephron has microvilli).
    • c) Simple Columnar: Tall, slender cells; nuclei usually at the base. Free surface may have microvilli.
      • Location: Lining of stomach and intestine.
      • Function: Secretion, absorption.
    • d) Ciliated Epithelium: Cuboidal or columnar cells bearing cilia on their free surface.
      • Location: Inner surface of hollow organs like bronchioles, fallopian tubes.
      • Function: Move particles or mucus in a specific direction.
    • e) Glandular Epithelium: Specialised cuboidal or columnar cells for secretion.
      • Unicellular: Isolated glandular cells (e.g., Goblet cells of alimentary canal - secrete mucus).
      • Multicellular: Cluster of cells (e.g., Salivary gland).
      • Exocrine Glands: Secrete products (mucus, saliva, earwax, oil, milk, digestive enzymes) through ducts or tubes.
      • Endocrine Glands: Ductless glands; secrete hormones directly into the fluid bathing the gland (blood).
  • 2. Compound Epithelium: More than one layer (multi-layered) of cells.
    • Function: Protective function against chemical and mechanical stresses. Limited role in secretion and absorption.
    • Location: Dry surface of the skin, moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and pancreatic ducts.
• Cell Junctions: Provide structural and functional links between individual cells.
  • Tight Junctions: Help stop substances from leaking across a tissue.
  • Adhering Junctions: Perform cementing to keep neighbouring cells together.
  • Gap Junctions: Facilitate communication between cells by connecting cytoplasm for rapid transfer of ions, small molecules, and sometimes bigger molecules.

B. Connective Tissue:

• Characteristics: Most abundant and widely distributed tissue. Links and supports other tissues/organs. Characterized by cells embedded in an extracellular matrix. Matrix consists of ground substance and fibres. All connective tissues (except blood) secrete structural fibres (collagen, elastin).
• Functions: Binding, supporting, protection, insulation, transportation.
• Types:
  • 1. Loose Connective Tissue: Cells and fibres loosely arranged in a semi-fluid ground substance.
    • a) Areolar Tissue: Present beneath the skin. Contains fibroblasts (produce fibres), macrophages, mast cells.
      • Function: Support framework for epithelium, reservoir for water and salts. Site of inflammation response.
    • b) Adipose Tissue: Located mainly beneath the skin. Cells (adipocytes) specialised to store fats. Excess nutrients converted to fats are stored here.
      • Function: Fat reservoir, insulation, cushioning.
  • 2. Dense Connective Tissue: Fibres and fibroblasts are compactly packed.
    • a) Dense Regular: Collagen fibres present in rows between parallel bundles of fibres.
      • Tendons: Attach skeletal muscles to bones (strong, inelastic - mainly collagen).
      • Ligaments: Attach one bone to another (elastic - contain elastin).
    • b) Dense Irregular: Fibroblasts and many fibres (mostly collagen) oriented differently.
      • Location: Skin (dermis).
      • Function: Provides strength.
  • 3. Specialised Connective Tissue:
    • a) Cartilage: Solid, pliable matrix resists compression. Cells (chondrocytes) enclosed in small cavities (lacunae) within the matrix secreted by them. Most cartilage in vertebrate embryos is replaced by bone in adults.
      • Location: Tip of nose, outer ear joints, between adjacent vertebrae, limbs and hands in adults.
    • b) Bone: Hard, non-pliable ground substance rich in calcium salts and collagen fibres, giving strength. Bone cells (osteocytes) present in spaces called lacunae.
      • Function: Structural frame, support and protection, muscle attachment, site of blood cell production (bone marrow).
      • Structure: Long bones have a marrow cavity. Compact bone shows Haversian systems.
    • c) Blood: Fluid connective tissue containing plasma, Red Blood Cells (RBCs), White Blood Cells (WBCs), and platelets.
      • Plasma: Fluid matrix (contains proteins, salts, hormones).
      • RBCs (Erythrocytes): Carry oxygen; lack nucleus in mammals.
      • WBCs (Leukocytes): Defence mechanism; various types (neutrophils, eosinophils, basophils, lymphocytes, monocytes).
      • Platelets (Thrombocytes): Cell fragments involved in blood clotting.
      • Function: Transport of gases, nutrients, hormones, waste products; defence.

C. Muscle Tissue:

• Characteristics: Composed of long, cylindrical fibres arranged in parallel arrays, made of fine fibrils called myofibrils. Contract (shorten) in response to stimulation, then relax (lengthen). Plays an active role in movement.
• Types:
  • 1. Skeletal Muscle: Attached to bones. Fibres are striated (striped appearance), bundled together. Voluntary control. Multinucleated (syncytium). Unbranched.
    • Function: Locomotion, voluntary movements.
  • 2. Smooth Muscle: Walls of internal organs (blood vessels, stomach, intestine). Fibres taper at both ends (fusiform), non-striated. Involuntary control. Uninucleate. Unbranched. Cells held together by cell junctions.
    • Function: Movement of food through digestive tract, contraction/relaxation of blood vessels.
  • 3. Cardiac Muscle: Only in the heart wall. Contractile tissue. Striated. Involuntary control. Uninucleate. Branched. Cell junctions (intercalated discs) fuse plasma membranes, allowing cells to contract as a unit.
    • Function: Pumping of blood.

D. Neural Tissue:

• Characteristics: Exerts greatest control over body's responsiveness to changing conditions. Composed of neurons and neuroglia.
• Neurons: Unit of neural system. Excitable cells.
  • Structure: Cell body (cyton) with nucleus and cytoplasm, Dendrites (short fibres branching from cell body), Axon (single long fibre).
  • Function: Detect, receive, and transmit stimuli (electrical impulses).
• Neuroglia: Rest of the neural tissue. Make up more than half the volume of neural tissue.
  • Function: Protect and support neurons.

III. Organ and Organ System:

• Tissues organize to form Organs (e.g., stomach has epithelial, connective, muscular, neural tissues).
• Organs performing related functions associate to form Organ Systems (e.g., Digestive system includes stomach, intestine, liver, etc.).
• Organisation into tissues, organs, and organ systems is essential for efficient functioning and survival of multicellular organisms.

IV. Morphology and Anatomy of Earthworm (Pheretima)

• Classification: Phylum Annelida, Class Oligochaeta.
• Habitat: Moist soil. Nocturnal.
• Morphology:
  • Long, cylindrical body, segmented (metameres, ~100-120).
  • 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 in segments 14-16. Secretes cocoon. Body divisible into preclitellar, clitellar, postclitellar regions.
  • Setae: S-shaped chitinous structures in each segment (except first, last, clitellum). Help in locomotion.
  • Apertures: Mouth, Anus, Spermathecal openings (ventro-lateral, segments 5-9), Female genital pore (mid-ventral, 14th), Male genital pores (ventro-lateral, 18th), Nephridiopores (numerous, all over body except first two).
• Anatomy:
  • Body Wall: Cuticle (non-cellular), Epidermis (columnar), Muscular layers (circular, longitudinal), Coelomic epithelium.
  • Coelom: True coelom (schizocoelom). Coelomic fluid acts as hydrostatic skeleton.
  • Digestive System: Straight tube. Mouth (1-3) -> Buccal cavity -> Pharynx -> Oesophagus (5-7) -> Muscular Gizzard (8-9, grinding) -> Stomach (9-14, neutralises humus acid via calciferous glands) -> Intestine (15 to last) -> Anus.
    • Typhlosole: Internal median fold of dorsal wall in intestine (after 26th segment), increases absorptive area.
  • Circulatory System: Closed type. Blood glands (4, 5, 6 segments) produce blood cells and haemoglobin (dissolved in plasma). Dorsal vessel (main collecting), Ventral vessel (main distributing), hearts (lateral, 7, 9, 12, 13 segments).
  • Respiratory System: No specialised organs. Gas exchange via moist body surface (cutaneous respiration).
  • Excretory System: Segmentally arranged coiled tubules called Nephridia.
    • Septal Nephridia: Both sides of intersegmental septa (segment 15 to last). Open into intestine.
    • Integumentary Nephridia: Attached to lining of body wall (segment 3 to last). Open on body surface.
    • Pharyngeal Nephridia: 3 paired tufts in segments 4, 5, 6. Open into pharynx/buccal cavity.
    • Function: Regulate volume/composition of body fluids. Excretion is ureotelic (mainly urea).
  • Nervous System: Paired cerebral ganglia -> sub-pharyngeal ganglia -> double ventral nerve cord with segmental ganglia. Sensory receptors for light, touch, chemo-receptors.
  • Reproductive System: Hermaphrodite (monoecious). Testes (2 pairs, seg 10, 11), seminal vesicles (2 pairs, seg 11, 12), vasa deferentia (run up to 18th seg), prostate ducts, male genital pores (18th). Ovaries (1 pair, seg 12-13), oviducts, female genital pore (14th). Spermathecae (4 pairs, seg 6-9, receive sperm during copulation).
    • Cross-fertilization (mutual exchange of sperm). Cocoon formation by clitellum. Fertilization and development occur within the cocoon. Development is direct (no larva).

V. Morphology and Anatomy of Cockroach (Periplaneta americana)

• Classification: Phylum Arthropoda, Class Insecta.
• Habitat: Damp, warm places. Nocturnal omnivores. Pests, vectors of diseases.
• Morphology:
  • Segmented body (~34-53 mm long). Brown/black. Sexes separate.
  • Exoskeleton: Hard, chitinous plates called sclerites (dorsal tergites, ventral sternites, lateral pleurites). Joined by thin, flexible arthrodial membrane.
  • Body Divisions: Head, Thorax, Abdomen.
  • Head: Triangular, formed by fusion of 6 segments. Flexible neck. Bears compound eyes (pair), antennae (sensory), mouthparts adapted for biting and chewing type (labrum-upper lip, mandibles-grinding, maxillae-pair, labium-lower lip, hypopharynx-tongue).
  • Thorax: 3 parts - Prothorax, Mesothorax, Metathorax. Each bears a pair of walking legs. Two pairs of wings: Forewings (tegmina, mesothoracic, opaque, leathery, protective), Hindwings (metathoracic, transparent, membranous, used in flight).
  • Abdomen: 10 segments. 7th sternum (female) / 9th sternum (male) forms genital pouch.
    • Anal Cerci: Paired, jointed structures on 10th segment (both sexes, sensory).
    • Anal Styles: Paired, unjointed structures on 9th sternum (males only).
• Anatomy:
  • Digestive System: Alimentary canal divided into Foregut, Midgut, Hindgut.
    • Foregut: Mouth -> Pharynx -> Oesophagus -> Crop (storage) -> Gizzard (proventriculus, grinding - chitinous teeth). Lined by cuticle.
    • Midgut (Mesenteron): Site of digestion and absorption. Junction of foregut/midgut: 6-8 blind tubules (hepatic caecae or gastric caecae - secrete digestive juice). Not lined by cuticle.
    • Hindgut: Broader than midgut. Ileum -> Colon -> Rectum -> Anus. Lined by cuticle. Junction of midgut/hindgut: 100-150 yellow, thin filamentous Malpighian tubules (excretory).
  • Circulatory System: Open type. Blood vessels poorly developed, open into space (haemocoel). Visceral organs bathed in blood (haemolymph - colourless plasma + haemocytes). Heart is elongated tube along mid-dorsal line, differentiated into funnel-shaped chambers (13 chambers) with ostia (pores) on either side. Blood flows anteriorly.
  • Respiratory System: Network of trachea that open through 10 pairs of small holes called spiracles (lateral side). Trachea subdivide into tracheoles carrying oxygen directly to cells. No respiratory pigment.
  • Excretory System: Malpighian tubules (absorb waste from haemolymph, convert to uric acid). Also, fat body, nephrocytes, urecose glands contribute. Excretion is uricotelic.
  • Nervous System: Segmentally arranged ganglia joined by paired longitudinal connectives (ventral side). Supra-oesophageal ganglion ('brain') supplies nerves to antennae and compound eyes. Sense organs: Antennae, eyes (compound, mosaic vision), maxillary palps, labial palps, anal cerci.
  • Reproductive System: Dioecious.
    • Male: Testes (pair, 4-6th segments), vas deferens, ejaculatory duct, seminal vesicles (store sperm bundles - spermatophores), mushroom gland (accessory, 6-7th seg), phallic gland. External genitalia (male gonapophysis or phallomere).
    • Female: Ovaries (pair, 2nd-6th segments, each with 8 ovarioles), oviducts, common oviduct (vagina), genital chamber. Spermatheca (pair, 6th seg, stores sperm). Colleterial glands (secrete egg case). External genitalia (ovipositor).
    • Fertilization internal. Females produce ootheca (dark capsule containing ~14-16 fertilised eggs). Development is paurometabolous (nymph stage looks like adult, moults ~13 times).

VI. Morphology and Anatomy of Frog (Rana tigrina)

• Classification: Phylum Chordata, Class Amphibia.
• Habitat: Freshwater, land. Poikilotherms (cold-blooded). Exhibit camouflage (mimicry). Aestivation (summer sleep), Hibernation (winter sleep).
• Morphology:
  • Skin: Smooth, moist, slippery due to mucus. Absorbs water. Dorsal side olive green with dark spots, ventral side pale yellow.
  • Body Divisions: Head, Trunk. (Neck, tail absent).
  • Head: Snout, nostrils (pair), bulging eyes (covered by nictitating membrane), tympanum (ear drum) behind eyes.
  • Trunk: Forelimbs (4 digits, smaller), Hindlimbs (5 digits, larger, muscular, webbed - swimming).
  • Sexual Dimorphism: Males have sound-producing vocal sacs and copulatory pad (nuptial pad) on the first digit of forelimbs (absent in females).
• Anatomy:
  • Body Cavity: Coelom accommodates well-developed organ systems.
  • Digestive System: Short alimentary canal (carnivorous). Mouth -> Buccal cavity -> Pharynx -> Oesophagus -> Stomach (HCl, pepsinogen) -> Intestine (Duodenum, Ileum) -> Rectum -> Cloaca -> Cloacal aperture.
    • Tongue: Bilobed, attached anteriorly, free behind (captures prey).
    • Liver: Secretes bile (stored in gall bladder). Pancreas: Secretes pancreatic juice (digestive enzymes). Digestion completed in intestine. Absorption by villi and microvilli.
    • Cloaca: Common chamber for urinary, reproductive, faecal discharge.
  • Respiratory System:
    • Cutaneous Respiration: Through skin (in water and on land).
    • Buccal Respiration: Through lining of buccal cavity (on land).
    • Pulmonary Respiration: Through lungs (pair, elongated sacs) when active on land. Lungs open into buccal cavity via glottis.
  • Circulatory System: Closed type. Well-developed lymphatic system also present.
    • Heart: 3-chambered (2 atria, 1 ventricle). Covered by pericardium. Sinus venosus joins right atrium. Ventricle opens into conus arteriosus. Receives oxygenated blood (lungs/skin) and deoxygenated blood (body). Mixed blood (incomplete double circulation) supplied to body.
    • Blood: Plasma, RBCs (nucleated, contain haemoglobin), WBCs, Platelets.
    • Portal Systems: Hepatic portal system (intestine to liver), Renal portal system (lower body parts to kidney).
  • Excretory System: Pair of compact, elongated kidneys. Functional units are nephrons (uriniferous tubules). Ureters emerge from kidneys, open into cloaca (males: urinogenital duct). Thin-walled urinary bladder present, opens into cloaca. Excretion is ureotelic.
  • Control & Coordination: Endocrine glands (pituitary, thyroid, parathyroid, thymus, pineal, pancreatic islets, adrenals, gonads) secrete hormones. Nervous system well-developed.
    • CNS: Brain (forebrain - olfactory lobes, cerebral hemispheres, diencephalon; midbrain - optic lobes; hindbrain - cerebellum, medulla oblongata which passes into spinal cord), Spinal cord (enclosed in vertebral column).
    • PNS: Cranial nerves (10 pairs), Spinal nerves.
    • ANS: Sympathetic, Parasympathetic.
    • Sense Organs: Touch (sensory papillae), Taste (taste buds), Smell (nasal epithelium), Vision (eyes - simple), Hearing (tympanum + internal ear).
  • Reproductive System: Dioecious.
    • Male: Testes (pair, attached to kidney by mesorchium), vasa efferentia (10-12, enter kidney), Bidder's canal (in kidney), urinogenital duct (opens into cloaca).
    • Female: Ovaries (pair, near kidneys, no functional connection), oviducts (separate, open into cloaca separately). Mature female lays 2500-3000 eggs at a time.
    • Fertilization is external (in water). Development involves a larval stage (tadpole), which undergoes metamorphosis to form the adult.

Multiple Choice Questions (MCQs):

1. Which type of epithelial tissue lines the inner surface of bronchioles and fallopian tubes?
   a) Simple Squamous Epithelium
   b) Simple Cuboidal Epithelium
   c) Simple Columnar Epithelium
   d) Ciliated Epithelium

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

3. Intercalated discs are characteristic features found in:
   a) Skeletal Muscle Tissue
   b) Smooth Muscle Tissue
   c) Cardiac Muscle Tissue
   d) Neural Tissue

4. In earthworms, the function of the gizzard is primarily:
   a) Absorption of digested food
   b) Grinding of soil particles and decaying leaves
   c) Secretion of digestive enzymes
   d) Neutralising humic acid in soil

5. Malpighian tubules in cockroaches are involved in:
   a) Respiration
   b) Circulation
   c) Reproduction
   d) Excretion

6. Which structure is present in male cockroaches but absent in female cockroaches?
   a) Anal Cerci
   b) Antennae
   c) Anal Styles
   d) Tegmina

7. The heart of a frog has:
   a) Two atria and two ventricles
   b) One atrium and one ventricle
   c) Two atria and one ventricle
   d) One atrium and two ventricles

8. Gas exchange through moist skin in frogs is known as:
   a) Pulmonary respiration
   b) Buccal respiration
   c) Cutaneous respiration
   d) Branchial respiration

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

10. Which of the following cell junctions facilitates communication between adjoining cells by connecting their cytoplasm?
    a) Tight Junctions
    b) Adhering Junctions
    c) Gap Junctions
    d) Desmosomes

Answer Key:

1. d) Ciliated Epithelium
2. b) Dense Regular Connective Tissue
3. c) Cardiac Muscle Tissue
4. b) Grinding of soil particles and decaying leaves
5. d) Excretion
6. c) Anal Styles
7. c) Two atria and one ventricle
8. c) Cutaneous respiration
9. c) Blood Plasma
10. c) Gap Junctions

Study these notes thoroughly, focusing on the locations, structures, and functions. Pay special attention to the distinguishing features of the three example organisms. Good luck with your preparation!