Chapter 1: Structural Organisation in Animals

Introduction

Overview

• Unicellular organisms perform all life functions in a single cell.
• Multicellular organisms have specialized groups of cells performing specific functions.
• A tissue is a group of similar cells with common origin and function.

Memory Aids

• Tissue = group of similar cells + intercellular substance + common function.

Quick Checkpoints

• What defines a tissue in multicellular organisms?
• How do unicellular and multicellular organisms differ in function execution?

Animal Tissues

Types and Classification

• Four basic tissue types: Epithelial, Connective, Muscular, Neural.
• Each tissue type has distinct origin and function.
• Epithelial: protection, secretion, absorption, excretion, reproduction.
• Connective: support, attachment, storage, protection, transport.
• Muscular: movement and locomotion.
• Neural: control and nerve impulse transmission.

Memory Aids

• Remember: Epithelial = covering; Connective = support; Muscular = movement; Neural = control.

Quick Checkpoints

• List the four basic animal tissues.
• What are the main functions of connective tissue?

Epithelial Tissue

Structure and Types

• Epithelium has a free surface facing body fluid or environment.
• Cells are tightly packed with minimal intercellular matrix.
• Two main types: Simple (single layer) and Compound (multiple layers).
• Simple epithelium subtypes: Squamous, Cuboidal, Columnar.
• Squamous: thin, flat cells; found in blood vessels and lungs; functions include protection and gas exchange.
• Cuboidal: cube-shaped cells; found in gland ducts and kidney tubules; functions include secretion and absorption; may have microvilli.
• Columnar: tall cells with basal nuclei; found in stomach, intestine; may have microvilli (brush border) or cilia.
• Ciliated epithelium moves mucus, urine, eggs, cerebrospinal fluid.
• Compound epithelium protects against mechanical and chemical stress; found in skin, mouth lining, ducts.
• Glandular epithelium specialized for secretion; unicellular (goblet cells) or multicellular (salivary glands).
• Glands classified as exocrine (ducts) or endocrine (ductless, secrete hormones).
• Heterocrine glands have both exocrine and endocrine parts (e.g., pancreas).
• Cell junctions: Tight (prevent leakage), Adhering (cement cells), Gap (communication).

Memory Aids

• Simple epithelium = 1 layer; Compound = multiple layers.
• Squamous = flat; Cuboidal = cube; Columnar = tall.
• Ciliated epithelium moves substances; glandular epithelium secretes.
• Exocrine glands use ducts; endocrine glands are ductless.

Quick Checkpoints

• What are the types of simple epithelium?
• Where is ciliated epithelium found and what is its function?
• Differentiate exocrine and endocrine glands.
• What are the three types of cell junctions in epithelium?

Connective Tissue

Overview and Types

• Most abundant tissue; links and supports other tissues/organs.
• Cells secrete collagen or elastin fibers for strength and flexibility.
• Matrix contains modified polysaccharides.
• Types: Loose (areolar, adipose), Dense (regular, irregular), Specialized (cartilage, bone, blood).
• Loose connective tissue: cells and fibers loosely arranged in semi-fluid ground substance.
• Dense connective tissue: fibers and fibroblasts densely packed.
• Dense regular: collagen fibers in parallel; found in tendons and ligaments.
• Dense irregular: collagen fibers in multiple directions; found in skin.
• White fibrous connective tissue: collagen bundles, strong but less flexible.
• Yellow elastic connective tissue: elastic fibers, flexible; forms ligaments and vessel walls.

Memory Aids

• Loose = loose fibers; Dense = tightly packed fibers.
• White fibrous = strength; Yellow elastic = elasticity.

Quick Checkpoints

• What are the main functions of connective tissue?
• Differentiate loose and dense connective tissue.
• Where is white fibrous connective tissue found?

Specialised Connective Tissue

Cartilage

• Soft skeletal tissue with chondrocytes in lacunae.
• Matrix is solid, pliable, resists compression.
• Most embryonic cartilage replaced by bone in adults.
• Types: Hyaline (common, joints, trachea), White fibrous (strongest, intervertebral discs), Yellow elastic (ear, epiglottis).

Bone

• Osteocytes in lacunae; matrix rich in calcium salts and collagen.
• Provides body frame, support, protection.
• Limb bones aid movement; red marrow produces blood cells.
• Osteon (Haversian system) = lamellae + lacunae + Haversian canal; absent in spongy bone.

Blood

• Fluid connective tissue with plasma, RBCs, WBCs, platelets.
• Transports substances throughout the body.
• RBCs carry oxygen; platelets aid clotting; WBCs fight infection.

Memory Aids

• Cartilage = flexible support; Bone = hard support; Blood = transport.
• Osteon is the functional unit of compact bone.

Quick Checkpoints

• What are the types of cartilage and their locations?
• Describe the structure of an osteon.
• What are the components of blood and their functions?

Muscular Tissue

Structure and Function

• Made of long cylindrical fibers with myofibrils in sarcoplasm.
• Fibers contract and relax to produce movement or maintain posture.
• Three types: Skeletal (voluntary, striated), Smooth (involuntary, non-striated), Cardiac (involuntary, striated with intercalated discs).
• Skeletal muscles attach to bones; smooth muscles in internal organs; cardiac muscle in heart.

Memory Aids

• Skeletal = voluntary, striated; Smooth = involuntary, no striations; Cardiac = involuntary, striated with discs.

Quick Checkpoints

• What are the three types of muscle tissue?
• Where is smooth muscle found?
• What special features does cardiac muscle have?

Neural Tissue

Structure and Function

• Controls body's response to stimuli.
• Neurons are the main units; consist of cyton (cell body), dendrites, and axon.
• Axon ends in terminal arborisations; axon/dendrite with sheath called nerve fiber.
• Neuroglial cells support and protect neurons; >50% of neural tissue volume.
• Nerve fibers: medullated (with myelin sheath, nodes of Ranvier) and non-medullated (without sheath).
• Electrical impulses travel along neuron membrane when stimulated.

Memory Aids

• Neuron = cyton + dendrites + axon; neuroglia support neurons.
• Myelin sheath speeds impulse; nodes of Ranvier are gaps.

Quick Checkpoints

• What are the parts of a neuron?
• Difference between medullated and non-medullated nerve fibers?
• Role of neuroglial cells?

Organ and Organ System

Overview

• Basic tissues form organs (e.g., heart has epithelial, connective, muscular, neural tissues).
• Organs combine to form organ systems; organ systems form an organism.
• Organisation ensures efficient, coordinated cell activities.
• Morphology: Study of external features of animals.
• Anatomy: Study of internal organ morphology.

Memory Aids

• Organ = Tissues combined; Organ system = Organs combined.
• Morphology = External form; Anatomy = Internal structure.

Quick Checkpoints

• What tissues form an organ?
• Difference between morphology and anatomy?
• Why is organ organisation important?

Cockroach

General Characteristics

• Scientific name: Periplaneta americana.
• Class: Insecta; Phylum: Arthropoda.
• Brown or black, nocturnal, omnivorous.
• Body divided into head, thorax, abdomen; covered by chitinous exoskeleton.
• Exoskeleton plates called sclerites (tergites dorsal, sternites ventral) joined by flexible membranes.
• Head triangular, fused from 6 segments, flexible neck, with compound eyes and antennae.
• Mouthparts chewing type: labrum (upper lip), labium (lower lip), maxillae, mandibles, hypopharynx (tongue-like).
• Thorax has prothorax, mesothorax, metathorax; each with a pair of legs.
• Two pairs of wings: forewings (opaque, leathery), hindwings (transparent, membranous for flight).

Mouthparts Function

• Mandibles: strong jaws for cutting and crushing food; grinding and incising regions.
• Maxillae: hold and manipulate food.
• Labrum: upper lip, holds food in place.
• Hypopharynx: inside mouth, mixes food with saliva.
• Labium: lower lip, holds food during eating.

Memory Aids

• Mandibles = jaws; Maxillae = food holders; Labrum = upper lip; Labium = lower lip; Hypopharynx = tongue.

Quick Checkpoints

• What are the main mouthparts of cockroach?
• Function of mandibles and maxillae?
• Role of hypopharynx?

Morphology

Body Structure

• Body segmented into head, thorax, abdomen.
• Covered by hard chitinous exoskeleton with sclerites (tergites dorsal, sternites ventral) joined by flexible membranes.
• Head triangular, fused from 6 segments, flexible neck, with compound eyes and antennae.
• Mouthparts: labrum (upper lip), labium (lower lip), maxillae, mandibles, hypopharynx (tongue-like).
• Thorax: prothorax, mesothorax, metathorax; each segment has a pair of walking legs with segmented podomeres.
• Wings: two pairs from meso- and metathorax; forewings opaque and leathery, hindwings transparent and membranous for flight.

Memory Aids

• Head = 6 fused segments; Thorax = 3 parts with legs; Abdomen = 10 segments.
• Forewings cover hindwings at rest.

Quick Checkpoints

• How is cockroach body segmented?
• What are sclerites?
• Describe the wings and their function.

Anatomy

Body Segments and Sexual Differences

• Abdomen has 10 segments in both sexes.
• Female 7th sternum boat-shaped; 7th-9th sterna form brood pouch with female gonopore, spermathecal pores, collaterial glands.
• Male genital pouch at hind abdomen, bounded by 9th-10th terga and 9th sternum; contains anus, male genital pore, gonapophysis.
• Males have short anal styles; both sexes have anal cerci on 10th segment.

Memory Aids

• Female brood pouch = 7th-9th sterna; Male genital pouch = 9th-10th terga + 9th sternum.
• Anal cerci present in both sexes; anal styles only in males.

Quick Checkpoints

• How many abdominal segments in cockroach?
• Differences in male and female genital structures?
• What are anal cerci and anal styles?

Digestive system

Structure and Function

• Alimentary canal divided into foregut, midgut, hindgut.
• Foregut: Mouth → pharynx → oesophagus → crop (stores food) → gizzard (proventriculus) with 6 chitinous teeth for grinding.
• Midgut: Short, narrow, coiled; junction with foregut has 6-8 hepatic caecae secreting digestive juice.
• Midgut-hindgut junction has 100-150 Malpighian tubules removing excretory products.
• Hindgut: Ileum, colon, rectum with 6 rectal glands; opens via anus; more permeable to water than foregut.
• Foregut and hindgut ectodermal, lined by cuticle; midgut endodermal, no cuticle.

Memory Aids

• Crop stores food; Gizzard grinds food.
• Hepatic caecae = digestive juice; Malpighian tubules = excretion.
• Foregut/hindgut lined with cuticle; midgut not.

Quick Checkpoints

• What are the three regions of alimentary canal?
• Function of crop and gizzard?
• Role of hepatic caecae and Malpighian tubules?

Blood vascular system

Features

• Open type system; vessels open into haemocoel.
• Haemolymph bathes visceral organs; consists of colourless plasma and haemocytes.
• No respiratory pigment; does not aid respiration.
• Heart is elongated muscular tube with funnel-shaped chambers and ostia; pumps blood anteriorly.
• Heart is neurogenic.

Memory Aids

• Open system with haemocoel.
• Haemolymph lacks respiratory pigment.
• Heart has ostia and is neurogenic.

Quick Checkpoints

• Type of blood vascular system?
• Composition and function of haemolymph?
• What is neurogenic heart?

Respiratory system

Structure and Function

• Network of tracheae opening through 10 pairs of spiracles on body sides.
• Spiracles guarded by bristles to prevent dirt entry.
• Tracheal tubes carry oxygen to tissues; subdivide into tracheoles for gas exchange by diffusion.
• Most CO₂ exits through body cuticle, little through spiracles.

Memory Aids

• 10 pairs of spiracles with bristles.
• Tracheoles = site of gas exchange.
• CO₂ mostly leaves via cuticle.

Quick Checkpoints

• How does cockroach breathe?
• Function of spiracles and tracheae?
• Pathway of CO₂ exit?

Excretory system

Components and Function

• Excretion by Malpighian tubules lined with glandular and ciliated cells.
• Malpighian tubules absorb nitrogenous wastes, convert to uric acid; cockroach is uricotelic.
• Also reabsorb salts and water.
• Fat body, nephrocytes, uricose glands assist excretion.

Memory Aids

• Malpighian tubules = uric acid excretion.
• Insects are uricotelic.
• Fat body and nephrocytes aid excretion.

Quick Checkpoints

• What excretes nitrogenous wastes?
• Why are insects uricotelic?
• Other excretory aids?

Nervous system

Structure and Features

• Comprises central, peripheral, sympathetic systems.
• Fused, segmental ganglia joined by paired longitudinal connectives ventrally.
• 9 ganglia: 3 thoracic, 6 abdominal.
• Brain = bilobed supra-oesophageal ganglion; supplies antennae and compound eyes.
• Compound eyes have ~2000 hexagonal ommatidia; provide mosaic nocturnal vision (high sensitivity, low resolution).
• Other sense organs: antennae, maxillary palps, labial palps, anal cerci.

Memory Aids

• 9 ganglia: 3 thorax, 6 abdomen.
• Brain = supra-oesophageal ganglion.
• Compound eyes = mosaic vision with ommatidia.

Quick Checkpoints

• Number and location of ganglia?
• Function of supra-oesophageal ganglion?
• What is mosaic vision?

Reproductive system

Male and Female Structures

• Dioecious: sexes separate.
• Male: testes in 4th-6th abdominal segments, 3-lobed with follicles.
• Vas deferens opens into ejaculatory duct via seminal vesicles; stores sperms as spermatophores.
• Accessory mushroom-shaped gland in 6th-7th segments.
• External genitalia: male gonapophyses (phallomeres).
• Female: ovaries in 2nd-6th segments with ovarioles containing developing ova.
• Oviducts unite into median oviduct opening into genital chamber.
• Spermathecae in 6th segment open into genital chamber.
• Collaterial glands behind ovaries secrete ootheca (egg-case).
• Sperms transferred as spermatophores; fertilized eggs encased in reddish-brown oothecae.
• Females produce 9-10 oothecae, each with 14-16 eggs.
• Development is paurometabolous via nymphal stage; nymph moults ~13 times to adult.
• Some species are pests, contaminating food and spreading bacterial diseases.

Memory Aids

• Dioecious = separate sexes.
• Male: testes → vas deferens → ejaculatory duct → gonopore.
• Female: ovaries → oviduct → genital chamber; ootheca from collaterial glands.
• Development: paurometabolous with moulting.

Quick Checkpoints

• What does dioecious mean?
• Describe male reproductive tract.
• What forms the ootheca?
• Type of development in cockroach?

Frog

Characteristics

• Class Amphibia, Phylum Chordata; live in water and on land (amphibians).
• Common Indian frog: Rana tigrina.
• Cold-blooded (poikilotherms): body temperature varies with environment.
• Can change body color for camouflage (mimicry).
• Undergo aestivation (summer sleep) and hibernation (winter sleep) in extreme conditions.

Memory Aids

• Amphibians = live in both water and land.
• Poikilotherms = body temperature varies.
• Mimicry = protective coloration.
• Aestivation = summer sleep; Hibernation = winter sleep.

Quick Checkpoints

• What class and phylum does frog belong to?
• Define poikilotherms.
• What is mimicry in frogs?
• What are aestivation and hibernation?

Morphology

External Features

• Dorsal color: olive green with dark spots; ventral side pale yellow.
• Skin moist, smooth, slippery; absorbs water, does not drink.
• Body parts: head and trunk; no neck or tail.
• Nostrils above mouth; bulged eyes with nictitating membrane.
• Tympanum (ear) on sides of eyes for sound reception.
• Forelimbs: 4 digits; hindlimbs: 5 digits, muscular, webbed for swimming.
• Sexual dimorphism: males have vocal sacs and copulatory pads; males darker and slender.

Memory Aids

• Skin absorbs water, not drinking.
• Hindlimbs larger, webbed for swimming.
• Male vocal sacs and copulatory pads for mating.

Quick Checkpoints

• What are the body divisions of a frog?
• How do frogs absorb water?
• Describe sexual dimorphism in frogs.
• Function of tympanum?

Anatomy

Digestive System

• Short alimentary canal; frogs are carnivores.
• Mouth → buccal cavity → pharynx → oesophagus → stomach (cardiac and pyloric parts).
• Small intestine: duodenum (digestion) and ileum (absorption).
• Rectum opens into cloaca.
• Digestive glands: liver (bile), pancreas (pancreatic juice), gastric and intestinal glands.
• Food captured by bilobed tongue; digestion by HCl and gastric juices.
• Chyme passes to duodenum; bile emulsifies fats; enzymes digest carbs and proteins.
• Absorption by villi and microvilli in intestine.
• Undigested waste expelled via cloaca.

Respiratory System

• Three types of respiration: cutaneous (skin), buccopharyngeal (mouth and throat), pulmonary (lungs).
• Cutaneous respiration mainly in water; pulmonary on land via nostrils to lungs.

Circulatory System

• Closed circulatory system: heart, blood vessels, blood; lymphatic system present.
• Heart: 3 chambers (2 atria, 1 ventricle), covered by pericardium.
• Sinus venosus joins right atrium; ventricle opens into conus arteriosus.
• Arteries carry blood from heart; veins return blood to heart.
• Hepatic portal system (liver-intestine) and renal portal system (kidney-lower body) present.
• Blood: plasma + cells (nucleated RBCs with hemoglobin, WBCs, platelets).
• Blood transports nutrients, gases, water; heart pumps blood.

Excretory System

• Components: paired kidneys, ureters, cloaca, urinary bladder.
• Kidneys: dark red, bean-shaped, contain nephrons (uriniferous tubules).
• Male ureters act as urinogenital ducts; female ureters and oviduct open separately into cloaca.
• Urinary bladder thin-walled, opens into cloaca.
• Frog is ureotelic; excretes urea.
• Excretory wastes filtered from blood by kidneys.

Memory Aids

• Short intestine due to carnivorous diet.
• Three respiration types: skin, mouth/throat, lungs.
• Heart has 3 chambers; closed circulation.
• Ureotelic animal: excretes urea.

Quick Checkpoints

• What are the parts of frog's digestive system?
• Explain the three types of respiration in frogs.
• Describe the structure of frog's heart.
• What is the excretory system composed of?

Control and Co-ordination

Neural and Endocrine Systems

• Control system includes nervous and endocrine systems.
• Endocrine glands: pituitary, thyroid, parathyroid, thymus, pineal, pancreatic islets, adrenals, gonads.
• Nervous system: central (brain, spinal cord), peripheral (cranial, spinal nerves), autonomic (sympathetic, parasympathetic).
• Brain enclosed in cranium; divided into forebrain, midbrain, hindbrain.
• Ten pairs of cranial nerves arise from brain.
• Sense organs: touch, taste, smell, vision (eyes), hearing (tympanum and internal ears).

Memory Aids

• Brain parts: forebrain, midbrain, hindbrain.
• 10 pairs cranial nerves.
• Endocrine glands regulate body functions via hormones.

Quick Checkpoints

• What are the components of frog's nervous system?
• Name major endocrine glands in frogs.
• How many cranial nerve pairs are present?
• List the sense organs of frog.

Reproductive System

Male and Female Systems

• Male: paired yellowish testes, vasa efferentia, urinogenital ducts.
• Testes attached to kidneys by mesorchium.
• Vasa efferentia open into Bidder's canal, which connects to urinogenital duct opening into cloaca.
• Cloaca passes faeces, urine, and sperms.
• Female: paired ovaries, oviducts, cloaca.
• Mature female lays 2500-3000 ova at a time.
• Fertilisation is external in water.
• Development includes larval tadpole stage; metamorphosis forms adult.

Memory Aids

• Mesorchium connects testes to kidneys.
• External fertilisation in water.
• Tadpole undergoes metamorphosis.

Quick Checkpoints

• Describe male reproductive organs in frog.
• How does fertilisation occur?
• What is metamorphosis?
• Number of ova laid by female frog?

Economic Importance

Benefits to Humans and Ecosystem

• Frogs eat insects, protecting crops.
• Maintain ecological balance as part of food chain and web.
• Frog legs consumed as food in some countries.

Memory Aids

• Frogs control insect population.
• Important link in ecosystem food chains.
• Edible frog legs in some cultures.

Quick Checkpoints

• How do frogs benefit agriculture?
• What role do frogs play in ecosystems?
• Are frogs used as food?