Chapter 1: Structural Organisation in Animals

• Unicellular organisms: A single cell performs functions such as digestion, respiration, excretion and reproduction.
• Multicellular animals: Different groups of cells carry out specialised functions; tissues are organised in patterns to form organs.
• Four basic animal tissues: Epithelial, connective, muscular and neural.

• Simple epithelium: One cell layer; suited to functions such as absorption, secretion and exchange.
• Compound epithelium: More than one cell layer; mainly protects against mechanical and chemical stresses, with limited secretion and absorption.

Ciliated epithelium

• Structure: Cuboidal or columnar epithelium with cilia on the free surface; it is a ciliated modification, not a fourth structural type of simple epithelium.
• Location and role: Lines hollow organs such as bronchioles and fallopian tubes; cilia move mucus, urine, eggs or cerebrospinal fluid in a particular direction.

Compound epithelium

• Locations: Dry skin surface; moist buccal cavity and pharynx; inner linings of salivary and pancreatic ducts.
• Main role: Protection from mechanical and chemical stress; secretion and absorption are limited.

• Junctions: Special links in animal tissues provide structural and functional connections between cells.

• Matrix: Cells secrete modified polysaccharides that accumulate between cells and fibres.
• Fibres: Except in blood, connective-tissue cells secrete collagen or elastin fibres, which provide strength, elasticity and flexibility.
• Range: Includes loose and dense connective tissues, cartilage, bone, adipose tissue and blood.

• Matrix: Solid but pliable; resists compression.
• Development: Most cartilage in vertebrate embryos is replaced by bone in adults.

• Ground substance: Hard and non-pliable, rich in calcium salts and collagen fibres.
• Functions: Provides the body’s structural frame; supports and protects organs. Limb bones bear weight and work with skeletal muscles to produce movement.
• Red bone marrow: Site of blood-cell production.
• Osteon: A Haversian canal and its surrounding lamellae and osteocytes form a cylindrical unit called the Haversian system or osteon; absent from mammalian spongy bone.

• Main role: Circulates through the body and transports substances.

• Structure: Muscle tissue consists of many long, cylindrical fibres; contractile filaments lie in parallel arrays and contain fine fibrils called myofibrils in the sarcoplasm.
• Action: Coordinated contraction and relaxation move body parts or maintain their position.

Neuron structure and neural tissue

• Cell body: Also called cyton or soma.
• Processes: Dendrites and an axon; the axon ends in terminal arborisations.
• Nerve fibre: An axon or dendrite covered by a sheath.
• Neuroglia: Make up more than 50% of neural-tissue volume and protect and support neurons.
• Response: Stimulation generates an electrical disturbance that travels rapidly along the neuron's plasma membrane.

• Example: The heart contains epithelial, connective, muscular and neural tissues.
• Organisation: Tissues form organs → organs form organ systems → organ systems make up an organism.
• Importance: This organisation enables efficient, coordinated activities among an organism’s cells.

• Scientific name: *Periplaneta americana*; Class Insecta, Phylum Arthropoda.
• Habit: Brown or black-bodied, nocturnal and omnivorous.

• Body regions: The segmented body is divided into head, thorax and abdomen.
• Exoskeleton: The hard chitinous covering has plates called sclerites—dorsal tergites and ventral sternites—joined by flexible arthrodial membrane.
• Head: Triangular and formed by fusion of six segments; the flexible neck allows movement. The head bears compound eyes and sensory-receptor-rich antennae.
• Thorax: Prothorax, mesothorax and metathorax each bear one pair of walking legs; each leg consists of segments called podomeres.
• Wings: Two pairs arise from the mesothorax and metathorax. Dark, opaque, leathery forewings cover the transparent, membranous hindwings at rest; hindwings are used for flight.

Mouthparts

• Type: Mouthparts are adapted for chewing and biting.
• Parts: Labrum (upper lip), labium (lower lip), one pair each of mandibles and maxillae, and the hypopharynx, which acts like a tongue.

• Abdomen: Both sexes have 10 segments.
• Female pouch: The boat-shaped seventh sternum, with the eighth and ninth sterna, forms the brood or genital pouch. Its anterior part contains the female gonopore, spermathecal pores and collaterial glands.
• Male pouch: The hind-end genital chamber is bounded dorsally by the ninth and tenth terga and ventrally by the ninth sternum; it contains the anus, male genital pore and gonapophyses.
• Anal structures: Males have a pair of short, thread-like anal styles, absent in females. Both sexes have a pair of jointed anal cerci on the tenth segment.

Digestive-System Junctions and Lining

• Excretion at junction: About 100–150 thin Malpighian tubules at the midgut–hindgut junction remove excretory products from haemolymph.
• Lining: Foregut and hindgut are ectodermal and lined with cuticle; the endodermal midgut lacks cuticle.

• Type: Open circulatory system; vessels open into the haemocoel, where haemolymph bathes visceral organs.
• Haemolymph: Colourless plasma and haemocytes; it lacks respiratory pigment and transports food and metabolic wastes, not respiratory gases.
• Heart: An elongated muscular tube divided into funnel-shaped chambers, with ostia on either side.
• Flow: Haemolymph enters the heart from sinuses through ostia and is pumped anteriorly back into the sinuses.
• Control: The cockroach heart is neurogenic.

• Air entry: A tracheal network opens outside through 10 pairs of lateral spiracles, guarded by bristles or hairs that keep out dirt.
• Gas transport: Tracheae branch into tracheoles, which carry oxygen to body parts; gas exchange occurs by diffusion.
• Carbon dioxide: Only a small amount leaves through spiracles; most exits through the body’s cuticular covering.

• Main organs: Glandular and ciliated Malpighian tubules absorb nitrogenous wastes and convert them into uric acid.
• Water and salts: Malpighian tubules also reabsorb certain salts and water.
• Other structures: Fat body, nephrocytes and uricose glands also assist in excretion.
• Excretory type: Cockroaches are uricotelic because they excrete nitrogenous waste as uric acid.

• Divisions: Central, peripheral and sympathetic nervous systems.
• Ventral nerve cord: Segmentally arranged fused ganglia are joined by paired longitudinal connectives; there are nine ganglia—three thoracic and six abdominal.
• Brain: The bilobed supra-oesophageal ganglion supplies nerves to the antennae and compound eyes.
• Compound eyes: Each dorsal eye has about 2,000 hexagonal ommatidia, which together produce mosaic vision.
• Vision: Mosaic vision suits nocturnal activity; it has greater sensitivity but lower resolution.
• Other sense organs: Antennae, maxillary palps, labial palps and anal cerci.

• Sexes: Cockroaches are dioecious; males and females are separate individuals.

Fertilisation and Development

• Sperm transfer: Sperms are transferred in spermatophores during copulation.
• Ootheca: Fertilised eggs are enclosed in reddish-brown capsules, which are dropped or glued to a humid surface.
• Egg number: A female produces about 9–10 oothecae on average, each containing 14–16 eggs.
• Development: Paurometabolous development includes a nymphal stage; the nymph moults about 13 times before reaching adulthood.

• Pest species: Some cockroaches damage food and contaminate it with foul-smelling excreta.
• Disease transmission: Cockroaches can spread various bacterial diseases by contaminating food.