STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS

Structural Organization in Animals

Hamid Ali January 20, 2025 3 0

Tissues
Tissues are groups of cells that are similar in structure and function and work together to perform a specific activity. There are four types of tissues in animals:

Epithelial Tissue
- Covers external surfaces and lines internal cavities and organs.
- Cells are tightly packed with minimal intercellular space and rest on a non-cellular basement membrane.
- Lacks blood vessels and receives nutrients by diffusion from underlying connective tissues.
- Has specialized junctions:
  - Tight junctions: Prevent substances from leaking between cells.
  - Adhering junctions: Cement neighboring cells together.
  - Gap junctions: Allow communication between adjacent cells through cytoplasmic connections.
Classification of Epithelial Tissues:
a) Simple Epithelium (Single-layered):
- Squamous epithelium: Flat cells; found in the lining of alveoli and blood vessels.
- Cuboidal epithelium: Cube-shaped cells; found in ducts of glands and nephron tubules.
- Columnar epithelium: Tall and pillar-like cells; found in the lining of the stomach and intestines.
- Pseudostratified epithelium: Appears multilayered but is single-layered; found in the respiratory tract.
b) Compound Epithelium (Multilayered):
- Stratified epithelium: Multiple layers, providing protection; found in skin.
- Transitional epithelium: Specialized for stretching; found in the urinary bladder.
Muscular Tissue
Specialized for contraction and movement due to the presence of contractile proteins, actin, and myosin.
- Striated (Skeletal/Voluntary) Muscle: Multinucleated, cylindrical cells with striations; under voluntary control; attached to bones.
- Unstriated (Smooth/Involuntary) Muscle: Spindle-shaped, uninucleate cells without striations; found in walls of internal organs.
- Cardiac Muscle: Branched, uninucleate cells with faint striations; interconnected by intercalated discs; found in the heart.
Nervous Tissue
- Specialized for receiving and transmitting impulses.
- The basic unit is the neuron, the longest cell in the body.
- Structure of a neuron:
  - Dendrites: Receive signals.
  - Cyton (Cell Body): Contains the nucleus.
  - Axon: Long projection transmitting impulses; may be covered by a myelinated sheath with Nodes of Ranvier.
  - Axon Terminals: Transmit signals to other neurons or muscles.

ORGAN AND ORGAN SYSTEM

Cockroach (Periplaneta americana)

Phylum: Arthropoda
Class: Insecta
Habitat: Nocturnal, omnivorous, found in warm and moist environments.

Morphology

Body size: 1/4 to 3 inches.
Covered with a chitinous exoskeleton divided into hardened plates called sclerites (tergites on the dorsal side, sternites on the ventral side), connected by a flexible arthrodial membrane.
Head: Triangular, with compound eyes and long, segmented antennae.
Mouthparts:
- Labrum: Upper lip.
- Mandibles: Chewing structures.
- Maxillae: Assist in handling food.
- Labium: Lower lip.
- Hypopharynx: Tongue-like structure.
Thorax: Divided into prothorax, mesothorax, and metathorax, each with a pair of legs.
Abdomen: Segmented with spiracles for respiration.

Anatomy

Digestive System
- Path: Mouth → Oesophagus → Crop (food storage) → Gizzard (grinding food) → Hepatic caeca → Midgut → Hindgut → Rectum → Anus.
- Hepatic caeca: Secrete digestive enzymes.
Circulatory System
- Open type with haemolymph (blood-like fluid).
- Heart: A tubular structure with ostia (valvular openings) that pump blood anteriorly.
Respiratory System
- Composed of tracheae, with external openings called spiracles.
- Tracheoles carry oxygen directly to tissues.
Excretory System
- Malpighian tubules: Excrete nitrogenous wastes as uric acid (uricotelic).
- Other organs: Fat bodies, nephrocytes, and urecose glands.
Nervous System
- Ganglia: Three pairs in the thorax and six pairs in the abdomen.
- Sense Organs: Antennae, compound eyes, maxillary palps, labial palps, and anal cerci.
- Compound eyes have 2000 ommatidia, providing mosaic vision.
Reproductive System
- Male: Testes → Vas deferens → Seminal vesicle → Ejaculatory duct.
- Female: Ovaries → Oviduct → Vagina → Genital chamber.
- Fertilized eggs are enclosed in oothecae (9–10 per female).
- Development: Paurometabolous (through nymphal stages), with 13 moults to reach adulthood.