Overview
This lecture covers the structural organization of animals, focusing on the morphology and anatomy of frogs, highlighting their body structure, organ systems, and key physiological functions.
Levels of Structural Organization in Animals
- Cells are the basic building blocks of animals.
- Unicellular organisms (e.g., amoeba) perform all functions with one cell.
- Multicellular organisms have division of labor among specialized cells.
- Similar cells form tissues; tissues form organs; organs form organ systems; multiple systems form an organism.
Animal vs. Plant Tissues
- Animal tissues are mostly living and allow uniform growth.
- Plant tissues often serve support and are mostly dead.
- Four main animal tissue types: epithelial, connective, muscular, and nervous.
- Organs (e.g., heart) are made of multiple tissue types.
Frog: Morphology (External Structure)
- Frogs are vertebrates, cold-blooded (poikilotherms), and amphibians (live on land and water).
- Use camouflage for protection by changing body color.
- Exhibit summer sleep (aestivation) and winter sleep (hibernation).
- Body has two main parts: head and trunk; lacks neck and tail.
- Bulging eyes are protected by nictitating membrane; tympanum acts as eardrum.
- Dorsal skin is olive green with dark spots; ventral side pale yellow; skin is moist due to mucus.
- Locomotion aided by four limbs (with 4 digits), hind limbs (with 5 digits, more muscular for jumping), and webbed feet (for swimming).
- Exhibit sexual dimorphism: males have vocal sacs and copulatory pads.
Frog: Anatomy (Internal Structure & Organ Systems)
Digestive System
- Frogs are carnivorous; alimentary canal: mouth → buccal cavity → pharynx → esophagus → stomach → intestine → rectum → cloaca.
- Digestion starts in stomach (HCl, gastric juices), is completed in intestine (bile from liver, pancreatic juice).
- Absorption occurs in intestine via villi; undigested food exits via cloaca.
Circulatory System
- Closed circulatory system: blood confined in vessels.
- Main parts: heart (3 chambers—2 auricles, 1 ventricle), blood vessels (arteries, veins), and blood.
- Sinus venosus receives deoxygenated blood from body; conus arteriosus directs mixed blood.
- Hepatic portal system (blood from digestive tract to liver), renal portal system (blood from hind body to kidneys).
- Arteries carry oxygenated blood from heart to body; veins carry deoxygenated blood to heart.
- Blood components: plasma, RBCs (with nucleus), WBCs, platelets.
Respiratory System
- Respiration via skin (cutaneous, in water), lungs (pulmonary, on land), and buccal cavity.
- During hibernation/aestivation, respiration is mainly cutaneous.
Nervous and Endocrine System
- Nervous system: central (brain, spinal cord), peripheral (cranial/spinal nerves), autonomic (sympathetic/parasympathetic).
- Brain divided into forebrain (olfactory lobes, cerebrum), midbrain (optic lobes), hindbrain (cerebellum, medulla oblongata).
- Endocrine glands present: thyroid, parathyroid, thymus, adrenal.
Sensory Organs
- Olfactory receptors (smell), tympanum (hearing), eyes (vision), sensory papillae (touch), taste buds (taste).
Reproductive System
- Frogs are dioecious (separate sexes), fertilization is external, development indirect (involves larval tadpole stage).
- Male: testes (sperms), vasa efferentia, urinogenital duct, cloaca.
- Female: ovaries (eggs), oviduct, cloaca.
Key Terms & Definitions
- Unicellular organism — organism made of a single cell.
- Tissue — group of similar cells performing a specific function.
- Organ system — group of organs working together for a major function.
- Amphibian — animal living both on land and water.
- Poikilotherm/Cold-blooded — internal temperature varies with environment.
- Camouflage — ability to blend with surroundings.
- Nictitating membrane — protective eye covering in frogs.
- Tympanum — external frog structure for hearing (eardrum).
- Cloaca — common chamber for digestive, urinary, reproductive tracts.
- Cutaneous respiration — gas exchange through skin.
- Dioecious — separate male and female individuals.
- External fertilization — fusion of gametes occurs outside the body.
Action Items / Next Steps
- Review NCERT textbook chapter on "Structural Organization in Animals" and highlight key points.
- Compare frog organ systems with human systems for deeper understanding.
- Complete pending assignments or sample papers related to animal morphology and anatomy.