I. Unicellular Organisms:

• In unicellular organisms, such as amoebas, a single cell performs all essential functions, including digestion, respiration, and reproduction.

II. Multicellular Organisms:

• In complex multicellular animals like Hydra, various types of cells collaborate to carry out functions. The number of cells in each type can be extensive, reaching thousands.

III. Basic Unit: The Tissue:

• Multicellular animals exhibit a higher level of an organization known as tissues.
• A tissue is a group of similar cells, along with intercellular substances, that work together to perform a specific function.

IV. Four Basic Types of Tissues:

• All complex animals are composed of four fundamental types of tissues.
  1. Epithelial Tissue: Covers surfaces, lines cavities, and forms glands.
  2. Connective Tissue: Provides support, and protection, and binds together various tissues and organs.
  3. Muscular Tissue: Enables movement by contracting and relaxing.
  4. Nervous Tissue: Facilitates communication through electrical impulses.

V. Organization into Organs and Organ Systems:

• Tissues are organized in specific proportions and patterns to form organs, such as the stomach, lungs, heart, and kidney.
• Multiple organs working together in a coordinated manner constitute an organ system.
• Examples of organ systems include the digestive system and respiratory system.

VI. Division of Labour:

• Cells, tissues, organs, and organ systems collaborate, exhibiting a division of labor.
• This division of labor ensures the survival and functioning of the entire organism.

ORGAN AND ORGAN SYSTEM

I. Basic Tissues Form Organs:

• Basic tissues, including epithelial, connective, muscular, and neural, combine to form organs in the body.
• For instance, the heart, a vital organ, comprises all four types of tissues, emphasizing their collaborative role.

II. Evolutionary Trend in Organ Complexity:

• The complexity observed in the structure and function of organs and organ systems reveals an evolutionary trend.
• Evolutionary trends signify the gradual changes and adaptations in the structure of organs over time.

III. Introduction to Frog Morphology and Anatomy:

• This chapter delves into the morphology and anatomy of frogs, providing insights into their external and internal features.
• Morphology refers to the study of externally visible features, while anatomy specifically deals with the internal morphology of animals.

IV. Evolutionary Trend in Organ Systems:

• As we explore the morphology and anatomy of the frog, we may identify evolutionary trends that have shaped the complexity of its organ systems.
• Evolutionary trends provide a narrative of how organs and organ systems have evolved to meet the demands of survival and function.

V. Morphology in Animals:

• In animals, morphology encompasses the external appearance of organs or body parts.
• It involves the study of form, structure, and features visible on the outside.

VI. Anatomy and the Study of Internal Organs:

• Anatomy traditionally refers to the study of the internal morphology of animals.
• It involves a detailed examination of the structure and organization of internal organs.

FROGS

I. Classification and Habitat:

• Frogs, members of class Amphibia within the phylum Chordata, demonstrate a versatile lifestyle by inhabiting both land and freshwater environments.
• The prevalent frog species in India is Rana tigrina.

II. Thermoregulation and Poikilothermy:

• Frogs exhibit poikilothermy, characterized by variable body temperatures dependent on the external environment.
• They lack a constant body temperature, making them cold-blooded organisms.

III. Adaptive Coloration – Camouflage and Mimicry:

• Frogs display remarkable adaptive coloration, altering their color to blend into their surroundings.
• This ability aids in camouflage, serving as a defense mechanism against potential predators.
• The protective coloration, known as mimicry, enhances their survival by making them less conspicuous.

IV. Seasonal Adaptations:

• Frogs undergo noticeable changes in behavior based on seasons.
• Aestivation: During peak summer, frogs engage in aestivation, seeking refuge in deep burrows to avoid extreme heat.
• Hibernation: In the winter months, frogs enter a state of hibernation, taking shelter to endure the cold.

V. Environmental Sensitivity:

• The fluctuations in environmental temperature directly impact the physiological state of frogs.
• Their reliance on the external environment for temperature regulation reflects their sensitivity to climatic changes.

VI. Behavioral Strategies for Survival:

• The dual habitat lifestyle, color adaptation, and seasonal behaviors showcase the evolutionary strategies frogs employ for survival.
• Adapting to environmental conditions is crucial for their overall well-being and reproductive success.

Morphology

I. Skin and Moisture Maintenance:

• The frog’s skin, smooth and slippery, is coated with mucus, ensuring constant moisture.
• Dorsal skin exhibits an olive-green hue adorned with dark irregular spots, while the ventral side is uniformly pale yellow.
• Frogs maintain skin moisture, vital for respiration, and absorb water directly through their skin.

II. Body Division and Features:

• The frog’s body is segmented into a distinct head and trunk, lacking a neck and tail.
• Nostrils, situated above the mouth, facilitate respiration.
• Prominent, bulged eyes are shielded by a nictitating membrane, offering protection in aquatic environments.
• The membranous tympanum, located on each side of the eyes, serves as the auditory organ, receiving sound signals.

III. Limb Adaptations for Varied Functions:

• Forelimbs and Hind Limbs: Essential for diverse activities such as swimming, walking, leaping, and burrowing.
• Digit Configuration: Hind limbs terminate in five muscular digits, with webbed feet facilitating swimming. Forelimbs have four digits.
• Sexual Dimorphism: Male frogs exhibit vocal sacs for sound production and a copulatory pad on the first digit of the forelimbs, distinguishing them from females.

IV. Adaptive Features for Aquatic Life:

• Webbed Feet: Aid inefficient swimming, reflecting adaptations for life in aquatic habitats.
• Tympanum: Enhances auditory sensitivity, crucial for detecting environmental cues in both land and water.

V. Respiration and Water Absorption:

• Frogs employ cutaneous respiration, absorbing oxygen through their skin.
• Avoiding traditional water intake, frogs absorb water directly through their skin, contributing to overall hydration.

Anatomy

I. Digestive System:

• Alimentary Canal: Short due to carnivorous diet; includes buccal cavity, pharynx, esophagus, stomach, intestine, and rectum.
• Digestive Glands: The liver secretes bile stored in the gall bladder; the pancreas produces pancreatic juice with digestive enzymes.
• Digestion Process: Food captured by the bilobed tongue; HCl and gastric juices aid digestion; chyme formation in the stomach; final digestion in the intestine.
• Absorption: Villi and microvilli in the intestine absorb nutrients; undigested waste moves to the rectum and exits through the cloaca.

II. Respiratory System:

• Aquatic Respiration: Skin acts as an aquatic respiratory organ, facilitating cutaneous respiration.
• Pulmonary Respiration: Lungs perform respiration on land; air enters through the nostrils into the buccal cavity and then reaches the lungs.
• Adaptations: Webbed feet aid swimming; gaseous exchange during aestivation and hibernation occurs through the skin.

III. Circulatory System:

• Vascular System: Well-developed closed type with arteries, veins, and capillaries.
• Heart Structure: Three-chambered heart (two atria, one ventricle) covered by the pericardium; sinus venosus receives blood; ventricle connects to the conus arteriosus.
• Blood Composition: Plasma, RBCs, WBCs, and platelets; RBCs contain hemoglobin.
• Special Connections: Hepatic portal system and renal portal system for specific venous connections.

IV. Excretory System:

• Organs: Kidneys, ureters, cloaca, and urinary bladder.
• Ureotelic Excretion: Frogs excrete urea; ureters act as urinogenital ducts; urine is eliminated through the cloaca.
• Structural Units: Kidneys consist of uriniferous tubules or nephrons.

V. Nervous System and Endocrine Glands:

• Nervous System Components: Central nervous system (brain and spinal cord), peripheral nervous system (cranial and spinal nerves), autonomic nervous system (sympathetic and parasympathetic).
• Brain Division: Forebrain, midbrain, and hindbrain; cranial nerves originate from the brain.
• Sense Organs: Touch (sensory papillae), taste (taste buds), smell (nasal epithelium), vision (simple eyes), and hearing (tympanum with internal ears).
• Endocrine Glands: Pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals, and gonads.

VI. Reproductive System:

• Male Reproductive Organs: Testes attached to kidneys by mesorchium; vasa efferentia enter Bidder’s canal; urinogenital duct communicates with cloaca.
• Female Reproductive Organs: Ovaries near kidneys; oviducts open separately into the cloaca.
• Reproductive Process: External fertilization in water; tadpole larval stage undergoes metamorphosis into the adult.

VII. Ecological Importance:

• Ecological Balance: Frogs contribute to the food chain and food web, maintaining ecological balance.
• Agricultural Benefit: Control insect populations, protecting crops.
• Culinary Use: In some cultures, frog legs are consumed as food.