Detailed Notes Chapter7-Structural Organisation In Animals

Introduction

Unicellular vs. Multicellular Organisms:
- In unicellular organisms, all vital functions like digestion, respiration, and reproduction are performed by a single cell.
- In multicellular organisms, these functions are divided among different groups of cells in a well-organized manner.
Cell Collaboration in Multicellular Organisms:
- In multicellular organisms, cells collaborate to perform specific functions.
- Each group of similar cells, along with intercellular substances, forms a specialized unit called tissue.
Tissue and its Function:
- Tissues are specialized groups of cells that work together to perform a specific function.
- Examples include muscle tissue for movement and nervous tissue for communication.
Four Basic Types of Tissues:
- Despite the diversity of complex animals, they are composed of only four basic types of tissues.
- These tissues are organized in specific proportions and patterns to form organs such as the stomach, lung, heart, and kidney.
Organ Formation:
- Organs are formed when tissues are organized in a specific arrangement to perform a particular function.
- For example, the stomach is composed of different types of tissues working together to facilitate digestion.
Organ Systems:
- When two or more organs collaborate to perform a common function through physical and/or chemical interactions, they form an organ system.
- Examples include the digestive system and the respiratory system.
Division of Labour:
- Cells, tissues, organs, and organ systems divide the work in a way that demonstrates division of labour.
- This division of labour contributes to the overall survival and functioning of the organism as a whole.

7.1 ORGAN AND ORGAN SYSTEM

Organization of Tissues into Organs and Organ Systems:
- Basic tissues organize to form organs, and organs associate to form organ systems in multicellular organisms.
- This organization is crucial for efficient and coordinated activities among the millions of cells in an organism.
Composition of Organs:
- Each organ in the body is composed of one or more types of tissues.
- For example, the heart consists of all four basic types of tissues: epithelial, connective, muscular, and neural.
Evolutionary Trend in Organ Complexity:
- There is a discernible trend in the complexity of organs and organ systems, known as evolutionary trend.
- Details about this trend are typically studied in higher classes (Class XII in this context).
Introduction to Frog Morphology and Anatomy:
- The chapter introduces the morphology and anatomy of the frog, which represents vertebrates.
- Morphology refers to the study of form or externally visible features.
- In animals, morphology specifically refers to the external appearance of organs or body parts.
- Anatomy traditionally refers to the study of the internal morphology of organs in animals.
Distinction between Morphology and Anatomy:
- Morphology focuses on the external features, while anatomy delves into the internal structure of organs.
Frog as a Representative Vertebrate:
- The frog is used as a model organism to study vertebrate morphology and anatomy.

7.2 FROGS

Habitat and Classification:
- Frogs are amphibians that can inhabit both land and freshwater environments.
- They belong to the class Amphibia within the phylum Chordata.
Common Frog Species in India:
- The most common frog species found in India is Rana tigrina.
Body Temperature and Thermoregulation:
- Frogs do not maintain a constant body temperature; instead, their body temperature fluctuates with the temperature of their environment.
- Animals with variable body temperatures, like frogs, are referred to as cold-blooded or poikilotherms.
Camouflage and Protective Coloration:
- Frogs have the ability to change their skin color to match their surroundings, such as grass or dry land.
- This adaptive mechanism helps them blend in with their environment and avoid predators.
- The protective coloration exhibited by frogs is known as mimicry.
Seasonal Adaptations:
- Frogs exhibit seasonal behaviors to cope with extreme temperatures.
- They are not commonly seen during the peak of summer and winter.
- During hot summers, frogs take shelter in deep burrows to protect themselves from extreme heat, a behavior known as aestivation.
- Similarly, during cold winters, frogs go into a state of dormancy called hibernation to conserve energy and survive the harsh conditions.

7.2.1 Morphology

Skin Characteristics:
- The skin of a frog is smooth and slippery due to the presence of mucus.
- It is always kept moist to facilitate respiration through the skin.
- The dorsal side of the body is typically olive green with dark irregular spots, while the ventral side is uniformly pale yellow.
Water Absorption:
- Frogs do not drink water through their mouths; instead, they absorb it through their skin.
Body Division:
- The body of a frog is divided into a head and trunk; it lacks a distinct neck and tail.
Head Features:
- A pair of nostrils is present above the mouth.
- The eyes are bulged and covered by a nictitating membrane, which protects them while the frog is underwater.
- Membranous tympana (ears) are present on either side of the eyes to receive sound signals.
Limbs:
- Frogs have both forelimbs and hind limbs.
- These limbs serve various functions, including swimming, walking, leaping, and burrowing.
- Hind limbs are larger and more muscular than forelimbs and end in five digits, while forelimbs end in four digits.
- The feet have webbed digits that aid in swimming.
Sexual Dimorphism:
- Male frogs can be distinguished from females by the presence of sound-producing vocal sacs and a copulatory pad on the first digit of the forelimbs, which are absent in females.

7.2.2 Anatomy

Digestive System:
- Alimentary Canal:
  - Mouth: Opening for food intake.
  - Buccal Cavity: Initial site of food processing, contains tongue for manipulation.
  - Esophagus: Tube connecting buccal cavity to stomach.
  - Stomach: Site of chemical digestion with hydrochloric acid and gastric juices.
  - Intestine: Further digestion and absorption of nutrients, lined with villi and microvilli.
  - Rectum: Storage of undigested material before excretion.
  - Cloaca: Common chamber for excretion and reproductive functions.
- Digestive Glands:
  - Liver: Produces bile for fat digestion, stored in gall bladder.
  - Pancreas: Secretes pancreatic juice with enzymes for carbohydrate and protein digestion.
- Digestion Process:
  - Food capture by sticky, bilobed tongue.
  - Chyme (partially digested food) moves from stomach to duodenum, where bile from gall bladder and pancreatic juice mix for further digestion.
  - Final digestion and absorption occur in the intestine via finger-like villi and microvilli.
Respiratory System:
- Aquatic Respiration:
  - Skin acts as respiratory surface, absorbing oxygen and releasing carbon dioxide through diffusion.
- Pulmonary Respiration:
  - Lungs: Located in thorax, oxygen and carbon dioxide exchange occurs in lung sacs.
  - Air enters through nostrils, passes through buccal cavity, and reaches lungs.
- Special Conditions:
  - During aestivation and hibernation, skin acts as primary respiratory organ.
Circulatory System:
- Vascular System:
  - Closed type, comprising heart, blood vessels, and blood.
- Heart:
  - Three-chambered organ: two atria and one ventricle, covered by pericardium.
  - Receives deoxygenated blood from body, pumps oxygenated blood to tissues.
- Blood Composition:
  - Plasma: Liquid portion containing nutrients, gases, and waste products.
  - Cellular Components: RBCs (carry oxygen), WBCs (immune defense), platelets (blood clotting).
- Circulation:
  - Arterial system carries oxygenated blood from heart to tissues.
  - Venous system returns deoxygenated blood from tissues to heart.
  - Special venous connections between liver-intestine and kidney-lower body (hepatic and renal portal systems).
Excretory System:
- Organs:
  - Kidneys: Bean-shaped structures on either side of vertebral column, filter blood to remove nitrogenous waste products.
  - Ureters: Carry urine from kidneys to cloaca (males) or cloaca and oviducts (females).
  - Urinary Bladder: Stores urine before excretion.
- Nephrons:
  - Functional units of kidneys, filter blood and regulate electrolyte balance.
  - Each nephron consists of renal corpuscle and renal tubule.
Nervous System:
- Components:
  - Central Nervous System (CNS): Brain (forebrain, midbrain, hindbrain) and spinal cord.
  - Peripheral Nervous System (PNS): Cranial and spinal nerves.
  - Autonomic Nervous System (ANS): Sympathetic and parasympathetic divisions.
- Endocrine Glands:
  - Pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals, gonads.
- Brain:
  - Divided into forebrain (olfactory lobes, cerebral hemispheres, diencephalon), midbrain (optic lobes), and hindbrain (cerebellum, medulla oblongata).
- Sense Organs:
  - Touch (sensory papillae), taste (taste buds), smell (nasal epithelium), vision (eyes), hearing (tympanum with internal ears).
Reproductive System:
- Male:
  - Testes produce sperm, connected to kidneys via mesorchium.
  - Sperm carried from testes through vasa efferentia to Bidder’s canal, then to cloaca.
- Female:
  - Ovaries produce eggs, not functionally connected to kidneys.
  - Ova released into body cavity, captured by oviducts and transported to cloaca.
- Fertilization and Development:
  - External fertilization in water, eggs laid in masses.
  - Tadpole stage undergoes metamorphosis into adult frog.
Ecological Importance:
- Predation:
  - Frogs eat insects, contribute to pest control and protect crops.
- Ecosystem Role:
  - Maintain ecological balance as part of food chain and web.
  - Serve as prey for larger organisms, help control insect populations.
- Human Interaction:
  - Frog legs consumed as food in some cultures, providing a source of protein.