Structural Organization in Animals Class 11 Biology Chapter 7 Notes

Structural Organization in Animals Class 11 Biology Chapter 7 Notes

Organ and Organ System

1. Basic Tissues: The fundamental building blocks of multicellular organisms are basic tissues. These tissues, such as epithelial, connective, muscular, and neural tissues, are composed of cells with specific functions.
2. Organization into Organs: Basic tissues organize themselves to form organs. Each organ is typically made up of one or more types of tissues. For instance, the heart is an organ that consists of epithelial, connective, muscular, and neural tissues.
3. Organ Systems: Organs, in turn, associate and work together to form organ systems within the body of multicellular organisms. Organ systems are a collection of organs with a common function or related functions. Examples of organ systems in the human body include the circulatory system, respiratory system, and digestive system.
4. Importance of Organization: The organization of tissues into organs and organs into organ systems is crucial for the efficient and coordinated activities of the millions of cells in a multicellular organism. This organization allows the body to perform various functions and maintain homeostasis.
5. Evolutionary Trends: The complexity observed in organ and organ systems displays discernable evolutionary trends. These trends reflect the changes and adaptations that have occurred over the course of evolution, leading to the diversity of organisms we see today.
6. Morphology and Anatomy: In the context of studying living organisms, “morphology” refers to the study of the form and externally visible features. In plants and microbes, morphology specifically pertains to the external appearance of organs or body parts. In animals, the term “anatomy” is commonly used to describe the study of the internal morphology of organs. This includes the examination of the structure and organization of internal organs within the body.

Frogs

Frogs are fascinating amphibians that exhibit unique characteristics and behaviors. Here are some key points about frogs:

1. Habitat: Frogs are versatile in their habitat, being capable of living both on land and in freshwater. They belong to the class Amphibia in the phylum Chordata.
2. Common Species: In India, one of the most common frog species is Rana tigrina.
3. Poikilotherms: Frogs are poikilothermic or “cold-blooded” animals, which means their body temperature varies with the temperature of their environment. They cannot regulate their body temperature internally.
4. Camouflage: Frogs have the ability to change their color, which can help them blend in with their surroundings. This ability to change color for camouflage is a form of protective coloration known as mimicry.
5. Seasonal Behavior:
   • Summer Sleep (Aestivation): Frogs are not commonly seen during the peak of summer. During this period, they take shelter in deep burrows or other cool, moist areas to protect themselves from extreme heat and desiccation. This period of inactivity is called aestivation.
   • Winter Sleep (Hibernation): Similarly, during the cold winter months, frogs undergo a state of dormancy known as hibernation. They seek shelter to escape freezing temperatures and reduce metabolic activity.

Frogs’ ability to adapt to changing environmental conditions, including their seasonal behaviors, helps them survive and thrive in diverse ecosystems. Their amphibious nature allows them to exploit both aquatic and terrestrial environments, making them an interesting group of organisms in the animal kingdom.

Morphology of Frogs

The external features and structure of frogs are distinct and well-suited to their amphibious lifestyle. Here are some key aspects of the morphology of frogs:

1. Skin: The skin of frogs is smooth and slippery due to the presence of mucus. It is always kept moist, which is vital for respiration. The dorsal side of the body is usually olive green with dark irregular spots, while the ventral side has uniformly pale yellow skin.
2. Respiration: Frogs do not drink water; instead, they absorb it through their skin. The maintenance of moist skin is essential for respiration.
3. Body Division: The body of a frog is divided into two main parts: the head and trunk. Frogs lack a neck and tail.
4. Nostrils: Above the mouth, a pair of nostrils is present for breathing.
5. Eyes: The eyes of frogs are bulged and covered by a nictitating membrane, which protects them when the frog is underwater.
6. Tympanum (Ear): On either side of the eyes, there are membranous tympana (ears) that receive sound signals, allowing frogs to detect sounds in their environment.
7. Limb Structure:
   • Forelimbs: Frogs have forelimbs that assist in swimming, walking, and burrowing. These limbs end in four digits (fingers).
   • Hind Limbs: The hind limbs are larger and more muscular than the forelimbs, and they end in five digits (toes). The digits have webbing between them, which aids in swimming.
8. Sexual Dimorphism: Male and female frogs can be distinguished based on certain features:
   • Male frogs have sound-producing vocal sacs, which they use to create mating calls.
   • Male frogs may also have a copulatory pad on the first digit of their forelimbs, which is absent in females.

The morphology of frogs is adapted to their semi-aquatic lifestyle, allowing them to move both on land and in water. Their skin plays a crucial role in respiration and water absorption, and their limbs are specialized for various activities such as swimming and jumping. The presence of sexual dimorphism helps in identifying the gender of frogs.

Anatomy of Frogs

Frogs have a well-organized body with various organ systems and structures, which allow them to adapt to both aquatic and terrestrial environments. Here is an overview of the anatomy of frogs:

1. Digestive System:
   • The digestive system of frogs consists of the alimentary canal and digestive glands.
   • The alimentary canal includes the mouth, buccal cavity, esophagus, stomach, intestine, rectum, and cloaca.
   • The liver secretes bile stored in the gall bladder, while the pancreas produces pancreatic juice containing digestive enzymes.
   • Food is captured by the bilobed tongue, and digestion occurs with the help of HCl and gastric juices in the stomach.
   • The final digestion takes place in the intestine, and the digested food is absorbed by finger-like folds called villi and microvilli in the intestinal wall.
2. Respiratory System:
   • Frogs can respire both in water and on land. In water, they use cutaneous respiration, where the skin acts as an aquatic respiratory organ.
   • On land, frogs employ buccal cavity, skin, and lungs for pulmonary respiration. Lungs are present in the upper part of the trunk region (thorax).
   • During aestivation and hibernation, gas exchange occurs through the skin.
3. Circulatory System:
   • The circulatory system of frogs is a well-developed closed system.
   • It includes the heart, blood vessels, and blood.
   • The heart has three chambers: two atria and one ventricle, and it is covered by a pericardium.
   • A structure called the sinus venosus joins the right atrium, receiving blood from major veins like the vena cava.
   • The ventricle pumps blood into the conus arteriosus, and the circulation of blood is achieved through the arterial and venous systems.
4. Excretory System:
   • Frogs have a well-developed excretory system that includes a pair of kidneys, ureters, cloaca, and a urinary bladder.
   • The kidneys are situated posteriorly, on both sides of the vertebral column.
   • Each kidney consists of uriniferous tubules or nephrons.
   • Urea is excreted, making frogs ureotelic.
5. Nervous System:
   • The nervous system includes the central nervous system (brain and spinal cord), peripheral nervous system (cranial and spinal nerves), and an autonomic nervous system (sympathetic and parasympathetic).
   • There are ten pairs of cranial nerves that originate from the brain.
   • The brain is divided into forebrain, midbrain, and hindbrain, and it is enclosed in a bony structure called the cranium.
   • Frog sense organs include touch (sensory papillae), taste (taste buds), smell (nasal epithelium), vision (eyes), and hearing (tympanum with internal ears).
6. Reproductive System:
   • Frogs exhibit sexual dimorphism with distinct male and female reproductive organs.
   • Male reproductive organs include testes, vasa efferentia, Bidder’s canal, and a urinogenital duct.
   • Female reproductive organs consist of ovaries, oviducts, and a cloaca.
   • Fertilization is external in water, and the development involves a tadpole stage that undergoes metamorphosis to become an adult frog.

Frogs play a vital role in ecosystems by consuming insects and maintaining ecological balance. They are also used as a food source in some countries, particularly their muscular legs.