7.3. SUMMARY

Cells, tissues, organs and organ systems split up the work in a way that ensures the survival of the body as a whole and exhibit division of labour.

The body of multicellular organisms is made up of a hierarchy of structural units: cells, tissues, organs, and organ systems. Each unit has specific roles that contribute to the overall functioning of the organism. Cells group together to form tissues, which in turn make up organs. Organs that work together for a specific function form an organ system. This division of labor ensures efficiency and overall survival of the organism.

Think of a school as an analogy. Just like a school has students, teachers, administrative staff, and different classes that work together, a living organism has cells, tissues, organs, and organ systems that work together to keep the organism alive.

A tissue is defined as group of cells along with intercellular substances performing one or more functions in the body.

Tissue is a specific term used in biology to describe a group of similar cells that perform a common function. For example, muscle tissue is made up of muscle cells that work together to facilitate movement in the body. Tissues are essential because they enable the organism to perform complex functions more efficiently than isolated cells.

Consider a sports team. Just like players with different skills come together to form a team that performs better than individuals, groups of cells work together to form a tissue that achieves a particular function.

Epithelia are sheet like tissues lining the body’s surface and its cavities, ducts and tubes. Epithelia have one free surface facing a body fluid or the outside environment.

Epithelial tissue serves as a protective layer covering the surfaces of organs and lining cavities within the body. This tissue can be found on external surfaces (like skin), as well as internal surfaces (like the lining of the digestive tract). It plays roles in protection, absorption, secretion, and sensation, with one side exposed to an external environment or a body cavity.

You can think of epithelial tissue like the walls of a building. Just as walls protect what is inside and define the structure of the building, epithelial tissues protect and define the boundaries and structures of organs.

The Indian bullfrog, Rana tigrina, is the common frog found in India. Body is covered by skin. Mucous glands are present in the skin which is highly vascularised and helps in respiration in water and on land.

Rana tigrina, commonly known as the Indian bullfrog, is a species well-adapted to both aquatic and terrestrial environments. Its skin plays a crucial role in respiration, being both breathable and moisturizing due to the presence of mucous glands. This adaptation is vital for the frog’s survival, allowing it to absorb moisture and oxygen whether it is in water or on land.

Imagine wearing a suit that keeps you comfortable in both wet and dry environments. Similarly, the bullfrog's skin allows it to thrive in different habitats, ensuring it can survive rain-soaked fields as well as dry land.

The alimentary canal consists of oesophagus, stomach, intestine and rectum, which open into the cloaca. The main digestive glands are liver and pancreas.

The digestive system of the Indian bullfrog is structured to efficiently process food. It starts from the mouth and goes through the oesophagus, stomach, and intestine finally reaching the rectum and cloaca. Essential organs like the liver and pancreas assist in digestion by producing bile and pancreatic juices, which help break down food in the digestive tract.

Think of your digestive system as a factory assembly line. Each section performs a specific task to process raw materials (food) into a finished product (nutrients absorbed by the body), with different machines (organs) performing special functions.

It can respire in water through skin and through lungs on land. Circulatory system is closed with single circulation. RBCs are nucleated.

Frogs have a unique ability to breathe through their skin in addition to using their lungs, which is especially useful when they are submerged in water. Their circulatory system is closed, meaning blood circulates within blood vessels, and they have a single circulation system where the heart pumps blood through the lungs and then to the rest of the body. The red blood cells (RBCs) in frogs are nucleated, distinguishing them from those of mammals, which do not have a nucleus.

Imagine a two-lane highway: on one lane (the lungs), cars (blood) go to pick up oxygen, and on the other lane (the rest of the body), they drop off nutrients. Just like efficient traffic flow, frogs' circulatory system ensures nutrients and oxygen are efficiently delivered.

Nervous system is organised into central, peripheral and autonomic. The organs of urinogenital system are kidneys and urinogenital ducts, which open into the cloaca.

The nervous system in frogs is well-structured with three main divisions: the central nervous system (CNS) consisting of the brain and spinal cord; the peripheral nervous system (PNS) which includes all other nerves; and the autonomic nervous system, controlling involuntary functions. The urinogenital system in frogs includes organs responsible for excretion and reproduction, with the kidneys filtering wastes and the ducts transporting urine and reproductive cells to the cloaca.

Think of froggy's nervous system as the command center of a city: the central command (CNS) makes big decisions, local commands (PNS) ensure operations run smoothly, and the automatic systems keep everything in check without needing direct input.

The male reproductive organ is a pair of testes. The female reproductive organ is a pair of ovaries. A female lays 2500-3000 ova at a time. The fertilisation and development are external.

In frogs, males have testes for producing sperm, while females have ovaries for producing eggs. The unique reproductive strategy of frog includes external fertilization where eggs are laid in water and then fertilized by sperm. A female can lay thousands of eggs at once, increasing the chances of offspring survival, as many eggs will be eaten or not survive.

This reproductive method can be compared to planting seeds in a garden: by scattering many seeds (eggs), the chance of some growing and thriving into plants (frogs) increases despite many facing harsh conditions.

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