7. [ Auto-Generated ] Structural Organization In Animals

From Cells to Systems

Ever wonder how complex animals are built? It’s all about teamwork! Unlike unicellular organisms where one cell does it all, multicellular animals organize their bodies to handle complex functions.

The Hierarchy of Organization

Just like bricks build a house, biological units build up step-by-step:

• Cells: The starting point. In humans, billions of cells work together.
• Tissues: A group of similar cells working together with intercellular substances to perform a specific function.
• Organs: Tissues organized in specific proportions to form structures like the stomach, heart, or kidney.
• Organ Systems: Two or more organs interacting physically or chemically to perform a common function (e.g., the digestive system).

Division of Labour

In complex animals, not every cell does every job. Instead, they split up the work.

Division of Labour means that specialized cells, tissues, organs, and systems handle specific tasks. This efficient organization allows the body to function better and ensures the survival of the organism as a whole!

Meet the Frog: Rana tigrina

Did you know frogs can live on both land and in freshwater? The most common species found in India is the Rana tigrina (Indian Bullfrog).

Classification

Biologists classify these jumping creatures under:

• Phylum: Chordata
• Class: Amphibia

Cold-Blooded Nature

Frogs are cold-blooded animals, or poikilotherms. This means they do not have a constant body temperature; instead, it changes with the environment.

To survive extreme weather, they take shelter in deep burrows:

• Aestivation: Summer sleep to protect against heat.
• Hibernation: Winter sleep to protect against cold.

Did you know? Frogs can change color to hide from enemies! This protective camouflage is called mimicry.

Skin and Senses

Let's explore the frog's unique body covering and specialized sensory organs found on the head!

🐸 The Skin

A frog's skin is vital for its survival:

• Texture: It feels smooth and slippery due to the presence of mucus.
• Moisture: The skin is always maintained in a moist condition.
• Color: Generally olive green with dark spots on the back (dorsal side) and uniformly pale yellow on the belly (ventral side).
• Hydration: Frogs never drink water! Instead, they absorb water directly through their skin.

👀 Sensory Organs

Frogs have specialized features to help them sense their environment:

• Eyes: These are bulged and covered by a nictitating membrane. This membrane acts like built-in goggles, protecting the eyes while the frog is underwater.
• Tympanum: Located on either side of the eyes, this membranous structure acts as the ear and receives sound signals.

Frog Digestion 101

Frogs have a well-developed digestive system tailored to their specific needs. Let's break down how they process food!

The Alimentary Canal

Did you know the frog's alimentary canal is quite short? This is because frogs are carnivores.

Since meat is easier to digest than plant matter, the length of their intestine is reduced. The food journey looks like this:

• Mouth to Buccal Cavity to Pharynx.
• Oesophagus: A short tube that leads to the stomach.
• Stomach: Where gastric juices and HCl start digestion.
• Intestine, Rectum, and finally the Cloaca (the exit).

Key Digestive Glands

Special glands release fluids to help break down the food:

• Liver: Secretes bile (stored in the gall bladder). Bile acts to emulsify fat.
• Pancreas: Produces pancreatic juice filled with digestive enzymes. These digest carbohydrates and proteins.

Both bile and pancreatic juices enter the small intestine (duodenum) through a common bile duct to complete digestion!

Two Worlds, Two Ways to Breathe

Frogs are unique because they can breathe both on land and in water using different systems. Let's break it down!

1. In Water: Cutaneous Respiration

When a frog is in the water, its skin acts as the respiratory organ. This is called cutaneous respiration.

• Dissolved oxygen in the water is exchanged through the skin by diffusion.
• This is why a frog's skin is always moist!

2. On Land: Pulmonary Respiration

On land, frogs use their buccal cavity, skin, and lungs. Respiration through the lungs is called pulmonary respiration.

• Lungs are a pair of elongated, pink, sac-like structures in the upper trunk (thorax).
• Air enters through the nostrils $\rightarrow$ buccal cavity $\rightarrow$ lungs.

Special Case: Deep Sleep

During aestivation (summer sleep) and hibernation (winter sleep), frogs stay in deep burrows.

Note: During these periods, all gaseous exchange takes place solely through the skin.

Excretion and Control

Let's dive into how frogs handle waste and process information!

The Excretory System

Frogs are ureotelic animals, which means they excrete nitrogenous waste mainly as urea.

• Blood carries waste to the kidneys to be separated and removed.
• The system includes a pair of kidneys, ureters, the cloaca, and a urinary bladder.
• In males, ureters act as a urinogenital duct; in females, they open separately from the oviduct.

The Neural System

The frog's control center is highly evolved. The brain is safely enclosed in a bony structure called the cranium and is divided into three parts:

• Fore-brain: Includes olfactory lobes and paired cerebral hemispheres.
• Mid-brain: Characterized by a pair of optic lobes.
• Hind-brain: Consists of the cerebellum and medulla oblongata (which connects to the spinal cord).

Quick Fact: The system also includes 10 pairs of cranial nerves that help coordinate body functions!

Economic Importance of Frogs

Frogs aren't just fascinating creatures to watch; they are actually very helpful to humans and nature! Here is why they matter:

• Crop Protection: Frogs serve as natural pest controllers. They eat insects that would otherwise damage plants, helping farmers protect their crops.

• Ecological Balance: Frogs maintain balance in the ecosystem. They serve as an important link in the food chain and food web, connecting insects to larger predators.

• Food Source: Did you know frogs are edible? In some countries, the muscular legs of the frog are used as food by humans.

Frogs play a vital role in keeping our environment healthy!