STRUCTURAL ORGANISATION IN ANIMALS

Animal Body Organization

Multicellular animals have complex bodies. Different groups of cells work together to do specific jobs. This sharing of tasks is called division of labor. It helps the whole body survive and function smoothly.

From Cells to Systems

Life in multicellular animals is organized in steps:

• Cells: These are the basic units of life.
• Tissues: Similar cells group together to perform a specific function.
• Organs: Different tissues work together to form an organ, like your stomach or lungs.
• Organ Systems: Two or more organs work together for a common goal, forming an organ system (e.g., the digestive system).

Building Blocks: Animal Tissues

All complex animals are built from just four basic types of tissues. These tissues are the fundamental building blocks of the body:

• Epithelial tissue: This tissue covers body surfaces and lines internal cavities, ducts, and tubes.
• Connective tissue: It supports, connects, and separates different types of tissues and organs.
• Muscular tissue: This tissue is responsible for movement, allowing parts of the body to contract and relax.
• Neural tissue: It carries electrical signals and messages throughout the body, enabling communication and control.

Tissues Working Together

Organs are not made of just one type of tissue. They are complex structures built from several. For example, your heart contains all four basic tissue types working in harmony to pump blood throughout your body.

Understanding Form and Structure

We use specific terms to describe the study of body parts:

• Morphology: This is the study of the external features of an organism. For animals, it means looking at the outside appearance of body parts, like a frog's head and limbs.
• Anatomy: This term is used for the study of internal organs. It involves looking inside the body to understand the structure of organs like the heart, lungs, or stomach.

Frog External Morphology

Let's explore the outside features of a frog! Frogs are amazing creatures with special body parts that help them live both in water and on land. Understanding these parts helps us see how they survive and thrive.

Skin Characteristics

Have you ever touched a frog? Its skin is smooth and slippery! This is because of mucus that keeps it moist.

• The top side is usually olive green with dark spots.
• The belly side is a plain pale yellow.

Frogs don't drink water. Instead, they absorb it directly through their skin!

Body Divisions

A frog's body is quite simple in its main parts. It is divided into two clear sections:

• The head
• The trunk (the main body part)

Interestingly, frogs do not have a neck or a tail, which is different from many other animals.

Sensory and Locomotive Structures

Frogs have special features to sense their world and move around:

• Nostrils: A pair is found above the mouth for breathing.
• Bulged Eyes: Their eyes stick out and are covered by a clear nictitating membrane. This membrane acts like goggles, protecting their eyes underwater.
• Tympanum: This is a round, membranous patch on each side of the head, behind the eyes. It works like an eardrum to pick up sound signals.

Limbs: Forelimbs and Hind Limbs

Frogs have two pairs of limbs, each with different roles:

• Forelimbs: These are the front legs. They have four digits (like fingers).
• Hind limbs: These are the back legs. They are much larger and more muscular than the forelimbs. They have five digits, and these digits are webbed (connected by skin).

These powerful limbs help frogs with many activities like swimming, walking, leaping (jumping far), and even burrowing into the ground.

Male-Specific Features

Male and female frogs have a few differences you can spot (sexual dimorphism):

• Vocal Sacs: Male frogs have special vocal sacs that inflate to help them make loud croaking sounds, especially during mating season.
• Copulatory Pad: Males also have a rough copulatory pad on the first digit of their forelimbs. This pad helps them hold onto the female during mating.

Female frogs do not have these features.

Frog's Digestive Journey

Frogs have a special system to process their food. It helps them get energy from what they eat. This system has two main parts: the alimentary canal (the tube food travels through) and digestive glands (which make helpful juices). Because frogs are carnivores (meat-eaters), their alimentary canal is quite short. This helps them digest their prey quickly.

The Food Pathway

Food enters the frog's body through the mouth. It then moves into the buccal cavity and passes through the pharynx. Next, it goes down a short tube called the oesophagus. This leads to the stomach. From the stomach, food enters the intestine, then the rectum, and finally exits through the cloaca. This entire pathway is shorter than in plant-eaters.

Helping Hands: Digestive Glands

Two important glands help with digestion.

• The liver makes a substance called bile. Bile helps break down fats. It is stored in the gall bladder until needed.
• The pancreas produces pancreatic juice. This juice contains many digestive enzymes that break down different types of food.

How Frogs Digest Food

First, the frog uses its sticky, bilobed tongue to catch insects. Once swallowed, food reaches the stomach. Here, strong hydrochloric acid (HCl) and gastric juices from the stomach walls start breaking it down. This partially digested food then turns into a thick liquid called chyme.

Finishing the Job

The chyme moves from the stomach into the duodenum, the first part of the small intestine. Here, it mixes with bile from the gall bladder, which emulsifies fat (breaks large fat drops into smaller ones). Pancreatic juices also join in, digesting carbohydrates and proteins. The final digestion of food happens in the rest of the intestine.

Absorbing Nutrients and Eliminating Waste

The inner wall of the intestine has many tiny, finger-like folds called villi and even smaller structures called microvilli. These greatly increase the surface area for absorbing digested nutrients into the blood. Any food that cannot be digested becomes undigested solid waste. This waste moves into the rectum and is then passed out of the body through the cloaca.