Structural Organisation in Animals - Comprehensive NEET Biology Notes

1. Introduction to Structural Organisation in Animals

Multicellular animals show a highly complex structure, with cells organized into tissues, organs, and organ systems to carry out essential functions like digestion, respiration, and reproduction. This organization ensures division of labor among cells, promoting efficient functioning and survival of the animal.

Did You Know?

While humans have billions of cells working together, simple organisms like Hydra consist of different types of cells that perform basic functions in a much simpler way.

2. Organ and Organ Systems

2.1 Overview of Organ Systems

Cells in multicellular animals are grouped to form tissues, and different tissues come together to form organs like the heart, lungs, and kidneys. Organs that work together to perform a common function form organ systems, such as the digestive system and the circulatory system.

NEET Tip:

Focus on understanding the division of labor among different organ systems, as questions may test the roles of these systems in maintaining body functions.

Visual Aid Suggestion:

A diagram representing major organ systems like the digestive, circulatory, and nervous systems can help visualize their interconnectedness.

Quick Recap

  • Multicellular animals have cells organized into tissues, organs, and organ systems.
  • The division of labor among these systems ensures efficient functioning of the body.

3. Morphology and Anatomy of Frogs

3.1 Morphology of Frogs

Frogs are amphibians that can live both on land and in water. They have smooth, moist skin, which helps in respiration. Their body is divided into the head and trunk, with no neck or tail. Frogs are cold-blooded and can change color to camouflage themselves. During extreme temperatures, they hibernate or aestivate to survive.

NEET Tip:

Pay attention to terms like poikilotherms, camouflage, and mimicry, as these concepts often appear in NEET.

Visual Aid Suggestion:

A labeled diagram of a frog’s external features, highlighting the head, trunk, limbs, and sensory organs like eyes and tympanum, can enhance understanding.

3.2 Anatomy of Frogs

The internal anatomy of frogs reveals well-developed organ systems:

  • Digestive System: Frogs have a short alimentary canal as they are carnivores. The stomach, small intestine, and associated glands like the liver and pancreas play important roles in digestion.
  • Respiratory System: Frogs respire through their skin in water (cutaneous respiration) and lungs on land (pulmonary respiration). The skin must remain moist for effective cutaneous respiration.
  • Circulatory System: Frogs have a closed circulatory system, with a three-chambered heart (two atria and one ventricle) that pumps blood to the body.
  • Excretory System: The kidneys filter waste products, and the frog excretes urea, making it a ureotelic animal. Urine is passed through the cloaca.
  • Reproductive System: Frogs exhibit sexual dimorphism. Males have vocal sacs and copulatory pads, while females lay eggs externally in water, where fertilization occurs.

Real-life Application:

Frogs play a significant role in maintaining the ecological balance by controlling insect populations and serving as prey for other animals.

Quick Recap

  • Frogs possess specialized organ systems for digestion, respiration, circulation, excretion, and reproduction.
  • They use different respiratory methods on land and in water, and they exhibit external fertilization.

4. Types of Tissues in Animals

4.1 Epithelial Tissue

Epithelial tissue forms the covering or lining of body surfaces, organs, and cavities. It can be classified into different types based on the number of cell layers and shape of the cells:

  • Simple Epithelium: Single layer of cells, such as squamous, cuboidal, and columnar.
  • Stratified Epithelium: Multiple layers of cells that provide protection.

NEET Problem-Solving Strategy:

Focus on understanding the types and functions of different epithelial tissues, as questions often test their locations and roles in the body.

4.2 Connective Tissue

Connective tissue provides support and connects different parts of the body. It includes:

  • Loose Connective Tissue: Binds structures together, found beneath the skin.
  • Dense Connective Tissue: Forms tendons and ligaments.
  • Adipose Tissue: Stores fat.
  • Blood: A fluid connective tissue involved in transportation and defense.

Visual Aid Suggestion:

A table comparing different types of connective tissues, highlighting their functions and locations, can help clarify their roles.

Quick Recap

  • Epithelial tissues cover body surfaces and organs, while connective tissues provide support, binding, and transportation.
  • Different types of connective tissues, such as blood, adipose, and tendons, have specialized roles.

5. Muscular and Neural Tissues

5.1 Muscular Tissue

Muscular tissue is responsible for movement and can be classified into:

  • Skeletal Muscle: Voluntary, striated muscles that attach to bones and control movement.
  • Smooth Muscle: Involuntary, non-striated muscles found in organs like the stomach and intestines.
  • Cardiac Muscle: Involuntary, striated muscles found only in the heart.

5.2 Neural Tissue

Neural tissue is specialized for transmitting signals throughout the body. Neurons are the functional units that transmit electrical impulses, while neuroglial cells provide support and protection.

NEET Tip:

Pay attention to the structure and function of neurons, especially the transmission of impulses via axons and dendrites.

Quick Recap

  • Muscular tissues are involved in movement, with skeletal, smooth, and cardiac muscles performing different functions.
  • Neural tissues, composed of neurons, are essential for transmitting electrical signals in the body.

NEET Exam Strategy

  • Focus on the different types of tissues and their specialized functions, especially in epithelial, connective, muscular, and neural tissues.
  • Practice diagram-based questions, particularly those involving the structure of tissues and organs in frogs and humans.
  • Understand the anatomy of frogs, including their digestive, circulatory, respiratory, and reproductive systems.

Practice Questions

  1. Which tissue type lines the cavities and surfaces of organs?
    Solution: b) Epithelial tissue
    • a) Connective tissue
    • b) Epithelial tissue
    • c) Muscular tissue
    • d) Nervous tissue
  3. What is the primary mode of respiration for frogs in water?
    Solution: c) Cutaneous respiration
    • a) Buccal respiration
    • b) Pulmonary respiration
    • c) Cutaneous respiration
    • d) Gill respiration
  5. Which of the following is a connective tissue?
    Solution: a) Blood
    • a) Blood
    • b) Cardiac muscle
    • c) Simple squamous epithelium
    • d) Neuron
  7. How many chambers does a frog’s heart have?
    Solution: b) Three
    • a) Two
    • b) Three
    • c) Four
    • d) Five
  9. Which structure in frogs allows them to sense vibrations in the environment?
    Solution: c) Tympanum
    • a) Nostrils
    • b) Nictitating membrane
    • c) Tympanum
    • d) Cloaca

Glossary

  • Tissue: A group of similar cells that perform a specific function.
  • Cloaca: A common chamber in frogs for the passage of urine, feces, and reproductive materials.
  • Nephron: The functional unit of the kidney involved in filtration and excretion.
  • Notochord: A rod-like structure that provides support in the embryonic stage of all chordates.