Understand Animal Structure: Cells, Tissues, Organs, Functions Explained
All organisms in the animal kingdom are multicellular, however, they do not show the same pattern of organization in cells. Based on the patterns of cellular organization, levels of organization in animals are classified into:
The Cellular Level of Organization: Animals with this type of cell organization have cells arranged in the form of loose cell aggregates. This type of organization can be observed in sponges.
Tissue Level of Organization: The cells of the animals show divisions in cell activities. The cells which perform the same functions are arranged as tissues. Example: Coelenterates.
Organ Level of Organization: Tissues in a certain group of animals that have the same function are grouped to form an organ. Each organ has a specific function. Example: Platyhelminthes
Organ System Level of Organization: In animals where organs have associated to form functional systems where each system is concerned with a certain physiological function are observed to exhibit organ system level of organization. Example: Annelids, Arthropods, Echinoderms, Mollusks, and Chordates.
What is Structural Organization in a Cell?
The cell is the structural and functional unit of any animal or plant. It consists of various cellular components that carry out the functions of the cell. These structures are called cell organelles and they make up the structural organization of a cell.
Cell Organelles and its Functions
Tissues are organic material that makes up organs and other bodily structures. Tissues are formed from cells and have similar structures and functions. There are four types of tissues in animal bodies:
Tissue
Organ Level of Organization
Human body organs like the lungs, heart, stomach, etc are made of two or more types of tissues that serve a particular function. The lungs bring in oxygen and eliminate CO2, the heart pumps blood through the body- just to name a few examples. Most of the organs have all four types of tissues and they make up the whole organ system.
Organs are grouped into organ systems and they work together to carry out a particular function. The major organ systems of the human body are listed below:
Organ System Level of Organization
FAQs on Structural Organization in Animals: Key Concepts
1. What is meant by the structural organisation in animals?
Structural organisation in animals refers to the hierarchical arrangement of different body parts, from the simplest to the most complex levels. This organisation begins with cells, which group together to form tissues. Tissues then combine to form organs, and multiple organs work together in an organ system. This systematic arrangement allows for a highly efficient division of labour, enabling complex organisms to perform various life processes effectively.
2. What are the main levels of organisation found in the animal kingdom?
The animal kingdom exhibits four main levels of structural organisation, which reflect increasing complexity:
- Cellular Level: The body is an aggregation of cells with a basic division of labour. Example: Sponges.
- Tissue Level: Cells performing the same function are arranged into tissues. Example: Coelenterates (like Hydra).
- Organ Level: Tissues are grouped together to form organs, each specialised for a particular function. Example: Platyhelminthes (like Flatworms).
- Organ System Level: Organs are associated to form functional systems, where each system handles a specific physiological function. Examples: Annelids, Arthropods, Mammals.
3. What are the four primary types of animal tissues and their main functions?
The four primary types of animal tissues, as per the CBSE Class 11 syllabus for 2025-26, are:
- Epithelial Tissue: Forms the covering or lining of body parts. Its main functions are protection, secretion, absorption, and filtration.
- Connective Tissue: The most abundant tissue, it connects, supports, and binds other tissues or organs. Examples include bone, cartilage, blood, and adipose tissue.
- Muscular Tissue: Composed of cells that can contract, it is responsible for all types of movement and locomotion in the body.
- Neural Tissue: Comprises neurons and is responsible for control and coordination by transmitting electrical signals throughout the body.
4. Why is blood considered a specialised type of connective tissue?
Blood is considered a specialised connective tissue because it fulfils the main criteria of this tissue type. Firstly, it has a fluid extracellular matrix, known as plasma. Secondly, suspended within this matrix are living cellular components like Red Blood Cells (RBCs), White Blood Cells (WBCs), and platelets. Its primary function is to 'connect' various body systems by transporting nutrients, gases, hormones, and waste products, which is a key role of connective tissues.
5. What is adipose tissue and what are its key functions in the body?
Adipose tissue is a type of loose connective tissue primarily located beneath the skin. Its cells, called adipocytes, are specialised to store fat. The key functions of adipose tissue include:
- Fat Storage: It serves as a major reservoir of energy.
- Insulation: It forms a layer under the skin that reduces heat loss.
- Protection: It acts as a cushion, protecting vital organs like the kidneys and heart from shock and injury.
6. How does the structure of a neuron enable it to perform its function of signal transmission?
The structure of a neuron is perfectly adapted for transmitting nerve impulses. The cell body contains the nucleus and cytoplasm. Branching fibres called dendrites receive signals from other neurons. A long fibre called the axon carries the electrical signal away from the cell body, often over long distances. The axon terminal then passes the signal to the next neuron or a muscle cell. This specialised structure ensures one-way, rapid communication, which is essential for body control and coordination.
7. What are the three types of muscle tissue and where are they located?
The three types of muscle tissue are differentiated by their structure, function, and location:
- Skeletal Muscle: This is a voluntary muscle attached to bones, responsible for body movements. Its fibres are striated (striped).
- Smooth Muscle: This is an involuntary muscle found in the walls of internal organs like the intestine, stomach, and blood vessels. Its fibres are non-striated.
- Cardiac Muscle: This is an involuntary, striated muscle found only in the walls of the heart. It is responsible for pumping blood.
8. What is the main difference between an exocrine and an endocrine gland?
The main difference lies in how they release their secretions. Exocrine glands have ducts through which they secrete their products (like mucus, saliva, earwax, or oil) onto a surface or into a body cavity. In contrast, endocrine glands are ductless glands that release their products, called hormones, directly into the fluid bathing the gland, which then diffuses into the bloodstream for transport throughout the body.
9. Why is a complex organ system essential for the survival of large, multicellular animals?
In small or simple animals, processes like nutrient delivery and waste removal can occur via simple diffusion across the body surface. However, for large animals, the volume of the body increases much faster than its surface area. This makes diffusion highly inefficient for reaching deep internal cells. Organ systems (like the circulatory, respiratory, and digestive systems) solve this problem by providing specialised and highly efficient networks for transporting substances and coordinating functions across the entire body, thus enabling greater size and complexity.
10. How do the different types of cell junctions in epithelial tissue contribute to its overall function?
Cell junctions are crucial for the integrity and function of epithelial tissue. The three main types are:
- Tight Junctions: These junctions press adjacent cell membranes together, forming a seal that prevents the leakage of substances across the tissue. This is vital in places like the intestinal lining.
- Adhering Junctions: These act like cement, fastening neighbouring cells together to form a strong structural unit.
- Gap Junctions: These are communicating junctions that form channels connecting the cytoplasm of adjacent cells, allowing for the rapid transfer of ions and small molecules between them.
