Class 9 Science Notes | Tissues Notes

Class 9 Science: Tissues

Introduction to Tissues In biology, a tissue is a group of cells that work together to perform a specific function. The study of tissues is called Histology. Tissues are essential for the organization of life, forming the various structures in plants and animals.

Types of Tissues

Tissues are broadly categorized into two main types based on the type of organisms: plant tissues and animal tissues.

Plant Tissues

1. Meristematic Tissue Meristematic tissues are responsible for the growth of plants. These tissues have cells that are continuously dividing and are found in the regions of the plant where growth is taking place. Meristematic tissues are of three types based on their location in the plant:

Apical Meristem: Found at the tips of roots and shoots, responsible for the increase in length of the plant.
Lateral Meristem: Found in the vascular and cork cambium, responsible for the increase in the girth of the plant.
Intercalary Meristem: Found at the base of leaves or internodes, helping in the growth of leaves and internodal regions.

2. Permanent Tissue Once meristematic tissues have divided and specialized, they form permanent tissues. Permanent tissues are divided into simple and complex tissues:

Simple Permanent Tissues:

Parenchyma: Composed of thin-walled cells, found in soft parts of the plant like cortex and pith. Functions include storage, photosynthesis, and secretion.
- Chlorenchyma: Parenchyma with chloroplasts, involved in photosynthesis.
- Aerenchyma: Parenchyma with large air cavities, provides buoyancy to aquatic plants.
Collenchyma: Composed of cells with unevenly thickened cell walls, found in stems and leaves. Provides flexibility and mechanical support.
Sclerenchyma: Composed of thick-walled, dead cells. Provides strength and support. Includes:
- Fibers: Long, slender cells.
- Sclereids: Short, irregular cells.

Complex Permanent Tissues:

Xylem: Transports water and minerals from roots to other parts of the plant. Consists of tracheids, vessels, xylem parenchyma, and xylem fibers.
Phloem: Transports food from leaves to other parts of the plant. Consists of sieve tubes, companion cells, phloem fibers, and phloem parenchyma.

Animal Tissues

1. Epithelial Tissue Epithelial tissues cover body surfaces, line cavities and organs, and form glands. They are classified based on the number of layers and the shape of cells:

Simple Epithelium: Single layer of cells.
- Squamous: Flat and thin, found in the lungs and blood vessels.
- Cuboidal: Cube-shaped, found in glands and kidney tubules.
- Columnar: Tall and column-like, found in the intestines.
Stratified Epithelium: Multiple layers of cells, found in areas subject to wear and tear, like the skin.
Glandular Epithelium: Specialized for secretion, forms glands.

2. Connective Tissue Connective tissues support, bind, and protect organs. They are characterized by the presence of an extracellular matrix. Types include:

Areolar Tissue: Loose connective tissue, fills spaces between organs.
Adipose Tissue: Stores fat, provides insulation and protection.
Dense Regular Connective Tissue: Provides tensile strength, found in tendons and ligaments.
Cartilage: Provides flexibility and support, found in joints, ear, and nose.
Bone: Hard and rigid, forms the skeleton.
Blood: Fluid connective tissue, transports nutrients, gases, and waste.

3. Muscular Tissue Muscular tissues are responsible for movement. Types include:

Skeletal Muscle: Voluntary muscles attached to bones, striated appearance.
Smooth Muscle: Involuntary muscles found in internal organs, non-striated.
Cardiac Muscle: Involuntary muscles found in the heart, striated and branched.

4. Nervous Tissue Nervous tissues are responsible for transmitting impulses. They consist of neurons and neuroglia. Neurons have three main parts:

Cell Body: Contains the nucleus.
Dendrites: Receive signals.
Axon: Transmits signals.

Functions and Importance of Tissues

Support and Structure: Tissues like bone and cartilage provide a framework and structure to the body.
Protection: Epithelial tissues protect underlying tissues from physical damage, dehydration, and infection.
Transport: Xylem and phloem in plants, and blood in animals, are responsible for the transport of nutrients, gases, and waste.
Storage: Parenchyma in plants stores food and water, while adipose tissue in animals stores fat.
Growth and Repair: Meristematic tissues in plants and certain connective tissues in animals are involved in growth and repair.
Movement: Muscular tissues enable movement in animals.
Coordination: Nervous tissues coordinate and control body functions by transmitting electrical signals.

Conclusion

Understanding tissues is crucial for studying the complex organization and function of living organisms. Each type of tissue plays a specific role, contributing to the overall functioning and survival of the organism. In plants, tissues are primarily involved in growth, support, and transport, while in animals, they play roles in movement, protection, and internal coordination. The study of tissues not only helps in understanding basic biological processes but also in medical and agricultural advancements, providing insights into disease mechanisms, tissue repair, and crop improvement.

MITRAM

Search This Blog