CBSE Class 9 Science Chapter 6 Tissues Notes

Key Points: Must Remember

• Tissue: A group of cells similar in structure and function, working together to achieve a specific task.
• Plant Tissues: Primarily supportive, mostly dead cells, less energy requirement, limited growth regions.
• Animal Tissues: Actively mobile, mostly living cells, high energy requirement, uniform growth.
• Meristematic Tissues: Actively dividing cells, found in growth regions (apical, lateral, intercalary), responsible for plant growth.
• Permanent Tissues: Derived from meristematic tissues, have lost the ability to divide, take up a permanent shape and function.
• Simple Permanent Tissues: Made of only one type of cell (Parenchyma, Collenchyma, Sclerenchyma).
• Complex Permanent Tissues: Made of more than one type of cell (Xylem, Phloem) for transportation.
• Animal Tissues Types: Epithelial (covering/lining), Connective (connecting/supporting), Muscular (movement), Nervous (communication).
• Nervous Tissue: Composed of neurons, responsible for transmitting messages.
• Blood: A type of fluid connective tissue with a matrix (plasma) and cells (RBCs, WBCs, platelets).

Essential Definitions

Tissue

A group of cells similar in origin, structure, and function, organized to perform a specific task.

Meristematic Tissue

Plant tissue composed of undifferentiated, actively dividing cells, responsible for growth in length and girth.

Permanent Tissue

Plant tissue derived from meristematic tissue, whose cells have lost the ability to divide and have differentiated to perform specific functions.

Parenchyma

A type of simple permanent plant tissue with unspecialized cells, large intercellular spaces, involved in food storage and photosynthesis.

Sclerenchyma

A type of simple permanent plant tissue characterized by thick, lignified cell walls, providing mechanical strength to the plant; cells are usually dead.

Xylem

A complex permanent plant tissue responsible for the transport of water and dissolved minerals from roots to other parts of the plant.

Phloem

A complex permanent plant tissue responsible for the transport of food (sugars) from leaves to other parts of the plant.

Epithelial Tissue

Animal tissue that forms the outer covering of the body, and lines internal organs and cavities, providing protection, secretion, and absorption.

Connective Tissue

Animal tissue that connects various body parts, provides support, and transports substances; includes blood, bone, cartilage, ligaments, tendons.

Neuron

The structural and functional unit of the nervous system, specialized for transmitting electrical signals (nerve impulses).

Understanding Plant Tissues in Detail

Plant tissues are primarily classified into two main types: Meristematic Tissues and Permanent Tissues, based on their ability to divide. Understanding their characteristics and functions is crucial.

Meristematic Tissues are characterized by their ability to actively divide and are responsible for the plant's growth. They consist of small, spherical or oval cells with thin cell walls, dense cytoplasm, and prominent nuclei, lacking intercellular spaces and vacuoles. Based on their location, they are further classified:

1. Apical Meristem: Located at the tips of roots and shoots, responsible for increase in length of the plant (primary growth).
2. Lateral Meristem (Cambium): Found along the sides of the stem and root, responsible for increase in girth or diameter of the plant (secondary growth).
3. Intercalary Meristem: Present at the base of leaves or internodes (e.g., in grasses), responsible for growth in length of organs like leaves and internodes.

Permanent Tissues are formed from meristematic tissues and have differentiated to perform specific functions, losing their ability to divide. Their cells have a definite shape, size, and function. They can be simple or complex:

A. Simple Permanent Tissues: Composed of only one type of cell.

1. Parenchyma: The most common simple permanent tissue. Cells are generally unspecialized, living, with thin cell walls and large intercellular spaces. They primarily function in food storage, photosynthesis (chlorenchyma), and providing turgidity.
2. Collenchyma: Consists of living cells with irregularly thickened corners due to pectin and cellulose deposition. They provide mechanical support and flexibility to young stems and petioles without hindering growth.
3. Sclerenchyma: Composed of dead cells with thick, lignified cell walls, making them hard and stiff. They provide mechanical strength and rigidity to the plant, found in fruit walls of nuts, seeds, and vascular bundles.

B. Complex Permanent Tissues: Composed of more than one type of cell, all working together as a unit to perform a common function.

1. Xylem: Known as water-conducting tissue. It transports water and minerals from the roots to all aerial parts of the plant. It consists of tracheids, vessels, xylem parenchyma, and xylem fibres.
2. Phloem: Known as food-conducting tissue. It transports food (sugars) prepared in the leaves to other parts of the plant. It consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibres.

Comparison: Plant Tissues vs. Animal Tissues

Exam Tip: Identifying Tissues and Their Functions

In your exams, pay close attention to diagram-based questions. You might be asked to identify a specific tissue from a provided diagram (e.g., neuron, cross-section of xylem, muscle fibre) and state its function or location. Practice drawing neat, labeled diagrams for key tissues like neuron, different muscle types, and a cross-section of a vascular bundle. Remember to link the structure of a tissue directly to its function (e.g., thick, lignified walls of sclerenchyma for strength; branched structure of neuron for communication). Also, distinguish clearly between simple and complex permanent tissues, and between the different types of animal tissues. Use your YoLearn AI Flashcards to drill these structural-functional relationships.

Quick Revision Check

• Q: What are the three types of meristematic tissues and their locations? A: Apical meristem (tips of roots/shoots), Lateral meristem (sides of stem/root), Intercalary meristem (base of leaves/internodes).
• Q: Name the components of phloem and state its primary function. A: Sieve tubes, companion cells, phloem parenchyma, and phloem fibres. Primary function is transport of food (sugars).
• Q: Which animal tissue is responsible for movement in our body? A: Muscular tissue.
• Q: Give two examples of fluid connective tissue. A: Blood and Lymph.

Frequently Asked Questions