NOTES Chapter 6: "Tissues" from Class 9 Science CBSE NCERT:

notes for Chapter 6: "Tissues" from Class 9 Science CBSE NCERT:

Tissues are groups of cells that are similar in structure and function and work together to perform a particular task.
In multicellular organisms, cells group together to form tissues, and these tissues work together to carry out various functions of the body.

Plants have two main types of tissues:

Meristematic tissues are responsible for the growth of plants. They consist of cells that are actively dividing and have the ability to develop into various other types of cells.
Characteristics:
- Cells are small, thin-walled, and rich in nucleus.
- No intercellular spaces between cells.
- These cells divide frequently and are found in specific regions of the plant.
Types of Meristematic Tissue:
1. Apical Meristem:
  - Located at the tips of roots and stems.
  - Responsible for primary growth (growth in length).
2. Lateral Meristem:
  - Found on the sides of roots and stems.
  - Responsible for secondary growth (growth in thickness).
3. Intercalary Meristem:
  - Found at the base of leaves or internodes.
  - Helps in regeneration and growth.

Permanent tissues are formed when meristematic cells stop dividing and differentiate into specific types of cells with specific functions.
Characteristics:
- Cells in permanent tissues may be specialized for storage, photosynthesis, support, etc.
Types of Permanent Tissues:
1. Simple Permanent Tissue: Made of similar cells.
  - Parenchyma:
    - Found in the soft parts of the plant such as leaves, roots, and stems.
    - Involved in storage, photosynthesis, and gas exchange.
  - Collenchyma:
    - Provides flexibility and mechanical support.
    - Found in growing parts like the stems and petioles (leaf stalk).
  - Sclerenchyma:
    - Provides strength and rigidity.
    - Cells have thick lignified walls. Found in hard parts like seed coats, nuts, and bark.
2. Complex Permanent Tissue: Made of different types of cells.
  - Xylem:
    - Transports water and minerals from roots to other parts of the plant.
    - Composed of vessels, tracheids, xylem parenchyma, and xylem fibers.
  - Phloem:
    - Transports food (mainly sugars produced during photosynthesis) from leaves to other parts of the plant.
    - Made up of sieve tubes, companion cells, phloem parenchyma, and phloem fibers.

Animals have four main types of tissues:

Epithelial tissue forms the covering or lining of body parts and organs.
Characteristics:
- Cells are tightly packed, with very little intercellular space.
- Cells are often arranged in layers.
- They serve as barriers for protection and help in secretion and absorption.
Types of Epithelial Tissue:
1. Squamous Epithelium:
  - Thin, flat cells that form the lining of the lungs and blood vessels.
  - Helps in the exchange of gases and nutrients.
2. Cuboidal Epithelium:
  - Cube-shaped cells found in the lining of kidney tubules and glands.
  - Responsible for secretion and absorption.
3. Columnar Epithelium:
  - Tall, column-like cells found in the lining of the intestines and stomach.
  - Involved in absorption and secretion.

Connective tissue supports, binds, and connects various body parts.
Characteristics:
- Cells are widely spaced, with a large amount of intercellular matrix between them.
- The matrix may be liquid, semi-solid, or solid, depending on the function.
Types of Connective Tissue:
1. Blood:
  - Composed of red blood cells, white blood cells, and platelets.
  - Transports nutrients, gases, and waste throughout the body.
2. Bone:
  - Provides rigidity and structural support.
  - Contains cells known as osteocytes embedded in a hard matrix of calcium salts.
3. Cartilage:
  - Provides flexibility and support.
  - Found in joints, ears, nose, etc.
4. Adipose Tissue:
  - Stores fat and acts as a shock absorber and insulator.
  - Found under the skin and around internal organs.
5. Lymph:
  - A fluid connective tissue that helps in the transport of immune cells and fighting infections.

Muscle tissue is responsible for movement in the body.
Characteristics:
- Cells are elongated and can contract to produce movement.
Types of Muscle Tissue:
1. Skeletal Muscle:
  - Voluntary muscle tissue attached to bones.
  - Responsible for voluntary movements like walking, running, etc.
2. Smooth Muscle:
  - Involuntary muscle tissue found in the walls of internal organs (e.g., stomach, blood vessels).
  - Responsible for internal movements, such as the movement of food through the digestive system.
3. Cardiac Muscle:
  - Involuntary muscle found in the heart.
  - Responsible for pumping blood throughout the body.

Nervous tissue is composed of neurons (nerve cells) that transmit electrical impulses.
Characteristics:
- Neurons have a cell body, axon (long extension), and dendrites (short extensions).
- The nervous tissue is responsible for communication, coordination, and control of body functions.

Feature	Plant Tissues	Animal Tissues
Cell Division	Occurs in specific regions (meristems)	Occurs throughout the body
Cell Wall	Present in plant cells (made of cellulose)	Absent in animal cells
Vacuole	Large central vacuole (stores water)	Small vacuoles or absent
Chloroplasts	Present in photosynthetic cells (e.g., in leaves)	Absent in animal cells
Shape of Cells	Regular, angular or rectangular	Irregular or round

Plant tissues help in growth, storage, photosynthesis, and transport of water and food.
Animal tissues help in movement, support, protection, and coordination of body activities.

Tissues are made of groups of cells that work together to perform specific functions.
Plant tissues include meristematic tissue (growth) and permanent tissue (for storage, transport, and support).
Animal tissues include epithelial tissue (protection), connective tissue (support), muscle tissue (movement), and nervous tissue (coordination).
The structure and function of tissues are adapted to the needs of the organism.

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