Tissues class 9 notes, Class 9 science chapter 6 notes

Tissues - Class 9 Science Chapter 6

Tissue:
➥ A group of cells that are similar in structure and work together to achieve a particular function is called a tissue.

Plant Tissue

1. Meristematic Tissues

2. Permanent Tissues

Histology

➥ The microscopic study of tissue is called histology.

1. Meristematic Tissue (growth tissue)

➥ The expansion or growth of plants is limited to particular regions due to the presence of specialized dividing tissue known as meristematic tissue.

➥ Meristematic tissue is found only at specific points in plants.

➥ They are small, spherical, or polygonal cells with dense cytoplasm. The nucleus is large and prominent. Vacuoles are absent or very small in number.

➯ Meristematic tissues can be classified on the basis of their position into:

1. Apical Meristem: Occurs at the growing tips of stems and roots and increases the length of the stem and the root. Longitudinal section of shoot apex showing location of meristem and young leaves.

2. Lateral Meristem: (cambium, cork cambium) Occurs on the sides both in stem and root. It is exclusively present in dicot plants where it increases the girth of stem and root. It is of two main types - Vascular and Cork cambium.
3. Intercalary Meristem: (internodes) Present at the base of leaves and internodes. It increases the length between the two nodes. It is usually found in monocot plants.

2. Permanent Tissue

➥ Permanent tissues are derived from meristematic cells which have lost the ability to divide. They undergo differentiation to perform a particular function.

➥ Their cells may be living or dead, thin or thick-walled. The thickening may be regular or irregular.

➯ There are two main groups of permanent tissues:

1. Simple Permanent Tissue
2. Complex Permanent Tissue

(1.) Simple Permanent Tissues

➥ A few layers of cells beneath the epidermis are generally simple permanent tissue.

➥ A simple tissue is a group of one type of cells that perform the same function.

➯ Simple tissue is classified into three main types:

1. Parenchyma
2. Collenchyma
3. Sclerenchyma

(i) Parenchyma Tissue

• ➥ Fundamental backing tissue with loosely packed thin-walled cells, large central vacuole for food and water storage.
• ➥ Primary function is food storage and packing.

➥ In aquatic plants, parenchyma cells are associated with large air spaces. These air spaces store gases and provide buoyancy to the plants. Such a specialized parenchyma tissue is known as aerenchyma.

⟹ Types of Parenchyma:-

• Idioblast: Storage of excretory substances such as resin, tannin, gum, and oils.
• Chlorenchyma: Chloroplast containing parenchyma tissues perform photosynthesis e.g., mesophyll of leaves.
• Aerenchyma: In hydrophytic plants, provides buoyancy.

(ii) Collenchyma

➥ These cells are living cells having thickened corners.

➥ The uneven thickenings of pectocellulose provide mechanical support and flexibility to plants. Because of collenchyma, plants can bend without breaking.

(iii) Sclerenchyma

➥ These cells are usually dead, thick, and lignified cells with a narrow lumen.

⟹ Sclerenchyma cells are of two types:

1. Fibres are elongated spindle-shaped cells pointed at both ends.
2. Sclereids are short and broad cells that occur singly or in small groups. They are also known as stone cells. This tissue provides mechanical support and enables plants to bear various stresses.

➥ They are also known as stone cells. This tissue provides mechanical support and enables plants to bear various stresses.

Protective Tissues

➥ Protective tissues constitute the outermost layer of stems, roots, leaves, flowers, and fruits. They provide protection against environmental factors and pathogens.

⟹ They are of two types:

• (a). Cork
• (b). Epidermis

(a). Cork or Phellem

• ➥ In older roots and stems, tissues at the periphery become cork cells or phellem cells.
• ➥ Made up of dead cells with thick walls and no intercellular spaces.
• ➥ Walls deposit a waxy substance called suberin, making cells impermeable to water and gases.

Functions of Cork:

• ➥ Protects the plant from drying out, infection, and mechanical injury.
• ➥ Commercially valuable due to its imperviousness, lightness, toughness, compressibility, and elasticity.

(b). Epidermis

• ➥ Forms a one-cell thick outermost layer of various body organs of plants such as leaves, flowers, stems, and roots.
• ➥ Covered outside by cuticle, a waterproof layer of waxy substance called cutin.
• ➥ Each stoma is guarded by a pair of bean-shaped cells called guard cells.

Functions of Epidermis:

• ➥ Protects the plant from drying out and from infection.
• ➥ The cuticle reduces the rate of water loss through transpiration and evaporation, preventing wilting.

Stomata

• ➥ Small pores in the epidermis of leaves allow gaseous exchange during photosynthesis, respiration, and transpiration.

(2.) Complex Permanent Tissue

➥ Complex permanent tissues are the tissues that are made up of more than one type of cell.

➥ Helps in transportation of organic materials, water, and minerals.

➥ Also known as conducting or vascular tissue.

Xylem Tissue

➥ Also known as wood, a vascular and mechanical tissue.

➥ Helps in transporting water and minerals from soil to plant.

⟹ It consists of:

• Tracheids
• Xylem vessels
• Xylem fibers
• Xylem parenchyma

Types of Xylem:

1. Tracheids: Elongated dead cells involved in the conduction of water and minerals in gymnosperms.
2. Xylem Vessels: Cylindrical tube-like structures found in angiosperms that form a continuous channel for efficient water conduction.
3. Xylem Sclerenchyma (Fibres): Non-living fibers with thick walls and narrow cavities providing mechanical support.
4. Xylem Parenchyma: Small, thick-walled cells designed for starch storage.

Phloem:

➥ Transports food from leaves to other parts of the plant.

Types of Phloem:

1. Sieve Tubes: Tubular structures made up of elongated, thin-walled cells. The end walls have numerous pores called sieve plates.
2. Companion Cells: Have dense cytoplasm and prominent nuclei. Sieve tubes and companion cells are called sister cells as they originate from a single mother cell.
3. Phloem Fibres: Provide mechanical support to sieve tubes.
4. Phloem Parenchyma: Stores food and helps in radial conduction of food.

Animal Tissues

➥ Animal tissues are groups of cells with similar structures and functions that work together to perform specific tasks within the bodies of animals.

⟹ Types of Animal Tissues:

1. Epithelial tissue
2. Connective tissue
3. Muscular tissue
4. Nervous tissue

1. Epithelial Tissue

• ➥ Serves as the protective covering for most organs and body cavities.
• ➥ Forms a barrier to separate different body systems.
• ➥ Examples include skin, mouth lining, blood vessels, lung alveoli, and kidney tubules.
• ➥ Consists of tightly packed cells with minimal intercellular spaces.

• ⟹ Types include:
  1. Simple Squamous Epithelium: Thin and flat cells, lining blood vessels and lung alveoli.
  2. Stratified Squamous Epithelium: Layered cells, found in the skin.
  3. Columnar Epithelium: Tall cells, lining the intestine, facilitating absorption and secretion.
  4. Ciliated Columnar Epithelium: Cells with cilia, found in the respiratory tract.
  5. Cuboidal Epithelium: Cube-shaped cells, lining kidney tubules and salivary gland ducts.
  6. Glandular Epithelium: Specialized for secretion, forming glands.

2. Connective Tissue

• ➥ Provides structural support and connects different body parts.
• ➥ Includes blood, bone, cartilage, ligament, tendon, areolar, and adipose tissues.

• ⟹ Types based on matrix:-
  1. 1. Skeletal Tissue:
     • ➥ Our skeleton is made up of bone (non-flexible) and cartilage (flexible).
     • ➥ Bone becomes hard due to the deposition of calcium and phosphorus in the matrix.
     • ➥ Bone cells are known as osteocytes and contain Haversian canals with blood vessels and nerve fibers.
  2. 2. Connective Tissue Proper:
     • ➥ Tendons are strong and connect muscle to bone.
     • ➥ Ligaments are elastic and connect bone to bone.
     • ➥ Areolar Tissue forms a packaging tissue between organs in the body cavity.
     • ➥ Adipose Tissue stores fats.
     
  3. 3. Vascular Tissue:
     • ➥ Blood is a fluid connective tissue with a fibreless fluid matrix.
     • ➥ Blood comprises plasma and blood cells or corpuscles.
     • ➥ Plasma is a straw-colored fluid containing inorganic and organic substances.
     • ➥ Albumin, globulin, and fibrinogen are major soluble proteins in the plasma.
     • ➥ Na+, Cl-, glucose, amino acids, vitamins, and fatty acids are constituents of plasma.
     • ➥ Lymph is similar to plasma but lacks RBCs and blood platelets.
     • ➥ Lymph contains many lymphocytes and helps maintain blood volume by removing or adding plasma.
     • ➥ Lymph nodes and lymphoid organs trap microbes for destruction.
     

3. Muscular Tissue

• ➥ Specialized for contraction and movement.
• ⟹ Types include:-
  1. Striated Muscles: Attached to bones, voluntary muscles with dark and light bands.
  2. Unstriated or Smooth Muscles: Involuntary muscles found in organs like the stomach and intestines, without bands.
  3. Cardiac Muscle: Found in the heart, involuntary with branched cells and intercalated discs.

4. Nervous Tissue

• ➥ Fundamental for rapid communication within the body.
• ➥ Consists of neurons that transmit nerve impulses.
• ➥ Includes the intricate network of nerves and the brain.