NCERT Class 9 Science Chapter 6 TISSUES Notes

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In this chapter, we revisit the fundamental concept that all living organisms are composed of cells. While unicellular organisms rely on a single cell to perform all basic functions, multicellular organisms exhibit a division of labor among millions of specialized cells. Each cell is adept at carrying out specific functions, such as muscle cells contracting for movement or nerve cells transmitting messages. This specialization allows for enhanced efficiency in performing tasks. In multicellular organisms, cells with similar structures and functions are organized into tissues. These tissues, such as blood, phloem, and muscle, are meticulously arranged to optimize their collective function within the organism.

6.1 Are Plants and Animals Made Are Plants and Animals Made of Same Types of Tissues? of Same Types of Tissues?

1. Plant Structure and Functions:

• Plants are stationary organisms, lacking mobility.
• Most plant tissues are supportive, providing structural strength.
• Many plant tissues are dead, offering mechanical support with minimal maintenance.
• Growth in plants is limited to certain regions, with specific tissues responsible for continuous growth.
• Plant tissues are classified into growing (meristematic) and permanent tissues based on their division capacity.

2. Animal Structure and Functions:

• Animals are mobile organisms, actively moving in search of food, mates, and shelter.
• Most animal tissues are living, reflecting the high energy requirements of mobility.
• Cell growth in animals is more uniform without distinct dividing and non-dividing regions.
• Structural organization of organs and organ systems is highly specialized and localized in complex animals.
• Animals exhibit a greater diversity and specialization in organ system design compared to plants.

B. Differences in Growth Patterns:

1. Plant Growth Patterns:

• Growth in plants is limited to specific regions, with certain tissues continuously dividing throughout their lifespan.
• Tissues responsible for plant growth are localized in specific regions, such as meristems.

2. Animal Growth Patterns:

• Animal cell growth is more uniform throughout the body without distinct dividing regions.
• There is no clear demarcation between dividing and non-dividing regions in animal bodies.

C. Specialization and Adaptation:

1. Specialization in Complex Animals:

• Complex animals exhibit highly specialized and localized structural organization of organs and organ systems.
• Specialization reflects the diverse feeding methods and modes of life pursued by animals.

2. Adaptation for Mobility:

• Animals are adapted for active locomotion, requiring specialized organ systems for mobility.
• This adaptation contrasts with the sedentary existence of plants, contributing to differences in organ system design.

 6.2 Plant Tissues Plant Tissues

6.2.1 MERISTEMATIC TISSUE

Meristematic Tissues in Plants:

1. Definition and Localization:

• Meristematic tissues are regions of active cell division responsible for plant growth.
• They are located only in specific regions of the plant, where growth occurs.

2. Classification of Meristematic Tissues:

• Apical Meristem: Found at the growing tips of stems and roots, increasing the length of the plant.
• Lateral Meristem (Cambium): Located in the vascular tissues of stems and roots, responsible for increasing stem and root girth.
• Intercalary Meristem: Present at the base of leaves or internodes on twigs, contributing to leaf and stem elongation.

3. Characteristics of Meristematic Cells:

• Initially, new cells produced by meristem resemble the meristematic cells themselves.
• As they mature, these cells differentiate into components of other plant tissues.

4. Features of Meristematic Cells:

• Cells in meristematic tissue are highly active, with dense cytoplasm and prominent nuclei.
• They have thin cellulose walls to facilitate cell division.
• Meristematic cells lack vacuoles, which may be attributed to their active metabolic state and need for space to accommodate rapid cell division.

6.2.2 PERMANENT TISSUE

6.2.2 (i) SIMPLE PERMANENT TISSUE

Types of Permanent Tissues:

1. Parenchyma Tissue:

• Consists of relatively unspecialized live cells with thin cell walls.
• Loosely packed cells with intercellular spaces.
• Provides support, stores food, and may contain chlorophyll for photosynthesis.
• Aerenchyma type found in aquatic plants for buoyancy.

2. Collenchyma Tissue:

• Provides flexibility and mechanical support to plants.
• Living, elongated cells with irregularly thickened corners.
• Commonly found in leaf stalks below the epidermis.

3. Sclerenchyma Tissue:

• Makes plant hard and stiff.
• Cells are dead, long, and narrow with thickened walls containing lignin.
• Provides strength to stems, vascular bundles, leaves, and seeds.

B. Epidermal Tissue:

1. Structure and Function:

• Outermost layer of cells covering the entire surface of the plant.
• Single layer in most cases, thicker in plants adapted to dry habitats.
• Protects against water loss, mechanical injury, and invasion by fungi.
• Epidermal cells often secrete a waxy, water-resistant layer for further protection.
• Contains stomata for gas exchange and transpiration.
• Root epidermal cells may bear elongated structures for increased water absorption.

2. Adaptations in Different Environments:

• Some plants, like desert plants, have thick waxy coatings on their epidermis to prevent water loss.

C. Changes in Protective Tissues as Plants Age:

1. Formation of Cork or Bark:

• As plants age, secondary meristem replaces the epidermis, forming a several-layer thick cork or bark.
• Cork cells are dead, compactly arranged, and impervious to gases and water.
• Contains suberin in cell walls for waterproofing.

6.2.2 ii) COMPLEX PERMANENT TISSUE

Types of Permanent Tissues:

1. Simple Permanent Tissue:

• Consists of one type of cells that resemble each other.
• Performs specific functions.
• Examples include parenchyma, collenchyma, and sclerenchyma.

2. Complex Permanent Tissue:

• Made of more than one type of cells that coordinate to perform common functions.
• Examples include xylem and phloem.
• Found in vascular bundles, which are characteristic features of complex plants.

3. Xylem Tissue:

• Consists of tracheids, vessels, xylem parenchyma, and xylem fibers.
• Cells have thick walls, many of which are dead.
• Tracheids and vessels are tubular structures facilitating vertical transport of water and minerals.
• Xylem parenchyma stores food and aids in lateral conduction of water.
• Xylem fibers provide support.

4. Phloem Tissue:

• Comprises sieve tubes, companion cells, phloem fibers, and phloem parenchyma.
• Sieve tubes are tubular cells with perforated walls facilitating bidirectional movement of materials.
• Companion cells support sieve tubes.
• Phloem fibers provide structural support.
• Phloem parenchyma stores food and aids in transport from leaves to other parts of the plant.

6.3 Animal Tissues Animal Tissues

6.3.1 EPITHELIAL TISSUE

Epithelial Tissues in Animal Bodies:

1. Function and Distribution:

• Epithelial tissues cover most organs and cavities within the body, forming a protective barrier.
• They separate different body systems and regulate the exchange of materials between the body and the external environment.
• Found in the skin, lining of the mouth, blood vessels, lung alveoli, and kidney tubules.

2. Characteristics:

• Epithelial tissue cells are tightly packed and form a continuous sheet.
• Minimal intercellular spaces with a small amount of cementing material between cells.
• All epithelium is separated from underlying tissue by an extracellular fibrous basement membrane.

Types of Epithelial Tissues:

a. Simple Squamous Epithelium:

• Thin and flat cells forming a delicate lining.
• Found in blood vessels, lung alveoli, oesophagus, and mouth lining.

b. Stratified Squamous Epithelium:

• Consists of many layers to prevent wear and tear.
• Forms the protective skin covering.

c. Columnar Epithelium:

• Tall cells facilitating absorption and secretion.
• Present in the inner lining of the intestine and respiratory tract.
• Ciliated columnar epithelium in the respiratory tract has cilia for moving mucus.

d. Cuboidal Epithelium:

• Cube-shaped cells providing mechanical support.
• Forms the lining of kidney tubules and salivary gland ducts.

e. Glandular Epithelium:

• Specialized epithelial cells capable of secreting substances at the epithelial surface.
• Forms multicellular glands through inward folding of epithelial tissue.

6.3.2 CONNECTIVE TISSUE

Connective Tissues:

1. Definition and Structure:

• Connective tissues are characterized by loosely spaced cells embedded in an intercellular matrix.
• The matrix can be jelly-like, fluid, dense, or rigid, depending on the function of the tissue.

2. Blood:

• Blood is a connective tissue with a fluid matrix called plasma.
• Contains red blood cells (RBCs), white blood cells (WBCs), and platelets suspended in plasma.
• Transports gases, digested food, hormones, and waste materials throughout the body.

3. Bone:

• Bone forms the framework supporting the body and anchors muscles.
• Composed of a hard matrix containing calcium and phosphorus compounds.
• Strong and non-flexible, providing support and protection to organs.

4. Ligaments and Tendons:

• Ligaments connect bones to each other and are highly elastic with considerable strength.
• Tendons connect muscles to bones, providing strength with limited flexibility.

5. Cartilage:

• Cartilage has widely spaced cells and a solid matrix composed of proteins and sugars.
• Smoothens bone surfaces at joints and provides structural support in areas like the nose, ear, trachea, and larynx.

6. Areolar Connective Tissue:

• Found between the skin and muscles, around blood vessels and nerves, and in bone marrow.
• Fills spaces inside organs, supports internal organs, and aids in tissue repair.

7. Adipose Tissue:

• Fat-storing adipose tissue is found below the skin and between internal organs.
• Cells filled with fat globules act as insulation and energy storage.

6.3.3 MUSCULAR TISSUE

Muscular Tissues:

1. Skeletal Muscle Tissue:

• Consists of elongated cells called muscle fibers.
• Responsible for voluntary movements and attachment to bones.
• Contains contractile proteins that cause movement.
• Under the microscope, exhibits alternate light and dark bands or striations.
• Cells are long, cylindrical, unbranched, and multinucleate.

2. Smooth Muscle Tissue:

• Controls involuntary movements such as those in the alimentary canal and blood vessels.
• Also found in the iris of the eye, ureters, and bronchi of the lungs.
• Cells are long, spindle-shaped, and uninucleate.
• Often called unstrained muscles due to the absence of visible striations.

3. Cardiac Muscle Tissue:

• Found in the heart and responsible for rhythmic contraction and relaxation.
• Involuntary muscles exhibiting constant activity throughout life.
• Cells are cylindrical, branched, and uninucleate.

4. Structural Comparison:

• Shape: Skeletal muscle cells are long and cylindrical, smooth muscle cells are spindle-shaped, and cardiac muscle cells are cylindrical with branching.
• Nuclei: Skeletal muscle cells are multinucleate, smooth muscle cells are uninucleate, and cardiac muscle cells are also uninucleate.
• Striations: Skeletal muscles exhibit visible striations, while smooth muscles lack visible striations, and cardiac muscles may have faint striations.

6.3.4 NERVOUS TISSU

Nervous Tissue:

1. Composition:

• Highly specialized cells called nerve cells or neurons.
• Forms the brain, spinal cord, and nerves.
• Neurons consist of a cell body with a nucleus and cytoplasm.
• Long thin extensions called axons and short branched extensions called dendrites.

2. Neurons:

• Each neuron typically has a single axon and many dendrites.
• Neurons can be up to a meter long.
• Nerve impulses transmitted by neurons enable rapid responses to stimuli.
• Functional combination of nerve and muscle tissue enables movement in response to stimuli.

3. Nerves:

• Many nerve fibers bound together by connective tissue form a nerve.

4. Key Points:

• Nervous tissue specialized for rapid transmission of stimuli.
• Neurons transmit nerve impulses allowing movement in response to stimuli.
• Functional combination of nerve and muscle tissue fundamental for most animals' movement.