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Sound – Class 9 Science Complete Notes

1. What is Sound? Sound is a form of energy which produces a sensation of hearing in our ears. Sound is produced by vibrating objects. Examples include vibrating tuning fork, vocal cords in humans, bells, musical instruments, etc. Vibration: Rapid to-and-fro (back and forth) motion of an object. Short Question: Can sound be produced without vibration? Answer: No, sound cannot be produced without vibration. 2. Medium of Sound The substance through which sound travels is called a medium . Sound can travel through solids, liquids, and gases but cannot travel through vacuum . Process of Sound Propagation: When an object vibrates, it makes the air particles around it vibrate. These air particles move back and forth from their original (rest) position. The vibrating air particles push nearby air particles. This causes the nearby particles to also start vibrating. In this way, vibrations pass from one particle to another. This process continues through the medi...
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CLASS 9 SCIENCE NOTES: CHAPTER - TISSUES

What Are Tissues?

  • Group of cells with a common origin and similar function are called tissues.
  • Multicellular organisms have specialized cells forming tissues.
  • Utility: Provide structure, mechanical strength, and division of labor.

Types of Tissues

  • Plant Tissues
  • Animal Tissues

Plant Tissues


1. Meristematic Tissues

  • Cells actively divide for growth.
  • Intercellular spaces are absent.
  • Shapes: spherical, oval, polygonal, or rectangular.
  • Have thin walls, few/no vacuoles, dense cytoplasm, prominent nuclei.
Type Location Function
Apical Tips of stems/roots Increase length (primary growth)
Intercalary Base of leaves/internodes Longitudinal growth
Lateral Sides of stems/roots Increase thickness (secondary growth)

2. Permanent Tissues

  • Cells loose ability to divide, differentiate to form structure.
  • Formed from meristematic tissue
  • Categories: Simple and Complex Permanent Tissues.

Simple Permanent Tissues

Tissue Nature and Structure Location/Occurrence Functions
Parenchyma Common, rounded, living, thin walls Stems, roots, leaves, soft parts Store food, packing, transport, maintains shape
Collenchyma Living, elongated, thick at corners, no intercellular spaces Below epidermis of stems Support, elasticity
Sclerenchyma Dead, thick lignified walls, closely packed Stems, roots, veins, seeds, nut covers, jute fibres Mechanical support, rigidity, flexibility, elasticity

Protective Tissues

Type Features Functions
Epidermis Outer covering, single layer, cuticle Prevents water loss, infection, gas exchange (stomata)
Cork (Phellem) Bark of woody plants, dead, suberin wax Water/gas proofing, extra protection

Complex Permanent Tissues

Xylem: 



Xylem Component Key Features & Function
Tracheids
  • Elongated, angular, dead cells (primitive).
  • Mainly conduct water and minerals.
  • Primarily found in gymnosperms.
Vessels
  • Have advanced elements (generally in angiosperms).
  • Cylindrical tubes placed end-to-end for a continuous channel.
  • Function: Efficient water conduction.
Xylem Parenchyma
  • Small, thick-walled living cells.
  • Function: Storage of starch (food).
Xylem Sclerenchyma (Xylem Fibre)
  • Non-living fibres with thick walls and narrow cavities.
  • Function: Provide mechanical support.

Important Note: Except for Xylem Parenchyma, all other xylem elements are dead.

Phloem:



Sieve Tubes

  • Slender, tube-like structures made of elongated, thin-walled cells placed end to end.
  • End walls have many pores (sieve plates).
  • Nucleus degenerates at maturity, but cytoplasm continues via connection to companion cell.
  • Contain slime protein for growth and repair.

Companion Cells

  • Dense cytoplasm and prominent nuclei.
  • Originates from the same mother cell as sieve cells ("sister cells").

Phloem Fibre

  • Gives mechanical support to sieve tubes.

Phloem Parenchyma

  • Stores food and helps in radial conduction of food.

Comparison between xylem and phloem

Feature Xylem Phloem
Function Conducts water and minerals Conducts organic solutes or food materials
Direction of Conduction Mostly unidirectional (from roots to apical parts) Bidirectional (from leaves to storage/growing parts or vice versa)
Conducting Channels Tracheids and vessels (dead elements) Sieve tubes (living elements)
Living Elements Xylem parenchyma (only living element) Sieve tubes, companion cells, and phloem parenchyma
Dead Elements Tracheids, vessels, and fibers Phloem fibers
Mechanical Support Provides mechanical strength to the plant Does not perform a mechanical function

Animal Tissues

1. Epithelial Tissue

  • Cover organs and surfaces; continuous sheets form barriers between body systems.
  • Single layer of cells, almost no intercellular space; all on basement membrane.
Type Structure Location Function
Simple squamous Flat, single layer Mouth, oesophagus, lungs Delicate lining
Stratified squamous Multiple layers Skin Prevents wear/tear
Cuboidal Cube-shaped, basement membrane Kidney tubules, salivary ducts Absorption, secretion
Columnar / Ciliated Tall, cylindrical, may have cilia Intestine, stomach, respiratory tract, fallopian tube Absorbs nutrients, moves particles

2. Connective Tissue

Type Location/Structure Function
Areolar (Loose) Skin-muscle interface, vessels Supports, fills spaces, repair
Adipose Below skin, internal organs Fat storage, insulation
Dense (Tendon/Ligament) Tendon: muscle-bone | Ligament: bone-bone Tendons: strong, less flexible | Ligaments: strength, little matrix
Skeletal (Cartilage/Bone) Cartilage: ear, nose | Bone: skeleton Support, flexibility, anchors muscles
Fluid (Blood/Lymph) Throughout body Transports gases, food, hormones

3. Muscular Tissue

  • Movements are brought about in our body with the help of muscular tissues.
  • They are long fibre-like cells called muscle fibres.
  • They are capable of contraction or relaxation.

    • Types of Muscle Tissue

    Feature Striated Muscle (Voluntary Muscles) Non-Striated Muscle (Smooth Muscles) Cardiac Muscle
    Control Voluntary (under the control of one's will) Involuntary Involuntary
    Location Attached to the skeleton Walls of stomach, intestine, urinary bladder, bronchi, iris, etc. Walls of the heart
    Structure Multinucleated and unbranched fibers Uninucleated, spindle-shaped fibers Uninucleated and branched fibers
    Membrane Enclosed by a thin membrane called sarcolemma Not enclosed by a membrane; fibers joined in bundles Enclosed by sarcolemma with intercalated discs
    Cytoplasm Called sarcoplasm Called sarcoplasm Called sarcoplasm
    Fatigue Get tired and need rest Do not get tired easily Do not get tired; rhythmic contraction/relaxation occurs
    Appearance Striated (striped appearance) Non-striated (smooth appearance) Intermediate structure between striated and non-striated
    Function Responsible for voluntary movements Controls involuntary movements like peristalsis Controls rhythmic contraction and relaxation of the heart

    4. Nervous Tissue

    • Specialized for receiving/transmitting stimuli rapidly.
    • Form brain, spinal cord, nerves.
    • Neuron cell: cell body, axon (transmits impulses), dendrites (bring info).

    Key Differences: Plant vs Animal Tissues

    Characteristic Plant Tissues Animal Tissues
    Function Growth, support, transport Protection, movement, connection
    Types Meristematic, Permanent Epithelial, Connective, Muscular, Nervous
    Growth regions Specific (meristems) Not confined
    Cell Wall Present Absent

    Summary: Tissues help in the efficient functioning of multicellular organisms by dividing labor. Plants have tissues for growth and support, while animals have tissues for movement, protection, and coordination.

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