CBSE CLASS 9 CHAPTER 6 NOTES

 

CHAPTER 6

CBSE SCIENCE
CLASS 9

TISSUES

 

TISSUES

·        Cell – structural & functional unit of life

·        Tissue – group of cells – similar in structure &/or work together – to achieve a particular function

·        Examples: Muscle, phloem, blood, etc.,

 

DIFFERENCE BETWEEN PLANT & ANIMAL TISSUE

 

PLANT TISSUE

·        Plant tissues – based on dividing capacity – classified into 2 types

o   Meristematic tissues

o   Permanent tissues

 

(I) MERISTEMATIC TISSUE

·        Growth of plants – occurs only in certain regions

·        Because Meristematic tissue (dividing tissue) – located only at these points

·        New cells – produced by meristem – slowly changes into other tissues

·        3 types – based on their region of location

o   (i) Apical meristem

o   (ii) Lateral meristem

o   (iii) Intercalary meristem

 

MERISTEMATIC TISSUES

(i) APICAL MERISTEM

·        Present in the tips of stems & roots

·        Increase the length

 

(ii) LATERAL MERISTEM

·        Also known as cambium

·        Increase the girth of stems & roots

 

(iii) INTERCALARY MERISTEM

·        Present at the leaf base & either side of nodes (internodes)

·        Cells of meristematic tissue are

·        very active

·        have dense cytoplasm

·        thin cellulose walls &

·        prominent nuclei

·        Lack vacuole

 

(II) PERMANENT TISSUES

·        Meristematic tissue – take up a specific role – lose the ability to divide – form a permanent tissue

·        Process – taking up a shape, size & function – differentiation

·        2 types

o   (i) Simple Permanent Tissue

o   (ii) Complex Permanent Tissue

 

(I) SIMPLE PERMANENT TISSUE
(a) PARENCHYMA

·        They are basic packing tissues – a type of permanent tissue

·        Have unspecialized cells – with thin walls

·        Live cells – loosely packed with intercellular spaces

·        Provides support to plants & stores food

·        Chlorenchyma – a parenchyma tissue – stores chlorophyll – helps in photosynthesis

·        Aerenchyma – a parenchyma tissue – seen in aquatic plants – have air cavities – helps in buoyancy

 

              

(b) COLLENCHYMA

·        Collenchyma – a permanent tissue – gives flexibility to plants

·        Allows easy bending in various parts of a plant – without breaking – Ex: leaf, stem

·        Collenchyma cells – have thick corners – are living & elongated

·        Have very little intercellular space

·        Provides mechanical support

(c) SCLERENCHYMA

·        Sclerenchyma – a permanent tissue – makes plant hard & stiff

·        They are dead cells – long narrow with thick walls – made of lignin

·        Provides strength to plant parts

·        Donot have intercellular spaces

·        Present in stems, veins of leaves, walls of vascular bundles, hard covering of seeds & nuts

 

(d) EPIDERMIS

·        Outermost covering of all plant parts – single layer of cells – Epidermis

·        Epidermis – protects all the parts of the plant

·        Aerial parts – epidermis secrets a waxy coating – protects the plant parts from

o   (i) Loss of water

o   (ii) Mechanical injury &

o   (iii) Parasitic fungi

·        Epidermis of leaf – small pores – Stomata

·        Stomata – enclosed by 2 kidney shaped cells – Gaurd cells

·        Epidermal cells (roots) – bear hair like structures – helps in absorption of water

·        Epidermal cells (stem) – projections - Trichomes

 

(II) COMPLEX PERMANENT TISSUE

·        Simple permanent tissues – made of single type of cells

·        Complex permanent tissues – made of more than one type of cells

·        All cells in permanent tissue – coordinate to perform a common function

·        Eg: Xylem & Phloem – Vascular bundles / conductive tissue

 

(a) XYLEM

·        It consists of

o   (i) Tracheids

o   (ii) Vessels

o   (iii) Xylem Parenchyma

o   (iv) Xylem fibres

·        Except Xylem Parenchyma – other cells are dead

·        Cells have thick walls

·        Tracheids & Vessels – tubular structures – allows  transport of water & minerals vertically 

·        Xylem parenchyma – stores food & helps in sideways conduction of water

·        Xylem fibres – are supportive

 

(b) PHLOEM

·        Phloem – made up of 4 elements

o   (i) Sieve tubes

o   (ii) Companion cells

o   (iii) Phloem fibre

o   (iv) Phloem Parenchyma

·        Except Phloem fibres – other elements are living

·        Sieve tube – tubular cells – with perforated walls (holes)

·        Phloem – helps to transport food from leaves to other parts

·        Unlike Xylem – In phloem – materials travel on both sides

 

ANIMAL TISSUES

·        In our body – each organ – specific function – made possible by different cells they are made of

·        On the basis of function – Animal tissues are classified as

o   (i) Epithelial Tissue

o   (ii) Connective Tissue

o   (iii) Muscular Tissue &

o   (iv) Nervous Tissue

 

(I) EPITHELIAL TISSUE

·        Epithelial Tissue – Covering or protective tissue in animal body

·        Forms a barrier – to keep different body systems – separate from the environment

·        Cells – tightly packed – no intercellular space – forms continuous sheet

·        Anything entering or leaving the body – must cross atleast one layer of epithelium

·        Permeability of epithelial tissue – helps in exchange of materials

·        Epithelial tissue – separated from the underlying tissue – by Extracellular fibrous basement membrane

·        Skin, lining of the mouth, lining of blood vessels, lung alveoli & kidney tubules – made up of epithelial tissue

 

TYPES OF EPITHELIAL TISSUES

·        Epithelial tissues – following types

o   (a) Simple Squamous Epithelium

o   (b) Stratified Squamous Epithelium

o   (c) Columnar Epithelium

o   (d) Ciliated Columnar Epithelium

o    (e) Cuboidal Epithelium

o    (f) Glandular Epithelium

 

(A) SIMPLE SQUAMOUS EPITHELIUM

·      ·   Extremely thin & flat – forms a delicate lining

· Oesophagus, lining of blood vessels or lung alveoli – covered with simple Squamous epithelium

 

(B) STRATIFIED SQUAMOUS EPITHELIUM

·        Skin – that protects the body – made of Squamous epithelium

·        Skin epithelium – made of many layers of Squamous epithelium – to prevent wear & tear

·        Since they are arranged in a pattern of layers – Called Stratified Squamous Epithelium 

 

(C) COLUMNAR EPITHELIUM

·        Where absorption occurs – like in inner lining of the intestine – tall epithelial cells are present – called Columnar epithelium (pillar like)

·        Columnar epithelium – facilitates movement across epithelial barrier

 

COLUMNAR EPITHELIUM

(D) CILIATED COLUMNAR EPITHELIUM

·        Respiratory tract – columnar epithelial cells – have hair like structure – called Cilia

·        These tissues – called Ciliated Columnar Epithelium

·        Cilia – moves – & pushes the mucus forward to clear it

(E) CUBOIDAL EPITHELIUM

·        Lining of kidney tubules & ducts of salivary glands – made of epithelial tissue – made of cube shaped cells

·        These tissues – called Cuboidal Epithelium

·        Provides mechanical support

 

(F) GLANDULAR EPITHELIUM

·        Often Epithelial cells – acts as gland cells & secrets substances at its surface

·        Sometimes a portion of epithelial tissue – folds inwards – form a multicellular gland

·        This is called Glandular Epithelium

 

GLANDULAR EPITHELIUM

(II) CONNECTIVE TISSUE

·        Cells of Connective Tissue – loosely spaced – embedded in intercellular matrix

·        Matrix – jelly like, fluid, dense or rigid

·        Nature of matrix differs – according to the function of the tissue

·        Example: Blood, bone, ligament, tendons, cartilage, Areolar tissue, etc.,

 

(A) BLOOD

·        Blood – has a liquid (fluid ) matrix – called plasma

·        RBCs, WBCs & platelets – suspended in plasma

·        Plasma – contains proteins, salts & hormones

·        Blood – flows & transports gases, digested food, hormones & waste materials – to different parts of the body

(B) BONE

·        Bone – connective tissue

·        Forms the framework – anchors the muscles – supports the main organs of the body

·        It is a strong & non-flexible tissue – whose matrix is made of Calcium & Phosphorus

(C) LIGAMENT

·        Ligament – a connective tissue – connects two bones

·        This Tissue – very elastic & has a considerable strength

·        Ligaments – contain very little matrix

 

(D) TENDONS

·        Tendons – connective tissue – connects muscles to bones

·        They are fibrous – with great strength – but limited flexibility

 

(E) CARTILAGE

·        Cartilage – connective tissue – widely spaced cells

·        Solid matrix – contains proteins & sugars

·        Cartilage – smoothens bone surfaces at joints

·        Cartilage – present in ear, nose, trachea & larynx

·        Cartilages – bones that can bend

 

CARTILAGE

(F) AREOLAR TISSUE

·        Areolar connective tissue – found between skin & muscles, around blood vessels & nerves & in bone marrow

·        It fills the space inside the organs – supports internal organs & helps in repair of tissues

·        Example: Adipose tissue – found below the skin & in between internal organs

·        Cells of Adipose Tissue – stores fat globules

·        Storage of fats – acts as an insulator

 

(III) MUSCULAR TISSUE

·        Muscular tissue – consists of elongated cells – called muscle fibres

·        Muscle – responsible for movement in our body

·        Muscles – contain special proteins – called Contractile proteins – which contract & relax – cause movement

·        Muscle Tissues – 3 types – they are

o   (a) Voluntary Muscles

o   (b) Involuntary Muscles

o   (c) Cardiac Muscles

 

(A) VOLUNTARY MUSCLES

·        Muscles – that move when we want them to move – stop when we decide to stop – called voluntary muscles

·        Example: Muscles in our hand & legs

·        Also called Skeletal muscles – mostly attached to bones – help in body movement

·        Under microscope – these muscles show alternate light & dark bands (striations) – also called Striated Muscles

·        Cells of these tissue – long, cylindrical, unbranched & multinucleate

 

(B) INVOLUNTARY MUSCLES

·        Muscles – cannot move or stop moving when we want to  - involuntary muscles

·        Example: Movement of food in alimentary canal, contraction & relaxation of blood vessels

·        Also called Smooth muscles or Unstriated muscle

·        Also found in Iris of eye, ureters & bronchi of lungs

·        Cells – long with pointed ends (spindle shape), uninucleate

 

(C) CARDIAC MUSCLE

·        Muscles of the heart – show rhythmic contraction & relaxation – throughout life – involuntary muscles – Cardiac muscles

·        Heart muscle cells – cylindrical, branched & uninucleate

(IV) NERVOUS TISSUE

·        Nervous tissue – specialised for receiving & transmitting stimulus very rapidly – from one place to another within the body

·        Brain, Spinal cord & nerves – Nervous Tissue

·        Cells of nervous tissue – Nerve cells or Neurons

 

NEURON

·        Neuron – has cell body with a nucleus & cytoplasm – hair-like parts arise

·        Each neuron  - long part – axon; many short branched parts – dendrites

·        An individual nerve cell – a metre long

 

NERVOUS TISSUE

·        Many nerve fibres – come together by a connective tissue – make a nerve

·        Nerve impulses – allow us to move our muscles when we want to

·        Combination of nerve & muscles – enables the rapid movement in response to stimuli