TISSUE

TISSUE

TISSUE: A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.

PLANT TISSUES

→ Most of the tissues in plants are supportive, which provides them with structural strength.

→ These tissues are dead, since dead cells can provide mechanical strength as easily as live ones, and need less maintenance.

→ Plant Tissues are of two types Meristematic & Permanent tissues.

1. Meristematic Tissue: These are simple living tissues having thin walled compactly arranged cells which are capable of division and formation of new cells.

→ Intercellular spaces are absent (compact tissue).

→ Generally, vacuoles are absent, dense cytoplasm & prominent nuclei are present.

→ Large numbers of cell organelles are present.

→ Active metabolic state, stored food is absent.

→ Actively dividing cells are present in growing regions of plants, example: root & shoot tips.

Classification of Meristematic Tissues

• Apical Meristem: It is present at the growing tips of stems and roots. Cell division in this tissue leads to the elongation of stem & root, thus it is involved in primary growth of the plant.

• Intercalary Meristem: These are present at the base of leaf & internode region. These lead to the increase in the length of leaf (Primary), example: in grass stem, bamboo stem, mint stem etc.

• Lateral Meristem: It occurs along the sides of longitudinal axis of the plant. It gives rise to the vascular tissues and causes growth in girth of stem & root.

2. Permanent Tissue

→ The permanent tissues are composed of those cells which have lost their capability to divide.

→ They have definite shape, size and thickness. The permanent tissue may be dead or living.

→ The division & differentiation of the cells of meristematic tissues give rise to permanent tissues.

→ The cells of permanent tissue lose the capacity to divide and attain a permanent shape, size and function.

Permanent tissues are classified into two types on the basis of Structure and Composition i.e. Simple Permanent Tissues and Complex Permanent Tissues.

Simple Permanent Tissues: These are made up of same type of cells which are similar structurally and functionally.

(i) Parenchyma

→ Large central vacuole for food & water storage.

→ Primary function is food storage.

→ Parenchyma provides turgidity (swollen structure) to cells.

→ Some parenchyma involved in excretory substance storage are so called as idioblast, storing such as resin, tannin, gums & oils.

→ In typical parenchyma chlorophyll is absent. Chloroplast containing parenchyma tissue are chlorenchyma which perform photosynthesis.

→ In hydrophytic plants aerenchyma (a type of parenchyma containing air spaces) provides buoyancy.

(ii) Collenchyma

→ It is the living mechanical tissue.

→ Elongated cells with thick corners.

→ Provides flexibility to plant parts & easy bending of various parts of plant.

→ Present at thin margin of leaves.

→ Few chloroplasts may be present.

→ Gives mechanical strength & elasticity to the growing stems.

(iii) Sclerenchyma (Scleras–hard) Strengthening tissue.

→ Composed of extremely thick-walled cells with little or no protoplasm.

→ Cells are dead & possess very thick lignified walls. Lignin is water-proof material.

→ Intercellular spaces are absent.

Cells of sclerenchyma are of two types Sclereids and Fibres.

 

Difference between Parenchyma, Collenchyma and Sclerenchyma

Features	Parenchyma	Collenchyma	Sclerenchyma
Cell shape	Isodiametric cells which are oval, spherical or polygonal in shape.	Circular, oval or polyhedral.	Variable in shape. Fibres and sclereids.
Cell wall	Thin cellulosic cell wall.	Uneven thickening on their cell wall.	Lignified secondary cell wall present.
Cytoplasm	Abundant	Present	Absent
Nucleus	Present (Living tissue)	Present (Living tissue)	Absent (Dead tissue)
Vacuoles	Large vacuole	Vacuolated	Absent
Intercellular spaces	Present	Absent	Absent
Occurrence	Basically, packing tissue, all soft part of plant-pith, cortex, medullary rays.	Dicot stems, petiole and beneath the epidermis. Absent in monocot and roots.	Dicot hypodermis, bundle sheath, pericycle, seed, pulp of fruits.
Functions	Food storage, photosynthesis.	Provide tensile strength, mechanical support, photosynthesis.	Protection from stress and strain, mechanical strength.

 

Complex Permanent Tissues

→ It consists of more than one type of cells which work together as a unit.

→ It helps in transportation of organic materials, water & minerals.

→ It is also known as conducting or vascular tissue.

→ Xylem & phloem together form vascular bundles.

 

Xylem
→ It is also known as wood and is a vascular and mechanical tissue.

→ Thick-walled cells are found in the form of tubular passages.

→ Xylem consists of four types of cells called as elements Tracheid, Vessels, xylem parenchyma and xylem sclerenchyma.

1.     Tracheid: They are elongated angular dead cells (primitive elements) mainly involved in conduction of water and minerals.

2.     Vessels: They are advance element. Vessels are cylindrical tubelike structures placed one above the other end to end which form a continuous channel for efficient conduction of water.

3.     Xylem parenchyma

→ They are small & thick-walled parenchymatous cells subjected for storage of starch (food).

4.     Xylem sclerenchyma

→ Thy are non-living fibres with thick walls and narrow cavities provide mechanical support.

→ Except xylem parenchyma all other xylem elements are dead.

→ The annual rings present in the trunk of a tree are xylem rings.

→ By counting the number of annual rings, we can determine the age of a tree.

Phloem

→ They also consist of both parenchymatous and schlerenchymatous cells.

→ Phloem consists of four types of elements which are Sieve tubes, Companion cells, Phloem fibre and Phloem parenchyma.

1.     Sieve tubes

→ Sieve tubes are slender tubelike structures made up of elongated, thin-walled cells placed end to end.
→ The end walls of sieve tube cells are perforated by numerous pores, called as sieve plates.

→ Nucleus of sieve cell degenerates at maturity. However, cytoplasm persists, because of protoplasmic continuation of sieve tube with companion cell through plasmodesmata.

→ Sieve cells possess slime protein or protein which is concerned with growth and repair of sieve cells.

2.     Companion cells

→ Companion cells have dense cytoplasm and prominent nuclei.

→ Sieve cells & companion cells are so called sister cells because they originate from single mother cell.

3.     Phloem fibre

→ They give mechanical support to sieve tubes.

4.     Phloem parenchyma

→They store food and help in radial conduction of food.

5.     Leptome

→ Main part of phloem involved in conduction of food, which is sieve tube.

→ In xylem, only unidirectional movement is possible while in phloem bidirectional movement can occur.

→ In phloem, except phloem sclerenchyma all elements are living.

 

 

Features	Xylem	Phloem
Cells: Living/dead	Dead	Living
Cell walls: Thickness	Thick	Thin
Material	Lignin	Cellulose
Permeability	Impermeable	Permeable
Cross walls	None	Sieve plates
Cytoplasm	None	Yes
Function	Carries water and salts	Carries sugars
Direction of flow	Upwards	Down and up
Special features	Fibres	Companion cells

 

 

 

ANIMAL TISSUES

Epithelial Tissue

→ Always grows on some other types of tissue.

→ Cells of epithelium are set very close to each other and the tissue rests on a non-cellular basement membrane.

→ Consists of single layer of cells.

→ Blood vessels are absent and non-nervous in nature.

→ It covers all the organs and lines the cavities of hollow organs like stomach.

→ It is primarily protective in function.

Types of Epithelium

→ Epithelium tissues are classified as Squamous epithelium, Cubical epithelium, Columnar epithelium and Ciliated epithelium.

 

(i) Squamous epithelium:

→ It is also called pavement epithelium.

→ Cells arranged end to end like tiles on a floor.

→ Cells are polygonal in surface view.

→ It forms the delicate lining of cavities (mouth, oesophagus, nose, pericardium, alveoli etc.) blood vessels and covering of the tongue and skin.

→ Epithelial cells are arranged in many layers (stratum) to prevent wear and tear in skin. This pattern is stratified squalors epithelium.

 (ii) Cubical epithelium

→ They are cubelike cells that fit closely, cells look like squares in section, but free surface appears hexagonal.
→ It is found in kidney tubules, thyroid vesicles & in glands (salivary glands, sweat glands).

→ It forms germinal epithelium of gonads (testes & ovaries).

→ It involves in absorption, excretion & secretion. It also provides mechanical support.

 (iii) Columnar epithelium

→ Columnar means ‘pillar-like’ epithelium. It forms lining of stomach.

→ Small intestine & colon, forming mucous membranes.

→ Border of micro villi is present at the free surface end of each cell which increases absorption efficiency in small intestine.

(iv) Ciliated epithelium

→ Cells may be cubical or columnar.

→ On its free surface are present protoplasmic outgrowths called cilia.

→ It helps in the movement of ova in the fallopian tube.

Connective Tissue

→ The cells of the connective tissue are widely spaced and embedded in an intercellular matrix.

→ The mature of matrix decides the function of tissue.

→ White and yellow fibres are present in the matrix.

→ Their basic function is to provide support to different organs & keeping them in place.

(i) Fluid or vascular tissue

• Blood and lymph: Blood is a connective tissue, fluid matrix of blood is plasma having wandering or floating cells, called corpuscles, blood helps in the transportation of various materials such as nutritive substances, gases, excretory products, hormones etc.

• Plasma: It forms 55% part of blood. It constitutes of 90-91% of water, 7% of protein (Albumin, fibrinogen, globulin), 0.9% of inorganic salt etc.

• Corpuscles: Forms 45% part of blood.

• RBCs: They are also called as erthyrocytes, containing red coloured respiratory pigment called haemoglobin that helps in transportation of oxygen.

• WBCs (Leucocytes)

→ They are also called as ‘Soldiers of the body’.

→ They are irregular, amoeboid, phagocyte cells that protect our body by engulfing bacterial & other foreign particles.

• Blood platelets

→ They are spindle shaped cells which are involved in clotting of blood.

(ii) Skeletal Tissue

→ It is hard connective tissue that forms supportive framework of the body.

→ It is of two types: Bone and Cartillage.

• Bone

→ Matrix of bone is very hard because of salts such as calcium phosphate, CaCO₃ (60-70%) etc. and a protein ossein.
→ Bone cells (osteoblasts) are embedded in this hard matrix.

→ Matrix is deposited in the form of concentric layers of lamellae formed round a central canal, the done cells occupy small spaces between the concentric layers of matrix.

→ The long bones are usually hollow containing cavity called as marrow cavity. It is full of bone marrow.

 • Cartilage

→ This tissue is elastic, less hard as compared to bones.

→ Elasticity is due to presence of chondrin (protein). Cells are called as chondroblast, which are widely spaced and matrix is reinforced by fibres.

→ It occurs at joint of bones, in the nose, ear, trachea & larynx.

→ It provides flexibility and great tensile strength.

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 Muscular Tissue are Striated muscles, cardiac muscle fibres and Non-striated muscles.

(i) Striated muscles

→ They are also called as voluntary muscles because these are under the control of one’s will.

→ Muscle fibres or cells are multinucleated and unbranched.

→ Each fibre is enclosed by thin membrane which is called as sarcolemma.

→ Cytoplasm is called as sarcoplasm.

→ These muscles get tired and need rest.

 (ii) Cardiac muscle fibres

→ They are only involuntary muscles.

→ Only found in the walls of heart.

→ Their structure is in between the striated and non-striated muscles.

→ They are unnucleated and branched. Branches are united by intercalated disc.

→ In these muscles rhythmic contraction and relaxation occurs throughout the life.

(iii) Non-striated muscles

→ They are involuntary muscles also called as smooth muscles.

→ These muscle fibres are unnucleated and spindle shaped.

→ They are not enclosed by membrane but many fibres are joined together in bundles.

→ Such muscles are found in the walls of stomach, intestine, urinary bladder, bronchi, iris of eye etc.

→ Peristaltic movements in alimentary canal are brought about by smooth muscles.

 Nervous Tissue

 

 → They are highly specialized tissue due to which the animals are able to perceive and respond to the stimuli.

→ Their functional unit is called as nerve cell or neuron.

→ Cell body is called cyton which is covered by plasma membrane.

Dendron: Short hairlike extensions rising from the cell body are Dendron which are further subdivided into dendrites.
Axon
→ Axon is long, tail like cylindrical process with fine branches at the end.

→ Axon is covered by a sheath.

→ Axon of one neuron is very closely placed to the dendrons of another neuron to carry impulses from one to another neuron in the form of electrochemical waves.

→ This close proximity is called as synapse.