English Class X Biology Chapter02

8/8/2019 English Class X Biology Chapter02

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Tissues – meaning – Plant tissues & Types – Structure – Function

and importance; Animal tissues – Types, structures – Function andimportance.

You are familiar with unicellular organisms like Amoeba, Paramaecium andEuglena . Do you remember that they exist as free living organisms? The cellbody in these organisms is capable of performing various life processes likeespiration, digestion, excretion and reproduction. But in multicellular organismshe structure of the body is more complex. It consists of groups of cells specialisedor specific functions.

Groups of cells which have a common origin, with similar structure andunction are called tissues.

Tissues exhibit great variety in their structure including shapes of cells,hickness of cellwalls and other characteristics. Different types of tissues togetherake up a particular function and form an organ.

As we go higher up in the ladder of evolution, the body organization in

plants and animals becomes more complex. The body consists of specialisedissues and organs to perform various metabolic activities. Thus, specialisationof the tissues in higher organisms has enabled them to perform life processesmore efficiently. A group of organs performing a set of common functions iscalled an organ system.

The branch of biology which deals with the study of tissues and theirorganization in organs, is called histology.

We shall now study the various plant tissues and animal tissues and findout how they are organised to carry on the various life processes.

2.1 PLANT TISSUES

In an angiosperm plant body there are different types of tissues to performa variety of functions such as growth, protection, absorption, photosynthesis andconduction of water and minerals.

Plant tissues are classified into two major groups on the basis ofdevelopment. They are (1) Meristematic Tissue (2) Permanent Tissues.

2 STUDY OF CELLS - TISSUES



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Plant Tissues

↓

↓ ↓Meristematic Tissues Permanent Tissues

↓

↓ ↓Simple Permanent Tissues Complex Permanent Tissues

↓ ↓

↓ ↓ ↓ ↓ ↓ ↓Parenchyma Collenchyma Sclerenchyma Xylem Phloem Epidermal Tissue

2.11 MERISTEMATIC TISSUE (MERISTEM)Meristematic Tissue is composed of

embryonic cells which keep on dividing

orming new cells. Meristematic tissues occur

n growing regions like root tip, stem apex,

and buds. The meristems located at the

stem tip add to the height of the plant and

ateral meristems add to the girth of the plant

body.

2.12 PERMANENT TISSUES (MATURE

TISSUES)

Permanent tissues are tissues derived

rom meristems. The cells of permanent

issues are specialised for a specific function

and they vary accordingly in size, shape andhickness of cell wall. Permanent tissues are

of two types. They are : (1) Simple permanent

issues (2) Complex permanent tissues.

SIMPLE PERMANENT TISSUES

Simple permanent tissues are composed of cells which are similar in

structure and function. There are three types of simple permanent tissues namely:

1) Parenchyma (2) Collenchyma (3) Sclerenchyma.

Fig 2.1 - Scheme showing types of plant tissues

Meristem

YoungLeaf

Fig 2.2 Longitudinal section of Shoot apexshowing location of meristem



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PARENCHYMA : Parenchyma is a simple tissueound in all the regions in herbs and in soft partsike root, stem, leaf, flower, fruit and seed inshrubs and trees.

The cells in this tissue contain living

protoplasm and are bound by thin cellwalls.Parenchyma is regarded as primary tissue, sincet is found commonly in plants and the cells haveetained the capacity to divide. The cells are least

specialised.

Parenchyma cells may be round, elongated or star shaped. More often,parenchyma cells are loosely arranged and usually carry on functions likeabsorption of water and storing food and water. Parenchyma cells also help in

oining other tissues. The leaves and the other green parts of the plants consistof parenchyma cells and have chloroplasts. These cells take part in photosynthesis.

COLLENCHYMA : Collenchyma tissue consists of cellscontaining living protoplasm and are capable of cell division.The cells are closely packed and thick walled at the cornerswhere the cells join. The cellwall is made up of a substancecalled lignin. The main function is to provide mechanical

support and flexibility to the regions where they occur, suchas the veins of the leaf and stems of young plants. It isound in growing regions where strength is required for theparenchyma tissue.

SCLERENCHYMA : Sclerenchyma tissue consists of thickwalled elongated cells. The living cells of this tissue losenucleus and protoplasm when they are mature. They

become elongated tube-like structures. The hard shells ofseeds and fruits consist of thick-walled cells called sclereids.They are not elongated but short and irregular in shape andare brittle. The cellwall of sclerenchyma cells in plants likephlox, jute and hemp contain elongated thread like thickwalled cells called fibres. The cellwall is made up ofcellulose, hemicellulose and lignin. Since the fibres arelexible and elastic they are used in coir industries to makegunny bags, ropes and also in textile industries. Fibres aremore commonly found associated with xylem and phloem.

Fig 2.3 - Parenchyma

Fig 2.4 - Collenchyma

Parenchymacells

Intercellular

spaces

A

Fig 2.5 - SclerenchymaA. Cells in the tissueB. A fibre in L.S.

B

Cells

Thickenings

Thick cell wallLumen



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COMPLEX PERMANENT TISSUES.

Complex permanent tissues compriseof both living and non-living cells. The cellsare of different kinds and they are closelyarranged. Xylem and phloem are the two

ypes of complex permanent tissues. Sinceboth the tissues transport materials, they areogether called vascular tissues.

XYLEM : Xylem is a vascular tissue whichransports water and mineral salts absorbedby the roots, to all the parts of the plantespecially to the leaves. Hence, it is calledwater conducting tissue. This tissue alsoprovides mechanical strength to the variousparts of the plant body.

Xylem tissue consists of xylemparenchyma, xylem fibres, xylem vesselsand tracheids. xylem parenchyma helps inateral conduction of water and storage ofmetabolic substances. It consists of thin-

walled living cells.Xylem fibres provide mechanical strength

o other tissues. The cells lose protoplasm atmaturity.

Xylem vessels and tracheids consist of aseries of elongated dead cells joined togetherrom end to end forming tube like structures

hat are suitable for conduction of water andsalts.

PHLOEM : Phloem tissue is known as foodconducting tissue, since it transports the foodprepared in the green parts of the plant to allhe other regions.

Phloem tissue is composed of four types

of cells. They are sieve tubes, companion cells,phloem fibres and phloem parenchyma.

Angiosperm plants exhibit tracheids andtrachea in their xylem tissue. Xylem tracheaeor vessels are elongated hollow cells.

Fig 2.6 - Vascular bundle of Sunflower

stem

1. Parenchyma 2 and 4. Xylem vessel.3. Tracheids 5. Cambium 6. Phloem7. Sclerenchyma

Xylem vessel

Tracheid

Fig 2.7 - Conducting elements ofXylem

In gymnosperms phloem does notcontain companion cells or fibres, instead

they have independent sieve cells.



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Sieve tubes play an important role in

he conduction of food. Sieve tubes compriseof longitudinally arranged cells.

The cells are joined end to end in a series.A plate like structure with a number of minute

pores is present between two cells, called sieveplate. The food passes through these pores andhence, the name sieve tube. Cells closelyassociated with sieve tube are called companioncells. They are living cells and are believed tocontrol the passage of food through the phloem.

The phloem fibres provide tensile strength

o the plant body. Jute fibre is an example. Thephloem fibres are of economic importance.

Phloem parenchyma is composed of living cells. They carry on the normalunctions of parenchyma cells.

Xylem and phloem are together arranged in the form of bundles calledvascular bundles. The vascular bundles are arranged in the form of a ring indicots. In monocots they are scattered.

EPIDERMAL TISSUE : The plant body is externally covered by a tissue knownas epidermis. Usually epidermis is covered by a layer of waxy substance calledcutin. It is called cuticle. Cuticleprevents the excessive loss of waterrom the cells. In aquatic plants likeotus, the cuticle is thick. It prevents thedecaying of tissues of leaves and other

parts of the plant.Epidermis protects the inner

issues of the plant just like the skinn animals. Epidermis is modified indifferent parts to perform variousunctions. The root hairs present in theoots are the extensions of epidermal

cells. They are modified to absorb

water and mineral salts from the soil.

Phloem in monocot plants does notcontain parenchyma.

PhloemParenchymacell

Sievetube

Sieve plate

Companion

cell

Fig 2.8 - Phloem in L.S.

Fig 2.9 - Epidermal Tissue with stomata

2. Column shaped palisade cellslie beneath the upper surface:

they are packed withchloroplasts.

3. Pores, called stomata, on thelower surface are flanked bysausage-shaped guard cells.

Guardcell

Stoma

1. The upper and lower surfaceof the leaf are each coveredby a single layer of cells.



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Epidermis of the leaf consists of tiny pores called stomata. Each stomahas a pair of bean shaped cells called guard cells. The guard cells help in closingand opening of the stomata thereby control the rate of transpiration. Innsectivorous plants like Drosera and Nephenthes the epidermal cells in someof the leaves are modified into digestive glands.

2.2 ANIMAL TISSUES

Animal tissues are more complex in structure and function when comparedo plant tissues. We shall now study the major tissues found in the body ofanimals and their functions.

The animal tissues can be broadly classified as follows.

Animal Tissues

↓↓ ↓ ↓ ↓

Epithelial tissue Muscular tissue Connective tissue Nervous tissue

↓ ↓ ↓Unstriped Striped Cardiac

Muscle Muscle Muscle

↓ ↓ ↓ ↓ ↓Simple Stratified Loose Dense Fluid

Epithelial Epithelial Connective Connective Connectivetissue tissue tissue tissue tissue

↓↓ ↓ ↓

Squamous Columnar Cuboidal

Epithelium Epithelium Epithelium

2.21 EPITHELIAL TISSUEYou are familiar with the skin which is the

outer covering of the body. The inner wall of thebody is also lined with a similar tissue. Theseouter and inner layers are made up of a type ofissue called epithelial tissue. The epithetialissue consists of a single layer of cells calledsimple epithelium. If it contains more than one

ayer, it is called stratified epithelium.

Fig 2.10 - Scheme showing types of animal tissues

Fig 2.11a - Squamous epithelium



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Simple epithelium consisting of flat plate likecells is called squamous epithelium. It is foundn the alveoli of lungs, and in oesophagus, inblood vessels, blood capillaries and chambers ofhe heart. This tissue is referred to as endothelium.

t permits materials to diffuse through it.The epithelial tissue containing elongated

cells is called columnar epithelium. It is foundn the inner layer of the stomach, small intestine,pharynx, larynx and oviducts. The mucus secretedby the cells in the stomach protects the wall ofhe stomach from acidic contents and digestiveenzymes. The mucus produced in the intestine

ubricates the passage of food. The epitheliumbearing numerous cilia is called ciliatedepithelium.

Epithelium consisting of cube shaped cellss known as cuboidal epithelium. It forms theining of many ducts such as pancreatic duct,salivary duct and sweat ducts. In many glands like

salivary glands and thyroid gland, cuboidalepithelium is involved in secretion.

FUNCTIONS OF EPITHELIAL TISSUES

. The epithelium forms a thick tough barrier and protects the underlyingtissues in the form of external skin. The epithelium of the skin also helpsin controlling the body temperature constant.

2. The ciliated epithelium helps in the movement of materials.

3. The epithelium cells in glands facilitate secretion.

4. Epithelium helps in absorption of nutrients and excretion.

5. The epithelium in sense organs contain receptor cells.

2.22 MUSCULAR TISSUE

Muscular tissue is concerned with the movements of the body. It is madeup of muscle cells, which appear like fibres. Hence they are called muscle fibres

myofibres). The muscle fibres are specialised cells capable of contraction and

The presence of endothelium

prevents the clotting of blood whenit is flowing in the blood vessels.

Fig 2.11b

ColumnarEpithelium

Fig 2.11cCiliated ColumnarEpithelium

Fig 2.11d - Cuboidal epithelium

The mucus producing cells in theepithelium are called goblet cells.



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elaxation. This property is responsible for movement of limbs and bending ofhe body.

The movements of internal organs like heart, stomach and alimentary canalare caused by muscles. These muscles are not under the control of the animal.Hence they are called involuntary muscles. The muscles of organs like limbs

which are under the control of the animal, are called voluntary muscles.

The muscles are classified into three typesbased on the structure, function and location.They are (1) Unstriped muscles (2) Stripedmuscles (3) Cardiac muscles.

UNSTRIPED MUSCLES : Unstriped muscles are

made up of spindle shaped elongated muscleibres without stripes (cross bands). They are also

called smooth muscles. A number of muscle fibres

are held together by a membrane to form bundles

called muscles. The peristaltic movements of the

oesophagus, intestine and stomach are due to

hese muscles. Smooth muscles are found in the

wall of the body cavity. They are also found in

kidneys, blood vessels and glands.

STRIPED MUSCLES : The muscles which are

made up of elongated unbranched cylindrical

ibres with striations are called striped muscles.

The striped muscles are usually attached to the

bones and hence, are also known as skeletal

muscles. They are voluntary muscles and areesponsible for locomotion.

CARDIAC MUSCLES : The heart is made up of

special type of muscles called Cardiac muscles.These muscle fibres are striped and branched.The branches are connected with one another ina criss-cross form. They are involuntary muscles.They do not fatigue easily. They are responsible

or the continuous heart beat throughout one’s life.

The muscles can contract nearly100 times per second, when aperson is doing hard work.

Fig 2.12(a) Unstriped muscles

Fig 2.12(b) Striped muscles

Fig 2.12(c) Cardiac muscles



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Physical exercises and games are necessaryo keep the muscles in good working condition.Hard work not only strengthens the muscles butalso intensifies the rate of respiration and bloodcirculation. Activities like yoga, sports and gamescombine pleasure with muscular activity. Theseactivities keep a person active and mentally alertwith a sense of well being.

2.23 CONNECTIVE TISSUES

The tissues which connect various other tissues of the body and providesupport are called connective tissues. They occur in all parts of the body.

Connective tissues basically consist of cells and fibres enclosed in a ground

substance. The non-living substances like fibres and other materials surroundinghe living cells form the matrix. It may be soft or hard or liquid. The connectiveissues are identified on the basis of the nature of the matrix and classifiednto three types. They are (1) Loose connective tissues (2) Dense connectiveissues (3) Fluid connective tissues.

LOOSE CONNECTIVE TISSUES : The tissue in which the fibres in the matrixare loosely arranged is called loose connective tissue. The areolar tissue, adiposeissue and reticular tissue are included under this group.

AREOLAR TISSUE : Areolar tissue is foundbelow the skin. The fibres are loosely connectedwith one another. Air spaces are found in betweenhe fibres. Hence, it is called areolar tissue. Itbinds the other tissues and provides a framework. The nutrients and oxygen present in theblood pass through areolar tissue and reach otherissues. It consists of a particular type of cells

which engulf bacteria and foreign bodies thatenter the body. They also digest toxic substancesand destroy them. Thus, they help in body

defence.

ADIPOSE TISSUE : The tissue consists of closely packed fat cells. The cells

are surrounded by fine reticular fibres. This tissue stores nutrients which are

used as and when the body requires. It also provides insulation against cold

and protects the body like a shock absorber.

The human heart beats 65 times perminute on an average. In 70 yearstotal number (70 x 365 x 24 x 60 x65) of beats will be 2391480000. Themost wonderful pump ever! Help thesemuscles to serve you for life time.Avoid smoking, obesity, and using

saturated fats in the diet.

Matrix of connective tissue containscalcium phosphate, collagen, proteinsand elastin.

Fig 2.13 Areolar Tissue



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RETICULAR TISSUE : Tendons are made up of

ibrocytes and collagen fibres. Reticular tissue provides

ramework for important organs such as liver, spleen,

bone marrow, tonsils and mucous membrane lining in

he respiratory tract and alimentary canal. It consists

of reticular fibres.

TENDONS AND LIGAMENTS : Tendons attach the

muscles to the bones or cartilage. Ligaments consist

of elastic fibres. They connect one bone to another. They

help in the movement of bones.

DENSE CONNECTIVE TISSUE : The connective tissues consisting of hard matrix

are called dense connective tissues. The cells are embedded in a dense matrix.The major functions of dense connective tissues are :

. They form the skeletal system of the body providing an internal supporting

frame work.

2. They enclose the internal organs. The skull protects the brain, ears, eyes,

nose and other organs in the face.

The rib cage protects heart and lungs. The vertebral column protects the

spinal cord. The organs of digestion, excretion, reproduction and many other

organs in the abdomen are protected by the pelvic girdle and limbs are provided

with support.

The dense connective tissues are of two types, namely cartilage and bone.

CARTILAGE TISSUE : Cartilage takes up different

unctions depending on the type of matrix. The ‘C’

shaped cartilage rings in the trachea, bronchi and thecartilage in the rib cage help in their movement by

binding the surrounding organs. The cartilages present

n larynx, epiglottis, wall of the eustachian tube and

pinna contains elastic fibres in the matrix. They are

elastic and flexible. The cartilages found in between

he vertebrae in the vertebral column chiefly contains

collagen fibres. They bring about bending and stretching movements.

Fig 2.14 Adiposeconnective tissue

Fig 2.14(a) Fibrous Cartilage



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BONE TISSUE : The bone tissue is the mostabundant skeletal material found in the body. Aarge part of the body weight is due to the boneissue.

The bone tissue consists of cells embedded

n a firm calcified matrix. The matrix chieflyconsists of collagen fibres, proteins and inorganicsalts like calcium phosphate, chlorides ofpotassium, sodium and magnesium. The structureof the bone is designed to withstand stress andstrain. The long and strong bones of the limbsare filled with a fluid called bone marrow. whichconsists of fat and blood vessels. It producesblood cells.

FLUID CONNECTIVE TISSUES : The blood andhe lymph are the liquid connective tissues of thebody. They have a fluid matrix.

BLOOD TISSUE : You have studied the detailsof composition and functions of blood in yourprevious class. Let us study blood as a connective

issue.

The fluid matrix of the blood tissue is calledplasma. The red blood cells, white blood cells andplatelets are found floating in it. The liquid natureof the plasma facilitates easy transport of thevarious substances from one part of the body toanother.

The red blood cells are involved in supplyingoxygen to every cell in the body. They also removecarbondioxide from the cells and transport it tohe lungs.

The white blood cells help in body defenceand are of different types. Some of them destroyhe bacteria and enable the body to fight againstnfections.

The platelets are tiny cell fragments whichbring about the clotting of blood.

Fig 2.14(b) Elastic Cartilage

Fig 2.15(c) Bone - T.S.

Note this :

1. The longest bone in the humanbody is the thigh bone calledFemur.

2. The middle ear bones are thesmallest bones.

3. Bone consists of 30% organicsubstances, collagen fibres andglycoprotein. 70% is made upof salts out of which 85% iscalcium phosphate.

The red pigment haemoglobin inRBC absorbs oxygen andbecomes oxyhaemoglobin.



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LYMPH TISSUE : Lymph is a colourless fluid similar to blood in structure. When

he blood passes through capillaries, only red blood cells can squeeze into the

capillaries. The rest of the fluid is called lymph tissue. Lymph enters another

set of capillaries known as lymphatic capillaries. These capillaries form lymph

glands or lymph nodes.

The composition of lymph is similar to that of blood except that it doesnot contain red blood cells and proteins. The lymphatic vessels empty lymph

nto the circulatory system. Lymph produces antibodies which form an essential

part of immune system of the body. It contains a type of white blood cells

phagocytes) which remove bacteria and foreign bodies from the tissues.

2.24 NERVOUS TISSUE

Irritability is one of the basic characteristicsof living organisms. This property is very well

developed in nervous tissue. The nervous tissue

esponds to external and internal stimuli of the

body. It transmits nerve impulses from all parts

of the body to nerve centres very quickly and

brings back the responses.

The structural and functional unit of nervousissue is the ‘nerve cell’ or neuron. Observe the

igure 2.16. The part consisting of a prominent

nucleus is the cell body. The short brush like

structures arising from the cell body are called

dendrites. The long extension of the cell body is

he axon. The axon ends in a bunch of branches.

The axon is covered by a fatty sheath called

myelin sheath.

Dendrites carry the impulses towards the

cell body. Axons carry the messages away from

he cell body. There is a tiny gap between two

successive neurons. This gap is known as synapse.

The impulses are transmitted from the axon of

one neuron to the dendrite of another neuron

across the synapse through chemical substances.

The fastest nerve impulses inhumans travel at 8 metres persecond

Dendrite

Nucleus

Axon

Myelin Sheath

Nerve ending

Cell body

Fig 2.16 - Structure of a Neuron



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A number of neurons held together by a sheath form thread like structurescalled nerve fibres. Several neurons together form knot like structures calledganglia.

The human nervous system consists of brain, spinal cord and nerve fibres.t is highly developed. The thinking power, reasoning, imagination, will power,

memory and such other special qualities of man are due to the highly evolvednervous system especially the brain. You will study more about this in a laterchapter.

After studying this chapter you will ....

. recognise the importance of various types of tissues in plants and animalsrespectively.

2. relate the structures and functions of different types of tissues.

3. draw sketches showing the important features of various types of tissues.

4. explain the important characteristics of various plant and animal tissues.

Activities

. Observe the permanent slide of various types of plant and animal tissueunder microscope in the laboratory.

2. Prepare models to show the structures of various type of tissues that you

have studied.

3. Collect information on how various types of plants tissues are useful toman.

EXERCISES

. Choose the most appropriate answer and fill in the blanks

1. The study of tissues is called ....................

a) cytology b) embryology c) histology d) pathology

2. The long extension from the cell body of neuron is known as ............

a) dendrite b) axon c) cilia d) flagellum

3. The xylem tissue consists of ....................

a) tracheids b) sclereids c) sieve plates d) sieve tubes

4. In animal fat is stored in ................

a) areolar tissue b) cartilage tissue c) adipose tissued) reticular tissue



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I. Answer the following questions :

1. What is a tissue?

2. Where is the meristem located in plants?

3. What is the main function of collenchyma?

4. Name four fibre-yielding plants.

5. Why are xylem and phloem called vascular tissues?

6. What are tracheids?

7. What is the main function of epidermal tissue?

8. Name the different cells present in phloem.

9. Mention the three types of simple epitherial tissues in animals.

10. Point out the special features of cardiac muscle.

11. What is the function of areolar tissue?

12. Explain briefly the structure of bone tissue.

13. How does lymph tissue protect the body?

14. Draw a neat labelled diagram of the following.

a) Stoma b) Neuron

15. Differentiate the following

a) Bone and cartilage b) Ligament and tendon

16. Why does the body store fat?

English Class X Biology Chapter02

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