CBSE Class 9 Biology Tissues Worksheet

Very Short Answer Type Questions

Question. What are areolar tissues’ junctions?
Answer : Areolar tissues are connective tissue found in animals. We can find them between skin and muscles, around blood vessels and nerves, in bone marrow. These tissues fill the space inside the organs. They support internal organs and help to repair tissues.

Question. What are permanent tissues?
Answer : The cells of meristematic tissue lose the ability to divide and get differentiated into specialised cells. These differentiated cells form different types of tissues which are known as permanent tissues. Some examples of permanent tissues are : parenchyma, sclerenchyma, etc.

Question. Where is apical meristem found?
Answer : Growing tips of stems and roots of plants are the main are where apical meristem is present . It helps in increasing the length of the stem and the root.

Question. What is the utility of tissues in multicellular organisms?
Answer : In multicellular organisms, the body system is based on the division of labour( like muscle cells form muscular tissue to which helps in movement ). It means the cells performing a specific function are grouped together to form a particular tissue. The different tissues are organized in a way to provide highest efficiency in functioning of the body.

Short / Long Answer Type Questions

Question. What are the constituents of phloem?
Answer : The constituents of phloem tissue are:
1. Sieve tubes (tubular living cells with perforated end walls)
2. Companion cell (living cells)
3. Phloem parenchyma (living cells)
4. Phloem fibres (non-living and sclerenchyma cells)

Question. What does a neuron look like?
Answer : A neuron consists of a cell body with a nucleus and cytoplasm.
It has two important extension name as axon and dendrites. Each neuron has a single long part, called the axon and many short, branched parts called dendrites. Many nerve fibres bound together by connective tissue to make up a nerve.

Question. What are the functions of areolar tissue?
Answer : Functions of areolar tissue:
1. It fills the space inside the organs, thus acts as a packing tissue between the organs.
2. It supports many delicate organs in the body.
3. It plays role in repair of tissues.
 

Question. How many types of elements together make up the xylem tissue? Name them.
Answer : The following four types of elements make up xylem tissue:
1. Xylem tracheids.
2. Xylem vessels.
3. Xylem parenchyma.
4. Xylem fibres.

Question. Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.
Answer : Differences between parenchyma, collenchyma and sclerenchyma
Parenchyma
These are living cells with thin walls.
Cells are uniformly thin.
The cells are loosely packed with large intercellular spaces.
Collenchyma
These are living cells with slightly thick walls.
Cells are elongated.
The cells are irregularly thickened at the corners with very little intercellular spaces.
Sclerenchyma
These are dead cells with thick cell walls.
Cells are long and narrow.
The cells are thickened due to lignin. These are so thick that there is no internal space inside the cell.

Question. Diagrammatically show the difference between the three types of muscle fibres.
Answer : The three type of muscles fiber are:
1. Streated muscle
2. Smooth muscle
3. Cardiac muscle

Question. Explain the structure of three types of muscle fibres. Also write the locations where they are found in the body.
Answer : The followings are the three types of muscle cells :
1. Unstriated muscles (also known as smooth, involuntary muscles) : This type of muscular tissue consists of spindle-shaped, long uninucleated cells. This type of muscles are present in alimentary canal, blood vessels, iris of eye, in ureters and bronchi of lungs, etc.
2. Striated muscles (also known as voluntary muscles because oftheir function being in our control or will) : This type ofmuscular cells are long multinucleated and enclosed in a membrane called sarcolemma. Each fibre has several longitudinal filaments embedded in cytoplasm. These filaments give these muscles striated appearance. These muscles are attached to the skeleton; so they are called skeletal muscles.
3. Cardiac muscles : These muscles are found in heart. They are not under the control of the will. They contract rhythmically and involuntarily throughout life without the sign of fatigue. Structurally they show the characters of both unstriated and striated muscles. They are made up of branched fibres. These fibres are uninucleated and show alternate light and dark bands (striation).

Question. How many types of meristems are present in plants, on the basis of position?
Answer : On the basis of location of meristem, it is classified into three types :
1. Apical meristem is present at the tip of stem, roots and their branches.
2. Intercalary meristem is found at the leaf base, above the nodes (i.e. at the base of internodes as in grasses) or below the nodes (i.e. at the uppermost region of internode as in mint).
3. Lateral meristem
4. Vascular cambium and cork cambium are the examples of lateral meristem.
5. Vascular cambium is found in vascular bundles while cork cambium is found underneath the bark of trees. Both of these cause increase in girth of plants.

Question. Name the two types of tissues.
Answer : (i) Animal tissues
(ii) Plant tissues

Question. Name two types of plant tissues.
Answer : (i) Permanent tissue
(ii) Meristematic tissue

Question. Explain plant tissue in detail.
Answer : Plant tissue is mainly divided into two categories :
• Meristematic tissue
• Permanent tissue
Meristematic tissue : The cells divide very fast. It helps in the growth of the plants. The shape of the cell is oval, round and polygonal. There is no intercellular space. There are three types of meristematic tissues :
(i) Apical meristem : Growth in length
(ii) Lateral meristem : Growth in breadth or thickness
(iii) Intercalary meristem : Growth in inter-nodes Permanent tissue : When meristematic tissue stops dividing and gets mature, then it forms permanent tissue. There are two types of permanent tissues : (i) Simple tissue (ii) Complex tissue (i) Simple
Tissue : Simple tissues are same in structure and perform the same functions. There are three types of simple
tissues : (a) Parenchyma : It is present in soft parts.
(b) Collenchyma : It provides mechanical strength to plants and is found in stalks.
(c) Sclerenchyma : It provides support as well as flexibility to plants.
(ii) Complex Tissue : They are different in structure but perform the same function in group. There are two
types of complex tissues :
(a) Xylem : It transports water from roots to shoot in plants.
(b) Phloem : Transports foods to all parts of the plant.

Question. Explain epidermis in plants.
Answer : It forms the outermost layer of the plant. It is comprised of a single cell layer. This tissue forms a protective layer for plants and that helps to protect the internal parts of plants. It helps in protection against loss of water, attack by parasitic fungi and mechanical injury. Epidermis has small pores known as stomata. They are small holes or pores on the surface of leaves which help in exchange of gases and also in transpiration. Epidermis has long parts like hair that provide greater surface area for water absorption in roots. In plants found in deserts, epidermis consists of a thick waxy coating called cutin which makes the outer layer water resistant.

Key points to remember for Chapter 6 Tissues 

PLANT TISSUE – Meristematic & Permanent
Meristematic Tissue
These are simple living tissues having thin walled compactly arranged immature cells which are capable of division and formation of new cells.
Main features of Meristematic tissues are :
• Thin primary cell wall made up of cellulose.
• Intercellular spaces are absent.
• 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 e.g., root & shoot tips.
Classification on the Basis of Origin
(A) Primary (Promeristem)
• Derived directly from the meristems of embryo.
• They consist of cells derived from primary meristem.
• They add to primary growth of plants.

(B) Secondary
• Formed by permanent tissues.
• These are having cells derived from primary permanent tissue.
• They usually add to the diameter of plants.

Classification on the Basis of Location
(A) 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.

(B) Intercalary Meristem
• It is present behind the apex.
• It is the part of apical meristem which is left behind
during growth period.
• These are present at the base of leaf & internode region.
• These lead to the increase in the length of leaf (Primary) e.g., in grass stem, bamboo stem, mint stem etc.
(C) Lateral Meristem
• It is also called as secondary meristem.
• It occurs along the sides of longitudinal axis of the plant.
• It gives rise to the vascular tissues.
• Causes growth in girth of stem & root.
• They are responsible for secondary growth.

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.
• In cell differentiation, developing tissue and organs change from simple to more complex forms to become specialized for specific functions.
• The cells of permanent tissue loose the capacity to divide and attain a permanent shape, size and function.
Depending upon the Structure and Composition, the

Permanent tissues are classified into two types :

(A) Simple Permanent Tissues
• These are made up of same type of cells which are similar structurally and functionally.
• They include two types of tissue :
(a) Protective Tissues : These tissues are primarily protective in function. They consist of :
(i) Epidermis
• Epidermis forms one cell thick outermost layer of various body organs of plants such as leaves, flowers, stems and roots.
• Epidermis is covered outside by cuticle. Cuticle is a waterproof layer of waxy substance called as cutin which is secreted by the epidermal cells.
• Cuticle is very thick in xerophytes.
• Cells of epidermis of leaves are not continuous at some places due to the presence of small pores called as stomata.
• Each stomata is guarded by a pair of bean-shaped cells called as guard cells. These are the only epidermal cells which possess chloroplasts, the rest being colourless.

Functions of Epidermis
• The main function of epidermis is to protect the plant from desiccation and infection.
• Cuticle of epidermis cuts the rate of transpiration and evaporation of water and prevents wilting.
• Stomata in epidermis allow gaseous exchange to occur during photosynthesis respiration.
• Stomata also helps in transpiration.
(ii) Cork or Phellem
• In older roots and stems, tissues at the periphery become cork cells or phellem cells.
• Cork is made up to dead cells with thick walls and do not have any intercellular spaces.
• The cell walls in cork deposit waxy substance called as suberin.
• The cells of cork become impermeable to water and gases due to the deposition of suberin.
• The cork cells are without any protoplasm but are filled with resins or tannins.
Functions of Cork :
• Cork is protective in function. Cork cells prevent desiccation, infection and mechanical injury.
• Imperviousness, lightness, toughness, compressibility and elasticity make the cork commercially valuable.
• Cork is used for insulation, as shock absorber in linoleum.
• Cork is used in the making of a variety of sport goods such as cricket balls, table tennis, shuttle cocks, wooden paddles etc.
(b) Supporting Tissues : These are supportive in function and are of three types :

(i) Parenchyma : It is the fundamental tissue.
• Tissue first time evolved in bryophyte.
• Thin walled cells, oval or spherical in structure.
• Cell wall mainly composed of cellulose & pectin.
• Large central vacuole for food & water storage.
• Primary function is food storage.
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 e.g.,
mesophyll of leaves.
• In hydrophytic plants aerenchyma (a type of parenchyma containing air spaces) provides buoyancy.
• Parenchyma provides turgidity to cells.

(ii) Collenchyma : It is the living mechanical tissue.
• Elongated cells with thick corners.
• Localized cellulose & pectin thickening.
• Provides flexibility to plant parts & easy bending of various parts of plant.
• Present only in herbaceous dicot stem.
• 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. They are 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 :
• These are also called grit cells or stone cells.
• These are small cells, where lumen is so small due to higher thickening of cell wall, as present in drup fruit (mango, coconut, walnut) in legume seeds (Macrosclereid).
Fibers :
• They are very long, narrow, thick, lignified cells. Lumen is large as compared to sclereids. Generally 1-3 mm long.
• In the thick walls of both the fibres and sclereids are present thin areas called as pits.
Sclrenchyma Fibres
• These are used in the manufacture of ropes, mats & certain textile fibres.
• Jute and coir are obtained from the thick bundle of fibres.

(B) 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 &m minerals.
• It is also known as conducting or vascular tissue.
• Xylem & phloem together form vascular bundles.
Xylem : 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 :
(i) Tracheids :
• They are elongated angular dead cells (primitive elements) mainly involved in conduction of water and minerals in gymnosperms.
(ii) Vessles : They are advance element (generally found in angiosperms).
• Vessels are cylindrical tube like structures placed one above the other end to end which form a continuous channel for efficient conduction of water.
(iii) Xylem parenchyma :
• They are small & thick walled parenchymatous cells subjected for storage of starch (food).
(iv) 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 element :
(i) Sieve tubes :
• Sieve tubes are slender tube like 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.
(ii) 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.
(iii) Phloem fibre :
• They give mechanical support to sieve tubes.
(iv) Phloem parenchyma :
• They store food and help in radial conduction of food.
• In xylem, only unidirectional movement is possible while in phloem bidirectional movement can occur.
In phloem, except phloem sclerenchyma all elements are living.

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 :
(a) Squamous epithelium : 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) toprevent wear and tear in skin. This pattern is stratified squalors epithelium.
(b) Cubical epithelium :
• They are cube like 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.
(c) 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.
(d) 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.
(a) 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
• Form 55% part of blood. Constitution : 90-91% : water, 7% : protein (Albumin, fibrinogen, globulin), 0.9% : 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.
They are of five types :
Monocytes, Lymphocytes, Basophiles, Neutrophiles, Eosinophils.
Blood platelets or thrombocytes
• They are spindle shaped cells which are involved in clotting of blood.
(b) Skeletal Tissue
It is hard connective tissue that forms supportive framework of the body. It is of two types :

Bone
• Matrix of bone is very hard because of salts such as calcium phosphate,
CaCO 3 (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 harder 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.
(c) Connective tissue
It is the most abundant type of connective tissue. It is further divided into following types :
(i) Yellow fibrous connective tissue
• They are very elastic due to the presence of a network of yellow fibres in its matrix called as ligament which attaches bone to bone.
(ii) White fibrous connective tissue
• They are very little matrix containing abundant white fibres forming layers.
• Bundles of this tissue are called as tendons, which attaches muscles to the bones.
(d) Aerolar tissue :
• It is the most distributed connective tissue in the body.
• This tissue fills spaces inside organs and is found between the skin & muscles, around blood vessels, nerves and in the bone marrow.
(e) Adipose tissue :
• These are oval and round cells, filled with fat globules.
• The cells are called as adipocytes.
• It is found in subcutaneous layer below the skin, around the heart, brain and below the eyeballs. It acts as an insulator and prevents loss of heat from the body.

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
(a) 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.
(b) Cardiac muscle fibres
• They are only involuntary muscles.
• Only found in the walls of heart.
• Their structure is in between the striated and nonstriated muscles.
• They are uninucleated and branched. Branches are united by intercalated disc.
• In these muscles rhythmic contraction and relaxation occurs throughout the life.
(c) Non-striated muscles
• They are involuntary muscles also called as smooth muscles.
• These muscle fibres are uninucleated 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 cyton covered by plasma membrane.
• Short hair like extensions rising from cyton are Dendron which are further subdivided into dendrites.
• Axon is long, tail like cylindrical process with fine branches at the end. Axon is covered by a sheath.

Very Short Answer Type Questions

Question. What do you mean by aerenchyma?
Answer : Aerenchyma is the cell with large air-filled cavities of parenchyma. It helps aquatic plants to float.

Question. Name the tissues which are present in the plants at the nodes.
Answer : Intercalary tissues.

Question. What is the location of stratified squamous epithelium? Also, mention its functions.
Answer : Stratified squamous epitheliums are found in the skin. They are present in layers to prevent wear and tear.

Question. Which tissue is present in the husk of a coconut?
Answer : Sclerenchyma.

Question. Which tissue gives flexibility in plants?
Answer : Collenchyma.

Question. Define tracheids.
Answer : Tracheids have tapering ends and are basically elongated cells.

Question. What is a tissue?
Answer : Group of cells that are similar in structure and are organized together to achieve a particular function is called tissue.

Question. Which tissue makes up the husk of coconut?
Answer : The husk of coconut is made up of sclerenchymatous tissue.

Question. Name the tissue responsible for movement in our body.
Answer : Muscular tissue.

Question. Define the term 'tissue’
Answer : Group of cells that are similar in structure and are organized together to achieve a particular function is called tissue.

Question. What are the functions of the stomata?
Answer : Stomata are essential for gas exchange with the atmosphere and help in transpiration in the form of water vapour through leaves.

Short Answer Type Questions

Question. Mention the types of simple and complex tissues.
Answer : Simple : (i) Sclerenchyma, (ii) Parenchyma, (iii) Collenchyma Complex : (i) Phloem (ii) Xylem

Question. Explain complex tissue in plants.
Answer : Generally, complex tissues consist of more than one type of cell. They are different in structure but together perform the same function.
There are two types of complex tissues :
1. Xylem : It transports water from roots to shoot in plants. The movement is only in one direction that is, from roots to shoot. It provides mechanical support to the plant. It has mostly dead elements. Its elements are tracheids, xylem sclerenchyma, xylem parenchyma, vessel elements.
2. Phloem : Conduct foods to all parts of the plant. The movement of phloem is bidirectional that is, movement in both the directions is possible. Its elements are mostly living. Its elements are sieve tubes, phloem parenchyma, companion cells and intermediary cells. Above given both complex tissues are conductive tissues and form the vascular bundle.

Question. Give one function of each of the following :
(a) Stomata, (b) Root nodules, (c) Cardiac muscle fibres. 
Answer : (a) Exchange of gases in plants.
(b) Root nodules are found in leguminous plants. They harbour bacteria which can fix free atmospheric nitrogen into nitrates and nitrites which plants like pulses can use for protein synthesis.
(c) Cardiac muscles show rhythmic contraction and relaxation throughout life. Because of this heart can pump the blood.

Question. What is the main function of vascular tissue in plants?
Answer : Vascular tissue transport :
(i) Water and dissolved minerals from roots to various parts of the plant (xylem).
(ii) Prepare food material from leaves to different plant parts (phloem).

Question. Give the types of meristematic tissues.
Answer : (i) Intercalary tissue — nodes (ii) Apical tissue — tips of shoot and roots (iii) Lateral tissue — stem sides

Question. Name the types of simple tissues.
Answer : The three main types of simple tissues are:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma

Question. Give three features of cardiac muscles:
Answer : Below are features of cardiac muscles:
1. These are involuntary, show rhythmic contraction and relaxation throughout life.
2. The cells are cylindrical, branched, and uninucleate having faint cross striations.
3. These muscles do not get fatigued under normal conditions.

Question. How are simple tissues different from complex tissues in plants?
Answer :
Simple Tissue
Made up of only one type of cells.
Mainly responsible for mechanical support and storage.
Examples : Parenchyma, collenchyma and sclerenchyma
Complex Tissue
Made up of more than one type of cells.
Mainly responsible for the transport of water, minerals, sugars and other metabolites.
Examples Xylem and phloem.

Question. What are characteristic structural features of meristematic cells?
Ans : Meristematic cells have :
1. Thin cell walls.
2. Abundant or dense cytoplasm and single large nucleus.
3. Spherical, oval, polygonal or rectangular shape.
4. No intercellular spaces between them.
5. Either no vacuoles at all or few vacuoles.

Question. Name the following tissues.
(i) Which tissue covers the external surface in animals?
(ii) Which tissue stores fat in animals?
(iii) Which tissue joins bone to bone?
(iv) Which tissue divides and re-divides and responsible for growth in plants?
Ans : (i) Epithelial tissue
(ii) Adipose tissue
(iii) Ligament
(iv) Meristematic tissue

Question. Write the characteristics of collenchyma.
Ans : The cells in this type of tissue are living, elongated and thickened with cellulose at the corners. There is very little intercellular space. This tissue provides flexibility and mechanical support to plants. This tissue is found in hypodermis of stems and leaf stalks.

Question. What are blood platelets?
Ans : Blood platelets are minute (about 2 to 4 μm in diameter), anucleated, disc like bodies. The main function of platelets is to help in clotting of blood. 

Question. Where is parenchyma tissue present?
Ans : Parenchyma tissue is present below the epidermis.

Question. What is the function of connective tissue?
Ans : Connective tissue connects different tissues and organs. It provides support to different parts of the body by forming packing around different organs of the body.

Question. Describe the structure of sclerenchyma. Write its major functions.
Ans : Sclerenchyma is the chief mechanical tissue of plants. The cells of this tissue are usually long, narrow and pointed at both ends. Due to deposition of lignin their walls are often very highly thickened hence the lumen or cell cavity is nearly obliterated. They are usually provided with simple pits which may be oblique or straight. It provides strength to the plant parts.

Question. Define differentiation.
Ans : The process of taking up permanent size, shape and function of cell is called differentiation.

Question. Why do meristematic cells lack vacuoles?
Ans : Meristematic cells divide frequently to give rise to new cells. So, they need dense cytoplasm and soft cell wall. Vacuoles cause hindrance in cell division as they are full to cell sap and provide turgidity and rigidity to the cell.

Question. There was a paralytic patient, who cannot walk.
(i) Which tissues are responsible for the movement of the body?
(ii) Which tissues are present in spine and brain?
Ans : (i) Muscular and nervous tissues are responsible for the movement of the body.

Question. What is epithelial tissue?
Ans : Epithelial tissue : Epithelial tissue forms covering of entire surface of the body and lines the internal organs, because of this epithelial tissue is called protective tissue. It also forms a barrier to keep different body system separate. In this tissue, cells are closely associated and arranged on a very thin extracellular fibrous basement membrane. Epithelial tissue may be composed of one (simple epithelium) or more layers of cells (compound epithelium).

Question. What are muscular tissue? What is their function?
Ans : This is a specialised tissue which is composed of contractile, fibre-like cell. This tissue is responsible for movement in our body. Function : The movement of the body or limbs is brought about by contraction and relaxation of contractile proteins present in muscle cells.