NCERT Exemplar Class 9 Science Chapter 6 Tissues

NCERT Exemplar Class 9 Science Chapter 6 Tissues are part of NCERT Exemplar Class 9 Science. Here we have given NCERT Exemplar Class 9 Science Solutions Chapter 6 Tissues.

NCERT Exemplar Class 9 Science Solutions Class 9 Science Chapter 6 Tissues

Multiple Choice Questions

Question 1.
Which of the following tissues has dead cells?
(a) Parenchyma
(b) Sclerenchyma
(c) Collenchyma
(d) Epithelial tissue
Solution:
(b) Sclerenchyma is a simple permanent tissue comprising of dead cells. The cells are long and narrow with lignified cell walls. The cells of sclerenchyma are closely packed without any intercellular spaces. Sclerenchyma tissue is present in stems (around the vascular bundles), roots, veins of leaves, hard covering of seeds and nuts etc. Besides, cells of surface layers in stratified epithelium are dead, but this tissue does not has both dead and living cells unlike sclerenchyma.

Question 2.
Find out incorrect sentence.
(a) Parenchymatous tissues have intercellular spaces.
(b) Collenchymatous tissues are irregularly thickened at corners.
(c) Apical and intercalary meristems are permanent tissues.
(d) Meristematic tissue, in its early stage, lacks vacuoles.
Solution:
(c) Apical and intercalary meristems are not permanent tissues but they are meristematic tissues which remain in continuous state of division. These tissues differentiate to give rise to the permanent tissues.

Question 3.
Girth of stem increases due to
(a) apical meristem
(b) lateral meristem
(c) intercalary meristem
(d) vertical meristem.
Solution:
(b) Lateral meristem occurs on the sides almost parallel to the long axis of the root, stem and its branches. It is responsible for an increase in girth of the stem, i.e. secondary growth.

Question 4.
Which cell does not have perforated cell wall?
(a) Tracheids
(b) Companion cells
(c) Sieve tubes
(d) Vessels
Solution:
(b) Companion cells are narrow, elongated, thin-walled, living cells. They lie on the sides of the sieve tubes and are closely associated with them through plasmodesmata. Companion cells do not possess perforated cell walls.

Question 5.
Intestine absorbs the digested food materials. What type of epithelial cells are responsible for that?
(a) Stratified squamous epithelium
(b) Columnar epithelium
(c) Spindle fibres
(d) Cuboidal epithelium
Solution:
(b) Columnar epithelium consists of pillar-like cells that are much taller than wide. The nuclei are generally elongated along the long axis of cells. It lines the stomach, intestine and gall bladder. Columnar epithelium of intestine is specialised for the absorption of water and digested food.

Question 6.
A person met with an accident in which two long bones of hand were dislocated. Which among the following may be the possible reason?
(a) Tendon break
(b) Break of skeletal muscle
(c) Ligament break
(d) Areolar tissue break
Solution:
(c) It may be ligament break because ligaments serve to bind the bones together. A ligament is an elastic connective tissue which has great strength.

Question 7.
While doing work and running, you move your organs like hands, legs etc. Which among the following is correct?
(a) Smooth muscles contract and pull the ligament to move the bones.
(b) Smooth muscles contract and pull the tendons to move the bones.
(c) Skeletal muscles contract and pull the ligament to move the bones.
(f) Skeletal muscles contract and pull the tendon to move the bones.
Solution:
(d) Skeletal muscles or striated muscles are found in the body wall and the limbs (biceps and triceps of arms, legs). The contraction and relaxation of these muscles are under the control of organism, so they are also called voluntary muscles. These are attached to the bones by tendons. When they contract, they pull the tendon to move the bones and help in the movement of limbs.

Question 8.
Which muscles act involuntarily?
(i) Striated muscles
(ii) Smooth muscles
(iii) Cardiac muscles
(iv) Skeletal muslces
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Solution:
(b) The muscles which are not under the control of our will, are called involuntary muscles. Smooth (unstriated) muscles and cardiac muscles are involuntary muscles.

Question 9.
Meristematic tissues in plants are
(a) localised and permanent
(b) not limited to certain regions
(c) localised and dividing cells
(d) growing in volume. .
Solution:
(c) Meristematic tissues are groups of living cells which are localised at specific parts in the plant body and divide continuously to add new cells.

Question 10.
Which is not a function of epidermis?
(a) Protection from adverse condition
(b) Gaseous exchange
(c) Conduction of water
(d) Transpiration
Solution:
(c) Epidermis is the outermost layer of cells covering a plant. Its function are principally to protect the plant from injury or adverse conditions and to reduce water loss. It also helps in gaseous exchange and transpiration as it possesses stomata. Conduction of water occurs by xylem which is a complex permanent tissue.

Question 11.
Select the incorrect sentence.
(a) Blood has matrix containing proteins, salts and hormones.
(b) Two bones are connected with ligament.
(c) Tendons are non-fibrous tissue and fragile.
(d) Cartilage is a form of connective tissue.
Solution:
(c) Tendons are white fibrous connective tissues having great strength and join skeletal muscles with bones.

Question 12.
Cartilage is not found in
(a) nose
(b) ear
(c) kidney
(d) larynx.
Solution:
(C) Cartilage is a soft skeletal tissue (a type of connective tissue) which has widely spaced cells. The solid matrix is composed of proteins and sugar. Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx.

Question 13.
Fats are stored in human body as
(a) cuboidal epithelium
(b) adipose tissue
(c) bones
(d) cartilage.
Solution:
(b) Adipose (connective tissue) is primarily a fat storing tissue in which the matrix is packed with large, spherical or oval fat cells (or adipocytes). Each fat cell contains a large fat globule. The adipose tissue is found beneath the skin, in the covering of the heart, around the blood vessels and kidneys and in yellow bone marrow. This tissue stores fat and insulates the body against heat loss.

Question 14.
Bone matrix is rich in
(a) fluoride and calcium
(b) calcium and phosphorus
(c) calcium and potassium
(d) phosphorus and potassium.
Solution:
(b) Bone is a very strong and non- flexible vertebrate connective tissue which forms the framework that supports the body. The bone matrix contains both inorganic and organic substances. The inorganic salts present in the matrix are mainly phosphates and carbonates of calcium and magnesium e.g. calcium phosphate, calcium carbonate, magnesium phosphate etc.

Question 15.
Contractile proteins are found in
(a) bones
(b) blood
(c) muscles
(d) cartilage.
Solution:
(c) Muscular tissue consists of muscle fibres and is responsible for movement in the body. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.

Question 16.
Voluntary muscles are found in
(a) alimentary canal
(b) limbs
(c) iris of the eye
(d) bronchi of lungs.
Solution:
(b) Refer to answer 7.

Question 17.
Nervous tissue is not found in
(a) brain
(b) spinal cord
(c) tendons
(d) nerves.
Solution:
(c) The nervous tissue, which contains densely packed nerve cells, called neurons (Gk. neuro = nerve), is present in the brain, spinal cord and nerves. The neurons are specialised for conduction of nerve impulses. Tendon is a type of connective tissue.

Question 18.
Nerve cell does not contain
(a) axon
(b) nerve endings
(c) tendons
(d) dendrites.
Solution:
(c) A nerve cell or neuron comprises of three parts
(i) Cyton or cell body which contains nucleus and cytoplasm with characteristic deeply stained particles called Nissl’s granules.
(ii) Dendrons which are short processes arising from the cyton and further branching into dendrites.
(iii) Axon which is a single, long cylindrical process and forms fine branches terminally (axon endings).

Question 19.
Which of the following helps in repair of tissue and fills up the space inside the organ?
(a) Tendon
(b) Adipose tissue
(c) Areolar
(d) Cartilage
Solution:
(c) Areolar connective tissue is the most widely distributed connective tissue is animal’s body. It is found between the skin and muscles, around blood vessels and nerves, and in the bone marrow. It fills the space inside the organs, supports internal organs and helps in repair of tissues.

Question 20.
The muscular tissue which function through-out the life continuously without fatigue is
(a) skeletal muscle
(b) cardiac muscle
(c) smooth muscle
(d) voluntary muscle.
Solution:
(b) Cardiac muscles are found in the wall of the heart and in the wall of large veins (e.g. pulmonary veins and superior vena cava) where these veins enter the heart. Cardiac muscle fibres are richly supplied with blood vessels and they never get fatigued.

Question 21.
Which of the following cells is found in the cartilaginous tissue of the body?
(a) Mast cells
(b) Basophils
(c) Osteocytes
(d) Chondrocytes
Solution:
(d) Chondrocytes are the cells present in the cartilaginous tissue. These cells produce and maintain the cartilaginous matrix.

Question 22.
The dead element present in the phloem is
(a) companion cells
(b) phloem fibres
(c) phloem parenchyma
(d) sieve tubes.
Solution:
(b) Phloem is a complex permanent tissue of vascular plants which conducts organic food material from leaves to different plant parts. Phloem consists of four types of component viz. sieve tubes, companion cells, phloem parenchyma and phloem fibres. Out of all these components only the phloem fibres are dead and the remaining ones are living.

Question 23.
Which of the following does not lose their nucleus at maturity?
(a) Companion cells
(b) Red blood cells
(c) Vessel
(d) Sieve tube cells
Solution:
(a) Companion cells are narrow, elongated, thin walled, living cells. They have dense cytoplasm and a prominent nucleus. Red blood cells of mammals, vessels (xylem elements) and sieve tube cells (phloem elements) lose their nuclei at maturity.

Question 24.
ln desert plants, rate of water loss gets reduced due to the presence of
(a) cuticle
(b) stomata
(c) lignin
(d) suberin.
Solution:
(a) Cuticle is the continuous waxy layer that covers the aerial parts of a plant. Composed mainly of cutin, it is secreted by the epidermis and its primary function is to prevent water loss.

Question 25.
A long tree has several branches. The tissue that helps in the sideways conduction of water in the branches is
(a) collenchyma
(b) xylem parenchyma
(c) parenchyma
(d) xylem vessels.
Solution:
(b) Xylem (a complex permanent tissue) is the chief conducting tissue of vascular plants responsible for conduction of water and inorganic solutes. The tissue is composed of four kinds of cell: tracheids, vessels (or tracheae), xylem parenchyma and xylem fibres. Vessels and tracheids help in long distance vertical conduction of water and minerals from the roots to different parts of the shoot system. The main stem along with all of its branches are all supplied with water and mineral by mean by xylem vessels and tracheids. Radial conduction i.e., sideways conduction of water occurs by xylem parenchyma.

Question 26.
If the tip of sugarcane plant is removed from the field, even then it keeps on growing in length. It is due to the presence of
(a) cambium
(b) apical meristem
(c) lateral meristem
(d) intercalary meristem.
Solution:
(d) Intercalary meristem is present at the base of intemodes or at the base of nodes and at the base of leaves. This meristem brings about elongation (growth in length) of the part of the plant in which it is present. So even if the tip of the sugarcane plant is removed i.e. apical meristem is removed, it keeps on growing in length due to the activity of intercalary meristem.

Question 27.
A nail is inserted in the trunk of a tree at a height of 1 metre from the ground level. After 3 years the nail will
(a) move downwards
(b) move upwards
(c) remain at the same position
(d) move sideways.
Solution:
(c) The nail will remain at the same position after 3 years, but will appear to have sunk into the tree. This is because of the secondary growth of the tree which increases the girth of a tree. The increase in height of the plant will occur due to primary growth which occurs only in the regions of the apical meristems i.e. at the tips of the main stem or branches. As increase in height of the tree takes place from top only, therefore the nail will remain at the same position as it is inserted near the ground level.

Question 28.
Parenchyma cells are
(a) relatively unspecified and thin walled
(b) thick walled and specialised
(c) lignified
(c) none of these.
Solution:
(a) Parenchyma is a living, simple permanent tissue which consists of relatively unspecified cells with thin walls. The cells contain intercellular spaces. Parenchyma tissue stores food, nutrients, water and performs many other functions.

Question 29.
Flexibility in plants is due to
(a) collenchyma
(b) sclerenchyma
(c) parenchyma
(d) chlorenchyma.
Solution:
(a) Collenchyma is a living, simple permanent tissue which is present below the epidermis in petiole, leaves and stems of herbaceous dicots e.g. sunflower, tomato etc. Collenchyma provides flexibility to the plant parts and allows their easy bending without breaking. Cells of this tissue are elongated, irregularly thickened at the comers with very little intercellular spaces.

Question 30.
Cork cells are made impervious to water and gases by the presence of
(a) cellulose
(b) lipids
(c) suberin
(d) lignin.
Solution:
(c) Cork is the outermost layer of an old woody stem which comprises of dead cells with no intercellular spaces. The cell walls of cork cells are deposited with suberin which makes them impervious to water and gases.

Question 31.
Survival of plants in terrestrial environment has been made possible by the presence of
(a) intercalary meristem
(b) conducting tissue
(c) apical meristem
(d) parenchymatous tissue.
Solution:
(b) Xylem and phloem are the complex permanent tissues which constitute a vascular bundle. Vascular or conducting tissue is a distinctive feature of higher plants, which has made their survival possible in terrestrial environment as .they make it possible for plants to survive without being surrounded with water.

Question 32.
Choose the wrong statement.
(a) The nature of matrix differs according to the function of the tissue.
(b) Fats are stored below the skin and in between the internal organs.
(c) Epithelial tissues have intercellular spaces between them.
(d) Cells of striated muscles are multinudeate and unbranched.
Solution:
(c) Epithelial tissues form the covering or protective tissues in the animal body. The cells of this tissue are tightly packed and form a continuous sheet. They have only a small amount of cementing material between then and almost no intercellular space.

Question 33.
The water conducting tissue generally present in gymnosperm is
(a) vessels
(b) sieve tube
(c) tracheids
(d) xylem fibres.
Solution:
(c) Xylem tissue of gymnosperms lacks the vessels and comprises of tracheids, fibres and parenchyma. Thus, the main water conducting tissue of gymnosperms is xylem tracheid. Sieve tubes translocate food material.

Short Answer Type Questions

Question 34.
Animals of colder regions and fishes of cold water have thicker layer of subcutaneous fat. Describe why?
Solution:
A thick layer of subcutaneous fat functions as an insulating coat that prevents heat loss from the body and helps to keep the body of the animal warm in colder environment. Moreover, fat also functions as reserve food during the periods of scarcity.- Thus, animals of colder regions and fish of cold water have thicker layer of subcutaneous fat.

Question 35.
Match the column (A) with the column (B).Match the column (A) with the column (B).
imageee
Solution:
(a) (v)
(b) (iv)
(c) (iii)
(d) (i)
(e) (ii)

Question 36.
Match the column (A) with the column (B).Match the column (A) with the column (B).
imageee
(a) (i)
(b) (ii)
(c) (iv)
(d) (iii)
(e) (v)

Question 37.
If a potted plant is covered with a glass jar, water vapours appear on the wall of glass jar. Explain why?
Solution:
In a potted plant, transpiration occurs through the stomata present on the surface of leaves. When a potted plant is covered with a glass jar, water vapours released by transpiration condense and appear as water droplets on inner walls of glass jar.

Question 38.
Name the different components of xylem and draw a living component.
Solution:
Different components of xylem are tracheids, vessels, xylem parenchyma and xylem fibres. Xylem parenchyma is the only living component of xylem whose diagram is drawn below:

Question 39.
Draw and identify different elements of phloem.
Solution:
Different elements of phloem are sieve tubes, companion cells, phloem fibres and phloem parenchyma. Different phloem elements are shown in the following diagram:

Question 40.
Write true (T) or false (F).
(a) Epithelial tissue is protective tissue in animal body.
(b) The lining of blood vessels, lung alveoli and kidney tubules are all made up of epithelial tissue.
(c) Epithelial cells have a lot of intercellular spaces.
(d) Epithelial layer is permeable layer.
(e) Epithelial layer does not allow regulation of materials between body and external environment.
Solution:
(a) T
(b) T
(c) F – Epithelial cells have almost no intercellular spaces.
(d) T
(e) F – Due to its permeability, epithelial layer plays an important role in regulating exchange of materials between body and external environment.

Question 41.
Differentiate between voluntary and involuntary muscles. Give one example of each type.
Solution:
Voluntary muscles are the muscles which are under the control of our will e.g. skeletal muscles. Muscles present in our limbs (arms and legs) are skeletal muscles and can be moved by our conscious efforts. not under the control of our will, e.g., smooth muscles and cardiac muscles. Muscles present in stomach, intestine etc. are smooth muscles and muscles present is our heart are cardiac muscles, which cannot be moved by our conscious efforts.

Question 42.
Differentiate the following activities on the basis of voluntary (V) or involuntary (I V) muscles.
(a) Jumping of frog
(b) Pumping of the heart
(c) Writing with hand
(d) Movement of chocolate in your intestine
Solution:
(a) V
(b) IV
(c) V
(d) IV

Question 43.
Fill in the blanks.
(a) Lining of blood vessels is made up of _____.
(b) Lining of small intestine is made up of _____.
(c) Lining of kidney tubules is made up of _____.
(d) Epithelial cells with cilia are found in_____ of our body.
Solution:
(a) squamous epithelium
(b) columnar epithelium
(c) cuboidal epithelium
(d) respiratory tract

Question 44.
Water hyacinth floats on water surface. Explain
Solution:
Water hyacinth (Eichhornia crassipes) is a free-floating aquatic plant which possesses aerenchyma in its spongy petiole. Aerenchyma consists of a network of which enclose very large air cavities. These air cavities store gases, making the plant light and help it to float on the surface of water.

Question 45.
Which structure protects the plant body against the invasion of parasites?
Solution:
Epidermis is a layer of parenchymatous cells that forms the outermost covering of plant body. Epidermis consists of compactly arranged cells without any intercellular spaces. On the aerial plant parts, it secretes a thick, waxy, water-resistant layer called cuticle on its outer surface. These features .make the epidermis protective against loss of water, mechanical injury and the invasion of parasites.

Question 46.
Fill in the blanks.
(a) Cork cells possess _____ on their walls that makes them impervious to gases and water.
(b) _____ have tubular cells with perforated walls and are living in nature.
(c) Bone possesses a hard matrix composed of _____and _____.
Solution:
(a) suberin
(b) Sieve tubes
(c) inorganic, organic substances

Question 47.
Why is epidermis important for the plants?
Solution:
Epiderms is important for the plants as it performs the following important functions :

1. It protects the internal tissues from mechanical injuries.
2. It acts as a water-resistant layer and checks loss of water by transpiration.
3. It protects the plant against invasion of parasitic microorganisms.
4. It bears stomata on leaves and on young stems, which help in exchange of gases during photosynthesis and respiration. Stomata also act as sites of transpiration.
5. Root hairs arising from the epidermis of roots help in absorption of water and minerals from the soil.

Question 48.
Fill in the blanks.
(a) ______ are forms of complex tissue.
(b) ______ have guard cells.
(c) Cells of cork contain a chemical called ______.
(d) Husk of coconut is made of ______ tissue.
(e) ______ gives flexibility to plants.
(f) ______ and ______ are both conducting tissues.
(g) Xylem transports ______ and ______ from soil.
(h) Phloem transports ______ from ______ to other parts of the plant.
Solution:
(a) Xylem and phloem
(b) Stomata
(c) suberin
(d) sclerenchyma
(e) Collenchyma
(f) Xylem; phloem
(g) water; minerals
(h) food; leaves

Long Answer Type Questions

Question 49.
Differentiate between sclerenchyma and parenchyma tissues. Draw well labelled diagrams.
Solution:
Differences between parenchyma and sclerenchyma are as follows:

	Parenchyma	Sclerenchyma
(i)	Cells are thin walled with cellulosic cell walls.	Cella are thick walled with lignified cell walls.
(ii)	It is made up of living cells.	It is made up of dead cells.
(iii)	Cells are usually loosely packed with large intercellular spaces.	No intercellular spaces occur between the cells
(iv)	It is primarily a storage tissue and stores nutrients and water in stem and roots.	It is primarily a mechanical tissue and provides mechanical strength to the plant part It is primarily a storage tissue and stores nutrients and water in stem and roots.
(v)	Some cells contain chlorophyll and form chlorenchyma and perform photosynthesis Other cells have large air cavities and form aerenchyma which provides buoyancy to the hydrophytic plants.	The cells are long and narrow, make the plant hard and stiff. The tissue is present in the stem around vascular bundles, in veins of leaves and hard covering of seeds and nuts.

Question 50.
Describe the structure and function of different types of epithelial tissues. Draw diagram of each type of epithelial tissue.
Solution:
Types of Epithelial Tissue: Depending upon the shape and function of the constituent cells, epithelial tissues are of following types:

• Squamous (cells flattened)
• Columnar (cells tall, columnar or pillar¬like)
• Cuboidal (cells cube-like)
• Ciliated (cells with cilia)
• Glandular (cells secretory in nature)
• Stratified (cells many layered)

Squamous epithelium: The cells in this epithelium are extremely thin and flat and are arranged edge to edge forming a delicate lining or covering. It forms the lining of cavities of ducts and blood vessels, lines the chambers of the heart, covers the skin, and lining of the mouth. It also lines pharynx, oesophagus, anal canal, vagina and lower part of urethra. It provides protection to the underlying parts against abrasion (mechanical injury) and entry of germs or chemicals. It also helps in excretion, gas exchange and secretion of coelomic fluid.
Columnar epithelium: This epithelium consists of cells which are much longer than broad; and look like a column. It forms the lining of stomach and intestines; also found in salivary glands in the mouth, sweat glands and oil glands of the skin. It also lines mammary gland ducts and parts of urethra. It helps in protection, absorption and secretion. Columnar epithelium of intestine is specialised for the absorption of water and digested food.
Cuboidal epithelium: Cells are as long as broad and appear cube-like; a centrally located nucleus is present. The cuboidal epithelium * lines the small salivary ducts, pancreatic ducts, sweat glands, salivary glands and thyroid glands. It also covers the ovaries and lines the sperm-producing tubules. It helps in protection, secretion, absorption, excretion and gamete formation.
Ciliated epithelium: This epithelium, usually consisting of cuboidal or columnar cells, has numerous, thin, delicate, hair-like projections called cilia arising from the outer free surface of the cells. It is found lining the wind-pipe (trachea), kidney tubules, oviducts (Fallopian tubes) and ventricles of the brain. This epithelium helps in the movement of mucus, urine, eggs, sperms and cerebrospinal fluid in a particular direction.
Glandular epithelium: This epithelium consists of columnar cells modified to secrete chemicals. It lines the glands such as gastric glands, pancreatic lobules, intestinal glands, etc.
Stratified epithelium: This is a compound epithelium in which cells are arranged in many layers one above the other. It is found in places where there is much wear and tear, such as the epidermis of skin, lining of the mouth cavity.

Question 51.
Draw well labelled diagrams of various types of muscles found in human body.
Solution:
The three main types of muscular tissues found in human body are :
(i) Skeletal (striated) muscle tissue
(ii) Smooth (Non striated) muscle tissue
(iii) Cardiac muscle tissue.
The well labelled diagrams of these tissues are as follows:

Question 52.
Give reasons for:
(a) Meristematic cells have a prominent nucleus and dense cytoplasm but they lack vacuole.
(b) Intercellular spaces are absent in sclerenchymatous tissues.
(c) We get a crunchy and granular feeling, when we chew pear fruit.
(d) Branches of a tree move and bend freely in high wind velocity.
(e) It is difficult to pull out the husk of a coconut tree.
Solution:
(a) Meristematic cells have a prominent nucleus and dense cytoplasm because they are metabolically highly active and are in continuous state of division. Meristematic cells lack vacuole because they do not store food material, waste material, sap etc.
(b) Sclerenchyma cells have lignified cell walls which makes them compact and leaves no intercellular spaces.
(c) Pear fruit contains sclerenchymatous stone cells or sclereids which provide gritty texture to the fruit. Thus, when we chew pear fruit, we get a crunchy and granular feeling.
(d) Collenchyma tissue present in the branches of a tree provides flexibility to them and allows their easy bending without breaking. Thus the branches move and bend freely in high wind velocity.
(e) The husk of a coconut is made up of sclerenchymatous fibres which consist of compactly arranged cells with thick lignified cell walls and no intercellular spaces. So, they are tightly joined together. Thus, it is difficult to pull out the husk of a coconut.

Question 53.
List the characteristics of cork. How are they formed? Mention their role.
Solution:
Cork covers the old stems of woody trees. Characteristics of cork are as follows:

1. Cells of cork are dead at maturity.
2. These cells are compactly arranged.
3. Cells do not possess intercellular spaces.
4. Cells possess a chemical substance suberin in their walls.
5. They are several layers thick.
6. Cork is impervious to gases and water.

As plants grow older, a strip of secondary lateral meristem (called cork cambium) develops in the cortical region. It cuts cells towards both outer and inner sides. Gradually, this secondary tissue replaces the epidermal layer of the stem. This forms the several layer thick cork.
Role of cork is as follows:

1. It protects the internal tissues from mechanical injury and from parasitic attack.
2. It contains small pores (called lenticels) for gaseous exchange.
3. It provides mechanical strength.

Question 54.
Why are xylem and phloem called complex tissues? How are they different from one other?
Solution:
Both xylem and phloem consist of more than one type of cells, which coordinate to perform a common function. Therefore, they are called complex tissues. Differences between xylem and phloem are:

	Xylem	Phloem
(i)	Xylem consists of tracheids, vessels, xylem, parenchyma and xylem fibers.	Phloem consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres.
(ii)	It transports water and minerals vertically from soil to aerial parts of the plant.	It transports food from leaves to other parts of the plant and from storage parts to other parts
(iii)	Most of the components of xylem except xylem parenchyma are dead cells.	Most of the components of phloem except phloem fibres are living cells.

Question 55.
(a) Differentiate between meristematic and permanent tissues in plants.
(b) Define the process of differentiation.
(c) Name any two simple and two complex permanent tissues in plants/
Solution:
(a) Differences between meristematic and permanent tissues are :

	Meristematic tissue	Permanent tissue
(i)	Cells of this tissue divide throughout their life.	Cells of this tissue lose the ability to divide to take up specific function.
(ii)	Meristematic tissues are located at specific regions of the plant e.g. apical meristem is located in apices (tips) of roots and shoots, etc.	Permanent tissues are distributed throughout the plant body.
(hi)	Cells of this tissue are very active, have dense cytoplasm, thin walls and prominent nuclei. They lack vacuoles.	Cells of this tissue are vacuolated, vary in shape and size. Their cell walls may be thin or thick.
(iv)	Cell wall of the cells is cellulosic.	Cells wall may be made up of cellulose or lignin or suberin.
(v)	Cells of this tissue are living.	Cells of this tissue may be living (parenchyma) or dead(sclerenchyma).
(vi)	Intercellular spaces are absent in cells.	Intercellular spaces may be present or absent.

(b) Differentiation can be defined as the phenomenon of transformation of unspecialised cells into specialised cells by the loss of ability to divide and by taking up permanent shape, size, structure and function.
(c) Simple permanent tissues in plants are parenchyma, collenchyma and sclerenchyma. Complex permanent tissues in plants are xylem and phloem.

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