NCERT Exemplar Solutions Class 9 Science Tissues

Multiple Choice Questions (MCQs).........................

Question 1: Which of the following tissues has dead cells?

(a) Parenchyma                            

(b) Sclerenchyma

(c) Collenchyma                             

(d) Epithelial tissue

Answer 1:  (b) Sclerenchyma. 

Plants have sclerenchyma cells, which are permanent tissues. They are made up of dead cells and provide the plant with toughness and stiffness. This tissue can be found in stems around vascular bundles, leaf veins, and the hard coverings of seeds and nuts.

For example, the husk of a coconut is made up of sclerenchyma tissues. Due to lignin, sclerenchyma cells are long, thin, and thickened.

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 tissues, in its early stage, lack vacuoles.

Answer 2:  (c) Apical and intercalary meristems are permanent tissues. 

Plants do not have intercellular spaces because parenchyma acts as a packing tissue. Collenchyma tissues are mechanical tissues in plants that are distinguished by cellulose deposition at the cell's corners, resulting in localized thickenings of the cell wall.

The apical and intercalary meristems, which are known as meristematic tissues, carry primary growth (increase in height) and secondary growth (increase in diameter) respectively. Meristematic tissue is a form of plant tissue that has dense cytoplasm and a large nucleus, but few or no vacuoles.

Question 3:  Girth of stem increases due to

(a) apical meristem                                 

(b) Lateral meristem

(c) vertical meristem                             

(d) Intercalary meristem 

Answer 3:  (b) lateral meristem.

Because of lateral meristematic tissues, the stem's girth grows. They are found as thin layers underneath the bark (cork cambium) and in the vascular bundles of dicot roots and stems (vascular cambium). Secondary growth refers to the expansion of the plant's diameter and girth.
The apical meristem can be found at the rising tips of stems, roots, and leaf apices. They cause elongation, or an increase in the plant's height (primary growth). The intercalary meristem, which is found at the base of the leaf and internode, causes an organ to grow longer.

Question 4: Which cell does not have perforated cell wall?

(a) Tracheids                                           

(b) Companion cells

(c) Sieve tubes                                         

(d) Vessels

Answer 4: (b) Companion cells.

Water is transported through xylem elements such as tracheids and vessels. They are long tube-like structures with partially or fully dissolved walls that serve as water pipes (in vessels) and water-conducting pits in cell walls (in tracheids). Sieve tubes, also known as sieve plates, are slender tube-like structures with multiple pores perforated into their end walls. They are phloem elements, and they are the key food conductors. Companion cells are sieve tube supporting units with various mitochondria and ribosomes.

Question 5: Intestine absorb the digested food materials. What type of epithelial cells is responsible for that?

(a) Stratified squamous epithelium                             

(b) Columnar epithelium

(c) Spindle fibres                                                               

(d) Cuboidal epithelium

Answer 5:  (b) Columnar epithelium.

Columnar epithelium is made up of pillar-like cells with nuclei at the bottom. They form the mucous membrane that lines the stomach, small intestine, and colon. Absorption (e.g., bladder, intestine) and secretion are their primary functions (e.g., mucous by goblet cells).
The stratified squamous epithelium, also known as pavement epithelium, is covered by keratin, a fibrous protein. This epithelium is waterproof and mechanically immune. Kidney tubules, thyroid vesicles, and glands all have cuboidal epithelium.

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

Answer 6:  (c) Ligament break.

Dislocation of a joint happens when the ligaments that hold the joint together separate abnormally. As a consequence, ligaments will split and cause bone dislocation. Areolar tissue connects the skin to the tissues, fills gaps inside organs, and surrounds muscles, blood vessels, and nerves. As a result, they are unconcerned with bones.
Tendon rupture can result in inflammation and is caused by a variety of factors such as age, body weight, diet, sports, and so on.

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
(d) Skeletal muscles contract and pull the tendon to move the bones

Answer 7:  (d) Skeletal muscles contract and pull the tendon to move the bones. 

Because of the inclusion of alternating dark and light bands, skeletal muscles are striped, voluntary muscles. They are named voluntary because they operate at our request. Skeletal muscles contract and pull the tendon (which attaches muscles to bones) to move the bone when working or moving.

Question 8: Which muscles act involuntarily?

(i) Striated muscles                             

(ii) Smooth muscles

(iii) Cardiac muscles                           

(iv) Skeletal muscles

(a) (i) and (ii)                                             (b) (ii) and (iii)

(c) (iii) and (iv)                                          (d) (i) and (iv) 

Answer 8:  (b) (ii) and (iii).

The smooth muscles that line the insides of hollow visceral organs are called smooth muscles. They don't function in accordance with our wishes. They help with peristaltic movements in the gastrointestinal tract and the male genital tract. The heart contains cardiac muscles. They contract and relax at a rapid, rhythmic, and unending rate. They assist in the circulation of blood to different parts of the body. Smooth and cardiac muscles function involuntarily, while skeletal and striated muscles move in response to our will and are thus voluntary.

Question 9:  Meristematic tissues in plants are

(a) localized and permanent                   

(b) Not limited to certain regions

(c) localized and dividing cells               

(d) Growing in volume

Answer 9:  (c) localized and dividing cells.

Meristematic tissues are found in the developing regions of plants, such as the tips of roots and stems, and are made up of actively dividing cells. Meristematic tissue cells are circular, oval, polygonal, or rectangular in shape. They have thin cellulose walls, thick cytoplasm, and prominent nuclei, and are packed tightly without intercellular spaces. Since these cells are fully packed with sap, vacuoles are almost non-existent.

Question 10:  Which is not a function of epidermis?

(a) Protection from adverse condition                           

(b) Gaseous exchange

(c) Conduction of water                                                      

(d) Transpiration

Answer 10:  (c) Conduction of water. 

The epidermis is the outermost layer of the plant's body, including leaves, buds, stems, and roots. It is encased in cuticle (a waterproof layer of waxy substance cutin).
The epidermis' primary function is to protect the plant from dehydration and infection. In fact, the epidermis cuticle aids in reducing water loss through evaporation from the plant surface, as well as preventing pathogen entry (bacteria, fungi etc.). Many plants have cutinized hair (trichomes) on their aerial surfaces to minimize transpiration.

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.

Answer 11:  (c) Tendons are non-fibrous tissue and fragile.

Tendons are cord-like structures that connect skeletal muscles to bones. They are heavy and inelastic.

A tendon is a white fibrous tissue that is strong but not very flexible. It is made up of rows of fibroblasts in between parallel bundles of collagen fibres (called tendinocytes).

Question 12: Cartilage is not found in

(a) nose                   

(b) ear                      

(c) kidney                

(d) larynx

Answer 12:  (c) kidney.           

Cartilage is a form of connective tissue that is compact, and devoid of blood vessels. The chondroblasts (cartilage cells) are widely spaced, and the matrix is reinforced by fibres. Cartilage can be found in the nose, ear, trachea, and larynx, as well as at the joints of bones. It aids in the smoothing of the joint surface. It provides body parts with support and versatility.

Question 13:  Fats are stored in human body as

(a) cuboidal epithelium                         

(b) adipose tissue

(c) bones                                                       

(d) cartilage

Answer 13:  (b) adipose tissue. 

Adipose tissue is made up of a matrix of oval and circular cells filled with fat globules. This tissue can be located under the skin, in the yellow bone marrow, and between internal organs. It functions as an insulator and stores fat.

The cuboidal epithelium supports in absorption, excretion, and secretion, whereas bones and cartilage are specialized connective tissue that protect the internal organs.

Question 14: Bone matrix is rich in

(a) fluoride and calcium                        

(b) calcium and phosphorus

(c) calcium and potassium                    

(d) phosphorus and potassium

Answer 14: (b) calcium and phosphorus. 

Bone cells are encased in a tough matrix that is reinforced by fibres and hardened by calcium and phosphorus salts. The matrix is laid down in concentric layers of lamellae that form a Haversian canal in the middle. The bone cells occupy small spaces between the concentric layers of matrix.

Question 15:  Contractile proteins are found in

(a) bones                         

(b) blood                  

(c) muscles              

(d) cartilage

Answer 15: (c) muscles.

Muscles contain contractile proteins, which are involved in the movement of the body or limbs. Movement of limbs, internal organs, and other body parts is caused by the contraction and relaxation of contractile proteins found in muscles.
The endoskeleton of a vertebrate body is made up of bones, which are the major supporting tissues.

Blood is a fluid connective tissue that transports oxygen, nutrients, hormones, and other substances, as well as generating antitoxins and antibodies.

Cartilage supports and flexes body parts while also smoothing the surface of joints.

Question 16:  Voluntary muscles are found in

(a) alimentary canal                                

(b) limbs

(c) iris of the eye                                        

(d) bronchi of lungs

Answer 16: (b) limbs.

Voluntary muscles are those that we have full control over, such as those that function and move our limbs. Involuntary muscles, on the other hand, are regulated rhythmically by the hypothalamus, such as the alimentary canal, iris of the eye, and bronchi of the lungs.

Question 17:  Nervous tissue is not found in

(a) brain                   

(b) spinal cord                     

(c) tendons                       

(d) nerves

Answer 17:  (c) tendons. 

Tendons are the connective tissue that connects skeletal muscles to bones, so they are devoid of nervous tissue. Nervous tissue is designed to carry signals in our bodies. Nerve cells, also known as neurons, are highly specialized unit cells. They can receive stimuli from both within and outside the body, as well as conduct (send) impulses (signals) to various parts of the body. The brain and spinal cord are all made up of nervous tissue and are involved in the regulation of body function.

Question 18: Nerve cell does not contain

(a) axon               

(b) nerve endings                     

(c) tendons                

(d) dendrites

Answer 18: (c) tendons.             

There are three parts of each nerve cell or neuron.

i)        Cyton or cell body - It has a central nucleus and cytoplasm with Nissl's granules, which are deeply stained particles (i.e., clumps of ribosome).

ii)       Dendron -These are short processes that begin in the cyton and branch out into dendrites.

iii)     Axon - Axon is a single long cylindrical process with a uniform diameter that terminates in fine branches. The dendrite receives impulses from the cell body, while the axon sends them away.

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

Answer 19:  (c) Areolar. 

Areolar tissue is a cellular connective tissue that is loose. Its matrix is made up of two types of fibres: white collagen fibres (which turn into gelatin when heated in water) and yellow elastic fibres (also known as elastin). The matrix also contains a variety of abnormal cells (e.g., fibroblasts) that can engulf bacteria and prevent infection (e.g., macrophages).

Question 20:  The muscular tissue which function throughout the life continuously without fatigue is
(a) skeletal muscle                                     (b) cardiac muscle
(c) smooth muscle                                     (d) voluntary muscle

Answer 20: (b) cardiac muscle.

Cardiac muscles have both smooth and striated muscle features. The muscles in this group are striated, cylindrical, branched, and involuntary. These muscles have densely stained cross bands called intercalated discs in addition to the light and dark bands.

These serve as stimulants. Cardiac muscles contract and relax quickly, rhythmically, and incessantly during a person's life, from infancy to death. Voluntary muscles, such as skeletal muscles, are under our influence and function in response to our needs.

Smooth muscles, also known as striated, visceral, or involuntary muscles, can be located in the walls of hollow tubular organs such as the alimentary canal, gland ducts, urogenital ducts, and blood vessels, with the exception of the heart. Slow contractions occur, but they last a long time.

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

Answer 21:  (d) Chondrocytes. 

Collagen fibres and chondrocytes form a delicate network in the matrix of cartilage (living cells). Lacunae are fluid-filled spaces that contain these. Chondrocytes help cartilage expand internally by multiplying by mitosis.

Mast cells are granulocytes that live in a variety of tissues. It contains histamine and heparin-rich granules. They play an important role in allergy, as well as wound healing and pathogen protection.

Basophils are white blood cells (WBCs) that act as granulocytes in the body's defence system, engulfing bacteria and other foreign substances.

Bone cells are called osteoclasts.

Question 22:  The dead element present in the phloem is

(a) companion cells                                

(b) phloem fibres

(c) phloem parenchyma                          

(d) sieve tubes 

Answer 22:  (b) phloem fibres. 

Phloem fibres are dead cells with a thick walled, elongated spindle form and a narrow lumen. They offer the tissue mechanical support. Phloem parenchyma is a type of parenchyma with thin walls and living cells. Storage and lateral food conduction are two of their features.

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  

Answer 23:   (a) Companion cells. 

Companion cells can be found all along the sieve tube and are linked to them through plasmodesmata. These cells are metabolically active, and sieve tube elements depend on them; they do not lose their nucleus when they reach maturity. At maturity, RBC vessels and sieve tube cells lose their nucleus.

Question 24:  In desert plants, rate of water loss gets reduced due to the presence of

(a) cuticle                

(b) stomata              

(c) lignin                  

(d) suberin

Answer 24:  (a) cuticle.

Epidermal cells of leaves, young shoots, and other aerial parts produce cuticles, a protective, hydrophobic waxy covering. It reduces pathogen entry and minimizes water loss through transpiration (with the help of stomata).

Lignin hardens the cell wall and gives it flexibility, tensile strength, and compression strength. Suberin is found in cork cells and makes them water resistant.

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 

Answer 25:  (b) xylem parenchyma.

A row of cells positioned end to end forms xylem parenchyma, which are very long tube-like structures. To form continuous water channels, the transverse walls between these cells are partially or fully dissolved.

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 

Answer 26:  (d) intercalary meristem.

Apical meristem is located in the apices of growing roots and stem, removing the tip of a sugarcane plant also removes the apical meristem.

Intercalary meristems are found at the base of leaves or nodes, and they cause organs like leaves and internodes to grow longer.

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 

Answer 27:  (c) remain at the same position. 

Even after three years, a nail placed at a height of one metre from the ground in the trunk of a tree remains at the same position. It does not travel upwards because the apical meristem, which is responsible for growth (length), is only present in the apices, and the lateral meristem, which is responsible for increased girth, has no effect on length.

Question 28:  Parenchyma cells are
(a) relatively unspecified and thin walled
(b) thick walled and specialized
(c) lignified
(d) None of the above

Answer 28:  (a) relatively unspecified and thin walled. 

The parenchyma cells make up the majority of the plant's body. Its cells are alive, and they have the ability to divide. The cells are rounded or isodiametric, meaning that they have an equal amount of space on both sides. The cells have a thin cell wall and are oval, circular, polygonal, or elongated in form. It contains a thick cytoplasm that covers a large central vacuole and contains a small nucleus.

Question 29:  Flexibility in plants is due to

(a) collenchyma             

(b) sclerenchyma                        

(c) parenchyma             

(d) chlorenchyma

Answer 29: (a) collenchyma. 

Collenchyma is made up of living cells that are distinguished by the presence of cellulose.

Collenchyma is a mechanical tissue that provides mechanical support and elasticity to young dicotyledonous stems. It gives the organs in which it is located great tensile strength and flexibility. It permits easy bending of various parts of a plant, especially young growing stems, without breaking them.

Question 30: Cork cells are made impervious to water and gases by the presence of

(a) cellulose           

(b) lipids                   

(c) suberin               

(d) lignin

Answer 30:  (c) suberin. 

Cellulose is the most essential component of a plant's cell wall. Cellulose makes up almost every organism's cell wall, while lipids and a few proteins make up the plasma membrane's essential components.  The plasma membrane is semipermeable to water but not fully impervious to it.

Lignin is a complex polymer that hardens the cell wall and serves as cement. It gives the cell wall stability, great tensile and compressional strength, and makes it impermeable. It's only found in sclerenchyma cells, not cork cells. Suberin is an organic compound that thickens the walls of cork cells. These cells are impervious to water and gases because of the presence of Suberin.

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 

Answer 31: (b) conducting tissue.

Plant conducting tissues conduct various saps and have various structures.

Plant xylem and phloem are the main conducting tissues. Water is transported from the roots to other parts of the plant via xylem, while food and other materials are transported from the leaves to other parts of the plant via phloem.

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 multinucleate and unbranched.

Answer 32:  (a) The nature of matrix differs according to the function of the tissue.

The structure of matrix varies depending on its function; for example, cartilage contains calcium salts because it supports bones, while muscles pass contractile proteins for movement.

Question 33:  The water conducting tissue generally present in gymnosperm is

(a) vessels                     

(b) sieve tube                         

(c) tracheids                       

(d) xylem fibres

Answer 33:  (c) tracheids. 

The presence of tracheids as the primary conducting tissue distinguishes gymnosperms. These are dead cells with lignified walls that are elongated. They don't have open ends like the vessels and conduct water.

Short Answer Type Questions........................

Question 34:  Animals of colder regions and fishes of cold water have thicker layer of subcutaneous fat. Describe why?

Answer 34:    Subcutaneous fat, also known as adipose tissue, is found beneath the skin's surface or between internal organs. It acts as a good insulator because it is a poor conductor of heat. It regulates body temperature by reducing heat loss from the body.

Question 37:  If a potted plant is covered with a glass jar, water vapours appear on the wall of glass jar. Explain why?

Answer 37:    Because of the presence of tiny pores called stomata, the epidermis of a leaf is not continuous in all areas. A pair of specialized epidermal cells or two kidney-shaped cells known as guard cells surrounds each stoma. The stomatal opening is formed by the concave sides of these guard cells facing each other.

During photosynthesis and respiration, the stoma allows for gaseous exchange. Water vapour escapes through stomatal openings during transpiration, resulting in the presence of water vapour on the glass jar wall if a potted plant is coated with it.

Question 38:  Name the different components of xylem and draw a living component?

Answer 38:    The xylem consists of four distinct types of cells or components.

(a) Tracheids                     

(b) xylem vessels

(c) xylem fibre                     

(d) xylem parenchyma

The living part of xylem is xylem parenchyma. Living cells with a cellulose cell wall are known as xylem parenchyma cells. Water storage and radial conduction are the functions of the xylem parenchyma.

(a) Cross-section of xylem tissue
(b) Xylem parenchyma cells (living) 

Question 39:  Draw and identify different elements of phloem.

Answer 39:    The different elements of phloem 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.

Answer 40:

(a) True                   

(b) True                 

(c) False (In epithelial cells, intercellular spaces are virtually nonexistent.)                 

(d) True                  

(e) False (Because of its permeability, the epithelial layer controls the exchange of materials between the body and the external world.)

Question 41:  Differentiate between voluntary and involuntary’ muscles. Give one example of each type.

Answer  41:   
Voluntary muscles - The voluntary muscles are so named because they can be regulated by our willpower. Our own conscious control regulates the functions carried out by voluntary muscle cells, such as leg or arm movement by striated muscles.

Involuntary muscles - Our conscious muscles have no control over our subconscious muscles. The hypothalamus regulates the activities of these muscles, for example, cardiac muscles regulate heartbeat.

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

Answer 42:
(a) Frog jumping is a voluntary muscle movement that is regulated by skeletal muscles.

(b) Heart pumping is an Involuntary, i.e., it is regulated by cardiac muscles

(c) Using the hand to write is a voluntary muscle movement.

(d) Chocolate movement in your intestine is caused by involuntary muscles.

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.

Answer 43:
(a) squamous epithelium
(b) columnar epithelium
(c) cuboidal epithelium
(d) respiratory tract

Question 44:  Water hyacinth float on water surface. Explain.

Answer  44: The presence of large air cavities in the parenchyma tissue causes the water hyacinth to float in water. Aerenchyma is the name for this form of specialized parenchyma tissue.

Question 45:  Which structure protects the plant body against the invasion of parasites?

Answer 45: The epidermis is the layer of the plant's body that protects it from parasitic invasion. It has a thick cuticle and dermal tissue that aids in parasite prevention.

Question 46:   Fill in the blanks

(a) Cork cells possesses _____ on their walls that makes it 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 ______

Answer 46:

(a) Cork cells possess Suberin on their walls that make it impervious to gases and water.

(b) Sieve tubes have tubular cells with perforated walls and are living in nature.

(c) Bone possesses a hard matrix composed of calcium and Phosphorus.

Question 47: Why is epidermis important for the plants? 

Answer 47: It serves as a barrier between the plant and the outside world. The epidermis performs a number of functions, including preventing water loss, regulating gas exchange, secreting metabolic compounds, and absorbing water and mineral nutrients (especially in roots).

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…………….
(e) _____ gives flexibility in plants.
(f) _____ and _____ are both conducting tissues.
(g) Xylem transports ____ and ____ from soil.
(h) Phloem transport ____ from _____ to other parts of the plant.

Answer 48:

(a) Xylem and phloem                                 

(b) Stomata

(c) suberin                                                       

(d) sclerenchyma

(e) collenchyma                                             

(f) xylem and phloem

(g) water and minerals                                 

(h) food from leaves

Long Answer Type Questions.................................

Question 49:  Differentiate between sclerenchyma and parenchyma tissues. Draw well labeled diagram

Answer 49: The major difference between sclerenchyma and parenchyma tissues are-

Question 50:  Describe the structure and function of different types of epithelial tissues. Draw diagram of each type of epithelial tissue.

Answer 50:

The thin protective layer of cells that covers the body's surface and lines the internal organs is called epithelial tissue. This tissue's cells are normally tightly packed. The location and role of the tissue decide the form of the cells. The ectoderm is where epithelial tissue begins. The endoderm, on the other hand, creates the epithelial tissue that lines the intestine.

Simple epithelial tissue is made up of a single layer of cells, while stratified epithelial tissue is made up of many layers of cells. Epithelial tissues are categorized based on the form and function of the cells. These are as follows -  

(i) Squamous epithelial tissue – It is a type of epithelial tissue that is found on the skin. This tissue is made up of a single layer of plate-like cells that are thin and smooth. The cells form a smooth membrane by fitting together like bricks in a wall. It's also called tessellated epithelium or pavement epithelium. It occupies internal cavities and ducts and is embedded in the outer layer of the skin. Squamous epithelium makes up the tongue, oesophagus, and mouth lining.

It's also present in alveoli and blood vessels. It protects the body's underlying parts from mechanical damage, germ entry, chemical contamination, and drying. It also creates a filtration surface that is selectively permeable.

(ii) Cuboidal epithelial tissue - The cells in this tissue are shaped like cubes and fit together tightly. In segment, the cells resemble squares, but the free surface resembles a hexagon. This tissue lines the inside of kidney tubules (the tubes that lead from the cups of nephrons), thyroid vesicles, and glands such as sweat glands, exocrine pancreas, and salivary glands.

It is responsible for the formation of the gonads' germinal epithelium (testes and ovaries). It assists in the absorption, excretion, and secretion of nutrients. It also offers mechanical assistance.

(iii) Columnar ciliated epithelial tissue - In most cases, this tissue is made up of a single layer of column-like cells. Every cell's surface area for absorption and secretion is increased by the presence of a conspicuous striated border of microvilli at the free surface end. It's most often found in the alimentary canal's inner lining.

It also lines the gall bladder and the oviducts. Secretion (e.g., mucus of goblet cells) and absorption (e.g., stomach and intestine) are two of this tissue's main roles.

Columnar epithelium forms protoplasmic outgrowths called cilia in certain areas of the body. The cilia's frequent lashing movements assist in the passage of substances.
In the sperm ducts, it can be found. The trachea (windpipe), bronchi (lungs), kidney tubules, and oviducts are all lined with this substance (Fallopian tubes). The passage of ova in the fallopian tubes and mucus in the respiratory tract are both aided by ciliated epithelium.

(iv) Stratified squamous epithelial tissue - This tissue is embedded in the skin and protects the skin's dry exterior surface. This tissue's cells are organized in several layers, but the cells that make up the various layers of the epithelium are not the same. In the deeper layers of the tissue, cuboidal cells become polygonal, then flatten (squamous) as they reach the free surface.

Flattened cells in the superficial layer may contain keratin, a fibrous protein that causes them to die and become keratinized stratified squamous epithelium. This epithelium is impervious to water and highly resistant to mechanical damage.

(v) Glandular epithelial tissue - Gland cells, which can secrete substances at the epithelial surface, are commonly present in epithelial tissue.

A multicellular gland can develop when a portion of epithelial tissue folds inwards. The glandular epithelium is the name for this form of epithelium.

Question 51:  Draw well labeled diagrams of various types of muscles found in human body. 

Answer 51:    Muscles in the human body are divided into three categories:

(i) Skeletal muscle is normally connected to the skeleton and has striated, tubular, multinucleated fibres. These are optional (under the control of our will). Because of the presence of alternating dark and light bands, these muscles are often referred to as striated muscles (striations).

(ii) Smooth muscle is located in the walls of internal organs and has spindle-shaped, non-striated, uninucleated fibres. In action, it is involuntary.

(iii) Cardiac muscle is found only in the walls of the heart and has striated, branched, uninucleated fibres. In action, it is involuntary.

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.

Answer 52:

a)      Meristematic cells are the plant body's continuously dividing cells, meaning they are metabolically active, and vacuoles, as we know, function as storage in plant cells. As a result, meristematic cells do not need the presence of a vacuole.

b)      Sclerenchyma tissue is the plant's dead basic permanent tissue. Sclerenchyma cells are tightly packed without intercellular spaces, similar to tiles in a mosaic floor, to provide resilience, rigidity, durability, and elasticity to the plant, allowing it to withstand various strains.

c)       The presence of sclerenchyma tissue gives pear fruit a crunchy and granular texture when chewed. Owing to the presence of lignin, the cell walls of sclerenchyma are substantially thickened. Lignin is a complex polymer with high tensile strength (i.e., it does not easily crack when stretched) and compressional strength (i.e., it does not easily buckle).

d)      The accumulation of extra cellulose at the cell's corners separates collenchyma cells. Intercellular spaces are absent in collenchyma, and cells are elongated. It's a form of mechanical tissue that gives a tree's branches support and elasticity so they can move and bend freely in high winds.

e)      Owing to the presence of sclerenchyma tissue, it is difficult to remove the husk of a coconut tree. Sclerenchyma tissue cells are densely packed, with no intercellular spaces, and a middle lamella separates them. Pectin, lignin, and protein make up the middle lamella, which is a thin layer of binding material.

Question 53:  List the characteristics of cork. How are they formed? Mention their role.

Answer 53:    The outer defensive tissue (i.e., epidermis) of the plants changes as they get older. The epidermis of the stem is replaced by a strip of secondary meristem known as phellogen or cork cambium. 

Cork cambium is a simple tissue of rectangular cells and vacuolated protoplasts containing tannins and chloroplasts. The cork cambium produces new cells on both sides, resulting in cork (phellem) on the outside and secondary cortex (phelloderm) on the inside.

Cork cambium cuts a layer of cells on the outer side of the tree, resulting in many layers of dense cork (bark). Cork cells are dead and tightly packed, with no intercellular spaces. Cork cells' walls are heavily thickened with suberin, an organic material (a fatty substance) that makes them impervious to water and gases.

Cork serves as a safe barrier. Desiccation (loss of water from the plant body), fungus, and mechanical damage are all avoided by its cells. It is light and does not quickly catch fire. Cork is used as insulators, shock absorbers, linoleum (flooring), and sports equipment because of these properties (in making of shuttle cocks, cricket balls, wooden paddles of table tennis, etc.). The stem surface of the cork oak tree (Quercus suber) found in Southern Europe and North Africa is used to make commercial cork.

Question 54:  Why are xylem and phloem called complex tissues? How are they different from one other?

Answer  54:   A complex tissue is made up of multiple types of cells with a common origin that work together to perform a common purpose. Since they are made up of various types of cells, xylem and phloem are referred to as complex tissues.

The four types of cells (elements) that make up xylem are as follows:

(i) Tracheid
(ii) vessels
(iii) xylem parenchyma
(iv) xylem sclerenchyma (or fibre)

There are four different types of elements in phloem also-
(i)   sieve tubes
(ii)  companion cells
(iii) phloem parenchyma
(iv) phloem fibre

The basic difference between xylem and phloem is listed below:

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.

Answer 55:
(a) The fundamental differences between meristematic and permanent plant tissues are described below.

(b) Cells arising from meristematic tissue division take on new roles and lose their capacity to differentiate over time. As a result, permanent tissue is created. Differentiation is the mechanism by which cells divide meristematically to take on a permanent form, scale, and function.
(c) Plants have two simple permanent tissues, parenchyma and collenchyma, and two complex permanent tissues, xylem and phloem.