Tissues

So students, welcome to today's science lesson. Today we are going to study Chapter 6, which is about Tissues. This is a very important chapter in your science curriculum, and I am sure you will find it fascinating because it connects what we learned about cells in the previous chapter to how complex organisms like humans and plants function. So let's begin.

Now students, from your previous chapter on cell, you will remember that all living organisms are made of cells. In unicellular organisms, that is organisms made of just one cell like Amoeba, a single cell performs all the basic functions. This single cell carries out movement, intake of food, gaseous exchange and excretion all by itself. But what happens in multi-cellular organisms? In multi-cellular organisms there are millions of cells. Most of these cells are specialised to carry out specific functions. Each specialised function is taken up by a different group of cells. Since these cells carry out only a particular function, they do it very efficiently.

Let me give you some examples from our own body. In human beings, muscle cells contract and relax to cause movement, nerve cells carry messages, blood flows to transport oxygen, food, hormones and waste material and so on. In plants, vascular tissues conduct food and water from one part of the plant to other parts. So students, this is what we call division of labour in multi-cellular organisms. Cells specialising in one function are often grouped together in the body. This means that a particular function is carried out by a cluster of cells at a definite place in the body. This cluster of cells, students, is called a tissue.

Now let me give you the formal definition. A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue. Blood, phloem and muscle are all examples of tissues. So students, please remember this definition as it is very important.

Now, let us understand how plant tissues differ from animal tissues. There are noticeable differences between the two. Students, think about plants - plants are stationary or fixed, they don't move. They have to be upright, so they have a large quantity of supportive tissue. The supportive tissue generally has dead cells. Animals on the other hand move around in search of food, mates and shelter. They consume more energy as compared to plants. Most of the tissues they contain are living.

Another difference between animals and plants is in the pattern of growth. The growth in plants is limited to certain regions, while this is not so in animals. There are some tissues in plants that divide throughout their life. These tissues are localised in certain regions. Based on the dividing capacity of the tissues, various plant tissues can be classified as growing or meristematic tissue and permanent tissue. Cell growth in animals is more uniform. So, there is no such demarcation of dividing and non-dividing regions in animals.

The structural organisation of organs and organ systems is far more specialised and localised in complex animals than even in very complex plants. This fundamental difference reflects the different modes of life pursued by these two major groups of organisms, particularly in their different feeding methods. Also, they are differently adapted for a sedentary existence on one hand, that is plants, and active locomotion on the other, that is animals, contributing to this difference in organ system design.

So students, now that we understand this background, let us study tissues in detail.

## Section 6.1: Are Plants and Animals Made of Same Types of Tissues?

Let us compare their structure and functions. Do plants and animals have the same structure? Do they both perform similar functions?

From the above observations, answer the following questions. Students, I want you to think about these questions carefully.

First question: Which of the two onions has longer roots? Why?

Now students, when we conduct an experiment with onions, we generally find that the onion whose roots are allowed to grow for a longer period will have longer roots. The reason is simply that the roots continue to grow as long as the meristematic tissue at the tip is active. So the onion that was allowed to grow for more days will have longer roots.

Second question: Do the roots continue growing even after we have removed their tips?

Students, the answer is no. Once we remove the tips of the roots, the roots stop growing because the apical meristem, which is responsible for root growth, has been removed. The meristematic tissue is located at the tip of the root, and without it, the root cannot elongate.

Third question: Why would the tips stop growing in jar 2 after we cut them?

This is for the same reason I just explained. In jar 2, we cut the tips of the roots, which removes the meristematic tissue. Without this dividing tissue, no new cells are produced, and therefore the roots stop growing. This shows that growth in plants is limited to regions where meristematic tissue is present.

Now students, let us move on to study plant tissues in detail.

## Section 6.2: Plant Tissues

The growth of plants occurs only in certain specific regions. This is because the dividing tissue, also known as meristematic tissue, is located only at these points. Depending on the region where they are present, meristematic tissues are classified as apical, lateral and intercalary. New cells produced by meristem are initially like those of meristem itself, but as they grow and mature, their characteristics slowly change and they become differentiated as components of other tissues.

### Meristematic Tissue

Now students, let us study meristematic tissue in detail. Cells of meristematic tissue are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles. Now, can we think why they would lack vacuoles? Students, you might want to refer to the functions of vacuoles in the chapter on cells. Vacuoles in plant cells are mainly for storage of water and maintaining turgor pressure. But in meristematic cells, the main function is cell division, not storage. These cells need to divide rapidly, so they have dense cytoplasm and prominent nuclei to support this active division. The absence of large vacuoles allows more space for the organelles needed for cell division.

Now students, let me ask you another question: Can we think of reasons why there would be so many types of cells?

This is because different cells are specialized to perform different functions. For example, some cells are specialized for conducting water, some for providing support, some for photosynthesis, and so on. This division of labour among cells allows the plant to carry out all its life functions efficiently.

We can also try to cut sections of plant roots. We can even try cutting sections of root and stem of different plants. This is a good activity to understand the internal structure of plants.

Now students, let me summarize what we have learned about meristematic tissue. Meristematic tissue is the dividing tissue present in the growing regions of the plant. It has cells that are actively dividing, with dense cytoplasm, thin walls, prominent nuclei, and no vacuoles. Based on their location, they are classified as apical meristem (at the tips of roots and shoots), lateral meristem (in the sides of stems and roots for girth), and intercalary meristem (between mature tissues for growth).

### Permanent Tissue

Now students, what happens to the cells formed by meristematic tissue? They take up a specific role and lose the ability to divide. As a result, they form a permanent tissue. This process of taking up a permanent shape, size, and a function is called differentiation. Differentiation leads to the development of various types of permanent tissues.

Now students, permanent tissues are of two types: simple permanent tissue and complex permanent tissue. Let us study them one by one.

#### Simple Permanent Tissue

A few layers of cells beneath the epidermis are generally simple permanent tissue. Now students, simple permanent tissues are those made of one type of cells, where all cells look similar and perform similar functions.

First type: Parenchyma. Parenchyma is the most common simple permanent tissue. It consists of relatively unspecialised cells with thin cell walls. They are living cells. They are usually loosely arranged, thus large spaces between cells, which we call intercellular spaces, are found in this tissue. This tissue generally stores food. So students, whenever you think of parenchyma, remember it is the most common and versatile tissue that stores food and other substances.

In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma. For example, in the mesophyll cells of leaves, parenchyma contains chlorophyll and carries out photosynthesis.

In aquatic plants, large air cavities are present in parenchyma to help them float. Such a parenchyma type is called aerenchyma. Students, think about water hyacinth or pond lily - these plants float on water because of the air cavities in their parenchyma tissue.

Second type: Collenchyma. The flexibility in plants is due to another permanent tissue, collenchyma. It allows bending of various parts of a plant like tendrils and stems of climbers without breaking. It also provides mechanical support. We can find this tissue in leaf stalks below the epidermis. The cells of this tissue are living, elongated and irregularly thickened at the corners. There is very little intercellular space. Students, the key feature of collenchyma is that the corners of the cells are thickened, which gives them flexibility while still providing support.

Third type: Sclerenchyma. Yet another type of permanent tissue is sclerenchyma. It is the tissue which makes the plant hard and stiff. We have seen the husk of a coconut, students. It is made of sclerenchymatous tissue. The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin. Often these walls are so thick that there is no internal space inside the cell. This tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts. It provides strength to the plant parts. So students, remember sclerenchyma is the tissue that provides hardness and strength.

Now let us discuss the activity given in your textbook. Activity 6.3: Take a freshly plucked leaf of Rhoeo. Stretch and break it by applying pressure. While breaking it, keep it stretched gently so that some peel or skin projects out from the cut. Remove this peel and put it in a petri dish filled with water. Add a few drops of safranin. Wait for a couple of minutes and then transfer it onto a slide. Gently place a cover slip over it. Observe under microscope.

What you observe is the outermost layer of cells, called epidermis. The epidermis is usually made of a single layer of cells. In some plants living in very dry habitats, the epidermis may be thicker since protection against water loss is critical. The entire surface of a plant has an outer covering epidermis. It protects all the parts of the plant. Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface. This aids in protection against loss of water, mechanical injury and invasion by parasitic fungi. Since it has a protective role to play, cells of epidermal tissue form a continuous layer without intercellular spaces. Most epidermal cells are relatively flat. Often their outer and side walls are thicker than the inner wall.

Students, now we come to an important part - stomata. We can observe small pores here and there in the epidermis of the leaf. These pores are called stomata. Stomata are enclosed by two kidney-shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere. Transpiration, that is the loss of water in the form of water vapour, also takes place through stomata.

Now students, recall which gas is required for photosynthesis. The answer is carbon dioxide. And find out the role of transpiration in plants. Transpiration helps in the upward movement of water and minerals from roots to leaves, and it also helps in cooling the plant.

Now, epidermal cells of the roots, whose function is water absorption, commonly bear long hair-like parts that greatly increase the total absorptive surface area. These are root hairs. Students, when you look at a plant's root system, the fine hair-like structures you see are root hairs, which increase the surface area for water absorption.

In some plants like desert plants, epidermis has a thick waxy coating of cutin on its outer surface. Can we think of a reason for this? Students, desert plants need to conserve water, so the thick cutin coating prevents water loss through transpiration. This is an adaptation to dry environments.

Now, is the outer layer of a branch of a tree different from the outer layer of a young stem? Students, as plants grow older, the outer protective tissue undergoes certain changes. A strip of secondary meristem located in the cortex forms layers of cells which constitute the cork. Cells of cork are dead and compactly arranged without intercellular spaces. They also have a substance called suberin in their walls that makes them impervious to gases and water. This is what we see in the bark of trees. So yes, the outer layer of an old branch is different from a young stem - the old branch has cork which is more protective.

Now students, let me summarize simple permanent tissues. We have three types: parenchyma (living, thin walls, stores food), collenchyma (living, thickened corners, provides flexibility), and sclerenchyma (dead, thick lignified walls, provides strength).

#### Complex Permanent Tissue

Now students, the different types of tissues we have discussed until now are all made of one type of cells, which look like each other. Such tissues are called simple permanent tissue. Yet another type of permanent tissue is complex tissue. Complex tissues are made of more than one type of cells. All these cells coordinate to perform a common function. Xylem and phloem are examples of such complex tissues. They are both conducting tissues and constitute a vascular bundle. Vascular tissue is a distinctive feature of the complex plants, one that has made possible their survival in the terrestrial environment.

Now let us study xylem first. Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. Tracheids and vessels have thick walls, and many are dead cells when mature. Tracheids and vessels are tubular structures. This allows them to transport water and minerals vertically. The parenchyma stores food. Xylem fibres are mainly supportive in function.

Now students, think about the structure of tracheids and vessels. They are like long tubes through which water can flow easily. This is very efficient for transporting water from roots to leaves.

Now let us study phloem. Phloem is made up of five types of cells: sieve cells, sieve tubes, companion cells, phloem fibres and the phloem parenchyma. Sieve tubes are tubular cells with perforated walls. Phloem transports food from leaves to other parts of the plant. Except phloem fibres, other phloem cells are living cells.

So students, to summarize complex tissues: Xylem and phloem are both complex tissues. Xylem transports water and minerals, while phloem transports food. Both are essential for the survival of plants.

Now let me ask you to answer some questions from the textbook.

Question 1: Name types of simple tissues. Answer: The three types of simple tissues are parenchyma, collenchyma and sclerenchyma.

Question 2: Where is apical meristem found? Answer: Apical meristem is found at the tips of roots and shoots.

Question 3: Which tissue makes up the husk of coconut? Answer: Sclerenchyma tissue makes up the husk of coconut.

Question 4: What are the constituents of phloem? Answer: The constituents of phloem are sieve cells, sieve tubes, companion cells, phloem fibres and phloem parenchyma.

Now students, let us move on to animal tissues.

## Section 6.3: Animal Tissues

Now students, we have studied plant tissues in detail. Now let us study animal tissues. During breathing we inhale oxygen. Where does this oxygen go? It is absorbed in the lungs and then is transported to all the body cells through blood. Why would cells need oxygen? The functions of mitochondria we studied earlier provide a clue to this question. Blood flows and carries various substances from one part of the body to the other. For example, it carries oxygen and food to all cells. It also collects wastes from all parts of the body and carries them to the liver and kidney for disposal.

Blood and muscles are both examples of tissues found in our body. On the basis of the functions they perform we can think of different types of animal tissues, such as epithelial tissue, connective tissue, muscular tissue and nervous tissue. Blood is a type of connective tissue, and muscle forms muscular tissue.

### Epithelial Tissue

Now students, let us study epithelial tissue in detail. The covering or protective tissues in the animal body are epithelial tissues. Epithelium covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate. The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue. Epithelial tissue cells are tightly packed and form a continuous sheet. They have only a small amount of cementing material between them and almost no intercellular spaces. Obviously, anything entering or leaving the body must cross at least one layer of epithelium. As a result, the permeability of the cells of various epithelia play an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body. Regardless of the type, all epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.

Now students, different epithelia show differing structures that correlate with their unique functions. For example, in cells lining blood vessels or lung alveoli, where transportation of substances occurs through a selectively permeable surface, there is a simple flat kind of epithelium. This is called the simple squamous epithelium. Squama means scale of skin. Simple squamous epithelial cells are extremely thin and flat and form a delicate lining. The oesophagus and the lining of the mouth are also covered with squamous epithelium. The skin, which protects the body, is also made of squamous epithelium. Skin epithelial cells are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.

Where absorption and secretion occur, as in the inner lining of the intestine, tall epithelial cells are present. This columnar epithelium, meaning pillar-like, facilitates movement across the epithelial barrier. In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move, and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.

Cuboidal epithelium, with cube-shaped cells, forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support. Epithelial cells often acquire additional specialisation as gland cells, which can secrete substances at the epithelial surface. Sometimes a portion of the epithelial tissue folds inward, and a multicellular gland is formed. This is glandular epithelium.

So students, to summarize epithelial tissue: It is the protective covering tissue. Types include squamous (flat cells), cuboidal (cube-shaped cells), columnar (tall pillar-like cells), ciliated columnar (with hair-like projections), and glandular (secreting cells).

### Connective Tissue

Now students, blood is a type of connective tissue. Why would it be called connective tissue? A clue is provided in the introduction of this chapter! Now, let us look at this type of tissue in some more detail. The cells of connective tissue are loosely spaced and embedded in an intercellular matrix. The matrix may be jelly like, fluid, dense or rigid. The nature of matrix differs in concordance with the function of the particular connective tissue.

Now let us do Activity 6.4. Take a drop of blood on a slide and observe different cells present in it under a microscope.

Blood has a fluid matrix called plasma, in which red blood corpuscles, white blood corpuscles and platelets are suspended. The plasma contains proteins, salts and hormones. Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body.

Now students, let us study different types of connective tissues.

First, blood. Blood is a connective tissue with a fluid matrix called plasma. It transports substances throughout the body.

Second, bone. Bone is another example of a connective tissue. It forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body. It is a strong and nonflexible tissue. What would be the advantage of these properties for bone functions? Students, think about it - bones need to be strong to support our body weight and protect internal organs. They also need to be rigid to provide a firm framework.

Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.

Third, ligament. Two bones can be connected to each other by another type of connective tissue called the ligament. This tissue is very elastic. It has considerable strength. Ligaments contain very little matrix and connect bones with bones.

Fourth, tendon. Tendons connect muscles to bones and are another type of connective tissue. Tendons are fibrous tissue with great strength but limited flexibility.

Fifth, cartilage. Another type of connective tissue, cartilage, has widely spaced cells. The solid matrix is composed of proteins and sugars. Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx. We can fold the cartilage of the ears, but we cannot bend the bones in our arms. Think of how the two tissues are different! Cartilage is flexible but firm, while bone is rigid.

Sixth, areolar connective tissue. Areolar connective tissue 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.

Seventh, adipose tissue. Where are fats stored in our body? Fat-storing adipose tissue is found below the skin and between internal organs. The cells of this tissue are filled with fat globules. Storage of fats also lets it act as an insulator.

So students, to summarize connective tissues: They have loosely spaced cells embedded in a matrix. The matrix can be fluid (blood), jelly-like (areolar), dense (tendons and ligaments), or hard (bone). Types include blood, bone, cartilage, tendon, ligament, areolar tissue, and adipose tissue.

### Muscular Tissue

Now students, when we breathe we can actually feel the movement of our chest. How do these body parts move? For this we have specialised cells called muscle cells. The contraction and relaxation of these cells result in movement.

Muscular tissue consists of elongated cells, also called muscle fibres. This tissue is responsible for movement in our body. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.

Now students, there are three types of muscular tissue.

First, skeletal muscle. These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement. Under the microscope, these muscles show alternate light and dark bands or striations when stained appropriately. As a result, they are also called striated muscles. The cells of this tissue are long, cylindrical, unbranched and multinucleate, meaning having many nuclei.

Second, smooth muscle. The movement of food in the alimentary canal or the contraction and relaxation of blood vessels are involuntary movements. We cannot really start them or stop them simply by wanting to do so! Smooth muscles or involuntary muscles control such movements. They are also found in the iris of the eye, in ureters and in the bronchi of the lungs. The cells are long with pointed ends, spindle-shaped, and uninucleate, having a single nucleus. They are also called unstriated muscles. Why would they be called that? Because they do not show striations or bands under the microscope.

Third, cardiac muscle. The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles. Heart muscle cells are cylindrical, branched and uninucleate.

Now students, let us do Activity 6.5. Compare the structures of different types of muscular tissues. Note down their shape, number of nuclei and position of nuclei within the cell in the table.

Based on the information I gave you, let me fill in the table:

For striated muscles: Shape is long and cylindrical, number of nuclei is many (multinucleate), and position of nuclei is at the periphery (near the cell membrane).

For smooth muscles: Shape is spindle-shaped (long with pointed ends), number of nuclei is one (uninucleate), and position of nucleus is at the centre.

For cardiac muscles: Shape is cylindrical and branched, number of nuclei is one (uninucleate), and position of nucleus is at the centre.

### Nervous Tissue

Now students, we can move some muscles by conscious will. Muscles present in our limbs move when we want them to, and stop when we so decide. Such muscles are called voluntary muscles.

All cells possess the ability to respond to stimuli. However, cells of the nervous tissue are highly specialised for being stimulated and then transmitting the stimulus very rapidly from one place to another within the body. The brain, spinal cord and nerves are all composed of the nervous tissue. The cells of this tissue are called nerve cells or neurons. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. Usually each neuron has a single long part in the form of a fibre, called the axon, and many short, branched parts called dendrites. An individual nerve cell may be up to a metre long. Many nerve fibres bound together by connective tissue make up a nerve.

The signal that passes along the nerve fibre is called a nerve impulse. The nerve impulse from the nerve endings is transmitted to the dendrites of the next nerve cell. Nerve impulses allow us to move our muscles when we want to. The functional combination of nerve and muscle tissue is fundamental to most animals. This combination enables animals to move rapidly in response to stimuli.

Now students, let me ask you to answer some questions from the textbook.

Question 1: Name the tissue responsible for movement in our body. Answer: Muscular tissue is responsible for movement in our body.

Question 2: What does a neuron look like? Answer: A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. It has a single long part called axon and many short branched parts called dendrites.

Question 3: Give three features of cardiac muscles. Answer: Three features of cardiac muscles are: first, they are cylindrical and branched; second, they are uninucleate; third, they show rhythmic contraction and relaxation throughout life.

Question 4: What are the functions of areolar tissue? Answer: The functions of areolar tissue are: it fills the space inside the organs, supports internal organs, and helps in repair of tissues.

Now students, let us summarize what we have learned in this chapter.

## What You Have Learnt

Tissue is a group of cells similar in structure and function.

Plant tissues are of two main types - meristematic and permanent.

Meristematic tissue is the dividing tissue present in the growing regions of the plant.

Permanent tissues are derived from meristematic tissue once they lose the ability to divide. They are classified as simple and complex tissues.

Parenchyma, collenchyma and sclerenchyma are three types of simple tissues. Xylem and phloem are types of complex tissues.

Animal tissues can be epithelial, connective, muscular and nervous tissue.

Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated and glandular.

The different types of connective tissues in our body include areolar tissue, adipose tissue, bone, tendon, ligament, cartilage and blood.

Striated, unstriated and cardiac are three types of muscle tissues.

Nervous tissue is made of neurons that receive and conduct impulses.

Now students, let us solve the exercises at the end of the chapter.

## Exercises

Exercise 1: Define the term "tissue". Answer: A tissue is a group of cells that are similar in structure and/or work together to achieve a particular function.

Exercise 2: How many types of elements together make up the xylem tissue? Name them. Answer: Four types of elements together make up the xylem tissue. They are tracheids, vessels, xylem parenchyma and xylem fibres.

Exercise 3: How are simple tissues different from complex tissues in plants? Answer: Simple tissues are made of one type of cells, where all cells look similar and perform similar functions. Examples are parenchyma, collenchyma and sclerenchyma. Complex tissues are made of more than one type of cells that coordinate to perform a common function. Examples are xylem and phloem.

Exercise 4: Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall. Answer: Parenchyma has thin cell walls made of cellulose. Collenchyma has cells with thickened corners, meaning the walls are irregularly thickened at the corners. Sclerenchyma has cells with thick, lignified walls that are often so thick that there is no internal space.

Exercise 5: What are the functions of the stomata? Answer: The functions of stomata are: they allow exchange of gases with the atmosphere, and transpiration (loss of water vapour) takes place through them.

Exercise 6: Diagrammatically show the difference between the three types of muscle fibres. Answer: Students, for this question, you need to draw diagrams. Let me describe the differences:

Striated muscles: Long, cylindrical, unbranched cells with multiple nuclei at the periphery. They show alternating light and dark bands.

Smooth muscles: Spindle-shaped cells with pointed ends, single nucleus at the centre, no striations.

Cardiac muscles: Cylindrical and branched cells, single nucleus at the centre, have striations but less prominent than skeletal muscles.

You should draw three separate diagrams showing these differences.

Exercise 7: What is the specific function of the cardiac muscle? Answer: The specific function of cardiac muscle is to cause rhythmic contraction and relaxation of the heart throughout life, which helps in pumping blood.

Exercise 8: Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body. Answer: Let me explain this in detail:

Striated muscles: They have long, cylindrical, unbranched, multinucleate cells with striations (alternate light and dark bands). They are attached to bones and are responsible for voluntary movements.

Unstriated muscles: They have spindle-shaped, uninucleate cells with no striations. They are found in the lining of the alimentary canal, blood vessels, iris of the eye, ureters and bronchi. They control involuntary movements.

Cardiac muscles: They have cylindrical, branched, uninucleate cells with striations. They are found only in the heart and cause involuntary rhythmic contractions.

Exercise 9: Draw a labelled diagram of a neuron. Answer: Students, for this question, you need to draw a neuron. A neuron consists of a cell body (soma) with a nucleus and cytoplasm. From the cell body, there is one long fibre called axon and many short branched fibres called dendrites. The axon ends in axon terminals. You should label: cell body, nucleus, dendrites, axon, myelin sheath (in some neurons), and axon terminals.

Exercise 10: Name the following. (a) Tissue that forms the inner lining of our mouth. Answer: Squamous epithelium.

(b) Tissue that connects muscle to bone in humans. Answer: Tendon.

(c) Tissue that transports food in plants. Answer: Phloem.

(d) Tissue that stores fat in our body. Answer: Adipose tissue.

(e) Connective tissue with a fluid matrix. Answer: Blood.

(f) Tissue present in the brain. Answer: Nervous tissue.

Exercise 11: Identify the type of tissue in the following: skin, bark of tree, bone, lining of kidney tubule, vascular bundle. Answer: Skin: Stratified squamous epithelium. Bark of tree: Cork (protective tissue). Bone: Connective tissue (bone tissue). Lining of kidney tubule: Cuboidal epithelium. Vascular bundle: Complex permanent tissue (xylem and phloem).

Exercise 12: Name the regions in which parenchyma tissue is present. Answer: Parenchyma tissue is present in all parts of the plant - in the cortex, pith, mesophyll of leaves, and around vascular bundles.

Exercise 13: What is the role of epidermis in plants? Answer: The role of epidermis in plants is to protect all parts of the plant. It forms a continuous layer that prevents water loss, mechanical injury, and invasion by parasitic fungi. In roots, it also helps in water absorption through root hairs.

Exercise 14: How does the cork act as a protective tissue? Answer: Cork acts as a protective tissue because its cells are dead and compactly arranged without intercellular spaces. They have a substance called suberin in their walls that makes them impervious to gases and water. This protects the plant from mechanical injury, water loss, and pathogen invasion.

Exercise 15: Complete the following chart: Permanent tissue ├── simple │ ├── parenchyma │ ├── collenchyma │ └── sclerenchyma └── complex ├── xylem └── phloem

Answer: The chart is already complete in the question. This shows the classification of permanent tissues in plants into simple and complex tissues, and further into their subtypes.

Now students, let me give you a complete summary of everything we have learned in this chapter.

## Complete Summary

In this chapter on Tissues, we learned that:

A tissue is a group of cells similar in structure and function that work together to achieve a particular purpose.

We studied plant tissues in detail. Plants have two main types of tissues: meristematic and permanent. Meristematic tissue is the dividing tissue found in growing regions like root tips and shoot tips. Based on location, it is classified as apical, lateral, and intercalary meristem.

Permanent tissues are derived from meristematic tissue through differentiation. They are of two types: simple and complex. Simple tissues include parenchyma (stores food, thin walls, living cells), collenchyma (provides flexibility, thickened corners, living cells), and sclerenchyma (provides strength, thick lignified walls, dead cells). Complex tissues include xylem (transports water and minerals, consists of tracheids, vessels, xylem parenchyma and xylem fibres) and phloem (transports food, consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres).

We also learned about epidermal tissue which covers the plant surface and protects it. Stomata are pores in the epidermis that allow gas exchange and transpiration. Cork is another protective tissue in older plants.

Then we studied animal tissues. These are classified into four types: epithelial, connective, muscular, and nervous tissue.

Epithelial tissue covers body surfaces and lines cavities. Types include squamous (flat cells), cuboidal (cube-shaped), columnar (tall), ciliated columnar (with hair-like projections), and glandular (secreting cells).

Connective tissue connects different parts of the body. Types include blood (fluid matrix), bone (hard matrix of calcium and phosphorus), cartilage (firm but flexible), tendon (connects muscle to bone), ligament (connects bone to bone), areolar (fills spaces and helps repair), and adipose (stores fat).

Muscular tissue is responsible for movement. Types include striated or skeletal muscles (voluntary, attached to bones, multinucleate), smooth or unstriated muscles (involuntary, found in internal organs, uninucleate), and cardiac muscles (involuntary, found in heart, branched).

Nervous tissue is made of neurons that receive and transmit nerve impulses. A neuron has a cell body, dendrites (receiving branches), and an axon (transmitting fibre).

This chapter helps us understand how complex organisms like plants and animals are organized at the tissue level, with different tissues specialized to perform different functions efficiently through division of labour.

Students, this completes our lesson on Chapter 6: Tissues. I hope you have understood all the concepts clearly. Thank you for your attention, and keep studying!