tissues class 9 notes chapter 6 ncert important points

Let’s read about tissues class 9 notes chapter 6 ncert for all competitive examination.

CHAPTER – 6

Tissue

What is tissue

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

Utility of tissue in multicellular organism 

In multicellular organism , 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, called a tissue, is arranged and designed so as to give the highest possible efficiency of function.

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, multi-cellular organisms show division of labour.

Types of Tissue :-

1. Plant tissue
2. Animal tissue

Difference between plant tissues and animal tissues

Sr. No.	Points of difference	Plants tissue	Animal  tissue
1.	Dead Cells	Plants tissue generally has more dead              cells.	Animal  tissue has more living cells.
2.	The pattern of growth	The growth in plants is limited to certain         regions.	while this is not so in animals.
3.	Cell Division	There are some tissues in plants that divide throughout their life.	Cell growth in animals is more uniform.
4.	organs and organ systems	Less specialised and localised in very complex plants.	The structural organisation of organs and organ systems is far more specialised and localised in complex animals.

Plant tissue Is of two types-

1.  Meristematic tissue 
2.  Permanent tissue :-

• • Simple Permanent tissue 
  • Complex permanent tissue

1. Meristematic tissue

The meristematic tissue is the dividing tissue located only at a certain specific region of the plant that causes growth of plants. 

Characteristic/features of meristematic tissue:-

• Cells of meristematic tissue are very active,
• they have dense cytoplasm, 
• thin cellulose walls, 
• prominent nuclei, 
• They lack vacuoles.

Depending on the region where they are present, meristematic tissues are classified as :-

1. Apical meristem – Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root.
2. Lateral meristem –The girth of the stem or root increases due to lateral meristem (cambium).  
3. Intercalary meristem –  Intercalary meristem seen in some plants is located near the node. 

2. Permanent tissue

The cells formed by meristematic tissue 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.

1. Simple permanent tissue – A few layers of cells beneath the epidermis are generally simple permanent tissue. Types of simple permanent tissue :-

1. 1. 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 (intercellular  spaces) are found in this tissue. 
• This tissue generally stores food.
• Chlorenchyma – Parenchyma with chlorophyll.
• Aerenchyma – Parenchyma with air cavities

       B. Collenchyma 

 

• Collenchyma provides flexibility in plants.
• It allows bending of various parts of a plant like tendrils and stems of climbers without breaking.
• It also provides mechanical support. 
• Located  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 .

       C.  Sclerenchyma

•  It is the tissue which makes the plant hard and stiff.
•  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. 

      II. Complex permanent 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. Complex permanent tissue is of two types :-

1.  Xylem

• It 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.

     2. Phloem

 

• It 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

 Animal tissue is of four types-

1. Epithelial tissue
2. Connective tissue
3. Muscular tissue
4. Nervous tissue

1. Epithelial tissue:- 

• 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.. 
• Regardless of the type, all epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.  
• Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated and glandular.

Types of Epithelial tissue are :-

A. Squamous Epithelium 

• 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,The skin which protects the body, the cells lining blood vessels or lung alveoli 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.

B. Cuboidal Epithelium

Cuboidal epithelium (with cube-shaped cells) forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support.

C. Columnar Epithelium

 Where absorption and secretion occur, as in the inner lining of the intestine, tall epithelial cells are present. This columnar (meaning ‘pillar-like’) epithelium facilitates movement across the epithelial barrier.

D. Ciliated Epithelium

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. 

E. Glandular Epithelium 

 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

2. Connective tissue 

 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 the matrix differs in concordance with the function of the particular connective tissue.

1. Blood 

•  Blood has a fluid (liquid) matrix called plasma, in which red blood corpuscles (RBCs), white blood corpuscles (WBCs) 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.

II. Bone

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

III. Ligament 

• Two bones can be connected to each other by the ligament. 
• This tissue is very elastic. 
• It has considerable strength. 
• Ligaments contain very little matrix and connect bones with bones. 

IV. Tendons 

• Tendons connect muscles to bones . 
• Tendons are fibrous tissue with great strength but limited flexibility.

V. 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. 

VI. Areolar

• 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.

VII. Adipose

•  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.

3. Muscular tissue

Muscular tissue consists of elongated cells, also called muscle fibres. This tissue is responsible for movement in our body.

Three Types of muscular tissue:-

I. Striated muscles –

• Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.
•  Muscles present in our limbs move when we want them to, and stop when we so decide. Such muscles are called voluntary muscles. 
• These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement. 
•  These muscles show alternate light and dark bands or striations . As a result, they are also called striated muscles. 
• The cells of this tissue are – long, cylindrical, unbranched and multinucleate (having many nuclei). 

II. Unstriated muscles-

• The cells are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles.
•  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. 

III. Cardiac muscles- 

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

4. Nervous tissue

•  Nervous tissue is made of neurons that receive and conduct impulses.
•  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
• NEURON- 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 (process), called the axon, and many short, branched parts  (processes) 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. 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.

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