CBSE NCERT Notes for Class 9 Science Chapter 6 Tissues

CBSE Class 9 Science Notes on Tissues

We do know that matter is composed of particles organized in a certain manner. While the particles in gases are well separated and may move freely, the particles in solids are closely packed, with little space for movement.

CBSE Class 9 Science notes will assist students in studying the topic thoroughly and clearly.

These CBSE Class 9 Science notes were written by subject experts who made the study material very basic, both in terms of language and format.

Plant Tissues

Plant tissues may be categorised into two fundamental types based on their ability to divide: Meristematic Tissue and Permanent Tissue

MERISTEMATIC TISSUE

Meristematic tissues are those in which cells continually divide, giving rise to new cells. These tissues are necessary for plant growth. Plants grow only in locations with meristematic tissues, such as the root and shoot tip.

Additionally, it is referred to as growing tissue. This tissue’s cells are very active, with a thick cytoplasm, thin cellulose walls, and conspicuous nuclei. They are free of vacuoles.

Meristem produces new cells that are first like those meristem cells. Once they grow and become differentiated as components of other tissues, their characteristics alter.

Meristematic tissue is categorised according to the areas in which it is found.

• Apical Meristem : These are found at the tips of developing stems and roots. As a result, they help in the growth of stems and roots. It functions as a pro-meristem, actively dividing cells that give rise to other meristems.
• Intercalary Meristem : These are found near the base of twigs’ leaves and internodes (on each side of the node). It helps in the longitudinal growth of plants (elongation).
• Lateral Meristem (Cambium) : On the lateral sides of stems and roots, they are found. It increases to the girth of the stem and root.

PERMANENT TISSUE

This tissue is generated from meristematic tissue cells that have lost their capacity to divide and develop a stable shape, size, and function via a process called differentiation.

The meristematic tissues tend to do so as a consequence of differentiation.

The many forms of permanent tissues include the following:

• Simple Permanent Tissue : It is composed completely of a single kind of cell, i.e. the cells that compose these tissues are structurally and functionally identical.

Additional classifications for simple permanent tissue include:

1. Parenchyma : The basic packing tissue is made of a few layers of cells. They are found in the cortex and pith of stems, as well as in the mesophyll of leaves and roots.

Characteristics

• These are unspecialized living cells with a thin cell wall.
• Typically, cells are loosely packed with significant gaps between them (intercellular spaces).

Functions

• It serves as a food store tissue; This tissue supports plants;
• In certain circumstances, when the parenchyma cell includes chlorophyll, it performs photosynthesis. This form of parenchyma tissue is referred to as chlorenchyma.
• Large air spaces are found in parenchyma cells of aquatic plants to provide buoyancy to planes, which aids in their flotation. Aerenchyma is a form of parenchyma tissue.
• Additionally, the parenchyma of stems and roots retains nutrients and water.

1. Collenchyma : These tissues are often found under the epidermis of leaves and in leaf midribs.

Characteristics

• Cells are alive, elongated, and irregularly thickened at the corners owing to pectin deposition.
• They have a small amount of intercellular space.

Functions

• It gives mechanical support and elasticity (flexibility) to plants.
• It also enables simple bending of different plant components (leaf and stem) without breaking.

1. Sclerenchyma : Some of this tissue is found in stems, surrounding vascular bundles, in leaf veins, and in the hard coverings of seeds and nuts.

Characteristics

• Sclerenchymatous tissue cells are dead.
• The cells seem to be long and narrow.
• Cell walls become thicker as a result of lignin deposition, which acts as a cement and hardens them.
• Due to the thick walls of the cells, there is no internal space.

Functions

• It is recognised as the primary mechanical tissue that contributes to the plane’s hardness and stiffness; for example, the husk of the coconut is composed of sclerenchymatous tissue.
• It envelops seeds and nuts in a protective sheath. It provides the plant body with stiffness, flexibility, and suppleness.

PROTECTIVE -TISSUES

(A) EPIDERMIS (B) CORK

• Complex Permanent Tissue : It is formed of many cell types that have a similar origin. Regardless of their appearance, all cells work together to fulfill a common function.

The following are examples of complex permanent tissue:

• Phloem
• Xylem

Both are conducting tissues that form a vascular bundle. This is a characteristic of complex plants. le enables them to survive in a terrestrial environment.

Xylem : It is in charge of the movement of water and minerals from the roots to the rest of the plant. The xylem cells have thick walls, and many of the chem cells are dead. Xylem is composed of a variety of different elements, which are as follows:

• Tracheids : These are non-living, long, tapering tubular structures that convey water and minerals upward.
• Vessels : Long, tube-like structures generated by a row of cells laid end to end. These are also dead cells with lignified walls. Additionally, they assist in the conduction of water.
• Xylem Parenchyma : These are the only living xylem cells with thin celJ walls. They store food and assist in water’s sideways conduction.
• Xylem Fibres  : They are elongated dead cells with tapering Xylem parenchyma ends and thick cell walls. They are xylem-associated fibres that help in the xylem’s function.

Phloem : It is responsible for transporting food from the leaves to other areas of the plant. It is capable of material movement in both directions. Except for phloem fibres, all phloem cells are alive.

Phloem is composed of four basic types of elements:

• Sieve Tubes : These are tubular cells with perforated walls and a thin cytoplasmic layer.
• Companion Cells : These are small elongated cells with perforated walls and active cytoplasm. They assist in the transfer of food via sieve tubes.
• Phloem Fibres : They are thick-walled sclerenchyma cells that provide the tissue its mechanical strength.

Phloem Parenchyma : They are thin-walled cells that help in the storage of food and its slow lateral conduction.

Animal Tissues

Animal tissues are classified into four fundamental categories based on their functions: epithelial, connective, muscular, and nerve tissue.

Epithelial Tissue

Epithelial tissues are the covering or protecting tissues of the animal body. Ir is the animal body’s most basic defensive tissue. Ir is found in the majority of the body’s organs and cavities.

• It works as a barrier, separating various bodily systems. These tissues have tightly packed cells that create a continuous sheet. Between chem, there is essentially no intercellular space. They are connected by a very small quantity of cementing substance.
• An extracellular fibrous basement membrane containing collagen separates the epithelium from the underlying tissue.
• Epithelial tissues are further categorised based on the form and arrangement of the cells:

1. Squamous Epithelium : The skin, which protects the body, is made up of squamous epithelial tissue. It is further classified as follows:
   1. Simple Squamous Epithelium
      1. It is a single-layered material that fits tightly.
      2. It creates a delicate lining of blood vessels and lung alveoli, where substance transfer happens through a selectively permeable membrane.
      3. It also protects the oesophagus and mouth lining.

1. Stratified Squamous Epithelium : It is located on the outside part of the skin because it is very resistant to mechanical harm and is waterproof. To avoid wear and tear, cells are arranged in many layers.
2. Cuboidal Epithelium : It is made of cube-shaped cells with spherical nuclei. It covers the tubules of the kidney and the ducts of the salivary glands, providing mechanical support. Additionally, it forms the germinal epithelium of the gonads. Additionally, it assists in absorption, excretion, and secretion.
3. Columnar Epithelium : It is formed of tall, pillar-like cells with elongated nuclei. It is often found in the inner lining of the intestine, where absorption and secretion occur.
4. Ciliated Columnar Epithelium : Ciliated columnar epithelium occurs when columnar epithelial cells contain cilia (hair-like extensions). The cilia are capable of movement. Their movement pushes mucus forward.

It is present in the respiratory system and also lines oviducts, sperm ducts, and kidney tubules, among other places.

1. Glandular Epithelium : At the epithelial surface, gland cells produce substances. Occasionally, a part of epithelial tissue folds inward. As a consequence, a multicellular gland forms. Its epithelium is referred to as glandular epithelium.

Functions Of Epithelial Tissue

• It shields the underlying cells from dehydration, injury, infection, and the toxic effects of chemicals.
• It is critical for controlling material exchanges between the body and the external environment, as well as between various bodily parts.
• It assists in the absorption of water and nutrients, as well as gas diffusion.
• It assists in the removal of waste produced by the body.

Connective Tissue

This tissue is highly specialised in order to link numerous human organs to one another. For instance, it connects two or more bones together, muscles to bones, connects other tissues together, and also provides support to various sections of the body.

Connective tissue cells are loosely packed, living, and immersed in an intercellular matrix that may be jelly-like, fluid, thick, or solid.

Blood : It is a fluid connective tissue that connects various bodily parts. It contributes to the body’s continuity. Ir is made up of a fluid matrix termed plasma and blood cells such as RBCs (Red Blood Cells), WBCs (White Blood Cells), and platelets.

Proteins, ions, and hormones are also found in plasma. Blood carries nutrients, gases, hormones, and vitamins to the body’s numerous tissues. The excretory products are transported from tissues to excretory organs by radiation. Additionally, it conducts sound and controls the body’s temperature.

• RBCs assist in the movement of breathing gases, oxygen and carbon dioxide, to and from the different parts of our body through haemoglobin. RBCs have an average lifetime of 120 days.
• White blood cells, also known as leukocytes, fight disease by creating antibodies.
• Platelets of blood Additionally referred to as thrombocytes, these cells assist in the clotting of blood.

Bone : It is an incredibly strong and inflexible tissue. It is porous, densely vascularized, mineralized, and stiff. Its matrix is composed of proteins and is abundant in calcium and phosphorus ions. It provides the framework for the body. Additionally, it attaches the muscles and provides support for the major organs.

Ligaments : They join one bone to another. A ligament is very elastic and strong. It includes a negligible amount of matrix. Ligaments support joints and allow for natural movement. Their overextension results in sprain.

Tendons : They are stiff and strong structures that connect skeletal muscles to bones. These are made of white fibrous tissues that have a limited range of motion but a high degree of strength.

Cartilage : It is a kind of connective tissue that is specialised in having cells that are widely separated. It contains a solid matrix termed chondrin that is made up of proteins and carbohydrates.

Cartilage smooths the surfaces of the bones at joints. The nose, ear, trachea, and larynx all contain this substance. Our ears’ cartilage can be folded, while the bones in our arms cannot be bent.

Areolar Tissue : It is a supporting and packing tissue that is present between the organs that are contained inside the body cavity. Between the skin and muscles, surrounding blood vessels and nerves, and in the bone marrow, it is found.

It is a fluid-filled, cellular tissue. It occupies space inside the organs and supports the internal organs. It aids in tissue repair.

Adipose Tissue : It acts as a fat store, supporting visceral organs. Due to the fat storage, it works as an insulator. It is found under the skin, in the space between the internal organs.

Muscular Tissue

It is composed of elongated cells known as muscle fibres. This tissue is responsible for our body’s mobility. It comprises a unique class of proteins called contractile proteins, which are responsible for the contraction and relaxation of muscles.

The following are the several kinds of muscle tissues:

Striated Muscles : The muscles in our limbs that move or stop in response to our commands are referred to as striated muscles. These are also referred to as voluntary muscles due to the fact that we can move them with our conscious volition.

Typically, they are linked to bones and assist in bodily movement, e.g., limb muscles. As a result, they are sometimes referred to as skeletal muscles. The muscle cells are long, cylindrical, unbranched, and multinucleate (have several nuclei). Under a microscope, striated muscles show alternating bands or striations of light and dark. As a result, they are sometimes referred to as striated muscles.

Unstriated Muscles Or Smooth Muscles : The muscles that cannot be moved by our volition are referred to as unstriated or smooth muscles. Additionally, they are referred to as involuntary muscles. For instance, the passage of food through the alimentary canal, the contraction and relaxation of blood vessels, the iris of the eye, and the muscles found in the ureters and bronchi of the lungs.

These muscles are composed of long cells with a pointed end (spindle-shaped) and a single nucleus. These muscles are completely free of black or light bands. As a result, they are often referred to as unstriated muscles.

Cardiac Muscles : These are involuntary muscles found only in the heart. Throughout their lives, they perform cyclic contractions and relaxations. The cells constituting cardiac muscles are cylindrical, uninucleated, and branching. Cardiac muscles are identified by stripes of bright and dark bands.

NERVOUS TISSUE

Nervous tissues are those that receive stimuli and transfer them from one area of the tissue to another. Nerve cells or neurons are the cells that make up nervous tissue. These are extremely specialised for receiving stimulus and then swiftly conveying it from one location inside the body to another. Nervous tissues make up the brain, spinal cord, and nerves.

A single nerve cell, or neuron, may be up to a metre long and is made up of three basic components:

• Cell Body : It is composed of cytoplasm, nucleus, and outer membrane of the cell.
• Axon : It is a single long conducting fibre that extends out from the neuron. It is responsible for transmitting impulses away from the cell body.
• Dendrites : These are the neuron’s small branching fibres that receive nerve signals.

DISTINCTION BETWEEN PLANT AND ANIMAL TISSUES

NCERT questions & answers from Tissues

What is a tissue ?

Answer: Tissue is a group of related cells that have a common origin and perform a common function.

What is the utility of tissues in multicellular organisms?

Answer:

1. Division of Labour: Tissues bring about a division of labour in multicellular organisms. It increases efficiency.
2. Higher Organisation: Organs and organ systems are formed when tissues become organised.
3. Individual Cells: Workload of individual cells has decreased.
4. Higher Survival: Multicellular organisms have a high survival rate due to their division of labour, increased efficiency, and organisation.

What are the functions of areolar tissue ?

Answer:

1. Packing : Areolar tissue provides packing material in various organs.
2. Binding :It connects numerous components together in such a way that their dislocation is prevented while still enabling Macrophage limited movement.
3. Covering : It provides covering over nerves, muscles and blood vessels.
4. Repair : The tissue provides materials for repair of injury.

Define the term “tissue”.

Answer: Tissue is a group of related cells that have a common origin and perform a common function.

How many types of elements together make up the xylem tissue ? Name them.

Answer: The xylem tissue is composed of four distinct parts. Tracheids, vessels, xylem parenchyma, and xylem fibres are all examples.

How are simple tissues different from complex tissues in plants ? (CCE 2014)

Answer:

Differences between Simple and Complex Tissues

Simple Tissues:

1. Cells: A simple tissue consists entirely of a single type of cell.
2. Activity: All cells serve the same purpose.
3. Types: Simple plant tissues are classified into three types: parenchyma, collenchyma, and sclerenchyma.
4. Function: They are responsible for the plant’s basic structure.

Complex Tissues:

1. A complex tissue is composed of multiple cell types.
2. Different cells do varying degrees of a function.
3. Complex plant tissues are classified into two types: xylem and phloem.
4. They comprise the plant’s transportation system.

Differentiate amongst parenchyma, collenchyma and sclerenchyma on the basis of the cell wall.

Answer:

Parenchyma:

1. Thickness: The cell wall is thin
2. Smoothness: It is smooth
3. Nature: Wall is formed of cellulose.

Collenchyma:

1. Thickness: It is thick
2. Smoothness: It is unevenly thickened.
3. Nature: The thickening is pecto cellulosic.

Sclerenchyma:

1. Thickness: It is thick
2. Smoothness: The wall is uniformly thickened
3. Nature: The thickening is generally of lignin.

What are the functions of stomata ?

Answer:

Functions of Stomata:

1. Gaseous Exchange : Stomata are locations where gases (carbon dioxide and oxygen) are exchanged between the plant’s interior and the surrounding environment.
2. Transpiration : The majority of transpiration happens via stomata. Transpiration removes surplus water from the plant’s surface and keeps it cool, even in direct sunlight.
3. Regulation : They are responsible for regulating both gaseous exchange and transpiration.

What is the specific function of cardiac muscle ?

Answer: Continuous rhythmic contraction and relaxation throughout life without becoming fatigued.

Differentiate amongst striated, unstriated and cardiac muscles on the basis of their structure and site/ location in the body.

Answer:

Striated Muscle Fibres :

• Cells: They are long cylindrical cells.

• Ends: The fibres have blunt ends.

• Striations: They possess striations or alternate light and dark bands.

• Intercalated Discs and Cross Connections: They are absent.

• Nucleus: The muscle fibre is multinucleate. Nuclei are oval in outline. They occur peripherally below the sarcolemma.

1. Arrangement: They occur in bundles.

Smooth Muscle Fibres : 

• Cells: The fibres are elongated and spindle-shaped.

• Ends: The fibres have pointed ends.

• Striations: Striations or light and dark bands are absent.

• Intercalated Discs and Cross Connections: Intercalated discs and cross-connections are absent.

• Nucleus: Smooth muscle fibre is uninucleated. Nucleus is centrally placed, oval or elongated.

• Arrangement: They generally form sheets.

Cardiac Muscle Fibres: 

• Cells: The cells are small and cylindrical.

• Ends: The fibres have broad ends.

• Striations : Striations are present but they are fainter than those of striated muscle fibres.

• Intercalated Discs and Cross Connections : Intercalated discs and cross-connection are present.
• Nucleus: The cells are uninucleate. Nucleus in oval-rounded. It is centrally placed.
• Arrangement: They form a network.