Class 9 Science Chapter 6 Tissues NCERT Notes
Class 9 Science Chapter 6 Tissues NCERT Notes are very useful in making you memorize things easily and quickly. The main objective of these notes are to make sure that students will be able to understand the details of every chapter in clear and precise manner.
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Chapter 6 Tissues Class 9 Science CBSE NCERT Notes
Tissue is a group of cells having similar structure and function. In plants and animals groups of cells called tissues carry out specific functions. For example, In human beings the cells of the muscular tissue contract and relax and help in movements. In plants the cells of the vascular tissue conduct water and food from one part of the plant to the other.
Differences between plant and animal tissues
| Animal Tissues | Plant Tissues |
| Animals move from place to place and need more energy than plants. So most cells and tissues in animals are living cells. | Plants do not move from place to place. Most of the cells and tissues in plants provide mechanical support and strength. So most of the tissues consists of dead cells because they provide mechanical support and strength to the plant. |
| The growth of animals is more uniform so animals do not have separate dividing and non dividing cells. Animals have organs having specialised functions. So the organs have specialised tissues. | The growth of plants takes place only in some regions. So plants have tissues called meristematic tissues which divide and help in growth and permanent tissues which do not divide. |
Plant tissues
Plant tissues are of two main types:
- Meristematic tissues
- Permanent tissues
Meristematic tissues
Plant tissues in which cells keep on dividing are called meristematic tissue. Meristematic tissues are present in those parts of plants which keep on growing. Meristematic tissues are classified on the basis of their location. They of three types. They are Apical meristematic tissues, Intercalary meristematic tissues and Lateral meristematic tissues.
Apical Meristem
Apical Meristem: Apical meristem is present on root apex, stem apex, leaf buds and flower buds. They are responsible for growth in length, i.e. primary growth.
Lateral Meristem: Lateral meristem is present along the side of the stem. They are responsible for growth in girth, i.e. secondary growth.
Intercalary Meristem: Intercalary meristem is present at the base of leaf or internodes. They are present on either side of the node.
Permanent Tissue
The permanent tissues are formed from those meristematic cells which are left behind and have lost their capability to divide. The division and differentiation of the cells of meristematic tissues give rise to permanent tissues. They have definite shape, size and thickness. The permanent tissue may be dead or living.
As a result of cell differentiation the meristematic tissues tend to form different type of permanent tissues. In cell differentiation, developing tissues changes from simple to more complex forms to perform various specialized functions.
Permanent tissues are of two types. They are:
- Simple permanent tissues
- Complex permanent tissues.
Simple permanent tissues are of three types:
- Parenchyma
- Collenchyma
- Sclerenchyma.
Complex permanent tissues are of two types:
- Xylem
- Phloem
Parenchyma
The cells of parenchyma have thin cell wall. They are loosely packed; with lot of intercellular spaces between them. Parenchyma makes the largest portion of a plant body.
Parenchyma mainly works are packing material in plant parts. The main function of parenchyma is to provide support and to store food.
In some plant parts, parenchyma has chlorophyll as well. In that case, parenchyma carries out photosynthesis and is then termed as chlorenchyma. In aquatic plants, large air cavities are present in parenchyma. This provides buoyancy to the plant, and then the parenchyma is known as aerenchyma.
Collenchyma
The cell wall of collenchyma is thickened at corners. Intercellular spaces are very few. Collenchymas provides some degree of structural rigidity with flexibility.
Collenchymas is present in leaf stalk, below the epidermis. Due to this, the leaf talk can easily bend but does not break.
Sclerenchyma
The cell wall in sclerenchyma is highly thickened all around. The cells are dead and intercellular space is absent. Sclerenchyma provides structural rigidity to plant parts. Bark is composed of sclerenchyma. Another example of sclerenchyma can be seen in the coconut husk.
Stomata
The epidermis of leaves has small pores called stomata. A stoma is a composed of two guard cells which regulate the opening and closing of stoma. Stomata facilitates exchange of gases and transpiration.
Complex permanent Tissues
It consists of more than one type of cells which work together as a unit. It helps in transportation of organic materials, water and minerals. It is also known as conducting or vascular tissue.
Xylem and phloem together form vascular bundles.
Xylem
It is also known as wood and is a vascular and mechanical tissue. Xylem help in Transportation of water and minerals from soil to plant.
Xylem consists of four types of cells called as components or elements:
Tracheids: They are elongated dead cells (primitive elements) mainly involved in conduction of water and minerals in gymnosperms.
Vessles: They are advance element (generally found in angiosperms). Vessels are cylindrical tube like structures placed one above the other end to end which form a continuous channel for efficient conduction of water.
Xylem parenchyma: They are small and thick walled parenchymatous cells designed for storage of starch (food).
Xylem sclerenchyma (fibres): They are non-living fibers with thick walls and narrow cavities which provide mechanical support.
Except xylem parenchyma all other xylem elements are dead.
The annual rings present in the trunk of a tree are xylem rings. By counting the number of annual rings, we can determine the age of a tree.
Phloem
It transport (translocation) food from leaves to other parts of the plant. All phloem cells are living except phloem fibres. Phloem consist of four types of components/elements:
Sieve tubes: Sieve tubes are tubular structures made up of elongated, thin walled cells placed end to end. The end walls of sieve tube cells are perforated by numerous pores called as sieve plates. Nucleus of sieve cell degenerates at maturity. However, cytoplasm persists, because of protoplasmic continuation of sieve tube with companion cell through plasmodesmata.
Companion cells: Companion cells have dense cytoplasm and prominent nuclei. Sieve tubes and companion cells are also called sister cells because they originate from single mother cell.
Phloem fibre/Phloem Sclerenchyma: They give mechanical support to sieve tubes and are dead.
Phloem parenchyma: They store food and help in radial conduction of food.
Animal Tissues
Animal tissues are of four types:
- Epithelial tissue
- Connective tissue
- Muscular tissue
- Nervous tissue
Epithelial Tissue
The epithelial tissue forms the covering or lining of most of the organs. The cells of epithelial tissue are tightly packed and form a continuous sheet. There is small amount of cementing materials between the cells and no intercellular space is present.
Permeability of the epithelial tissue plays a great role in exchange of materials among various organs it also plays an important role in osmoregulation.
All epithelial tissues are separated by the underlying tissue by an extracellular fibrous basement membrane. Epithelial tissues are of following types:
Simple Epithelium: The simple epithelium is composed of a single layer of cells. This type of epithelial tissue forms the lining of blood vessels and alveoli. Thin layer of cells facilitates exchange of substances in such cases.
Cuboidal Epithelium: The cells are cube-shaped in cuboidal epithelium. Linings of kidney tubules and ducts of salivary glands are composed of cuboidal epithelium. Cuboidal cells provide mechanical support. Cells of epithelium may play the role of secretion and then they are called glandular epithelium.
Columnar Epithelium: Cells are column-shaped in columnar epithelium. Columnar epithelium facilitates secretion and absorption. For example; the lining of intestine is composed of columnar epithelium. In some organs, columnar epithelium has cilia present on the outer surface. Cilia facilitate movements of certain substances. The ciliated epithelium in the respiratory tract pushes the mucus forward.
Stratified Epithelium: Cells of the stratified epithelium are in many layers. Skin is an example of stratified epithelium. Stratification of layers prevents wear and tear.
Connective Tissue
The cells of a connective tissue are loosely scattered in a matrix. The matrix can be a fluid, jelly like, dense or rigid. The nature of matrix depends on the function a connective tissue serves. Following are the various connective tissues:
Areolar Connective Tissue: Areolar tissue is found between skin and muscles, around blood vessels and nerves and in bone marrow. Areolar tissue fills the gap between tissues and provides support. It also helps in repair of tissues.
Adipose Tissue: Adipose tissue is composed of fat globules. This tissue is found below the skin and beneath the organs. Adipose tissue provides insulation and works as a cushion.
Bone: Bone is mainly composed of osteoblasts. Bone makes the skeletal system. Skeletal system is responsible for providing structural framework to the body. It provides protection to important organs and facilitates movements.
Cartilage: Cartilage is mainly composed of chondrioblasts. Cartilage is present at the ends of articulatory bones. Cartilage is also present in external ear, bronchii, etc.
Blood: Blood is composed of blood cells, platelets and plasma. Blood plays an important role in transportation of various substances in the body. It also helps in osmoregulation and temperature control.
Muscular Tissue
Muscular tissue is composed of muscle cells. Muscle cells are specialized cells which have the capability to contract and expand. Due to contraction and expansion, muscles facilitate various kinds of movements in the body. Muscular tissues are of three types:
Striated Muscles: The cells of striated muscles are in the form of long, unbranched fibres. Cells are multinucleate. Light and dark bands (striations) are present on muscle fibres; which gives the name striated muscles. Striated muscles are found in those organs where voluntary movement is possible, e.g. hands, legs, back, neck, etc.
Smooth Muscles: The cells of smooth muscles are spindle shaped and each has one nucleus. Smooth muscle is found in those organs where involuntary movement is possible, e.g. alimentary canal.
Cardiac Muscles: The cells of cardiac muscles are in the form of branched fibres. Striations are present and cells are uninucleate. These are found in the heart. Cardiac muscles are capable continuous contraction and relaxation throughout the life.
Nervous Tissue
They are highly specialized tissues due to which the animals are able to perceive and respond to the stimuli. Their functional unit is called as nerve cell or neuron.
Cell body is cyton covered by plasma membrane. Short hair like extensions rising from cyton are dendrons which are further subdivided into dendrities.
Axon is long, tail like cylindrical structure with fine branches at the end Axon is covered by a sheath, which is known as myelin sheath.
Nerve ending of one neuron is very closely placed to the dendrons of another neuron to carry impulses from one neuron to another neuron in the form of electrochemical waves. This close proximity is called as synapse.