TISSUE, Class 9 notes

TISSUES

Tissue can be defined as a group of cells with similar shape and function are termed as tissues. They form a cellular organisational level, intermediate between the cells and organ system. Organs are then created by combining the functional groups of tissues.

Types of Plant Tissues

The classification of plant tissues are mainly based on the two important criteria:

Based on the different part of plants.
Based on the different types of cells.

Plant Tissues are broadly categorised into three tissue systems. This classification is on the basis of parts of the plants they are present.

Epidermis Tissues – cells formed from the outermost surface of the leaves.
Vascular Tissues – involved in transporting fluid and nutrients internally.
Ground Tissue – involved in producing nutrients by photosynthesis and preserve nutrients.

Plant tissue is divided into two types. This classification is on the basis of the types of cells, they comprise.

Meristematic tissues.
Permanent tissues.

Meristematic Tissue

Meristematic tissue is the plant tissue that has the ability to divide actively throughout its life. They are the group of young cells, which consists of continually dividing cells and helps in the increase of length and width of the plant.

Characteristics of Meristematic Tissue

1. The cells of these tissues are commonly called meristems. The zone where these cells exist is known as meristem.

2. Meristematic tissues contain living cells with varied shapes

3. They possess a large nucleus devoid of the vacuole.

4. The cells have no intercellular space.

5. The meristematic tissue has the quality of self-renewal. Every time the cell divides, one cell remains identical to the parent cell, and the others form specialized structures.

6. They have very small and few vacuoles.

7. The meristematic tissue is living and thin-walled.

8. The protoplasm of the cells is very dense.

9. The meristematic tissues heal the wounds of an injured plant.

10. The cells of the meristematic tissue are young and immature.

11. They do not store food.

12. They exhibit a very high metabolic activity.

13. They possess a single, large and prominent nucleus.

Functions of Meristematic Tissue

It is responsible for the growth of the new organs.
Involved in the movement of water and nutrition within the plants.
These tissues are responsible for both primary and secondary growth of the plant.
It is the outermost tissue, functions by providing protection from mechanical injury.
It gives rise to epidermis layer, cortex, endodermis, ground tissue and vascular tissue.

There are different types of meristematic tissues, which are classified on the basis of positions, functions, plane of divisions, origin and development. The three main types of meristematic tissues depending on the occurrence of the meristematic tissue on the plant body are:

Apical Meristem.
Lateral Meristem.
Intercalary Meristem.

Apical Meristem

· These are present at the tips of the roots and shoots and helps in the increase of the height of the plants.

· Various cell divisions facilitate the growth of the cells in the roots and shoots and help in cellular enlargement.

· Apical meristem is divided into-promeristem zone, which contains actively dividing cells, and the meristematic zone, which contains protoderm, procambium and ground meristem.

Intercalary Meristem

· It is located in the leaves and internodes at the intercalary position.

· These help to increase the length of the internode.

· It is found in grass, monocots and pines.

· It is a part of apical meristem and adds to the height of the plant.

Lateral Meristem

· It is located in the stems and roots on the lateral side.

· It increases the thickness of the plant.

· Vascular cambium and cork cambium are the two lateral meristems.

· These divide preclinically or radially and give rise to secondary permanent tissues.

Permanent Tissues

A group of cells which are similar in origin, structure and in function. They are involved in complete growth and differentiation during the ineffective of meristematic activity. There are two types of permanent tissues:

Simple Permanent Tissues.
Complex Permanent Tissues.

Functions of Permanent Tissues

In aquatic plants, these tissues help in floating.
Stores food in the form of starch, proteins, oils and fats.
They provide hardness to fruits such as nuts, coconut, almond etc.
These tissues contain chloroplast which helps in carrying out photosynthesis.
Permanent Tissues are also involved in the Secretion, Transportation, and provides mechanical support to the plants.

Types of Permanent Tissue

Simple Permanent Tissue

These are also known as homogenous tissues. They are made up of a single cell type, usually with the same origin, structure, and function.

Simple permanent tissue is further classified into three types:

Parenchyma

The cells have an oval or round shape.
The cell wall is made up of hemicellulose or cellulose.
The cell is thin-walled.
The cells have vacuoles and very small nucleus.
It is found in all parts of the plant.
The protoplasm is living and dense.

Collenchyma

Cells are long and thick-walled.
The cell wall is made up of cellulose and pectin.
It is the only tissue with the highest refractive index due to the presence of pectin.
It is found in the epidermis and the vascular bundle of dicot leaf.
The amount of chloroplast is less in the cells.
The cells have no intercellular spaces.

Sclerenchyma

These are dead tissues, very hard and rigid in texture.
Cells are thick-walled with various size and shapes.
These provide mechanical support and rigidity to the plant.

Complex permanent Tissue

The complex tissues are made up of various types of cells carrying out distinct functions and are of two types:

Xylem

It transports water and nutrients from the roots to the leaves of the plant.
It provides support to the plants.
It is divided into-tracheids, vessels, xylem fiber, and xylem parenchyma.

Phloem

It translocates the prepared organic food from the leaves to different parts of the plant.
It is also known as bast.
It is composed of sieve tubes, companion cells, phloem parenchyma, and phloem fibres.

Differences between Xylem and Phloem

Xylem	Phloem
Definition
Xylem tissues are the tubular-shaped structure, with the absence of cross walls. This tissue resembles the shape of a star.	Phloem tissues are tubular-shaped, elongated, structures with the presence of walls with thin sieve tubes.
Location
It is located in the centre of the vascular bundle.	It is located on the outer side of the vascular bundle.
Fibres
Xylem fibres are smaller.	Phloem fibres are larger.
Found In
They are present in roots, stems and leaves.	They are present in stems and leaves, which later transports and grow in roots, fruits and seeds.
Movements
These tissues move in a Unidirectional. (only in one direction – upward direction)	These tissues move in a Bidirectional. (both ways – up and down)
Comprises
They live with hollow dead cells.	They live with cytoplasm without the nucleus.
No of Tissues
The total amount of xylem tissue is more.	The total amount of phloem tissue is less.
Features
It consists of tracheids, vessel elements, xylem parenchyma, xylem sclerenchyma and xylem fibres.	It consists of four elements: companion cells, sieve tubes, bast fibres, phloem fibres, intermediary cells and the phloem parenchyma.
Functions
Transports soluble mineral nutrients and water molecules from the roots to the aerial parts of the plant.	Transports food and other nutrients including sugar and amino acids from leaves to storage organs and growing parts of the plant.
Vascular Bundles
Forms vascular bundles with phloem.	Forms vascular bundles with xylem.
Functions
Provides mechanical strength to the plant and helps in strengthening the stem.	Translocates the synthesized sugars by the photosynthetic areas of plants to storage organs like roots, bulbs and tubers.
Functions
It is responsible for replacing the total amount of lost water molecules through transpiration and photosynthesis.	It is responsible for transporting proteins and mRNAs throughout the plant.

Animal Tissue

A group of cells similar in structure, function, and origin is called tissues. In animals, the structure of tissue depends on its function. An animal body is made of four different types of tissues. They have been classified based on the type of cell, function, and location in the body. They include:

Epithelial Tissue
Muscle Tissue
Connective Tissue
Nerve Tissue

A) Epithelial Tissue

All layers and organs in the body are lined by a group of tissues called epithelial tissues which are commonly referred to as epithelium. They cover the surface of all internal as well as external organs. Epithelial tissue is highly permeable. Thus, it plays a significant role in the exchange of substances across the cells and helps in maintaining the osmoregulation. Depending on the number of layers of cells it is composed of, the epithelium has been divided into the simple epithelium and compound epithelium. The main functions of epithelial tissue are protection, secretion, absorption, and sensation.

Squamous Epithelium
Squamous epithelium form an extremely thin and flat layer of tissues. They are semi-permeable and thus, perfect for gaseous exchange. They are present in the lining of oesophagus and mouth.

Cuboidal Epithelium
As the name suggests, they are cuboidal in shape and form the lining of salivary glands and kidney tubules. They provide mechanical support. They also form glandular epithelium when they form glands.

Columnar Epithelium
These tissues line the organs which help in absorption and secretion, such as lining of intestines. They are made up of elongated cells. When cilia is present on these cells, they form ciliated columnar epithelium like those present in the respiratory tract.

Stratified Squamous Epithelium
This kind of tissue is formed when multiple layers of squamous epithelium are arranged in a pattern. Our skin is made up of this kind of tissue.

B) Muscular Tissue

These tissues make up our muscles which are responsible for almost all the movements that take place in the body.

Properties of Muscular Tissue

1. Contractibility– It is the ability of muscle cells to shorten forcefully.

2. Extensibility– A muscle has the ability to be stretched.

3. Elasticity– The muscles have the ability to recoil back to its original length after being stretched.

4. Excitability– The muscle tissue responds to a stimulus delivered from a motor neuron or hormone.

Types of Muscular Tissue

The muscular tissue is of three types:

· Skeletal Muscle Tissue

· Smooth Muscle Tissue

· Cardiac Muscle Tissue

Skeletal Muscle Tissue

· These muscles are attached to the skeleton and help in its movement.

· These muscles are also known as striated muscles because of the presence of alternate patterns of light and dark bands.

· These light and dark bands are sarcomeres which are highly organized structures of actin, myosin, and proteins. These add to the contractility and extensibility of the muscles.

· Skeletal muscles are voluntary muscles composed of muscle fibers.

· 40% of our body mass comprises skeletal muscles.

· Each skeletal tissue contains myofibrils.

· The cells of these tissues are multinucleated.

· These are provided with blood vessels and many elongated mitochondria and glycogen granules.

· They bring about the movement of the organs of the body.

· They are long, cylindrical, unbranched with striations and are multinucleated.

· They are called skeletal because these tissues are mostly attached to the bones.

Smooth Muscle Tissue

· These are non-striated, involuntary muscles controlled by the Autonomous Nervous System.

· It stimulates the contractility of the digestive, urinary, reproductive systems, blood vessels, and airways.

· The actin and myosin filaments are very thin and arranged randomly, hence no striations.

· The cells are spindle-shaped with a single nucleus.

· They are long, smooth, spindle shaped and uninucleate.

Cardiac Muscle Tissue

· These are found only in the heart.

· These are involuntary muscles and the heart pumps the blood through cardiac contractions.

· The cells of the cardiac muscles known as the cardiomyocytes are striated.

· They are single-celled and uninucleated.

The ends of the cells are joined and the junctions are called intercalated discs. The cells are attached to each other by desmosomes.
Structurally they may look quite similar to striated muscles but they are branched, uninucleate and have intercalated discs.
These muscles are involuntary in nature and show rhythmic contractions and relaxations.,

Cardiac muscle	Striated muscle
Cardiac muscles are multinucleate and branched	Striated muscles are multinucleate and unbranched
These are involuntary	These are voluntary
These are found in the heart	Attached to bones of the entire body
Shorter in length	Longer in length
Controlled by Autonomic nervous system	controlled by somatic nervous system
Semi-spindle	cylindrical
Help in Pumping blood	Help in Movement of the body
Gap junctions present	Gap junctions absent
Speed of contraction is fast	Speed of contraction is low
Never fatigue	Fatigue

C) Connective Tissue

Connective tissues are made up of a matrix consisting of living cells and a non-living substance, called the ground substance. The ground substance is made of an organic substance (usually a protein) and an inorganic substance (usually a mineral or water). The principal cell of connective tissues is the fibroblast. This cell makes the fibers found in nearly all of the connective tissues. Fibroblasts are motile, able to carry out mitosis, and can synthesize whichever connective tissue is needed.

1. Loose/Areolar Connective Tissue

Loose connective tissue is found around every blood vessel and helps to keep the vessel in place. The tissue is also found around and between most body organs. Aaeolar tissue is tough, yet flexible, and comprises membranes. Loose connective tissue is composed of loosely woven collagen and elastic fibers. The fibers and other components of the connective tissue matrix are secreted by fibroblasts.

It is found underneath the skin; also around nerves and blood vessels.
It is composed of fibroblasts, macrophages and mast cells.
It provides support and repair tissues.
These tissues are widely distributed and serve as a universal packing material between other tissues.
The functions of areolar connective tissue include the support and binding of other tissues.

2. Fibrous Connective Tissue

Fibrous connective tissues contain large amounts of collagen fibers and few cells or matrix material. The fibers can be arranged irregularly or regularly with the strands lined up in parallel. Irregularly arranged fibrous connective tissues are found in areas of the body where stress occurs from all directions, such as the dermis of the skin.

3. Cartilage

Cartilage is a connective tissue with a large amount of the matrix and variable amounts of fibers. The cells, called chondrocytes, make the matrix and fibers of the tissue. Chondrocytes are found in spaces within the tissue called lacunae.

Cartilage is made of chondrocytes with dense, flexible intercellular materials.
In the majority of vertebrates, cartilages in embryos get replaced by bones on maturity.
They are present at the tips of external ears, bronchi, vertebral column, etc.

4. Adipose Tissue:

Adipose tissue, or fat tissue, is considered a connective tissue even though it does not have fibroblasts or a real matrix and only has a few fibers. Adipose tissue is made up of cells called adipocytes that collect and store fat in the form of triglycerides, for energy metabolism. Adipose tissues additionally serve as insulation to help maintain body temperatures, allowing animals to be endothermic, and they function as cushioning against damage to body organs.

It is present in skin and organs.
It is composed of fat globules and is characterized by fat storage
It provides insulation due to the fat present.

Areolar tissue and adipose tissue are two types of loose connective tissues where the cells and fibres are loosely scattered in the semi-fluid matrix.

5. Bone

Bone, or osseous tissue, is a connective tissue that has a large amount of two different types of matrix material. The organic matrix is similar to the matrix material found in other connective tissues, including some amount of collagen and elastic fibers. This gives strength and flexibility to the tissue.

Bone is a hard connective tissue which forms the framework of the body.
It has a rigid matrix rich in calcium and collagen fibres.
Functions include protection, support, facilitates movements and serves as a site for blood cell production.

6. Blood:

Blood is a fluid connective tissue that consists of plasma, blood cells and platelets. It circulates throughout our body delivering oxygen and nutrients to various cells and tissues. It makes up 8% of our body weight. An average adult possesses around 5-6 litres of blood.

Blood is the only fluid connective tissue composed of blood cells (RBC, WBC, and platelets) and plasma.
Functions: Transportation, defence and blood clotting.

D) Nervous Tissue

They are the main tissue components of the brain and spinal cord in the central nervous system. While, in the peripheral nervous system, the neural tissue forms the cranial nerves and spinal nerves.

Functions of Nervous Tissue

The nervous tissue forms the communication network of the nervous system and is important for information processing. The other major functions of nervous tissue in the body are:

Response to stimuli.
Stimulates and transmits information within the body.
Plays a major role in emotions, memory, and reasoning.
Maintains stability and creates an awareness of the environment.
Nervous tissue is involved in controlling and coordinating many metabolic activities.

Neurons

Neurons, also known as nerve cells, send and receive signals from your brain. While neurons have a lot in common with other types of cells, they’re structurally and functionally unique.

Parts of a neuron

Cell body

Also known as a soma, the cell body is the neuron’s core. The cell body carries genetic information, maintains the neuron’s structure, and provides energy to drive activities.

Like other cell bodies, a neuron’s soma contains a nucleus and specialized organelles. It’s enclosed by a membrane which both protects it and allows it to interact with its immediate surroundings.

Axon

An axon is a long, tail-like structure which joins the cell body at a specialized junction called the axon hillock. Many axons are insulated with a fatty substance called myelin. Myelin helps axons to conduct an electrical signal. Neurons generally have one main axon.

Dendrites

Dendrites are fibrous roots that branch out from the cell body. Like antennae, dendrites receive and process signals from the axons of other neurons. Neurons can have more than one set of dendrites, known as dendritic trees. How many they have generally depends on their role.

For instance, Purkinje cells are a special type of neuron found in the cerebellum. These cells have highly developed dendritic trees which allow them to receive thousands of signals.