Chapter 6 – Tissues

Topics

• 1. Introduction
• 2. Tissue
• 3. Types of tissues
• 4. Plant Tissues
• 5. Merismatic Tissues
• 6. Permanent Tissues
• 7. Simple Permanent Tissues
• 8. Parenchyma
• 9. Collenchyma
• 10. Sclerenchyma
• 11. Complex Permanent Tissues
• 12. Xylem

Introduction

• Till now we studied that all the organisms are made of cells.
• On the basis of cell they are divided into unicellular (single-celled) and/or multicellular (two or more celled).
• Example-Amoeba (unicellular), in case of amoeba all the functions are carried out by the single cell, whether it is digestion, excretion, respiration, but in case of human beings or plants (multicellular), all these functions are assigned to different cells rather different tissues or organs or organ systems.

• Now the question here arises “How the cells form multicellular organisms? How they are connected to each others? What are the tissues? How they are formed? etc.
• So, the answer is that the cells of multicellular organisms grow and divide and form small groups of cells, these groups of cell combine and specialize each other for specific function of the body. These groups or clusters of cells are called tissues.
• Similarly, tissues form groups and combine to form organs and organs then form organ systems.

TISSUE

• The name tissue was coined by Grew.
• The group of cells with similar in origin, structure and function are called tissues.
• Histology- the study of tissues.
• It is one of the building blocks of an organism (animal or plant).
• An organism is comprised of tissues, which are made up of individual cells.
• These cells share a similar structure (how they’re built) and function (what they do).
• Why tissues are important? It’s simple… Tissues are what makes up our bodies; everything from our bones to organs like our heart and brain! Even blood is considered to be a tissue.

Types of tissues

The tissues are divided into plant tissues and animal tissues.

1. PLANT TISSUES
2. ANIMAL TISSUES

PLANT TISSUES

• Plants are stationary and are fixed to their place; they don’t move and have limited growth.
• Plants have special supportive tissues which provide them structural strength.
• Most of the plant tissues are dead.
• The dead cells provide mechanical strength to the plants.

MERISMATIC TISSUES

• The cells of meristematic tissue have the power of division, which mean these are the dividing tissues of the plant.
• In meristematic tissues, the cells are highly active, have dense cytoplasm, large nucleus, thin cytoplasm and vacuole smaller in size or may be absent.
• The new cells produced by meristematic cells are initially like meristem but later on maturation they differentiate into other tissues.

• On the basis of position they are divided into 3 parts:-

APICAL

• Present at the tip (growing region) of the plant’s stem and root.
• It helps the plant to grow in length.

INTERCALARY

• Present at the base of the leaves or internodes on twigs

LATERAL

• It helps to increase the girth (thickness) of stem and root in the plants.

PERMANENT TISSUES

• The meristem after attaining maturition loses their ability to divide and take up a specific role and form permanent tissues.
• The process in which the meristematic tissues take a permanent shape, size and function is known as differentiation. This implies the cells of meristematic tissues differentiate to form different types of permanent tissues.

SIMPLE PERMANENT TISSUES

• The simple permanent tissues are made of similar cells performing similar functions.
• These are the basic packaging tissues in the plants.

PARENCHYMA

• Consist of live unspecialized cells having thin cell wall.
• They are loosely packed and have large intercellular space (space between the cells).
• Provides support to the plant and present in all parts like roots, stems, leaves, fruits and seeds.
• Storage of food (eg. Fruits) and water (in stems eg. cactus) is the main function.
• Sometimes, these tissues also contain chlorophyll and perform photosynthesis, and known as chlorenchyma.
• In case of aquatic plants, parenchyma is modified into aerenchyma.
• Aerenchymais the tissues having large air cavities which provides buoyancy to the plants and help them to float.

COLLENCHYMA

• The cells of the tissue are living, elongated, and have irregularly thickened corners.
• The term was coined by Schleiden.
• It provides flexibility and mechanical support to the plants.
• They have a little intercellular space.
• It allows easy bending of plants (leaf and stem) without breaking.

SCLERENCHYMA

• The tissues are dead which makes the plant hard and stiff (eg. Husk of coconut).
• Structurally they are long and narrow.
• The walls of the cell are thick due to the presence of lignin.
• They lack intercellular space.
• These tissues are present in stem, covering of seeds, nuts, around the veins of the leaves, around vascular bundles.

COMPLEX PERMANENT TISSUES

• These are the tissues made of different types of cells; all the cells combine to perform a common function.
• They constitute of vascular bundles.
• Complex permanent tissues are of two types:-

XYLEM

• These are dead and thick walled cells.
• Xylem is the water conducting element (transportation of water) which also provides mechanical strength to the plant.

• They are further divided into four components:-

TRACHEIDS

• It is a tubular structure.
• The cells are elongated with sharp ends
• Help in the transportation of water and minerals vertically.
• Their main function is conduction of water.

VESSELS

• It is a tubular structure.
• The cells are elongated and aligned end to end.
• Help in the transportation of water and minerals vertically.
• Their main function is conduction of water.

XYLEM PARENCHYMA

• Help in storage of food.
• It conducts water in sideways.

XYLEM FIBRES

• They are supportive in function.
• The cells are both elongated and pointed at the end.

PHLOEM

• Phloem is the food conducting element (transportation of food).
• The material (food) can move in both the directions (i.e. toward the root and shoot) because phloem transports food from leave to other parts of the plant.

• Phloem is divided into four components:-

SIEVE TUBES 

• These are the tubular cells having perforated walls (small pores in the wall).

COMPANIAN CELLS

• They are living parenchymatous cells.
• The cell wall is thin.
• The sieve tube and companion cells are originated from the same mother cells.

PHLOEM FIBRES

• They are the dead cells made of sclerenchymatous tissues.
• Examples: jute, flex, hemp.

PHLOEM PARENCHYMA  

• They are the living parenchymatous
• They help in storage of food.
• They have nucleus and cellulosic cell wall.
• They are absent in monocots.

ANIMAL TISSUES

• Animals move around in search of food and shelter.
• Animals consume more energy as compared to plants.
• Most of the animal tissues are living.
• The structural organization of organ and organ system is more complex in animals.
• Animal tissues are divided into four types:-

EPITHELIAL TISSUES

• It consists of cells which form membranes.
• This membrane covers the body surface and the glands.
• 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.
• The 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.
• These are divided into four types:-

SIMPLE

• The cells are extremely thin and flat and form a delicate lining.
• The lining of oesophagus and the mouth are covered with squamous epithelium.

STRATIFIED

• The 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
• The skin, which protects the body, is made of squamous epithelium.

COLUMNAR

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

• 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.

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CONNECTIVE TISSUES

• It protects and supports the body.
• The cells 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.

AREOLAR

• It fills the space inside the organs, and supports internal organs.
• It helps in repair of tissues.
• It is found between the skin and muscles, around blood vessels and nerves and in the bone marrow.

ADIPOSE

• They are the Fat storing tissues, which are filled with fat globules
• These tissues are found below the skin and between internal organs.
• Due to the storage of fats, it acts as an insulator.

COMPACT BONE

• It forms the framework which 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.
• Two bones can be connected to each other by another type of connective tissue called the ligament.
• This tissue is very elastic and has considerable strength.
• Ligaments contain very little matrix.
• Another type of connective tissue is tendons
• Tendons are fibrous tissue which connects bones to muscles.
• They are with great strength but limited flexibility.

HYALINE CARTILAGE

• They are widely spaced cells.
• The solid matrix is composed of proteins and sugars.
• Cartilage smoothen bone surfaces at joints.
• It is present in the nose, ear, trachea and larynx.

BLOOD CELLS

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

MUSCULAR TISSUES

• It consists of elongated cells, which are also known as muscle fibres.
• It helps in movement of body structure.
• They contain special proteins called contractile proteins, which contract and relax to cause movement in the body.

STRIATED

• The cells are long, cylindrical, unbranched and multinucleate (having many nuclei).
• These muscles are called voluntary muscles, because they show movement when we want.
• These muscles are also called skeletal muscles.
• They are mostly attached to bones and help in body movement.
• These muscles show alternate light and dark bands or striations when observed under the microscope, due to this reason they are also called striated muscles.

SMOOTH/UNSTRIATED

• The cells are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus).
• They are also called unstriated muscles.
• They are under the control of involuntary muscles.
• The movement of food in the alimentary canal or the contraction and relaxation of blood vessels are involuntary movements.
• They are also found in the iris of the eye, in ureters and in the bronchi of the lungs.

CARDIAC

• The muscles of the heart are involuntary in nature and called cardiac muscles.
• The cells are cylindrical in shape, branched and uninucleate.
• The heart muscles show rhythmic contraction and relaxation throughout life.

NERVOUS TISSUE

The cells of nervous tissue are highly specialized and the cells of this tissue are called nerve cells or neurons.

• Nervous tissue stimulates and transmits the stimulus very rapidly from one place to another within the body.
• The brain, spinal cord and nerves are composed of the nervous tissue.
• A neuron consists of a cell body which comprises of nucleus and cytoplasm, from which long thin hair-like parts arise.
• The neuron has a single long part, called the axon, which transmit the nerve impulse to body parts.
• The neuron has short, branched parts called dendrites.
• Many nerve fibers combine together by connective tissue and form a nerve.
• Nerve impulse enables animals to move rapidly in response to stimuli.