Tissues

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Introduction

• Every cell/ tissues performs a specific function.
• A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.

Tissues

Plant Tissues

• Meristematic tissues : These are dividing tissues, which divide throughout during a plant life span.

1. Apical meristems : These are present at the tip of root or stems, it helps in increasing the length of the plant.
2. Lateral meristems : The girth of the root/stem increases. Also known as cambium.
3. Intercalary meristems : Seen in some plants located near node. These are regenerating tissues.

Plant: Simple Permanent Tissues

• Here, the plant take up specific function and loose the ability to divide.
• The process of taking up a permanent shape, size, and a function is called differentiation.
• Parenchyma :

1. It has thin cell walls.
2. These are living cells.
3. They have large intercellular spaces in between.
4. This tissue photosynthesizes and stores food.

• Sometimes parenchyma modifies into :

1. Chlorenchyma: Contains chlorophyll, helps in photosynthesis.
2. Aerenchyma: Present in aquatic plants, helps in buoyancy.

• Collenchyma :

1. Provides flexibility to plant parts.
2. Allows bending of tendrils, stems of climbers.
3. Also provides mechanical support.
4. These are living, there is very little intercellular space.

• Sclerenchyma :

1. Makes the plant hard and stiff.
2. This is a dead tissue.
3. Its walls are thickened due to the deposition of lignin.
4. Walls are thick with no intercellular space in between.
5. Provides mechanical strength to the plants.
6. Present in the husk of coconut.
7. Constitutes the hard covering of seeds and nuts.

Plant: Complex Permanent Tissues

• Xylem Tissues

Xylem parenchyma	Xylem fibre	Vessels	Tracheid
Living	Dead	Dead	Dead
Helps in photosynthesis, and storage of food.	Helps in providing mechanical strength.	Have thick walls, Tubular structures, Helps in transporting water and minerals.	They too have thick walls and tubular structures. Help in transporting water and minerals.

• Phloem Tissues

Phloem  parenchyma	Phloem fibre	Companion cells	Sieve tube
Living	Dead	Living	Living
It stores food materials in the form of starch and fats. It also helps in the translocation of  food.	Provides mechanical support to the plant body.	Works in association with sieve tubes.	These are tubular structures with perforated walls, Transports food throughout the whole plant body.

Epidermis

• The outer most layer of cells, covering the plant body is known as epidermis.
• Epidermis is usually made up of single layer of cells.
• Desert plants, have thicker epidermis so to prevent excess loss of water.
• Epidermal cells on the aerial parts of the plant often secrete a waxy, water resistant layer on their outer surface. This aids in protection against loss of water, mechanical injury and invasion by parasitic fungi.
• On the epidermis of the leaf there are pores called as stomata.
• Stomata are enclosed by two kidney-shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere.
• Transpiration (loss of water in the form of water vapor) also takes place through stomata.
• Epidermal cells of the roots bear long hair-like structures for absorption as it increases the total surface area for absorption.

Picture Showing Loss Of Water From Aerial Parts Of The Plant : Transpiration

• In some plants like desert plants, epidermis has a thick waxy coating of cutin (chemical substance with waterproof quality) on its outer surface.
• A strip of secondary meristem located in the cortex forms layers of cells which constitute the cork. They also have a substance called suberin in their walls that makes them impervious to gases and water.

Animal Tissues

Epithelial Tissue

1. The covering or protective tissue in animal body is known as epithelial tissue.
2. It covers most organs and cavities within the body.
3. These are tightly packed.
4. They have almost no intercellular space between them.
5. Epithelial tissue is of 4 major types :

Squamous epithelium
Cuboidal epithelium
Columnar epithelium
Stratified epithelium

• Squamous epithelium:

1. This is very thin and flat tissue.
2. It makes a protective layer as lining of the esophagus.
3. The makes the lining of the mouth.
4. It also makes the lining of the skin.

• Cuboidal epithelium :

1. As the name suggests , it has cube like structure.
2. Forms the lining of kidney tubules and ducts of salivary glands.
3. Sometimes, it also provides mechanical support.

• Columnar epithelium :

1. As the name suggests its shape is pillar-like or column-like.
2. It lines the inner surface of the intestine.
3. It also lines the respiratory tract.
4. Sometimes, it can have hair-like projections on the outer surface of the epithelium, these cilia can move particles and other substances to the destination, this type of epithelium is known as ciliated columnar epithelium.

• Note: Sometimes the epithelium tissue modifies into specialized gland cells, which secrete substances, it folds inward into a multicellular gland and thus known as glandular epithelium.

• Note – Cuboidal and columnar epithelium is found in places where absorption and secretion occurs.

Connective Tissue

• As the name suggests “connective tissue” is the one which connects different parts of our body.
• These are loosely packed and embedded in an intercellular matrix.
• The matrix may be jelly-like fluid, dense or rigid.

• Areolar tissue :

1. Found between the skin and muscles, around blood vessels and nerves and in the bone marrow.
2. It fills the space inside the internal organs .

• Adipose tissue :

1. Found below the skin and between internal organs.
2. The cells of this tissue are filled with fat globules. Storage of fats also lets it act as an insulator.

• Blood :

1. Cellular elements :
   RBC (erythrocytes)
   WBC (leucocytes)
   Platelets (thrombocytes)
2. Fluid : The fluid component of blood is plasma.
3. Plasma contains proteins, salts and hormones.
4. Blood transports gases, hormones, digested foods, and waste products.

• Bone:

1. It forms the framework that supports the body.
2. It also supports and protects the main organs of our body.
3. It is strong, hard and non-flexible.
4. Bones embedded in a hard matrix which is composed of calcium and phosphorus compounds.

• Bones to bones connection – Ligament
• Muscles to bones – Tendons

• Cartilage :

1. Its matrix is composed of proteins and sugars.
2. Present in :
   Ear
   Nose
   Trachea
   Larynx

Matrix of Bone

Matrix Of Cartilage

Muscular Tissue

Striated muscles	Unstriated muscles	Cardiac muscles
Found in skeletal muscles	Found around internal organs like alimentary canal, iris of eye etc.	Found in heart.
These muscles show striations or stripes.	These have no striations hence appear smooth.	These are also smooth in appearance.
These are long and cylindrical.	These are spindle shaped.	These are cylindrical.
Unbranched.		Branched.
Multinucleated.	Uninucleated.	Uninucleated.

Nervous Tissue

• The structural and functional unit of nervous system is a neuron.
• A neuron has the following parts:

1. Dendrites
2. Cell body also known as perikaryon
3. Axon
4. Nerve endings also known as synaptic bulb.

• The gap between two neurons is known as synaptic cleft.
• Pre-synaptic region + Synaptic cleft + Post-synaptic region = Synapse