EduDias: ICSE 7 Biology Tissues Basic

1.0 Introduction to Tissues

While unicellular organisms perform all life activities within a single cell, multicellular organisms like plants and animals require a division of labor. This is achieved through the formation of tissues.

Definition

Tissue: It is a group of similar or dissimilar cells that work together to perform a specific function.

2.0 Classification of Plant Tissues

2.1 Meristematic Tissue (Meristems)

Meristematic tissue is composed of immature cells that divide continuously throughout the life of the plant. They are the primary engines of plant growth.

Laboratory Observation: Onion Root Growth

If you place an onion in water, the roots grow due to active meristematic cells at the tips. If you cut the tips (0.5 cm), growth stops immediately because you have removed the meristematic tissue.

Characteristics of Meristematic Cells

Feature	Description
Cell Nature	Immature, small, and undifferentiated.
Cytoplasm	Dense cytoplasm with a prominent nucleus.
Intercellular Spaces	Absent; cells are very tightly packed.
Cell Wall	Thin and flexible to facilitate division.

Types Based on Position

A. Apical Meristem: Found at the tips of roots and shoots. They are responsible for axial growth (length).

B. Intercalary Meristem: Located at the base of leaves or internodes. They help in the elongation of the internodal region.

C. Lateral Meristem: Located on the lateral sides of stems and roots. They increase the radial growth (girth/thickness).

⚠️ Important Note:

Remember that permanent tissues like Xylem and Phloem are not separate from birth; they are actually derived from meristematic tissues after they stop dividing!

Fig 1.1: Longitudinal section showing Meristematic Zones

3.0 Permanent Tissues

When cells formed by meristematic tissues stop dividing and attain a definite shape, size, and function, they become Permanent Tissues. They may be living or dead.

Two Major Groups:

Simple Permanent Tissue: Made of only one type of cell.
Complex Permanent Tissue: Made of different types of cells working together.

3.1 Simple Permanent Tissues

There are three main types based on their structure and function:

A. Parenchyma (The Bulk Tissue)

The most common tissue. Cells are living, thin-walled, and loosely packed with large intercellular spaces.

Function: Stores food and provides support. In leaves, it contains chlorophyll to perform photosynthesis.

B. Collenchyma (The Flexible Tissue)

Cells are living and elongated. Walls are irregularly thickened at the corners. There is very little space between cells.

Function: Provides flexibility and mechanical support, allowing plant parts (like leaf stalks) to bend without breaking.

C. Sclerenchyma (The Hard Tissue)

Cells are dead, long, and narrow. Walls are very thick due to the deposition of lignin.

Function: Provides strength, rigidity, and elasticity to plant parts (e.g., husk of coconut, hard shell of nuts).

3.2 Complex Permanent Tissues (Vascular Tissues)

These are conducting tissues responsible for transport. They consist of Xylem and Phloem.

Feature	Xylem	Phloem
Main Function	Transports water and minerals.	Transports food (sugar).
Direction	Vertical (Upwards).	Bi-directional (All parts).
Components	Vessels, Tracheids, Xylem Parenchyma/Fibres.	Sieve tubes, Companion cells, Phloem Parenchyma/Fibres.

3.3 Epidermis

The Epidermis: The outermost layer of the entire plant body. It is continuous without intercellular spaces.

Protects against mechanical injury and infection.
Allows gas exchange via stomata.

Did You Know?

The "wood" of a tree is primarily composed of old Xylem tissue, while the "husk" of a coconut is pure Sclerenchyma!

Fig 1.2: Cross-section of Xylem and Phloem

4.0 Introduction to Animal Tissues

Animal bodies are highly complex. To perform diverse life processes like movement, digestion, and coordination, cells are organized into four broad categories of tissues: Epithelial, Connective, Muscular, and Nervous.

4.1 Epithelial Tissues (The Covering)

Epithelium: It forms the outermost covering of the body, internal organs, and body cavities. Cells are tightly packed with no intercellular spaces.

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Classification based on Cell Shape

Type	Appearance	Location & Function
Squamous	Thin, flat, and delicate.	Lining of mouth, esophagus, and blood vessels. Provides protection.
Columnar	Tall, pillar-like cells.	Lining of intestine. Helps in absorption and secretion.
Ciliated	Columnar with hair-like cilia.	Respiratory tract. Cilia move mucus forward.
Cuboidal	Cube-shaped cells.	Kidney tubules and salivary ducts. Provides mechanical support.

5.0 Connective Tissues (The Binder)

Connective tissues are loosely packed cells embedded in an intercellular matrix. They are divided into three types:

A. Fluid Connective Tissue

Blood: Consists of Plasma (liquid), RBCs (transport oxygen), WBCs (fight infection), and Platelets (clotting).

Lymph: Blood minus RBCs. Helps in body defense and immunity.

[Image showing components of human blood: red cells, white cells, and platelets in plasma]

B. Skeletal Tissue

Bone: Strong, non-flexible, made of calcium and phosphorus. Provides structural support.

Cartilage: Flexible matrix of proteins and sugars. Found in the nose, ear, and trachea.

⚠️ Important Note: Connective Tissue Proper

Ligaments: Elastic and strong; Connects Bone to Bone.
Tendons: Fibrous and strong; Connects Muscle to Bone.
Areolar Tissue: Found between skin and muscles; fills space inside organs and supports tissue repair.

Did You Know?

Your ears and nose can bend easily because they are made of cartilage, which is much more flexible than bone!

Fig 1.3: Diverse forms of Connective Tissue

6.0 Muscular Tissues (The Movers)

Movement in animals is brought about by Muscular Tissues. They are made of elongated cells called muscle fibers which contain contractile proteins that contract and relax to cause movement.

Classification of Muscles

Type	Structure	Function & Nature
Striated (Voluntary)	Cylindrical, unbranched, multinucleated. Has dark/light bands.	Attached to bones. Movements can be controlled by our will.
Non-striated (Involuntary)	Spindle-shaped, uninucleated, smooth (no bands).	Alimentary canal, blood vessels. Movements cannot be controlled.
Cardiac	Cylindrical, branched, uninucleated.	Found only in the Heart. Performs rhythmic contraction for heartbeat.

7.0 Nervous Tissue (The Controller)

Nervous Tissue: It is specialized to respond to stimuli and transmit impulses rapidly throughout the body. It forms the brain, spinal cord, and nerves.