What Is A Tissue?

A **tissue** is defined as a group of cells that are **similar in structure** and/or **work together** to perform a **specific function**. These cells are often organised in a particular way to achieve the highest possible efficiency for that function.

Examples of tissues include:

• In animals: Blood, muscle tissue, nerve tissue.
• In plants: Phloem, xylem.

The formation of tissues in multicellular organisms allows for division of labour and increased efficiency in carrying out complex life processes.

---

Are Plants and Animals Made of Same Types of Tissues?

Despite both being multicellular organisms, plants and animals are fundamentally different in their structure, function, and lifestyle, which is reflected in the types of tissues they possess.

• **Mobility:** Plants are typically fixed or stationary, while animals move around in search of resources.
• **Energy Consumption:** Animals generally require more energy than plants due to locomotion.
• **Supportive Tissue:** Plants require a large amount of supportive tissue to stand upright. This supportive tissue in plants often consists of dead cells. Animals have supportive tissues (like bone and cartilage), but a larger proportion of animal tissues are living.
• **Growth Pattern:** Growth in plants is often limited to certain regions containing actively dividing tissues (meristems), which continue to divide throughout the plant's life. Animals exhibit more uniform growth, and there is no clear demarcation of dividing and non-dividing regions.
• **Structural Organisation:** The organisation of organs and organ systems is generally more complex and highly specialised in animals compared to plants. This difference is linked to their different modes of obtaining nutrition (plants are autotrophs, animals are heterotrophs) and movement (sedentary plants vs. motile animals).

These differences mean that the types of tissues found in plants and animals are distinct and adapted to their specific needs and lifestyles.

Answer:

Answer:

Plant Tissues

Plant tissues can be classified into different types based on their dividing capacity. These are meristematic tissue and permanent tissue.

---

Meristematic Tissue

**Meristematic tissue** is the actively dividing tissue in plants. It is responsible for plant growth. Meristematic tissue is located in specific regions of the plant where growth occurs. The cells in this tissue are very active, with dense cytoplasm, thin cellulose cell walls, prominent nuclei, and they typically lack vacuoles (as they are rapidly dividing and not storing significant amounts).

Based on their location, meristematic tissues are classified into three types:

• **Apical meristem:** Present at the **tips of stems and roots**. Responsible for increasing the **length** of the plant (primary growth).
• **Lateral meristem:** Found along the **sides of stems and roots** in some plants (especially woody plants), forming the cambium. Responsible for increasing the **girth or diameter** of the stem and root (secondary growth).
• **Intercalary meristem:** Located at the **base of leaves or internodes** (between nodes) in some plants, such as grasses. Responsible for growth in length of the internode and is involved in the regeneration of parts removed by grazing.

Cells produced by meristems initially resemble meristematic cells, but as they mature, they undergo **differentiation**, developing into specific types of permanent tissues with specialized shapes, sizes, and functions.

---

Permanent Tissue

**Permanent tissues** are formed from meristematic tissues after the cells have undergone differentiation and lost their ability to divide. They have taken up a permanent shape, size, and function.

Permanent tissues are broadly classified into two types: simple permanent tissue and complex permanent tissue.

---

Simple Permanent Tissue

Simple permanent tissues are composed of cells that are **similar in structure and function**. There are three main types:

• **Parenchyma:** This is the most common simple permanent tissue. It consists of relatively **unspecialised, living cells** with **thin cell walls**. Parenchyma cells are typically loosely arranged, leaving **large intercellular spaces** between them.
  • Function: Primarily involved in **storage of food**.
  • Modifications: If parenchyma contains chlorophyll and performs photosynthesis, it's called **chlorenchyma**. In aquatic plants, parenchyma with large air cavities for buoyancy is called **aerenchyma**.
• **Collenchyma:** This tissue provides **flexibility** and **mechanical support** to plant parts like leaf stalks and young stems, allowing them to bend without breaking. Collenchyma cells are **living, elongated, and irregularly thickened at the corners**. They have **very little intercellular space**.
• **Sclerenchyma:** This tissue provides **strength and rigidity** to the plant, making it hard and stiff. Cells of sclerenchyma are **dead** and have **thickened walls** due to the deposition of **lignin** (a hard, waterproof substance). The cell walls are often so thick that the internal space (lumen) is very narrow or absent.
  • Location: Found in stems, around vascular bundles, in the veins of leaves, and in the hard coverings of seeds and nuts (like the husk of a coconut).
  • Function: Provides **mechanical strength** and support.

---

Protective Tissues (Epidermis and Cork)

The outermost layer of cells covering the entire surface of a plant is called the **epidermis**. Epidermis is usually a single layer thick (thicker in dry habitats for water conservation). Epidermal cells are flat and form a continuous sheet with no intercellular spaces, providing protection against water loss, mechanical injury, and pathogen invasion. On aerial parts, epidermal cells may secrete a waxy, waterproof layer called the **cuticle**.

Small pores called **stomata** are present in the epidermis of leaves (and sometimes stems). Each stoma is surrounded by two kidney-shaped cells called **guard cells**, which regulate the opening and closing of the pore. Stomata are essential for **gaseous exchange** ($\text{CO}_2$ intake for photosynthesis and $\text{O}_2$ release) and **transpiration** (loss of water vapour).

Epidermal cells of roots involved in water absorption often have long, hair-like extensions called root hairs, which greatly increase the surface area for absorption.

As plants grow older, especially in stems and roots, the outer protective tissue changes. A layer of cells in the cortex becomes the **cork cambium** (a secondary meristem), which produces layers of **cork** (or bark). Cork cells are **dead** and are arranged compactly without intercellular spaces. Their walls contain a substance called **suberin**, which makes them **impervious to gases and water**, providing excellent protection to the underlying tissues against water loss, mechanical injury, and infection.

---

Complex Permanent Tissue

Complex permanent tissues are made up of **more than one type of cells**, but all these cell types work together to perform a **common function**. The main types of complex permanent tissues are **xylem** and **phloem**. Together, they form the vascular tissues and are often bundled together in **vascular bundles**.

Vascular tissues are crucial for the survival of complex plants on land, enabling the efficient transport of water, minerals, and food over long distances.

• **Xylem:** The primary function of xylem is the **conduction of water and dissolved minerals** from the roots upwards to the leaves. It also provides **mechanical support** to the plant. Xylem is composed of four main types of elements:
  • **Tracheids:** Elongated, tapering, dead cells with thickened, lignified walls.
  • **Vessels:** Tubular structures formed from dead cells joined end to end, with thickened, lignified walls. Tracheids and vessels form continuous tubes for water transport.
  • **Xylem parenchyma:** Living cells that store food and help in the lateral transport of water.
  • **Xylem fibres:** Sclerenchymatous cells that provide mechanical support.

  Except for xylem parenchyma, xylem elements are generally dead cells at maturity, providing a continuous pipeline for water transport.

• **Phloem:** The primary function of phloem is the **translocation (transport)** of **food** (sugars produced during photosynthesis) from the leaves to other parts of the plant (roots, storage organs, growing regions). Phloem is composed of five main types of elements:
  • **Sieve cells and Sieve tubes:** Tubular cells responsible for transporting food. Sieve tubes have perforated walls (sieve plates) at the ends.
  • **Companion cells:** Living cells closely associated with sieve tubes, providing metabolic support.
  • **Phloem parenchyma:** Living cells involved in food storage and lateral transport.
  • **Phloem fibres:** Sclerenchymatous cells that provide mechanical strength (the only dead cells in phloem).

  Except for phloem fibres, all phloem components are living cells.

Answer:

Answer:

Answer:

Answer:

Animal Tissues

Animal bodies are complex structures with various tissues specialised for different functions like movement, transport, protection, and communication. Based on the functions they perform, animal tissues are broadly classified into four main types: Epithelial tissue, Connective tissue, Muscular tissue, and Nervous tissue.

---

Epithelial Tissue

Epithelial tissue is the covering or lining tissue that forms the outer protective layer of the body (skin) and lines internal organs and cavities (like the lining of the mouth, blood vessels, lung alveoli, kidney tubules). Epithelium acts as a **barrier** to separate different body systems or the body from the external environment.

Characteristics of Epithelial tissue:

• Cells are **tightly packed** and form continuous sheets.
• There is a **small amount of cementing material** between cells and almost **no intercellular spaces**.
• Any substance entering or leaving the body must cross at least one layer of epithelium. The permeability of epithelial cells is crucial for regulating exchange of materials.
• Epithelial tissue is usually separated from the underlying tissue by an **extracellular fibrous basement membrane**.

Epithelial tissues show different structures adapted to their specific functions:

• **Simple Squamous Epithelium:** Consists of extremely thin and flat, irregularly shaped cells forming a delicate lining. Found where transport across a selectively permeable surface occurs, like in the lining of blood vessels (endothelium) and lung alveoli. Also lines the oesophagus and mouth.
• **Stratified Squamous Epithelium:** Consists of several layers of squamous cells arranged in sheets. This multilayered arrangement provides protection against wear and tear. Found in the skin.
• **Cuboidal Epithelium:** Composed of cube-shaped cells. Provides mechanical support and is involved in absorption and secretion. Found in the lining of kidney tubules and ducts of salivary glands.
• **Columnar Epithelium:** Consists of tall, pillar-like cells. Found where absorption and secretion occur, such as the inner lining of the intestine. Facilitates movement across the epithelial barrier.
• **Ciliated Columnar Epithelium:** Columnar epithelium with hair-like projections called **cilia** on their free surface. Cilia move in a coordinated manner to push substances along. Found in the respiratory tract, where cilia move mucus to clear airways.
• **Glandular Epithelium:** Formed when epithelial tissue folds inwards to form a multicellular gland. Cells specialise to **secrete substances** at the epithelial surface (e.g., sweat, saliva, mucus).

---

Connective Tissue

As the name suggests, **connective tissue** serves to **connect** different parts of the body. It binds tissues together, supports the body, and transports substances. The cells of connective tissue are typically **loosely spaced** and embedded in an **intercellular matrix**. The nature of this matrix varies greatly and determines the specific function of the connective tissue.

Types of connective tissues:

• **Blood:** A fluid connective tissue. It has a liquid matrix called **plasma**, which contains proteins, salts, and hormones. Different types of blood cells (red blood corpuscles - RBCs, white blood corpuscles - WBCs, and platelets) are suspended in the plasma.
  • Function: Transports gases (oxygen, $\text{CO}_2$), digested food, hormones, and waste materials throughout the body.
• **Bone:** A strong, rigid, and nonflexible connective tissue that forms the **skeleton**. Bone cells are embedded in a hard matrix made of calcium and phosphorus compounds.
  • Function: Provides **structural support** and framework to the body, protects vital organs, anchors muscles, and facilitates movement.
• **Ligament:** Elastic connective tissue that connects **bone to bone**. Contains very little matrix and has considerable strength.
• **Tendon:** Fibrous connective tissue that connects **muscles to bones**. Has great strength but limited flexibility.
• **Cartilage:** Connective tissue with widely spaced cells embedded in a solid, yet flexible, matrix made of proteins and sugars.
  • Location: Found in the nose, ear, trachea, larynx, and at the ends of bones at joints (where it smoothens bone surfaces).
  • Function: Provides support and flexibility.
• **Areolar tissue:** Loose connective tissue found between the skin and muscles, around blood vessels, nerves, and in bone marrow.
  • Function: Fills spaces inside organs, supports internal organs, and helps in tissue repair.
• **Adipose tissue:** Fat-storing tissue found below the skin and between internal organs. Its cells are filled with fat globules.
  • Function: Stores fat (energy reserve), acts as an **insulator** against heat loss, and cushions organs.

---

Muscular Tissue

Muscular tissue is composed of elongated cells called **muscle fibres**. This tissue is responsible for **movement** in our body through the contraction and relaxation of its cells. Muscle cells contain special proteins called **contractile proteins**.

There are three types of muscular tissue:

• **Striated Muscles (Skeletal Muscles / Voluntary Muscles):** Muscle fibres are long, cylindrical, unbranched, and **multinucleate** (contain many nuclei). They show alternate light and dark bands or **striations** under a microscope due to the arrangement of contractile proteins.
  • Location: Mostly attached to bones (skeletal muscles).
  • Function: Responsible for **voluntary movements** (movements we can control consciously), such as moving limbs.
• **Smooth Muscles (Unstriated Muscles / Involuntary Muscles):** Muscle fibres are long, spindle-shaped (tapering at both ends), and **uninucleate** (contain a single nucleus). They **lack striations**.
  • Location: Found in the walls of internal organs like the alimentary canal, blood vessels, ureters, and iris of the eye.
  • Function: Responsible for **involuntary movements** (movements we cannot control consciously), such as the movement of food through the digestive tract or the contraction of blood vessels.
• **Cardiac Muscles (Involuntary Muscles):** Muscle fibres are cylindrical, branched, and typically **uninucleate** (though sometimes binucleate). They show faint **striations**.
  • Location: Found only in the **wall of the heart**.
  • Function: Exhibit rhythmic contraction and relaxation throughout life, causing the heart to pump blood (involuntary action).

Comparison of Muscle Tissues:

Features	Striated Muscle	Smooth Muscle	Cardiac Muscle
Shape	Long, cylindrical	Spindle-shaped (tapering ends)	Cylindrical, branched
Number of nuclei	Multinucleate	Uninucleate	Uninucleate (sometimes binucleate)
Striations	Present	Absent	Present (faint)
Control	Voluntary	Involuntary	Involuntary
Location	Attached to bones (limbs, etc.)	Walls of internal organs (intestine, blood vessels, iris, etc.)	Wall of the heart

---

Nervous Tissue

All cells have the ability to respond to stimuli, but cells of the **nervous tissue** are highly specialised for this. They are designed to be stimulated and then rapidly **transmit the stimulus** (in the form of electrical signals or nerve impulses) from one part of the body to another.

The brain, spinal cord, and nerves are all composed of nervous tissue. The functional unit of nervous tissue is the **nerve cell**, or **neuron**.

Structure of a Neuron:

• A neuron consists of a **cell body (cyton)** containing the nucleus and cytoplasm.
• From the cell body, long, thin, hair-like extensions arise.
• Typically, there is a single, long projection called the **axon**, which transmits nerve impulses away from the cell body.
• There are usually many short, branched projections called **dendrites**, which receive nerve impulses from other neurons and transmit them towards the cell body.

Individual neurons can be very long, up to a metre. Nerve fibres (axons) bound together by connective tissue form nerves. The signal transmitted along a nerve fibre is called a **nerve impulse**. Nerve impulses enable rapid communication and coordination within the body. The close functional relationship between nervous tissue and muscular tissue allows animals to respond quickly to changes in their environment (stimuli) by causing muscles to contract or relax.

Answer:

Answer:

Answer:

Answer:

Page No. 61

Answer:

Answer:

---

Page No. 65

Answer:

Answer:

Answer:

Answer:

---

Page No. 69

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer: