Tissues Class 9 Notes Science Chapter 6

Introduction

A tissue is a group of similar cells working together to perform a specific function, like blood, phloem, or muscle.

Are Plants and Animals Made of the Same Types of Tissues? 

Think of plants and animals as two very different machines, each designed for their own unique tasks!

1. Structure and Movement:

• Plants: Imagine plants as strong , stationary buildings. They don’t move, so they need a strong, supportive structure with tough, often dead cells to stay upright and handle the elements.

• Animals: Picture animals as active, moving  vehicles. They’re always on the move, hunting for food or exploring. To stay flexible and active, their tissues are living and constantly working.

2. Growth Patterns:

• Plants: Plant growth happens in specific zones, like construction sites where new sections are built. Special areas called meristems keep adding new cells, while other parts of the plant stop growing once they reach maturity.

• Animals: Animal growth is more even and continuous. They grow uniformly without special zones, so their whole body develops together.

3. Complexity and Specialization:

• Plants: Even complex plants have simpler systems. They don’t need complex organs because they stay in one place and don’t interact with their surroundings like animals do. 

• Animals: Animals have highly specialized and complex organ systems. Their bodies are built to handle various tasks like hunting, escaping danger, and finding mates efficiently.
  
  

Plant Tissues

Both plants and animals have similar life processes. However, they do not have similar types of tissues because of differences in their organization, growth patterns, mode of living, lifestyle, movement and locomotion.

Plant tissue is of two types:
(i) Meristematic tissue
(ii) Permanent tissue

1. Meristematic Tissue

• The expansion or growth of plants is limited to particular regions due to the presence of specialized dividing tissue known as meristematic tissue. 
• Meristematic tissue is found only at specific points in plants.
• They are small, spherical, or polygonal cells with dense cytoplasm. Cells of meristematic tissue are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei.  
• Vacuoles are absent . 

Meristematic tissues can be classified on the basis of their position into  - Apical Meristem, Intercalary Meristem, and Lateral Meristem. 

(i) Apical Meristem (root and shoot apex) occurs at the growing tips of stems and roots and increases the length of the stem and the root.

(ii) Lateral Meristem (cambium) occurs on the sides both in stem and root.  it increases the girth of stem and root.

(iii) Intercalary Meristem  is present at the near the nodes (Nodes are the points on a plant stem where leaves, branches, or buds are attached ) . It increases the length between the two nodes. 

           Diagram representing the nodes 

Longitudinal section of shoot apex showing location of meristem and young leaves

2. Permanent Tissues

• Permanent tissues are derived from meristematic cells which have lost the ability to divide. They undergo differentiation to perform a particular function. 
• Their cells may be living or dead, thin or thick-walled. The thickening may be regular or irregular.
• There are two main groups of permanent tissues:
  (i) Simple Permanent Tissue
  (ii) Complex Permanent Tissue

(i) Simple Permanent Tissue

A few layers of cells beneath the epidermis are generally simple permanent tissue.

A simple tissue is a group of one type of cells that perform the same function.
Simple tissue is classified into three main types:

(a) Parenchyma

• These cells are thin-walled, living, isodiametric cells which form the basic packing tissue of all the plant organs. 
• The cells are oval, spherical or polygonal in the outline, that are loosely packed with small and large intercellular spaces in between them. Their primary function is the storage of food.
  Parenchyma Tissues in Transverse and Longitudinal Section
• Parenchyma containing chlorophyll is referred to as chlorenchyma which is the seat of photosynthesis.
• In aquatic plants, parenchyma cells are associated walk large air spaces. These air spaces store gases and provide buoyancy to the plants. Such a specialized parenchyma tissue is known as aerenchyma.

(b) Collenchyma

• These cells are living cells having thickened corners. The uneven thickenings of pectocellulose provide mechanical support and flexibility to plant. Because of collenchyma plant can bend without breaking.

(c) Sclerenchyma

• These cells are usually dead, thick, and lignified cells with a narrow lumen.
  Sclerenchyma Tissue
• Sclerenchyma cells are of two types:
  (i) Fibres are elongated spindle-shaped cells pointed at both ends
  (ii) Sclereids are short and broad cells that occur singly or in small groups. 
• They are also known as stone cells. This tissue provides mechanical support and enables plants to bear various stresses.

Know Let's know about Epidermis and cork 
(a) Epidermis

• The epidermis is the outer protective layer of the plant parts that prevent the entry of pathogens and pests. 
• Cells of the epidermis are elongated and closely packed. The cells are generally thick on their outer and radial sides and thin-walled on the inner side. 
• The outer thick walls are impregnated with an impermeable fatty substance called cutin. 
• Generally, the epidermis is single-layered and is discontinuous at certain places as it is interrupted by small pore-like structures called stomata. 
  Epidermis

Transpiration is the process of loss of excess water in the form of vapours through stomata.

• Epidermal cells of root bear long hair-like projections called root hair. Root hairs increase the absorptive surface area thereby facilitating increased absorption of water and minerals from the soil.
• In many plants, the aerial surface also bears cutinised hair over their epidermis. They are called trichomes. Trichomes may be glandular or non-glandular in nature. It produces an insulating stationary layer of air on the surface.

(b) Cork

• Cork is the outer protective tissue of older stems and roots. It is formed by a secondary lateral meristem called cork cambium. 
• Cork cambium produces a secondary cortex or phelloderm on the inner side and cork or phellem on the outer side. 
• Cork cells are rectangular in outline which are compactly arranged and are multilayered. Their walls become impermeable due to the deposition of suberin. 
• At certain places they possess small aerating pores called lenticels through which exchange of gases takes place. 
• Older cells become dead and are filled with tannins, resins and air. 
• Since cork is light, impervious, compressible and non-reactive it is commercially used in the manufacture of sport goods, stoppers for bottles, linoleum, insulation boards and shock absorbers.

(ii) Complex Permanent Tissues

Complex permanent tissues are the tissues that are made up of more than one type of cell. All these cells coordinate to perform a common function.

Complex tissue is classified into two main types:

(a) Xylem

• The xylem is a complex permanent plant tissue that plays an important role in the conduction of water and minerals from the soil to the various plant parts via roots.
• Consists of tracheids, xylem vessels, xylem fibers, and xylem parenchyma.
• Dead tubular tracheids and xylem vessels facilitate water transport from roots to shoots.
• Living xylem parenchyma stores food.

• Dead xylem fibers provide structural support.
• Vessels are long tubes that are formed by the end-to-end union of a large number of dead cells. The walls are lignified and possess pits.
• Xylem parenchyma stores food while xylem fibers provide mechanical support.
  Working of Xylem and Phloem in plant

(b) Phloem

• Phloem is the conducting tissue that translocates food manufactured in leaves to other parts of the plant. 
• Cells of phloem are living and consist of four tracheary elements namely — phloem sieve tubes and sieve cells, companion cells for short-distance transport, parenchyma for storage and phloem fibres for mechanical support.

Animal Tissues

Animal tissues are groups of cells with similar structures and functions that work together to perform specific tasks within the bodies of animals. Animal tissues are of four different types depending upon their structure and function.

1. Epithelial Tissue

2. Connective Tissue

• Cells are loosely spaced.
• Embedded in an intercellular matrix that can be jelly-like, fluid, dense, or rigid, depending on the tissue's function.
• On the basis of the nature of the matrix, the connective tissue is of three types:
  

3. Muscular Tissue

Definition: Muscular tissue consists of elongated cells called muscle fibers responsible for movement in the body.
Special Proteins: Contains contractile proteins that allow muscles to contract and relax, facilitating movement.
Types of Muscular Tissue
(i) Skeletal Muscles (Striated Muscles):
Function: Responsible for voluntary movements, such as moving limbs.
Characteristics:
1. Attached to bones, aiding in body movement.
2. Under a microscope, these muscles show alternate light and dark bands (striations).
3. Cells are long, cylindrical, unbranched, and multinucleate (contain many nuclei).
(ii) Smooth Muscles (Unstriated Muscles):
Function: Control involuntary movements, like the movement of food in the alimentary canal or the contraction of blood vessels.
Locations: Found in the iris of the eye, ureters, bronchi of the lungs, and other areas.
Characteristics:
1. Cells are spindle-shaped (long with pointed ends) and uninucleate (contain a single nucleus).
2.Do not have striations, hence called unstriated muscles.

(iii) Cardiac Muscles:
Function: Control the rhythmic contraction and relaxation of the heart throughout life.
Characteristics:
1. Cells are cylindrical, branched, and uninucleate.
2.These are involuntary muscles, meaning they function without conscious control.

Voluntary vs. Involuntary Muscles

• Voluntary Muscles: Muscles that can be moved by conscious will (e.g., muscles in the limbs).
• Involuntary Muscles: Muscles that operate without conscious control (e.g., smooth and cardiac muscles).

4. Nervous Tissue

Nervous tissue, fundamental to rapid communication within the body, consists of neurons.