NCERT Science Notes - Class 9
Chapter 6 - Tissues

Welcome to AJs Chalo Seekhen. This webpage is dedicated to Class 9 | Science | Chapter 6 - Tissues. This chapter helps students understand the organization of cells into tissues. It covers the different types of tissues found in plants and animals, highlighting their structure and functions. Plant tissues are classified into meristematic and permanent tissues, while animal tissues include epithelial, connective, muscular, and nervous tissues. By studying these tissues, students learn how complex organisms are structured and how various tissue types contribute to their overall functioning. This chapter forms a basis for understanding advanced biological concepts and the functioning of living organisms. 🌱🧬📚

NCERT Science Notes - Class 8 Chapter 9 - Friction notes ajs, cbse notes class 10 ajslearning, cbse notes ajs, ajs notes class 10, ajslearning, ajs chalo seekhen

NCERT Science Notes - Class 9
Chapter 6 - Tissues

Overview

• All living organisms are composed of cells, which are the basic units of life.
• Unicellular organisms: A single cell performs all necessary functions (e.g., Amoeba).
• Multicellular organisms: Composed of millions of cells, each often specialized for specific functions.

• In multicellular organisms, cell specialization allows for division of labor:
  • Muscle cells: Contract and relax to facilitate movement.
  • Nerve cells: Transmit signals and messages throughout the body.
  • Blood: Transports oxygen, nutrients, hormones, and waste products.
  • Vascular tissues in plants: Conduct food and water to various parts of the plant.

• A tissue is defined as a group of similar cells that work together to perform a specific function efficiently.
• Tissues are organized in a way to maximize their functional efficiency, often located in a definite place in the body.
• Examples of tissues include:
  • Blood: A fluid tissue that circulates throughout the body.
  • Phloem: A plant tissue responsible for transporting nutrients.
  • Muscle tissue: Responsible for movement.

• Tissues are groups of similar cells that collaborate to achieve a particular function, which enhances efficiency and specialization in multicellular organisms.

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

Key Differences Between Plant and Animal Tissues

1. Movement and Stationarity:
   • Plants: Fixed in one place; do not move.
   • Animals: Capable of movement in search of food, mates, and shelter.
2. Supportive Tissue:
   • Plants: Have a large quantity of supportive tissue composed mostly of dead cells. This structure is necessary to keep them upright.
   • Animals: Contain primarily living tissues that support active movement and functions.
3. Energy Consumption:
   • Plants: Generally consume less energy as they primarily produce their own food through photosynthesis.
   • Animals: Require more energy for movement and other bodily functions, as they often rely on consuming other organisms for food.
4. Growth Patterns:
   • Plants:
     • Growth is limited to specific regions known as meristematic tissues, which can divide throughout the plant's life.
     • Two types of plant tissues based on growth:
       • Meristematic Tissue: Actively dividing cells found in specific areas.
       • Permanent Tissue: Cells that have completed division and serve specific functions.
   • Animals:
     • Growth is more uniform with no specific areas of division; cells grow and develop throughout the organism.
     • Animals do not have a clear distinction between dividing and non-dividing tissues.
5. Structural Organization:
   • Plants: While complex, the structural organization of organs and systems is less specialized compared to animals.
   • Animals: Exhibit a higher degree of specialization in organ systems, reflecting more complex interactions and functions required for survival.

• The differences in tissue structure and organization reflect the different lifestyles and feeding methods of plants and animals.
• Plants are adapted for a sedentary existence, requiring specialized tissues for support and growth in fixed locations.
• Animals are adapted for active locomotion and require a more complex and specialized organ system to efficiently perform their biological functions.

6.2 - Plant Tissues

6.2.1 - Meristematic Tissue

Activity 6.1: Observing Root Growth in Onion Bulbs

• Materials Needed:
  • Two glass jars
  • Water
  • Two onion bulbs

1. Fill two glass jars with water.
2. Place one onion bulb on each jar.
3. Observe root growth over a few days.
4. Measure and record the length of the roots on Days 1, 2, and 3.
5. On Day 4, cut the root tips of the onion bulb in Jar 2 by about 1 cm.
6. Continue measuring and recording the root lengths in both jars for five more days.

1. Which of the two onions has longer roots? Why?
   • Answer: The onion in Jar 1 likely has longer roots because it has not undergone any interruption in growth. The presence of the root tip allows for continuous growth due to the activity of meristematic tissue.
2. Do the roots continue growing even after we have removed their tips?
   • Answer: The roots may initially continue to grow, but their growth will eventually slow down or stop after the removal of the root tips. This is because the meristematic tissue responsible for growth is located at the tips.
3. Why would the tips stop growing in Jar 2 after we cut them?
   • Answer: The tips stop growing because the meristematic tissue, which is responsible for producing new cells for growth, has been removed. Without this tissue, the plant can no longer generate new cells to increase root length.

Characteristics of Meristematic Tissue

• Definition: Meristematic tissue is a type of plant tissue that contains actively dividing cells. It is responsible for the growth of plants in specific regions.
• Location:
  • Apical Meristem: Found at the tips of stems and roots, responsible for increasing the length of these structures.
  • Lateral Meristem (Cambium): Located along the sides of stems and roots, contributes to the increase in girth (thickness).
  • Intercalary Meristem: Found near the nodes in some plants, aiding in growth between the mature regions.
• Cell Characteristics:
  • Active Cells: Cells in meristematic tissue are very active and continuously divide.
  • Dense Cytoplasm: They have a high density of cytoplasm, allowing for metabolic activity.
  • Thin Cell Walls: Their walls are thin, making it easier for them to divide and expand.
  • Prominent Nuclei: The nuclei are large and prominent, indicating high metabolic activity.
  • Lack of Vacuoles: These cells generally lack vacuoles, which is crucial for their function.
    • Reason: Vacuoles are often involved in storage and maintaining turgor pressure. In actively dividing cells, having vacuoles could hinder cell division and growth, so meristematic cells maintain a flexible structure conducive to growth.

6.2.2 - Permanent Tissue

After cells formed by meristematic tissue undergo differentiation, they take on specific roles and lose their ability to divide. This process results in the formation of permanent tissues. Differentiation is the process through which cells develop distinct shapes, sizes, and functions to carry out specific tasks within the plant.

Activity 6.2: Observing Permanent Tissues

Materials Needed:

• A plant stem
• Knife or razor blade (for cutting, to be used with teacher supervision)
• Staining solution (safranin)
• Glycerine
• Microscope
• Cover-slip
• Microscope slides

1. Take a plant stem and, with the help of your teacher, cut it into very thin slices or sections.
2. Stain the slices with safranin to enhance visibility under the microscope.
3. Place one neatly cut section on a slide, add a drop of glycerine, and cover it with a cover-slip.
4. Observe the section under a microscope. Look for various types of cells and their arrangement.
5. Compare your observations with a reference image (Fig. 6.3).

1. Are all cells similar in structure?
   Answer: No, the cells are not all similar in structure. Different types of cells can be observed, each specialized for specific functions.
2. How many types of cells can be seen?
   Answer: The number of cell types observed will depend on the specific plant stem examined, but common types include parenchyma, collenchyma, and sclerenchyma, among others.
3. Can we think of reasons why there would be so many types of cells?
   Answer: Yes, the diversity in cell types arises from the need for different functions within the plant. For instance:
   • Parenchyma: Involved in storage, photosynthesis, and tissue repair.
   • Collenchyma: Provides flexible support for growing stems and leaves.
   • Sclerenchyma: Offers rigid support and protection to mature parts of the plant.
   This specialization allows plants to efficiently perform various physiological processes and adapt to their environments.

6.2.2 (i) Simple Permanent Tissue

Simple permanent tissues are composed of a few layers of cells that perform specific functions in plants. The three primary types of simple permanent tissues are parenchyma, collenchyma, and sclerenchyma. Each of these tissues has distinct characteristics and functions.

1. Parenchyma

• Structure: Parenchyma consists of relatively unspecialized living cells with thin cell walls. These cells are usually loosely arranged, resulting in large intercellular spaces.
• Function:
  • Storage: Primarily involved in the storage of food and nutrients.
  • Photosynthesis: In certain conditions, such as in green parts of the plant, parenchyma cells contain chlorophyll and can perform photosynthesis. This specialized form of parenchyma is known as chlorenchyma.
  • Aerenchyma: In aquatic plants, parenchyma cells may develop large air cavities that assist in buoyancy and floating. This type is called aerenchyma.

2. Collenchyma

• Structure: Collenchyma is characterized by living cells that are elongated and have irregularly thickened cell walls, especially at the corners. The arrangement of these cells allows for minimal intercellular spaces.
• Function:
  • Support: Provides mechanical support and flexibility, enabling parts of the plant, such as tendrils and stems of climbers, to bend without breaking.
  • Location: This tissue is commonly found in the leaf stalks just beneath the epidermis.

3. Sclerenchyma

• Structure: Sclerenchyma consists of dead cells that are long and narrow. The cell walls are thickened due to the presence of lignin, making these cells rigid. Often, the thickened walls have no internal space.
• Function:
  • Strength and Support: Provides mechanical strength and rigidity to various plant parts, contributing to their overall structural integrity.
  • Examples: Found in the husk of coconuts, stems, around vascular bundles, in the veins of leaves, and in the hard coverings of seeds and nuts.

Activity 6.3: Observing the Epidermis of Rhoeo Leaf

Materials Needed:

• Freshly plucked leaf of Rhoeo
• Petri dish
• Water
• Safranin dye
• Microscope
• Cover slip

1. Take a freshly plucked leaf of Rhoeo.
2. Stretch and break the leaf by applying gentle pressure while keeping it stretched so that some peel or skin projects out from the cut.
3. Remove the peel and place it in a petri dish filled with water.
4. Add a few drops of safranin dye to the water.
5. Wait for a couple of minutes to allow the dye to stain the cells.
6. Transfer the stained peel onto a microscope slide.
7. Gently place a cover slip over the peel.
8. Observe the slide under a microscope.

• The observed layer of cells is the epidermis, which is typically a single layer of cells.
• In plants adapted to very dry habitats, the epidermis may be thicker to provide better protection against water loss.

• Protection: The epidermis serves as the outermost layer that protects all parts of the plant.
• Waxy Layer: Epidermal cells on aerial parts often secrete a waxy, water-resistant cuticle that helps prevent water loss, mechanical injury, and invasion by pathogens, such as fungi.
• Structure: The cells form a continuous layer without intercellular spaces. Most epidermal cells are relatively flat, and their outer and side walls are generally thicker than their inner walls.
• Stomata: Small pores called stomata can be observed in the leaf epidermis. These stomata are enclosed by two kidney-shaped cells known as guard cells, which regulate gas exchange with the atmosphere.

• Gas Exchange: Stomata are essential for the exchange of gases, such as oxygen and carbon dioxide, between the plant and the atmosphere.
• Transpiration: Stomata also play a vital role in transpiration, which is the loss of water vapor from the plant. This process is crucial for several reasons:
  • Cooling: Transpiration helps cool the plant and maintain its temperature.
  • Nutrient Transport: It creates a negative pressure in the plant's vascular system, aiding in the transport of water and nutrients from the roots to the leaves.
  • Water Regulation: Transpiration helps regulate water levels within the plant and maintains turgor pressure, which is necessary for structural integrity.

6.2.2 (ii) Complex Permanent Tissue

6.3 - Animal Tissues

6.3.1 - Epithelial Tissue

6.3.2 - Connective Tissue

Connective tissue is a diverse group of tissues that play crucial roles in supporting, binding, and connecting various structures and organs in the body. Here's an in-depth look at its characteristics, types, and functions:

Characteristics of Connective Tissue

1. Cell Diversity: Connective tissue is composed of various types of cells, including fibroblasts, adipocytes (fat cells), macrophages, and mast cells, each with specialized functions.
2. Extracellular Matrix (ECM): The cells are embedded in an intercellular matrix, which can vary in composition and consistency (gel-like, fluid, dense, or rigid). The ECM is critical for providing structural support, regulating cell behavior, and facilitating the exchange of nutrients and waste.
3. Loosely Packed Cells: Unlike epithelial tissue, connective tissue cells are often spaced apart, allowing for the presence of the matrix.
4. Vascularity: Many connective tissues are vascular (contain blood vessels), which is important for nutrient supply and waste removal. However, some types, like cartilage, are avascular.
5. Regenerative Capacity: Connective tissues have varying capacities for regeneration and healing, depending on the type.

Connective tissue can be classified into several categories based on its structure and function:

1. Loose Connective Tissue:
   • Structure: Composed of a gel-like matrix with loosely arranged fibers and a variety of cells.
   • Function: Provides support and elasticity; found beneath the skin and surrounding organs.
2. Dense Connective Tissue:
   • Structure: Contains closely packed collagen fibers, providing strength and resistance to stretching.
   • Function: Forms tendons (connecting muscles to bones) and ligaments (connecting bones to other bones).
3. Adipose Tissue:
   • Structure: Composed of adipocytes that store fat.
   • Function: Provides energy storage, insulation, and cushioning for organs.
4. Cartilage:
   • Structure: A rigid matrix with chondrocytes embedded in it.
   • Function: Provides support and flexibility; found in joints, the nose, and ear structures. Cartilage is avascular, limiting its healing capacity.
5. Bone:
   • Structure: A mineralized matrix with osteocytes embedded in lacunae.
   • Function: Provides structural support, protection for vital organs, and facilitates movement. Bone tissue is highly vascularized, allowing for quick healing.
6. Blood:
   • Structure: A fluid connective tissue composed of plasma (the liquid matrix) and formed elements (red blood cells, white blood cells, and platelets).
   • Function: Transports oxygen, nutrients, hormones, and waste products throughout the body; plays a key role in immune response and clotting.
7. Lymph:
   • Structure: A fluid connective tissue similar to blood but with a different composition (fewer cells and a clear matrix).
   • Function: Involved in immune response and fluid balance in the body.

Functions of Connective Tissue

• Support and Structure: Connective tissues provide structural integrity to organs and body systems, allowing for proper function and protection.
• Transport: Blood, as a fluid connective tissue, transports gases, nutrients, hormones, and waste products, playing a vital role in homeostasis.
• Storage: Adipose tissue stores energy in the form of fat, while bones store minerals and other essential substances.
• Protection: Connective tissues like cartilage protect joints and bones, while adipose tissue provides cushioning around organs.
• Defense: Connective tissue, particularly blood, plays a key role in immune defense against pathogens.

6.3.3 - Muscular Tissue

Muscular tissue is essential for movement in the body and consists of elongated cells known as muscle fibers. These fibers contain special proteins called contractile proteins, which enable muscles to contract and relax, facilitating various movements.

Types of Muscular Tissue
Muscular tissue can be categorized into three main types based on structure, control, and location:

1. Skeletal Muscle (Voluntary Muscle):
   • Control: Voluntary (can be consciously controlled).
   • Location: Mostly attached to bones, enabling body movement.
   • Structure:
     • Cell Characteristics: Long, cylindrical, unbranched, and multinucleate (having multiple nuclei).
     • Appearance: Under the microscope, skeletal muscle fibers exhibit alternating light and dark bands, known as striations, when stained appropriately.
   • Function: Responsible for voluntary movements such as walking, lifting, and other actions involving the skeletal system.
   • Example: Muscles of the arms and legs.
2. Smooth Muscle (Involuntary Muscle):
   • Control: Involuntary (not consciously controlled).
   • Location: Found in the walls of hollow organs such as the alimentary canal, blood vessels, ureters, and bronchi of the lungs.
   • Structure:
     • Cell Characteristics: Long, spindle-shaped cells that are uninucleate (having a single nucleus).
     • Appearance: Smooth muscles do not exhibit striations, giving them a uniform appearance under the microscope. This is why they are referred to as unstriated muscles.
   • Function: Control involuntary movements, such as the contraction of blood vessels and the movement of food through the digestive system.
3. Cardiac Muscle:
   • Control: Involuntary (not consciously controlled).
   • Location: Exclusively found in the heart.
   • Structure:
     • Cell Characteristics: Cardiac muscle cells are cylindrical, branched, and uninucleate.
     • Appearance: These muscles also exhibit striations, similar to skeletal muscles, but with a unique branching structure.
   • Function: Responsible for the rhythmic contraction and relaxation of the heart, maintaining blood circulation throughout life.

Activity 6.5 : Compare the structures of different types of muscular tissues.

Here’s a comparison of the structures of different types of muscular tissues based on the features outlined in Table 6.1:

Table 6.1: Comparison of Muscular Tissues

• Striated Muscle:
  • Found primarily in skeletal muscles.
  • Voluntary control; responsible for body movements.
• Smooth Muscle:
  • Located in walls of hollow organs (e.g., intestines, blood vessels).
  • Involuntary control; regulates involuntary movements like digestion.
• Cardiac Muscle:
  • Exclusive to the heart.
  • Involuntary control; responsible for pumping blood throughout the body.

6.3.4 - Nervous Tissue

Nervous tissue is specialized for communication within the body, enabling the rapid transmission of signals. It is crucial for responding to stimuli and coordinating various body functions. Below is a detailed overview of the structure and function of nervous tissue.

Key Features of Nervous Tissue

1. Composition:
   • Neurons: The primary cells of nervous tissue, responsible for transmitting impulses. Each neuron consists of:
     • Cell Body: Contains the nucleus and cytoplasm.
     • Dendrites: Short, branched extensions that receive signals from other neurons.
     • Axon: A long, slender projection that transmits nerve impulses away from the cell body.
2. Structure of Neurons:
   • Neurons can vary in size, with some being very long (up to a meter) to accommodate the distance between the brain and the extremities.
   • The axon is typically surrounded by a myelin sheath, which insulates the nerve fiber and increases the speed of impulse transmission.
3. Nerve Fibers:
   • A group of neurons is bundled together to form a nerve, which is further wrapped in connective tissue.
   • The electrical signal that travels along the axon is known as a nerve impulse.
4. Functionality:
   • Nervous tissue allows for rapid communication between different parts of the body.
   • The interplay of nerve and muscle tissue is essential for movement and reflex actions.

• Response to Stimuli: Nervous tissue enables organisms to detect changes in their environment and respond accordingly, facilitating survival.
• Coordination of Activities: It integrates sensory input, processes it, and triggers appropriate responses, coordinating muscle contractions and various physiological functions.

NCERT Science Notes - Class 9 | Science | Chapter 6 - Tissues

NCERT Science Notes - Class 9 | Science | Chapter 6 - Tissues