Class 9 Science Tissues Notes with PDF | NCERT Science Notes - Monelitho

Class 9 Science Tissues

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1. Introduction

In the previous chapter, we learned that all living organisms are made up of cells. But in multicellular organisms, cells do not work as isolated units. Instead, many similar cells come together to perform a specific function. Such a group of cells, which may be similar in structure and work together to do a particular job, is called a tissue.

The study of tissues is very important because it helps us understand how plants and animals are organized. In simple organisms, a single cell performs all life activities, but in complex organisms, different groups of cells become specialized for specific tasks. This division of labour makes life more efficient. Just as a society works better when different people perform different roles, a living body works better when different tissues handle different functions.

This chapter explains the meaning of tissues, the different types of plant tissues and animal tissues, their structure, functions, locations, and importance. It also helps us understand how organisms are organized at a higher level than cells. Once tissues are understood properly, the next steps such as organs and organ systems become much easier to study.

2. What Is a Tissue?

A tissue is a group of cells that are similar in structure, origin, and function, and work together to perform a specific task. These cells may be identical or closely related in form and activity. In multicellular organisms, tissues help bring efficiency and specialization to life processes.

For example, muscle tissue helps in movement, nervous tissue helps in carrying messages, and vascular tissue in plants helps in transportation of water, minerals, and food. In every case, the cells are coordinated so that the whole tissue works as one unit.

Why Tissues Are Important

• They provide specialization in multicellular organisms.
• They allow division of labour among cells.
• They make body functions more efficient.
• They form organs, and organs form organ systems.
• They help plants and animals adapt to their life processes in a better way.

3. Organization of Life: Cell, Tissue, Organ, Organ System

Living organisms are organized in a clear hierarchy. A cell is the basic unit of life. Similar cells form a tissue. Different tissues work together to form an organ. Different organs then form an organ system. Many organ systems together make an organism.

For example, in the human body, muscle tissue and nervous tissue help the heart function properly. The heart is an organ. The heart, blood vessels, and blood together support the circulatory system. All these systems work together to maintain life.

In plants too, roots, stems, and leaves are organs made up of different tissues. Each tissue has a specific role, and together they allow the plant to grow, transport materials, and respond to the environment.

4. Plant Tissues

Plant tissues are broadly divided into two main groups: meristematic tissue and permanent tissue. Meristematic tissue contains actively dividing cells, while permanent tissue contains cells that have stopped dividing and have taken up specific functions.

Plants continue to grow throughout life in many parts, unlike animals whose growth is generally limited to a certain period. This continuous growth is possible because of meristematic tissues.

4.1 Meristematic Tissue

Meristematic tissue consists of living cells that divide repeatedly and produce new cells. These cells are small, thin-walled, tightly packed, and have dense cytoplasm with a prominent nucleus. Vacuoles are either absent or very small. Since the cells are actively dividing, they remain undifferentiated.

Meristematic tissues are responsible for growth in plants. They are found in specific regions where new cells are needed for length and thickness.

Characteristics of Meristematic Tissue

• Cells divide actively.
• Cells are living and undifferentiated.
• Cell walls are thin.
• Cells have dense cytoplasm and large nuclei.
• Vacuoles are absent or very small.
• Cells are closely packed with no intercellular spaces.

Types of Meristematic Tissue

Apical Meristem

Apical meristem is found at the growing tips of roots and shoots. It helps in the increase in length of the plant. Because of this tissue, roots grow deeper into the soil and shoots grow upward.

Intercalary Meristem

Intercalary meristem is found at the base of leaves or internodes, especially in grasses. It helps in the elongation of stems and leaf growth. This tissue also allows regrowth after cutting or grazing in some plants.

Lateral Meristem

Lateral meristem is found along the sides of stems and roots. It helps in the increase in girth or thickness of the plant. This tissue is responsible for secondary growth, which is common in woody plants.

4.2 Permanent Tissue

Permanent tissue is made of cells that have stopped dividing and have become specialized for particular functions. These cells arise from meristematic tissue and then take on specific roles such as storage, support, transport, or protection.

Once cells are differentiated, their structure changes according to their function. Some permanent tissues consist of living cells, while others consist of dead cells.

Types of Permanent Tissue

Permanent tissues are mainly of two kinds: simple permanent tissue and complex permanent tissue. In addition, protective tissues are also studied separately because they form the outer covering of the plant body.

5. Simple Permanent Tissue

Simple permanent tissue is made up of only one type of cell, and all the cells perform similar functions. The main simple permanent tissues are parenchyma, collenchyma, and sclerenchyma.

5.1 Parenchyma

Parenchyma is the most common simple permanent tissue in plants. Its cells are living, thin-walled, and usually loosely packed. They have large vacuoles and intercellular spaces. Parenchyma cells are found in roots, stems, leaves, fruits, and flowers.

The main function of parenchyma is storage, but depending on location, it may also help in photosynthesis, secretion, and healing.

Functions of Parenchyma

• Stores food and water.
• Helps in photosynthesis when chloroplasts are present; such parenchyma is called chlorenchyma.
• Provides temporary support through turgidity.
• Helps in gas exchange due to air spaces in aquatic plants; such tissue is called aerenchyma.

Special Forms of Parenchyma

• Chlorenchyma: Parenchyma containing chloroplasts, found in green parts of plants.
• Aerenchyma: Parenchyma with large air spaces, found in aquatic plants for buoyancy and gas exchange.

5.2 Collenchyma

Collenchyma consists of living cells with thickening at the corners. These cells are elongated and have little or no intercellular space. Collenchyma is found below the epidermis in dicot stems, in leaf stalks, and along leaf veins.

Its main function is to give mechanical support and flexibility. This tissue allows plant parts to bend without breaking, which is particularly useful in young stems and leaf stalks.

Functions of Collenchyma

• Provides strength and support to growing plant parts.
• Allows flexibility.
• Prevents tearing of leaves and stems during bending.

5.3 Sclerenchyma

Sclerenchyma consists of dead cells that have thick, lignified walls. These walls are very hard and strong. Since the cells are dead at maturity, they no longer carry out metabolic activities, but they provide great mechanical support.

Sclerenchyma is found in coconut husk, seed coats, nutshells, and around vascular bundles. The cells may be fibers or sclereids.

Functions of Sclerenchyma

• Provides rigidity and strength.
• Protects plant parts.
• Helps plants withstand mechanical stress.

Difference Between Parenchyma, Collenchyma, and Sclerenchyma

• Parenchyma: Living cells, thin walls, storage and photosynthesis.
• Collenchyma: Living cells, corner thickening, flexible support.
• Sclerenchyma: Dead cells, thick lignified walls, strong support.

6. Complex Permanent Tissue

Complex permanent tissue is made up of more than one type of cell, and the different cells work together for a common function. In plants, the two main complex tissues are xylem and phloem. Together they are called vascular tissues because they are involved in transport.

6.1 Xylem

Xylem is a complex tissue that transports water and minerals from the roots to the rest of the plant. It also gives support to the plant body. Xylem is made of four main elements: tracheids, vessels, xylem parenchyma, and xylem fibers.

Functions of Xylem

• Conducts water and minerals upward from roots.
• Provides mechanical strength.
• Helps maintain the structure of the plant.

Main Elements of Xylem

• Tracheids: Long, thin, dead cells that conduct water and provide support.
• Vessels: Tube-like structures made of joined dead cells that conduct water efficiently.
• Xylem parenchyma: Living cells that store food and help in sideways transport.
• Xylem fibers: Thick-walled dead cells that provide support.

6.2 Phloem

Phloem is a complex tissue that transports food made in the leaves to all parts of the plant. This movement of food is called translocation. Phloem is made of sieve tubes, companion cells, phloem parenchyma, and phloem fibers.

Functions of Phloem

• Transports food from leaves to other parts.
• Moves food in both upward and downward directions as needed.
• Helps distribute nutrients throughout the plant body.

Main Elements of Phloem

• Sieve tubes: Conduct food through living tube-like cells.
• Companion cells: Help sieve tubes in transporting food.
• Phloem parenchyma: Stores food and assists in transport.
• Phloem fibers: Provide strength.

Difference Between Xylem and Phloem

• Xylem: Transports water and minerals, mostly upward.
• Phloem: Transports food, in both directions depending on need.
• Xylem: Contains mostly dead elements.
• Phloem: Contains mostly living elements.

7. Protective Tissue in Plants

Plants also have protective tissues that cover and protect their outer surfaces. The epidermis is the outermost layer of the plant body. It protects the plant from injury, water loss, and infection.

Epidermis

The epidermis is composed of a single layer of cells. These cells are tightly packed and usually do not have intercellular spaces. The outer surface of epidermal cells is often covered by a waxy layer called the cuticle, which helps reduce water loss.

Functions of Epidermis

• Protects the plant from mechanical injury.
• Reduces water loss by evaporation.
• Prevents entry of harmful microorganisms.
• Helps in gas exchange and transpiration through stomata.

Stomata

Stomata are tiny pores present mainly on the leaves. Each stoma is surrounded by two guard cells. These guard cells control the opening and closing of the stomatal pore.

Stomata help in the exchange of gases and loss of water vapour. They are essential for photosynthesis, respiration, and transpiration.

Root Hairs

Root epidermal cells form root hairs that increase the surface area for absorption of water and minerals from the soil. This is one of the most important functions of epidermal tissue in roots.

8. Animal Tissues

Animal tissues are broadly classified into four main types: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Each of these has a distinct structure and function.

Animal tissues are specialized for protection, support, movement, transport, communication, and coordination. Since animals have active movement and complex body systems, their tissues are highly organized.

8.1 Epithelial Tissue

Epithelial tissue forms the covering or lining of body surfaces and cavities. It protects underlying tissues and also helps in absorption, secretion, filtration, and exchange of materials.

Epithelial cells are tightly packed with very little intercellular space. They rest on a basement membrane, which supports them.

Types of Epithelial Tissue

• Simple squamous epithelium: Thin, flat cells for diffusion and filtration.
• Stratified squamous epithelium: Multiple layers for protection.
• Cuboidal epithelium: Cube-shaped cells for absorption and secretion.
• Columnar epithelium: Tall cells for absorption and secretion.
• Ciliated epithelium: Cells with cilia that help move substances.
• Glandular epithelium: Specialized for secretion.

Functions of Epithelial Tissue

• Protection
• Absorption
• Secretion
• Excretion
• Diffusion and filtration

Examples of Epithelial Tissue Locations

• Skin
• Lining of mouth
• Lining of intestine
• Kidney tubules
• Respiratory tract

8.2 Connective Tissue

Connective tissue connects, supports, binds, or separates different tissues and organs. Unlike epithelial tissue, connective tissue has cells scattered in a large amount of intercellular matrix. This matrix may be solid, liquid, or jelly-like depending on the tissue type.

Types of Connective Tissue

• Areolar tissue: Loose connective tissue found between skin and muscles and around blood vessels and nerves.
• Adipose tissue: Stores fat and provides insulation and cushioning.
• Tendon: Connects muscle to bone and is very strong and flexible.
• Ligament: Connects bone to bone and is strong but slightly elastic.
• Cartilage: Flexible support tissue found in nose, ear, and joints.
• Bone: Hard connective tissue that provides support and protection.
• Blood: Fluid connective tissue that transports materials throughout the body.
• Lymph: Helps in transport of fluids and immune defense.

Functions of Connective Tissue

• Binds different body parts together.
• Provides support and shape.
• Protects organs.
• Stores energy in the form of fat.
• Transports oxygen, nutrients, hormones, and wastes.

8.3 Muscular Tissue

Muscular tissue is responsible for movement. Its cells are long, contractile, and capable of shortening and relaxing. This tissue makes movement possible in the body and in internal organs.

Muscle cells contain special proteins that allow contraction. This contraction and relaxation produce movement and force.

Types of Muscular Tissue

• Striated muscle: Also called skeletal muscle; voluntary and attached to bones.
• Smooth muscle: Also called unstriated or involuntary muscle; found in internal organs like the stomach and intestine.
• Cardiac muscle: Found in the heart; involuntary and rhythmic.

Characteristics of Different Muscles

• Striated muscle: Long, cylindrical, multinucleate, voluntary.
• Smooth muscle: Spindle-shaped, single nucleus, involuntary.
• Cardiac muscle: Branched, single or two nuclei, involuntary, found only in the heart.

Functions of Muscular Tissue

• Produces movement of body parts.
• Helps in internal movement of organs.
• Supports posture.
• Generates force for breathing, pumping blood, and digestion.

8.4 Nervous Tissue

Nervous tissue is specialized for communication and control. It receives stimuli and transmits messages in the form of electrical impulses. The main cell of nervous tissue is the neuron.

Structure of a Neuron

A neuron has three main parts: cell body, dendrites, and axon. The cell body contains the nucleus. Dendrites receive signals from other cells. The axon carries impulses away from the cell body.

Functions of Nervous Tissue

• Receives information from the environment.
• Transmits impulses quickly.
• Coordinates body activities.
• Helps in response to stimuli.

Nervous tissue works with muscular tissue and other tissues to create coordinated actions such as movement, reflexes, thinking, and sensation.

9. Differences Between Plant Tissues and Animal Tissues

Plant and animal tissues differ because plants and animals have different lifestyles and body organization.

• Plant tissues: Include meristematic, permanent, and protective tissues.
• Animal tissues: Include epithelial, connective, muscular, and nervous tissues.
• Plant growth often continues throughout life in specific regions.
• Animal growth is usually more limited and occurs in a more coordinated way.
• Plant tissues often provide support through rigid cell walls and lignified cells.
• Animal tissues depend more on connective tissue, muscles, and bones for support and movement.

Plants do not move from place to place, so they need strong supporting tissues and transport tissues. Animals are mobile, so they need tissues for movement, coordination, and rapid response.

10. Plant Tissue System

In plants, tissues are often grouped into tissue systems based on function and location. These tissue systems make plant body organization easier to understand.

10.1 Epidermal Tissue System

This includes the epidermis, stomata, guard cells, and root hairs. It protects the plant surface and helps in water absorption and gas exchange.

10.2 Ground Tissue System

This includes parenchyma, collenchyma, and sclerenchyma. It is responsible for storage, photosynthesis, support, and packing of plant parts.

10.3 Vascular Tissue System

This includes xylem and phloem. It transports water, minerals, and food throughout the plant body.

11. Importance of Tissues in Everyday Life

Tissues are not just a school topic. They are a practical part of biology and explain many things we observe in daily life. When we see a leaf transpire, a plant bend without breaking, a heart beat rhythmically, or a muscle contract when we move, we are seeing the work of specialized tissues.

In medicine, the study of tissues helps in understanding diseases, wound healing, organ repair, and transplantation. In agriculture, knowing plant tissues helps in understanding growth, support, transport, and water movement. In sports and physical activity, knowledge of muscles and connective tissues helps explain strength, movement, and injury.

Tissues are therefore essential for understanding life at a deeper level.

12. Common Mistakes Students Make

Students often confuse similar terms in this chapter. Careful reading can avoid these problems.

• Thinking all plant tissues are dead; many plant tissues are living.
• Confusing xylem and phloem functions.
• Assuming all connective tissues are solid; blood is also connective tissue.
• Mixing up tendons and ligaments.
• Assuming muscular tissue is only for movement of arms and legs, while it also helps in internal organ movement.
• Thinking nervous tissue only exists in the brain, while it is present throughout the nervous system.
• Confusing epidermis of plants with epithelial tissue in animals.

13. Quick Revision Points

• A tissue is a group of cells performing a common function.
• Plant tissues are meristematic and permanent.
• Meristematic tissue helps in plant growth.
• Permanent tissue includes simple and complex tissues.
• Parenchyma stores food and may photosynthesize.
• Collenchyma gives flexible support.
• Sclerenchyma gives hard support.
• Xylem transports water and minerals.
• Phloem transports food.
• Animal tissues are epithelial, connective, muscular, and nervous.
• Epithelial tissue covers and protects body surfaces.
• Connective tissue binds and supports body parts.
• Muscular tissue causes movement.
• Nervous tissue carries messages and coordinates actions.

14. Short Practice Questions

1. Define tissue and explain why tissues are important.
2. What is the difference between meristematic and permanent tissue?
3. Name the three types of meristematic tissue and state their locations.
4. Differentiate between parenchyma, collenchyma, and sclerenchyma.
5. What is the function of xylem and phloem?
6. What is stomata and what is its role in plants?
7. What are the four main types of animal tissues?
8. How are tendons different from ligaments?
9. What is the structure and function of a neuron?
10. Why is connective tissue called a connecting tissue?

Class 9 Science Tissues Notes PDF

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15. Final Understanding

The chapter on tissues shows that life is organized in layers of complexity. Cells combine to form tissues, tissues combine to form organs, and organs combine to form organ systems. This organization makes the body efficient, stable, and adaptable. Plants and animals both use tissues, but the types and roles of tissues differ according to their needs.

In plants, tissues help with growth, support, transport, and protection. In animals, tissues help with protection, movement, support, transport, and control. Each tissue is specialized, yet all tissues are connected in function. This coordination is what keeps living organisms alive and active.

If you understand this chapter properly, you will not only do well in exams but also begin to see how living bodies are built from simple units into highly organized systems. Tissues are the bridge between cells and organs, and they form a very important step in the study of biology.