Tissues (Class 9 Science)



Introduction

Living organisms are made up of cells. In multicellular organisms, similar cells combine together to form tissues. A tissue is a group of similar cells that have a common origin and work together to perform a specific function. The concept of tissues allows division of labour, making organisms more efficient in carrying out different life processes.

The study of tissues helps us understand how different parts of plants and animals are specialized to perform various functions.

Definition of Tissue

A tissue is a group of similar cells having a common origin that work together to perform a particular function.

The term "Tissue" was introduced by the French scientist Marie François Xavier Bichat, who is known as the Father of Histology.

Why Do Organisms Need Tissues?

In unicellular organisms, a single cell performs all life activities. However, multicellular organisms contain millions of cells. If every cell performed every function, the body would become less efficient.

Tissues allow different groups of cells to perform specialized functions. This division of labour increases efficiency, improves coordination, and enables complex organisms to survive successfully.

Plant Tissues

Plant tissues are broadly classified into two major categories known as Meristematic Tissue and Permanent Tissue.

Meristematic tissue is responsible for the growth of plants, whereas permanent tissue performs specialized functions after growth is completed.

Meristematic Tissue

Meristematic tissue consists of actively dividing cells. These cells continuously divide to produce new cells, helping the plant grow throughout its life.

The cells are small, thin-walled, closely packed, rich in cytoplasm, and contain a large nucleus. Vacuoles are absent or very small because these cells are actively dividing.

Types of Meristematic Tissue

Apical meristem is present at the tips of roots and shoots. It increases the length of the plant and is responsible for primary growth.

Intercalary meristem is present at the base of leaves and internodes. It helps grasses and other plants grow rapidly even after grazing or cutting.

Lateral meristem is found along the sides of stems and roots. It increases the thickness or girth of the plant and is responsible for secondary growth.

Permanent Tissue

Permanent tissue is formed when meristematic cells stop dividing and become mature. These cells lose the ability to divide and become specialized to perform particular functions.

Permanent tissues are classified into Simple Permanent Tissue and Complex Permanent Tissue.

Simple Permanent Tissue

Simple permanent tissue is made up of only one type of similar cell.

Parenchyma is the most common living tissue in plants. It stores food, water and nutrients. It also helps in healing damaged tissues. When parenchyma contains chlorophyll, it is called chlorenchyma and performs photosynthesis. When it contains large air spaces, it is called aerenchyma and helps aquatic plants float.

Collenchyma consists of living elongated cells with unevenly thickened corners. It provides flexibility and mechanical support to young stems and leaves, allowing them to bend without breaking.

Sclerenchyma is made up of dead cells with thick lignified walls. It provides strength, rigidity and mechanical support to mature plant parts such as seed coats and coconut husk.

Complex Permanent Tissue

Complex permanent tissue consists of different types of cells working together to perform a common function.

Xylem transports water and minerals from the roots to all parts of the plant. It also provides mechanical support. Xylem is composed of tracheids, vessels, xylem fibres and xylem parenchyma.

Phloem transports food prepared during photosynthesis from leaves to different parts of the plant. This movement of food is called translocation. Phloem consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma.

Animal Tissues

Animal tissues are classified into four major types known as epithelial tissue, connective tissue, muscular tissue and nervous tissue.

Each tissue performs a specific function that helps the body work efficiently.

Epithelial Tissue

Epithelial tissue forms the outer covering of the body and lines the internal organs and cavities. It protects the body against injury, infection and dehydration. It also performs absorption, secretion and excretion.

Squamous epithelium consists of thin flat cells and allows easy diffusion of gases. It is found in the lungs and blood vessels.

Cuboidal epithelium consists of cube-shaped cells and performs secretion and absorption. It is present in kidney tubules and glands.

Columnar epithelium consists of tall cells and is mainly responsible for absorption and secretion. It is found in the stomach and intestine.

Ciliated epithelium contains tiny hair-like structures called cilia. These cilia help move mucus, dust particles and the ovum. It is found in the respiratory tract and fallopian tubes.

Glandular epithelium consists of specialized cells that produce and secrete hormones, enzymes and mucus.

Connective Tissue

Connective tissue connects different organs and body parts. It provides support, protection, transportation and storage.

Blood is a fluid connective tissue that transports oxygen, nutrients, hormones and waste materials throughout the body.

Bone is a hard connective tissue that provides support, protects internal organs and stores minerals such as calcium and phosphorus.

Cartilage is a flexible connective tissue found in the nose, ears and joints. It reduces friction and provides flexibility.

Tendons connect muscles to bones. They are strong and inelastic.

Ligaments connect bones to bones. They are strong but elastic, allowing movement at joints.

Adipose tissue stores fat beneath the skin and around internal organs. It acts as an energy reserve, provides insulation and cushions delicate organs.

Muscular Tissue

Muscular tissue is responsible for body movement by contracting and relaxing.

Striated muscle is voluntary muscle attached to bones. It helps in body movement and is under conscious control.

Smooth muscle is involuntary muscle found in the stomach, intestine, urinary bladder and blood vessels. It functions automatically without conscious control.

Cardiac muscle is found only in the heart. It contracts continuously throughout life and pumps blood to all parts of the body.

Nervous Tissue

Nervous tissue consists of specialized cells called neurons.

Neurons receive, process and transmit nerve impulses throughout the body.

A neuron consists of dendrites, a cell body and an axon.

The nervous tissue coordinates body activities and enables quick responses to internal and external stimuli.

Difference Between Plant Tissue and Animal Tissue

Plant tissues mainly provide support and help in growth. Animal tissues mainly provide movement, coordination and protection.

Growth in plants is restricted to meristematic regions, whereas growth in animals occurs throughout the body.

Plant supporting tissues are often dead, while animal supporting tissues are mostly living.

Plants do not require muscular and nervous tissues because they do not move from one place to another.

Importance of Tissues

Tissues improve the efficiency of multicellular organisms by dividing work among specialized cells.

They provide strength, protection, support, movement, transportation and coordination.

Without tissues, complex life forms would not be able to survive or perform essential life processes effectively.

Important Definitions

A tissue is a group of similar cells working together to perform a specific function.

Meristematic tissue consists of actively dividing cells responsible for plant growth.

Permanent tissue consists of mature cells that have lost the ability to divide.

Xylem transports water and minerals.

Phloem transports food.

A neuron is the structural and functional unit of the nervous system.

Chapter Summary

Tissues are groups of similar cells that perform specific functions. Plant tissues are divided into meristematic and permanent tissues. Permanent tissues include simple and complex tissues. Animal tissues are classified into epithelial, connective, muscular and nervous tissues. Each tissue is specialized to perform important functions that help organisms survive, grow and reproduce.