Class 9 Science Chapter – Tissues | NCERT Nation Notes
Every living organism on Earth is made of cells, the fundamental units of life. But when an organism becomes more complex, one cell alone cannot perform all the necessary life processes efficiently. That’s where tissues come in. A tissue is a group of cells that are similar in structure and work together to perform a specific function.
This chapter, “Tissues,” is one of the most interesting topics in biology because it helps us understand how living things are organized. From the green tissues of plants that make food to the muscles and nerves that move and coordinate our bodies, tissues are what make life possible.
🌱 Understanding Tissues
In unicellular organisms like Amoeba or Paramecium, a single cell performs all the life functions such as nutrition, respiration, excretion, and reproduction. However, in multicellular organisms such as humans and plants, different groups of cells perform different functions. For example, some cells help in movement, some in transportation, some in protection, and others in storage.
This organization of work among different groups of cells is called division of labour. The cells that perform a particular kind of work together form a tissue. Thus, in plants and animals, tissues are the reason behind structural and functional efficiency.
🌿 Plant Tissues
Plants have a simpler structural organization than animals, and they do not move from one place to another. Their needs are different, so the arrangement of their tissues is also different. Broadly, plant tissues are of two types — Meristematic tissues and Permanent tissues.
Meristematic Tissues
These are the tissues responsible for plant growth. The cells in these tissues are small, actively dividing, and have thin walls. The cytoplasm is dense, and the nuclei are large. Depending on their location, meristematic tissues are of three types — apical, intercalary, and lateral.
The apical meristem is present at the growing tips of roots and shoots and is responsible for increasing the length of the plant. The intercalary meristem is found at the base of leaves or internodes, helping in elongation and regeneration (for example, in grasses). The lateral meristem, found on the sides of roots and stems, is responsible for increasing the thickness or girth of the plant.
When meristematic cells divide and mature, they lose the ability to divide and become permanent tissues.
Permanent Tissues
Once the cells of meristematic tissues mature, they take up specific roles and become permanent. These tissues no longer divide and perform fixed functions such as storage, transport, and support.
Permanent tissues are of two kinds: Simple permanent tissues and Complex permanent tissues.
Simple permanent tissues consist of only one type of cell and include parenchyma, collenchyma, and sclerenchyma.
Parenchyma cells are living, have thin cell walls, and are found in soft parts of plants such as fruits and leaves. They store food and sometimes perform photosynthesis when chlorophyll is present (then they are called chlorenchyma). In aquatic plants, parenchyma cells have air cavities to provide buoyancy — such tissue is called aerenchyma.
Collenchyma cells are also living but have unevenly thickened cell walls at the corners. They provide flexibility and mechanical support to growing parts of the plant like stems and leaves.
Sclerenchyma cells, on the other hand, are dead cells with thick, lignified walls. They provide strength and rigidity. Coconut husk and seed coats are examples of sclerenchyma tissues.
Complex Permanent Tissues
Complex tissues consist of more than one type of cell working together for a common purpose — mainly the transport of materials. There are two types: xylem and phloem.
Xylem transports water and minerals from the roots to the rest of the plant. It consists of tracheids, vessels, xylem fibres, and xylem parenchyma. Water conduction mainly happens through tracheids and vessels. The flow in xylem is always upward.
Phloem transports food prepared by leaves to all parts of the plant. It consists of sieve tubes, companion cells, phloem fibres, and phloem parenchyma. Unlike xylem, phloem carries substances both upward and downward, depending on the plant’s needs.
🌳 Animal Tissues
Animals are more active and complex, so they need tissues capable of movement, coordination, and communication. Animal tissues are divided into four major types — epithelial, connective, muscular, and nervous tissues.
Epithelial Tissue
Epithelial tissue covers the entire body surface and lines all internal organs and cavities. It acts as a protective barrier against mechanical injury, dehydration, and infection. Cells are tightly packed, leaving almost no intercellular spaces.
Depending on their shape and function, epithelial tissues are classified as squamous, cuboidal, columnar, ciliated, and glandular epithelium.
The squamous epithelium consists of flat, thin cells that form delicate linings such as the walls of blood vessels and alveoli in the lungs, allowing easy diffusion. The cuboidal epithelium is cube-shaped and found in kidney tubules and glands, helping in secretion and absorption. The columnar epithelium, which is tall and pillar-like, lines the stomach and intestine, aiding absorption. The ciliated epithelium has hair-like structures called cilia, which help move substances like mucus in the respiratory tract. The glandular epithelium secretes substances such as enzymes and hormones.
Connective Tissue
Connective tissues bind, support, and protect other tissues and organs. They are the most abundant and diverse tissues in the animal body.
One of the simplest connective tissues is areolar tissue, which fills the space between organs and connects different tissues. It also helps in tissue repair. Adipose tissue stores fat beneath the skin and around organs, serving as an insulator and energy reserve.
Ligaments connect bones to other bones, while tendons connect muscles to bones. Ligaments are strong and elastic, while tendons are less flexible but very strong.
Cartilage is a smooth, elastic tissue found at the ends of bones, ear pinna, and nose. It provides support and flexibility. Bone is the hardest connective tissue, forming the skeletal framework that supports the body and protects internal organs.
Finally, blood is a fluid connective tissue that circulates throughout the body, transporting oxygen, carbon dioxide, nutrients, and waste materials.
Muscular Tissue
Muscular tissue enables movement in the body. Muscle cells, also called muscle fibres, can contract and relax, causing movement in body parts.
There are three types of muscles — striated (voluntary), unstriated (involuntary), and cardiac muscles.
Striated muscles are attached to bones and help in voluntary movements. They appear striped under a microscope. Unstriated muscles are spindle-shaped, without stripes, and found in internal organs like the stomach and intestines. Cardiac muscles are found only in the heart; they are branched and involuntary but do not get tired easily.
Nervous Tissue
The nervous system coordinates and controls body functions. It is made up of nerve cells called neurons. A neuron has three main parts — the cell body, dendrites, and axon.
The cell body contains the nucleus, while dendrites receive impulses from other neurons or sensory cells. The axon carries these impulses away to other cells or muscles. The messages are transmitted in the form of electrical impulses, making the body respond quickly to changes in the environment.
🌏 Comparison Between Plant and Animal Tissues
Plants and animals are made of different kinds of tissues because their lifestyles differ. Plants are stationary, while animals move around. Plant tissues focus on support and transport, whereas animal tissues are specialized for movement and coordination.
Plant tissues grow only in specific regions due to meristematic activity, while animal tissues grow uniformly throughout the body. Plant cells have cell walls, while animal cells don’t. Animal tissues repair faster, and plants have a slower repair process.
💡 Importance of Studying Tissues
Studying tissues helps us understand how living organisms function efficiently. It explains how division of labour occurs at the cellular level and how various organs and systems work together. Tissues also help us understand growth, repair, disease, and even how to design treatments and biotechnology applications.
For example, tissue culture is used in plant breeding, and stem cell research in animals is based on understanding tissue formation and regeneration.
🌻 Summary
Tissues are essential for the structural and functional organization of all living organisms. In plants, tissues like xylem and phloem manage transportation, while in animals, tissues like muscles and nerves manage movement and coordination. The study of tissues forms the foundation for advanced biological sciences such as anatomy, physiology, and medicine.
