Class 9 Chapter 6
Tissues
Tissues are groups of cells with similar structures and functions that work together to perform specific functions within an organism. Tissues are the building blocks of organs, which are further organized into organ systems to enable the overall functioning of complex multicellular organisms.
Are plants and animals made of the same type of Tissues ?
PLANTS are stationary or fixed, they don’t move.
They have to be upright, they have a large quantity of supportive tissue.
The supportive tissue generally has dead cells.
The growth of plants is limited to certain regions.
There are some tissues of plants that divide throughout their life. These tissues are localised to some regions.
The structural organization is less complex when compared with animals.
ANIMALS are motile. They move around in search of food, mates, and shelter.
They consume more energy as compared to plants.
Most of the tissues they contain are living.
The growth of animals is uniform. So there is no such demarcation of dividing and non-dividing regions in animals.
The structural organization is more complex when compared with animals.
Plant Tissues –
1. Meristematic tissue – Meristematic tissues are a type of plant tissue that consists of rapidly dividing cells and is responsible for the growth and development of plants. They are found in specific regions of the plant where active cell division takes place. Meristematic tissues play a crucial role in the formation of new organs, such as leaves, stems, roots, and flowers.
There are three main types of meristematic tissues:
- Apical Meristem: This tissue is located at the tips of stems and roots, and it is responsible for primary growth. Apical meristems enable the plant to increase its height and length by producing new cells that differentiate into various tissues.
- Lateral (or Cambial) Meristem: Lateral meristems are responsible for secondary growth in plants, primarily in woody species. They are found in the vascular cambium and cork cambium. The vascular cambium produces new vascular tissues (xylem and phloem) which contribute to the increase in girth or thickness of stems and roots. The cork cambium produces the protective outer layer of bark.
- Intercalary Meristem: Intercalary meristems are located between mature tissues, such as nodes and internodes in grasses. They contribute to the elongation of stems and leaves.
Meristematic tissues are characterized by their small, densely packed cells with thin cell walls and large nuclei. As cells divide in these regions, some of them remain in the meristematic state to continue the process of growth and differentiation, while others start to differentiate into specialized cells of various plant tissues.
Once cells have differentiated, they exit the meristematic state and become part of the plant’s permanent tissues, which include various types like parenchyma, collenchyma, and sclerenchyma, as well as the vascular tissues (xylem and phloem).
Overall, meristematic tissues are fundamental to plant growth, allowing plants to develop and adapt.
2. Permanent Tissue –
Permanent tissue refers to mature plant cells that have completed their growth and have specialized functions. These cells are no longer actively dividing and are in a state of differentiation. The process of taking up a permanent shape, size, and function is called differentiation. Permanent tissues are divided into two main types: simple permanent tissues and complex permanent tissues.
- Simple Permanent Tissues: These tissues are composed of cells that are structurally and functionally similar. They are all made up of one type of cells which look like each other. There are three types of simple permanent tissues:
a. Parenchyma: Parenchyma cells are relatively simple in structure and are found in various parts of the plant, such as leaves, stems, and roots. They often serve functions such as storage, photosynthesis, and secretion. This a few layers of cells that form the basic packing tissue. It consists of relatively unspecialized cells with thin cell walls. They are live cells. They are usually loosely packed so that large spaces between cells are found in this tissue.
It contains chlorophyll and performs photosynthesis so they are called chlorenchyma.
In aquatic plants, large air cavities are present in parenchyma to give buoyancy to the plants to help them float. Such a parenchyma is called aerenchyma. The parenchyma of stems and roots also stores nutrients and water.
b. Collenchyma: Collenchyma cells provide mechanical support to growing plant parts, such as young stems and petioles. They have thickened cell walls and are often found in regions where flexibility is needed. It allows easy bending in various parts of the plant(leaf,stem) without breaking. These are present in leaf stalks below the epidermis. The cells of this tissue are living, elongated and irregularly thickened at the corners. There is very little intercellular space.
c. Sclerenchyma: Sclerenchyma cells are highly specialized for providing structural support to mature plant parts. They have thick, lignified cell walls and are usually dead at maturity. This tissue makes the plant hard and stiff. For example the husk of a coconut. It is made of sclerenchyma tissue. They are long and narrow as the walls are thickened due to lignin (a chemical substance which acts as cement and hardens them). These walls have no internal space inside the cell. This tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts.
Sclerenchyma cells can be of two types: fibres and sclereids.
d. Epidermis and Guard cells – Epidermis is made of a single layer of cells. In some plants living in very dry habitats, the epidermis may be thicker since protection against water loss is critical. The entire surface of a plant has this outer covering of the epidermis. It protects all the parts of the plant. Epidermis cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface. This aids in the protection against loss of water, mechanical injury and invasion by parasitic fungi.
They are mostly flat. Often their outer and side walls are thicker than the inner wall.
Epidermis has small pores on its surface that are called stomata. Stomata are enclosed by two kidney-shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere. Transpiration also takes place through stomata.
Epidermis has a thick waxy coating of cutin (A chemical substance with waterproof quality) on its outer surface.
As plants grow older, the outer protective tissue undergoes certain changes. Epidermis form the several layer thick cork or bark of the tree. They also have chemical called suberin in their walls that makes them impervious to gases and water.
- Complex Permanent Tissues: These tissues are composed of different types of cells that work together to perform specific functions. They are more than one type of cells. They are conducting tissues and constitute a vascular bundle. There are two types of complex permanent tissues:
a. Xylem: The xylem is responsible for transporting water and minerals from the roots to other parts of the plant. It consists of various cell types, including tracheids, vessels, xylem fibres, and parenchyma cells. The cells have thick walls and many of them are dead cells.
Trecheids and vessels are tubular structures. This allows them to transport water and minerals vertically.
The parenchyma stores food and helps in the sideways conduction of water.
Xylem fibres are mainly supportive in function.
b. Phloem: Phloem transports organic nutrients, such as sugars, from the leaves (where they are produced through photosynthesis) to other parts of the plant. Phloem contains sieve tubes, companion cells, phloem fibres, and parenchyma cells.
Sieve tubes are tubular cells with perforated walls.
Phloem is unlike xylem in that materials can move in both directions in it. Phloem transports food from leaves to other parts of the plant. Except for phloem fibres, phloem cells are living cells.
These permanent tissues are crucial for the growth, development, and functioning of plants. They provide structural support, aid in transportation of fluids and nutrients, and perform various physiological functions.
Top of Form
Animal Tissues – “Animal tissue” refers to the group of specialized cells that make up the various structures and organs within an animal’s body. Animal tissues can be broadly categorized into four main types:
1. Epithelial tissue
2. Connective tissue
3. Muscular tissue
4. Nervous tissue
- Epithelial Tissue: This tissue covers the surfaces of the body, both externally and internally. It forms the skin and lines the cavities and tubes within the body, such as the respiratory and digestive tracts. Epithelium covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate. The skin, the lining of the mouth, lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue.
Epithelial tissue cells are tightly packed and form a continuous sheet. They have only a small amount of cementing material between them and almost no intercellular spaces.
There are different types of epithelia that show different structures that correlate with their unique functions –
(a) Simple squamous epithelium – Consists of a single layer of flat, scale-like cells. It is found in areas where diffusion and filtration are important, such as the lining of blood vessels (endothelium) and the air sacs of the lungs (alveoli). The oesophagus and the lining of the mouth are also covered with squamous epithelium. The skin which protects the body, is also made of squamous epithelium and these are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.
(b) Cuboidal Epithelium: Comprises a single layer of cube-shaped cells. It is involved in secretion and absorption and is found in kidney tubules, certain glands, and the surface of the ovaries. It is also found in the ducts of salivary glands. It provides mechanical support.
(c) Columnar Epithelium: Composed of a single layer of tall, column-like cells. It lines the digestive tract, where it can have micro villi (for absorption) and goblet cells (for mucus secretion). In the respiratory tract the columnar epithelial tissue also has cilia, which are hair like projections on the outer surfaces of epithelial cells.
– Ciliated Columnar Epithelium: Contains cilia (hair-like structures) on the surface, often involved in moving substances along the surface. Found in the respiratory tract and fallopian tubes.
- (d) Glandular Epithelium : Comprises cells specialized for secretion and forms glands. Glands can be classified as exocrine (release products onto a surface through ducts) or endocrine (release hormones directly into the bloodstream).
2. Connective Tissue : Connective tissue is one of the fundamental types of tissue found in the human body and other multicellular organisms. It serves as a structural framework that supports, connects, and protects various organs and tissues. Connective tissue is composed of cells dispersed within an extracellular matrix, which consists of fibers and ground substance. The matrix may be jelly like fluid, dense or rigid. This tissue type plays a crucial role in maintaining the integrity and function of organs and structures throughout the body.
(a) Blood – Blood has a fluid matrix called plasma, in which red blood cells(RBCs), White blood cells(WBCs) and platelets are suspended. The plasma contains proteins, salts and hormones. Blood flows and transport gases, digested food, hormones and waste materials to different parts of the body.
(b) Bone – A rigid connective tissue that forms the skeleton and provides structural support. It is strong and nonflexible tissue. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.
(c) Ligament – Two bones are connected to each other by another type of connective tissue called ligament. Tissue is very elastic. It has considerable strength. Ligaments contain very little matrix.
(d) Tendons – It connects muscles to bones and are fibrous tissue with great strength but limited flexibility.
(e) Cartilage – It has widely spaced cells. It is composed of proteins and sugars. It smoothens bone surfaces at joints and it is present in the nose, ear, trachea and larynx.
(f) Areolar connective tissue – It is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It supports internal organs and helps in repair of tissues.
(g) Adipose tissue – Fat storing adipose tissue found below the skin and between internal organs.
3. Muscular tissue –
Muscular tissue, also known as muscle tissue, is a specialized type of tissue found in animals that is responsible for producing movement and generating force within the body. Muscular tissue is made up of individual cells called muscle fibers, which contract and relax in response to electrical impulses from the nervous system. This contraction and relaxation allow for various types of movement, including voluntary movements like walking and running, as well as involuntary movements like the beating of the heart and the movement of food through the digestive system.
There are three main types of muscular tissue in the human body:
(a) Striated muscle tissues – This type of muscle tissue is attached to bones and is responsible for voluntary movements. It enables you to move your limbs, maintain posture, and perform various physical activities. Skeletal muscle fibers are striated (striped in appearance) and have multiple nuclei.
(b) Smooth muscle tissues – Smooth muscle tissue is found in the walls of internal organs and structures such as the digestive tract, blood vessels, and the respiratory system. It’s responsible for involuntary movements like peristalsis (the movement of food through the digestive tract) and regulating the diameter of blood vessels. Smooth muscle fibers are not striated and have a single nucleus.
(c) Cardiac Muscle tissues – Cardiac muscle tissue makes up the walls of the heart. It is responsible for the contraction of the heart, which pumps blood throughout the body. Cardiac muscle fibers are striated like skeletal muscle but are interconnected in a network and exhibit involuntary rhythmic contractions. They have a single nucleus.
Muscles are composed of bundles of muscle fibers held together by connective tissue. The connective tissue also provides support and structure to the muscle.
4. Nervous Tissue – Nervous tissue is a specialized type of tissue found in the nervous system, which includes the brain, spinal cord, and nerves. It is responsible for transmitting and processing information throughout the body. Nervous tissue is composed of nerve cells or neurons.
Neurons: Neurons are the primary functional cells of the nervous system. They are specialized for transmitting electrical signals, known as nerve impulses or action potentials, to communicate with other cells. Neurons consist of several components, including:
- Cell body (soma): Contains the nucleus and most of the cell’s organelles.
- Dendrites: Branched extensions that receive signals from other neurons or sensory receptors.
- Axon: A long, slender extension that carries the nerve impulse away from the cell body toward other neurons, muscles, or glands.
- Synapses: Junctions where neurons communicate with each other or with other target cells (such as muscles or glands).