NCERT Gist: Tissues | Additional Study Material for UPSC PDF Download

- Blood, phloem and muscle are all examples of tissues.
- A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.
- Cell growth in animals is more uniform.
- The growth of plants occurs only in certain specific regions.
- This is because the dividing tissue, also known as meristematic tissue, is located only at these points.
- Depending on the region where they are present, meristematic tissues are classified as apical, lateral and intercalary.
- Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root.
- The girth of the stem or root increases due to lateral meristem (cambium).
- Intercalary meristem is the meristem at the base of the leaves or internodes (on either side of the node) on twigs. They lack vacuoles.

Simple Permanent Tissues

- A few layers of cells form the basic packing tissue.
- This tissue is parenchyma, a type of permanent tissue.
- It consists of relatively unspecialised cells with thin cell walls are live cells usually loosely packed.
- Provides support to plants and also stores food.
- Contains chlorophyll and perfonns photosynthesis, and then it is 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 type is called aerenchyma.
- The parenchyma of stems and roots also stores nutrients and water.
- The flexibility in plants is due to another permanent tissue, collenchyma.
- It allows easy bending in various parts of a plant (leaf, stem) without breaking.
- It also provides mechanical support to plants.
- Permanent tissue is sclerenchyma. It is the tissue which makes the plant hard and stiff.
- husk of a coconut. It is made of sclerenchymatous tissue. The cells of this tissue are dead.
- They are long and narrow as the walls are thickened due to lignin (achemical substance which acts as cement and hardens them). It provides strength to the plant parts.
- Stomata are enclosed by two kidney-shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere.
- Transpiration (loss of water in the form of water vapour) also takes place through stomata.
- Epidermal cells of the roots, whose function is water absorption, commonly bear long hair-like parts that greatly increase the total absorptive surface area.

Complex Permanent Tissues

- Made of more than one type of cells.
- All these cells coordinate to perform a common function.
- Xylem and phloem are examples of such complex tissues.
- They are both conducting tissues and constitute a vascular bundle.
- Vascular or conductive tissue is a distinctive feature of the complex plants, one that has made possible their survival in the terrestrial environment.
- Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres
- The cells have thick walls, and many of them are dead cells.
- Tracheids 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.
- Fibres are mainly supportive in function.
- Phloem is made up of four types of elements: sieve tubes, companion cells, phloem fibres and the phloem parenchyma.
- 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.

Epithelial Tissues

- The covering or protective tissues in the animal body are epithelial tissues.
- Covers most organs and cavities within the body.
- Forms a barrier to keep different body systems separate.
- The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue.
- Tightly packed and form a continuous sheet.
- They have only a small amount of cementing material between them and almost no intercellular spaces.
- Anything entering or leaving the body must cross at least one layer of epithelium.
- The permeability of the cells of various epithelia play an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body.
- All epithelium is usually separated from the underlying tissue by anextracellular fibrous basement membrane.
- Simple squamous epithelial cells are extremely thin and flat and form a delicate lining.
- 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.
- Skin epithelial cells 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.
- In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move, and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.
- Cuboidal epithelium (with cube-shaped cells) forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support.
- Epithelial cells often acquire additional specialisation as gland cells, which can secrete substances at the epithelial surface.
- Sometimes a portion of the epithelial tissue folds inward, and a multicellular gland is formed. This is glandular epithelium.
- Blood is a type of connective tissue.
- The cells of connective tissue are loosely spaced and embedded in an intercellular matrix.
- The matrix may be jelly like, fluid, dense or rigid.
- Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds. The plasma contains proteins, salts and hormones.
- Tendons connect bones to muscles and are another type of connective tissue.
- Tendons are fibrous tissue with great strength but limited flexibility.
- Another type of connective tissue, cartilage, has widely spaced cells.
- The solid matrix is composed of proteins and sugars.
- Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx.
- We can fold the cartilage of the ears, but we cannot bend the bones in our arms.
- Areolar connective tissue is found between the skin and muscles, around blood vessels and nerves and in the bone marrow.
- It fills the space inside the organs, supports internal organs and helps in repair of tissues.
- Muscles contain special proteins called contractile proteins, which contract and relax to cause movement, striated muscles.
- The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei).
- involuntary muscles control such movements.
- They are also found in the iris of the eye, in ureters and in the bronchi of the lungs.
- The cells are long with pointed ends (spindle-shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles.
- The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles.
- Heart muscle cells are cylindrical, branched and uninucleate.
- A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise.