A group of cells that have a similar structure and perform a specific function.
➢ Meristematic Tissue
- It consists of cells that are continuously dividing.
- It helps in the growth of the plant and is found in the growing regions of the plant such as the root tip and the shoot tip.
- The cells of meristematic have a dense cytoplasm because it is rich in food material for the dividing cells.
- The food is not stored but utilized during division so they do not even have vacuoles.
Meristematic tissue is further classified into three categories:
1. Apical meristem: Found on the apical regions of the plant such as the root tips and the shot tip. It increases the height of the plant.
2. Lateral meristem or cambium: It increases the girth or diameter of a plant. It is present inside the stem of the plant between xylem and phloem (later in the chapter).
3. Intercalary meristem: It is present between the nodes of the plant or at the base of the leaves. It increases the height of the nodal region.
➢ Permanent Tissue
Differentiation: The process of taking up a permanent shape, size and function by a cell is called differentiation. Permanent tissues are formed once the cells have been differentiated.
Permanent tissues are of two types :
1. Simple Permanent Tissue
- Made up of only one type of cells.
- They are protective and supportive in nature.
Types of simple permanent tissues:
(a) Parenchyma tissues
- Contains living cells.
- Packaging tissue to fill up spaces.
- Unspecialized cells.
- Thin cell walls.
- Loosely packed and have large spaces between them.
- Provide support and store food.
- Chlorenchyma: Parenchyma tissue that contains chlorophyll and performs photosynthesis.
- Aerenchyma: Parenchyma tissue that contains large air spaces and provides buoyancy (floating ability) to plants.
- Contains living cells.
- Provides flexibility to the plants.
- Present in leaf and stem.
- Provides mechanical strength to the plant.
- Cells are irregularly thickened at corners.
- Cells have very little intercellular spaces.
- It makes the plant hard and tough.
- The cells in this tissue are dead.
- The cell walls are thickened with lignin.
- Lignin is a chemical that hardens the cell walls.
- There are no intercellular spaces.
- It is present in stems around vascular bundles (later in the chapter), seeds and nuts.
- Provides strength to the plants.
- Outermost layer of cells in a plant.
- It protects the internal parts of the cell.
- Waxy and water resistant in the aerial parts of the plant.
- There are no intercellular spaces to prevent water loss.
- Although small pores called stomata are present in the epidermis of the leaves that help in exchange of gases and transpiration (loss of water).
- Epidermis in roots have root hair, which increases the surface area to absorb water and minerals from the soil.
- In desert pants it has a thick layer of cutin (waterproof chemical substance) to prevent water loss.
- As it grows older it is replaced by several layer of secondary meristem called cork or bark, which consist of dead cells arranged without intercellular spaces.
- A chemical substance called suberin in found in the walls of cork cells, which make it impervious to water and gases.
2. Complex Permanent Tissue
- It is composed of two or more types of cells.
- They are conducting or transporting tissues.
Complex tissues are of the following two types :
- Different types of cells present in xylem are tracheid, vessels, xylem parenchyma and xylem fibers.
- All the cells except xylem parenchyma are dead at maturity.
- The cells have thick cell walls.
- Tracheid and vessels are tubular structure and helps in transportation of water and minerals vertically.
- Xylem parenchyma stores food and helps in sideways conduction of water and minerals.
- Xylem fibers play supportive role in conduction.
- Xylem transports water and minerals from the roots to the leaves. Xylem can transport only in one direction.
- Different types of cells present in phloem are sieve tube, companion cells, phloem fibers and phloem parenchyma cells.
- Sieve tube are tubular structures with punctured walls that help in transportation of prepared food from the leaves to various parts of the body.
- All the cells except phloem fibers are living.
- Phloem transports prepared food from leaves to all the other parts of the plant. Phloem ca transport bi-directionally
➢ Epithelial Tissue
- Protective innermost and outermost layer of cells present on various organs.
- E.g. Skin, the linings of mouth, blood vessels and lungs.
- Cells are tightly packed with no intercellular spaces to form a continuous sheet.
- Permeability (ability to allow entry or exit through itself) varies and plays an important role to regulate exchange of materials.
Types of Epithelial Tissue:
1. Squamous Epithelial
- Extremely thin and consist of simple flat epithelial cells.
- Have a selectively permeable membrane (allows the passing of few substances and blocks other).
- Present in the walls of blood vessels, alveoli in lungs, esophagus (food pipe) and mouth lining.
2. Stratified Epithelial
- The epithelial tissue, which consists of several layers of cells is known as stratified epithelial tissue.
- Skin is an example of stratified epithelial tissue.
- Skin consist of the outer layer called epidermis, the middle layer is called dermis and the innermost layer is known as hypodermis.
3. Columnar Epithelial
- Columnar epithelial cells consist of column like cells that have secretory function.
- They also have finger like projections called cilia in the respiratory tract that helps in clearing the mucus.
- The columnar epithelia tissue with cilia are also known as ciliated columnar epithelial tissue.
- It is present in respiratory tract and intestinal lining.
4. Cuboidal Epithelial
- Consists of cube-shaped cells.
- Present in kidney tubules and salivary glands.
- Provides mechanical support.
- Often acquire secretory function and folds to form multilayer gland. Such type of cuboidal epithelial tissue is also called glandular epithelium.
➢ Connective Tissue
It connects, supports and separates various other tissues present inside the body. Cells are loosed packed and buried in a matrix.
Various connective tissues are:
- The cells are present in a liquid matrix called plasma.
- Red blood cells, white blood cells, and platelets are present in the plasma.
- It also contains proteins, hormones and various salts.
- Blood transports gases, food and waste material to appropriate organs.
- It forms the skeleton of the body and supports.
- It supports other organs of the body with the help of muscles. It is strong, non-flexible and the matrix is made of calcium and phosphorus.
- The bone cells are called osteoblasts.
- It connects two bones.
- It is elastic.
- Contain little matrix.
- Connects bone to muscles.
- Limited flexibility but great strength.
- Widely spaced cells present in a matrix of proteins and sugars.
- Smoothens bones and joints.
- Present in nose, ear, trachea and larynx.
- The cells of cartilage are called chondrocytes.
- It can be folded e.g. ear pinna.
6. Areolar Tissue
- Found between the skin and the muscles.
- It is also present around blood vessels and nerves.
- Fills the empty spaces between organs.
- Helps in tissue repair.
7. Adipose Tissue
- Present under the skin and between internal organs.
- Stores fat and provide insulation.
- The cells of adipose tissue are called adipocytes.
➢ Muscular Tissue
- Cells are called muscle fibers, which are elongated
- Helps in movement
- Contain contractile proteins, which helps in contraction and relaxation of muscles
Types of Muscle Fibers:
1. Striated Muscles
- Shows light and dark bands when seen under a microscope.
- Cells are cylindrical, unbranched and have many nuclei.
- Responsible for voluntary movement (movements that can be controlled by us).
2. Smooth Muscles (Unstriated Muscles)
- Responsible for involuntary actions such as movement of blood vessels, digestive tract, iris of eyes, uterus and lungs.
- Cells are spindle-shaped (pointed from both ends).
- Cells have a single nucleus (uni-nucleate).
3. Cardia Muscles
- Present in the heart.
- Regular contraction and relaxation.
- Cylindrical, branched and have a single nucleus.
4. Nervous Tissue
- Receives a stimulus, carries it to the brain where it is processed and bring the response.
- Brain, spinal cord and nerves are made up of nervous tissue.
- A nerve cell is called a neuron.
- It consists of a cell body that contains several hairs like structures called dendrites.
- A tubular structure arises from one end of the cell body, which is called an axon.
- The axon ends into several branched structures called nerve endings.
- The axon is filled with neurotransmitters such as acetylcholine that carries the signal and transmits signals from one neuron to another.