Chapter 6 - Tissue Notes | Study Science - Short Notes Class IX - Class 9

Tissue

A group of cells that have a similar structure and perform a specific function. 

Plant Tissues 

➢ 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.

(b) Collenchyma

• 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.

(c) Sclerenchyma

• 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.

(d) Epidermis

Stomata

• 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 : 
(a) Xylem

• 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.

(b) Phloem

• 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

Animal Tissues

➢ 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:

1. Blood

Blood Tissue

• 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. 

2. Bone

• 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.

3. Ligament

• It connects two bones.
• It is elastic.
• Contain little matrix.

4. Tendons

• Connects bone to muscles.
• Fibrous
• Limited flexibility but great strength.

5. Cartilage

• 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

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.