Chapter – 6

Tissues

In this post we have given the detailed notes of class 9 Science Chapter 6 (Tissues) in English. These notes are useful for the students who are going to appear in class 9 board exams.

Chapter 6: Tissues

What are Tissues? 🔬

• A tissue is a group of cells that are similar in structure and work together to perform a particular function.  
• In multicellular organisms, tissues help in the division of labor, allowing different groups of cells to specialize in specific functions, leading to greater efficiency.  
• Examples of tissues include blood, phloem, and muscle.  

Are Plant and Animal Tissues the Same?

• No, plant and animal tissues are different due to differences in their structure, functions, and growth patterns.  
• Plants are stationary and have a large quantity of supportive tissue, generally made of dead cells.  
• Animals move around and consume more energy, so their tissues are mostly living.  
• Plant growth is limited to certain regions with meristematic tissues, while animal growth is more uniform.  

Plant Tissues 🌿

1. Meristematic Tissue 🌱

• Meristematic tissue is the dividing tissue present in the growing regions of the plant.  
• It is responsible for the growth of the plant.  
• Based on their location, meristematic tissues are classified as apical, lateral, and intercalary.  
• Apical meristem is present at the growing tips of stems and roots, increasing their length.  
• Lateral meristem increases the girth of the stem or root.  
• Intercalary meristem is located near the node and is responsible for the growth of branches and leaves.  
• Cells of meristematic tissue are very active, with dense cytoplasm, thin cellulose walls, prominent nuclei, and lack vacuoles.  

2. Permanent Tissue 🌳

• Permanent tissues are derived from meristematic tissue once they lose the ability to divide.  
• They are classified as simple and complex tissues.  

(i) Simple Permanent Tissue 🧱

• Parenchyma:
  • It is the most common simple permanent tissue, consisting of relatively unspecialized cells with thin cell walls.  
  • They are living cells with large spaces between them.  
  • Parenchyma generally stores food.  
  • Chlorenchyma is a type of parenchyma that contains chlorophyll and performs photosynthesis.  
  • Aerenchyma is a type of parenchyma found in aquatic plants that has large air cavities to help them float.  
• Collenchyma:
  • It provides flexibility to plants, allowing bending of various parts without breaking.  
  • It also provides mechanical support.  
  • The cells of this tissue are living, elongated, and irregularly thickened at the corners.  
• Sclerenchyma:
  • It is the tissue that makes the plant hard and stiff.  
  • The cells of this tissue are dead, long, and narrow with thickened walls due to lignin.  
  • It provides strength to the plant parts.  

(ii) Complex Permanent Tissue 🏗️

• Complex tissues are made of more than one type of cell, all coordinated to perform a common function.  
• Xylem:
  • It consists of tracheids, vessels, xylem parenchyma, and xylem fibers.  
  • Tracheids and vessels are tubular structures that transport water and minerals vertically.  
  • Xylem parenchyma stores food.  
  • Xylem fibers are mainly supportive.  
• Phloem:
  • It is made up of sieve cells, sieve tubes, companion cells, phloem fibers, and phloem parenchyma.  
  • Sieve tubes are tubular cells with perforated walls that transport food from leaves to other parts of the plant.  

Animal Tissues 🐾

1. Epithelial Tissue 👥

• Epithelial tissue covers most organs and cavities within the body, forming a barrier to keep different body systems separate.  
• The cells of epithelial tissue are tightly packed and form a continuous sheet with little intercellular space.  
• They regulate the exchange of materials between the body and the external environment.  
• Based on their shape and function, epithelial tissues are classified as squamous, cuboidal, columnar, ciliated, and glandular.  

2. Connective Tissue 🔗

• Connective tissue connects, supports, binds, or separates other tissues or organs.  
• The cells of connective tissue are loosely spaced and embedded in an intercellular matrix.  
• Different types of connective tissues include:
  • Blood: It has a fluid matrix called plasma, in which red blood cells, white blood cells, and platelets are suspended.  
  • Bone: It forms the framework that supports the body and anchors the muscles.  
  • Ligament: It connects bones with bones and is very elastic.  
  • Tendon: It connects muscles to bones and is fibrous with great strength.  
  • Cartilage: It smoothens bone surfaces at joints and is also present in the nose, ear, trachea, and larynx.  
  • Areolar Tissue: It fills the space inside organs, supports internal organs, and helps in the repair of tissues.  
  • Adipose Tissue: It stores fat, acting as an insulator.  

3. Muscular Tissue 💪

• Muscular tissue consists of elongated cells, also called muscle fibers, responsible for movement in our body.  
• Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.  
• There are three types of muscle tissues:
  • Striated Muscles: These are voluntary muscles attached to bones and help in body movement.  
  • Smooth Muscles: These are involuntary muscles that control movements like the movement of food in the alimentary canal or the contraction and relaxation of blood vessels.  
  • Cardiac Muscles: These are involuntary muscles found in the heart, showing rhythmic contraction and relaxation throughout life.  

4. Nervous Tissue 🧠

• Nervous tissue is composed of neurons, which are highly specialized cells that can receive and transmit stimuli very rapidly from one place to another within the body.  
• The brain, spinal cord, and nerves are all composed of nervous tissue.  
• A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts called dendrites and a single long part called the axon arise.  
• Nerve impulses allow us to move our muscles when we want to.  

Remember:

• Tissues are groups of cells that are similar in structure and function.  
• Plant tissues are of two main types: meristematic and permanent.  
• Animal tissues can be epithelial, connective, muscular, and nervous tissue.  

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