Tissues

Tissues

Introduction

• All living organisms are made of cells.
• Unicellular organisms (like Amoeba) have one cell doing all functions: movement, intake of food, gaseous exchange, and excretion.
• Multicellular organisms have millions of cells, each specialized for specific functions.

Division of Labour

• Humans:
  • Muscle cells: contract and relax for movement.
  • Nerve cells: carry messages.
  • Blood: transports oxygen, food, hormones, and waste.
• Plants:
  • Vascular tissues: conduct food and water.
• Specialized cells group together to form tissues, enhancing efficiency.

Examples of Tissues

• Blood
• Phloem
• Muscle

Are Plants and Animals Made of the Same Types of Tissues?

• Structural and Functional Differences:
  • Plants: stationary, have a lot of supportive (often dead) tissues to stay upright.
  • Animals: move around, consume more energy, most tissues are living.
• Growth Patterns:
  • Plants: growth limited to certain regions, tissues that divide throughout life (meristematic tissue) and permanent tissue.
  • Animals: uniform cell growth, no specific regions for dividing cells.
• Organ and Organ System Organization:
  • More specialized and localized in complex animals.
  • Differences reflect different lifestyles and feeding methods:
    • Plants: sedentary existence.
    • Animals: active locomotion.

Now, let’s dive into the details of plant and animal tissues.

Plant Tissues

Meristematic Tissue

Key Points on Meristematic Tissue

• Growth Regions: Plant growth occurs only in specific regions with meristematic tissue.
• Types of Meristematic Tissues:
  • Apical Meristem: Found at the growing tips of stems and roots; increases length.
  • Lateral Meristem (Cambium): Increases the girth of stems and roots.
  • Intercalary Meristem: Located near the nodes in some plants.
• Characteristics of Meristematic Cells:
  • Very active with dense cytoplasm.
  • Thin cellulose walls.
  • Prominent nuclei.
  • Lack vacuoles (due to their role in cell division and growth).

Permanent Tissue

Formation of Permanent Tissue

• Process: Cells from meristematic tissue take up specific roles and lose the ability to divide, forming permanent tissue.
• Differentiation: Cells develop a permanent shape, size, and function, leading to different types of permanent tissues.

Types of Permanent Tissue

Simple Permanent Tissue

• Parenchyma:
  • Most common type.
  • Thin cell walls, living cells.
  • Large spaces between cells (intercellular spaces).
  • Stores food.
  • Chlorenchyma: Parenchyma with chlorophyll for photosynthesis.
  • Aerenchyma: In aquatic plants, Parenchyma has large air cavities for floating.
• Collenchyma:
  • Provides flexibility and mechanical support.
  • Found in leaf stalks below the epidermis..
  • Living, elongated cells with irregular thickening at corners.
  • Little intercellular space.
• Sclerenchyma:
  • Makes plants hard and stiff.
  • Dead cells with thick lignin walls, no internal space.
  • Provides strength.
  • Found in stems, around vascular bundles, husk of coconut, veins of leaves, and hard coverings of seeds and nuts.

Epidermis

• Outermost cell layer of the plant.
• Single layer of cells, thicker in dry habitats.
• Protects plant parts and prevents water loss.
• Secretes a waxy, water-resistant layer.
• Continuous layer without intercellular spaces.
• Flat cells with thicker outer and side walls.

Stomata

• Small pores in the epidermis.
• Surrounded by two guard cells.
• Allow gas exchange and water transpiration.

Root Epidermis

• Has hair-like structures to increase water absorption.

Cork

• As plants age, outer protective tissue changes.
• Secondary meristem forms cork layers.
• Cork cells are dead and compact with suberin in walls, making them impervious to gases and water.

Complex Permanent Tissue

• Xylem:
  • Made of tracheids, vessels, xylem parenchyma, and xylem fibers.
  • Tracheids and vessels transport water and minerals, are tubular and mostly dead when mature.
  • Parenchyma stores food.
  • Fibers provide support.
• Phloem:
  • Made of sieve cells, sieve tubes, companion cells, phloem fibers, and phloem parenchyma.
  • Sieve tubes transport food from leaves, are tubular with perforated walls.
  • Most phloem cells are living, except fibers.

Animal Tissues

Examples – Movement and Oxygen Transport

• Muscle Cells:
  • Special cells that help body parts move by contracting and relaxing.
• Oxygen Transport:
  • Oxygen from breathing is absorbed in the lungs and transported by blood to body cells.
  • Blood carries oxygen and food to cells and removes wastes to the liver and kidneys.

Types of Animal Tissues

1. Epithelial Tissue
   • Covers and protects the body and its organs.
2. Connective Tissue
   • Supports, binds, and connects different parts of the body.
   • Blood is a type of connective tissue.
3. Muscular Tissue
   • Enables movement through contraction and relaxation.
   • Muscles are made up of muscular tissue.
4. Nervous Tissue
   • Transmits signals between different parts of the body.

1. Epithelial Tissue

• Function: Covers and protects organs and cavities in the body.
• Examples: Skin, mouth lining, blood vessel lining, lung alveoli, kidney tubules.
• Characteristics:
  • Tightly packed cells forming a continuous sheet.
  • Very little intercellular space.
  • Acts as a barrier and regulates material exchange.
• Types of Epithelial Tissue:
  • Simple Squamous Epithelium:
    • Thin, flat cells.
    • Found in blood vessels and lung alveoli.
    • Allows easy exchange of substances.
  • Stratified Squamous Epithelium:
    • Multiple layers of cells.
    • Found in skin, esophagus, mouth lining.
    • Provides protection against wear and tear.
  • Columnar Epithelium:
    • Tall, pillar-like cells.
    • Found in the inner lining of the intestine.
    • Facilitates absorption and secretion.
  • Ciliated Columnar Epithelium:
    • Columnar cells with cilia.
    • Found in the respiratory tract.
    • Cilia move mucus.
  • Cuboidal Epithelium:
    • Cube-shaped cells.
    • Found in kidney tubules and salivary gland ducts.
    • Provides mechanical support.
  • Glandular Epithelium:
    • Specialized for secretion.
    • Forms glands.

2. Connective Tissue

• Function: Connects and supports different parts of the body.
• Characteristics:
  • Cells are loosely spaced.
  • Embedded in an intercellular matrix (jelly-like, fluid, dense, or rigid).
• Types of Connective Tissue:
  • Blood:
    • Fluid matrix called plasma.
    • Contains RBCs, WBCs, and platelets.
    • Transports gases, food, hormones, and wastes.
  • Bone:
    • Strong, non-flexible.
    • Hard matrix of calcium and phosphorus.
    • Supports body structure and anchors muscles.
  • Ligaments:
    • Connects bones to bones.
    • Very elastic with little matrix.
  • Tendons:
    • Connects muscles to bones.
    • Fibrous, strong, but less flexible.
  • Cartilage:
    • Smoothens bone surfaces at joints.
    • Found in nose, ear, trachea, larynx.
    • Solid matrix of proteins and sugars.
  • Areolar Tissue:
    • Found between skin and muscles, around blood vessels and nerves.
    • Supports internal organs and helps repair tissues.
  • Adipose Tissue:
    • Stores fat.
    • Found below the skin and between internal organs.
    • Acts as an insulator.

3. Muscular Tissue

• Function: Responsible for body movement.
• Muscle Fibres: Elongated cells that contain contractile proteins which help in contraction and relaxation.

Types of Muscles

1. Voluntary Muscles (Skeletal Muscles)
   • Control: We can move them by conscious will.
   • Location: Attached to bones, help in body movement.
   • Appearance: Show alternate light and dark bands (striations).
   • Cell Structure: Long, cylindrical, unbranched, and multinucleate.
2. Involuntary Muscles (Smooth Muscles)
   • Control: We cannot control them consciously.
   • Location: Found in the alimentary canal, blood vessels, iris of the eye, ureters, and bronchi.
   • Appearance: Do not have striations.
   • Cell Structure: Long, spindle-shaped, and uninucleate.
3. Cardiac Muscles
   • Control: Involuntary, responsible for the rhythmic contraction and relaxation of the heart.
   • Location: Found only in the heart.
   • Appearance: Cylindrical, branched, and uninucleate.

4. Nervous Tissue

• Function: Specialized for transmitting stimuli rapidly within the body.
• Location: Found in the brain, spinal cord, and nerves.
• Cells: Called nerve cells or neurons.

Structure of a Neuron

• Cell Body: Contains the nucleus and cytoplasm.
• Processes:
  • Axon: A single long part that transmits impulses.
  • Dendrites: Many short, branched parts that receive stimuli.
• Nerve: Made up of many nerve fibres bound together by connective tissue.

Nerve Impulses

• Allow movement of muscles in response to stimuli.
• The combination of nerve and muscle tissue enables rapid movement in response to stimuli.

Chapter Summary:

• Tissue is a group of cells similar in structure and function.
• Plant tissues are of two main types: meristematic and permanent.
• Meristematic tissue is the dividing tissue present in the growing regions of the plant.
• Permanent tissues are derived from meristematic tissue once they lose the ability to divide. They are classified as simple and complex tissues.
• Parenchyma, collenchyma, and sclerenchyma are three types of simple tissues.
• Xylem and phloem are types of complex tissues.
• Animal tissues can be epithelial, connective, muscular, and nervous tissue.
• Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated, and glandular.
• The different types of connective tissues in our body include areolar tissue, adipose tissue, bone, tendon, ligament, cartilage, and blood.
• Striated, unstriated, and cardiac are three types of muscle tissues.
• Nervous tissue is made of neurons that receive and conduct impulses.