Detailed Notes on Plant and Animal Tissues

Plant and Animal Tissues

Organ systems are composed of organs, which are composed of tissues. Each type of tissue has cells with specific responsibilities.

Plant Cells

Plants are essential for life, providing food and oxygen, and regulating water and carbon cycles. Plant cells have:

Defined nucleus and specialized organelles.
Cell Wall: Shapes, supports, and protects the cell.
Chloroplast: Carries out photosynthesis.
Vacuole: Stores metabolites and maintains turgor pressure.

Plant Structural Systems

Plants have two structural systems:

Shoot System: Above ground (leaves, stems, fruits, flowers).
Root System: Below ground (roots, tubers).

Plant Tissues

Plant tissues are classified based on structure and function:

Dermal Tissue
- Outer protective covering.
- Epidermis: Outermost layer of cells in young plants.
  - Closely packed epidermal cells covered with Cuticle (minimizes water loss and protects from pathogens).
  - Root hairs (in roots): Increase surface area for water and mineral absorption.
  - Trichomes (in stems): Protect from sunlight and conserve moisture.
  - Guard cells (in leaves): Contain chloroplasts and surround stomata (pores for gas exchange).
Ground Tissue
- Fills up the inner part of the plant.
- Parenchyma: Most abundant tissue.
  - Big, thin-walled cells with large vacuoles and air spaces.
  - Provides support and food storage.
  - Contributes to light penetration and gas exchange.
- Collenchyma
  - Thick-walled cells with uneven thickness.
  - Found in bundles underneath the epidermis.
  - Flexible and strong; supports immature regions of plants.
- Sclerenchyma
  - Thick cell walls filled with lignin (provides toughness and hardness).
  - Cells are mostly dead at maturity.
  - Provides support to mature regions.
  - Classified as fibers (long, slender, grouped in bundles) and sclereids (shorter, varying shapes, found in seed coats and nutshells, give gritty texture).
Vascular Tissue
- Transports water and nutrients.
- Xylem
  - Transports water and minerals from roots to leaves.
  - Tracheid: Elongated cell with oblique and tapering end walls.
  - Vessel elements: Long tubes made of individual cells open at each end.
- Phloem
  - Transports sucrose and organic compounds from leaves to roots.
  - Sieve tube elements: Elongated cells arranged to form continuous sieve tubes; have cytoplasm but no nucleus.

Animal Cells

Animal bodies are highly organized, starting from a single cell that differentiates into various tissues.

Animal Tissues

Four major types:

Epithelial Tissue
- Tightly packed cells forming continuous layers.
- Covers body surfaces, lines body cavities, and forms glands.
- Functions: Secretion, absorption, excretion, filtration.
- Types:
  - Simple Epithelium: Single layer of cells.
    - Simple squamous epithelia: Thin, flattened cells (lining of blood vessels and air sacs of lungs).
    - Simple cuboidal epithelia: Box-shaped cells (lining of kidney tubules).
    - Simple columnar epithelia: Rectangular pillars with nuclei near the bottom (lining of the digestive tract).
  - Stratified Epithelial Tissue: Two or more layers of cells (nose, mouth, esophagus, anal canal, vagina).
    - The outer layer of the skin is made of stratified epithelium, and these cells are keratinized, which means they provide strength.
  - Glandular Epithelial Tissue: Cells that secrete molecules.
    - Unicellular: Single epithelial cell (e.g., mucus-secreting goblet cells).
    - Multicellular: Clusters of cells.
Connective Tissue
- Most abundant and distributed tissue.
- Supports, connects, and separates tissues and organs.
- Components: Specialized cells, ground substance, and protein fibers.
- Primary cells: Fibroblasts and immune system cells.
- Extracellular matrix (ECM): Ground substance and fibers.
- Types:
  - Loose connective tissue: Equal number of cells, fibers, and ground substance; collagen fibers sparsely distributed (lining of lungs, arteries, urinary bladder).
  - Dense connective tissue: Many collagens packed together, fewer cells, densely packed ECM (tendons and ligaments).
- Specialized Connective Tissue
  - Reticular connective tissue: Produced by reticular cells; supports lymphoid organs, red bone marrow, lymph nodes, and the spleen.
  - Cartilage: Non-vascular tissue connecting bones and joints (walls of upper respiratory airways and external ear).
    - Principal cells: Chondrocytes located in lacunae.
    - Types: Hyaline cartilage, elastic cartilage, and fibrocartilage.
  - Bone: Cells within the ECM of fibers and ground substance.
    - Cells: Osteoblasts (bone-forming), osteoclasts (bone-absorbing), and osteocytes (matured cells in lacunae).
  - Blood: Fluid connective tissue in blood vessels.
    - Components: Formed elements (erythrocytes, leukocytes, and thrombocytes) and plasma.
    - Cells are produced through hematopoiesis in the bone marrow.
  - Adipose tissue: Primary energy reservoir; cells filled with lipids (adipocytes).
    - Found beneath the skin, around kidneys, and surface of the heart.
    - Number of adipocytes is fixed; cells enlarge or shrink with weight gain or loss.
    - Types: white fat and brown fat (thermogenesis - heat production).
Nervous Tissue
- Principal cells: Neurons and neuroglia.
- Neurons: Nerve cells with three parts: dendrites, cell body, and axon.
  - Dendrites conduct signals toward the cell body.
  - Cell body contains cytoplasm and nucleus.
  - Axon conducts nerve impulses from the cell body to the synapse.
- Neuroglia: Supporting cells that nourish neurons.
Muscular Tissue
- Muscle fibers comprised of actin and myosin filaments.
- Types: Skeletal, smooth, and cardiac.
  - Skeletal muscle: Striated cells with multiple nuclei; responsible for voluntary movement.
  - Smooth muscle: Spindle-shaped cells with a single nucleus; involuntary; found in walls of digestive tract and blood vessels.
  - Cardiac muscle: Branching striated cells with a single nucleus; responsible for heartbeat.