Plant & Animal Cells, Tissues, and Their Roles in Multicellular Organization

Eukaryotic vs. Prokaryotic Cells

  • Eukaryotic cells

    • Include typical plant and animal cells.

    • Characterized by membrane-bound organelles and a true nucleus.

    • Key organelles mentioned:
      • Cell/plasma membrane – boundary regulating molecular traffic.
      • Nucleus with nucleolus and chromosomes – genetic control center.
      • Cytoplasm – aqueous matrix where metabolism occurs.
      • Mitochondrion – aerobic ATP generation (“powerhouse”).
      • Ribosomes – ext70S(prokaryote)/80S(eukaryote)ext{70 S (prokaryote) / 80 S (eukaryote)}; sites of translation.
      • Endoplasmic reticulum (smooth/rough) – synthesis & transport of lipids/proteins.
      • Golgi complex – modification & shipping of macromolecules.
      • Vacuole (large central in plants, small/variable in animals) – storage, turgor.
      • Chloroplast (plants) – photosynthetic organelle containing chlorophyll.
      • Centriole/centrosome (animals) – spindle organization during mitosis.

    • Plant-exclusive structures: cell wall (cellulose), chloroplasts, plasmodesmata (inter-cell communication).

    • Animal-exclusive structures: centrioles, lysosomes (implied), flexible cell membrane

  • Prokaryotic cells (bacteria; bacillus type)

    • Lack true nucleus; genetic material in nucleoid.

    • Structural features:
      • Cell wall (peptidoglycan) – rigidity.
      • Capsule – outer gelatinous layer; pathogenic protection.
      • Plasma membrane – selective barrier.
      • Ribosomes (70 S) – protein synthesis.
      • Mesosome (infolded membrane region; debated structure) – respiration.
      • Pili – attachment/ DNA conjugation.
      • Flagella – motility.

    • Demonstrates evolutionary dichotomy with eukaryotes.

Biological Levels of Organization

  • Progression: Cells → Tissues → Organs → Organ Systems → Organism.

  • Each level shows emergent properties supporting homeostasis (steady internal balance).

Plant Tissues

  • Two broad categories: Meristematic (undifferentiated, mitotically active) and Permanent (differentiated).

Meristems

  • Primary meristems – responsible for length (apical, intercalary, floral meristems).
    • Apical meristem (shoot & root tips) – initiates primary growth; seen in dicot micrographs at 100 μm100\,\mu\text{m} scale.

  • Secondary meristems – lateral growth (vascular cambium, cork cambium).

  • Injury/Reversion meristems – dedifferentiation for healing.

Permanent Tissues

  • Simple (one cell type)
    • Parenchyma – thin-walled, living, versatile; photosynthesis, storage, wound repair.
    • Collenchyma – unevenly thick primary walls; support in growing organs.
    • Sclerenchyma – thick lignified secondary walls; fibers & sclereids for rigid support.

  • Complex (more than one cell type)
    • Dermal – epidermis, guard cells.
    • Vascular – xylem (tracheids/ vessels) & phloem (sieve tubes/ companion cells).

Stem Cross-Section (Young Woody Dicot)

  • Components (moving inward):
    • Epidermis → Cortex → Phloem → Vascular cambium (lateral meristem) → Xylem → Pith.

  • Vascular bundle shows discrete phloem above cambium and xylem below; critical for radial transport.

Animal Tissues – Overview & Objectives

  1. Identify four main groups: Epithelial, Connective, Muscular, Nervous.

  2. Differentiate epithelial sub-types by shape & layering.

  3. Appreciate tissue contribution to homeostasis (temperature, pH, nutrient distribution).

Epithelial Tissue

  • General traits:
    • Sheets of tightly packed cells; apical surface free, basal lamina anchored.
    • Functions: protection, absorption, secretion, filtration.

  • Classification by shape and number of layers.
    • Shapes: Squamous (flat), Cuboidal (cube-like), Columnar (tall).
    • Layers: Simple (one), Stratified (>1), Pseudostratified (appears layered; all touch basal lamina).

  • Named Types & Sites:
    • Simple squamous – air sacs (alveoli) of lungs; rapid diffusion.
    • Simple cuboidal – kidney tubules; secretion & absorption.
    • Simple columnar – intestine; nutrient uptake, may bear microvilli.
    • Pseudostratified ciliated columnar – respiratory tract; mucus propulsion.
    • Stratified squamous – esophagus, skin; resists abrasion.

Connective Tissue

  • All share mesenchymal origin & extracellular matrix (fibers + ground substance).

  1. Loose (Areolar)
    • Collagen & elastic fibers spaced; fibroblasts predominant.
    • Underlies epithelia, wraps organs – flexible support & fluid reservoir.

  2. Dense Fibrous
    • Packed collagen bundles; fibroblasts aligned.
    • Tendons (muscle→bone) & ligaments (bone→bone) – tensile strength.

  3. Adipose
    • Adipocytes with large fat vacuole; nuclei peripherally displaced.
    • Energy storage, insulation, cushioning; endocrine role (leptin).

  4. Cartilage
    • Matrix: chondroitin sulfate + collagen; avascular.
    • Cells: chondrocytes in lacunae.
    • Provides flexible support (ear, fetal skeleton).

  5. Bone
    • Matrix calcified (hydroxyapatite Ca<em>5(PO</em>4)<em>3OH\text{Ca}<em>5(\text{PO}</em>4)<em>3\text{OH}) layered in lamellae. • Structural unit: osteon with central canal for vessels. • Supports, protects, mineral storage (Ca2+^{2+}, PO</em>43−\text{PO}</em>4^{3-}).

  6. Blood (fluid connective tissue)
    • Matrix: plasma.
    • Cells: erythrocytes, leukocytes (neutrophils, monocytes, etc.), platelets.
    • Transports gases, nutrients, hormones; immune defense, clotting.

Muscular Tissue

  • Specialized for contraction via actin–myosin.

  1. Smooth Muscle
    • Visceral organs (stomach, intestine, blood vessels).
    • Non-striated, spindle-shaped cells, single central nucleus.
    • Involuntary; regulates lumen diameter and peristalsis.

  2. Skeletal Muscle
    • Attached to bones; also tongue sections.
    • Long multinucleate fibers, striated; voluntary.
    • Functions: posture, locomotion, heat production.

  3. Cardiac Muscle
    • Heart wall (myocardium).
    • Striated, branching cells interconnected by intercalated discs (gap junctions & desmosomes) enabling synchronized contraction.
    • Involuntary; pumps blood, maintains BP.

Nervous Tissue

  • Components: Neurons (excitable) + Neuroglia (support).

  • Structure of a typical neuron:
    • Cell body (soma) with nucleus.
    • Dendrites – input regions.
    • Axon – conducts impulse; may be myelinated (Schwann cells, nodes of Ranvier).

  • Functions:
    • Sensory input, integration, motor output.
    • Regulates muscles, glands; maintains homeostasis; enables cognition.

  • Locations: brain, spinal cord, peripheral nerves.

Integrated View & Significance

  • Homeostasis relies on coordinated activity among all tissue types:
    • Epithelial barriers regulate exchange.
    • Connective matrices distribute force & metabolites.
    • Muscle contractions move body & internal contents.
    • Nervous impulses orchestrate rapid systemic responses.

  • Plants showcase continual growth through meristems, with vascular tissues paralleling animal circulatory systems for resource distribution.

  • Comparative insight: both kingdoms demonstrate hierarchical organization, specialization, and reliance on cellular cooperation – foundational themes in biology.