Cell Types, Tissues & Key Modifications – Quick Review

Prokaryotic Cells

  • Name origin: Greek pro (before) + karyon (kernel)
  • No membrane-bound nucleus; DNA concentrated in nucleoid
  • Key structures: cell wall, plasma membrane, ribosomes, nucleoid
  • Domains
    • Bacteria → thinner, more permeable wall
    • Archaea → thicker wall, heat/chemical resistant, thrive in extremes
  • Ecological roles: nutrient recycling, metabolic assistance (e.g., gut microbiota)

Eukaryotic Cells

  • Name origin: Greek eu (true) + karyon (nucleus)
  • Membrane-bound nucleus + diverse organelles (mitochondria, ER, lysosomes, etc.)
  • Occur as unicellular or multicellular forms
  • Kingdoms: Plantae, Animalia, Fungi, Protista
    • Plants: photosynthetic, cell walls, reproductive tissues
    • Animals: no wall, locomotion, internal digestion
    • Fungi: external digestion, absorb via wall
    • Protists: mostly single-celled, motile, photo- or heterotrophic

Animal Tissues (four basic types)

  • Epithelial: tight cell layers; protection, secretion, absorption
    • cuboidal, simple/stratified squamous, simple/pseudo-stratified columnar
  • Connective: matrix-rich; binding, support, transport
    • blood, loose & fibrous CTP, adipose, cartilage, bone
  • Muscle: contractile fibres; movement
    • skeletal (voluntary, striated), cardiac (striated, intercalated discs), smooth (involuntary, unstriated)
  • Nervous: neurons + glia; signal detection & transmission

Plant Tissues

  • Meristematic (dividing)
    • apical → length growth
    • lateral/cambium → thickness; cork vs. vascular cambium
  • Permanent (non-dividing)
    • epidermal (guard & hair cells)
    • vascular: xylem (water/mineral up), phloem (food down)
    • ground: parenchyma (thin), collenchyma (thick, living), sclerenchyma (thick, dead)

Cell Modifications

Apical Surface

  • Cilia: short, hair-like; coordinated waves for movement/clearance
  • Flagella: long, whip-like; propulsion
  • Villi & microvilli: finger-like/mini projections; greatly increase absorptive area
  • Pseudopods: temporary lobes for amoeboid movement & phagocytosis
  • Extracellular Matrix (ECM): secreted mesh (glycoprotein-rich); structural “glue”

Basal Surface

  • Desmosomes / Hemidesmosomes: rivet-like anchors linking cytoskeleton to basal lamina; keratin & integrin dependent

Lateral Surface (Cell Junctions)

  • Tight junctions: seal adjacent cells; control paracellular flow
  • Adhering/anchoring junctions: cadherin-based; mechanical fastening between neighbours
  • Gap junctions: connexon channels; direct cytoplasmic communication