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  • Introduction to Cellular Organization

    • Multicellular organisms consist of various cell types, not just one.
    • Cells organize into tissues, which are essential for function.

  • Types of Tissues in Animals

    • Four major tissues in animals:
    • Nervous Tissue: Involved in receiving and transmitting nerve impulses.
    • Muscle Tissue: Responsible for movement, including smooth muscle in guts.
    • Epithelial Tissue: Covers body surfaces and lines cavities.
    • Connective Tissue: Supports and protects other tissues.
    • Tissues consist of cells and extracellular matrix (ECM).
    • Cells secrete molecules that compose ECM, enabling connections between cells.

  • Plant vs. Animal Cells

    • Plants and animals evolved multicellular structures independently due to differing needs:
    • Animals: Mobile, requiring strong and adaptable tissue.
    • Plants: Stationary, requiring rigid yet flexible tissue for support.

  • Plant Cell Walls

    • Cell walls surround, protect, and define plant cell shapes.
    • Considered a form of extracellular matrix.
    • Plant cells can synthesize and secrete components affecting cell wall characteristics (thick/thin).
    • Cell walls are tough but can be fragile due to sensitive cell membranes.
    • Lacking intermediate filaments, plant cells depend on osmotic pressure.
    • Loss of water leads to plant wilting.

  • Composition of Cell Walls

    • Primary Cell Wall: Formed during initial cell growth; can expand as cells grow.
    • Secondary Cell Wall: Formed when cells stop growing; results from thickening of primary wall or adding layers.
    • Different plant cells can have unique secondary wall structures.

  • Observation of Cell Walls

    • Cross sections show primary walls (roots) versus secondary walls (stems).
    • Staining methods reveal components such as pectin (primary wall) and cellulose (secondary wall).

  • Strength and Structure of Cell Walls

    • Extracellular matrices provide tensile strength via long fibers aligning with stress lines.
    • Cellulose microfibrils resist compression and tension, formed from long unbranched chains of glucose.
    • Orientation of cellulose microfibrils determines the growth direction of cells.
    • Cells must overcome microfibril resistance to expand in specific directions.

  • Growth Dynamics

    • Turgor pressure facilitates cell growth, influencing direction based on microfibril orientation.
    • Enzyme complexes on the plasma membrane elongate microfibrils, creating new cellulose.
    • While most ECM molecules are made intracellular, cellulose synthesis is unique.
    • Microtubules guide cellulose synthesizing proteins, aligning with interior cell structure; microtubules control microfibril orientation.

  • Summary of Cell Wall Composition

    • The mechanism of cellulose production illustrates a direct link between intracellular processes and extracellular components.
    • Microtubules inside the cell shape how cellulose forms in the extracellular space, directly influencing plant growth and stability.