2.3

Study Guide - Smart Notes

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Describe the extracellular walls produced by plant cells: Plant cells synthesize a rigid extracellular structure known as the cell wall, which provides support and protection.
Explain how the structure of the extracellular layer impacts its function: The composition and organization of extracellular layers determine their mechanical properties and roles in cell communication and defense.
Describe the extracellular matrix produced by animal cells: Animal cells secrete a complex network of proteins and carbohydrates called the extracellular matrix (ECM), which provides structural and biochemical support.
Describe how adjacent cells attach to one another: Cells use specialized junctions to adhere to each other and communicate, maintaining tissue integrity.

The plant cell wall is a strong, semi-rigid structure that surrounds the plasma membrane, providing shape, support, and protection to the cell.

Primary Cell Wall: Composed mainly of cellulose microfibrils embedded in a matrix of polysaccharides and proteins.
Secondary Cell Wall: May be deposited inside the primary wall in some cells, containing additional substances like lignin for extra strength.
Middle Lamella: A pectin-rich layer that glues adjacent plant cells together.
Function: Maintains cell shape, prevents excessive water uptake, and provides protection against pathogens.

Example: The rigidity of wood is due to the presence of thick secondary cell walls in xylem cells.

Animal cells lack cell walls but are surrounded by an extracellular matrix, which is a network of proteins and polysaccharides secreted by the cells.

Main Components: Collagen fibers (provide tensile strength), proteoglycans (form a gel-like matrix), fibronectin, and laminin (help cells attach to the ECM).
Functions: Provides structural support, segregates tissues, and regulates intercellular communication.
Example: The ECM in connective tissues like tendons is rich in collagen, giving them strength and flexibility.

Tight junctions are specialized connections between adjacent animal cells that create a seal, preventing the passage of materials between the cells.

Structure: Formed by networks of claudin and occludin proteins in the plasma membranes of neighboring cells.
Function: Maintain distinct environments on either side of an epithelial layer by blocking the movement of solutes.
Example: Tight junctions in the intestinal epithelium prevent leakage of digestive enzymes and pathogens into underlying tissues.

Desmosomes are strong, spot-like cell attachments found in animal tissues that experience mechanical stress, such as skin and heart muscle.

Structure: Composed of cadherin proteins that link the cytoskeletons of adjacent cells via intermediate filaments.
Function: Provide mechanical strength and stability to tissues by anchoring cells together.
Example: Desmosomes are abundant in the epidermis, helping skin cells resist tearing.

Feature	Plant Cell Wall	Animal Extracellular Matrix (ECM)
Main Components	Cellulose, hemicellulose, pectin, proteins	Collagen, proteoglycans, fibronectin, laminin
Function	Structural support, protection, shape maintenance	Structural support, cell signaling, tissue organization
Location	Outside plasma membrane of plant cells	Surrounds animal cells, especially in connective tissue
Additional Layers	Primary and secondary walls, middle lamella	Basal lamina (in some tissues)

Cellulose: A polysaccharide consisting of glucose monomers, main component of plant cell walls.
Collagen: The most abundant protein in the animal ECM, providing tensile strength.
Proteoglycan: A protein-polysaccharide complex that forms a gel in the ECM.
Cadherin: A type of cell adhesion molecule important in the formation of desmosomes.
Tight Junction: A type of cell junction that seals adjacent cells together.
Desmosome: A strong cell-cell adhesion structure that connects the cytoskeletons of adjacent cells.