Tissues: groups of similar cells
Organisation • Principles of organisation
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Definition and explanation of a tissue
A tissue consists of cells with similar structure and the same primary function. Groups of similar cells produce collective effects: structure specialization → improved efficiency of the shared function. The organisation chapter describes tissues as the organisational level between single cells and whole organs, demonstrating how cell specialisation produces tissue properties distinct from individual cells .
Animal tissue types and functions
Epithelial tissue forms continuous sheets that protect surfaces and line cavities; tight cell packing → barrier and selective exchange. Muscle tissue contains cells that can contract; contraction → movement and force generation. Connective tissue supports and binds structures using extracellular matrix materials such as collagen; support structures → mechanical strength. Nervous tissue transmits electrical signals between receptors and effectors; signal transmission → rapid coordination and response.
Plant tissue types and functions
Epidermal tissue covers shoots and roots; tightly packed cells and waxy cuticles → reduced water loss and protection. Mesophyll tissue contains many chloroplasts; high chloroplast density → efficient photosynthesis. Xylem tissue transports water and mineral ions; hollow, lignified cells → unidirectional water flow and structural support. Phloem tissue transports sugars; sieve-tube arrangements and companion cells → bidirectional translocation of assimilates.
How tissues form organs and systems
Two or more tissues combine to form an organ that performs one or more complex functions. Tissue combination → emergent organ-level functions that no single tissue can provide. Multiple organs then form organ systems that coordinate at the organism level, allowing exchange, movement, or reproduction through integrated tissue and organ actions .
Limits on tissue function
Diffusion limits apply where tissues rely on passive transport; small size or specialised exchange surfaces become necessary when diffusion alone cannot meet metabolic demands. Damage to cell structure or reduced blood/vascular supply causes decreased tissue performance. Structural defects in extracellular components, such as collagen, reduce the mechanical function of connective tissues.
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