Plant Structure (Structure-Function Relationship)

PLAnT STRuCTuRE Structure-Function Relationship Leaf Tissue The structure of a plant is related to its various functions: • Leaves contain chloroplasts and stomatal pores (for photosynthesis and gas exchange respectively) • Roots are highly branched, with a high SA:Vol ratio (necessary for water and mineral uptake) • Stems transfer essential materials in vascular bundles (transpiration of water and translocation of nutrients) A leaf possesses two layers of inner tissue: • Palisade mesophyll – upper layer of tightly packed cells that are rich in chloroplasts (⬆︎︎ light absorption) • Spongy mesophyll – lower layer of cells interspersed by space and located near the stomata (⬆ gas exchange) Xylem Palisade Leaves (sugars) Mesophyll Roots (water) Translocation Spongy Phloem Transpiration Vascular Bundle Stomatal Pore Root Tissue Root systems display extensive branching in order to maximise the available surface area for material uptake • Fibrous (adventitious) root systems contain many branching roots that are thin and very spread out • Tap root systems have a deeply penetrating central root (for stability) with many connected lateral branches The root epidermis additionally may have many small extensions called root hairs (to further increase available surface area) Vascular Bundles In vascular plants, the vessels of xylem and phloem are arranged into bundles that extend from the roots to the shoots • The organisation of these vascular bundles differ according to the plant section (root vs stem) and plant type (monocot vs dicot) Roots • Vascular bundles are radially arranged within a big stele in monocots, but are centrally arranged within a small stele in dicots STEM SYSTEM ROOT SYSTEM SYSTEM ROOT Stems • Vascular bundles are scattered haphazardly in monocots, but form a ring around a circular cambium in dicots Monocotyledon Dicotyledon Monocotyledon Dicotyledon