Biology: Plants - Xylem and Phloem

reason why plants need a transport system to move substances efficiently

multicellular organism; multiple layers of cells; distance between surface and internal cells is too long

function of the xylem (vascular tissue)

transports dissolved minerals/water around the plant (root to leaf); structural support; food storage

reason why plants need a transport system to move substances efficiently

multicellular organism; multiple layers of cells; distance between surface and internal cells is too long

function of the xylem (vascular tissue)

transports dissolved minerals/water around the plant (root to leaf); structural support; food storage

four cell types of xylem

tracheids; vessel elements to move water; parenchyma; sclerenchyma cells

xylem: lignified cell walls

add strength to withstand hydrostatic pressure so it doesn’t collapse

xylem: no end walls/plates

allow mass flow of dissolved minerals/water

xylem: no protoplasm (dead cells when mature)

doesn’t impede mass flow of water/dissolved solutes

function of the phloem sieve tube tissue

transport food: organic compounds (sucrose, amino acids) from source (e.g: leaf) to sink (e.g: root); two-way flow

four cell types of phloem

bulk flow is through sieve tube elements, the main conducting cells and companion cells for translocation of food | parenchyma cells: thin wall living cells (food storage and lateral transport) | companion cells: mature phloem tissue w/ living cells, for translocation of food | fibers (sclerenchyma) for mechanical strength

phloem sieve tube

sieve plate with sieve pores (perforations): allow continuous movement of organic substances like phloem sap which has assimilated particles | cellulose cell wall: strengthening wall to withstand hydrostatic pressure that moves the assimilates | no nucleus/ribosome/vacuole in mature cells: maximize space for movement of assimilates