CH.7 Transport In Plants Flashcards
What is Xylem
a tissue containing tubes called vessels and other types of cells, responsible for the transport of water and mineral salts through a plant and support. Uni-directional
What is Phloem
a tissue containing tubes called sieve tubes and other types of cells, responsible for the transport through the plant of organic solutes (assimilates) such as sucrose. Bi-directional
Parenchyma
cells outside vascular tissue are parenchyma calls
cortex is mainly made up of parenchyma
used as a packing tissue between more specialised structures, metabolically active, food storage and support, play an important role in the movement of water and food products in xylem and phloem
Collenchyma
it is like parenchyma with thicker walls (more cellulose) for more support. Found outside stems just below the epidermis and in the midrib of leaves
Sclerenchyma
vascular bundles in stems have a cap of fibres, sclerenchyma, for extra strength in the stem. Mechanical function. Cell walls are impregnated with lignin. Mostly takes the form of fibres.
Transpiration
The loss of water vapour from a plant (mesophyll cells) to its environment by diffusion down a water potential gradient. Most transpiration takes place through the stomata in the leaves.
Stomata close at night so transpiration only takes during the day.
xerophyte
a plant adapted to survive in conditions where water is in short supplu
xerophyte adaption
stomata found in the upper epidermis
hairs trap a layer of moist air close to the leaf surface, to reduce the water potential gradient
leafs rolled up to trap air
sunken stomata
thick waxy cuticle to reduce water evaporation from the surface
structural features of xylem
xylem vessels are made from cells joined end to end to form tubes
cells are dead
walls are thickened with lignin, a hard, strong material
pits in the walls allow water in and out of the tubes
How does cohesion and adhesion help water move in a continuous column?
cohesion-
water molecules are attracted to each other by hydrogen bonding
adhesion-
water molecules are attracted to cellulose and lignin which are hydrophilic
How is the problem of airlocks solved?
xylem vessels have a small diameter which prevents air locks from forming
pits allow water to move out of one vessel to a neighbouring vessel, bypass airlocks because air bubbles cannot move through cellulose cell wall
vascular bundle position in root and stem
root-
in the centre (xylem in the centre, phloem on outside)
stem-
arranged in a ring and near the outside (xylem facing the center, phloem on the outside )
describe the apoplast pathway
water enters the cell wall
water moves through the cell wall
water may move from cell wall to cell wall through the intercellular spaces
water may move directly from cell wall to cell wall
describe the symplast pathway
water enters the cytoplasm by osmosis through the partially permeable cell surface membrane
water moves into the sap in the vacuole, through the tonoplast by osmosis
water may move from cell to cell through the plasmodesmata
water may move from cell to cell through adjacent cell surface membrane and cell walls
Explain why the apoplast pathway is blocked by the endodermis and how water moves through the endodermis
pg. 178
