Xylem Flashcards
The walls of the cells in xylem are…
thickened with hard, strong material lignin.
Xylem tissue 2 functions are…
transport and support.
Vessel elements and…
tracheids are the cells involved in the transport of water.
Sclerenchyma fibres are…
elongated cells with lignified walls that help to support the plant. They are dead cells.
Xylem vessels are made of many…
elongated cells called vessel elements.
The vessel element during its life…
lays down lignin.
Lignin is…
a very hard, strong substance which is impermeable.
Wood is made of…
xylem and gets its strength from the lignin.
As lignin builds up around the cell…
the contents of the cell die, leaving an empty space or lumen.
In the parts of the original cell wall where…
plasmodesmata are found, no lignin is laid down. These gaps are called pits.
Pits are not open…
pores. They are crossed by a permeable unthickened cellulose cell wall.
The pits in one cell…
link with neighbouring cells, so water can pass freely from one cell to the next.
The end walls of the neighbouring vessel…
elements break down completely, to form a continuous tube.
The removal of water from xylem…
vessels in the leaf reduces the hydrostatic pressure in the xylem vessels, so at the top, there is lower.
The water moves through the xylem in…
continuous columns.
The high pressure at the bottom of the plant…
pushes the water up to the leaves.
The lignified walls help to withstand…
the hydrostatic pressure.
Mass flow is…
the movement of water up through xylem vessels.
Cohesion is…
the attraction of water molecules together by hydrogen bonding.
Adhesion is…
the attraction of water to the cellulose and lignin in the walls of the xylem.
Cohesion and adhesion help to…
keep the water in xylem vessel moving as s continuous column.
Pits are important as they allow water…
to move out of the xylem vessels to surrounding living cells.
Plants can increase the pressure difference by…
rising the water pressure at the base of the xylem vessels.
The pressure is raised at the base by active…
secretion of solutes.
Cells surrounding the xylem vessels use…
energy to pump solutes across their membranes and into xylem by active transport.
The presence of solutes in xylem at the base lowers…
the water potential of the solution in the xylem, so water is drawn from the surrounding root cells. This increases the hydrostatic pressure.
In roots the xylem vessels are…
in the centre of the root.
Water from soil taken up by…
root hairs crosses the cortex of the root and enters the xylem.
An apoplastic pathway is…
the uptake of water through the cell wall and through the intercellular spaces.
A symplastic pathway is…
the uptake of water through the cell membrane into the cytoplasm by osmosis.
In a symplastic pathway, after the water entered the cytoplasm it…
moves into the sap in the vacuole, through the tonoplast by osmosis.
In a symplastic pathway, the water moves from one cell to another through…
the plasmodesmata or through adjacent cell surface membranes and cell walls.
The cells of the cortex, like all…
plant cells have cell walls surrounded by several layers of cellulose fibres criss-crossing one another. Water can soak into these walls.
When high rates of transpiration take place…
the apoplastic pathway is more common.
When the water reaches the endodermis…
the apoplastic pathway is blocked, as endodermis have a waterproof band of suberin(Casparian strip) in their cell walls.
Water must move through endodermis by…
osmosis through the cytoplasm.
As the endodermal cells get older…
the suberin deposits become more extensive, except certain cells called passage cells.
This endodermis helps plant to control…
which ions can pass to the xylem vessel.
Water moves to the hair roots by…
osmosis as the water potential of the cytoplasm and cell sap is lower.
Mycorrhizas are…
fungi located in or on the roots, acting as root hairs.
Mineral ions in solution are absorbed…
along with water by root hairs.
Minerals can be also absorbed by…
active transport.
