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Biology A-level > Xylem > Flashcards

Xylem Flashcards

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1
Q

The walls of the cells in xylem are…

A

thickened with hard, strong material lignin.

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2
Q

Xylem tissue 2 functions are…

A

transport and support.

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3
Q

Vessel elements and…

A

tracheids are the cells involved in the transport of water.

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4
Q

Sclerenchyma fibres are…

A

elongated cells with lignified walls that help to support the plant. They are dead cells.

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5
Q

Xylem vessels are made of many…

A

elongated cells called vessel elements.

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6
Q

The vessel element during its life…

A

lays down lignin.

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7
Q

Lignin is…

A

a very hard, strong substance which is impermeable.

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8
Q

Wood is made of…

A

xylem and gets its strength from the lignin.

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9
Q

As lignin builds up around the cell…

A

the contents of the cell die, leaving an empty space or lumen.

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10
Q

In the parts of the original cell wall where…

A

plasmodesmata are found, no lignin is laid down. These gaps are called pits.

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11
Q

Pits are not open…

A

pores. They are crossed by a permeable unthickened cellulose cell wall.

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12
Q

The pits in one cell…

A

link with neighbouring cells, so water can pass freely from one cell to the next.

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13
Q

The end walls of the neighbouring vessel…

A

elements break down completely, to form a continuous tube.

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14
Q

The removal of water from xylem…

A

vessels in the leaf reduces the hydrostatic pressure in the xylem vessels, so at the top, there is lower.

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15
Q

The water moves through the xylem in…

A

continuous columns.

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16
Q

The high pressure at the bottom of the plant…

A

pushes the water up to the leaves.

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17
Q

The lignified walls help to withstand…

A

the hydrostatic pressure.

18
Q

Mass flow is…

A

the movement of water up through xylem vessels.

19
Q

Cohesion is…

A

the attraction of water molecules together by hydrogen bonding.

20
Q

Adhesion is…

A

the attraction of water to the cellulose and lignin in the walls of the xylem.

21
Q

Cohesion and adhesion help to…

A

keep the water in xylem vessel moving as s continuous column.

22
Q

Pits are important as they allow water…

A

to move out of the xylem vessels to surrounding living cells.

23
Q

Plants can increase the pressure difference by…

A

rising the water pressure at the base of the xylem vessels.

24
Q

The pressure is raised at the base by active…

A

secretion of solutes.

25
Q

Cells surrounding the xylem vessels use…

A

energy to pump solutes across their membranes and into xylem by active transport.

26
Q

The presence of solutes in xylem at the base lowers…

A

the water potential of the solution in the xylem, so water is drawn from the surrounding root cells. This increases the hydrostatic pressure.

27
Q

In roots the xylem vessels are…

A

in the centre of the root.

28
Q

Water from soil taken up by…

A

root hairs crosses the cortex of the root and enters the xylem.

29
Q

An apoplastic pathway is…

A

the uptake of water through the cell wall and through the intercellular spaces.

30
Q

A symplastic pathway is…

A

the uptake of water through the cell membrane into the cytoplasm by osmosis.

31
Q

In a symplastic pathway, after the water entered the cytoplasm it…

A

moves into the sap in the vacuole, through the tonoplast by osmosis.

32
Q

In a symplastic pathway, the water moves from one cell to another through…

A

the plasmodesmata or through adjacent cell surface membranes and cell walls.

33
Q

The cells of the cortex, like all…

A

plant cells have cell walls surrounded by several layers of cellulose fibres criss-crossing one another. Water can soak into these walls.

34
Q

When high rates of transpiration take place…

A

the apoplastic pathway is more common.

35
Q

When the water reaches the endodermis…

A

the apoplastic pathway is blocked, as endodermis have a waterproof band of suberin(Casparian strip) in their cell walls.

36
Q

Water must move through endodermis by…

A

osmosis through the cytoplasm.

37
Q

As the endodermal cells get older…

A

the suberin deposits become more extensive, except certain cells called passage cells.

38
Q

This endodermis helps plant to control…

A

which ions can pass to the xylem vessel.

39
Q

Water moves to the hair roots by…

A

osmosis as the water potential of the cytoplasm and cell sap is lower.

40
Q

Mycorrhizas are…

A

fungi located in or on the roots, acting as root hairs.

41
Q

Mineral ions in solution are absorbed…

A

along with water by root hairs.

42
Q

Minerals can be also absorbed by…

A

active transport.

Biology A-level (58 decks)

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