9.2 Water transport in multicellular plants?

In a plant, what two things is water key in?

both the structure and metabolism of plants

What is turgor pressure (hydrostatic pressure) a result of in plant cells?

osmosis

What does turgor pressure (hydrostatic pressure) - as a result of osmosis - provide the plant with?

a hydrostatic skeleton to support the stems and leaves

What does turgor also drive?

cell expansion

Why is the loss of water by evaporation beneficial?

helps to keep the plant cool

What is transported in aqueous solutions (2)?

mineral ions and the products of photosynthesis

What is water a raw material for?

photosynthesis

Low water potential?

higher salt concentration

High water potential?

low salt concentration

If the water potential inside the cell is high where will water go?

water will move out of the cell by osmosis

If the water potential inside the cell is low where will water go?

will move into the cell by osmosis

What does water enter the cell down?

the water potential gradient

Where does water move when there is a low external water potential?

water moves out of the cell

When is a cell said to be plasmolysed?

when plants survive water moving out of the cell for short periods of time by shrinking their cell membrane away from the cell water

Where does water move when moving between cells?

water moves from the cell with the higher water potential to the cell with the lower (more negative) water potential

Root hair cells?

specialised exchange surfaces in plants

Root hair cells: function?

for the uptake of water and mineral ions into the plant from the soil

Root hair cells: size?

200 – 250μm

Root hair cells: a root hair?

a long, thin extension from a root hair cell - specialised epidermal cell

Root hairs: what are they well adapted as?

exchange surfaces

Root hairs - well adapted: what does their microscopic size allow them to do?

penetrate easily between soil particles

Root hairs - well adapted: how many are there on each root tip?

thousands - maximise surface area in contact with the soil

Root hairs - well adapted: size of each hairs SA:V ratio?

large

Root hairs - well adapted: why is having a thin surface layer (on each hair) beneficial?

diffusion and osmosis can take place through it quickly

Root hairs - well adapted: what is maintained between the soil water and the cell?

the water potential gradient - through the concentration of solutes in the cytoplasm of root hair cells

Root hairs - well adapted: Water potential of soil water?

high water potential - low concentration of dissolved minerals

Root hairs - well adapted: water potential of root hair cells?

low - contains many different solvents including su

Root hairs - well adapted: as a result, how does water move into the root hair cell?

by osmosis

Root hairs - well adapted: plasma membrane?

partially permeable

Where does the water continue to move across the root to once it has moved into the root hair cell?

moves across the root to the xylem

What are the 3 pathways water moves through the roots cells and into the xylem tube by?

Symplast pathway, vacuolar pathway and apoplast pathway

What do all of these pathways allow the plant to do?

to get water in as fast as possible

The symplast pathway: symplast?

the continuous cytoplasm of the living plant cells that is connected through the plasmodesmata

The symplast pathway: what creates the continuous cytoplasmic network that is the symplast?

Plasmodesmata

The symplast pathway?

the movement of water through the living spaces of the cell (cytoplasm)

The symplast pathway: how does the water change between cells?

through the plasmodesmata

The symplast pathway: how does water move through the symplast?

by osmosis

The symplast pathway: how does water move from the root hair cell into the cell next door by osmosis?

the root hair cell has a higher water potential than the next cell along

The symplast pathway: why does the root hair cell has a higher water potential than the next cell along?

due to water diffusing in from the soil, which has made the cytoplasm more dilute

The symplast pathway: when does this process continue, from cell to cell across the root until?

until the xylem is reached

The symplast pathway: how is a steep water potential gradient between the soil and cell maintained?

as water leaves the root hair cell by osmosis, the water potential of the cytoplasm falls again

The symplast pathway: why is important to maintain a steep water potential gradient between the cell and soil?

to ensure that as much water as possible continues to move into the cell from the soil

The symplast pathway: why is water drawn up the plant?

each cell further away from the roots has a lower water potential so water is drawn up by the pant

The vacuolar pathway?

the same as the symplast pathway when the water moves through the cells vacuoles in addition to the cytoplasm

The vacuolar pathway: key feature of this route?

the slowest route

The Apoplast Pathway?

the movement of water through the apoplast - the cell wall and intracellular spaces

Apoplast?

the cell wall and intracellular spaces

The Apoplast Pathway: what does water fill?

the spaces between the loose, open network of fibres in the cellulose cell wall

The Apoplast Pathway: as water molecules move into the xylem, why are more water molecules pulled through the apoplast behind them?

due to cohesive forces between the water molecules

The Apoplast Pathway: what does the pull from water moving into the xylem and up the plant along with the cohesive forces between the water molecules create?

a tension that means there is a continuous flow of water through the open structure of the cellulose wall - which offers little or no resistance

The Apoplast Pathway: therefore, what pulls water up the plant?

cohesive and tension forces acting on the cell

The apoplast, symplast and vacuolar pathways along which water moves across the root diagram?

…

The apoplast and symplast pathways along which water moves across the root diagram?

…

Water moves across the root in the apoplast, vacuolar and symplast pathways until it reaches what?

the endodermis

The endodermis?

the layer of cells surrounding the vascular tissue (xylem and phloem) of the roots

Why is the endodermis particularly noticeable in the roots?

the effects of the casparian strip (which the endodermis is home to)

The casparian strip?

impermeable, waxy layer of suberin around the endodermal cells

The casparian strip: at this point what is the apoplast pathway forced into as it can go no further?

forced into the cytoplasm of the cell, joining the water in the symplast pathway