exchange and transport Flashcards
what tissue do water and soluble minerals travel up/down in a plant?
xylem tissue
what tissue do sugars travel up/down in a plant?
phloem tissue
where are the xylem and phloem found?
in the vascular bundles
what does the arrangement of the phloem and xylem provide?
strength to withstand the pulling forces that the roots are exposed to
what is the endodermis?
a special sheath of cells, role is to get water from the xylem vessels
name one xylem adaptation (1)
narrow tubes, so water column doesn’t break easily and capillary action can be effective
name one xylem adaptation (2)
pits in the lignified walls allow water to move sideways from one vessel to another
name one xylem adaptation (3)
lignin in spiral patterns, allows the xylem to stretch and bend as the plant grows. Also it strengthens the walls and prevents them from collapsing
name one xylem adaptation (4)
made of dead cells that form a continuous column, hence no cell contents, nucleus or cytoplasm, to impede the flow of water
what does phloem consist of?
sieve tube elements and companion cells
what are sieve tube elements?
they contain very little cytoplasm and no nucleus. they’re lined up end-to-end to form a sieve tube, to transport sugars (sucrose). the sugar is dissolved in water to from sap.
the sieve tubes contain sieve plates, what do they allow/contain?
they contain many pores to allow the sap to flow
what do the companion cells have?
a large amount of mitochondria, to produce the atp needed for the active process
what do the companion cells carry out?
the metabolic process needed by the sieve tube elements
the cytoplasm of the sieve tube elements and companion cells are linked through many…
plasmodesmata
what do the gaps in the cell walls of companion cells allow?
communication and flow of materials between the cells
what is transpiration?
the loss of water vapour from the aerial parts of the plant
what three processes does transpiration involve?
1) osmosis: from the xylem to the mesophyll cells
2) evaporation: from the surface of the mesophyll cells into the intercellular spaces
3) diffusion: of water vapour down a water vapour potential gradient out of the stomata
the movement of water up the stem is called the…
transpiration stream
how is the transpiration stream useful?
1) it enables leaves to acquire water for photosynthesis
2) it keeps cells turgid
3) evaporation of water can help keep plant cool
4) it enables cells to acquire water for growth and elongation
how is the rate of transpiration measured?
using a potometer
what’s a factor that effects the rate of transpiration? (1)
the amount of leaves.
the more leaves the larger the surface area over which water vapour can be lost
what’s a factor that effects the rate of transpiration? (2)
presence of waxy cuticle.
reduces evaporation from the leaf surface
what’s a factor that effects the rate of transpiration? (3)
the number of stomata.
the more stomata, the faster the rate of water vapour loss.
what’s a factor that effects the rate of transpiration? (4)
air movement/wind.
wind will take away water vapour, maintaining a high water vapour potential gradient.
what are xerophytes?
plants that are well adapted to living in very dry/arid conditions
what are the xerophytes adaptations to reduce water loss? (1)
pits:
containing stomata at their base which also trap air
what are the xerophytes adaptations to reduce water loss? (2)
hairs:
on the surface of leaves which trap a layer of air which can be saturated with moisture to reduce the water vapour potential
what are the xerophytes adaptations to reduce water loss? (3)
densely packed spongy mesophyll:
reduces cell SA exposed to air inside the leaves so less water will evaporate into the air spaces
reduces cell SA exposed to air inside the leaves so less water will evaporate into the air spaces (4)
closing the stomata:
when water availability is low, reducing water loss and the need to take up water.
describe the apoplast pathway
the cellulose cell wall has many water-filled spaces between the cellulose molecules. water can move through these spaces and between the cells, and as the water doesn’t pass through any plasma membranes, it can carry dissolved mineral ions and salts
describe the symplast pathway
water enters the cytoplasm through the plasma membrane, and pass form one cell to the next through the plasmodesmata. once inside the cytoplasm, water can move through the continuous cytoplasm from cell to cell
what is the function of the root hair cells in the roots?
they use atp to absorb minerals via active transport
what do the minerals absorbed by the root hair cells do?
reduce the water potential of the cell cytoplasm, making it lower than the soil. the result is that water is taken up across the plasma membrane by osmosis, as molecules move down the water potential gradient
what is the movement of water across the root?
the movement is driven by an active process that occurs at the endodermis
what does the casparian strip consist of?
special cells that have a waterproof strip in some of their cells.
what’s the function of the casparian strip?
it blocks the apoplast pathway, forcing water into the symplast pathway
what is ensured when the apoplast pathway is blocked?
this ensures that water and dissolved nitrates have to pass into the cell cytoplasm through the cell membrane
