transport in plants Flashcards
function of xylem
- conduct water and dissolved mineral salts from roots to the stems and leaves
- provide mechanical support for the plant
xylem vessel adaptation
- empty lumen without protoplasm –> reduces resistance to water flowing through the stem
- walls are thickened with lignin –> prevents collapse of the vessel
function of phloem
conduct manufactured food from the green parts of the plant, especially the leaves, to the other parts of the plant
what is the phloem made up of?
sieve tubes and companion cells
adaptations of phloem
- companion cells have many mitochondria –> provide energy needed for companion cells to load sugars from mesophyll cells into sieve tubes via active transport
- holes in sieve tubes allow rapid flow of manufactured food substances through the sieve tubes
how does water enter a plant?
- thin film of moisture surrounding each soil particle is a dilute solution of mineral salts
- cell sap of root hair cell is a relatively concentrated solution of sugars and various salts
- cell sap has lower wp than soil solution
- net movement of water molecules from soil into cell via osmosis through the cell’s partially permeable cell membrane
- entry of water dilutes cell sap, cell sap of cell now has higher wp than that of next cell
- osmosis of water molecules from first cell to second cell
how do root hairs absorb ions or mineral salts?
- when concentration of ions in soil solution is lower than that of cell sap
- root hairs absorb ions against a conc gradient by active transport
- energy comes from cellular respiration
adaptations of root hair cell
- root hair is long and narrow –> increase surface area to volume ratio –> increase rate of absorption of water and mineral salts
- cell surface membrane prevents cell sap from leaking out
- root hair cell contains many mitochondria, aerobic respiration in mitochondria releases energy for active transport of ions
what is transpiration?
the loss of water vapour from a plant, mainly through the stomata of the leaves
how does transpiration pull come about?
- evaporation of water from leaves removes water from xylem vessels
- results in a suction force which pulls the water up the xylem vessel
importance of transpiration
- transpiration pull draws water and mineral salts from roots to stem and leaves
- evaporation of water from cells in leaves removes latent heat of vaporisation –> cools plant, prevent it from being scorched by sun
factors affecting rate of transpiration
- humidity
- intercellular air spaces normally saturated with water vapour
- water vapour conc gradient between leaf and atmosphere
- increase in humidity –> decrease in wv conc gradient –> decrease in rate of transpiration - wind or air movement
- wind blows away the water vapour that accumulates outside the stomata
- maintains the conc gradient between leaf and atmosphere
- increase in rate of transpiration
temperature
- increases rate of evaporation of water from cell
- increase rate of transpiration
light
- in sunlight, stomata opens and becomes wider
- increase rate of transpiration
wilting
- turgor pressure in mesophyll cells help support the leaf and keep it firm and spread out widely for photosynthesis
- in strong sunlight, when rate of transpiration exceeds rate of absorption of water, cells lose their turgor
- they become flaccid, plant wilts
advantages of wilting
- when leaf folds up, surface area that is exposed to sunlight is reduced
- excessive loss of water causes guard cells to become flaccid and stomata to close –> rate of transpiration decreases
disadvantages of wilting
- rate of photosynthesis is reduced because water becomes a limiting factor
- as the stomata are closed, the amt of co2 entering the leaf is reduced –> decreases rate of photosynthesis
