3.4 Transport in flowering plants
● Root hair cells increase surface area of root in contact with soil water
● Helps water passing into root by osmosis
○ Cytoplasm inside root hair cells contains lots of dissolved molecules
(including sugars and mineral salts) → ***root hair cells are less watery than
soil water
○ Soil water passes into root hair cells by osmosis (from high to low water
potential, down the concentration gradient)
○ Cell membrane of root hair cell acts as partially/selectively permeable
membrane
○ ***Movement of water by osmosis: soil water → root hair cell → cell wall → cell
membrane → cytoplasm → vacuole ⇒ (other cells interior) ⇒ xylem (in centre
of root)
Xylem (木質部)
● Transport water and mineral ions up plant (from roots to other parts of plant)
● Made up of several types of cells, including dead cells
● Many of the end walls have broken down, forming long vessels with very narrow
diameter
● Long xylem vessels run through plant, from roots, up stems, then spread out as leaf
veins
● Xylem cell walls are strengthened with lignin (木質素)
● Strong and hard xylem walls (what forms wood of tree)
● ***Transpiration (蒸騰作用): loss of water from leaf (stomata allowing gas exchange
to take place, AT SAME TIME water vapour is lost through stomata)
● ***Transpiration pull (蒸騰拉力): as water transpires through stomata, more is
drawn up from xylem to take its place
● Other adaptations of xylem
○ Capillarity - water can rise up a very narrow capillary tube, xylem cells
have very narrow diameter, ∴ capillarity (毛細作用) contributes to water
being lifted up xylem in stem
○ Cohesion (凝聚) - individual water molecules (H2O , H2O) linking to their
neighbours by bonds between water molecules, pulling one another in an
unbroken column (forming basis of transpiration pull)
● Mineral ions (i.e.: salts) dissolve in water, forming dilute solution of ions
● If concentration of ions in soil water is higher than that in root hair cells, then ions can
pass through membrane into root hair cell by diffusion down the concentration
gradient
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● Root hair cells increase surface area of root in contact with soil water
● Helps water passing into root by osmosis
○ Cytoplasm inside root hair cells contains lots of dissolved molecules
(including sugars and mineral salts) → ***root hair cells are less watery than
soil water
○ Soil water passes into root hair cells by osmosis (from high to low water
potential, down the concentration gradient)
○ Cell membrane of root hair cell acts as partially/selectively permeable
membrane
○ ***Movement of water by osmosis: soil water → root hair cell → cell wall → cell
membrane → cytoplasm → vacuole ⇒ (other cells interior) ⇒ xylem (in centre
of root)
Xylem (木質部)
● Transport water and mineral ions up plant (from roots to other parts of plant)
● Made up of several types of cells, including dead cells
● Many of the end walls have broken down, forming long vessels with very narrow
diameter
● Long xylem vessels run through plant, from roots, up stems, then spread out as leaf
veins
● Xylem cell walls are strengthened with lignin (木質素)
● Strong and hard xylem walls (what forms wood of tree)
● ***Transpiration (蒸騰作用): loss of water from leaf (stomata allowing gas exchange
to take place, AT SAME TIME water vapour is lost through stomata)
● ***Transpiration pull (蒸騰拉力): as water transpires through stomata, more is
drawn up from xylem to take its place
● Other adaptations of xylem
○ Capillarity - water can rise up a very narrow capillary tube, xylem cells
have very narrow diameter, ∴ capillarity (毛細作用) contributes to water
being lifted up xylem in stem
○ Cohesion (凝聚) - individual water molecules (H2O , H2O) linking to their
neighbours by bonds between water molecules, pulling one another in an
unbroken column (forming basis of transpiration pull)
● Mineral ions (i.e.: salts) dissolve in water, forming dilute solution of ions
● If concentration of ions in soil water is higher than that in root hair cells, then ions can
pass through membrane into root hair cell by diffusion down the concentration
gradient
1
