Transcript File

9.2 Transport in Angiosperms
9.2.1: Root System
• Huge, ever growing root
system increases the
surface area for
absorption of water and
essential nutrients
• Surface area is also
increased by the addition
of root hairs
• Cortex cells have a
structure that also
facilitates the uptake of
water
• Water can move in two
routes symplastic and
apoplastic
9.2.2: Ion Uptake
• Minerals needed by the plants and found in soil are:
–
–
–
–
N as NO3- or NH4+
K as K+
P as PO43Ca as Ca2+
• Diffusion
– Minerals are more concentrated in the soil than in the root
– When dissolved in water the minerals will diffuse into the roots
• Fungal Hyphae
– Plants work together with fungus to absorb minerals
– Threads of the fungus grow through the soil and absorb the
minerals
– The threads also grow into the roots and transport the minerals
into the roots
– These minerals would not be absorbed without the fungus
– Plants give the fungus sugars
• Mass flow of water
– Uptake of water which includes dissolved minerals
9.2.3:
• Xylem- Stem:Tracheids & Vessel Members (see photo)
• Use of metabolic energy to obtain minerals in root
• Can occur against the concentration gradient
– Cytosol of the cell holds some reserves of ions
– Allows the cells to pull in more of these ions when available
– Cells tend to horde ions
• Highly selective – plant will choose from different forms
of the same ion
• Ions cross into the cell through pump molecules
• If roots are deprived of oxygen then active transport
stops
– The formation of the necessary metabolic energy is from
respiration
• Vessel Members and Tracheids are dead at
maturity and are arranged end to end
• Thick lignified walls have pits or pores so water
can move laterally
9.2.4: Plant Support
• Stem is used to support the leaves of the plant and to
transport water, ions and organic nutrients
• Made up mostly of ground tissues (non-woody plants)
– Cells are known as parenchyma
– Stay rigid using cell turgor: exerting pressure on surrounding
cells using a water filled vacuole
– Outermost layers have additional layers of thickened cellulose
laid down unevenly
• Called collenchyma cells
• In woody plants
– Xylem tissue has cellulose thickenings that are hardened with a
chemical called lignin
– Provides almost all the strength of the stem
9.2.5: Transpiration
• The loss of water vapor form the leaves
and stems of a plant
• Water generally moves into plants through
their roots and upwards through the
vascular system and out of the stomata in
the leaves
9.2.6:
• Water transport occurs in the xylem
– Begins as elongated cells connected end to end
– During development the end walls are dissolved
away so long hollow tubes develop
– Living tissues of xylem lay down cellulose which is
thickened by lignin
• Water lost by transpiration raises the osmotic pressure
in the cells causing water uptake from surrounding cells
• Water comes from the xylem
• As water leaves the xylem more is pulled up through
transpiration pull
• As water leaves the xylem more is pulled into the xylem
at the root
• Water coheres to the lateral walls of the xylem
maintaining a continuous column of water
• Much of the water pulled into the plants is lost to
evaporation
9.2.7: Stomata
• Transpiration is regulated by the stomata
– Tiny pores for gas exchange
– Occur mostly in the leaves but sometimes found in
the stem
• Made of 2 elongated guard cells
– attached to normal epidermis cells on one side
– Not attached to each other
• Open and close based on turgor pressure
– Open when water is absorbed by the guard cell from
its neighboring epidermis cell
– Water is then lost through the pore
– Close when enough water is lost that the cell
becomes flaccid
• Tend to be open during the day and closed at night
• Will close during the day if plant becomes short of water
– Regulates transpiration & prevents excess water loss
9.2.8: Hormone Regulation of the
Stomata
• Abscisic acid (ABA) is a plant growth
hormone that helps regulate the rate of
transpiration in plants
• In time of physiological stress (like
drought) the levels of ABA increase in the
leaves
• Maintains stomata closure preventing
excess water loss
9.2.9: Abiotic Factors and transpiration
• Light
– Stomata tend to be open in light
– Light can warm the leaf and raise its temperature
• Temperature
– Causes evaporation of water molecules from the surface cells of
the plant
– Evaporation rate doubles for every 10 degree increase in
temperature
• Wind
– Sweeps away water vapor causing an increase in transpiration
• Humid Air
– Decreases transpiration
• Soil Water
-If intake of water at roots does not keep up stomata then close
• Carbon Dioxide
-High Carbon Dioxide levels usually cause stomata to close
C4 and CAM Plants
• C4 ("four-carbon") plants initially attach CO 2 to PEP to form the fourcarbon compound OAA (oxaloacetate) using the enzyme PEP
carboxylase. This takes place in the loosely packed cells called
mesophyll cells. OAA is then pumped to another set of cells, the
bundle sheath cells, which surround the leaf vein. There, it releases
the CO 2 for use by Rubisco. By concentrating CO 2 in the bundle
sheath cells, C4 plants promote the efficient operation of the CalvinBenson cycle and minimize photorespiration. C4 plants include corn,
sugar cane, and many other tropical grasses.
• CAM ("crassulacean acid metabolism") plants initially attach CO 2 to
PEP and form OAA. However, instead of fixing carbon during the day
and pumping the OAA to other cells, CAM plants fix carbon at night
and store the OAA in large vacuoles within the cell. This allows them
to have their stomata open in the cool of the evening, avoiding water
loss, and to use the CO 2 for the Calvin-Benson cycle during the day,
when it can be driven by the sun's energy. CAM plants are more
common than C4 plants and include cacti and a wide variety of other
succulent plants.
9.2.10: Adaptations of Xerophytes
• Thick cuticle
– Prevents water loss through the external wall of the epidermis
• Hairs on the epidermis
– Traps moist air over the leaf
• Reduction in number of stomata
– Reduces areas where loss can occur
• Rolled or folded leaves
– Reduces area for transpiration to occur
– Lower epidermis is rolled inside the leaf protecting it
• Superficial roots
– Takes advantage of condensation on the soil overnight
• Deep and extensive roots
– Allows access to the deep water
• Reduced leaf numbers
– Less surface area for transpiration
• Low growth
– Limits plant exposure to wind
• Often show CAM photosynthesis
9.2.11:
• Translocation
– The movement of manufactured food (sugars&amino acids)
– Occurs in the phloem
– Takes sugars to new growth in young plants & to storage in
older plants
– Amino acids are produced in the roots and transported to
where they are needed for protein synthesis (usually
growing parts of the plant)
– Chemicals sprayed on the plant also moved in this manner
• Phloem tissue
– Sieve tubes: narrow elongated cells connected end to end;
no real organelles
– Sieve plates: end walls which have pores for material to
move through
– Companion cells: services and maintains the sieve tubes;
attached to the sieve tube by cytoplasm strands
• Transport requires energy
• Can occur in any direction