Adaptations for transport in plants
Root cross section diagram
stem cross section diagram
resists vertical stresses and anchors the plant.
gives flexible support and resists bending.
leaf cross section diagram
Gives flexible strength and resistance to tearing
Xylem
Vessels occur only in angiosperms. as lignin builds in cell walls , content dies leaving an empty lumen, the end of the cell breaks down
Tracheids in ferns and conifer(flowering plants)
It transports water and dissolved material, provides mechanical strength and support.
Vacuole and cytoplasm has high solute concentration so that water will move into the root hair cell by osmosis.
Movement of water through the root
Apoplast pathway- water moves though cell walls until it reaches casparian strip and is forced inward.
Symplast pathway- water moves through cytoplasm and plasmodesmata.
Vacuolar pathway water moves from vacuole to vacuole.
Vascular tissue is surrounded by the pericycle, surrounded by endodermis.
Movement of water from roots to leaves
cohesion-tension, water is drawn up after water evaporates and water I attracted to the hydrophyllic lining of the xylem by adhesion.
cohesion-tension, adhesion and tension in water column.
root pressure, osmotic pressure of water in the roots pushes water up further along the xylem.
Factors affecting rate of transpiration
Genetic factors eg.stomata size, environmental factors eg.temperature light intensity
Adaptations of flowering plants
Mesophytes, shed leaves for winter, low metabolic rates over winter.
Xerophytes, interlocking hair to trap water vapour, thick cuticle, sclerenchyma fibres, folded leaf
Hydrophytes, no lignified support tissue, poorly developed xylem, upper surface stomata, no cuticle, stems and leaves have large air spaces to produce buoyancy.
Translocation
Phloem, sieve tube elements and companion cells. living cells, end walls do not break down. Sieve tube elements lose nucleus and most organelles during development. Companion cells have large nucleus, RER and many mitochondria. plasmodesmata.
Theories
Ringing experiments Radioactive tracers and autoradiography. Aphid experiments.
Mass flow, passive flow from the the source to the sink.
Active process, protein filament, cytoplasmic streaming.