Adaptations for transport(plants). Flashcards
Structure of the root.
Epidermis
Exodermis
Cortex(parenchyma)
Endodermis
Phloem
Xylem.
Structure of stem.
Epidermis
Cortex(collenchyma, parenchyma)
Vascular bundle
Pith
Interfascicular cambium.
Xylem structure and function.
Vessels, tracheids, fibres, parenchyma.
-Dead cells
-Transport water and minerals up the plant
-Provides mechanical strength/support
-Strengthened by lignin(waterproof).
Phloem structure and function.
Sieve tubes, sieve plates, fibres, parenchyma, companion cells.
-Carry sucrose and amino acids.
-Sieve tubes have sieve plates w/ pores where cells are linked
-No other organelles present in sieve elements
-Companion cells have mitochondria(ATP) and organelles for protein synthesis.
-Proteins and ATP passed to sieve elements through plasmodesmata.
Transpiration.
Loss of water as water vapour
By evaporation and diffusion out of open stomata
From the leaves
Leads to transpiration stream.
Transpiration stream.
Water moves into root and enters xylem(root pressure)
Cohesive forces between water molecules and adhesive forces between water molecules and the hydrophilic lining of the xylem=transpiration pull as water leaving the xylem into leaf cells pulls on molecules below
Cohesion-tension theory.
Factors increasing transpiration.
Lower humidity
Higher temperature.
higher light intensity
Large amounts of air movement.
Hydrophyte adaptations.
Live in water
Little/no waxy cuticle
Stomata on upper surface
Poorly developed xylem
Large air spaces=buoyancy/reservoirs of gas.
Mesophytes adaptations.
Live with adequate water
Close stomata at night=reduce water loss
Shed leaves in winter
Underground organs and dormant seeds survive winter.
Xerophytes adaptations.
Live in dry conditions
Thick waxy cuticle=reduce water loss by evaporation
Sunken stomata=increase humidity in air chamber above stomata=lower diffusion gradient, less water loss
Stiff interlocking hairs=traps water vapour
Rolled leaves=traps water=reduces water potential=less water loss.
Translocation.
Phloem transports photosynthesis products(glucose and oxygen)
From the source(leaf) to the sink(where used)
Bidirectional.
Experimental evidence for translocation bidirectional flow.
Ringing experiments:
-removal of phloem=accumulation of sucrose
Aphids to sample phloem sap:
-analyse sap which has amino acids and sucrose from phloem
-using an aphid stylus extending into sieve tube elements
Radioactive labelling:
-label CO2 w/ radioactive substance
-will become incorporated into sucrose
-can determine rate of transport in phloem
-can determine sources and sinks in a plants.
Evidence for mass flow theory in the phloem.
Sucrose made at source=lower water potential
Water enters cells and sucrose is forced into phloem(loading)
Increases hydro static pressure
Mass flow occurs along phloem to the root
Where sucrose stored as starch
Water potential is then less negative and water moves into the xylem.
Evidence against mass flow theory in the phloem.
Sieve plates impede flow
Translocation is faster than expected w/ diffusion
Does not explain bidirectional flow or different rates of flow of amino acids and sucrose
Does not explain companion cell mitochondria, high O2 intake or translocation stopping by cyanide.
Apoplast pathway.
H2O moves through intercellular spaces
Cell wall to cell wall
Down water potential gradient by osmosis.
