mass transport in plants 3.3.4 Flashcards
how is water transported in plants
xylem vessels
what are xylem vessels
dead cells
long continuous tubes
provide structural support to the stem
explain cohesion-tension theory
water molecules from H bonds with each other
causes cohesion
surface tension of water also creates sticking effect
as water is lost through transpiration more can be drawn up the stem
what are the three components of phloem vessels
sieve tube elements
companion cells
plasmodesmata
what is plasmodesmata
gaps between cell walls where the cytoplasm links, allowing substances to flow
what are companion cells
involved in ATP production for active loading of sucrose into sieve tubes
what do sieve tube elements do
form a tube to transport sucrose in the dissolved form of sap
name the process whereby organic materials are transported around a plant
translocation
how does sucrose in the leaf move into the phloem
sucrose enters the companion cells by active loading using ATP and a diffusion gradient of H+ ions
sucrose then diffuses from the companion cells into the sieve tube elements via the plasmodesmata
how do phloem vessels transport sucrose around the plant
as the sucrose moves into the sieve tube elements water potential in the phloem is reduced
water enters via osmosis from the xylem and increases hydrostatic pressure
water moves through sieve tubes to areas of lower hydrostatic pressure
sucrose diffuses into surrounding cells where it is needed
give evidence for the mass flow hypothesis of translocation (3)
- sap is released when a stem is cut therefore there must be pressure in the phloem
- there is a higher concentration gradient of sucrose in the leaves than the roots
- increasing sucrose levels in the leaves results in increased sucrose in the phloem
give evidence against the mass flow hypothesis of translocation (3)
- the structure of sieve tubes seems to hinder mass flow
- not all solutes move at the same speed, as they would in mass flow
- sucrose is delivered at the same rate throughout the plant, rather than areas with the lowest concentration first
how can ringing experiments be used to investigate transport in plants
the bark and phloem of a tree are removed a ring, leaving behind the xylem
tissues above the ring swells due to accumulation of sucrose as the tissue below begins to die
therefore sucrose must be transported in the phloem
how can tracing experiments be used to investigate transport in plants
plants are grown in the presence of radioactive CO2
will be incorporated into the plants sugars
using autoradiography, we can see the areas exposed to radiation correspond to where the phloem is
what does the xylem transport
water and mineral salts
what does the phloem transport
sugars and amino acids
