7.9 - Investigating Transport in Plants

Cards (6)

ringing experiment - method
a section of outer layers (bark & phloem) is removed around the complete circumference of a stem while still attached to the rest of the plant
ringing experiments - observations
region of stem above ring swells with liquid rich in sugars and dissolved organic substances
non-photosynthetic tissues below ring died - interuption of flow below ring
ringing experiments - conclusion
phloem is the tissue responsible for translocating sugars
tracer experiments - method
isotope 14-C is used to make radioactively labelled CO2
plant grown in atmosphere containing 14-CO2 so 14-C is incorporated into sugars made during photosynthesis
radioactive sugars are moved around plant by translocation
movements can be traced using autoradiography
take thin cross-section of the plant and place them on a piece of x-ray film
film becomes blackened where it has been exposed to radiation produced by 14 C in sugars
what results of tracer experiments show
translocation of substances from source to sink over time
evidence that translocation happens in the phloem
when phloem is cut a solution of organic molecules flows out
plants provided with radioactive CO2 have radioactively labelled carbon in the phloem after a short time
aphids have a needle-like mouth part that penetrate them so can extract contents of sieve tubes that contain sucrose content
removal of a ring of phloem around circumference of a stem leads to accumulation of sugars above it & their disappearance below it