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Summary Investigating transport in plants
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Year 1 Biology AQA A level notes. Achieved an A* in my final exam using these notes. They are based on the mark scheme requirements.
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Investigating transport in plants summary notes18 May 2023 17:24
Ringing experiments
- Section of the outer layers including the protective layer and the phloem is removed
around the complete circumference of the woody stem which is still attached to the re
of the plant
- Region of the stem immediately above the missing ring of tissues swells
- Samples of accumulated liquid in the swollen region are rich in sugars and other dissol
organic substances
- Some non photosynthetic tissues in region below the ring die, others above the ring
continue to grow
Removing the phloem around the stem has led to:
1. The sucrose in the phloem accumulating above the ring leading to swelling
2. The interruption of flow of sucrose to the region below the ring and the death of tissue
this region
- Therefore conclude that it is phloem rather than xylem that is responsible for
translocating sucrose in plants
- Ring of tissue removed had not extended into xylem so its continuous water column w
not broken- if it was the tissue responsible for translocation the sugars would not
accumulate above the ring and the tissues below would not die
Tracer experiments
- Plant grown in atmosphere containing radioactive carbon dioxide
- Carbon 13 isotope is incorporated into sugars produced during photosynthesis
- These radioactive sugars can be traced as they move within plant using autoradiograph
- Ie taking thin cross sections of the plant stem and placing them on piece of X ray film-
becomes blackened where it is exposed to radiation produced by carbon 13 in sugars -
blackened regions correspond with where phloem tissue is in the stem
- Other tissues do not blacken film- do not carry sugars- phloem responsible for
translocation
Evidence that translocation occurs in phloem
1. When phloem is cut, a solution of organic molecules flows out
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