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Welcome!. Grab a whiteboard and pen and write what you see!. - i. - O + A. - e. - o + i. - D + C. - L + H. - G + S. - K. Phloem. What are we going to do today? Describe the structure of the Phloem Explain the mass flow theory for translocation of sugars

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Welcome!

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  1. Welcome! Grab a whiteboard and pen and write what you see!

  2. - i

  3. - O + A

  4. - e - o + i

  5. - D + C - L + H - G + S

  6. - K

  7. Phloem What are we going to do today? • Describe the structure of the Phloem • Explain the mass flow theory for translocation of sugars • Apply knowledge of techniques to study transport in plants and translocation to interpret investigation results

  8. What is phloem? • Phloem is a tissue which transports biological molecules in flowering plants. • It consists of living cells called sieve tube elements, which form a long channel. • The sieve tube elements are separated from each other by sieve plates, which allow the movement of substances from element to element.

  9. What does the phloem carry? Minerals Amino acids Hormones Sucrose Why would the plant transport carbohydrates in the form of sucrose?

  10. Mass flow theory The exact mechanism for translocation within the phloem is still under debate and study, but the most widely accepted theory currently in the ‘mass (or pressure) flow theory’.

  11. Translocation of sugars

  12. Sources and SINKS?

  13. Your turn Create your own card sort! • Write down how mass flow theory works • Separate out into separate statements • Cut out your statements and mix them up. • Give to your neighbour to try!

  14. Exam q Have a go at Q9.1 You have 5 minutes!

  15. Ringing Experiments • Evidence for water movement in xylem and sugar movement in phloem. • Woody stems have an outer protective layer of bark, with a ring of phloem inside and a ring of xylem inside that. • Outer layers of bark and phloem are removed from a section of stem.

  16. Ringing Experiments • Stem above missing tissue ring swells with liquid rich in sugars. • Non-photosynthetic tissues below the ring wither and die.

  17. Ringing experiments Conclusions • Sugars of phloem accumulate above ring as they are unable to move down the stem. • Sugars don’t pass below the ring so tissues die. Phloem, rather than xylem, is responsible for the translocation of sugars in the plant.

  18. Tracer experiments • Radioactive carbon isotope 14C is used to make 14CO2. • The 14C is incorporated into the sugars produced during photosynthesis. • Autoradiography allows tracking of these sugars. Radioactive areas correspond to areas of phloem, not xylem.

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