Time / weeks 0 2 4 6 8 Diameter above ring / mm 12 14 17 20 23 Diameter below ring / mm 12 12 12 13 13 Increase above ring / mm - 2 3 A gardener removed a c...
Question 1 Report
| Time / weeks | 0 | 2 | 4 | 6 | 8 |
|---|---|---|---|---|---|
| Diameter above ring / mm | 12 | 14 | 17 | 20 | 23 |
| Diameter below ring / mm | 12 | 12 | 12 | 13 | 13 |
| Increase above ring / mm | - | 2 | 3 |
A gardener removed a complete ring of bark, together with the phloem inside it, from all the way around a young branch of an apple tree. Water-carrying tissue deeper in the wood was left in place. Over the next 8 weeks a swelling formed on the upper side of the ring. The gardener measured the diameter of the branch just above the ring and just below the ring. The results are shown in Table 2.1.
(a) State the name of the tissue that was removed with the bark and that normally carries sucrose towards the roots. [1]
(b) Measure, using Table 2.1, the diameter of the branch above the ring at week 8. [1]
(c) Measure, using Table 2.1, the diameter of the branch below the ring at week 8. [1]
(d) Complete Table 2.1 by calculating the two missing values in the row showing the increase in diameter above the ring. [2]
(e) Describe how the diameter of the branch above the ring changed over the 8 weeks. [3]
(f) The diameter of the branch below the ring hardly changed. Explain this difference in terms of the direction of transport in the phloem. [3]
(g) Calculate the percentage increase in the diameter above the ring over the 8 weeks. Show your working. [2]
(h) State why removing the bark did not stop water reaching the leaves above the ring. [2]
(i) Predict what will happen to the roots of the tree over several months and explain why. [3]
(j) Suggest a suitable control branch that the gardener could use for comparison. [2]
Fig. 2.1 shows the ringed branch.
Answer Details
This task tests ideas about transport tissues, reading a table, calculating a percentage change, and reasoning about the direction of translocation.
(a) The tissue removed with the bark that normally carries sucrose towards the roots is phloem. [1]
(b) Diameter above the ring at week 8 = 23 mm (read from the table). [1]
(c) Diameter below the ring at week 8 = 13 mm. [1]
(d) The increase in diameter above the ring is each reading minus the value two weeks earlier: week 4 \(= 17 - 14 = 3\ \text{mm}\) [1]; week 8 \(= 23 - 20 = 3\ \text{mm}\) [1]. Completed row:
| Time / weeks | 0 | 2 | 4 | 6 | 8 |
|---|---|---|---|---|---|
| Increase above ring / mm | - | 2 | 3 | 3 | 3 |
[2]
(e) The diameter above the ring increased at every reading [1], rising from 12 mm to 23 mm over the 8 weeks [1]; the increase per two weeks was fairly steady at about 2 to 3 mm [1]. [3]
(f) Sugars (sucrose) made in the leaves are normally carried downwards in the phloem towards the roots [1]; removing the ring of phloem cuts this pathway, so sucrose collects in the tissues just above the ring [1]; this extra sugar is used for growth, producing the swelling above the ring, while the tissue below the ring is starved of sugar and hardly grows [1]. [3]
(g) Percentage increase = (increase / original) x 100: \(\frac{23 - 12}{12} \times 100 = \frac{11}{12} \times 100 = 91.7\%\) (accept 92%). Working [1], answer [1]. [2]
(h) Water travels up in the xylem, which lies deeper in the wood [1]; only the outer bark and phloem were removed, so the xylem was undamaged and could still carry water to the leaves [1]. [2]
(i) Over several months the roots will grow poorly and may eventually die [1]; because the phloem is cut they no longer receive sugars from the leaves [1]; without sugar the root cells cannot respire enough to release the energy needed for growth [1]. [3]
(j) A suitable control is a similar branch on the same tree that has had no ring of bark removed [1], measured over the same time period and in the same conditions [1]. [2]
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