Fig. 7 shows an aphid feeding from a stem of a squash plant. The aphid's mouthpart enters vessel S. A researcher collected a drop of liquid from the severed...
Question 1 Report
Fig. 7 shows an aphid feeding from a stem of a squash plant. The aphid's mouthpart enters vessel S. A researcher collected a drop of liquid from the severed mouthpart and found a high concentration of sucrose and amino acids. On another branch, several leaves had been covered with opaque paper for two days.
(a) Name vessel S. [1]
(b) Describe the process by which sucrose is moved from leaves to other parts of a plant. [2]
(c) Explain why covering leaves with opaque paper reduces the sucrose concentration in vessel S after two days. [3]
(d) State two possible sinks for sucrose in a flowering plant. [2]
Answer Details
(a) Vessel S is phloem. The high sucrose and amino-acid concentration identifies it as phloem sap. [1]
(b) This movement is called translocation. Dissolved sucrose is transported in the phloem from sources, usually photosynthesising leaves, to sinks, such as growing or storage tissues. [2]
(c) Opaque paper prevents, or greatly reduces, light reaching the covered leaf cells. Photosynthesis therefore decreases or stops. Less glucose is made, so less glucose can be converted to sucrose for transport in the phloem, reducing the sucrose concentration in vessel S. [3]
(d) Possible sucrose sinks include any two of: roots, growing shoots, flowers, fruits, seeds or storage organs. These are sinks because they use or store assimilates. [2]
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