7.2. Transport mechanisms
A subsection of Biology, 9700, through 7. Transport in plants
Listing 10 of 310 questions
is a diagram drawn from a photomicrograph of a transverse section through part of a leaf. The arrows in show the movement of water through the cells of the leaf after it has left the xylem. C B A P X Q D Y Water from the xylem can enter cell A and then moves to cells B and C without crossing their cell walls. The cell structures through which water passes from cell A to cell B are not visible in . Name the cell structures through which water passes from cell A to cell B without crossing their cell walls. Explain what causes water to move from cell B to cell C. Name the pathway taken by water between cell A and cell C. Most of the water that arrives at the leaf passes to the external atmosphere. With reference to , describe and explain the sequence of events occurring between point P and point Q. The actual diameter of cell D in along the length X–Y is 25 µm. Calculate the magnification of the image. Write down the formula used to make your calculation. Show your working. formula answer = ×
9700_w20_qp_22
THEORY
2020
Paper 2, Variant 2
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Barlinka is a variety of the common grapevine, Vitis vinifera. Barlinka grapes are used for making wine and are sold as fruit. There are economic and ecological benefits from using less water to irrigate grapevine plants, while still producing a high crop yield. The rate of flow of sap within xylem vessels from roots to leaves can be used as an estimate of the rate of transpiration. This also indicates water uptake. The hydrogen bonding of water molecules is important in the transport of sap within xylem vessels. State the terms used to describe: • water molecules sticking together within the xylem vessel • water molecules sticking to the cellulose molecules in the lining of the xylem vessel An experiment was carried out to investigate the effect of leaf area on the rate of flow of the xylem sap during fruit development. The flow rate was measured over a three-day period in three Barlinka grapevine plants with different total leaf area. The plants were growing in the same conditions. The results are shown in . day flow rate of xylem sap / cm3 per plant per hour P leaf area grapevine 1 / 13.7 m2 leaf area grapevine 2 / 9.6 m2 leaf area grapevine 3 / 3.2 m2 Key The general pattern of results in is the same for the three Barlinka grapevines. Explain why the general pattern of results is the same. With reference to , explain the differences in the results between the three grapevines, 1, 2 and 3. Suggest an explanation for the decrease in flow rate of xylem sap shown at time P in . Outline how you would determine the surface area of one side of a leaf.
9700_w21_qp_22
THEORY
2021
Paper 2, Variant 2
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Questions Discovered
310