1. 1
   A student examines two transverse sections from a young sunflower plant (Helianthus annuus). Section 1 shows an outer epidermis, a cortex, and about 15 separate vascular bundles arranged in a ring near the edge, around a central pith. Section 2 shows an epidermis bearing root hairs, a wide cortex and a single central column of vascular tissue in which the xylem forms a four-armed star, with phloem between the arms.

   (a)

   Which conclusion about the sections is correct?

   [1 mark]

   • ASection 1 is a root, because its vascular tissue is near the edge
   • BBoth sections are stems, because both have an epidermis and cortex
   • CSection 2 is a stem, because its xylem is central
   • DSection 1 is a stem and Section 2 is a root

   (b)

   In each vascular bundle of Section 1, where is the phloem found relative to the xylem?

   [1 mark]

   • ATowards the outside of the stem
   • BTowards the centre of the stem
   • CMixed randomly with the xylem
   • DOnly in the pith

   (c)

   Explain how the structure of xylem vessels allows them to transport water under tension.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Grapevines (Vitis vinifera) pruned in early spring, before their buds open, 'bleed': sap drips from the cut stems for several days. This sap contains mineral ions but almost no sugar. Vines pruned in midsummer, when the leaves are fully open, do not bleed. In a separate investigation, an aphid feeding on a vine stem was anaesthetised and its mouthparts (stylet) cut off, leaving the stylet tip inside a single sieve tube. Sap containing about 20% sucrose flowed out of the stylet for several hours.

   (a)

   What generates the pressure that causes vines to bleed in early spring?

   [1 mark]

   • ATension created by transpiration from the leaves
   • BActive transport of mineral ions into the xylem in the roots, followed by water entering by osmosis
   • CLoading of sucrose into the phloem at sources
   • DCapillary action in the cell walls of the stem

   (b)

   Which feature of sieve tube elements eases the flow of the sap collected from the stylet?

   [1 mark]

   • ALignified walls with pits
   • BMany mitochondria to pump sap along the tube
   • CSieve plates, with reduced cytoplasm and no nucleus
   • DAbsence of end walls and death of the cell at maturity

   (c)

   Explain why vines pruned in midsummer do not bleed.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   At the arteriole end of a capillary in a leg muscle, blood pressure is 4.6 kPa; at the venule end it is 2.3 kPa. Plasma proteins, which are too large to leave the capillary, draw water back into the blood by osmosis with an effect equal to a pressure of 3.3 kPa along the whole capillary. In kwashiorkor, a disease caused by severe dietary protein deficiency, the plasma protein concentration falls and this effect drops to 2.0 kPa. Children with kwashiorkor develop swelling of the tissues caused by excess tissue fluid (oedema).

   (a)

   Using the data, explain how tissue fluid is formed and returned to the blood in a healthy capillary.

   [3 marks]

   (b)

   Using the data, explain why children with kwashiorkor develop oedema, and outline the role of the lymphatic system.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A 58-year-old man experiences chest pain when climbing stairs. Imaging shows that a branch of his left coronary artery is 70% narrowed by a fatty plaque. His blood pressure is recorded as 150/95 mm Hg, compared with a typical healthy value of about 120/80 mm Hg.

   (a)

   Explain how the plaque is likely to have formed and the consequences for the man's heart if it is not treated.

   [6 marks]

   (b)

   Explain the sequence of events in the left side of the heart during one cardiac cycle, starting at the sinoatrial node, and interpret the man's blood pressure reading.

   [6 marks]

   Total for question 4: 12 marks

End of questions