22 7 The primary productivity of plants depends on their ability to synthesise carbohydrates and transport solutes to cells. (a) The diagram shows the movement of water across a root. root hair epidermal cell Casparian strip xylem vessel water What is the name of the water movement pathway shown in the diagram? (1) A apoplastic pathway B diffusion pathway C osmotic pathway D symplastic pathway (b) Explain how the mass-flow hypothesis accounts for the movement of sugars from leaves to roots. 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Mistletoe has green leaves. Mistletoe also has a modified root that grows into the xylem of a tree. The diagram shows mistletoe growing on an apple tree branch. mistletoe apple tree branch The effect of mistletoe on the growth of apple trees was investigated. Every year for 20 years, scientists selected apple trees infected with mistletoe and measured the: • mean net primary productivity (NPP) of the apple trees • transpiration rate of the apple trees • transpiration rate of the mistletoe branches on the apple trees They also determined the mineral content of the apple tree leaves after 20 years. A control group of apple trees not infected with mistletoe was included in this investigation. 24 The graphs and table show the results of the investigation. 0 5 10 15 20 25 30 35 1995 2000 2005 2010 2015 Year NPP / kg dry mass of tree per year NPP of apple trees without mistletoe NPP of apple trees with mistletoe 1995 2000 2005 2010 2015 Year 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Transpiration rate / dm3 water per plant per year mistletoe apple tree without mistletoe apple tree with mistletoe Apple tree leaves from Nitrogen content / mg per g of leaf Calcium content / mg per g of leaf trees infected with mistletoe 8.50 6.45 trees not infected with mistletoe 10.60 8.90 25 Turn over Analyse the data to explain the effect of mistletoe on the NPP of apple trees. 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(Total for Question 7 = 11 marks)