page 05 10. The lipid bilayers of cell membranes contain a number of different phospholipids, which are present in different proportions and distributed unevenly across the extracellular and intracellular faces of the bilayer. Figures 1 and 2 show the proportions and distribution of four phospholipids in the cell membrane of human red blood cells. Figure 1 Proportions of four phospholipids in the cell membrane SP PS PE PC PC – phosphatidyl choline SP – sphingomyelin PS – phosphatidyl serine PE – phosphatidyl ethanolamine Figure 2 Distribution of the phospholipids in the two faces of the membrane 100 50 0 50 100 percentage of total extracellular face intracellular face SP PC PE PS The key can be used to identify each of the phospholipids. 1 more than 25 % of total lipid less than 25 % of total lipid go to 2 go to 3 2 found mainly on the extracellular face found mainly on the intracellular face A B 3 found mainly on the extracellular face found mainly on the intracellular face C D Which letter represents sphingomyelin? [Turn over page 06 Questions 11 and 12 refer to the following information. Short-term variations in the time interval between heart beats is termed heart rate variability (HRV). HRV is one measure that can be used to assess health. The box plots give information from one study about the influence of age and gender on HRV. 25–34 35–44 45–54 55–64 65–74 0 20 40 60 80 age (years) 100 heart rate variability (units) females maximum value minimum value upper quartile lower quartile median males Key 11. From the data shown, which of the statements about HRV is correct? A There is a trend towards lower HRV in females B The greatest error in measurements is for ages 25–34 C The mean HRV for females aged 35–44 is lower than 40 units D Gender-related differences in median values are greater than age-related differences 12. Which row in the table describes features of this study? Design of experiment Type of data collected A simple ranked B simple continuous C multifactorial ranked D multifactorial continuous