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1. A yeast and sugar mixture is sometimes used in the baking of bread. Once the bread dough is made it is left in a warm place to rise. Warm Bread dough (a) This reaction makes bread dough rise. yeast C6H12O6(aq) 2 C2H5OH(l) + 2 CO2(g) Use the words in the box to complete the sentences. Each word should only be used once or not at all. carbon carbon dioxide enzymes water Sugars are made up of ......................................................... , hydrogen and oxygen. The yeast has ............................................ which speed up the breakdown of sugar. The bread dough rises because ....................................................... gas is produced. (3) (b) As it gets warmer, the yeast cells multiply. The graph shows what happens to the number of yeast cells as the temperature increases. Number of yeast cells 0 20 40 60 80 Temperature in °C 100 120 As the temperature increases, the number of yeast cells rises and then falls rapidly. Explain why. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ (2) (Total 5 marks) 1. Bread contains starch, protein and fat. (a) Complete each sentence by choosing the correct words from the box. amino acids protein fat starch fatty acids sugar Amylase speeds up the digestion of .................................... . The product of this digestion is ............................. . Protease speeds up the digestion of ............................. . The product of this digestion is .............................................. . (4) (b) Why do molecules of starch, protein and fat need to be digested? ............................................................................................................................... ...... ............................................................................................................................... ...... (2) (c) In which part of the digestive system does the digestion of starch begin? Draw a ring around your answer. large intestine mouth small intestine stomach (1) (d) What do we call substances like amylase and protease which speed up chemical reactions? ............................................................................................................................... ...... (1) (Total 8 marks)