Download 1. A yeast and sugar mixture is sometimes used in the baking of

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.
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................................................................................................................................
................................................................................................................................
(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)