2.2. Carbohydrates and lipids
A subsection of Biology, 9700, through 2. Biological molecules
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shows a light micrograph of a section through a wheat grain. The structure of a wheat grain is very similar to that of a maize fruit. On , use label lines and letters to label each of the following parts. A endosperm B fused testa and pericarp (fruit coat) C embryo Wheat grains are ground to make flour, which can be used for making bread. Whole grain flour is made from the complete wheat grain. Refined flour is produced from wheat grains from which the embryo, aleurone layer and the fused testa and pericarp have been removed. Table 4.1 shows the carbohydrate, protein and dietary fibre content of bread made from whole grain flour and white flour. Table 4.1 bread made from whole grain flour bread made from white flour protein / g per 100 g 9.4 7.9 dietary fibre / g per 100 g 7.0 2.5 carbohydrate / g per 100 g With reference to the structure of a wheat grain, explain the differences between the composition of the two types of bread shown in Table 4.1. The glycaemic index, GI, of a carbohydrate-containing food is a measure of the effect of its consumption on blood glucose concentration. If two foods containing the same mass of carbohydrate, but different GIs, are consumed, the food with the higher GI will increase blood glucose concentration more rapidly than the food with the lower GI. Suggest an explanation for each of the following. Foods containing starch have lower GIs than foods containing glucose. Foods containing starch made up mostly of amylose have lower GIs than foods containing starch made up mostly of amylopectin. A diet containing large amounts of foods with a high GI can increase the risk of developing type II diabetes. A study was carried out into the effect of consuming whole cereal grains, refined cereal grains and fruit on the risk of developing type II diabetes. • In 1986, questionnaires about diet were completed by 41 836 women, all between the ages of 55–69 years old, in Iowa, USA. • The women were then divided into five groups according to their range of intake of each food type. • In 1992 the same women were asked whether or not they had developed type II diabetes. • Their answers were used to calculate the relative risk of developing type II diabetes for each of the five groups. For each food type, the group with the lowest intake of that food type was allocated a risk of 1.00. Table 4.2 shows the results of this study. Table 4.2 food type range of intake / servings per week relative risk of developing type II diabetes whole cereal grains 33.0 0.68 refined cereal grains 22.0 0.87 fruit 19.0 1.14 Describe the effect of increased intake of whole cereal grains on the risk of developing type II diabetes. Explain why the results in Table 4.2 cannot be used to make a direct comparison of the effects of consuming whole cereal grains and refined cereal grains on the risk of developing type II diabetes. The results in Table 4.2 suggest that eating large quantities of fruit may slightly increase the risk of developing type II diabetes. Suggest a reason for this.
9700_w12_qp_43
THEORY
2012
Paper 4, Variant 3
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368