Eduqas Biology for A Level Book 1: 2nd Edition

Test for fats and oils – the emulsion test A sample to be tested is mixed with absolute ethanol, which dissolves any lipids present. It is shaken with an equal volume of water. The dissolved lipids come out of solution, because they are insoluble in water. They form an emulsion, making the sample cloudy white. Implications of saturated fats for human health The main causes of heart disease are fatty deposits on the inner wall of the coronary arteries (atherosclerosis) and high blood pressure (hypertension). A diet that is high in saturated fats, smoking, lack of exercise and aging are all contributory factors and all except aging can be modified to reduce the risk of disease. Damage to the heart and blood vessels is the single leading cause of death in the UK. When food has been absorbed at the small intestine, lipids and proteins combine to make lipoproteins, which travel around the body in the bloodstream. ▪ If the diet is high in saturated fats, low-density lipoprotein (LDL) builds up and causes harm. Fatty material called atheroma gets deposited in the coronary arteries, restricting blood flow and, therefore, oxygen delivery to the heart. This can result in angina, and, if the vessel is completely blocked, a myocardial infarction or heart attack occurs. ▪ But if the diet has a high proportion of unsaturated fats, the body makes more high- density lipoprotein (HDL), which carries harmful fats away to the liver for disposal. The higher the ratio of HDL : LDL in a person’s blood, the lower their risk of cardio-vascular and coronary heart disease. Process of atherosclerosis inner wall of artery has smooth endothelium lining atheroma deposited on endothelium, reducing available volume for blood ow lumen of artery almost entirely blocked with atheroma Stretch & challenge Atherosclerosis is the build-up of atheroma. Don't confuse this with arteriosclerosis, which is the resulting hardening of the arteries. Stretch & challenge Blood clots can form where there is atheroma. This is called thrombosis. Sometimes part of the clot may break away and be carried in the circulation and block a blood vessel distant from where it formed. Blocking a blood vessel in the brain causes a stroke. Blocking a blood vessel in the heart wall can lead to a heart attack. Study point LDL contributes to atherosclerosis and is sometimes referred to as ‘bad cholesterol’. HDL carries fat away from artery walls and is sometimes called ‘good cholesterol’. Link Absorption of digested food at the small intestine is described on p237. Exam tip Make sure you can explain how to perform and interpret the test for fats and oils. Eduqas Year 1/AS Biology 24