Edexcel International A Level Biology Molecules, Transport and Health Exam Questions

About Edexcel International A Level Biology Molecules, Transport and Health

This topic is part of Unit 1 (Molecules, Diet, Transport and Health) of Edexcel International A Level Biology. It explains why large organisms need a mass transport system and how the heart and blood vessels deliver substances around the body. You study the dipolar nature of water, the cardiac cycle and the structure of arteries, veins and capillaries, then atherosclerosis and blood clotting. The biochemistry of carbohydrates and lipids is linked to diet, energy balance and obesity. You also evaluate risk factors for cardiovascular disease (CVD), treatments and how people perceive risk. Practicals on vitamin C content and caffeine and heart rate link to this topic.

What you need to know

• Water Water molecules are dipolar and form hydrogen bonds, making water a good solvent for transport in blood.
• Heart and vessels The cardiac cycle includes atrial systole, ventricular systole and diastole, with valves opening and closing due to pressure changes. Arteries have thick elastic walls, veins have valves, and capillaries are one cell thick.
• Atherosclerosis and clotting Damage to the endothelium leads to inflammation and plaque formation, narrowing the artery. Clotting involves thromboplastin, prothrombin to thrombin, and fibrinogen to fibrin.
• Carbohydrates and lipids Monosaccharides form disaccharides and polysaccharides by condensation reactions forming glycosidic bonds. Triglycerides contain ester bonds; saturated fats are linked with raised LDL levels.
• Risk factors and diet Risk factors include genetics, age, high blood pressure, smoking, inactivity, obesity and high salt or saturated fat intake. Energy budgets and BMI are used to assess diet.
• Treatments Antihypertensives, statins, anticoagulants and platelet inhibitors reduce CVD risk but have side effects that must be weighed against benefits.

Common mistakes in Molecules, Transport and Health

• Saying blood flows in the heart because valves pump it; contraction creates pressure differences that open and close valves.
• Describing thromboplastin as the clot itself; it is an enzyme that starts the cascade.
• Stating that obesity directly causes CVD; it is a risk factor that increases the probability.
• Confusing LDLs and HDLs; LDLs are associated with raised blood cholesterol, HDLs with removal of cholesterol to the liver.
• Assuming a large study shows causation; it can only show correlation unless variables are controlled.

Try three Molecules, Transport and Health exam-style questions