protein, fat, carbs, vitamins and minerals are definitely key because theyll more than likely be oart of long q1 and the short questions, a food usually comes up for q2 so you could learn the nutritional values of the most popular foods like milk and milk products, meat and fish. it depends on what you like obviously but q3 is usually kind microbiology based and q 4 is the consumer studies chapters. maybe go through old exam papers and look at what usually comes up for q3 and q4 so you can see properly and the n you can choose. definitely focus on the foods and basically all of unit 1 its really important :)