Question 1: Explain what happens to the starch content in potatoes when they are cooked thoroughly. Describe the chemical change involved.

Answer: When potatoes are cooked, the heat causes the starch granules to absorb water and swell. This process, called gelatinisation, is a chemical change where starch molecules absorb water and become more digestible, changing the texture of the potato.

Question 2: Describe the chemical change that occurs when fruit is exposed to air and turns brown. What is this process called?

Answer: The fruit undergoes oxidation, where enzymes react with oxygen in the air, causing the fruit to turn brown. This is a chemical change involving enzyme activity and oxidation of phenolic compounds.

Question 3: Identify two chemical changes that happen when cooking meat. Explain the effects on the meat's texture or taste.

Answer: One change is the denaturation of proteins, which causes the meat to firm up and change colour. Another is the Maillard reaction, which occurs at high temperatures and develops a browned crust, enhancing flavour.

Question 4: Describe what happens to egg proteins during cooking. How does this relate to the change in the egg’s appearance?

Answer: Egg proteins denature and coagulate when heated, causing the egg white and yolk to change from a liquid to a solid. This results in the egg becoming firm and opaque in appearance.

Question 5: Explain the chemical change that occurs when baking soda is used in bread dough. What gas is produced?

Answer: Baking soda reacts with moisture and acids in the dough, producing carbon dioxide gas. This gas causes the bread to rise by creating bubbles within the dough, a chemical change known as leavening.

Question 6: Describe the process and chemical change involved when milk is heated to make cheese.

Answer: Heating milk with rennet or acids causes the milk proteins (casein) to coagulate, forming curds. This is a chemical change where proteins are denatured and precipitated, separating curds from whey.

Question 7: Draw a simple diagram showing the process of caramelisation. Label the key stages that occur during caramelisation.

Answer: A correct sketch should depict sugar molecules breaking down when heated, leading to the formation of new compounds that give caramel its colour and flavour. Labels should include 'melting sugar', 'initial caramelisation', and 'dark caramel'.

Question 8: Explain why frying an egg causes a chemical change, and what physical change can be observed.

Answer: Frying an egg causes proteins to denature and coagulate, which is a chemical change. A physical change observed is the egg white turning from clear to opaque and solidifying.

Question 9: Describe what happens to the pH of bread dough as it ferments with yeast. Is this a chemical or physical change?

Answer: The pH of the dough decreases (becomes more acidic) as yeast produces carbon dioxide and alcohol during fermentation. This is a chemical change because new substances are formed.

Question 10: Sketch the appearance of a piece of cooked meat after it has undergone the Maillard reaction. Include labels for the key features.

Answer: A correct sketch should show a browned, slightly crispy surface on the meat, with labels indicating 'Maillard reaction', 'browning', and 'crust'. The interior should remain a different colour, indicating it is uncooked.