2025 Cambridge IGCSE Food and Nutrition (0648) Practice Paper with Answers

Basal Metabolic Rate refers to the minimum energy the body needs to keep its systems functioning (like respiration, cell repair, and circulation) while at rest in a warm environment, twelve hours after the last meal.

Award 1 mark for explaining that it is the minimum or basic energy required to maintain life processes (e.g. breathing, circulation). Award 1 mark for stating that this measurement must be taken when the body is at complete physical/mental rest (or warm, post-absorptive).

Phosphorus plays several crucial biological roles. Its main functions include combining with calcium to form calcium phosphate which strengthens bones and teeth, forming a key structural part of cell membranes as phospholipids, and taking part in energy metabolism through ATP formation.

Award 1 mark per correct function identified up to a maximum of 2 marks. Acceptable functions include: forming calcium phosphate for strong bones/teeth; essential for energy release/ATP production; forming phospholipids in cell membranes; component of DNA/RNA; buffer to maintain acid-base balance.

Bile is produced in the liver and stored in the gall bladder. When released into the duodenum, it performs two critical tasks for fat digestion: it emulsifies large fat molecules into tiny droplets (increasing surface area for lipase enzymes to act upon) and its alkaline nature neutralises acidic gastric secretions so pancreatic enzymes can work efficiently.

Award 1 mark for explaining emulsification / breaking fat into tiny droplets to increase surface area. Award 1 mark for explaining the neutralisation of acidic gastric juice / providing an optimum alkaline pH for lipase activity.

Bicarbonate of soda is an alkali. When mixed with liquid and heat, it releases carbon dioxide gas but also produces sodium carbonate, which has an unappealing yellow colour and a soapy, bitter taste. Adding an acidic ingredient (like black treacle, sour milk, or brown sugar in gingerbread) reacts with the sodium bicarbonate to produce carbon dioxide gas efficiently while neutralizing the unpleasant alkaline taste.

Award 1 mark for stating that it must react with an acid to release carbon dioxide gas to aerate/raise the mixture. Award 1 mark for explaining that without an acid, it leaves sodium carbonate which results in an unpleasant bitter/soapy taste or a yellow colour.

The correct proportion of fat to flour for shortcrust pastry is half fat to flour (for example, 100g fat to 200g flour). When rubbing in, the fingertips should be used because they are the coolest part of the hand. Over-handling warms and melts the fat, which is absorbed into the flour instead of coating the starch granules, causing the pastry to become greasy and tough due to excessive gluten development.

Award 1 mark for stating the correct proportion: half fat to flour or a 1:2 ratio (e.g. 100g fat to 200g flour). Award 1 mark for explaining that over-handling warms/melts the fat (due to hand heat), making the pastry oily/greasy, or causing gluten development which results in a tough/hard texture.

When a cake is placed in a domestic oven, heat is transferred primarily by convection (as hot air rises and circulates within the oven, transferring heat to the cake tin and exposed top surface) and conduction (heat passes from the hot metal baking tin directly into the outer edges of the cake mixture).

Award 1 mark for each correct heat transfer method listed up to a maximum of 2 marks. Acceptable answers: Convection, Conduction, Radiation (from the hot oven walls/elements).

Sugar acts as a chemical preservative in jam. When present in a concentration of 60% or above, it exerts high osmotic pressure on microbial cells. This draws water out of micro-organisms (such as bacteria, yeasts, and moulds) through their cell walls via osmosis. Without sufficient water/moisture, the micro-organisms are dehydrated, cannot grow or multiply, and eventually die.

Award 1 mark for identifying high osmotic pressure or water being drawn out of microbial cells by osmosis (plasmolysis). Award 1 mark for explaining that this deprives micro-organisms of the water/moisture required for metabolic growth, preventing spoilage.

The 'work triangle' is a concept used to determine efficient kitchen layouts. It connects the three main work centres: the sink (for washing and preparation), the cooker (for cooking and heating), and the refrigerator (for storing food and cold ingredients).

Award 2 marks if all three correct areas are named. Award 1 mark if only two correct areas are named. Acceptable areas: Sink / washing area; Cooker / oven / hob / cooking area; Refrigerator / fridge / larder / food storage area.

Protein digestion begins in the stomach, where the enzyme pepsin breaks down proteins into polypeptides. Digestion continues in the duodenum (small intestine) where trypsin, secreted by the pancreas, further digests proteins and polypeptides into peptides.

Award 1 mark for each correct enzyme identified, up to a maximum of 2 marks. Acceptable answers: Pepsin, Trypsin, Chymotrypsin, Peptidase (or Erepsin). Reject: Protease (too general), any non-proteolytic enzymes (e.g., Amylase, Lipase).

Steam acts as a physical raising agent in batters containing a high proportion of liquid. In a very hot oven, the water in the mixture is converted into steam. As steam expands, it pushes the mixture upwards. The intense heat of the oven simultaneously coagulates the protein (egg and gluten), setting the structure of the mixture so that it retains its risen shape.

Award 1 mark for stating that water/liquid in the batter evaporates/turns to steam in the hot oven and expands to push the mixture up. Award 1 mark for explaining that the heat coagulates/sets the proteins (egg/gluten) to lock/hold the risen structure.

Yeast is a living microorganism used as a biological raising agent. The required conditions for fermentation are: 1. Warmth: Activates the yeast (optimal 25 to 35 degrees Celsius); 2. Moisture: Solubilizes nutrients and allows yeast activity; 3. Food: Yeast feeds on simple sugars, converting them into carbon dioxide and ethanol; 4. Time: Allows fermentation to proceed. As carbon dioxide gas is released, it is trapped in the gluten network. During baking, the gas expands, stretching the elastic gluten. The gluten eventually coagulates around 80 degrees Celsius, setting the structure of the risen bread.

Award 1 mark for each point up to 5 marks: 1 mark for identifying warmth (optimum activation temp); 1 mark for identifying moisture (hydrates yeast); 1 mark for identifying food (sugar/starch for fermentation); 1 mark for explaining that carbon dioxide gas is trapped and expands when heated; 1 mark for explaining that the gluten network stretches and coagulates to set the shape.

1. Heat: Boiling fruit destroys vegetative microorganisms and deactivates enzymes that cause spoilage. 2. Sugar Concentration: Adding high amounts of sugar increases osmotic pressure. Water is drawn out of any remaining microbial cells by osmosis (plasmolysis), leaving them unable to survive or reproduce due to low water activity. 3. Sealing: Hot-filling and sealing jars creates a vacuum as the mixture cools, preventing airborne micro-organisms, yeast, and mold spores from contaminating the sterile jam.

Award up to 5 marks: 1 mark for heat destroying microorganisms/enzymes; 1 mark for high concentration of sugar (60-65%); 1 mark for osmosis/drawing water out of microbial cells; 1 mark for explaining lack of available water for microbial growth; 1 mark for sealing preventing airborne contamination/recontamination.

Vitamin D (cholecalciferol) is a fat-soluble vitamin. Its primary functions include: aiding the absorption of calcium and phosphorus from the digestive tract; regulating calcium levels in the blood; and promoting the deposition of these minerals into the bone matrix (calcification) to ensure strong bones and teeth. A deficiency of Vitamin D in growing children results in rickets. Because calcium cannot be properly absorbed, bones remain soft and pliable. This leads to physical deformities such as bow legs, malformed ribs (rachitic rosary), delayed walking, and poor dental development.

Award up to 5 marks: 1 mark for aiding absorption of calcium; 1 mark for aiding absorption of phosphorus; 1 mark for bone/teeth calcification (formation of strong bones/teeth); 1 mark for identifying rickets as the deficiency disease in children; 1 mark for describing symptoms of rickets (e.g., soft bones, bow legs, skeletal deformities).

Dietary guidelines to reduce CHD: 1. Reduce saturated fat and trans-fat intake (e.g., butter, fatty meat) because they increase LDL cholesterol, which can lead to plaque formation in arteries. 2. Increase soluble dietary fibre (e.g., oats, pulses) because it binds with bile acids and cholesterol in the gut, aiding their excretion and lowering blood cholesterol levels. 3. Reduce sodium/salt intake (e.g., processed foods) to prevent hypertension (high blood pressure), which strains the heart and arterial walls. 4. Eat oily fish (e.g., salmon, mackerel) for omega-3 fatty acids, which reduce blood clotting and lower triglyceride levels. 5. Limit intake of simple/refined sugars to prevent weight gain and obesity, reducing the physical strain on the cardiovascular system.

Award 1 mark for each valid recommendation with its accompanying nutritional explanation, up to 5 marks. Examples: reduction of saturated fat (1 mark), increase of soluble fibre (1 mark), reduction of salt (1 mark), inclusion of oily fish/omega-3 (1 mark), reduction of sugar/calories to prevent obesity (1 mark).

Part (a): Caster sugar plays multiple critical functional roles in the cake: it provides sweetness, aids in aeration by cutting into the fat during creaming to trap air bubbles, and retains moisture (hygroscopic property) to keep the cake soft. Part (b): The raising agents involved are: (1) Carbon dioxide gas released chemically from the baking powder (acid and sodium bicarbonate) in the self-raising flour. (2) Air incorporated mechanically during the creaming of butter and sugar and the beating of eggs. (3) Steam generated physically from the water content of the eggs and butter during baking. As heat is applied in the oven, these gases expand and push the cake mixture upwards before the flour and egg proteins coagulate to set the permanent structure. Part (c): A dense, heavy cake can occur due to: (1) Insufficient creaming of fat and sugar, resulting in too few air bubbles to raise the mixture. (2) An oven temperature that is too low, allowing the raising gases to escape before the gluten and egg proteins coagulate to set the cake structure.

Part (a) Function of sugar (max 2 marks): 1 mark for sweetness; 1 mark for aeration/trapping air during creaming; 1 mark for moisture retention (hygroscopic action) to soften gluten structure. Part (b) Raising agents (max 4 marks): 1 mark for identifying carbon dioxide (chemical from self-raising flour); 1 mark for identifying air (mechanical from creaming/beating); 1 mark for identifying steam (physical from water in ingredients); 1 mark for explaining that heat causes these gases to expand and push up the structure. Part (c) Dense texture (max 4 marks): 2 marks for each well-explained culinary reason (e.g., under-creaming, oven temperature too low, too much flour, eggs added too quickly causing curdling). Max 10 marks total.

Part (a): The dietary modifications target reducing saturated fat and sodium while maintaining calcium and increasing dietary fibre (NSP). (1) Replace minced beef with minced turkey or textured vegetable protein (TVP/soy) to lower saturated fat and reduce cardiovascular risk. (2) Use semi-skimmed or skimmed milk and low-fat cheddar cheese instead of whole milk and standard cheddar; this maintains vital calcium intake for bone density while lowering energy and saturated fat density. (3) Use wholemeal pasta sheets instead of refined white pasta to increase dietary fibre (NSP) to prevent constipation, a common issue in older adults. (4) Omit table salt and butter, using unsalted vegetable spread and flavouring with herbs (e.g., oregano, basil) or garlic to lower sodium intake, directly helping to manage high blood pressure. Part (b): Calcium is critical for an elderly person with osteopenia because it is the primary mineral that hardens bones and teeth. Adequate intake slows down bone resorption (bone loss), helping to preserve remaining bone mass and reducing the high risk of fractures.

Part (a) Modifications and Justifications (max 8 marks): 2 marks for each appropriate modification linked to a correct nutritional justification (1 mark for modification, 1 mark for justification). Examples: turkey/soy mince instead of beef (reduces saturated fat); semi-skimmed milk/low-fat cheese instead of whole milk/cheddar (maintains calcium, reduces saturated fat); wholemeal pasta instead of white (increases NSP/fibre); omitting salt/using herbs (reduces sodium to lower blood pressure). Part (b) Importance of Calcium (max 2 marks): 1 mark for explaining bone density maintenance/slowing bone loss; 1 mark for linking to prevention of osteoporosis/fractures. Max 10 marks total.

Part (a): During starch gelatinisation, starch granules from the flour are suspended in the milk. When heated to approximately 60 degrees Celsius, the granules begin to absorb liquid and swell. By 80 degrees Celsius, they have absorbed a significant amount of water and burst, releasing starch molecules (amylose and amylopectin) into the surrounding liquid. At 100 degrees Celsius (boiling), the mixture fully thickens and sets into a stable gel (the white sauce base) upon cooling. Part (b): Egg whites provide physical aeration. Whisking denatures the egg proteins (ovalbumin), which stretch and trap air to form a stable foam. During baking, the trapped air and moisture in the foam expand as they heat, acting as a raising agent. Simultaneously, the heat coagulates the egg proteins around the air cells, setting the light, airy structure so the soufflé remains raised. Part (c): To avoid deflating the trapped air when folding: (1) Use a metal spoon or rubber spatula rather than a wooden spoon, as their thin edges cut through the mixture cleanly without crushing the air bubbles. (2) Use a gentle figure-of-eight folding motion rather than stirring or beating, which would force the trapped air out of the egg white foam.

Part (a) Starch gelatinisation (max 4 marks): 1 mark for starch grains absorbing liquid; 1 mark for grains swelling (at approx 60C); 1 mark for grains bursting and releasing starch (at approx 80C); 1 mark for mixture thickening/gelatinising at boiling point (100C). Part (b) Role of egg whites (max 4 marks): 1 mark for whisking trapping air/forming protein foam; 1 mark for air acting as a physical raising agent; 1 mark for expansion of air/steam during baking; 1 mark for coagulation of egg proteins setting the airy structure. Part (c) Folding rules (max 2 marks): 1 mark for each practical tip (e.g., use a metal spoon/rubber spatula; fold gently in a figure-of-eight motion; do not over-mix/stir). Max 10 marks total.

To adapt the savory tart recipe for an elderly person recovering from a stroke (requiring lower sodium and saturated fat levels):

1. **First Modification**: Replace 75g Butter in the pastry with a vegetable fat spread high in polyunsaturated or monounsaturated fats (or reduce the overall fat content by using a low-fat spread suitable for baking). This helps lower low-density lipoprotein (LDL) cholesterol, reducing the risk of further arterial blockages.
2. **Second Modification**: Replace 100g Bacon with 100g of fresh skinless chicken breast or a mixture of mushrooms and bell peppers. Bacon is highly processed, cured with sodium, and contains high amounts of saturated fat. Chicken or vegetables provide protein and nutrients without high sodium or saturated fat.
3. **Third Modification**: Remove the \(\frac{1}{2}\) tsp Salt and replace it with a variety of fresh herbs (e.g., chives, parsley) or black pepper to maintain flavor. High sodium intake leads to elevated blood pressure (hypertension), which is a major risk factor for strokes.

**Cooking Technique for Filling**: Dry-frying or grilling the fresh chicken/mushrooms is highly suitable. Grilling allows any natural fat to drip away, while dry-frying in a non-stick pan eliminates the need for any added oil or cooking fat, keeping the fat content of the final dish as low as possible.

Total Marks: 7.5
- **Ingredient Modifications (3 marks)**: Award 1 mark for each of the three suitable ingredient replacements proposed (e.g., butter to vegetable spread/oil; bacon to chicken/vegetables; salt to herbs/spices; whole milk to skimmed milk).
- **Nutritional Justifications (3 marks)**: Award 1 mark for each corresponding nutritional explanation linking the modification to stroke recovery (e.g., reducing sodium lowers blood pressure; replacing saturated fats with unsaturated fats reduces blood cholesterol levels/risk of cardiovascular disease).
- **Cooking Technique & Explanation (1.5 marks)**: Award 1 mark for identifying a fat-minimizing cooking method (e.g., grilling, dry-frying, steaming, poaching) and 0.5 marks for explaining how it minimizes fat (e.g., requires no added fat/oil, or allows fat to drain off).

(a) **Ratio and Preservative Action**:
- Standard ratio: \(1:1\) (equal parts by weight of fruit and sugar).
- Preservative action: High sugar concentration (approx. 60-65% in final jam) exerts high osmotic pressure. It draws water out of any micro-organisms present (plasmolysis) and binds free water molecules, making water unavailable for microbial growth and multiplication.

(b) **Setting Point Tests** (Any two of the following):
- **Cold Plate / Wrinkle Test**: Place a small spoonful of jam on a chilled saucer. Let it cool for a minute, then gently push it with a finger. If the surface wrinkles, the setting point has been reached.
- **Flake / Slide Test**: Dip a wooden spoon into the boiling jam, lift it up, and let it cool slightly. Tilt the spoon; if the jam falls off in a flat flake or sheet rather than separate runs of liquid drops, it is set.
- **Temperature Test**: Insert a sugar thermometer into the boiling mixture. The jam is set when it reaches its setting point of \(105^\circ\text{C}\) (\(221^\circ\text{F}\)).

(c) **Hygienic Procedures for Bottling** (Any three of the following):
- Wash glass jars and metal lids thoroughly in hot soapy water, then sterilize them by placing them in an oven at \(110^\circ\text{C}\) to \(120^\circ\text{C}\) for 10-15 minutes or boiling them in water.
- Fill the sterilized jars while the jam is still hot (at least \(85^\circ\text{C}\)) to destroy any surface mold spores and to prevent condensation from forming inside the lid.
- Use a clean jam funnel when filling to keep the rims of the jars free from sticky residue, which could attract bacteria or mold.
- Seal the jars immediately after filling with airtight, sterilized screw-on metal lids or wax discs to prevent airborne micro-organisms from contaminating the product.

Total Marks: 7.5
- **Part (a) (2.5 marks)**:
- Award 0.5 marks for stating the correct sugar-to-fruit ratio (1:1 or equal weights).
- Award 1 mark for explaining high osmotic pressure/dehydration of micro-organisms.
- Award 1 mark for explaining that water activity is lowered/water is made unavailable for microbial growth.
- **Part (b) (2 marks)**:
- Award 1 mark for each of any two valid tests described (cold plate test, flake test, thermometer test at \(105^\circ\text{C}\)).
- **Part (c) (3 marks)**:
- Award 1 mark for each of any three valid hygienic bottling/sealing steps described (e.g., sterilizing jars, filling while hot, avoiding rim contamination, sealing immediately to prevent recontamination).

### 1. Nutritional Requirements of Adolescents
* **Protein:** Needed for the rapid growth spurts, muscle development, and repair of body tissues that occur during puberty.
* **Energy (Carbohydrates & Fats):** Adolescents have a high metabolic rate and are often physically active, meaning they require sufficient energy. Complex carbohydrates (starch) should be the primary source rather than simple sugars to provide sustained energy.
* **Calcium and Vitamin D:** Essential for rapid skeletal growth and achieving peak bone mass density, which helps prevent osteoporosis later in life. Vitamin D is required to facilitate calcium absorption.
* **Iron and Vitamin C:** Iron is crucial for the formation of haemoglobin in red blood cells. Adolescent females have increased iron requirements due to blood loss during menstruation, while males require iron for expanding muscle mass and blood volume. Vitamin C must be consumed in the same meal to convert non-haem iron into a soluble form for absorption.
* **Water/Fluids:** Essential for hydration, especially during sports, to regulate body temperature and support chemical reactions in the body.

### 2. Modifying Traditional Dishes to Meet Dietary Guidelines
* **Reducing Saturated Fat:**
* *Modification:* Trim visible fat from meats, choose lean cuts, or substitute meat with pulses (lentils, beans). Use low-fat cheeses and skimmed milk in traditional sauces (e.g., Béchamel sauce in lasagne).
* *Cooking Method:* Avoid shallow or deep frying. Instead, use grilling, baking, or steaming. Use non-stick pans to minimize the need for oil, or use unsaturated vegetable oils (like olive or rapeseed oil) in small quantities instead of lard or butter.
* **Reducing Sugar:**
* *Modification:* Replace refined sugar in baked goods with naturally sweet alternatives like mashed bananas, applesauce, or dried fruits (e.g., sultanas). Reduce the quantity of sugar specified in traditional recipes (often by up to half) without affecting the structure.
* *Example:* Modify a traditional fruit crumble by using whole oats in the topping and sweetening the fruit filling with naturally sweet apples and cinnamon instead of white sugar.
* **Reducing Salt:**
* *Modification:* Avoid adding salt at the table or during cooking. Instead, enhance flavours using fresh herbs (parsley, basil), spices (cumin, paprika), garlic, ginger, and lemon juice.
* *Example:* Modify a traditional tomato pasta sauce by using canned tomatoes with no added salt, seasoned with garlic, black pepper, and fresh oregano, rather than using highly processed, high-sodium pre-made sauces.
* **Increasing Non-Starch Polysaccharide (NSP / Dietary Fibre):**
* *Modification:* Use wholemeal flour instead of white flour for bread, pizza bases, or pastry. Leave the skins on potatoes (e.g., jacket potatoes or potato wedges) and vegetables to retain fibre and vitamins.
* *Example:* Serve brown rice or wholewheat pasta instead of white varieties to increase dietary fibre, which aids digestion and promotes satiety.

Maximum of 15 marks in total, distributed as follows:

**Part 1: Nutritional requirements of adolescents (Max 6 marks):**
* 1 mark for identifying the need for **protein** + 1 mark for linking to rapid growth/muscle development.
* 1 mark for identifying **calcium/Vitamin D** + 1 mark for linking to bone development/preventing osteoporosis.
* 1 mark for identifying **iron** + 1 mark for linking to menstruation in females/muscle growth in males.
* 1 mark for identifying **Vitamin C** + 1 mark for linking to iron absorption.
* 1 mark for identifying **energy/complex carbohydrates** + 1 mark for linking to active lifestyle/high metabolic rate.

**Part 2: Dietary guidelines and reasons for reduction (Max 4 marks):**
* 1 mark for explaining the need to reduce **saturated fat** to prevent obesity/coronary heart disease (CHD).
* 1 mark for explaining the need to reduce **refined sugar** to prevent dental caries/obesity/type 2 diabetes.
* 1 mark for explaining the need to reduce **salt (sodium)** to prevent high blood pressure (hypertension)/strokes.
* 1 mark for explaining the need to increase **NSP (fibre)** to prevent constipation/bowel disorders.

**Part 3: Practical modifications and cooking methods (Max 5 marks):**
* 1 mark for a specific example of reducing fat (e.g., grilling chicken instead of frying, using lean mince, or using low-fat dairy).
* 1 mark for a specific example of reducing sugar (e.g., using fruit purees in baking, reducing sugar in crumbles).
* 1 mark for a specific example of reducing salt (e.g., using garlic, herbs, or spices instead of table salt).
* 1 mark for a specific example of increasing NSP (e.g., using wholemeal flour for pizza bases, keeping skins on potato wedges).
* 1 mark for naming a specific traditional dish and showing how it is successfully adapted (e.g., modifying a beef lasagne by using lean mince, adding lentils, and using wholewheat pasta sheets).