2024 Cambridge IGCSE Food and Nutrition (0648) 模擬試題連答案詳解

To reduce the risk of osteoporosis, the diet should contain:
- Adequate calcium (e.g., from dairy products, green leafy vegetables) to maintain bone density.
- Adequate Vitamin D (e.g., from oily fish, eggs, sunlight) to facilitate calcium absorption.
- Minerals such as phosphorus and magnesium which work with calcium to strengthen bones.

To prevent constipation:
- Increase dietary fibre (NSP) intake (e.g., wholemeal bread, oats, fruit, and vegetables).
- Fibre absorbs water, making faeces softer, bulkier, and easier to expel, which stimulates the muscular walls of the gut to perform peristalsis.

Award marks as follows:
- 1 mark for each of the three valid dietary recommendations for osteoporosis (max 3 marks).
- 1 mark for identifying dietary fibre / NSP or drinking more water to prevent constipation.
- 1.71 marks for explaining the mechanism of fibre/water in preventing constipation (e.g., absorbing water/adding bulk = 0.85 marks; stimulating peristalsis/muscle contraction = 0.86 marks).

A whole egg consists of:
- Protein: High Biological Value (HBV) protein containing all essential amino acids (found in both white and yolk, e.g., ovalbumin, mucin).
- Fat: Easily digestible emulsified fat found exclusively in the yolk, containing unsaturated fatty acids and cholesterol.
- Vitamins: Rich in fat-soluble vitamins A, D, and E (in the yolk), and B-group vitamins like riboflavin and thiamin. Eggs contain no Vitamin C.
- Minerals: A valuable source of iron (in the yolk) and phosphorus.
- Water: Makes up the majority of the egg white.

Award marks for correct nutritional components (up to a maximum of 5.71 marks):
- High Biological Value (HBV) protein (1 mark)
- Emulsified fat / cholesterol in the yolk (1 mark)
- Fat-soluble vitamins (A, D, or E) (1 mark)
- B-group vitamins (e.g., riboflavin) (1 mark)
- Iron or phosphorus (1 mark)
- Statement that eggs lack Vitamin C (0.71 mark)

Retinol is preformed Vitamin A, meaning it is already in the active form that the body can readily use, and it is found only in animal-derived foods.
Beta-carotene is a provitamin (carotenoid pigment) found in plants. Once consumed, the body must convert beta-carotene into retinol in the wall of the small intestine and liver before it can be used.

Two animal sources of retinol: liver, kidney, oily fish, milk, cheese, butter, egg yolk.
Two plant sources of beta-carotene: carrots, spinach, sweet potato, butternut squash, red peppers, apricots, mangoes.

Award marks as follows:
- 1 mark for explaining retinol (preformed/active form, from animal sources).
- 1 mark for explaining beta-carotene (provitamin/precursor, converted in liver, from plant sources).
- 2 marks (1 mark each) for two correct animal sources of retinol.
- 1.71 marks (0.855 marks each) for two correct plant sources of beta-carotene.

The correct proportion of fat to flour in shortcrust pastry is \(1:2\) (half fat to flour, such as 100g fat to 200g flour).

Key rules for preparation and baking:
1. Keep all ingredients, utensils, and hands cold (e.g., use cold fat, ice-cold water, and rub in with fingertips). This prevents the fat from melting too early, which would make the pastry greasy and heavy instead of light and crumbly.
2. Handle and knead the dough as little as possible. Overworking the dough develops gluten in the flour, which makes the pastry tough and causes it to shrink during baking.
3. Bake in a hot oven (around 200°C / Gas Mark 6). This rapid heat sets the structure of the starch and gluten quickly and causes the trapped air and steam to expand, creating a crisp texture.

Award marks as follows:
- 1.71 marks for identifying the correct ratio of half fat to flour (e.g., 1:2 or 50% fat to flour).
- 4 marks for two rules with explanations (2 marks per rule: 1 mark for stating the rule, 1 mark for explaining why/the chemical effect).

Convenience foods are foods that have undergone commercial processing or pre-preparation (such as freezing, canning, dehydrating, or pre-cooking) to reduce the time, skill, and effort required by the consumer to prepare a meal.

Nutritional disadvantages of ultra-processed convenience foods:
- High Sodium Content: Used as a preservative and flavour enhancer, which can contribute to high blood pressure (hypertension) and stroke.
- High in Saturated and Trans Fats: Often used to extend shelf-life and improve mouthfeel, which increases LDL cholesterol levels and the risk of coronary heart disease (CHD).
- Loss of Vital Nutrients: Intensive processing often destroys heat-sensitive vitamins (like Vitamin C and B-group vitamins) and strips dietary fibre, leading to lower nutritional value and potentially leading to weight gain and constipation.

Award marks as follows:
- 1.71 marks for a clear, accurate definition of convenience food (focusing on commercial processing/saving preparation time and effort).
- 4 marks for discussing three nutritional disadvantages (award 1.33 marks per disadvantage with brief explanation of health impact).

When bicarbonate of soda (sodium bicarbonate) is heated alone, it undergoes thermal decomposition:
\(2\text{NaHCO}_3 \xrightarrow{\text{heat}} \text{Na}_2\text{CO}_3 + \text{CO}_2 + \text{H}_2\text{O}\)

This reaction produces carbon dioxide gas (which acts as the raising agent) and sodium carbonate (washing soda). Sodium carbonate is highly alkaline and leaves an unpleasant, bitter, soapy taste and a yellowish tinge in light-coloured mixtures (though disguised somewhat in gingerbread by the dark molasses and spices).

Cream of tartar (potassium hydrogen tartrate) is an acid. When moisture and heat are applied, the acid reacts with the alkaline bicarbonate of soda to neutralise it. This prevent the formation of sodium carbonate, eliminating the soapy taste and yellow colour, while producing sodium potassium tartrate (Rochelle salt), water, and carbon dioxide gas.

Award marks as follows:
- 2 marks for explaining the thermal decomposition reaction of bicarbonate of soda alone (releasing carbon dioxide, water, and sodium carbonate).
- 1.71 marks for identifying the consequence of sodium carbonate (causes a soapy/bitter taste and yellow discoloration).
- 2 marks for explaining the role of cream of tartar (acid reactants neutralise the alkali, preventing the soapy taste and releasing more gas).

Protein digestion begins chemically in the stomach:
- Gastric juice contains hydrochloric acid (HCl), which provides an acidic pH (about 1.5 - 2.0) necessary to activate pepsinogen into pepsin.
- Pepsin breaks down large protein molecules into smaller polypeptide chains.
- In infants, rennin coagulates the soluble milk protein caseinogen into insoluble casein so that pepsin can digest it.

Protein digestion continues in the duodenum (first part of the small intestine):
- Pancreatic juice contains trypsinogen, which is activated into trypsin by the enzyme enterokinase.
- Trypsin acts on the polypeptides, breaking them down into even smaller peptides and peptones.

Award marks as follows:
- Stomach (max 3 marks):
- 1 mark for identifying hydrochloric acid (creates acidic environment / activates pepsin).
- 1 mark for identifying the enzyme pepsin.
- 1 mark for identifying the product (polypeptides / peptones).
- Duodenum (max 2.71 marks):
- 1 mark for identifying pancreatic trypsin (activated from trypsinogen).
- 1.71 marks for identifying the product of trypsin action (peptides / amino acids).

(a) Dietary recommendations include: 1. Ensure adequate calcium and Vitamin D intake. 2. Increase dietary fibre. 3. Reduce salt/sodium intake. (Other acceptable: reduce saturated fat intake, maintain high fluid intake, focus on high-biological-value protein).

(b) Nutritional reasons: 1. Calcium and Vitamin D prevent the loss of bone density and help protect against osteoporosis. 2. Dietary fibre prevents constipation, which is common due to a slower digestive system and reduced physical activity. 3. Reduced sodium intake lowers the risk of developing hypertension (high blood pressure) and stroke.

(c) Practical factors: 1. Texture of food (ensure food is easy to chew/swallow due to loss of teeth or swallowing difficulties). 2. Ease of preparation (simple preparation methods if the person has arthritis or limited mobility). 3. Portion size and presentation (serve small, frequent, and visually appealing portions to encourage those with reduced appetites to eat).

(a) Award 1 mark for each valid dietary recommendation up to 3 marks.
- Acceptable: increase calcium/Vitamin D, reduce sodium, increase dietary fibre, reduce saturated fat, increase high-quality protein, increase fluid intake.

(b) Award 1 mark for each corresponding nutritional reason explained clearly up to 3 marks.
- Accept: bone density/osteoporosis prevention, digestive health/constipation prevention, hypertension/stroke prevention, cell repair/muscle maintenance, dehydration prevention.

(c) Award 1 mark for each valid practical factor up to 3 marks.
- Accept: texture/softness of food, ease of cooking, cost (fixed pensions), portion size, use of herbs/spices to enhance dulling taste buds.

(a) Nutrients in the yolk: Vitamin A (retinol), Vitamin D (cholecalciferol), Iron, Phosphorus, Fat (mostly unsaturated/saturated fats), and High Biological Value (HBV) Protein.

(b) Coagulation process: When heat is applied, the folded, coiled protein chains in the egg denature (unravel). As heating continues, these unfolded proteins collide and bond with one another to form a solid, three-dimensional network or gel, trapping water within the structure. If overheated, the protein network shrinks too much and squeezes out water (syneresis).

(c) Culinary uses and dishes:
1. Binding: e.g., rissoles, fishcakes, or burgers.
2. Emulsifying: e.g., mayonnaise or Hollandaise sauce.
3. Aerating / Lightening: e.g., meringues, soufflés, or sponge cakes.

(a) Award 1 mark for each correct nutrient identified up to 3 marks.
- Accept: Vitamin A, Vitamin D, Iron, Phosphorus, fat/lipids, HBV protein.
- Reject: Vitamin C (eggs contain none).

(b) Award up to 3 marks for the explanation of coagulation:
- 1 mark for mentioning heat denatures/uncoils protein chains.
- 1 mark for stating that proteins bond/link to form a solid network/gel.
- 1 mark for identifying that water is trapped (or describing syneresis/overcooking).

(c) Award 1 mark for each culinary use paired with a correct example up to 3 marks (0.5 marks for the use, 0.5 marks for the matching example).
- Accept: Binding (fishcakes/burgers), Emulsifying (mayonnaise), Aerating (meringues/souffles), Thickening (custard/lemon curd), Coating (Scotch eggs/fried fish), Glazing (pastry/bread).

(a) Biological functions of Vitamin C: 1. Formation of collagen (connective tissue for skin, blood vessels, and bones). 2. Promotes the absorption of non-haem iron from plant sources. 3. Acts as an antioxidant to protect cells from damage. 4. Aids in wound healing and tissue repair.

(b) Symptoms of scurvy: 1. Bleeding, swollen gums. 2. Loose teeth. 3. Easy bruising or slow-healing wounds. 4. Joint pain and fatigue.

(c) Minimizing Vitamin C loss: 1. Do not soak vegetables in water, as Vitamin C is water-soluble and will leach out. 2. Use a sharp knife and do not shred/chop too finely or too far in advance to prevent enzymatic oxidation. 3. Place vegetables directly into boiling water rather than cold water to quickly destroy oxidase enzymes. 4. Cook with the lid on and keep cooking times short (or use steaming/microwaving) to limit exposure to heat and air.

(a) Award 1 mark for each valid function up to 3 marks.
- Accept: collagen production, absorption of non-haem iron, antioxidant action, wound healing, maintaining healthy blood vessels/gums.

(b) Award 1 mark for each distinct symptom of scurvy up to 2 marks.
- Accept: bleeding/swollen gums, loose teeth, slow wound healing, easy bruising, joint pain.

(c) Award 1 mark for each valid preparation/cooking technique explained up to 4 marks.
- Accept: do not soak, do not chop too finely/too early, use boiling water, keep lid on pan, use minimal cooking water, reduce cooking time (steam/microwave/stir-fry), do not add bicarbonate of soda.

(a) Standard ratio of fat to flour: Half fat to flour (e.g., 1:2 ratio, or 100g fat to 200g flour).

(b) Rubbing-in method and gluten prevention: Using fingertips, the fat is rubbed gently into the flour until the mixture resembles fine breadcrumbs. This action coats the flour granules with a thin layer of waterproof fat. When liquid is added to bind the pastry, this fat barrier prevents the flour proteins (gliadin and glutenin) from absorbing water, which stops the development of long, elastic gluten strands. This results in a short, crumbly texture.

(c) Rules for rolling and baking: 1. Use a light dust of flour on the rolling board and pin to prevent sticking without altering proportions. 2. Roll in one direction only and avoid stretching the pastry to prevent shrinkage during baking. 3. Handle as little as possible and keep all ingredients cool to prevent the fat from melting. 4. Bake in a preheated hot oven (around 200°C) to set the starch and prevent the fat from melting and leaking out before the structure is set.

(a) Award 1 mark for stating the correct ratio (e.g., 1:2, half fat to flour, or a specific correct weight ratio like 100g fat to 200g flour).

(b) Award up to 4 marks for a detailed scientific explanation of rubbing-in:
- 1 mark for stating fingertips are used to rub fat into flour.
- 1 mark for stating fat coats the flour grains.
- 1 mark for explaining fat acts as a barrier/waterproof layer preventing water absorption.
- 1 mark for explaining that without water, gluten cannot develop, ensuring a 'short' crumbly texture.

(c) Award 1 mark for each distinct, valid rule for rolling or baking up to 4 marks.
- Accept: light dusting of flour, roll in one direction only, do not stretch pastry, keep ingredients and utensils cold, handle minimally, roll to an even thickness, bake in a hot/preheated oven (approx. 200°C / Gas 6).

(a) Definition: Food that has been partially or completely prepared commercially by food manufacturers to save the consumer time, effort, and skill during preparation.
Three types/categories:
1. Canned/tinned (e.g., canned soups, beans, fruit).
2. Frozen (e.g., frozen peas, fish fingers, ready-meals).
3. Dried/dehydrated (e.g., instant noodles, powdered gravy, dried soups).

(b) Advantages (any two):
1. Time-saving: Reduces the time needed for meal preparation and cooking.
2. Less skill required: Allows individuals with limited culinary skills to prepare meals.
3. Long shelf life: Easy to store and useful for emergency supplies.

Disadvantages (any three):
1. High in additives: Often contains chemical preservatives, flavorings, and colorings.
2. High in sodium, fat, or sugar: Regular consumption can increase risks of hypertension, obesity, and cardiovascular disease.
3. High cost: Commercially prepared foods are generally more expensive per portion than home-cooked equivalents.
4. Nutrient loss: Processing often destroys sensitive nutrients like Vitamin C and B-group vitamins.

(a) Award 1 mark for a clear definition of 'convenience food' (must mention commercial processing/preparation to save time/labor).
Award 1 mark for each distinct category/type listed up to 3 marks.
- Acceptable categories: canned, frozen, dried/dehydrated, chilled/ready-to-eat, pre-packaged mixes (e.g. cake mixes).

(b) Award 1 mark for each valid advantage discussed up to 2 marks.
- Accept: saves time, requires less skill, reduced wastage/pre-portioned, easy storage/long shelf life, less washing up.
Award 1 mark for each valid disadvantage discussed up to 3 marks.
- Accept: high in salt/sodium, high in saturated fats/sugars, contains artificial additives, loss of vitamins (C and B), more expensive, fixed portion sizes, lack of culinary creativity.

Part (a) Nutritional Requirements of Teenagers (Max 8 marks):
- Protein: Crucial for rapid growth spurts, muscle development, and repair of body tissues.
- Calcium and Vitamin D: Essential for the development of strong bones and teeth, achieving peak bone mass to prevent osteoporosis later in life.
- Iron: Required for the formation of haemoglobin to transport oxygen in the blood. Highly important for girls due to blood loss during menstruation, and for boys to support increased muscle mass and blood volume.
- Vitamin C: Enhances the absorption of non-haem iron from plant sources and helps with collagen production for skin and tissue health.
- Carbohydrates (especially complex carbohydrates): Provide the primary source of energy required for high metabolic rates and physical activity levels.
- B-group Vitamins (e.g., Thiamine, Riboflavin, Niacin): Required to release energy from carbohydrates, fats, and proteins.
- Dietary Fibre: Prevents constipation and promotes healthy bowel function.
- Water / Fluids: Prevents dehydration, particularly during sports or active outdoor play.

Part (b) Meal Planning Strategies for Families with Teenagers (Max 7 marks):
- Serve larger portion sizes of staple foods and proteins to teenagers relative to younger family members to meet their higher energy demands.
- Include nutrient-dense snacks (such as yoghurts, fresh fruit, nuts, and wholemeal toast) between meals rather than empty-calorie, high-sugar, or high-fat foods.
- Use healthier cooking methods such as grilling, baking, or steaming instead of deep frying to control fat intake while preserving nutrients.
- Ensure meals are balanced by following guidelines like the 'Eatwell Guide' (e.g., half the plate filled with vegetables and salad, one-quarter lean protein, one-quarter complex carbohydrates).
- Incorporate iron-rich foods (lean red meat, dark green leafy vegetables, lentils) alongside vitamin C-rich foods (citrus fruits, bell peppers) to maximise iron absorption.
- Involve teenagers in meal planning and preparation to encourage positive food habits and teach them life skills.
- Limit high-sugar beverages in the household by providing water, low-fat milk, or diluted unsweetened fruit juices.

Part (a): Maximum of 8 marks. Award 1 mark for each identified nutrient paired with a valid explanation of its specific role/importance during adolescence:
- Protein: Growth spurts / muscle tissue development (1 mark).
- Calcium: Strong bones / teeth / achieving peak bone density (1 mark).
- Vitamin D: Absorption of calcium (1 mark).
- Iron: Haemoglobin production / muscle growth / replaces menstrual loss in females (1 mark).
- Vitamin C: Absorption of iron / immunity / healthy skin (1 mark).
- Carbohydrates (Complex): Sustained energy release / high metabolic rate (1 mark).
- B Vitamins: Energy release from macronutrients (1 mark).
- Water / Fluid: Hydration (1 mark).
- Dietary Fibre: Prevent constipation / bowel health (1 mark).

Part (b): Maximum of 7 marks. Award 1 mark for each practical and well-explained meal planning/preparation strategy:
- Offer larger portions of nutrient-dense foods for teens (1 mark).
- Provide healthy snacks (e.g. nuts, fruit, seeds, dairy) instead of sugary junk foods (1 mark).
- Use low-fat cooking methods (e.g. baking, grilling, steaming) (1 mark).
- Adapt recipes to increase key nutrients, e.g., adding skimmed milk powder to sauces for extra calcium, or mixing lentils into minced meat (1 mark).
- Pair iron-rich foods with vitamin C-rich sources to enhance absorption (1 mark).
- Plan balanced meals using nutritional models like the Eatwell Guide (1 mark).
- Keep healthy, ready-to-eat foods accessible (e.g. cut-up fruit, raw vegetable sticks) (1 mark).
- Limit carbonated drinks / stock water or milk (1 mark).
- Involve teens in food prep to foster interest in healthy eating (1 mark).