2023 Cambridge IGCSE Food and Nutrition (0648) 模擬試題連答案詳解

Vitamin D is essential for the absorption of calcium in bones. A lack of this vitamin in children leads to soft, weak bones, a condition known as rickets.

Award [1 mark] for Rickets. Reject osteoporosis (this occurs in adults).

Salivary amylase (also known as ptyalin) is secreted by the salivary glands and initiates the breakdown of cooked starch into maltose in the mouth.

Award [1 mark] for salivary amylase or ptyalin. Reject amylase on its own unless specified as salivary.

Conduction is the transfer of heat through direct contact, where vibrating molecules pass kinetic energy to neighboring molecules.

Award [1 mark] for conduction.

Cow's milk contains several proteins, but the main protein is casein, which accounts for about 80% of the total protein content.

Award [1 mark] for casein (or caseinogen). Accept lactalbumin / lactoglobulin if identified as part of the whey protein, but casein is the principal protein.

Yeast metabolizes sugars during fermentation, releasing carbon dioxide gas and ethanol. The carbon dioxide gas bubbles expand during proving and baking, causing the bread dough to rise.

Award [1 mark] for carbon dioxide (or \(CO_2\)).

The danger zone is the temperature range between \(5^\circ\text{C}\) and \(63^\circ\text{C}\) where bacteria can grow and multiply rapidly.

Award [1 mark] for specifying the range: \(5^\circ\text{C}\) to \(63^\circ\text{C}\) (also accept \(5^\circ\text{C}\) to \(60^\circ\text{C}\)).

The standard proportion of fat to flour for shortcrust pastry is half fat to flour (for example, 100g of fat to 200g of flour, which is a 1:2 ratio).

Award [1 mark] for stating half fat to flour, 1:2 ratio, or giving a correct specific example (e.g., 100g fat to 200g flour).

Ultra-processed convenience foods often contain high levels of added sodium (salt) for preservation and flavor enhancement, which can contribute to hypertension. They are also often high in saturated fat and free sugars, and low in dietary fibre.

Award [1 mark] for any one of the following valid nutritional disadvantages: high in sodium/salt, high in saturated fats, high in free sugars, high in energy density/calories, low in dietary fibre, or loss of heat-sensitive vitamins (like Vitamin C) during processing.

Coagulation is the correct term. It describes the process where denatured proteins unfold and bond together to form a solid or semi-solid structure, such as the white of a boiled egg setting.

[1 mark] Coagulation. Reject: Denaturation (as denaturation is the initial unfolding of protein chains, not the final setting/hardening).

Casein is the primary protein found in milk, constituting about 80% of the total protein content.

[1 mark] Casein. Accept: Caseinogen.

Convection occurs when liquids or gases are heated, causing the warmer, less dense particles to rise, and the cooler, denser particles to sink, setting up a circulation current.

[1 mark] Convection.

The basic ratio for standard shortcrust pastry is half fat to flour (e.g., 100g fat to 200g flour, or a 1:2 ratio).

[1 mark] Half fat to flour / 1:2 ratio (fat to flour) / 50% fat to flour.

Highly processed convenience foods often contain high amounts of added salt (sodium) to enhance shelf life and flavour, which can contribute to high blood pressure.

[1 mark] High sodium/salt content OR High in saturated fat OR High in sugar/refined carbohydrates OR Low in dietary fibre OR Loss of water-soluble vitamins (Vitamin B/C) during processing.

Teenagers experience rapid skeletal growth and require calcium to mineralise and build strong bones and teeth, helping them reach peak bone mass and reduce the risk of osteoporosis later in life.

[1 mark] For the growth, development or strengthening of bones and teeth / to achieve peak bone mass.

Bicarbonate of soda (sodium bicarbonate) decomposes when heated to release carbon dioxide gas, which expands and helps the mixture rise.

[1 mark] Carbon dioxide or \(CO_2\).

Hydrochloric acid (HCl) is produced by the gastric glands in the stomach. Its key roles include: creating an acidic medium (around pH 1.5 to 2.0) which is optimal for pepsin to break down proteins; activating pepsinogen into its active form pepsin; and killing harmful bacteria and pathogens ingested with food, thus protecting the body from foodborne illnesses.

Award 1 mark for each of the following points, up to a maximum of 3 marks: - Destroys/kills harmful bacteria/microorganisms. - Provides an acidic medium / optimum pH (pH 1.5-2.0) for enzyme action. - Activates pepsinogen/pro-enzymes into active pepsin. - Denatures or uncoils proteins to facilitate enzymatic attack.

Conduction is the transfer of heat through a solid substance from molecule to molecule by direct contact. When a saucepan is placed on a hob, heat energy causes the molecules of the saucepan base to vibrate rapidly. These vibrating molecules collide with neighboring molecules, transferring kinetic energy throughout the pan and into the food. Copper and aluminium are excellent conductors of heat and are commonly used to make saucepans.

Award 1 mark for explanation of conduction: - Transfer of heat energy via direct contact / molecule-to-molecule vibration. Award 1 mark each for any two of the following metals (max 2 marks): - Copper - Aluminium - Cast iron - Stainless steel (with copper/aluminium base) - Mild steel / carbon steel.

Rubbing fat into flour is a critical step in making shortcrust pastry. The fat coats the flour particles, forming a waterproof barrier. This prevents the gluten-forming proteins (gliadin and glutenin) in the flour from absorbing the added water and forming long, elastic gluten strands. This lack of gluten structure ensures that the cooked pastry is tender, short, and crumbly rather than tough and chewy.

Award 1 mark for each correct reason up to a maximum of 3 marks: - Coats flour granules/particles with a waterproof layer of fat. - Prevents flour from absorbing water. - Inhibits / limits gluten development / prevents gluten from forming elastic strands. - Ensures a short / crumbly texture in the baked product. - Evenly distributes fat throughout the flour mixture.

Milk is rich in several key minerals, most notably calcium and phosphorus (it also contains small amounts of sodium and potassium). Calcium is crucial for the formation and maintenance of healthy bones and teeth, blood clotting, and nerve signal transmission. Phosphorus works closely with calcium to form calcium phosphate, providing structural rigidity to bones.

Award 1 mark for each correct mineral identified, up to 2 marks: - Calcium - Phosphorus - Potassium - Sodium (Note: Reject iron, as milk is a poor source of iron). Award 1 mark for a correct corresponding function: - Calcium: Bone/teeth formation/maintenance, blood clotting, muscle function, or nerve transmission. - Phosphorus: Bone/teeth formation, energy release (ATP production), or buffer system in cells.

Bacteria require specific conditions to survive and reproduce. These include: warmth (the danger zone of 5 deg C to 63 deg C is ideal for growth), moisture (which is needed for cellular processes), time (bacteria multiply by binary fission every 10 to 20 minutes under ideal conditions), and a source of food/nutrients.

Award 1 mark for each condition identified, up to a maximum of 3 marks: - Warmth / suitable temperature (accept 5 deg C to 63 deg C / danger zone) - Moisture / water - Time - Food / nutrients - Suitable pH (neutral or slightly alkaline) (Accept oxygen for aerobic bacteria, but do not accept 'air' without qualification).

When planning meals for an elderly person, nutrition must be tailored to their changing physiological needs:

1. **Recommendation:** Reduce total energy intake (fewer carbohydrates and fats).
**Reason:** Metabolism slows down (lower BMR) and physical activity levels usually decline, so excess calories will easily be stored as fat, leading to obesity.

2. **Recommendation:** Ensure a rich supply of Calcium and Vitamin D.
**Reason:** Bone mass naturally decreases with age; these nutrients help maintain bone strength and prevent osteoporosis.

3. **Recommendation:** Increase dietary fibre (NSP) and fluids.
**Reason:** Bowel muscles weaken and digestive processes slow down, increasing the risk of constipation. Fibre and water encourage regular peristalsis.

4. **Recommendation:** Limit sodium (salt) intake.
**Reason:** High sodium intake is closely linked to fluid retention and high blood pressure (hypertension), which increases the risk of stroke and heart disease.

5. **Recommendation:** Offer foods with a soft texture (e.g., stews, minced meats, mashed vegetables).
**Reason:** Many elderly people have poor dentition (missing teeth or ill-fitting dentures) or suffer from dry mouth, making hard or dry foods difficult to chew and swallow safely.

Award 1 mark for each correct dietary recommendation (maximum of 5) and 1 mark for each corresponding valid physiological or nutritional reason (maximum of 5).

**Example points (accept any 5 pairs):**
- **Reduce calorie/energy intake** (1 mark) because of a lower metabolic rate / less physical activity to prevent weight gain (1 mark).
- **Increase Calcium/Vitamin D** (1 mark) to maintain bone density / prevent osteoporosis / prevent fractures (1 mark).
- **Increase dietary fibre (NSP)** (1 mark) to prevent constipation / aid peristalsis as the digestive tract slows down (1 mark).
- **Reduce salt/sodium** (1 mark) to lower the risk of high blood pressure / hypertension / strokes (1 mark).
- **Provide soft/easy-to-chew foods** (1 mark) because of tooth loss / difficulty swallowing (dysphagia) / reduced saliva (1 mark).
- **Ensure adequate fluid intake** (1 mark) because the thirst reflex weakens with age / to prevent dehydration (1 mark).
- **Maintain adequate protein** (1 mark) to repair body tissues / prevent muscle loss (sarcopenia) (1 mark).
- **Increase Vitamin C / Iron** (1 mark) to boost a declining immune system / assist in preventing anaemia (1 mark).

*Note:* Do not award marks for a reason if the recommendation is incorrect or missing. Reject vague answers such as 'to be healthy' or 'to feel good'.

(a) Yeast requires: 1. Warmth (optimum temperature 25-37 degrees C) to activate enzymes; 2. Moisture to hydrate and activate the yeast; 3. Food (sugar or starch converted to sugar) to feed on; 4. Time to ferment and produce carbon dioxide gas. (b) (i) Kneading: Stretches and develops gluten (gliadin and glutenin) to form an elastic network; traps carbon dioxide gas; ensures even distribution of yeast and temperature. (ii) Proving: Allows the yeast to continue fermenting and producing carbon dioxide; causes the dough to expand and rise; stretches the elastic gluten network to hold the gas. (c) (i) Yeast: At first, yeast activity increases in warmth, releasing more carbon dioxide; at around 55-60 degrees C, yeast is killed and fermentation stops. (ii) Gluten: Coagulates and sets the structure of the bread around 80 degrees C, holding the expanded shape. (iii) Starch: Gelatinises as it absorbs moisture released during heating; dextrinises on the outer surface due to dry heat, turning the crust golden brown. (d) Reasons for heavy, close texture: 1. Water used was too hot, which killed the yeast; 2. Insufficient kneading, so gluten network did not develop; 3. Insufficient proving time, so not enough carbon dioxide was produced; 4. Too much salt was added, which inhibited yeast activity; 5. Low-gluten flour was used instead of strong flour. (e) Nutritional benefits of wholemeal flour: 1. Contains more dietary fibre (NSP) which prevents constipation and assists bowel movement; 2. Contains higher levels of B-group vitamins (thiamine, niacin) for energy release; 3. Contains more iron which prevents anaemia and forms haemoglobin; 4. Has a lower glycaemic index which helps maintain stable blood glucose levels.

Award marks as follows: (a) Award 1 mark for each correct condition identified: Warmth, Moisture, Food/Sugar, Time. (Max 4 marks) (b) (i) Kneading: 1 mark for development of gluten; 1 mark for creating an elastic network; 1 mark for trapping gas or even distribution of ingredients. (Max 3 marks) (b) (ii) Proving: 1 mark for yeast continuing fermentation/producing CO2; 1 mark for the dough rising/expanding; 1 mark for gluten network stretching to support the expanded structure. (Max 3 marks) (c) (i) Yeast: 1 mark for initial increase in yeast activity; 1 mark for yeast being killed at 55-60 degrees C. (Max 2 marks) (c) (ii) Gluten: 1 mark for coagulation/setting; 1 mark for holding/defining the structural shape of the bread. (Max 2 marks) (c) (iii) Starch: 1 mark for gelatinisation (absorbing water and swelling); 1 mark for dextrinisation on the crust (browning). (Max 2 marks) (d) Award 1 mark for each of any three valid reasons: liquid too hot (killed yeast), insufficient kneading, insufficient proving, too much salt, incorrect flour type (e.g. plain flour). (Max 3 marks) (e) Award 1 mark for each of any four nutritional benefits correctly stated and explained: e.g. more dietary fibre (prevents constipation); more B vitamins (energy release); more iron (prevents anaemia); slower release of energy. (Max 4 marks)

(a) Yeast requires: 1. Warmth (optimum temperature 25-37 degrees C) to activate enzymes; 2. Moisture to hydrate and activate the yeast; 3. Food (sugar or starch converted to sugar) to feed on; 4. Time to ferment and produce carbon dioxide gas. (b) (i) Kneading: Stretches and develops gluten (gliadin and glutenin) to form an elastic network; traps carbon dioxide gas; ensures even distribution of yeast and temperature. (ii) Proving: Allows the yeast to continue fermenting and producing carbon dioxide; causes the dough to expand and rise; stretches the elastic gluten network to hold the gas. (c) (i) Yeast: At first, yeast activity increases in warmth, releasing more carbon dioxide; at around 55-60 degrees C, yeast is killed and fermentation stops. (ii) Gluten: Coagulates and sets the structure of the bread around 80 degrees C, holding the expanded shape. (iii) Starch: Gelatinises as it absorbs moisture released during heating; dextrinises on the outer surface due to dry heat, turning the crust golden brown. (d) Reasons for heavy, close texture: 1. Water used was too hot, which killed the yeast; 2. Insufficient kneading, so gluten network did not develop; 3. Insufficient proving time, so not enough carbon dioxide was produced; 4. Too much salt was added, which inhibited yeast activity; 5. Low-gluten flour was used instead of strong flour. (e) Nutritional benefits of wholemeal flour: 1. Contains more dietary fibre (NSP) which prevents constipation and assists bowel movement; 2. Contains higher levels of B-group vitamins (thiamine, niacin) for energy release; 3. Contains more iron which prevents anaemia and forms haemoglobin; 4. Has a lower glycaemic index which helps maintain stable blood glucose levels.

Award marks as follows: (a) Award 1 mark for each correct condition identified: Warmth, Moisture, Food/Sugar, Time. (Max 4 marks) (b) (i) Kneading: 1 mark for development of gluten; 1 mark for creating an elastic network; 1 mark for trapping gas or even distribution of ingredients. (Max 3 marks) (b) (ii) Proving: 1 mark for yeast continuing fermentation/producing CO2; 1 mark for the dough rising/expanding; 1 mark for gluten network stretching to support the expanded structure. (Max 3 marks) (c) (i) Yeast: 1 mark for initial increase in yeast activity; 1 mark for yeast being killed at 55-60 degrees C. (Max 2 marks) (c) (ii) Gluten: 1 mark for coagulation/setting; 1 mark for holding/defining the structural shape of the bread. (Max 2 marks) (c) (iii) Starch: 1 mark for gelatinisation (absorbing water and swelling); 1 mark for dextrinisation on the crust (browning). (Max 2 marks) (d) Award 1 mark for each of any three valid reasons: liquid too hot (killed yeast), insufficient kneading, insufficient proving, too much salt, incorrect flour type (e.g. plain flour). (Max 3 marks) (e) Award 1 mark for each of any four nutritional benefits correctly stated and explained: e.g. more dietary fibre (prevents constipation); more B vitamins (energy release); more iron (prevents anaemia); slower release of energy. (Max 4 marks)

Guidelines:
- Place on bottom shelf: prevents raw juices from dripping.
- Cover/wrap securely: prevents contact and drip contamination, and limits moisture loss.
- Store away from ready-to-eat foods: prevents transferring bacteria.
- Maintain temperature at \(1\,^{\circ}\text{C}\) to \(5\,^{\circ}\text{C}\): slows down the reproduction and growth of spoilage and pathogenic bacteria.
- Do not wash raw poultry: prevents splashing of water droplets containing bacteria onto kitchen surfaces or other foods.

Scientific reason: Keeping raw poultry on the bottom shelf is essential because raw poultry naturally contains harmful bacteria like Salmonella. Storing it at the lowest point prevents juices from dripping, eliminating the main vector of cross-contamination in a refrigerator.

Guidelines: 2.5 marks total (0.5 marks for each of the 5 correct guidelines).
Scientific explanation: 3.0 marks total:
- 1.0 mark for identifying a pathogenic bacterium associated with poultry (e.g. Salmonella or Campylobacter).
- 1.0 mark for explaining the mechanism of cross-contamination (e.g. dripping juices or water droplet splashing).
- 1.0 mark for linking this to the prevention of food poisoning/spoilage.

(a) Clostridium botulinum is an anaerobic, spore-forming bacterium. In low-acid foods like vegetables, it can produce a deadly toxin unless processed at \(121\,^{\circ}\text{C}\) (under pressure) to destroy the heat-resistant spores.
(b) Storage guidelines:
- Cool, dry environment: prevents condensation, rusting of metallic lids, and spoilage.
- Dark storage: protects light-sensitive pigments and vitamins.
- Clear labelling: ensures first-in, first-out stock rotation.
- Inspection: ensures no leaks or unsealed lids are put into storage.

Part (a): 1.5 marks total:
- 1.0 mark for identifying Clostridium botulinum (must spell correctly or be highly recognisable).
- 0.5 marks for stating the correct temperature (\(121\,^{\circ}\text{C}\) or \(250\,^{\circ}\text{F}\)).
Part (b): 4.0 marks total:
- 1.0 mark for each of the four valid storage guidelines described (up to 4.0 marks).

(a) Proper milk storage includes maintaining a cold environment, preventing contamination, and avoiding sensory changes by keeping containers sealed.
(b) Vitamin B2 (Riboflavin) is highly sensitive to light and degrades quickly when exposed to direct sunlight. This reduces the nutritive value of the milk and can lead to a 'sunlight flavor' due to protein/lipid oxidation.
(c) A refrigerator operating between \(1\,^{\circ}\text{C}\) and \(5\,^{\circ}\text{C}\) inhibits the growth of spoilage bacteria (like lactobacilli) without freezing the milk.

Part (a): 3.0 marks total (1.0 mark for each valid storage guideline).
Part (b): 1.5 marks total:
- 1.0 mark for naming Riboflavin / Vitamin B2.
- 0.5 marks for explaining that light destroys/degrades this vitamin or causes off-flavors.
Part (c): 1.0 mark for stating the correct refrigerator temperature range (accept range within \(1\,^{\circ}\text{C}\) to \(5\,^{\circ}\text{C}\) / \(34\,^{\circ}\text{F}\) to \(41\,^{\circ}\text{F}\)).

(a) To preserve frozen peas, the temperature must remain constant at \(-18\,^{\circ}\text{C}\) or lower, and packaging must prevent moisture loss (freezer burn).
(b) Thawing allows bacteria to exit the dormant state and rapidly multiply in the moist, nutrient-rich environment of the peas. Refreezing will not sterilise the food. From a physical standpoint, refreezing results in slow ice crystal growth, which breaks down the cellular structure of the peas, making them mushy, faded, and nutritionally depleted upon the second thaw.

Part (a): 3.0 marks total (1.0 mark for each correct freezer storage guideline).
Part (b): 2.5 marks total:
- Safety reason (1.5 marks): 1.0 mark for explaining that bacteria multiply during thawing and freezing does not kill them; 0.5 marks for linking to increased food poisoning risk.
- Quality reason (1.0 mark): 0.5 marks for explaining cell wall damage due to ice crystal formation; 0.5 marks for describing loss of texture (mushiness) or nutrient loss.

Part (a) Comparison of Nutritional Value: 1. Protein: Both white and oily fish are excellent sources of High Biological Value (HBV) protein, containing all essential amino acids required for body growth, tissue repair, and the production of hormones and enzymes. 2. Fat: White fish (e.g., cod, haddock) contains very little fat (usually less than 2 percent) as fat is stored in the liver. Oily fish (e.g., salmon, mackerel) contains fats distributed throughout the flesh (up to 20 percent). This fat is unsaturated and rich in omega-3 fatty acids, which help lower blood cholesterol levels and reduce the risk of cardiovascular diseases. 3. Vitamins: White fish is a good source of water-soluble B vitamins (e.g., thiamine, riboflavin, niacin) for energy release. Oily fish contains fat-soluble Vitamin A (for healthy skin and night vision) and Vitamin D (for calcium absorption and strong bones/teeth), alongside B vitamins. 4. Minerals: Both types contain iodine (for thyroid function and regulating metabolic rate) and phosphorus. Oily fish (especially if small bones are consumed, like sardines) provides calcium for strong bones and teeth. 5. Water: White fish contains a higher percentage of water than oily fish. Part (b) Guidelines for Safety and Quality: 1. Buying: Choose fish with bright, bulging, clear eyes (not sunken or cloudy); bright red gills; firm, elastic flesh that springs back when touched; tight, shiny scales; and a fresh, salty sea smell (avoiding any sour or ammonia smells). 2. Storing: Keep fresh fish on a tray covered with foil or cling film in the coldest part of the refrigerator (0 to 4 degrees C) to slow down bacterial growth and enzymatic action. Store it below cooked foods to prevent cross-contamination from dripping juices. Use within 24 hours of purchase or freeze immediately. 3. Preparing: Wash hands thoroughly before and after handling raw fish. Use a dedicated, clean color-coded cutting board (usually blue for raw fish) and sanitized knives to prevent cross-contamination. Keep raw fish separate from ready-to-eat foods. Cook fish thoroughly until it reaches an internal temperature of at least 63 degrees C (or until the flesh becomes opaque and flakes easily with a fork) to ensure any food-poisoning bacteria are destroyed.

Award up to 15 marks in total. Part (a) Nutritional comparison (Maximum 7 marks): 1 mark for identifying HBV protein in both with its function (growth/repair). 1 mark for stating white fish is low in fat / fat stored in liver. 1 mark for stating oily fish is high in fat / unsaturated fat / omega-3. 1 mark for explaining omega-3 benefits (heart health / reduces cholesterol). 1 mark for identifying B vitamins in both / white fish (functions in metabolism). 1 mark for identifying Vitamin A or D in oily fish with their respective functions (vision / calcium absorption). 1 mark for identifying minerals like iodine (thyroid) or calcium (bones, if bones are eaten). 1 mark for noting water content differences. Part (b) Safety and hygiene guidelines (Maximum 8 marks, with a balanced distribution across buying, storing, and preparing): Buying (Max 3 marks): 1 mark per valid quality point: clear/prominent eyes, red gills, firm/elastic flesh, fresh sea smell, shiny/tight scales. Storing (Max 3 marks): 1 mark for cold storage temperature (0-4 degrees C / fridge) or on ice. 1 mark for covering to prevent odor transfer / cross-contamination. 1 mark for storing raw fish below cooked food / using within 24 hours. Preparing (Max 3 marks): 1 mark for clean/color-coded chopping board (blue) to prevent cross-contamination. 1 mark for personal hygiene (washing hands / clean utensils). 1 mark for thorough cooking (flesh opaque/flakes easily / safe temperature) to destroy pathogens.