2023 Cambridge IGCSE Food and Nutrition (0648) 模拟试题及答案详解

Appetite is the term used to describe the psychological or physiological desire to eat food.

Award 1 mark for: appetite. (Reject: hunger - as hunger is the physical drive to eat due to lack of food).

Marasmus is a severe form of protein-energy malnutrition (PEM) characterized by a deficiency in all macronutrients (protein, carbohydrates, and fats), leading to muscle wasting and loss of subcutaneous fat.

Award 1 mark for: marasmus. (Reject: kwashiorkor).

Salivary amylase (also known as ptyalin) is the enzyme present in human saliva that begins the chemical digestion of cooked starch into simpler maltose sugars.

Award 1 mark for: salivary amylase / amylase / ptyalin.

Lactose is the natural disaccharide carbohydrate present in milk.

Award 1 mark for: lactose.

Conduction is the process by which heat is directly transmitted through a substance when there is a difference of temperature between adjoining regions, without movement of the material itself.

Award 1 mark for: conduction.

Vitamin D is required for the efficient absorption of calcium from the gut, which is essential to support the high calcium demands of lactation without depleting the mother's own bone calcium stores.

Award 1 mark for: vitamin D / cholecalciferol.

Autoclaving is the commercial thermal processing method used during food canning to sterilise products by exposing them to high-pressure steam at temperatures typically around 121 degrees Celsius.

Award 1 mark for: autoclaving / commercial sterilisation / pressure canning.

Baking powder is a chemical raising agent that contains both an alkali (sodium bicarbonate) and an acid (usually cream of tartar or sodium acid pyrophosphate) which react to produce carbon dioxide gas in the presence of liquid and heat.

Award 1 mark for: baking powder. (Reject: baking soda / bicarbonate of soda).

The minimum energy required to maintain involuntary life-sustaining processes (such as breathing and cellular activity) at rest is called the Basal Metabolic Rate (BMR).

Award 1 mark for Basal Metabolic Rate or BMR.

Iodine is the trace element required by the thyroid gland to synthesise the hormone thyroxine, which regulates the body's metabolic rate.

Award 1 mark for Iodine.

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

Award 1 mark for salivary amylase / amylase / ptyalin.

Sodium bicarbonate (bicarbonate of soda) is the alkaline component of baking powder that reacts with acid (such as cream of tartar) in the presence of moisture and heat to produce carbon dioxide.

Award 1 mark for sodium bicarbonate / bicarbonate of soda.

Casein is the principal protein in milk, accounting for about 80% of the total protein content, and coagulates during cheese-making.

Award 1 mark for casein.

This specific high-temperature short-time (HTST) method of mild heat treatment is called pasteurisation.

Award 1 mark for pasteurisation.

Convection is the transfer of heat by the actual movement of the warmed matter (liquid or gas) in currents, such as in boiling water or a baking oven.

Award 1 mark for convection.

Elderly people generally require less energy-producing foods because:
1. Basal metabolic rate (BMR) decreases: The body's internal chemical processes slow down with age, requiring less baseline energy.
2. Decline in physical activity: Older adults are often more sedentary and engage in less vigorous physical work or exercise.
3. Loss of muscle tissue (sarcopenia): Active muscle mass declines with age and is replaced by fat tissue, which burns fewer calories at rest.

Award 1 mark for each correct reason up to a maximum of 3 marks:
- Basal metabolic rate (BMR) slows down / metabolism decreases [1 mark]
- Less active / more sedentary lifestyle / reduced physical activity [1 mark]
- Reduction in lean muscle tissue / sarcopenia [1 mark]

Advantages of using a microwave oven include:
1. Speed: Microwave ovens cook food much faster than conventional methods, saving time.
2. Nutritional Value: Because less water is used and cooking times are short, more heat-sensitive and water-soluble vitamins (like vitamin C and B vitamins) are retained.
3. Energy Efficiency: Less heat is lost to the surrounding kitchen environment, making it more energy efficient for cooking small to medium portions of food.

Award 1 mark for each valid advantage up to a maximum of 3 marks:
- Saves time / cooks food very quickly [1 mark]
- Retains more water-soluble vitamins / nutritional value (due to short cooking time/less water) [1 mark]
- Uses less energy / more economical than conventional oven [1 mark]
- Safer to use as the oven cavity itself does not get hot / less risk of burns [1 mark]
- Easy to clean [1 mark]
- Minimal washing up (can cook and serve in the same dish) [1 mark]
(Accept other reasonable answers)

Three key nutritional differences are:
1. Fat distribution: Oily fish contains fat distributed throughout its muscle fibers/flesh, whereas white fish stores fat only in its liver (with almost no fat in the flesh).
2. Fat-soluble vitamins: Oily fish flesh is a good source of vitamins A and D, whereas white fish flesh contains virtually none.
3. Fatty acid profile: Oily fish contains significant amounts of beneficial omega-3 polyunsaturated fatty acids, which are much lower in white fish flesh.

Award 1 mark for each distinct difference in nutritional composition up to a maximum of 3 marks:
- Fat location/amount: Oily fish has fat distributed throughout the flesh, whereas white fish has fat concentrated in the liver / white fish is very low fat [1 mark]
- Vitamin content: Oily fish contains fat-soluble vitamins (A and D) in its flesh, whereas white fish does not [1 mark]
- Essential fatty acids: Oily fish has higher levels of omega-3 fatty acids compared to white fish [1 mark]
- Water content: White fish flesh generally has a higher proportion of water than oily fish [1 mark]
(Do not accept vague answers like 'one is healthier than the other')

Air can be mechanically introduced via:
1. Creaming: Beating butter/margarine and sugar together traps tiny air bubbles in the fat.
2. Whisking: Beating eggs or egg whites rapidly traps air in a protein foam structure.
3. Sieving: Shaking flour through a sieve from a height allows air to be trapped between the falling flour particles.

Award 1 mark for naming the method and 1 mark for explanation, up to a maximum of 3 marks (e.g. 3 x 1 mark for clear brief points):
- Creaming: beating fat and sugar together traps air bubbles [1 mark]
- Whisking / beating: rapidly whisking eggs (or egg whites) traps air in the mixture [1 mark]
- Sieving: holding the sieve high above the bowl traps air between the flour particles [1 mark]
- Rubbing-in: rubbing fat into flour with fingertips traps some air as the mixture falls back into the bowl [1 mark]
(Maximum 3 marks total)

Regularly consuming ultra-processed convenience foods can lead to nutritional issues because:
1. High Sodium Content: Excess salt is added for preservation and flavor, which increases the risk of high blood pressure.
2. Unhealthy Fats: They often contain high levels of saturated fats or trans fats, contributing to elevated cholesterol and coronary heart disease risk.
3. Nutrient Loss: Intensive processing often destroys heat-sensitive vitamins (like vitamin C) and removes beneficial dietary fibre, leading to low nutrient density.

Award 1 mark for each distinct nutritional disadvantage up to a maximum of 3 marks:
- High in sodium / salt (linked to hypertension) [1 mark]
- High in saturated fats / trans fats (linked to CHD) [1 mark]
- Low in dietary fibre / NSP (can cause constipation) [1 mark]
- Loss of heat-sensitive / water-soluble vitamins (e.g., Vitamin C/B) during processing [1 mark]
- High in added sugars / refined carbohydrates (linked to tooth decay/obesity) [1 mark]
(Do not accept non-nutritional disadvantages such as cost or packaging waste)

1. **Guideline:** Prepare and cut vegetables just before cooking.
**Explanation:** Minimises the time cut surfaces are exposed to air, reducing the loss of vitamin C through oxidation.

2. **Guideline:** Cut vegetables into small, uniform pieces.
**Explanation:** Encourages rapid and even cooking, which minimises the total time the vegetables are exposed to heat.

3. **Guideline:** Use a minimal amount of oil/liquid.
**Explanation:** Prevents water-soluble vitamins (like vitamin C and B-group vitamins) from leaching out and dissolving into cooking juices.

4. **Guideline:** Stir-fry quickly over high heat.
**Explanation:** Shortens the cooking duration, preventing the thermal destruction of heat-sensitive vitamins.

5. **Guideline:** Serve the stir-fried vegetables immediately after cooking.
**Explanation:** Avoids holding the food warm, which continually destroys heat-sensitive vitamins over time.

For each of the five points:
Award 1 mark for stating a correct guideline and 1 mark for its scientific explanation.
Maximum 10 marks.

Suggested answers include:
- **Guideline:** Prepare/peel/cut vegetables just before cooking.
**Explanation:** Minimises exposure to atmospheric oxygen, preventing oxidation of vitamin C. [1 + 1]
- **Guideline:** Cut into small, uniform pieces.
**Explanation:** Ensures rapid, even heat penetration, reducing total cooking time and thermal damage. [1 + 1]
- **Guideline:** Use minimal oil / do not add water.
**Explanation:** Prevents water-soluble vitamins (thiamin, riboflavin, vitamin C) from dissolving/leaching into the liquid and being discarded. [1 + 1]
- **Guideline:** Cook for a very short duration at high temperature.
**Explanation:** Minimises the exposure of heat-sensitive vitamins to prolonged heat, preserving their nutritional value. [1 + 1]
- **Guideline:** Avoid peeling where appropriate (e.g., zucchini, carrots).
**Explanation:** The skin acts as a protective layer and often holds a high concentration of vitamins. [1 + 1]
- **Guideline:** Serve immediately.
**Explanation:** Standing/keeping food hot on a stove or counter continues to destroy heat-sensitive water-soluble vitamins. [1 + 1]

Do not credit duplicate explanations.

(a) Butter / block margarine.

(b) Any two from:
* Grated cheese
* Sugar / caster sugar / icing sugar
* Cocoa powder
* Spices (e.g. cinnamon, nutmeg, ginger)
* Citrus zest (e.g. lemon, orange)
* Ground nuts (e.g. almonds)

(c) Step-by-step instructions:
1. Sieve the plain flour and salt into a mixing bowl.
2. Cut the cold butter into small, even-sized cubes.
3. Rub the butter into the flour using only fingertips (avoid using palms as they are warmer).
4. Lift the mixture up during rubbing-in to introduce air.
5. Continue rubbing in until the mixture resembles fine breadcrumbs.
6. Sprinkle cold water gradually into the mixture.
7. Use a round-bladed knife to mix and bind the dough together.
8. Gently bring the dough together with your hands (do not over-handle).

(d) Gluten.

(e) Dextrinisation.

(f) Air and steam.

(g) Any two from:
* Fat melts.
* Fat is absorbed by starch granules.
* Water in the butter turns to steam, causing the layers to expand/rise.
* Melts to form spaces, giving the pastry a crumbly/short texture.

(h) Conduction.

(i) Any four from:
* Too much water was used to bind the dough.
* The dough was over-handled, kneaded, or over-worked (developing too much gluten).
* Too much extra flour was used during rolling out.
* The butter/fat was too warm or melted during the mixing process.
* Insufficient fat was rubbed in.
* The oven temperature was too low, causing the fat to melt out slowly rather than sealing the starch.

(j) To keep the fat solid / prevent the fat from melting or warming up (which would result in oily, greasy pastry and a hard baked texture).

(k) Any two from:
* Wrap tightly in cling film / foil / airtight container (to prevent drying out and absorbing fridge odours).
* Store in a refrigerator / cool place / below 5°C.
* Keep away from strong-smelling foods.
* Freeze if keeping for a longer duration.

(a) [1 mark] for butter.

(b) [2 marks] (1 mark per correct variation). Accept any logical ingredient added to dry flour (sugar, cheese, spices, cocoa, zest).

(c) [6 marks] (1 mark per step outlined). Must follow a logical chronological sequence. Fingertips must be mentioned for full marks on rubbing in.

(d) [1 mark] for gluten.

(e) [1 mark] for dextrinisation.

(f) [2 marks] (1 mark for air, 1 mark for steam).

(g) [2 marks] (1 mark per valid change described).

(h) [1 mark] for conduction.

(i) [4 marks] (1 mark per valid reason for tough texture).

(j) [1 mark] for explanation linked to keeping fat solid / preventing melting.

(k) [2 marks] (1 mark per guideline). Accept wrap in film/foil, refrigerate, store below 5°C.

(a) Bright red gills; clear, bright, bulging eyes (not sunken or cloudy); firm flesh that springs back when touched; scales that are tight and shiny; fresh, pleasant sea-like smell (no strong fishy or ammonia smell).

(b) Store on the bottom shelf of the refrigerator to prevent juices dripping onto other foods; keep wrapped tightly or in a sealed, covered container; place on a tray of ice if storing for up to 24 hours; ensure it is stored away from cooked/ready-to-eat foods.

(c) \(1^\circ\text{C}\) to \(4^\circ\text{C}\) (or up to \(5^\circ\text{C}\)).

(a) Award 1 mark for each correct sign of freshness up to 2 marks:
- Bright red/pink gills [1 mark]
- Clear/bright/bulging eyes [1 mark]
- Firm/elastic flesh [1 mark]
- Shiny/tight scales [1 mark]
- Fresh sea-smell [1 mark]
(Do not accept vague answers like "looks good" or "smells fresh" without clarification).

(b) Award 1 mark for each correct storage guideline up to 2 marks:
- Store on bottom shelf of the fridge [1 mark]
- Cover/wrap tightly or use an airtight container [1 mark]
- Keep separate from cooked/ready-to-eat foods [1 mark]
- Store on ice/use within 24 hours [1 mark]

(c) Award 1.5 marks for the correct temperature range:
- Range of \(1^\circ\text{C}\) to \(4^\circ\text{C}\) or \(1^\circ\text{C}\) to \(5^\circ\text{C}\) [1.5 marks]
(Award 1 mark if only a single correct value like \(4^\circ\text{C}\) is given without a range).

(a) Steam (or water vapour).

(b) High initial oven temperature to convert water to steam rapidly; sufficient liquid (water/milk) in the recipe to produce steam; beating the flour and liquid mixture thoroughly to gelatinise the starch and trap moisture.

(c) Opening the oven door lets cold air enter, which drops the oven temperature. This causes the steam to condense back into water before the egg and gluten proteins have fully coagulated to set the structure, causing the pastry to collapse.

(d) Eggs provide high biological value (HBV) protein for growth and repair of body cells; they provide vitamin A for healthy skin and vision; they provide iron for the formation of red blood cells.

(a) Award 1 mark for the correct raising agent:
- Steam / water vapour [1 mark]
(Do not accept air alone, though it is a secondary contributor).

(b) Award 1 mark for each correct condition up to 2 marks:
- High oven temperature (usually \(200^\circ\text{C}\) to \(220^\circ\text{C}\)) [1 mark]
- High proportion of liquid in the recipe [1 mark]
- Thorough boiling of water/fat and beating of flour to gelatinise starch [1 mark]
- Tight seal on oven/not letting steam escape [1 mark]

(c) Award 1.5 marks for a clear explanation:
- Drop in temperature causes steam to condense [1 mark]
- Happens before egg/gluten proteins have coagulated/set [0.5 mark]

(d) Award 1 mark for naming a correct nutrient and its valid function:
- HBV Protein for growth/repair [1 mark]
- Vitamin A for vision/skin [1 mark]
- Iron for red blood cells/preventing anaemia [1 mark]
- Vitamin D for calcium absorption [1 mark]

(a) Blanching destroys/inactivates enzymes that cause decay, loss of colour, flavour, and nutritional value during storage. It also helps to shrink the vegetables slightly, making them easier to pack, and kills surface microorganisms.

(b) \(-18^\circ\text{C}\) or below.

(c) Do not thaw vegetables before cooking (cook them straight from frozen) to prevent water-soluble vitamins leaching into thaw-water; cook using minimal water (such as steaming or microwaving instead of boiling); boil the water before adding the vegetables to shorten cooking time; use any cooking liquid in gravies or sauces.

(a) Award up to 2 marks for explaining the reasons for blanching:
- Inactivates/destroys enzymes [1 mark]
- Prevents loss of colour/flavour/nutrients [1 mark]
- Kills surface bacteria/microorganisms [1 mark]
- Shrinks/softens vegetables for easier packing [1 mark]

(b) Award 1.5 marks for the correct freezer temperature:
- \(-18^\circ\text{C}\) or below [1.5 marks]
(Accept any temperature within the range of \(-18^\circ\text{C}\) to \(-25^\circ\text{C}\). Deduct 0.5 marks if the minus sign is omitted).

(c) Award 1 mark for each valid cooking/thawing guideline up to 2 marks:
- Cook straight from frozen / do not thaw [1 mark]
- Use minimal cooking water / steam / microwave [1 mark]
- Keep cooking time as short as possible / boil water first [1 mark]
- Use cooking water in sauces/gravies [1 mark]
(Do not accept general advice like "cook quickly" without explanation).

(a) Gelation (or gel formation).

(b) Hydrate (sponge) the gelatine in cold water first to let the granules swell; dissolve the gelatine gently over warm water (indirect heat) or on a low setting; do not boil the gelatine directly, as high boiling heat breaks down the protein molecules and destroys its setting power.

(c) Raw pineapple, raw kiwi, raw papaya, or raw figs. These fruits contain proteolytic enzymes (such as bromelain or papain) that digest/break down the gelatine protein chains, preventing the liquid from forming a solid gel network.

(a) Award 1 mark for the correct term:
- Gelation / gel formation [1 mark]

(b) Award 1 mark for each correct preparation/dissolving rule up to 2 marks:
- Hydrate/sponge in cold water first [1 mark]
- Dissolve over gentle/indirect heat (e.g., bowl over hot water) [1 mark]
- Do not boil directly / avoid high temperatures [1 mark]
- Stir continuously to ensure even distribution and no lumps [1 mark]

(c) Award marks as follows (total 2.5 marks):
- Naming two correct fruits (e.g., pineapple, kiwi, papaya, figs) [1 mark]
- Explanation: Fruits contain proteolytic enzymes / proteases (such as bromelain/papain) [1 mark]
- Scientific impact: The enzymes digest/break down the gelatine protein chains, preventing gel formation [0.5 mark]

### Part 1: Causes and Symptoms of Iron-Deficiency Anaemia (Maximum 8 marks)

#### Causes:
* **Inadequate dietary intake:** Consuming insufficient amounts of iron-rich foods.
* **Poor absorption of iron:** Eating non-haem iron without enhancers, or high intake of inhibitors.
* **Lack of Vitamin C (ascorbic acid) in the diet:** Vitamin C is essential to reduce ferric iron to ferrous iron for absorption.
* **High intake of absorption inhibitors:** Consuming substances like phytates (in whole grains), polyphenols/tannins (in tea and coffee), or oxalates (in spinach) which bind to iron.
* **Excessive blood loss:** Caused by heavy menstruation, bleeding ulcers, or major surgery/trauma.
* **Increased physiological demand:** Rapid growth during adolescence, pregnancy, and lactation increase the body's iron requirements.
* **Gastrointestinal disorders:** Conditions like coeliac disease or Crohn's disease that damage the gut lining and impair absorption.

#### Symptoms:
* **Fatigue / extreme tiredness / lethargy:** Due to reduced haemoglobin levels causing less oxygen to be transported to tissues and muscles.
* **Paleness (pallor):** Pale skin, particularly visible inside the lower eyelids, nail beds, and palms.
* **Shortness of breath (dyspnea):** Feeling breathless easily, especially during mild physical exertion.
* **Dizziness or lightheadedness:** Caused by reduced oxygen supply to the brain.
* **Headaches:** Frequent headaches due to low oxygen levels in the brain.
* **Cold hands and feet:** Poor circulation and oxygen delivery to extremities.
* **Weakness:** General muscle weakness and lack of physical stamina.
* **Brittle or spoon-shaped nails (koilonychia):** Sign of chronic, severe iron deficiency.

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### Part 2: Planning and Preparing Family Meals to Maximise Iron Intake and Absorption (Maximum 8 marks)

#### Meal Planning & Food Selection:
* **Incorporate haem iron sources:** Include red meat (beef, lamb), offal (liver, kidney), poultry, and fish regularly in meals, as haem iron is highly bioavailable and easily absorbed by the body.
* **Incorporate non-haem iron sources:** For vegetarian members or to supplement meals, include pulses (lentils, chickpeas, kidney beans), dark green leafy vegetables (kale, broccoli), dried fruits (apricots, figs), and pumpkin seeds.
* **Use fortified foods:** Select commercial foods that are fortified with iron, such as breakfast cereals, wheat flour, and bread.

#### Enhancing Absorption:
* **Pair non-haem iron with Vitamin C:** Serve Vitamin C-rich foods (e.g., citrus fruits, bell peppers, tomatoes, kiwi) alongside non-haem iron foods (e.g., squeeze lemon juice over steamed spinach, or serve a glass of fresh orange juice with fortified breakfast cereal).
* **Combine haem and non-haem sources:** Small amounts of meat or fish cooked alongside plant sources of iron (the "meat factor") enhance the absorption of the non-haem iron.

#### Avoiding Inhibitors:
* **Limit tea and coffee with meals:** Do not serve tea, coffee, or cocoa during or immediately after meals, as the tannins and polyphenols bind to iron and prevent its absorption.
* **Separate calcium and iron intake:** Avoid serving high-calcium dairy foods (like cheese sauces or milk) with major iron-rich meals, as calcium competes with iron for absorption.

#### Preparation and Cooking Methods:
* **Use cast-iron cookware:** Cooking acidic foods (such as tomato-based sauces or stews) in cast-iron pots can significantly increase the iron content of the meal by leaching dietary iron into the food.
* **Soak, sprout, or ferment grains and pulses:** These processes reduce the phytate content, thereby increasing the bioavailability of non-haem iron.

Award 1 mark for each valid, explained point up to a total of 15 marks.

### Part 1: Causes and Symptoms (Maximum 8 marks)

#### Causes (1 mark per point):
* Inadequate dietary intake of iron-rich foods.
* Deficiency of Vitamin C (needed to absorb non-haem iron).
* High consumption of inhibitors (phytates, tannins, oxalates) with meals.
* Blood loss (e.g., heavy menstruation, ulcers).
* Increased demand during specific life stages (pregnancy, adolescence, lactation).
* Malabsorption disorders (e.g., coeliac disease).

#### Symptoms (1 mark per point):
* Fatigue / lethargy / constant tiredness.
* Pale skin / pallor (especially under eyelids/nails).
* Breathlessness / shortness of breath on exertion.
* Dizziness / lightheadedness.
* Headaches.
* General muscle weakness.
* Brittle or spoon-shaped nails (koilonychia).
* Cold extremities (hands/feet).

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### Part 2: Planning and Preparing Family Meals (Maximum 8 marks)

#### Diet and Meal Planning (1 mark per point):
* Include haem iron sources (red meat, liver, poultry, fish) which are easily absorbed.
* Include plant-based non-haem iron sources (pulses, dried fruits, dark green leafy vegetables).
* Choose fortified products (cereals, flours).

#### Promoting Absorption (1 mark per point):
* Serve Vitamin C-rich foods (citrus fruits, bell peppers, tomatoes) with non-haem iron sources.
* Combine plant sources with animal proteins ("meat factor") to boost non-haem absorption.

#### Avoiding Inhibitors (1 mark per point):
* Avoid serving tea, coffee, or cocoa with or immediately after meals (tannins inhibit absorption).
* Separate calcium-rich foods (dairy) from main iron-containing meals.
* Avoid excessive dietary fibre/bran at the same meal as iron sources.

#### Preparation and Cooking (1 mark per point):
* Use cast-iron pots/pans for cooking (especially for acidic/tomato dishes) to leach dietary iron.
* Employ techniques like soaking, sprouting, or fermenting of pulses/grains to reduce phytates and improve bioavailability.