2025 Cambridge IGCSE Food and Nutrition (0648) 模拟试题及答案详解

Malnutrition is a condition resulting from an incorrect intake of nutrients, including both undernutrition (too few nutrients) and overnutrition (too many nutrients or excess energy intake).

Award 1 mark for stating it is an incorrect or unbalanced nutrient intake. Award 1 mark for specifying that it encompasses both deficiency (undernutrition) and excess (overnutrition).

Hydrochloric acid provides an acidic medium (pH 1.5 to 2.0) which is essential to activate the protein-digesting enzyme pepsinogen into pepsin. It also acts as a barrier to infection by sterilising food and killing ingested bacteria.

Award 1 mark for activation of enzymes / providing acidic medium for pepsin. Award 1 mark for killing bacteria / sterilising food.

Vitamin D is required for the efficient absorption of calcium and phosphorus from the intestines. These minerals are the fundamental building blocks needed for the calcification and hardening of the enamel and dentine in teeth.

Award 1 mark for stating it is required for calcium absorption. Award 1 mark for stating it is required for phosphorus absorption / calcification / mineralisation of teeth.

Water is involved in many body processes, such as cooling the body through perspiration, transporting nutrients and waste products in blood and urine, lubricating joints, and providing a medium for chemical reactions.

Award 1 mark for each correct function (up to 2). Accept: temperature regulation / sweating; transport of nutrients/wastes; lubrication of joints/membranes; medium for chemical reactions.

Sugar acts as a preservative when its concentration is 60% or higher. It exerts osmotic pressure, drawing water out of the cells of bacteria, yeasts, and moulds (plasmolysis). It also reduces water activity, leaving insufficient free moisture for microbial growth.

Award 1 mark for explaining that it binds moisture / reduces water activity. Award 1 mark for explaining osmosis / drawing water out of microbial cells / plasmolysis.

As people age, they experience a natural decline in muscle mass (sarcopenia), which decreases their Basal Metabolic Rate (BMR). Additionally, elderly individuals are typically less physically active and lead more sedentary lifestyles, lowering their daily energy needs.

Award 1 mark for mentioning a reduction in physical activity / sedentary lifestyle. Award 1 mark for mentioning a decline in Basal Metabolic Rate (BMR) / muscle mass.

Yeast needs specific conditions to carry out fermentation: moisture (to hydrate the yeast cells), warmth (to activate yeast enzymes), and food (sugars or starches) to ferment and produce carbon dioxide gas and alcohol.

Award 1 mark for each correct condition mentioned (up to 2). Acceptable: warmth / suitable temperature; moisture / water / liquid; food / sugar / carbohydrate; time.

The kitchen work triangle is an ergonomic design principle connecting the three busiest work zones: the food storage zone (refrigerator), the preparation/washing zone (sink), and the cooking zone (stove/cooker).

Award 1 mark for correctly naming two areas. Award 2 marks for correctly naming all three areas: sink (washing), refrigerator (storage), and cooker (stove/hob).

Lipids have several vital non-energy functions in the human body, including: protecting delicate internal organs (such as kidneys) from physical damage; insulating the body against heat loss; acting as a carrier and source of fat-soluble vitamins (A, D, E, and K); forming an essential structural component of cell membranes; and contributing to satiety (the feeling of fullness after eating).

Award 1 mark for each valid function up to a maximum of 2 marks. Acceptable answers include: - Insulation / prevention of heat loss / keeping the body warm; - Protection of vital/internal organs (e.g. kidneys, heart) from shock/damage; - Structural component of cell membranes; - Source / carrier of fat-soluble vitamins (A, D, E, K); - Satiety / feeling of fullness.

The majority of chemical digestion and nutrient absorption takes place in the small intestine (specifically the ileum). The inner wall of the small intestine is highly folded and covered with millions of microscopic, finger-like projections called villi, which vastly increase the surface area available for absorption.

Award 1 mark for identifying the small intestine (accept ileum) and 1 mark for naming the villi (accept microvilli). [Total: 2 marks]

(a) Pepsin [1 mark]
(b) Explains that the stomach secretes hydrochloric acid [1 mark] which creates an acidic environment (low pH) necessary for the activation/optimum function of pepsin [1 mark].
(c) Amino acids [1 mark] and peptides / dipeptides / tripeptides [1 mark].

(a) Award 1 mark for pepsin.
(b) Award up to 2 marks:
- 1 mark for mentioning hydrochloric acid / acidic environment / low pH.
- 1 mark for explaining that pepsin needs this acidity to be activated or to work at its optimum level.
(c) Award up to 2 marks (1 mark for each valid end product):
- Amino acids
- Peptides / dipeptides / tripeptides

(a) 1 mark for each correct symptom up to a maximum of 3 marks:
- scurvy;
- bleeding / swollen gums;
- slow healing of wounds / cuts;
- bruising easily;
- pain / swelling in joints;
- weakened immune system / susceptibility to infections;
- fatigue / weakness;
- loose teeth;
- dry / rough skin.
(b) 1 mark for stating that it is water-soluble [1 mark] and 1 mark for explaining that excess is excreted / cannot be stored in the body [1 mark].

(a) Award 1 mark for each of three valid deficiency symptoms/conditions up to a maximum of 3 marks.
(b) Award 2 marks for a clear explanation:
- 1 mark for identifying it is water-soluble.
- 1 mark for explaining that it cannot be stored / is excreted in urine / needs daily replacement.

(a) 1 mark for each of the following conditions (max 3):
- warmth / suitable temperature;
- moisture / liquid;
- food / sugar / carbohydrate;
- time.
(b) Explains that yeast is a living organism/microorganism [1 mark] and that boiling liquid/excessive heat kills the yeast/denatures yeast enzymes, halting fermentation/preventing the production of CO2 gas [1 mark].

(a) Award 1 mark for each of three correct conditions (warmth, moisture, food/sugar, time) up to 3 marks.
(b) Award up to 2 marks:
- 1 mark for stating that yeast is a living organism / contains enzymes.
- 1 mark for explaining that boiling water kills the yeast / denatures enzymes, stopping fermentation / gas production.

(a) Explains that the sugar creates a concentrated solution / high osmotic pressure [1 mark] which draws water out of the micro-organisms by osmosis, dehydrating them and preventing multiplication [1 mark].
(b) 1 mark for each correct factor/step (max 3):
- boiling / high temperatures used during cooking (kills microbes);
- use of sterile / boiled jars;
- acid content / low pH of fruit;
- sealing jars with airtight lids / wax discs / excluding air / oxygen.

(a) Award up to 2 marks:
- 1 mark for mentioning high sugar concentration / high osmotic pressure / osmosis.
- 1 mark for explaining that water is drawn out of microbial cells / dehydrates cells, preventing growth.
(b) Award 1 mark for each of three valid preservation factors/steps up to 3 marks:
- High temperature / boiling (kills micro-organisms)
- Sterilising jars before filling
- Low pH / high acidity (from fruit/lemon juice)
- Airtight sealing / wax discs (excludes oxygen/microbes)

(a) (i) Keeping the butter cold ensures it doesn't melt while rubbing it into the flour. This keeps the fat solid, which helps create a light, crumbly texture (shortness) in the baked pastry and prevents oiliness.
(ii) Rolling in one direction avoids overworking the gluten, which would cause the pastry to shrink during baking. Turning the pastry ensures an even circular shape and thickness. Using minimal flour prevents the dough from becoming too dry and tough.
(b) (i) When the egg custard is baked, heat denatures the egg proteins. They untangle and then bond together (coagulate) to form a three-dimensional gel network that traps the liquid milk, creating a set structure.
(ii) Custard separates or weeps (syneresis) if the protein network squeezes out liquid. This is caused by overcooking, high oven temperatures, or having too little sugar to protect the proteins.

(a) (i) [2 marks]
- Prevents the fat/butter from melting during rubbing-in / keeps fat solid [1]
- Ensures a short/crumbly texture / prevents pastry from becoming greasy [1]

(ii) [3 marks]
Award 1 mark for each valid rule up to 3:
- Roll in one direction only / do not roll back and forth (to prevent gluten development) [1]
- Lift and rotate the pastry regularly / do not turn it over (to keep even thickness/shape) [1]
- Use a light dusting of flour on the board/pin (to prevent sticking without drying out dough) [1]
- Roll with light, even pressure / do not press too hard (to avoid squeezing out trapped air/fat) [1]

(b) (i) [2 marks]
- Definition of coagulation: setting/hardening of proteins due to heat [1]
- Application to egg custard: forming a solid/gel network that traps the liquid milk [1]

(ii) [3 marks]
Award 1 mark for each valid reason up to 3:
- Oven temperature was too high / baked too fast [1]
- Cooked for too long / overbaked [1]
- Incorrect ingredient ratios (e.g., too much liquid, too little egg) [1]
- Poor mixing/whisking of eggs and milk before baking [1]

(a) (i) Yeast is a living microorganism that requires warmth (around 25-37°C) to activate enzymes, moisture (water) to dissolve nutrients, and food (fermentable carbohydrates/starch from flour) to produce carbon dioxide.
(ii) The gas produced during fermentation is carbon dioxide, which expands when heated to make the dough rise.
(b) Kneading is the physical manipulation of dough to develop the gluten proteins. This forms an elastic network. Proving is the fermentation stage where the dough is left to rise in a warm, draft-free place, allowing yeast to produce gas bubbles that expand the gluten network.
(c) Baking causes rapid expansion of gases (oven spring) followed by the death of yeast at high temperatures. The gluten protein then coagulates, and starch gelatinises to set the crumb structure. Dextrinisation of starch on the outer surface produces a brown, flavorful crust.

(a) (i) [3 marks]
Award 1 mark for each correct condition:
- Warmth / correct temperature (25–37 °C) [1]
- Moisture / liquid/water [1]
- Food / starch/sugar [1]
- Time [1]

(ii) [1 mark]
- Carbon dioxide / \(CO_2\) [1]

(b) [4 marks]
- Kneading description/purpose: stretching/pulling the dough to develop gluten/elasticity [1] to trap gas / give structure [1]
- Proving description/purpose: leaving dough in a warm place to rise / double in size [1] to allow fermentation to continue / expand the dough [1]

(c) [2 marks]
Award 1 mark for each change up to 2:
- Yeast is killed by high heat, stopping fermentation [1]
- Carbon dioxide gas expands, causing rolls to rise / oven spring [1]
- Gluten coagulates/sets, forming permanent structure [1]
- Starch dextrinises on the outer surface, forming a brown crust [1]
- Moisture is lost / steam evaporates [1]

(a) (i) Starch thickening (gelatinisation) happens in stages: first, starch granules absorb milk liquid and swell as they are heated (around 60°C). Around 80°C, they rupture, releasing starch molecules that trap water and form a thick gel network near boiling point.
(ii) Continuous stirring is essential because ungelatinised starch granules are heavy and will sink to the bottom. Without stirring, they clump together and stick to the hot pan, burning and creating a lumpy, uneven sauce.
(b) (i) The main heat transfer method inside a closed oven cavity is convection, supplemented by radiation from the hot oven walls.
(ii) Convection works because hot air expands and rises, creating space for cooler, denser air to flow downwards. This continuous movement of air molecules creates convective currents that surround the pie, transferring heat energy from the air to the dish.
(c) Cheddar cheese is rich in essential nutrients: Calcium, which works with phosphorus to mineralise bones; and HBV protein, containing all essential amino acids necessary for cellular repair and maintenance.

(a) (i) [3 marks]
Award 1 mark for each stage of gelatinisation:
- Starch granules absorb liquid (milk) [1]
- Granules swell/expand as they heat up (at approx. 60°C) [1]
- Granules burst/rupture near boiling point (at approx. 80°C), releasing starch to form a thick gel/sauce [1]

(ii) [2 marks]
Award 1 mark for each reason:
- Prevents starch granules from settling at the bottom and forming lumps [1]
- Prevents the sauce from burning / sticking to the base of the pan [1]
- Distributes heat evenly throughout the mixture [1]

(b) (i) [1 mark]
- Convection [1]

(ii) [2 marks]
Award 1 mark for each explanation point:
- Air is heated, expands, becomes less dense and rises [1]
- Cooler, denser air sinks, creating circular convection currents to transfer heat [1]

(c) [2 marks]
Award 1 mark for each nutritional benefit (must state nutrient and function):
- Calcium for the development/maintenance of strong bones and teeth [1]
- HBV protein for growth / repair of body cells [1]
- Vitamin A for healthy skin / night vision [1]
- Fat/energy to provide warmth/vitality [1]
- Vitamin D to assist in the absorption of calcium [1]

(a) Roles of salt in yeast dough: 1. Controls yeast activity by slowing down fermentation, preventing the dough from over-rising. 2. Strengthens the gluten network, making the dough more elastic and able to trap gas. 3. Enhances the flavor of the finished bread. (b) Physical changes during proving: 1. The dough increases in volume / doubles in size. 2. The dough becomes lighter, less dense, and more aerated. 3. The surface of the dough becomes smooth and stretched/domed. (c) Reasons for a hot oven (220 degrees C): 1. Rapid expansion of gases (carbon dioxide and steam) occurs quickly, known as 'oven spring', giving the bread a good volume. 2. The high heat kills the yeast, stopping fermentation so the rolls do not collapse. 3. Starch gelatinises and gluten coagulates, setting the structure and shape of the rolls. 4. Dextrinisation of starch on the outer surface occurs, forming a brown, crisp crust.

(a) Award 1 mark for each valid role explained (max 2 marks): - Controls/regulates yeast activity / slows down fermentation. - Strengthens gluten / improves dough elasticity. - Adds/improves flavour. - Helps to tighten the dough structure. (b) Award 1 mark for each valid physical change described (max 3 marks): - Volume increases / doubles in size. - Dough becomes lighter/spongy/more aerated/less dense. - Surface becomes stretched / smooth / domed. - Gluten relaxes slightly, allowing expansion. (c) Award 1 mark for each valid reason stated (max 3 marks): - To achieve 'oven spring' / rapid expansion of gases (CO2/water vapour). - To kill yeast / stop fermentation / prevent over-fermentation. - To gelatinise starch / coagulate gluten to set the structure/shape. - To form the crust / dextrinise starch on the surface (browning).

(a) Process of gelatinisation: 1. When starch granules are heated in a liquid (at around 60 degrees C), they begin to absorb the liquid. 2. The starch granules swell significantly as they absorb more water. 3. Around 80 degrees C, the swollen starch granules rupture or burst, releasing starch (amylose and amylopectin) into the liquid. 4. The released starch forms a network that traps the water molecules, causing the mixture to thicken. 5. The process is completed at boiling point (100 degrees C), forming a thick, smooth gel. (b) Practical guidelines to prevent lumps: 1. Coat flour/starch grains with fat (forming a roux) before adding any liquid to keep the grains separated. 2. Add the milk/liquid gradually, stirring or whisking constantly to ensure the liquid is smoothly incorporated. 3. Stir or whisk the sauce continuously while heating to prevent the heavy starch grains from settling at the bottom and sticking together.

(a) Award 1 mark for each point up to a maximum of 4 marks: - Starch granules absorb water/liquid at around 60 degrees C. - Granules swell / increase in size. - Granules burst/rupture at around 80 degrees C. - Starch/amylose is released into the liquid. - Liquid is trapped in a starch network/grid to thicken the mixture. - Process completes / thick gel forms at boiling point (100 degrees C). (b) Award 1 mark for each practical guideline suggested (max 3 marks): - Mix starch with fat (roux) / blend starch with cold liquid before heating. - Add liquid gradually/slowly. - Stir / whisk continuously during the heating/thickening phase. - Heat gently/moderately to avoid localized overheating/clumping. - Use a balloon whisk to break up any tiny pockets of dry flour.

Nutritional Requirements of the Elderly:
- **Energy:** Requirements decrease with age due to a declining basal metabolic rate (BMR) and a generally less active lifestyle. Intakes of carbohydrates and fats should be reduced to avoid excess weight gain, but foods should remain nutrient-dense.
- **Protein:** Essential for the repair of worn-out tissues, muscle maintenance, and supporting the immune system. High biological value (HBV) sources (e.g., eggs, milk, lean fish/meat) are ideal.
- **Calcium & Vitamin D:** Crucial for maintaining bone mineral density, preventing bone loss, and reducing the risk of fractures/osteoporosis. Vitamin D is essential for the absorption of calcium.
- **Iron & Vitamin C:** Iron is required to prevent anaemia and transport oxygen. Vitamin C is needed to enhance the absorption of non-haem iron, maintain healthy skin, heal wounds, and act as an antioxidant to boost immunity.
- **Dietary Fibre (NSP):** Slower digestion and reduced muscle tone in the gut can lead to constipation in older adults. NSP encourages bowel movements and prevents digestive disorders.
- **Water & Fluids:** Preventing dehydration is vital, as the sensation of thirst often diminishes with age. Fluids also aid kidney function and prevent constipation.
- **B Vitamins (especially B12):** Crucial for nervous system health and red blood cell formation; absorption of B12 can decrease in older age.

Meal Planning, Preparation, and Cooking to Reduce Osteoporosis and CHD:
- **Preventing Osteoporosis:**
- Include dairy products (milk, yogurt, cheese) or calcium-fortified plant-based alternatives.
- Utilize canned fish with soft, edible bones (e.g., salmon, sardines) for both calcium and vitamin D.
- Include green leafy vegetables (e.g., spinach, broccoli) and sesame seeds as plant sources of calcium.
- Ensure vitamin D is present by using eggs, oily fish, and fortified breakfast cereals, alongside safe sunlight exposure.
- **Preventing Coronary Heart Disease (CHD):**
- **Reduce Saturated Fat:** Choose lean cuts of meat, skinless poultry, and low-fat dairy products. Use unsaturated plant oils (e.g., olive oil, rapeseed oil) instead of butter, lard, or ghee.
- **Incorporate Oily Fish:** Serve mackerel, salmon, or sardines twice a week to provide omega-3 fatty acids, which help prevent blood clots and reduce bad cholesterol.
- **Increase Soluble Fibre:** Plan meals with oats, barley, pulses (lentils, beans), and vegetables to help bind cholesterol in the gut and lower blood cholesterol levels.
- **Reduce Salt:** Avoid processed meats, canned soups, and salty snacks. Use herbs, spices, lemon juice, garlic, and onions to flavor dishes instead of adding salt during preparation, which helps manage hypertension (a risk factor for CHD).
- **Cooking Methods:** Employ healthy, low-fat cooking techniques such as grilling, baking, steaming, boiling, or poaching rather than deep-fat frying or roasting with excess fat.
- **Special Preparation Guidelines:**
- Prepare soft, easy-to-chew meals (e.g., stews, minced meat, purees, soups) if the individual suffers from dental decay or poorly fitting dentures.
- Serve smaller, more frequent meals throughout the day if appetite is low, and ensure food is visually appealing with a variety of colors to stimulate interest.

Award marks based on the quality and depth of the discussion, up to a maximum of 15 marks.

**Nutritional Requirements [Max 8 marks]**
- Energy: needs decrease due to lower BMR/activity; limit fats/carbs to prevent obesity [1]
- Protein: for repair of body tissues / muscle maintenance; HBV foods [1]
- Calcium: for strong bones / maintains bone density [1]
- Vitamin D: assists absorption of calcium / maintains bones [1]
- Iron: prevents anaemia / red blood cell formation [1]
- Vitamin C: assists absorption of iron / antioxidant / immune support [1]
- Dietary Fibre (NSP): prevents constipation / aids bowel movements [1]
- Water/Fluids: prevents dehydration / helps kidneys / works with fibre [1]
- Vitamin B12: for healthy nervous system / prevents pernicious anaemia [1]

**Meal Planning, Preparation, and Cooking [Max 8 marks]**
- Osteoporosis prevention: use calcium-rich foods (e.g. dairy, fortified alternatives, green leafy vegetables) [1]; use vitamin D sources (e.g. eggs, oily fish, fortified spreads) [1].
- CHD prevention: reduce saturated/trans fats (use lean meat, skinless poultry, low-fat dairy) [1]; use monounsaturated/polyunsaturated vegetable oils instead of solid animal fats [1]; include oily fish (omega-3) to lower cholesterol [1]; include soluble fibre (oats, pulses, fruits) to lower blood cholesterol [1]; reduce sodium/salt intake to prevent high blood pressure (use herbs/spices instead of salt) [1]; use healthy cooking methods (grilling, baking, steaming, poaching) instead of frying [1].
- Special preparation: make texture soft/easy to chew for dental/denture issues [1]; serve small, frequent, attractive meals to stimulate flagging appetites [1].