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

(a) Basal Metabolic Rate (BMR) is defined as the minimum amount of energy required by the body to maintain its life-sustaining vital processes (such as breathing and heart rate) when the body is at complete rest and in a post-absorptive state. (b) Factors that increase BMR include: 1. Younger age (due to rapid growth and cell division). 2. Male gender (higher proportion of muscle tissue). 3. Larger body surface area or height. 4. Higher percentage of muscle mass (metabolically active tissue). 5. Pregnancy or lactation (increased metabolic demands). 6. Fever, illness, or elevated body temperature.

(a) Award 1 mark for mentioning 'minimum energy required' and 1 mark for 'at complete rest/to maintain vital functions'. (Max 2 marks) (b) Award 1 mark for each of any four correct factors listed. (Max 4 marks)

(a) Megaloblastic anaemia (also accept folate-deficiency anaemia). (b) Three functions of folate are: 1. Essential for the synthesis of DNA and RNA, which is crucial for rapid cell division. 2. Required for the formation and maturation of red blood cells. 3. Essential for the normal development of the neural tube in a growing foetus to prevent spina bifida. (c) Two good plant sources of folate: 1. Green leafy vegetables (such as spinach or broccoli). 2. Legumes (such as lentils, chickpeas, or beans).

(a) Award 1 mark for megaloblastic anaemia (accept anaemia). (b) Award 1 mark for each of three correct functions. (Max 3 marks) (c) Award 1 mark for each of two correct plant sources. (Max 2 marks)

(a) Lactose is the carbohydrate found in milk. (b) Pasteurisation is a mild thermal process (e.g. heating to 72 degrees Celsius for 15 seconds) to destroy disease-causing micro-organisms and extend shelf-life. Homogenisation is a physical process that breaks fat globules into tiny droplets so they remain evenly dispersed throughout the milk and do not separate as a cream layer. (c) Whole milk is important for young children because: 1. It provides calcium and phosphorus, which are vital for the calcification of bones and teeth. 2. It contains high biological value (HBV) protein needed for muscle growth and tissue repair. 3. It is a good source of fat-soluble vitamin A, which supports healthy vision and immune function.

(a) Award 1 mark for lactose. (b) Award 1 mark for explaining pasteurisation (heat treatment/kills pathogens) and 1 mark for explaining homogenisation (breaking down fat globules/preventing fat separation). (c) Award 1 mark for each nutritional reason (nutrient + valid function for young children). (Max 3 marks)

(i) Gastric juice is secreted by the stomach walls. (ii) Hydrochloric acid (HCl) creates a highly acidic environment (pH 1.5 to 2.0) that: 1. Kills bacteria present in food. 2. Activates the inactive enzyme precursor pepsinogen into active pepsin. 3. Denatures proteins, unfolding their tertiary structure so digestive enzymes can easily access the peptide bonds. (iii) The active enzyme is pepsin. Its action is to break down complex proteins (long polypeptide chains) into shorter chains called peptones or polypeptides.

(i) Award 1 mark for gastric juice. (ii) Award 1 mark for mentioning 'activates pepsinogen/creates acidic pH' and 1 mark for 'denatures proteins'. (Max 2 marks) (iii) Award 1 mark for naming pepsin. Award 2 marks for its chemical action (converts proteins [1] into polypeptides/peptones [1]).

(a) The three points of the work triangle are: 1. The food storage area / refrigerator. 2. The preparation and wash-up area / sink. 3. The cooking area / cooker or hob. (b) Benefits: 1. Efficiency: It minimizes the distance the cook has to walk between these highly frequented areas, saving energy and time. 2. Safety: It prevents cross-traffic through the main preparation path, which reduces the risk of accidents, trips, or spilling hot liquids.

(a) Award 1 mark for each of the three points: refrigerator (storage), sink (wash-up), cooker (cooking). (Max 3 marks) (b) Award 1 mark for each of two well-explained benefits (one related to efficiency, one to safety, or both clearly explained). (Max 2 marks)

(a) The four essential conditions for rapid bacterial multiplication are: 1. Warmth (temperatures within the danger zone). 2. Moisture (water activity). 3. Food (nutrients, especially proteins). 4. Time (to replicate via binary fission). (b) The danger zone is the temperature range between 5 degrees Celsius and 63 degrees Celsius (or 40 degrees Fahrenheit to 140 degrees Fahrenheit) in which bacteria grow and multiply most rapidly.

(a) Award 1 mark for each correct condition listed (warmth, moisture, food, time, oxygen, neutral pH). (Max 4 marks) (b) Award 1 mark for defining the range as 5 degrees Celsius to 63 degrees Celsius (accept 4 degrees Celsius to 60 degrees Celsius depending on local standards, but 5 to 63 is standard).

(a) Guidelines: 1. Reduce consumption of saturated fats and trans fats. 2. Increase intake of soluble dietary fibre (NSP). 3. Reduce sodium (salt) intake. (b) Explanations: 1. Saturated and trans fats raise Low-Density Lipoprotein (LDL) cholesterol in the blood, which can build up as fatty plaques in coronary arteries (atheroma) and lead to heart attacks. 2. Soluble fibre binds to bile acids and dietary cholesterol in the digestive tract, promoting their excretion and thereby lowering overall blood cholesterol levels. 3. Excess sodium leads to fluid retention and high blood pressure (hypertension), which strains the cardiovascular system and damages arterial walls, increasing CHD risk.

(a) Award 1 mark for each of three valid dietary guidelines. (Max 3 marks) (b) Award 1 mark for each explanation that scientifically links the guideline to a mechanism reducing CHD (e.g. fat/cholesterol, fibre/excretion, salt/blood pressure). (Max 3 marks)

Part (a): 1. Short muscle fibres (myotomes). 2. Thin connective tissue (myocommata) holding the myotomes together. 3. Bones/skeleton.

Part (b): 1. Connective tissue (collagen) liquefies and converts to gelatin, causing the muscle flakes to separate easily. 2. Muscle proteins denature and coagulate, changing the texture from soft to firm and the appearance from translucent to opaque.

Part (c): 1. High in Omega-3 fatty acids for brain development and cognitive function. 2. Excellent source of high biological value (HBV) protein for rapid physical growth and cell repair. 3. Rich in Vitamin D to aid the absorption of calcium for strong bone mineralisation. 4. Provides Vitamin A for healthy eyesight and visual purple formation.

Part (a): Award 1 mark for each named structural component of white fish (max 3):
- Short muscle fibres / myotomes [1]
- Connective tissue / myocommata [1]
- Bones / skeleton [1]
- Skin [1]

Part (b): Award up to 2 marks for each well-described physical change during steaming (max 4):
- Conversion of collagen/connective tissue to soluble gelatin [1] which causes the fish to flake apart easily [1].
- Coagulation of muscle proteins [1] transforming the flesh from translucent/soft to opaque and firm [1].

Part (c): Award 1 mark for each distinct nutritional benefit clearly linked to adolescent health (max 4):
- Omega-3 fatty acids for cognitive function/brain health [1]
- HBV protein for rapid growth spurts / muscle development [1]
- Vitamin D to assist calcium absorption / strong teeth and bones [1]
- Vitamin A for night vision / clear skin / immune support [1]

Part (a): The primary raising agent is air. It is incorporated mechanically by intense whisking of whole eggs and sugar, trapping air bubbles in the protein foam.

Part (b): 1. Warmth (optimum temperature of 25-35°C). 2. Moisture (liquid like water or milk). 3. Food (sugar or starch).

Part (c): Choux pastry contains a very high proportion of liquid. During baking in a hot oven, the water boils and turns into steam. The steam expands rapidly, forcing the gluten network to stretch and rise. The intense heat eventually coagulates the egg and flour proteins, setting the structure with a hollow centre.

Part (a):
- Identify air as the raising agent [1]
- Explain mechanical incorporation: intense whisking of eggs and sugar traps air bubbles [1]
- Form a stable protein foam [1]

Part (b): Award 1 mark for each correct condition named (max 3):
- Warmth / suitable temperature [1]
- Moisture / liquid [1]
- Food / sugar [1]
- Time [1]
(Note: Reject oxygen as yeast can ferment anaerobically)

Part (c): Award 1 mark for each point explained (max 5):
- High liquid/water content in choux paste [1]
- Hot oven turns liquid to steam [1]
- Steam expands to 1600 times its original volume, pushing pastry up [1]
- Gluten/egg protein stretches to trap the expanding steam [1]
- Heat coagulates the proteins to set the shape [1]

Part (a): The work triangle is an ergonomic design concept representing the path between the three primary kitchen work areas: the food preparation/sink area, the cooking/cooker area, and the storage/refrigerator area. It aims to minimise movement and maximise efficiency.

Part (b): 1. Use a designated, separate colour-coded chopping board (e.g., red) for raw poultry. 2. Wash hands thoroughly with warm soapy water immediately after handling raw poultry. 3. Do not wash raw poultry under the tap to prevent aerosol splashing of bacteria.

Part (c): 1. Non-slip texture to prevent accidents from spills. 2. Seamless / minimal grout lines to prevent dirt and bacteria accumulation. 3. Waterproof / non-porous material for easy cleaning. 4. Durable and resistant to heavy wear and cleaning chemicals.

Part (a):
- Definition: Ergonomic design path to improve workflow/efficiency [1]
- Sink/washing area [1]
- Cooker/stove/cooking area [1]
- Refrigerator/food storage area [1]

Part (b): Award 1 mark for each valid safety practice (max 3):
- Separate chopping boards [1]
- Hand hygiene immediately after handling [1]
- Avoiding washing poultry [1]
- Sanitising utensils/surfaces after use [1]

Part (c): Award 1 mark for each feature with an explanation (max 4):
- Non-slip/slip-resistant to prevent falls [1]
- Non-porous/impermeable so liquids are not absorbed [1]
- Seamless/easy to clean to prevent dirt build-up [1]
- Durable/hard-wearing to withstand cleaning agents [1]

Part (a): Milk is heated to a very high temperature (around 135-150°C) for a very short duration (1-4 seconds) and then rapidly cooled. The high heat destroys all spoilage bacteria and pathogenic microorganisms, while the extremely short time limits the degradation of heat-sensitive vitamins (like B12 and C) and keeps the flavour intact.

Part (b): 1. To extend the shelf-life of products by inhibiting microbial growth. 2. To prevent oxidation and rancidity in fats/oils. 3. To maintain or enhance the colour/appearance of the food product.

Part (c): 1. Blanch the vegetables in boiling water before freezing to deactivate enzymes that cause spoilage and loss of colour. 2. Freeze the vegetables rapidly to minimize the size of ice crystals, which prevents cellular damage. 3. Use moisture-proof, airtight packaging to prevent freezer burn. 4. Label the packages with the date and food name to ensure proper rotation and use within safe timeframes.

Part (a): Award 1 mark for each point (max 4):
- Milk heated to 135-150°C [1]
- Short holding time of 1-4 seconds [1]
- Rapid cooling / aseptic packaging [1]
- Short exposure minimizes damage to heat-sensitive nutrients/taste [1]

Part (b): Award 1 mark for each valid reason (max 3):
- Shelf-life extension [1]
- Prevention of oxidation/rancidity [1]
- Preservation of colour/texture [1]
- Reduction of economic food waste [1]

Part (c): Award 1 mark for each guideline with justification (max 4):
- Blanching to destroy/inactivate enzymes [1]
- Quick freezing to keep ice crystals small/protect cell walls [1]
- Airtight packaging to prevent freezer burn/drying [1]
- Labeling with date for rotation/FIFO [1]

The solution should comprehensively address two main areas: the specific nutrients of concern for teenagers on a vegan diet (undergoing rapid growth and development) and practical meal planning strategies using plant-based foods. Candidates must demonstrate detailed knowledge of protein complementation, non-haem iron absorption, bone-building nutrients (calcium and vitamin D), and vitamin B12 sourcing, which are key vegan nutrition principles. Effective plant-based food examples (e.g., tofu, fortified milks, pulses, seeds) should be integrated throughout.

Nutritional requirements [max 9 marks]:
- Protein for growth/muscle repair [1 mark]; explanation of LBV/protein complementation [1 mark].
- Iron for haemoglobin/anaemia prevention [1 mark]; mention of teenage girls' needs due to menstruation [1 mark].
- Vitamin C to aid non-haem iron absorption [1 mark]; with practical source (e.g., citrus fruit) [1 mark].
- Calcium/Vitamin D for bone and teeth development [1 mark]; vegan source (e.g., fortified milk, tofu, green leafy vegetables) [1 mark].
- Vitamin B12 for red blood cells/nerves [1 mark]; must be from fortified foods or supplements [1 mark].
- Energy/Carbohydrate for high metabolic/activity rates [1 mark].
- Omega-3 for brain/heart health (e.g., seeds/nuts) [1 mark].

Meal planning strategies [max 6 marks]:
- Mixing grains and pulses (complementation) in meals [1 mark].
- Use of fortified foods for B12, D, and Calcium [1 mark].
- Pairing iron-rich foods with vitamin C-rich foods in the same meal [1 mark].
- Using nutrient-dense ingredients (seeds, nuts) to increase energy density [1 mark].
- Incorporating versatile soya-based HBV protein sources (tofu, soya mince) [1 mark].
- Providing a variety of textures/colours to make dishes appealing and nutritionally diverse [1 mark].