Diet

1. Overview

Diet refers to the food and drink consumed by an organism. This topic explores the components of a balanced diet, the specific biological roles of different nutrients, and the health consequences that arise when certain essential substances are missing from our intake.

Key Definitions

• Balanced Diet: A diet that contains all the essential nutrients (carbohydrates, fats, proteins, vitamins, minerals, fibre, and water) in the correct proportions to maintain health.
• Nutrient: A substance that provides nourishment essential for the maintenance of life and for growth.
• Deficiency Disease: A disease caused by the lack of an essential nutrient in the diet.
• Peristalsis: The wave-like muscular contractions of the digestive tract that move food along, aided specifically by dietary fibre.

Core Content

The Balanced Diet

A balanced diet is not the same for everyone; it varies depending on:

• Age: Children need more protein for growth and more energy per gram of body mass.
• Gender: Generally, males have higher energy requirements; females may require more iron due to menstruation.
• Activity Level: Active individuals require more carbohydrates for cellular respiration.
• Pregnancy/Lactation: Pregnant women need more energy, calcium, and iron to support fetal development.

Principal Dietary Sources and Importance

Nutrient	Principal Sources	Biological Importance / Function
(a) Carbohydrates	Rice, pasta, bread, potatoes	Primary source of energy for cellular respiration.
(b) Fats and Oils	Butter, oil, nuts, fatty fish	Long-term energy storage, thermal insulation, and making cell membranes.
(c) Proteins	Meat, fish, eggs, beans	Growth and repair of tissues; making enzymes and antibodies.
(d) Vitamin C	Citrus fruits (lemons, oranges)	Used in the synthesis of collagen (protein for skin, hair, and gums).
(e) Vitamin D	Eggs, oily fish, made in skin by sunlight	Helps the body absorb calcium for strong bones and teeth.
(f) Calcium (ion)	Milk, cheese, green leafy vegetables	Required for strong bones and teeth; essential for blood clotting.
(g) Iron (ion)	Red meat, spinach, liver	Component of haemoglobin; used to transport oxygen in red blood cells.
(h) Fibre	Vegetables, wholemeal bread, fruit	Provides bulk to help food move through the gut via peristalsis; prevents constipation.
(i) Water	Drinks, juicy fruits/vegetables	Acts as a solvent for chemical reactions; used for transport (blood) and temperature regulation (sweat).

Deficiency Diseases

• Scurvy:
  • Cause: A deficiency of Vitamin C.
  • Symptoms: Bleeding gums, loss of teeth, and wounds that do not heal properly because the body cannot produce enough collagen.
• Rickets:
  • Cause: A deficiency of Vitamin D or Calcium.
  • Symptoms: Softening and weakening of the bones, which can lead to "bow-leggedness" or bone deformities in children.

Linking Nutrients to Deficiency Diseases

When asked to explain a deficiency, connect: what the nutrient does → what happens without it.

Example: Why does iron deficiency cause tiredness? Iron is needed to make haemoglobin in red blood cells. Haemoglobin carries oxygen from the lungs to respiring cells. Without enough iron → less haemoglobin → less oxygen transported → cells cannot respire as efficiently → the person feels tired and weak. This condition is called anaemia.

Example: Why does vitamin C deficiency cause bleeding gums? Vitamin C is needed to make collagen, a protein that holds skin and gum tissue together. Without vitamin C → collagen breaks down → gums become weak and bleed easily. This condition is called scurvy.

The pattern is always: nutrient → what it builds/does → what fails without it → the symptom.

Extended Content (Extended Only)

There are no specific supplemental learning objectives for Topic 7.1: Diet.

Key Equations

There are no specific mathematical equations for this sub-topic; however, students should be able to compare nutritional data in tables.

Worked Example: Calculating Percentage Energy If a food item contains 2000kJ of total energy and 500kJ comes from fat:

• $\text{Percentage energy from fat} = (\frac{\text{Energy from fat}}{\text{Total energy}}) \times 100$
• $(500 \div 2000) \times 100 = 25%$

Common Mistakes to Avoid

• ❌ Wrong: Fibre is a nutrient that provides us with energy.
• ✓ Right: Fibre cannot be digested; its role is to provide bulk to the diet to help food move through the alimentary canal.
• ❌ Wrong: Vitamin D and Calcium have the same function.
• ✓ Right: While both are related to bone health, Calcium is the structural material, and Vitamin D is the chemical that allows the body to absorb and use that calcium.
• ❌ Wrong: Everyone needs the same "Balanced Diet."
• ✓ Right: A balanced diet is specific to an individual's age, gender, and activity level.

Exam Tips

• Command Words: If a question asks you to "State," provide a short, one-word or one-sentence answer (e.g., "Iron"). If it asks you to "Describe," you must explain the source or the function in more detail.
• Real-World Contexts: Expect questions comparing the diets of different people (e.g., an office worker vs. a marathon runner). Always link your answer to energy requirements or tissue repair.
• Typical Values: While you don't need to memorize exact numbers, remember that fat contains roughly twice as much energy per gram (37kJ/g) as carbohydrates or proteins (17kJ/g).
• Hemoglobin Link: When discussing Iron, always mention "haemoglobin" and "oxygen transport" to get the full biological marks.

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Exam-Style Questions

Practice these original exam-style questions to test your understanding. Each question mirrors the style, structure, and mark allocation of real Cambridge 0610 Theory papers.

Exam-Style Question 1 — Short Answer [6 marks]

Question:

(a) Define the term 'balanced diet'. [2]

(b) State two reasons why water is an essential part of a balanced diet. [2]

(c) Explain why a diet deficient in vitamin D can lead to weakened bones. [2]

Worked Solution:

(a)

1. A balanced diet contains all the necessary nutrients. A balanced diet is a diet that contains all the necessary nutrients. This is the basic definition.

2. These nutrients are present in the correct proportions. ...in the correct proportions. This completes the definition.

How to earn full marks:

• State that a balanced diet contains all necessary nutrients.
• State that these nutrients are in the correct proportions.

(b)

1. Water acts as a solvent in the body. Water acts as a solvent for reactions in cells. This is one reason.

2. Water transports substances around the body. Water transports substances, such as nutrients and waste products, around the body. This is the second reason.

How to earn full marks:

• State that water acts as a solvent.
• State that water transports substances.

(c)

1. Vitamin D helps the body absorb calcium. Vitamin D is needed for the absorption of calcium from food in the gut. This is the link between Vitamin D and calcium.

2. Calcium is needed for strong bones. Calcium is needed for the formation and maintenance of strong bones. This explains the effect on bones.

How to earn full marks:

• Explain that vitamin D is needed for calcium absorption.
• Explain that calcium is needed for strong bones.

Common Pitfall: A common mistake is to only give one part of the definition of a balanced diet, such as mentioning the nutrients but forgetting the correct proportions. Also, remember to be specific when explaining the link between vitamin D and calcium – it's about absorption, not just that both are needed for bones.

Exam-Style Question 2 — Short Answer [5 marks]

Question:

(a) Identify one principal dietary source of each of the following nutrients: (i) Iron [1] (ii) Vitamin C [1]

(b) State one function of fibre (roughage) in the diet. [1]

(c) A student eats a breakfast containing 60g of carbohydrate, 8g of fat, and 7g of protein. Calculate the total energy intake from this breakfast, given that: - 1g of carbohydrate provides 17kJ of energy - 1g of fat provides 38kJ of energy - 1g of protein provides 17kJ of energy [2]

Worked Solution:

(a) (i) Iron is found in red meat. Red meat $\boxed{}$ This is a good source of iron.

(ii) Vitamin C is found in citrus fruits. Citrus fruits $\boxed{}$ This is a good source of vitamin C.

How to earn full marks:

• State red meat or liver for iron.
• State citrus fruits, peppers, or broccoli for Vitamin C.

(b)

1. Fibre adds bulk to the faeces. Fibre adds bulk to the faeces, which aids in peristalsis. $\boxed{}$ This is the key function.

How to earn full marks:

• State that fibre adds bulk to the faeces.

(c)

1. Calculate energy from carbohydrates. Energy from carbohydrates: $60g \times 17kJ/g = 1020kJ$ Multiply mass by energy per gram.

2. Calculate energy from fat. Energy from fat: $8g \times 38kJ/g = 304kJ$ Multiply mass by energy per gram.

3. Calculate energy from protein. Energy from protein: $7g \times 17kJ/g = 119kJ$ Multiply mass by energy per gram.

4. Calculate total energy. Total energy: $1020kJ + 304kJ + 119kJ = 1443kJ$ Add up the individual energies.

   $\boxed{1443 kJ}$

How to earn full marks:

• Calculate the energy from carbohydrates (1020kJ).
• Calculate the energy from fat (304kJ).
• Calculate the energy from protein (119kJ).
• Calculate the correct total energy (1443kJ) with correct units.

Common Pitfall: When listing sources of nutrients, be specific – saying "fruit" isn't enough for Vitamin C; you need to name a specific fruit like citrus fruits. For the calculation, remember to include the correct units (kJ) in your final answer.

Exam-Style Question 3 — Extended Response [8 marks]

Question:

A group of students investigated the effect of different diets on the growth of young rats. They divided the rats into three groups:

• Group A: fed a diet deficient in protein
• Group B: fed a diet deficient in calcium
• Group C: fed a balanced diet

The students measured the mass of each rat every week for 8 weeks.

(a) State one function of protein in the body. [1]

(b) Describe the expected results of this investigation, comparing the growth of the rats in each of the three groups. [4]

(c) Suggest two ethical considerations that the students should have taken into account when carrying out this investigation. [3]

Worked Solution:

(a)

1. Protein is used for growth and repair. Protein is used for growth and repair of tissues. $\boxed{}$ This is a key function.

How to earn full marks:

• State that protein is used for growth and repair.

(b)

1. Group C (balanced diet) will show the most growth. The rats in Group C, fed a balanced diet, are expected to show the greatest increase in mass over the 8 weeks. This is the control group.

2. Group A (protein deficient) will show the least growth. The rats in Group A, fed a diet deficient in protein, are expected to show the least increase in mass, as protein is needed for growth. This is the experimental group.

3. Group B (calcium deficient) will show less growth than Group C but more than Group A. The rats in Group B, fed a diet deficient in calcium, are expected to show less growth than Group C, but more than Group A. Calcium is needed for bone development, so a deficiency will affect growth, but not as severely as a protein deficiency. This group is intermediate.

4. The mass of Group A rats may even decrease. The mass of the rats in Group A may even decrease over time. This is more detailed.

How to earn full marks:

• State that Group C will show the most growth.
• State that Group A will show the least growth.
• State that Group B will show intermediate growth.
• Explain the reasons for the differences in growth based on the role of protein and calcium.

(c)

1. The rats should be treated humanely. The rats should be treated humanely, with proper care and housing. This is an important principle.

2. The rats should be provided with sufficient food and water. The rats should be provided with sufficient food and water, even in the deficient groups, to prevent unnecessary suffering. This mitigates the negative impact of the deficient diet.

3. The rats should be killed humanely at the end of the experiment. The rats should be killed humanely at the end of the experiment to minimise suffering. This is a standard ethical consideration.

How to earn full marks:

• State that the rats should be treated humanely.
• State that the rats should be provided with sufficient food and water (even in deficient groups).
• State that the rats should be killed humanely.

Common Pitfall: When describing the expected results, it's not enough to just say which group will grow the most or least. You need to explain why, linking the nutrient deficiency to its role in growth. Also, remember that ethical considerations are about minimizing harm and suffering to the animals.

Exam-Style Question 4 — Extended Response [9 marks]

Question:

Scurvy is a disease caused by a deficiency of vitamin C. A group of scientists investigated the effect of different amounts of vitamin C in the diet on the severity of scurvy in guinea pigs. They fed four groups of guinea pigs different diets:

• Group 1: No vitamin C
• Group 2: 5mg of vitamin C per day
• Group 3: 10mg of vitamin C per day
• Group 4: 20mg of vitamin C per day

The scientists measured the severity of scurvy in each guinea pig after 4 weeks, using a scoring system where 0 = no scurvy and 10 = severe scurvy. The results are shown in Table 1.

Table 1

Group	Vitamin C intake (mg/day)	Average scurvy score
1	0	8.5
2	5	5.2
3	10	2.1
4	20	0.5

(a) Describe the relationship between vitamin C intake and the severity of scurvy, based on the data in Table 1. [2]

(b) Explain why a deficiency of vitamin C leads to the symptoms of scurvy. [4]

(c) Suggest two ways in which the reliability of this investigation could be improved. [3]

Worked Solution:

(a)

1. As Vitamin C intake increases, the scurvy score decreases. As the vitamin C intake increases, the average scurvy score decreases. This is the overall trend.

2. The decrease in scurvy score is greater between 0mg and 10mg than between 10mg and 20mg. The decrease in scurvy score is greater between 0mg and 10mg of vitamin C than between 10mg and 20mg. This adds detail about the rate of decrease.

How to earn full marks:

• State that as vitamin C intake increases, the scurvy score decreases.
• Describe the change in the rate of decrease, i.e., that the decrease is greater at lower vitamin C intakes.

(b)

1. Vitamin C is needed for the production of collagen. Vitamin C is needed for the production of collagen. This links Vitamin C to collagen.

2. Collagen is a protein found in connective tissues. Collagen is a protein found in connective tissues, such as skin, blood vessels, and gums. This states where collagen is found.

3. A lack of collagen leads to weakened connective tissues. A deficiency of vitamin C leads to reduced collagen production, resulting in weakened connective tissues. This explains the effect of the deficiency.

4. Weakened connective tissues cause the symptoms of scurvy. Weakened connective tissues cause the symptoms of scurvy, such as bleeding gums, skin lesions, and poor wound healing. This links weakened tissues to the symptoms.

How to earn full marks:

• State that vitamin C is needed for collagen production.
• State that collagen is found in connective tissues.
• Explain that a deficiency of vitamin C leads to weakened connective tissues.
• Explain that weakened connective tissues cause the symptoms of scurvy.

(c)

1. Increase the number of guinea pigs in each group. Increase the number of guinea pigs in each group to obtain more reliable average scurvy scores. This increases the sample size.

2. Repeat the investigation. Repeat the investigation to check the consistency of the results. This checks repeatability.

3. Control environmental factors. Control environmental factors such as temperature and humidity to ensure these do not affect the results. This controls variables.

How to earn full marks:

• Suggest increasing the number of animals in each group.
• Suggest repeating the investigation.
• Suggest controlling environmental factors.

Common Pitfall: When describing the relationship in part (a), be sure to mention the trend and also look for any patterns in the rate of change. For reliability, suggesting "be more careful" isn't specific enough; you need to suggest concrete actions like increasing sample size or controlling variables.