Cambridge IGCSE0610

Diet

Biology 0610 Chapter Notes

What this chapter covers

DietDigestive systemPhysical digestionChemical digestionAbsorption
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In this chapter

  1. 1The Seven Components of a Balanced Diet
  2. 2Energy Sources: Carbohydrates and Lipids
  3. 3Growth and Repair: The Role of Proteins
  4. 4Essential Helpers: Vitamins and Minerals
  5. 5Fibre and Water: The Unsung Heroes
  6. 6Balancing Your Energy Budget
  7. 7Malnutrition and Diet-Related Diseases

1. The Seven Components of a Balanced Diet

Living organisms need food for three main reasons: to provide energy for life processes like movement and keeping warm; to provide raw materials for growth and repairing tissues; and to provide substances to keep the body healthy and functioning correctly. A diet is the total of all the food a person eats. A balanced diet is one that provides all the essential nutrients in the correct amounts and proportions to maintain health. Not eating a balanced diet leads to malnutrition. There are seven key components: carbohydrates, proteins, lipids (fats and oils), vitamins, minerals, dietary fibre, and water.

Key term

Balanced Diet: A diet that contains all the essential nutrients in the correct proportions to maintain good health.

Examiner insight

Examiners award marks for specifically mentioning 'correct proportions' or 'correct amounts' when defining a balanced diet, not just listing the nutrient groups.

Common pitfall

Stating that a balanced diet just means 'eating lots of different foods'. While variety is important, the key is getting the right *proportions* of each nutrient type.

Worked example 13 marks

A student is asked to explain why humans need to eat. They write, 'We need food for energy'. Explain why this answer is incomplete and give a more detailed explanation. [3 marks]

  1. 1

    Step 1: Identify the correct part of the student's answer. The student is correct that food provides energy.

  2. 2

    Step 2: Identify the missing information. The student has omitted the other key reasons for eating: growth and repair, and maintaining overall health.

  3. 3

    Step 3: Construct a complete answer. Food is needed for energy to fuel metabolic reactions, movement, and warmth. It is also needed to provide building blocks (like amino acids from protein) for growth and to repair damaged tissues. Finally, it provides essential vitamins and minerals needed in small amounts for various chemical processes.

Recap

  • Food provides energy, materials for growth and repair, and substances for maintaining health.
  • A balanced diet provides all seven essential nutrients in the correct amounts.
  • The seven components of a balanced diet are carbohydrates, lipids, proteins, vitamins, minerals, water, and fibre.
  • An unbalanced diet can lead to a form of malnutrition.

Quick check

  1. List the seven components of a balanced diet.2 marks
  2. State the three main reasons why organisms need food.3 marks

2. Energy Sources: Carbohydrates and Lipids

Carbohydrates and lipids (fats and oils) are the body's primary energy sources. Carbohydrates are the main and quickest source of energy. They exist as simple sugars (like glucose) for immediate energy, and complex carbohydrates (like starch and glycogen) which are large molecules that release energy more slowly. Lipids are the most concentrated energy source, providing more than double the energy per gram compared to carbohydrates. They are vital for storing energy, providing insulation against heat loss, protecting organs, and forming cell membranes. While both are crucial, an excess of them, particularly saturated fats, can lead to health problems.

Key term

Macronutrient: A type of food (e.g., fat, protein, carbohydrate) required in large amounts in the diet.

Examiner insight

Marks are often available for comparing the relative energy content of macronutrients. A precise answer will state that lipids provide approximately 37 kJ/g while carbohydrates provide around 17 kJ/g.

Common pitfall

Confusing the energy values. Students often forget that lipids provide more than double the energy per gram compared to carbohydrates and proteins.

Worked example 13 marks

A marathon runner and a person with a desk job are planning their meals for the next day. Explain which of the two would need a higher proportion of carbohydrates in their diet and why. [3 marks]

  1. 1

    Step 1: Identify the person with higher energy needs. The marathon runner will have significantly higher energy demands due to intense physical activity.

  2. 2

    Step 2: Link energy needs to carbohydrate function. Carbohydrates are the primary and most readily available source of energy for the body, especially for muscle contraction.

  3. 3

    Step 3: Conclude and explain. The marathon runner would need a higher proportion of carbohydrates to provide sufficient, readily available energy for the race. Their muscles will use large amounts of glucose in respiration to release energy. The person with a desk job has lower energy needs and requires fewer carbohydrates.

Recap

  • Carbohydrates are the main source of energy for the body.
  • Simple carbohydrates provide quick energy; complex carbohydrates release it more slowly.
  • Lipids (fats) are a rich source of stored energy and provide insulation.
  • Lipids provide more than twice the energy per gram compared to carbohydrates.
  • Good sources of carbohydrates include bread, pasta, and rice; good sources of lipids include butter, oil, and nuts.

Quick check

  1. State two functions of lipids in the body, other than as an energy source.2 marks
  2. Which type of nutrient is the body's quickest source of energy?1 mark

3. Growth and Repair: The Role of Proteins

Proteins are essential macronutrients with a vast range of functions, but their primary role is for growth and repair. They are made from smaller units called amino acids. Your body uses proteins to build new tissues, for example during growth in childhood or for muscle development. They are also used to repair damaged tissues after an injury. Beyond this, proteins have other vital jobs: enzymes (which speed up chemical reactions) are proteins, antibodies (which fight disease) are proteins, and some hormones (chemical messengers) are proteins. While proteins can be used for energy, this only happens if the body has insufficient carbohydrates and fats.

Key term

Amino Acids: The small chemical units from which proteins are built.

Common pitfall

Forgetting the wide range of protein functions. Many students only state 'growth and repair' and forget their crucial roles as enzymes, hormones, and antibodies.

Fun fact

There are 20 different amino acids used to make proteins in the human body. Nine of these are 'essential', meaning our bodies cannot make them and we must get them from our diet.

Worked example 12 marks

A doctor advises a patient recovering from major surgery to eat a protein-rich diet. Explain why this advice is important for the patient's recovery. [2 marks]

  1. 1

    Step 1: Identify the patient's situation. The patient has undergone surgery, which involves cutting and damaging tissues.

  2. 2

    Step 2: Link the situation to the function of protein. A key function of protein is to repair damaged tissues and build new cells. Therefore, an increased supply of amino acids from protein is needed to heal the surgical wounds.

Worked example 22 marks

Explain why a body-builder would consume a diet high in protein. [2 marks]

  1. 1

    Step 1: Identify the goal of a body-builder. A body-builder aims to increase their muscle mass.

  2. 2

    Step 2: Link this goal to the function of protein. Muscles are made of protein. To build larger muscles (growth), the body needs a plentiful supply of amino acids from dietary protein to synthesise new muscle protein.

Recap

  • Proteins are essential for the growth of new cells and the repair of tissues.
  • The building blocks of proteins are called amino acids.
  • Proteins are also used to make vital molecules like enzymes, antibodies, and some hormones.
  • Good sources of protein include meat, fish, eggs, dairy, beans, and nuts.
  • Protein is only used for energy if carbohydrate and fat stores are low.

Quick check

  1. State two functions of proteins in the body, apart from growth and repair.2 marks

4. Essential Helpers: Vitamins and Minerals

Vitamins and minerals are micronutrients, meaning they are needed in very small quantities but are absolutely essential for health. They do not provide energy, but they play crucial roles in a wide range of metabolic processes. A lack of a specific vitamin or mineral can lead to a deficiency disease. Key examples include: Vitamin C, needed for healthy skin and gums (a lack causes scurvy); Vitamin D, which helps the body absorb calcium for strong bones and teeth (a lack causes rickets); Calcium, the mineral that builds bones and teeth; and Iron, a mineral needed to make haemoglobin in red blood cells for oxygen transport (a lack causes anaemia).

Key term

Deficiency Disease: A disease caused by the lack of a particular essential nutrient in the diet.

Examiner insight

For full marks, students must clearly link the specific nutrient (e.g., Vitamin C) to its specific deficiency disease (e.g., scurvy). Vague answers like 'you get sick' will not be credited.

Worked example 12 marks

The following table shows the composition of four foods. Which food would be best for preventing rickets? Explain your answer. [2 marks]

FoodVitamin C / mgVitamin D / µgIron / mg
A0400
B20000
C1008
D000
  1. 1

    Step 1: Identify the cause of rickets. Rickets is a deficiency disease caused by a lack of Vitamin D (and/or calcium).

  2. 2

    Step 2: Analyse the table to find the food rich in Vitamin D. Food A contains 40 µg of Vitamin D per 100g, while the others contain none.

  3. 3

    Step 3: Formulate the answer. Food A would be best for preventing rickets because rickets is caused by a Vitamin D deficiency, and Food A is the only food listed that contains a high amount of Vitamin D.

Worked example 22 marks

Using the same table, which food would be most needed by a person suffering from anaemia? Explain your answer. [2 marks]

  1. 1

    Step 1: Identify the cause of anaemia. Anaemia is often caused by a deficiency of the mineral iron, which is needed to make haemoglobin.

  2. 2

    Step 2: Analyse the table to find the food rich in iron. Food C contains 8 mg of iron per 100g.

  3. 3

    Step 3: Formulate the answer. Food C would be most needed because anaemia is caused by an iron deficiency, and Food C is the richest source of iron in the table.

Recap

  • Vitamins and minerals are micronutrients needed in small amounts for health.
  • Lack of Vitamin C causes scurvy.
  • Lack of Vitamin D causes rickets.
  • Lack of the mineral iron causes anaemia.
  • The mineral calcium is needed for strong bones and teeth.

Quick check

  1. Name the mineral needed to make haemoglobin.1 mark
  2. What disease is caused by a lack of Vitamin D?1 mark

5. Fibre and Water: The Unsung Heroes

Although they provide no energy, dietary fibre and water are vital components of a balanced diet. Dietary fibre, found in plant-based foods like wholemeal bread, fruit, and vegetables, is indigestible. Its main role is to add bulk to the food in our intestines. This stimulates the gut muscles to contract, pushing the food along in a process called peristalsis. A diet high in fibre helps prevent constipation. Water is arguably the most important nutrient. It makes up about 60-70% of the body and is crucial for almost every bodily function. It acts as a solvent for chemical reactions, helps transport substances in the blood, and is involved in temperature regulation.

Key term

Peristalsis: The wave-like muscular contractions of the wall of the alimentary canal that move food along.

Common pitfall

Believing that fibre provides nutrients or energy. Its benefit comes from the fact that it is *not* digested.

Fun fact

While you can survive for weeks without food, you can only survive for a few days without water, highlighting its critical importance.

Worked example 13 marks

A person's diet consists mainly of cheese, white bread, and meat. They frequently suffer from constipation. Explain the likely dietary cause of their constipation. [3 marks]

  1. 1

    Step 1: Analyse the person's diet. The diet described (cheese, white bread, meat) is low in foods that are good sources of dietary fibre.

  2. 2

    Step 2: State the function of dietary fibre. Dietary fibre adds bulk to the faeces and stimulates peristalsis, the muscular contractions that move food through the intestine.

  3. 3

    Step 3: Link the diet to the condition. A lack of fibre means there is less bulk to stimulate the gut muscles, leading to slower movement of faeces and difficulty passing them, which is known as constipation.

Recap

  • Dietary fibre is not digested but is essential for healthy bowel function.
  • Fibre adds bulk to faeces and stimulates peristalsis, preventing constipation.
  • Good sources of fibre include fruits, vegetables, and whole grains.
  • Water is a solvent, a transport medium, and essential for all chemical reactions in cells.
  • The human body is mostly composed of water.

Quick check

  1. What is the main function of dietary fibre?1 mark
  2. State two reasons why water is essential in the diet.2 marks

6. Balancing Your Energy Budget

The energy content of food is measured in joules (J) or, more commonly, kilojoules (kJ). Different foods provide different amounts of energy. A person's daily energy requirement depends on several factors, including their age (energy needs peak in adolescence), sex (males generally need more energy than females), body size, and, most significantly, their level of physical activity. To maintain a stable body weight, your energy intake (from food and drink) must be balanced with your energy expenditure (from metabolic processes and physical activity). If intake exceeds expenditure, the excess energy is stored as fat, leading to weight gain. If expenditure exceeds intake, the body uses its stored energy, leading to weight loss.

Energy transferred (J) = mass of water (g) x specific heat capacity of water (4.2 J/g°C) x temperature change (°C)

Key term

Metabolism: The sum of all the chemical reactions that occur within a living organism to maintain life.

Examiner insight

When answering questions about varying energy needs, always link the factor (e.g., activity level) to the reason for the energy demand (e.g., muscle contraction for movement).

Worked example 13 marks

A student burns a 0.5g piece of a nut under a boiling tube containing 20 cm³ of water. The temperature of the water increases from 21°C to 51°C. Calculate the energy released in joules. (Assume 1 cm³ of water has a mass of 1g and the specific heat capacity of water is 4.2 J/g°C). [3 marks]

  1. 1

    Step 1: Identify the values needed for the formula. Mass of water = 20g. Temperature change = 51°C - 21°C = 30°C. Specific heat capacity = 4.2 J/g°C.

  2. 2

    Step 2: Substitute the values into the formula: Energy (J) = mass × specific heat capacity × temperature change.

  3. 3

    Step 3: Calculate the result: Energy = 20g × 4.2 J/g°C × 30°C = 2520 J.

Worked example 22 marks

Explain why a professional footballer needs a higher energy intake than an office worker of the same age and sex. [2 marks]

  1. 1

    Step 1: State the key difference between the two individuals. The footballer has a much higher level of physical activity due to training and playing matches.

  2. 2

    Step 2: Link activity to energy demand. Physical activity, especially intense exercise, requires a lot of energy for muscle contraction. Therefore, the footballer expends more energy and needs a higher energy intake from their diet to balance this.

Recap

  • Energy in food is measured in kilojoules (kJ).
  • Daily energy needs depend on age, sex, and activity level.
  • To maintain a stable weight, energy intake must equal energy expenditure.
  • Consuming more energy than you use leads to weight gain.
  • Consuming less energy than you use leads to weight loss.

Quick check

  1. List two factors that determine a person's daily energy requirement.2 marks
  2. What happens to excess energy consumed in the diet?1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Define the term 'balanced diet' and list the seven types of nutrients it must contain.4 marks
  2. Match each dietary problem with the harm it may cause. (e.g., A-5) Dietary Problem: A) Too little iron B) Too much saturated fat C) Too little fibre D) Too little protein Harm Caused: 1) Constipation 2) Kwashiorkor 3) Anaemia 4) Coronary heart disease3 marks
  3. A food label for a cereal shows it contains 20g of carbohydrate, 5g of protein, and 2g of fat per serving. Given that carbohydrates provide 17 kJ/g, proteins 17 kJ/g, and fats 37 kJ/g, calculate the total energy in kJ for one serving.3 marks
  4. Explain why a pregnant woman has a higher dietary requirement for both iron and calcium than a non-pregnant woman.4 marks
  5. Describe the function of dietary fibre and explain the health consequences of a diet that lacks fibre.3 marks
  6. A child in a developing country has a swollen abdomen but is very thin in the arms and legs. Their diet is mainly starchy food like yams. Name the likely deficiency disease and explain its cause.3 marks
  7. Compare the energy needs of a teenage boy who is a competitive swimmer with those of a 70-year-old retired man. Explain the reasons for the differences.4 marks
  8. What is the role of Vitamin D in the body, and what is the name of the deficiency disease associated with it?2 marks
  9. Explain, step-by-step, how a long-term diet of high-energy foods combined with a sedentary lifestyle can lead to obesity and increase the risk of Type 2 diabetes.5 marks
  10. Water is a nutrient. State three different functions of water in the human body.3 marks

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