Ch 1 · Diet · O Level Biology 5090
Topic 1 of 5 in Human Nutrition — O Level Biology 5090 — 48 lessons.
Introduction
Humans cannot make their own food, so every nutrient must come from what we eat and drink. A diet that supplies the right nutrients in the right amounts keeps us healthy; one that does not leads to deficiency diseases or diet-related illness. Questions often present a food table or nutrition label and ask you to apply these ideas.
Key ideas — A balanced diet
A balanced diet contains all the nutrients needed by the body in the correct proportions, together with enough energy for the person's needs but not so much that excess is stored as fat. The seven components are carbohydrates, fats and oils, proteins, vitamins, mineral ions, fibre and water.
🧑🏫 Teacher's explanation
Think of your body like a high-performance car. To run smoothly, you don't just need fuel (carbohydrates); you also need engine oil (fats), structural parts (proteins), and coolant (water). If you put in too much fuel without driving enough, it just sits in the tank as sludge (stored fat). If you forget the oil, the engine wears down (deficiency diseases).
📖 Definitions
🔍 Worked example — Easy
A student's diet consists of 80\% carbohydrates, 10\% proteins, and 10\% fats. Calculate the percentage of the diet that is NOT carbohydrates.
🔍 Worked example — Standard
Compare the dietary requirements of a 15-year-old male athlete and a 70-year-old sedentary female regarding energy and protein.
🔍 Worked example — Exam-style
Explain why a pregnant woman requires an increased intake of iron and calcium compared to a non-pregnant woman.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Nutrients: sources and importance
Lack of iron causes anaemia, in which too little haemoglobin is made and the person feels tired and breathless.
🧑🏫 Teacher's explanation
Think of your body like a high-performance car. To run, you need fuel (carbohydrates); to maintain the engine and bodywork, you need spare parts (proteins); and to keep the electrical systems and fluids running smoothly, you need specific additives (vitamins and minerals). If you only provide fuel but no spare parts, the car eventually breaks down. If you provide too much fuel without enough engine maintenance, the system gets clogged.
📖 Definitions
🔍 Worked example — Easy
A patient presents with bleeding gums and slow wound healing. Identify the most likely nutrient deficiency and suggest a dietary change to rectify this.
🔍 Worked example — Standard
Compare the dietary requirements of a 15-year-old male athlete and a 70-year-old sedentary female regarding carbohydrates and protein.
🔍 Worked example — Exam-style
Calculate the percentage increase in energy intake if a person moves from a diet of 2000 ext kcal to 2500 ext kcal.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Deficiency diseases: scurvy and rickets
Scurvy is caused by a lack of vitamin C. Its effects are bleeding and swollen gums, loose teeth, easy bruising, joint pain and wounds that heal slowly, because vitamin C is needed to make the connective tissue that holds cells together.
🧑🏫 Teacher's explanation
Think of your body like a high-performance car. To keep it running, you need fuel (carbohydrates and fats), building materials (proteins and minerals), and specialized 'maintenance crew' (vitamins). Even if you have plenty of fuel, if the maintenance crew is missing, the car's structural integrity fails.
📖 Definitions
🔍 Worked example — Easy
A student is asked to identify the deficiency disease characterized by bleeding gums and slow wound healing. Name the disease and the specific nutrient deficiency.
🔍 Worked example — Standard
Explain why a child might develop bowed legs due to a dietary deficiency.
🔍 Worked example — Exam-style
A patient presents with easy bruising and loose teeth. Suggest the most likely deficiency and explain the biological reason for these specific symptoms.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
(a) Name the deficiency disease this child is likely to develop. [1] (b) Explain how a lack of Vitamin D leads to the development of this disease. [2] [3 marks]
Key ideas — Consequences of an unbalanced diet
Malnutrition means eating an unbalanced diet: too little food, too much food, or the wrong proportions of nutrients. It includes both starvation and obesity.
🧑🏫 Teacher's explanation
Think of your body like a high-performance car. To run smoothly, it needs the right fuel (carbohydrates), the right structural parts (proteins), and the right lubricants (fats/oils). If you put in too much fuel and never drive it, the tank overflows and gunk builds up in the engine. If you don't put in enough fuel, the engine eventually stalls and the metal parts start to wear down because the car is trying to use its own chassis for energy.
📖 Definitions
🔍 Worked example — Easy
A patient is experiencing muscle wasting, extreme weakness, and a weakened immune system. Identify the most likely dietary condition and explain the physiological cause.
🔍 Worked example — Standard
Compare the effects of a diet low in fibre versus a diet high in saturated fats on the human body.
🔍 Worked example — Exam-style
An individual consumes 2500 ext kcal per day but only uses 2100 ext kcal through metabolic processes and physical activity. Calculate the daily energy surplus and explain the long-term consequence.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
(a) State the term used to describe this nutritional state. [1] (b) Explain how this diet can lead to coronary heart disease. [3] [4 marks]
Worked example
Question. A 15-year-old girl who plays hockey every day and a 70-year-old man who spends most of the day sitting eat the same meals. Explain two ways in which the girl's dietary needs differ from the man's. [4]
🔍 Worked example — Easy
A student consumes 2500 ext kcal per day. If their basal metabolic rate is 1500 ext kcal and they burn 800 ext kcal through exercise, calculate the percentage of their energy intake that is used for non-exercise activity/basal metabolism.
🔍 Worked example — Standard
Compare the dietary requirements of a pregnant woman and a sedentary elderly man regarding specific mineral ions and vitamins.
🔍 Worked example — Exam-style
An individual shows symptoms of bleeding gums and slow wound healing. Identify the likely nutrient deficiency and explain the physiological consequence of this deficiency.
⚠️ Common errors
Common mistakes
Practice
Answers A diet containing all the required nutrients in the correct proportions [B1] with sufficient energy for the person's needs [B1]. (a) Milk or dairy products [B1]; hard bones and teeth or blood clotting [B1]. (b) Red meat, liver or green leafy vegetables [B1]; making haemoglobin [B1]. Lack of vitamin C [B1]; any two of bleeding or swollen gums, loose teeth, easy bruising, slow wound healing, joint pain [B1 each]. Fibre provides bulk that the gut muscles push against during peristalsis [B1]; without it, faeces move slowly, more water is absorbed and they become hard [B1]. Extra nutrients are needed for the growth of the fetus [B1]; any two of protein for new cells, calcium for bones and teeth, iron for the baby's blood, extra energy [B1, B1].