Nutrition is the study of the relationship between diet, health and diseases. It is studied so that people can select diets that keep them healthy and prevent diseases caused by nutrient imbalance.

Autotrophic nutrition: organisms manufacture their own food, e.g. green plants using photosynthesis.
Heterotrophic nutrition: organisms cannot manufacture their own food and depend on food already made by other organisms, e.g. all animals.

Because they can feed on both plant and animal material, they are able to take whatever food is available in their environment at a given time. This flexibility means they are not restricted to one food source and can survive in many different habitats.

Saprophytes secrete digestive enzymes onto the decaying substrate. The enzymes break complex organic molecules (such as starch and proteins) into simple soluble molecules (such as glucose and amino acids). This is extracellular digestion. The simple molecules are then absorbed into the body cells of the saprophyte.

Epiphytes only use the tree as a physical support to reach sunlight. They do not penetrate the tree's tissues and do not absorb food or water from the tree — they trap their own water and minerals from rain and air. The relationship is therefore commensalism, not parasitism.

• Macronutrients are required in large amounts; micronutrients are required in small amounts.
• Macronutrients supply energy (contain calories); micronutrients do not supply energy.
• Macronutrients are proteins, carbohydrates and lipids; micronutrients are vitamins and minerals.

Carbon, Hydrogen, Oxygen, Nitrogen and Sulphur.

Essential amino acids cannot be made by the body and must be supplied in the diet.
Non-essential amino acids can be synthesised by the body itself and so do not have to come from food.

Beans, lentils, peas, groundnuts and mushrooms (any three).

Fats are solid at room temperature while oils are liquid at room temperature. Both are lipids made of fatty acids and glycerol; the difference lies in the type of fatty acids present.

Lipids provide the highest energy per gram (9 kcal/g), which the body uses to generate heat. Stored fat under the skin also acts as an insulator, reducing heat loss from the body to the cold surroundings.

Condensation (a condensation reaction), in which a molecule of water is removed as the two sugars join.

• Insoluble in water.
• Tasteless (not sweet).
• Non-reducing sugars.
• Starch turns blue-black with iodine solution.

As glycogen in the liver and muscles, and as fat under the skin, in the lower abdomen and around the kidneys.

Vitamin D (calciferol). It builds and maintains teeth and bones by enabling the body to absorb and use calcium and phosphorus. Its deficiency causes rickets in children and osteoporosis in adults.

Vitamin C (ascorbic acid) — the condition is scurvy. Recommend citrus fruits such as oranges and lemons, tomatoes, and fresh green vegetables. The vegetables should be lightly cooked, since vitamin C is destroyed by heat.

Folic acid lowers the risk of birth defects such as spina bifida — a spinal disorder in which there is a hole in the spine resulting from incomplete formation of the spinal cord and the bones of the spine. It is also needed for the synthesis of new cells in the rapidly growing foetus.

Calcium and phosphorus (fluoride also contributes to the development of teeth and bones and prevents tooth decay).

Chloride is needed to form hydrochloric acid (HCl) in the stomach. HCl provides the acidic conditions required for the enzyme that digests protein to work. Without enough chloride, less HCl is produced and protein digestion is impaired.

Roughage adds bulk to the food in the alimentary canal. This bulk stimulates the muscles of the gut wall to contract and relax (peristalsis), pushing food and faeces along steadily so that waste is not held in the gut long enough to become hard and dry.

When the body is hot, sweat glands release water onto the skin surface. As this water evaporates it takes latent heat from the body, cooling the skin and the blood flowing beneath it. This lowers the body temperature back to normal.

A balanced diet contains foods from all food groups in the correct proportions — adequate carbohydrates, proteins, lipids, vitamins, minerals and water. A nutritious diet is food that supplies essential nutrients, but these may not necessarily be present in the correct proportions. Therefore all balanced diets are nutritious, but not all nutritious food makes a balanced diet.

Limited access to a variety of nutritious foods; economic constraints (cannot afford foods such as meat, fish or milk); lack of knowledge about nutrition; and cultural beliefs that restrict certain foods (any three).

The elderly often have weakened or missing teeth and reduced saliva production, which makes chewing and swallowing difficult. If only tough foods are offered they will avoid them, and this leads to deficiencies of protein, iron, zinc, calcium and vitamins. Soft foods such as eggs, liver, pureed fruits and vegetables allow them to obtain these nutrients.

• Protein — for milk production and repair of maternal tissues.
• Calcium — for the development of the baby's bones through breast milk.
• Water — it is the major constituent of breast milk.
• Iron — to restore blood lost during delivery (any three).

The condition is kwashiorkor, caused by protein deficiency. Recommend protein-rich foods such as beans, groundnuts, eggs, fish, milk or chicken. The parents should also be advised to seek medical attention.

It results from a dietary lack of vitamin D, calcium and phosphorus, but also from a lifestyle with insufficient exposure to sunlight, since the skin manufactures vitamin D when exposed to sunlight. A child could eat some calcium-containing food and still develop rickets if kept indoors, because without vitamin D the calcium cannot be properly absorbed and deposited in bone.

Height = 150 cm = 1.5 m
BMI = 70 ÷ (1.5)² = 70 ÷ 2.25 = 31.1 kg/m²
A BMI of 31.1 falls in the range 29.5–34.9, so Dina is in Class 1 obesity.

Because the person's body mass usually remains within the normal range, so there is no obvious outward sign of the disorder. In addition, the person deliberately keeps the eating behaviour secret from family and friends.

The acid hydrolyses the non-reducing sugar (sucrose) into its two reducing monosaccharides, glucose and fructose. These can then react with Benedict's solution and give a positive result.

The change is coagulation, caused by denaturation. Heat breaks the bonds holding the protein molecule in its specific three-dimensional shape, so the molecule unfolds and the protein becomes insoluble and solid. Denaturation is irreversible.

(i) Holozoic nutrition: the organism takes in complex food, digests it internally, absorbs the nutrients and assimilates them; undigested material is egested. Example: a lion feeding on a zebra, or a human eating ugali and beans.

(ii) Saprophytic nutrition: the organism feeds on decaying organic matter by secreting enzymes onto it (extracellular digestion) and absorbing the simple products. Example: mushrooms and bread mould.

(iii) Symbiotic nutrition: a feeding relationship between two species in which one or both benefit. Example: mutualism between a cow and the cellulose-digesting bacteria in its rumen.

They can eat both plant and animal material, so they take advantage of whatever food happens to be available. This allows them to survive in a wide range of habitats and through seasons when one type of food is scarce.

Enzymes are secreted onto the decaying substrate where they break down complex organic molecules such as starch and protein into simple soluble molecules such as glucose and amino acids. This is extracellular digestion. The simple molecules are then absorbed into the body cells and used for growth, respiration and other activities.

Epiphytes use the tree only as physical support to reach sunlight. They do not penetrate the tree's tissues and do not draw food or water from it; they obtain their own water and minerals from rain and air. The tree is therefore neither harmed nor benefited — the relationship is commensalism.

(i) Commensalism: a relationship in which one species benefits while the other is neither harmed nor benefited, e.g. remora fish and shark.

(ii) Parasitism: a relationship in which one species benefits while the other is harmed, e.g. tapeworm in the human gut.

(iii) Mutualism: a relationship in which both species benefit, e.g. cellulose-digesting bacteria in the gut of ruminants.

• Include foods from all food groups in the right proportions at every meal.
• Increase fruits and vegetables for vitamins and minerals.
• Include protein foods such as beans, groundnuts, eggs and fish for growth and repair.
• Include whole grains for roughage, and drink enough water.
• Limit sugary drinks, fried foods and excessive salt.
• Combine the diet with 30–40 minutes of daily physical activity.

Autotrophs are the producers that trap solar energy and manufacture food; they form the base of every food chain. Without them there would be no source of organic food and no oxygen from photosynthesis. Herbivores would starve first, then the carnivores that depend on them, and eventually all heterotrophs would die. Life as we know it would collapse.

Proper nutrition supplies energy for body activities, materials for growth and repair of tissues, and the vitamins and minerals needed for enzyme action, bone formation and immunity. It protects against deficiency diseases such as kwashiorkor, rickets and scurvy, and against disorders such as obesity and diabetes. It also strengthens the immune system so the body can resist infection and recover from illness.

Because they feed on both plant and animal material. Their teeth are adapted for a mixed diet — they possess incisors and canines for cutting and tearing flesh as well as premolars and molars for grinding plant material — and their digestive systems can handle both types of food.

(a) Food vs nutrient: Food is any substance consumed for nourishment; nutrients are the specific chemical components of food that are essential for life.

(b) Kwashiorkor vs marasmus: Kwashiorkor is protein deficiency accompanied by oedema and a swollen abdomen; marasmus is general starvation characterised by extreme thinness and wrinkled skin.

(c) Macronutrients vs micronutrients: Macronutrients are needed in large amounts (proteins, carbohydrates, lipids); micronutrients are needed in small amounts (vitamins, minerals).

(d) Monosaccharides vs polysaccharides: Monosaccharides are single sugars such as glucose; polysaccharides are complex carbohydrates made of many monosaccharide units, such as starch.

(e) Oils vs fats: Oils are liquid at room temperature; fats are solid at room temperature.

(a) BMI = 70 ÷ (1.5)² = 70 ÷ 2.25 = 31.1 kg/m².

(b) This falls in the Class 1 obesity range. Dina is at risk of heart disease, high blood pressure, diabetes, stroke and arthritis.

(c) She should eat properly, exercise regularly, avoid fatty and sugary foods, and balance her calorie intake with physical activity — because reducing excess body fat lowers the risk of these non-communicable diseases.

(a) Kwashiorkor — protein deficiency.

(b) Provide a diet with adequate proteins and other nutrients; include meat, fish, eggs, beans, groundnuts and milk in the child's diet; and seek medical advice at the nearest health centre.

(a) Elderly: vitamins, minerals (iron, zinc, calcium), vitamin D and roughage; foods that are easy to chew and swallow.

(b) Child: proteins for growth, calcium for bones and teeth, zinc, vitamins B₁₂ and C for immunity and brain development, carbohydrates and lipids for energy.

(c) Pregnant woman: protein, folic acid, calcium, zinc, iron, dietary fibre and water; alcohol must be avoided.

(d) Breastfeeding mother: the same as a pregnant woman, with extra water for milk production.

(a) Fat-soluble — vitamins A and D (also E and K); water-soluble — vitamins B and C.

(b) Animals store excess carbohydrate as glycogen; plants store it as starch.

(c) In the liver and muscles (as glycogen), and in the lower abdomen, around the kidneys and under the skin (as fat).

(a) Condensation reaction.

(b) They are soluble in water, sweet in taste, and are reducing sugars.

(c) Add Benedict's solution and heat gently; a colour change to brick red indicates a positive result.

(d) The acid hydrolyses the non-reducing sugar (sucrose) into the reducing sugars glucose and fructose, so that Benedict's solution can then react with them.

(a) Polysaccharides are complex carbohydrates formed by the condensation of many monosaccharide units. Examples: starch, glycogen and cellulose.

(b) They are insoluble in water and tasteless (not sweet). They are also non-reducing, and starch gives a blue-black colour with iodine.

(a)(i) Proteins: add 1M NaOH to the sample, then add 1% CuSO₄ drop by drop while shaking; a purple/violet colour shows protein is present.

(a)(ii) Starch: add 2–3 drops of iodine solution to the sample; a blue-black colour shows starch is present.

(b)(i) Proteins. (ii) Lipids. (iii) Lipids.

(a) Likely deficiencies: vitamins (A, C and the B complex), minerals (calcium, iron, zinc), roughage and good-quality protein.

(b) Effects: poor growth, weak bones from calcium deficiency, anaemia from iron deficiency, impaired brain function and concentration from B-vitamin deficiency, obesity from excess calories, constipation from lack of roughage, and a weakened immune system.

(a) They cannot eat tough foods, so they may avoid fruits, vegetables and meat. This reduces protein intake and leads to poor vitamin and mineral supply and absorption.

(b) Strategies: eat soft foods such as eggs and liver; take pureed fruits and vegetables; use ground meats, soups and smoothies; take fortified cereals and, where advised, liquid nutritional supplements.

(a) Mainly proteins; the child may also be lacking vitamins and minerals.

(b) Affordable alternative sources include beans, lentils, peas, groundnuts, eggs, fish, milk and chicken; soya products and mushrooms can also be used.

(a) Possible factors: inadequate carbohydrate intake (low energy stores), insufficient iron leading to anaemia, dehydration, and a lack of protein for muscle repair.

(b) Adjustments: increase carbohydrates for energy, increase iron-rich foods such as meat, liver and green vegetables, maintain proper hydration, take adequate protein for muscle repair, and ensure sufficient vitamins B and C.

A balanced diet contains foods from all food groups in the right proportions — adequate carbohydrates, proteins, lipids, vitamins, minerals and water. A nutritious diet refers generally to food that provides essential nutrients, but these may not be present in the correct proportions.

Symptoms: weight loss, slowed growth, decreased activity and lack of energy, wrinkled skin, extreme hunger and frequent crying.

Prevention: give the child adequate amounts of food containing all the nutrients in the right proportions.

Saprophytes release digestive enzymes externally onto the substrate. These enzymes convert complex organic molecules such as starch into simple molecules such as glucose. This process is called extracellular digestion. The simple molecules are then absorbed by the body cells and used for the organism's various activities.

Folic acid lowers the risk of birth defects such as spina bifida, a spinal disorder characterised by a hole in the spine resulting from incomplete formation of the spinal cord and the bones of the spine.

Roughage has no nutritional value but helps in the passage of food and faeces through the gut by aiding peristaltic movement. It also helps control body weight and protects against diseases such as heart disease.

Biuret test: tests for proteins; uses NaOH and CuSO₄; no heating required; positive result is a purple/violet colour.

Benedict's test: tests for reducing sugars; uses Benedict's solution with heating; positive result is a brick red precipitate.

Similarity: both are colour-change tests using copper compounds to identify a specific nutrient in a food sample.

Children are actively growing and require more nutrients per unit of body mass for development; an inadequate supply leads to stunted growth and deficiency diseases.

The elderly have weakened teeth, reduced saliva production and decreased nutrient absorption. They may therefore avoid certain foods, leading to deficiencies of iron, zinc, calcium and vitamins.

BMI (Body Mass Index) is a measure relating body weight to height, calculated as weight in kilograms divided by the square of height in metres. It helps to assess whether a person is underweight, of normal weight, overweight or obese, and therefore indicates the health risks associated with that weight status.

Anorexia nervosa involves the intentional refusal to eat enough food, leading to severe loss of body mass, an extreme fear of being fat and a distorted body image.

Bulimia nervosa involves excessive eating followed by attempts to remove the food from the body. Body mass often remains normal and the behaviour is kept secret, which makes the condition difficult to detect. Both are serious medical conditions requiring professional treatment.

Water is the major constituent of body fluids such as blood, tears and saliva, and forms a large part of the cell cytoplasm. It is needed for digestion, lubricates moving body parts, regulates body temperature through sweating, and maintains the shape of cells, tissues and organs.

Obesity leads to shortness of breath and snoring, and increases the likelihood of high blood pressure, heart disease, stroke, diabetes, certain cancers, arthritis and respiratory problems.

Monosaccharides: single sugars — glucose, fructose, galactose; these are reducing sugars.

Disaccharides: double sugars — sucrose, maltose, lactose; maltose and lactose are reducing, sucrose is non-reducing.

Polysaccharides: complex carbohydrates — starch, glycogen, cellulose; these are non-reducing.

• Introduction: define a balanced diet and state that requirements differ with age, sex, health and occupation.
• Pregnant women: protein, folic acid, calcium, zinc, iron. Consequences of failure — birth defects such as spina bifida, weak foetal bones, anaemia, poor progression of labour.
• Children: proteins, calcium, zinc, vitamins B₁₂ and C. Consequences — stunted growth, kwashiorkor or marasmus, weak bones, poor cognitive development, low immunity.
• The elderly: vitamins, iron, zinc, calcium, vitamin D and roughage in easily chewed form. Consequences — osteoporosis, anaemia, poor immunity, constipation.
• Sedentary workers: diet must be balanced with exercise, with carbohydrates and lipids limited. Consequences — obesity, diabetes and other non-communicable diseases.
• Conclusion: a balanced diet is essential at every stage of life for health, productivity and well-being.

• Introduction: food tests identify which nutrients are present in a sample.
• Reducing sugars — Benedict's test: add Benedict's solution and heat; blue → green → yellow → orange → brick red. Principle: the sugar reduces Cu²⁺ to Cu⁺, forming a brick-red copper(I) oxide precipitate. Negative: remains blue.
• Non-reducing sugars: hydrolyse first with dilute HCl, cool, neutralise with NaOH or NaHCO₃, then apply Benedict's test. Positive: brick red.
• Starch — iodine test: add iodine solution; positive is blue-black. Principle: iodine molecules become trapped within the coiled starch molecule. Negative: remains brown-yellow.
• Proteins — Biuret test: add NaOH then CuSO₄ drop by drop; positive is violet/purple. Principle: Cu²⁺ forms a coloured complex with peptide bonds. Negative: remains blue.
• Lipids: grease spot test gives a translucent spot; Sudan III gives a red layer on top; emulsion test gives a white milky suspension. Negative: paper dries clear, no red layer, no emulsion.
• Conclusion: each test is specific to a nutrient, and the reagent plus the colour change together confirm identity.

• Introduction: distinguish deficiencies (too little of a nutrient) from disorders (abnormal nutrition or eating behaviour).
• Marasmus: caused by general starvation; symptoms include weight loss, wrinkled skin, extreme hunger; prevented by adequate food in the right proportions.
• Kwashiorkor: caused by protein deficiency; symptoms include swollen abdomen, oedema, thin limbs, reddish weak hair; prevented by adequate protein intake.
• Rickets: caused by lack of vitamin D, calcium and phosphorus; symptoms include bow legs, knock knees and bone deformities; prevented by sunlight exposure and foods such as milk, sardines and green vegetables.
• Obesity: caused by overeating, inactivity, high-energy foods and genetic factors; effects include high blood pressure, heart disease, diabetes and arthritis; prevented by proper eating and regular exercise.
• Anorexia nervosa and bulimia nervosa: largely psychological in origin (depression, low self-esteem, pressure to meet standards of beauty); effects include weakened cardiac muscle, dehydration, dental erosion, anaemia and impaired mental function; management requires addressing the underlying psychological problems with professional medical help.
• Role of nutrition: promotes growth and repair, supplies energy, strengthens immunity and prevents disease.
• Conclusion: proper nutrition combined with a healthy lifestyle is the foundation of good health.