Chapter 3: Nutrition

Nutrition: the way in which living organisms obtain and use food.

Metabolism: sum of all chemical reactions in an organism.

Continuity of life: the way in which organisms arise from organisms of the same type.

Function of Food

• Food is a complex of chemicals required by a living organism to maintain metabolism and continuity of life

Six Common Elements in Food
– Carbon (C)
– Hydrogen (H)
– Oxygen (O)
– Nitrogen (N)
– Phosphorus (P)
– Sulphur (S)

Five Elements in Food as Dissolved Salts
– Sodium (Na)
– Magnesium (Mg)
– Calcium (Ca)
– Potassium (K)
– Chlorine (Cl)

Three Trace minerals
– Iron (Fe)
– Copper (Cu)
– Zinc (Zn)

Approximate amounts of zinc (top left), copper (bottom left) and iron (right) in the average human body

• Biomolecules are chemicals found in and produced by living organisms
• There are 4 major types of biomolecules:
– Carbohydrates
– Lipids
– Proteins
– Vitamins


• C, H, O: Ratio: Cx(H2O)y
• Three categories:
– Monosaccharides
– Disaccharides
– Polysaccharides  (CH2O)n

Glucose [C6H12O6] – a reducing sugar and formed by breakdown of glycogen
Fructose [C6H12O6] – a reducing sugar and found in many fruits
Galactose [C6H12O6] – a reducing sugar and formed by breakdown of lactose (found in milk)

• Maltose (a reducing sugar)
– Found in germinating seeds (e.g. barley)
– Glucose + Glucose → Maltose [C12H22O11] + H2O
• Sucrose (NOT a reducing sugar)
– Commonly known as table sugar
– Glucose + Fructose → Sucrose [C12H22O11] + H2O
• Lactose (a reducing sugar)
– Found in milk – some people have lactose-intolerance
– Glucose + Galactose → Lactose [C12H22O11] + H2O

• Starch (also known as amylose)
– Plants store glucose as starch, e.g. potatoes, bananas
– Long chains and some branching of glucose molecules making it easy to digest
• Cellulose (also known as fibre/roughage)
– Found in cell walls and stems of plants such as celery
– Composed of many glucose molecules bonded together in long chains making it difficult to digest
• Glycogen
– Animals store glucose as glycogen in liver and muscles
– Glycogen is more branched than starch

Structures of mono-, di-, and polysaccaharides

Structural and Metabolic roles of Carbohydrates
• Structural role:
– Cellulose: component of cell walls; keeps plant upright
• Metabolic role:
– Energy: Mono-, Di-, and Polysaccharides are metabolised to release energy


 • Lipids: consist of the elements C, H, and O, but have fewer O atoms than carbohydrates
–Two main categories:
• Triglycerides
• Phospholipids
– Food sources of lipids:
• Butter, oils, margarines, cream, olives, animal fat

• Triglycerides: one molecule of glycerol linked to three fatty acid molecules
– Fats:  solid at room temperature (RT)
– Oils:  liquids at RT – contain different types of fatty acids than fats

• Phospholipids: one fatty acid replaced by a phosphate

Structural and Metabolic roles of Lipids
• Structural role:
– Phospholipids: component of cell membranes of all living cells
– Triglycerides: form adipose tissue that surrounds important internal organs and acts as a shock absorber
• Metabolic role:
– Energy: triglycerides are stored by organisms as a source of energy


• Proteins consist of elements: C, H, O, N – no particular ratios
• Sulfur and phosphorus are also present in some proteins
• There are 20 common amino acids found in proteins
– Two main categories of protein:
1. Fibrous proteins – little or no folding (e.g. proteins found in hair, skin & nails)
2. Globular proteins – lots of folding (e.g. protein hormones, enzymes and antibodies)

Structural and Metabolic roles of Proteins
• Structural role:
– Skin, nails and hair contain keratin
– Muscle composed of actin and myosin
– Bone, ligaments and tendons contain collagen
• Metabolic role:
– Enzymes, antibodies and some hormones are proteins


• Complex organic substances needed only in tiny amounts
• Share no common chemical characteristics – all chemically unique
• Identified by letters based on their chemical structure
• A, D, E, and K are fat-soluble vitamins
• B-group and C are water-soluble vitamins

Structural and Metabolic roles of Vitamins
1. Structural role:
– Vitamins do not have any structural role in living organisms
2. Metabolic role:
– Homeostasis and normal metabolism (see tables below for specific metabolic roles of the vitamins)

Note: for the Leaving Certificate you need to know one fat-soluble and one water-soluble vitamin, their functions, and deficiency conditions

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Water-soluble vitaminsDeficiency disordersMetabolic roleSources
Vitamin B1 (thiamine)Beri beri (neurological disorder)Carbohydrate metabolismPork, wholemeal bread
Vitamin B2 (riboflavin)Swollen mouthCarbohydrate metabolismEggs, meat, milk
Vitamin B3 (niacin)Skin lesions (pellagra)Carbohydrate metabolismChicken, beef, tomatoes
Vitamin B5 (panthenic acid)Fatigue and low glucose levelsCarbohydrate metabolismWholegrain bread, eggs, meat
Vitamin B6 (pyridoxine)AnaemiaFormation of red blood cellsWholegrain bread, nuts, seeds
Vitamin B7 (biotin)Dermatitis and hair lossFat metabolismNuts, seeds, liver
Vitamin B9 (folic acid)Spina bifida in children
Anaemia in adults
Nervous system development
Formation of red blood cellsSpinach, egg yolk, sunflower seeds
Vitamin B12 (cobalamin)AnaemiaFormation of red blood cellsEggs, milk, fish
Vitamin C (ascorbic acid)ScurvyFormation of collagenCitrus fruits
Fat-soluble vitaminsDeficiency disordersMetabolic roleSources
Vitamin A (retinol)Night-blindnessFormation of rhodopsin (pigment in eye)Cod liver oil, butter, margarine
Vitamin D (calciferol)Rickets in children; osteomalacia in adultsAbsorption of calcium in the digestive systemSunlight, eggs, milk
Vitamin E (tocopherol)Poor nerve impulse conductionGrowth in children; antioxidant in adults (prevents damage to cell membranes)Eggs, milk, nuts and seeds
Vitamin K (quinone)Inability to clot bloodBlood clottingIntestinal bacteria, spinach


Water is vital to life as we know it…

  • It makes up 70 – 95% of cell mass
  • It is an excellent solvent in which all biochemical reactions occur
  • It participates in chemical reactions – e.g. photosynthesis, respiration and digestion and in hydrolysis and condensation reactions (see image below)
  • Carries substances around the body of animals and plants
  • Carries substances into and out of cells
  • Good absorber of heat energy

Anabolism and Catabolism

Anabolism is the building up of large biomolecules from smaller molecules using energy, e.g. photosynthesis and protein synthesisCatabolism is the breaking down of large biomolecules into smaller molecules with the release of energy, e.g. respiration and digestion

Mandatory Experiments: to conduct qualitative tests for:

a) Test for starch


  • Starch powder
  • Bread
  • Potato
  • Banana


  • Prepare a 1% starch solution (1 g/100ml water) and add three drops of iodine
  • Add three drops of iodine to each of the bread, potato and banana
  • Observe any changes
Testing a potato for starch


  • A colour change occurs: yellow-red to blue-black


  • Bread, potato and banana are foods containing starch

b) Test for fat


  • Sunflower oil
  • Butter
  • Milk (full-fat)
  • Orange juice


  • Rub the foods into brown paper
  • Add a few drops of water to a piece of brown paper (control)
  • Allow the papers to dry on a radiator
  • Observe any changes


  • The pieces of brown paper containing oil, butter and milk each have a translucent spot
  • The brown paper with the orange juice and water did not have a translucent spot
Brown paper test for lipid


  • Sunflower oil, butter and milk contain fat
  • Orange juice and water do not contain fat

c) Test for a reducing sugar


  • Benedict’s solution
  • Bunsen/hotplate
  • Glucose powder
  • Orange juice
  • Cranberry juice


  • Prepare a 1% glucose solution (1 g/100ml water)
  • Add 1 ml of the glucose solution and 1 ml of each of orange juice, cranberry juice, and water (control) to test tubes
  • Add 1 ml Benedict’s solution to each test tube
  • Heat all test tubes in a beaker of hot water
  • Observe any changes


  • A colour change occurs: blue to orange/brick-red


  • Orange juice and cranberry juice contain a reducing sugar

d) Test for a protein


  • Sodium hydroxide solution
  • Copper sulphate solution
  • Egg white/albumin powder
  • Milk


  • Prepare a diluted solutions of each of the egg white and milk by taking 1 ml of each food and adding 1 ml water
  • Add a few drops of sodium hydroxide to each test tube followed by a few drops of copper sulphate solution
  • Observe any changes


  • A colour change occurs: blue to violet


  • Milk and egg white contain protein