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 help with growth and repair and for the production of energy.

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

Carbohydrates

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

Monosaccharides
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)

Disaccharides
• 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

Polysaccharides
• 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

 • 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
• 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
• 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

• 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

Vitamins

• 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

If viewing this page on a mobile phone, please turn to landscape orientation
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

Minerals

Minerals are elements required by organisms everyday to maintain health. They all have varying functions within living organisms.

Animal mineralGood sourceFunctionDeficiency symptom
Iron (Fe)Red meatComponent of haemoglobinAnaemia
CalciumDairy productsComponent of boneOsteomalacia
Plant mineralSourceFunctionDeficiency in plant
CalciumSoilComponent of middle lamellaNo growth
MagnesiumSoilComponent of chlorophyllNo growth

Water

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

Equipment:

  • Starch powder
  • Bread
  • Potato
  • Banana

Method:

  • 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

Result:

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

Conclusion:

  • Bread, potato and banana are foods containing starch

b) Test for fat

Equipment:

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

Method:

  • 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

Result:

  • 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

Conclusion:

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

c) Test for a reducing sugar

Equipment:

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

Method:

  • 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

Result:

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

Conclusion:

  • Orange juice and cranberry juice contain a reducing sugar

d) Test for a protein

Equipment:

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

Method:

  • 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

Result:

  • A colour change occurs: blue to violet

Conclusion:

  • Milk and egg white contain protein