JWSS Biology Chapter 3 Nutrients

Sec 3 G3 Biology Nutrients - Notes 1 Name: _____________________ ( ) Class: _______ Date: ______________ Chapter 3: Nutrients Learning Outcomes: Candidates should be able to: (a) list the chemical elements which make up: • carbohydrates • fats • proteins (b) state the main roles of carbohydrates, fats and proteins in living organisms: • carbohydrates as an immediate source of energy • fats for insulation and long-term storage of energy • proteins for growth and repair of cells (c) describe and carry out tests for: • starch (using iodine in potassium iodide solution) • reducing sugars (using Benedict’s solution) • protein (using biuret solution) • fats (using ethanol) (d) state that large molecules are synthesised from smaller basic units: • cellulose, glycogen and starch from glucose • polypeptides and proteins from amino acids • lipids such as fats from glycerol and fatty acids Use the knowledge gained in this section in new situations or to solve related problems NUTRIENTS Nutrients are chemical substances in food that provide energy and materials needed by the body. Main nutrient groups: • Carbohydrates • Fats • Proteins • Vitamins • Minerals • Water Organic compounds that are obtained from living organisms and contain carbon. (Provide ENERGY)

Sec 3 G3 Biology Nutrients - Notes 2 CARBOHYDRATES Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. The hydrogen and oxygen atoms are present in the ratio 2:1 • General formula: CnH2mOm • E.g. glucose C6H12O6 Example: Glucose Maltose Glycogen Simple Complex * * * * * * Reducing sugars

Sec 3 G3 Biology Nutrients - Notes 3 Monosaccharides • Greek “monos”: single, “sacchar”: sugar • Simplest of all carbohydrates. • Cannot be broken down into smaller molecules. • Can pass through cell membranes. (Recall: via what process? Diffusion) • Examples: glucose, fructose, galactose Glucose Fructose Galactose Found in animals and plants Common in plants Milk sugar in animals Disaccharides • Consists of 2 monosaccharides chemically bonded together. • These 2 molecules of single sugars are bonded together via a condensation reaction. • Examples: maltose, lactose, sucrose Maltose Sucrose Lactose Found in malt, from wheat Cane sugar Milk sugar Glucose + glucose → maltose + water Glucose + fructose → sucrose + water Glucose + galactose → lactose + water

Sec 3 G3 Biology Nutrients - Notes 4 Polysaccharides (complex carbohydrates) • ‘Poly’: many • Many monosaccharide units joined together by condensation reaction • Examples: Starch, glycogen and cellulose Starch Glycogen Cellulose • A storage form of carbohydrates in plants • Found in storage organs in plants • A storage form of carbohydrates in mammals • Digested to form glucose when needed • Cellulose cell wall protects plant cells • Serve as dietary fibres to prevent constipation \

Sec 3 G3 Biology Nutrients - Notes 5 Function of carbohydrates: Test for carbohydrates Testing for starch – Iodine test 1. Add 2 cm3 of food sample to a clean test tube. 2. Add a few drops of iodine solution to the test tube. If starch is present: Iodine solution turns from brown to blue- black. If starch is absent: Iodine solution remains brown Testing for reducing sugars – Benedict’s test 1. Add 2 cm3 of Benedict’s solution to 2 cm3 of food sample in a test tube. 2. Shake the mixture. 3. Place the contents in a boiling water bath for 5 minutes. If reducing sugar is present - In trace amounts: A green precipitate is formed - In moderate amounts: A yellow precipitate is formed - In large amounts: A brick-red precipitate is formed If reducing sugar is absent: solution remains blue Blue Benedict’s solution forms green precipitate which then changes colour to yellow, then to brick-red. Scan to see the colour of Benedict’s solution when reducing sugar is present/ absent Scan to watch how the test for reducing sugar is carried out

Sec 3 G3 Biology Nutrients - Notes 6 FATS • Organic molecules consisting of carbon, hydrogen and oxygen. • Fats contain less oxygen in proportion to hydrogen • Proportions of elements in fats are not fixed, hence no general formula. • Animal fats, plant fats. From simple to complex • Fats are made of glycerol and fatty acids Fatty acids and glycerol Fat molecule A lipid molecule is made up of one glycerol molecule and 3 fatty acid chains. They are chemically joined together by a condensation reaction. Simple Complex

Sec 3 G3 Biology Nutrients - Notes 7 Function of fats: Testing for fats: Testing for fats – Ethanol emulsion test 1. Add 2 cm3 of ethanol to 2 cm3 of food sample in a test tube. 2. Shake the contents of the tube vigorously to dissolve 3. Add 2 cm3 of distilled water into the test tube and shake the mixture. If fats are present: A white emulsion is formed If fats are absent: The solution remains clear Scan to watch how the ethanol emulsion test is carried out

Sec 3 G3 Biology Nutrients - Notes 8 PROTEINS • Proteins are complex organic substances made of carbon, hydrogen, oxygen and nitrogen. Sulfur may also be present. • Each protein molecule is made up of smaller basic units called amino acids. • An amino acid is made of an amino group, acidic group and a side chain (denoted by R ) Amino acids can link up through condensation reactions *don’t need to know the exact chemical structure of amino acids. Just need to know wh ich elements make up proteins. Repeated condensation reactions with more amino acids gives rise to polypeptide chain. From simple to complex Amino acids Polypeptides Proteins The basic units of proteins. There are 20 different kinds of amino acids. Amino acids joined together by peptide bonds form a long chain known as a polypeptide. Proteins are formed when two or more polypeptide chains fold together to form a complex, three-dimensional molecule. Simple Complex

Sec 3 G3 Biology Nutrients - Notes 9 Function of proteins: • Proteins are used in the synthesis of new protoplasm for growth and repair of worn- out body cells. • In the synthesis of enzymes and some hormones. • In the formation of antibodies to combat diseases. Proteins are essential to human health. People who do not receive enough protein may develop a protein deficiency disease known as kwashiorkor. Testing for proteins Testing for proteins – biuret test 1. Add 2 cm3 of biuret’s solution to 2 cm3 of food sample into a test tube. 2. Shake thoroughly If proteins are present: Solution turns from blue to violet / lilac If proteins are absent: Solution remains blue Scan to see the colour of the solution when protein is present/ absent Scan to watch how the biuret’s test is carried out