[BIO] Chapter 3 - Biological Molecules

© Hee Xin Wei (Copyrighted) Topic 3: Biological Molecules

Chapter Analysis FOCUS EXAM WEIGHTAGE © Hee Xin Wei (Copyrighted)© Hee Xin Wei (Copyrighted) •Heavily linked to Digestion chapter •Usually tested in both MCQ and structured questions •tested in section B twice in the past 5 years •Constitute to around 4% in Paper 2 in the past 5 years •Enzyme has higher weightage

Role of Water Animals •required for chemical reaction such as hydrolysis of food molecules •key component for tissue and bodily fluid •regulation of body temperature through sweat •allow blood to transport substances Plants •reactant for photosynthesis •provides physical support to the plant in the form of turgor pressure. •allow dissolved mineral salts to be transported from roots to other part of plants •allow sugars to be transported from leaves to other parts of the plant.

Carbohydrate Food Test Key Concept © Hee Xin Wei (Copyrighted)© Hee Xin Wei (Copyrighted)

Carbohydrate -Carbohydrates are organic molecules made up of the elements carbon, hydrogen and oxygen. -Formula: CnH2nOn -3 broad types of carbohydrate: monosaccharides, disaccharides and polysaccharides Monosaccharides -Smallest unit of carbohydrate -Formula: C6H12O6 -Eg glucose (found in both plants and animal), fructose (found in plants), galactose (milk sugar) Monosaccharides © Hee Xin Wei (Copyrighted)

Carbohydrate Disaccharides -Two monosaccharides undergo condensation reaction to form a disaccharides, with removal of a water molecule -Disaccharides can be broken down to component monosaccharides by hydrolysis reaction in which a water molecule is added. -Enzyme is needed for both condensation reaction and hydrolysis reaction. -Formula: C12H22O11 Disaccharides Monosaccharides Maltose glucose + glucose Sucrose glucose + fructose Lactose glucose + galactose © Hee Xin Wei (Copyrighted)

Carbohydrate •Polysaccharides are formed when thousands of glucose molecules linked together in condensation reactions. •Eg, glycogen, starch and cellulose Polysaccharides glycogen starch cellulose Functions storage of carbohydrates in mammals storage of carbohydrates in plants The cellulose is used to make cell wall in plant cells from bursting or damage. Location found in liver and muscles of mammals found in storage organs of plants eg potato tubers found in plants cells © Hee Xin Wei (Copyrighted)

Food test Benedict test Test for reducing sugars (all monosaccharides and disaccharides except for sucrose) 1.Add 2cm3 of Benedict’s solution to 2cm3 of solution to be tested. 2.Shake the mixture 3.Heat the test tube in boiling water bath for 5 minutes. 4.Observe precipitate formation and colour changes. 5.Benedict solution is blue. Remain Blue (reducing sugar is absent) → Green (little amount) → Yellow (moderate amount) → Orange → Brick-red (most amount) Iodine test Test for starch 1.Place food substance on a white tile. Solid foods may need to be chopped up to smaller pieces. 2.Add 2-3 drops of dilute iodine solution to substance to be tested. 3.Iodine solution is yellowish brown, if it changes to blue black, starch is present. If it remains yellowish brown, starch is absent yellowish brown blue black © Hee Xin Wei (Copyrighted)

Fats Food Test Key Concept © Hee Xin Wei (Copyrighted)© Hee Xin Wei (Copyrighted)

Fats -Made up of carbon, hydrogen and oxygen. -No fixed formula, the ratio of hydrogen to oxygen is much higher in fats than in carbohydrates -One fat molecule contains 1 glycerol to 3 fatty acids, joined together via condensation reaction -Three molecules of water is needed to breakdown fat molecules into glycerol and fatty acids FUCTIONS (a)Fats are storage molecules that can store a large amount of energy. Each gram of fat supplies the body with about 9 calories, more than 4 calories by carbohydrate and protein. Therefore, Hibernating animals store fats as food reserve in cold seasons. (b)They are also an important component of cell membranes and myelin sheath in nerve cells. (c)Fats are used to make steroids and certain hormones. (d)Fats stored as adipose tissue are also used as insulating material to prevent the loss of body heat. (e)Fat is a solvent for fat-soluble vitamins. (f)Fat serves protective functions by cushioning vital organs such as kidney. (g)Large animals in cold seas have very thick layers of adipose tissues that gives buoyancy to aquatic animal. Also provide heat insulation to these animals. Fatty acid Fatty acid Fatty acid Glycerol © Hee Xin Wei (Copyrighted)