ClassWS_Ch02_e 2024 (Teacher's Edition) PDF

Classroom worksheet Chapter 2 Molecules of life Name: ( ) Class: Date: 2.1 Chemical constituents of organisms  Organisms are made up of various types of substances: (1) Organic substances (biomolecul...

Classroom worksheet Chapter 2 Molecules of life Name: ( ) Class: Date: 2.1 Chemical constituents of organisms  Organisms are made up of various types of substances: (1) Organic substances (biomolecules) (2) Inorganic substances Carbohydrates Water (3) Proteins (5) Minerals Lipids (4) Nucleic acids 2.2 Water  Water is a major component of cells, blood and other body fluids. Importance of water Description As a good (6) solvent  As the medium in which chemical reactions take place within organisms  Transport nutrients, gases and metabolic wastes 2-1 Classroom worksheet 2 Molecules of life Importance of water Description As a (7) reactant in some  Involved digestion which is the breakdown of metabolic reactions complex food molecules into smaller molecules  Used in photosynthesis during which the reactants are converted to carbohydrates and oxygen As a (8) cooling agent  Takes away heat during evaporation  Sweating in humans to cool the body  Transpiration in plants to prevent overheating As a temperature (9) buffer  Absorbs a large amount of heat to raise temperature by 1 ˚C  Maintains a stable body temperature  Provides a favourable habitat for aquatic organisms Provides support to organisms and aids  Provides a (10) hydrostatic skeleton movement for some animals  (11) Turgidity provides support to young seedlings and non-woody plants  Provides (12) buoyancy for aquatic organisms  As a good (13) lubricant that reduces friction between bones during movement Practise…  Checkpoint (Coursebook p.2-6) 2-2 Classroom worksheet 2 Molecules of life 2.3 Minerals  Minerals play important roles in regulating (14) metabolism. They are needed in small amount and occur as (15) inorganic ions. Inorganic ion Functions Nitrate (NO3-)  For making proteins, nucleic acids and chlorophyll Magnesium (Mg2+)  For making (16) chlorophyll in plants  Minor component of bones and teeth Calcium (Ca2+)  Major component of bones, teeth and shells  For (17) muscle contraction and blood clotting, transmission of nerve impulses Iron (Fe2+)  For making chlorophyll in plants  For forming (18) haemoglobin , a pigment in red blood cells Practise…  Checkpoint (Coursebook p.2-7) 2.4 Carbohydrates  Carbohydrates are organic substances made up of (19) carbon (C), (20) hydrogen (H) and (21) oxygen (O).  The general formula is (22) Cx(H2O)y , in which the ratio of hydrogen atoms to oxygen atoms is 2:1. 2-3 Classroom worksheet 2 Molecules of life A. Monosaccharides Characteristics  The simplest forms of carbohydrates  Soluble in water and taste sweet  Used as (23) building blocks to build other larger molecules  Are (24) reducing sugars that can be tested using the (25) Benedict’s test Examples  Glucose: used as a fuel in cell respiration to release energy  Fructose  Galactose B. Disaccharides (雙糖) Characteristics  (26) Condensation of two monosaccharides with the removal of a water molecule  Can be broken down by (27) hydrolysis  Soluble in water and taste sweet  Most are reducing sugars except (28) sucrose Examples  Maltose: glucose + glucose  Sucrose: glucose + fructose  Lactose: glucose + galactose Function of carbohydrates: (1) Main source of energy in the body 17 kJ per one gram of carbohydrates Monosaccharide (glucose) is most readily absorbed in alimentary canal. More complex sugars have to be changed to glucose first before they can be broken down to release energy in respiration. (2) Energy store Excess carbohydrates are taken into body, it will be converted in the liver to either glycogen or fats. Glycogen is stored in the liver and muscle. Fat is stored under the skin or round the kidneys. 2-4  Classroom worksheet 2 Molecules of life C. Polysaccharides Characteristics  Condensation of a large number of monosaccharide molecules resulting in long chains  Insoluble or only slightly soluble in water Examples  (29) Glycogen : storage form of carbohydrates in animals  (30) Starch : energy reserves in plants  (31) Cellulose : main component of cell walls in plants Different Types of Carbohydrates Carbohydrates Sources Remark Glucose Fruits Monosaccharides Fructose Fruits Simplest form of carbohydrate Galactose Milk Maltose (malt sugar) Germinating seeds and Hydrolyzed to glucose barley Disaccharides Sucrose (cane sugar) Sugar cane, beet root and Hydrolyzed to glucose & table sugar fructose Lactose (milk sugar) Milk Hydrolyzed to glucose and galactose Starch Potatoes, rice Hydrolyzed to glucose Polysaccharides Glycogen Pork, liver Hydrolyzed to glucose Cellulose Vegetable, fruits We cannot digest cellulose. Reversible processes Condensation with enzyme (releasing water) Hydrolysis with enzyme (requiring water) 2-5 Classroom worksheet 2 Molecules of life Practical 2.1 Test for glucose using glucose test strips Refer to Coursebook p.2-11. Steps of the experiment  Transfer a drop of testing liquid to the well of a spot plate.  Dip the test end of a Clinistix paper into the sample.  Observe any colour change. Results and discussion  In the presence of glucose, the colour of the Clinistix paper changes from pink to blue / purple.  When distilled water is tested with the Clinistix paper, the colour of remains pink. Practical 2.2 Benedict’s test for reducing sugars Refer to Coursebook p.2-12. Steps of the experiment  Put the same volume of Benedict’s solution (Blue) and testing liquid together in a test-tube.  Put the test-tube in a boiling water bath for 5 min.  Stand the test tubes for a few minutes. Results and discussion  When glucose solution is heated with Benedict’s solution, a (32) brick-red precipitate is formed. This indicates the presence of reducing sugar.  When (33) distilled water is heated with Benedict’s solution, there is no observable change. Practical 2.3 Iodine test for starch Refer to Coursebook p.2-12. Steps of the experiment  Transfer a drop of testing liquid to the well of a spot plate.  Add a drop of iodine solution to the sample.  Observe any colour change. Results and discussion  In the presence of starch, the colour of iodine solution changes from brown to (34) blue-black.  When distilled water is tested with iodine solution, the colour of the iodine solution remains (35) brown. 2-6