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© Manhattan Press (H.K.) Ltd.1 Do you think the bodies of the following animals are composed of similar chemical constituents? What are the chemical constituents.

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Presentation on theme: "© Manhattan Press (H.K.) Ltd.1 Do you think the bodies of the following animals are composed of similar chemical constituents? What are the chemical constituents."— Presentation transcript:

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2 © Manhattan Press (H.K.) Ltd.1 Do you think the bodies of the following animals are composed of similar chemical constituents? What are the chemical constituents that might exist in the bodies of animals? Do you think the bodies of plants and other organisms also contain these chemical constituents?

3 © Manhattan Press (H.K.) Ltd.2 Introduction A variety of organisms are made up of similar chemical constituents The chemical constituents are divided into: -Organic substances -Inorganic substances

4 © Manhattan Press (H.K.) Ltd.3 Organic substances are composed of carbon and other elements Inorganic substances do not contain any carbon Chemical constituents Organic substancesInorganic substances Carbohydrates LipidsMineralsDNAProteins Water

5 © Manhattan Press (H.K.) Ltd.4 What are carbohydrates? Organic substances composed of carbon, hydrogen and oxygen The ratio of hydrogen to oxygen = 2:1 General formula : C x (H 2 O) y (where x and y are whole numbers) Chemical formula of glucose : C 6 H 12 O 6 Energy-rich substances  important energy sources for organisms

6 © Manhattan Press (H.K.) Ltd.5 The simplest form of carbohydrates Characteristics: – Sweet in taste – Soluble in water –Have reducing power Simple sugars Glucose is the most common simple sugar found in organisms Other common example: fructose (in fruits) Glucose is used in supplements

7 © Manhattan Press (H.K.) Ltd.6 Formed by the combination of two simple sugar molecules Common examples: maltose (malt sugar), sucrose (cane sugar) and lactose (milk sugar) Double sugars Maltose (used as a kind of candy) Sucrose (cane sugar, rock sugar and table sugar)

8 © Manhattan Press (H.K.) Ltd.7 A double sugar molecule can be converted to two simple sugar molecules by specific digestive enzymes in the body. Characteristics: – Sweet in taste – Soluble in water – Have reducing power (except sucrose)

9 © Manhattan Press (H.K.) Ltd.8 How can we determine the presence of reducing sugar or glucose in a sample? Practical 3.1 Testing the presence of reducing sugar using the Benedict’s test Practical 3.2 Testing the presence of glucose using Clinistix paper

10 © Manhattan Press (H.K.) Ltd.9 Practical 3.1 Testing the presence of reducing sugar using the Benedict’s test Introduction Benedict ’ s test can be used to test the presence of a reducing sugar in a solution.  Wear safety spectacles when heating Benedict ’ s solution. Testing the presence of reducing sugar using Benedict’s test

11 © Manhattan Press (H.K.) Ltd.10 Procedure 1.Label two test tubes as A and B. 2.Pour 2 cm 3 of glucose solution into tube A, and 2 cm 3 of distilled water into tube B. 3.Add 2 cm 3 of Benedict ’ s solution to each tube and shake gently. 4.Boil the test tubes in a water bath for 5 minutes. Shake the tubes at intervals. Note the colour changes of the mixtures. 5.Stand the test tubes for a few minutes. Note any precipitate formed at the bottom of each tube.

12 © Manhattan Press (H.K.) Ltd.11 Analysis 1.Compare the results of tube A and tube B. What colour changes can be observed? How would you make use of Benedict’s solution to find out the content of a food sample? 2.Why should we test distilled water as a control experiment in this practical? Ans: Ans: Brick-red precipitate formed in tube A; no precipitate formed in tube B. The colour of Benedict’s solution changes from blue to green to yellow and then brick red and is used for testing the presence of reducing sugars Ans: Ans: To ensure that the experimental result is only due to the presence of reducing sugar

13 © Manhattan Press (H.K.) Ltd.12 Practical 3.2 Testing the presence of glucose using Clinistix paper Introduction Clinistix paper is commonly used to test for the presence of glucose. Testing the presence of glucose using Clinistix paper 2

14 © Manhattan Press (H.K.) Ltd.13 Procedure 1.Put a drop of glucose solution on a spot tile. 2.Dip a piece of Clinistix paper into the glucose solution. Note any colour changes. 3.Repeat the above test with distilled water and then solid glucose. Note any colour changes.

15 © Manhattan Press (H.K.) Ltd.14Analysis 1.What is the purpose of testing distilled water? 2.What is the purpose of testing solid glucose? 3.What is the use of Clinistix paper? Ans: Ans: As a control experiment; ensure that the colour change is due to glucose but not water Ans: Ans: To indicate that Clinistix paper can be applied for liquid samples only Ans: Ans: The change from pink to blue colour of Clinistix paper indicates the presence of glucose Further investigation People suffering from diabetes may use Clinistix paper to test their urine. Try to find out why they do so. Ans: Ans: To test whether glucose is present in the urine or not.

16 © Manhattan Press (H.K.) Ltd.15 Made up of a large number of simple sugar units Characteristics: –Do not give a sweet taste –Insoluble or very slightly soluble in water Polysaccharides

17 © Manhattan Press (H.K.) Ltd.16 Where comes the glucose for forming the starch and cellulose in plants? Common examples: –Starch – the main form of carbohydrate storage in plants –Cellulose – the main component of the plant cell walls – Glycogen – a common form of carbohydrate storage in animals. In mammals, it is mainly stored in the liver and skeletal muscles

18 © Manhattan Press (H.K.) Ltd.17 Condensation e.g. A large number of A polysaccharide simple sugar molecules molecule What processes are involved in building up and breaking down sugar molecules? Condensation 2 C 6 H 12 O 6 simple sugar C 12 H 22 O 11 + H 2 O Double sugar Water Condensation

19 © Manhattan Press (H.K.) Ltd.18 Hydrolysis A polysaccharide A large number of molecule simple sugar molecules Hydrolysis C 12 H 22 O 11 + H 2 O 2 C 6 H 12 O 6 Double sugar Water Simple sugar Hydrolysis

20 © Manhattan Press (H.K.) Ltd.19 Practical 3.3 Testing the presence of starch using the iodine test Introduction Iodine solution is commonly used to test for the presence of starch.  Handle iodine solution carefully as it is irritant. Testing the presence of starch using the iodine test 3

21 © Manhattan Press (H.K.) Ltd.20 Procedure 1.Add a drop of starch solution on a spot tile. 2.Add a drop of iodine solution to the starch solution. 3.Note any colour change of the mixture. 4.Design and perform a control experiment.

22 © Manhattan Press (H.K.) Ltd.21 Further investigation How would you perform the iodine test on solid food? Ans: Ans: The change from brown to blue- black colour of iodine solution indicates the presence of starch Ans: Ans: Just add a few drops of iodine solution directly on solid starch and observe the colour change Analysis From the results, what can you say about the use of the iodine test?

23 © Manhattan Press (H.K.) Ltd.22 1) Glucose releases energy when broken down during respiration. Double sugars and polysaccharides have to be converted into glucose or other simple sugars before being used in respiration. 2) Cellulose is the main component of plant cell walls, which make them strong and rigid. 3) In animals, cellulose, in the form of dietary fibres, stimulates peristalsis Functions of Carbohydrates

24 © Manhattan Press (H.K.) Ltd.23 What are lipids? Organic substances composed of carbon, hydrogen and oxygen The ratio of hydrogen to oxygen is always  2:1 Example: a common animal fat has the chemical formula C 54 H 110 O 3 where H:O  37:1 Characteristics: –Insoluble in water –Readily soluble in organic solvents such as alcohol, ether and chloroform

25 © Manhattan Press (H.K.) Ltd.24 Those which exist as solids or semi-solids at room temperature are called fats. Those which exist as liquid at room temperature are called oil

26 © Manhattan Press (H.K.) Ltd.25 The structure of a fat molecule Note that the three fatty acid molecules may be the same or different

27 © Manhattan Press (H.K.) Ltd.26 Practical 3.4 Testing the presence of fat using the grease spot test Introduction The grease spot test can be used to test for the presence of fat. Procedure 1.Place a small drop of peanut oil on a small piece of filter paper. 2.Alongside the oil spot place a drop of distilled water. Testing the presence of fat using the grease spot test 4

28 © Manhattan Press (H.K.) Ltd.27 3.Hold the paper up against light to examine the oil spot. 4.Leave the paper in the air to dry for 10 minutes. Examine the oil spot against light. 5.Dip the filter paper into ether and shake. After drying it in air, examine the oil spot against light.  The test using ether should be carried out in the fume cupboard.

29 © Manhattan Press (H.K.) Ltd.28 Analysis 1.Consider the results of the test, how do we know whether a liquid sample contains fat? 2.Describe the effect of ether on fat. Ans: Ans: The presence of a translucent spot on a filter paper after drying indicates the presence of fat Ans: Ans: Translucent spot disappears after dipping in ether; because fat dissolves in ether (an organic solvent)

30 What are the functions of fats? 1) Fats are important sources of energy for our body, releasing twice as much energy as carbohydrates and proteins during respiration 2) They act as energy reserves A mammal with a large amount of fat stored in the body

31 © Manhattan Press (H.K.) Ltd.30 3) They act as a heat-insulating layer under the skin and help to reduce heat loss from the body surface 4) Fat around internal organs absorbs shock and protects them from injury 5) In plants, fat stored in the form of oil in seeds serve as energy reserve. 6) Fats are major components of cell membrane and certain animal hormones To know more about fats, visit: asguru/biology/02biologicalmol ecules/03lipids/index.shtmlhttp://www.bbc.co.uk/education/ asguru/biology/02biologicalmol ecules/03lipids/index.shtml

32 © Manhattan Press (H.K.) Ltd.31 What are proteins? Large organic molecules composed of carbon, hydrogen, oxygen and nitrogen Some of them also contain sulphur The basic units of proteins are amino acids In the human body, there are 20 different kinds of amino acids The amino acid molecules combine in different numbers and sequences  to form a large variety of proteins

33 © Manhattan Press (H.K.) Ltd.32 Structure of an amino acid: The side chains specify different amino acids

34 © Manhattan Press (H.K.) Ltd.33 Two amino acids condense to form a dipeptide

35 © Manhattan Press (H.K.) Ltd.34 Many amino acid molecules  polypeptide

36 © Manhattan Press (H.K.) Ltd.35 One or more polypeptide chains  a protein molecule

37 © Manhattan Press (H.K.) Ltd.36 Practical 3.5 Testing the presence of protein using Albustix paper Introduction Albustix paper is often used to test for the presence of protein. Testing the presence of protein using Albustix paper 5

38 © Manhattan Press (H.K.) Ltd.37 Procedure 1.Put a drop of egg white on a spot tile. 2.Dip a piece of Albustix paper into the egg white. Note any colour changes. 3.Repeat the above test with peanut oil and distilled water. Note any colour changes.

39 © Manhattan Press (H.K.) Ltd.38 Analysis 1.Why do we test distilled water with Albustix paper? 2.Why do we test peanut oil with Albustix paper? Ans: Ans: As a control experiment Ans: Ans: Protein is present in peanut. It is tested to see whether it has the same effect on Albustix paper 3.What can you tell about the use of Albustix paper? Ans: Ans: The change from yellow to green colour of Albustix paper indicates the presence of protein

40 © Manhattan Press (H.K.) Ltd.39 What are the functions of proteins? Important components of cell membrane and cytoplasm, hence they are also important for the formation of new cells required for body growth and repair of worn- out parts in the body At what stages does a person need a greater supply of proteins in their diet? Proteins also provide energy for body activities To know more about proteins, visit: 2biologicalmolecules/01proteins/index.shtmlhttp://www.bbc.co.uk/education/asguru/biology/0 2biologicalmolecules/01proteins/index.shtml

41 © Manhattan Press (H.K.) Ltd.40 Many important molecules in the body of organisms are proteins, for example: –Enzymes: act as catalyst for chemical reactions in the cells –Antibodies: important for protecting the organisms from invading pathogens –Hormones: involved in controlling various processes in the body Can you name one hormone in your body that is a protein?

42 © Manhattan Press (H.K.) Ltd.41 What is DNA? DNA stands for deoxyribonucleic acid Structure: double helix

43 © Manhattan Press (H.K.) Ltd.42 What are the functions of DNA? Contains the information that controls the activities of the cells The information governs inherited characteristics

44 © Manhattan Press (H.K.) Ltd.43 What is the role of water in the body of organisms? A major component of cytoplasm, blood and body fluids A good solvent for many substances Water acts as: –the medium for chemical reactions in cells –the medium for transporting water-soluble substances (e.g. nutrient and wastes) in the body

45 © Manhattan Press (H.K.) Ltd.44 What is the role of water in breathing? In the gas exchange of organisms on land: oxygen and carbon dioxide  dissolves in a film of water lining the respiratory surface  enters or leaves the body

46 © Manhattan Press (H.K.) Ltd.45 What is the role of water in reactions in the body of organisms? Water takes part in many cellular reactions For example: –Photosynthesis –The breaking down of large molecules into smaller molecules in digestion Water is important for activating the enzymes

47 © Manhattan Press (H.K.) Ltd.46 What are other functions of water in the body of organisms? In plants The medium for transport of nutrients and minerals inside the plant body Acts as a cooling agent through evaporation Maintains the turgidity of the cells in non- woody plants Provides buoyancy to aquatic plants

48 © Manhattan Press (H.K.) Ltd.47 In mammals The medium for transport of substances inside the body Acts as a cooling agent through the evaporation of sweat  regulation of body temperature Acts as a lubricant, e.g. in swallowing Provides buoyancy to aquatic animals Water provides buoyancy to aquatic animal

49 © Manhattan Press (H.K.) Ltd.48 Minerals Minerals are inorganic substances Important for the normal functioning of the cells Present in all living cells In mammals Require a variety of minerals For example: calcium, sodium, potassium, magnesium, phosphorus, iron and iodine

50 © Manhattan Press (H.K.) Ltd.49 Some minerals are components of body structures Characteristics: Absorbed from food in the gut Have no energy value Usually needed in small amounts In plants Also needed by plants for healthy growth Required in small amounts Land plants obtain minerals from soil water

51 © Manhattan Press (H.K.) Ltd.50 The following statements contain some wrong concepts commonly held by students. Point them out and give correct statements. 1.Carbohydrates and fats are the only energy-giving food substances. 2.The appearance of a brick-red precipitate in Benedict ’ s test shows the presence of all sugars or the presence of glucose. 3.Only fat or oil can form a translucent spot on a piece of filter paper. Ans: Ans: Proteins are also energy-giving food substances Ans: Ans: The appearance of a brick-red precipitate in Benedict’s test shows the presence of reducing sugars only and glucose is only one example of reducing sugar Ans: Ans: Fat-containing substances can also form a translucent spot on a piece of filter paper


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