1. Warm-up Zone
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?
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2. Introduction
A variety of organisms are made up of similar chemical constituents
The chemical constituents are divided into:
- Organic substances
- Inorganic substances
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3. Organic substances are composed of carbon and other elements
Inorganic substances do not contain any carbon
Chemical constituents
Organic substances
Inorganic substances
Carbohydrates
Lipids
Proteins
DNA
Water
Minerals
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4. What are carbohydrates?
Organic substances composed of carbon, hydrogen and oxygen
The ratio of hydrogen to oxygen = 2:1
General formula : Cx(H2O)y (where x and y are whole numbers)
Chemical formula of glucose : C6H12O6
Energy-rich substances  important energy sources for organisms
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5. Glucose is used in supplements
Simple sugars
The simplest form of carbohydrates
Characteristics:
– Sweet in taste
– Soluble in water
– Have reducing power
Glucose is used in supplements
Glucose is the most common simple sugar found in organisms
Other common example: fructose (in fruits)
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6. Sucrose (cane sugar, rock sugar and table sugar)
Double sugars
Formed by the combination of two simple sugar molecules
Common examples: maltose (malt sugar), sucrose (cane sugar) and lactose (milk sugar)
Maltose (used as a kind of candy)
Sucrose (cane sugar, rock sugar and table sugar)
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7. – Have reducing power (except sucrose)
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)
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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
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9. Testing the presence of reducing sugar using Benedict’s test
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.
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10. Label two test tubes as A and B.
Procedure
Label two test tubes as A and B.
Pour 2 cm3 of glucose solution into tube A,   and 2 cm3 of distilled water into tube B.
Add 2 cm3 of Benedict’s solution to each   tube and shake gently.
Boil the test tubes in a water bath for 5   minutes. Shake the tubes at intervals. Note   the colour changes of the mixtures.
Stand the test tubes for a few minutes. Note   any precipitate formed at the bottom of   each tube.
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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?
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
Why should we test distilled water as a control experiment in this practical?
Ans: To ensure that the experimental result is only due to the presence of reducing sugar
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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.
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13. Put a drop of glucose solution on a spot tile.
Procedure
Put a drop of glucose solution on a spot tile.
Dip a piece of Clinistix paper into the glucose solution. Note any colour changes.
Repeat the above test with distilled water and then solid glucose. Note any colour changes.
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14. What is the purpose of testing distilled water?
Analysis
What is the purpose of testing distilled water?
Ans: As a control experiment; ensure that the colour change is due to glucose but not water
What is the purpose of testing solid glucose?
Ans: To indicate that Clinistix paper can be applied for liquid samples only
What is the use of Clinistix paper?
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.
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Ans: To test whether glucose is present in the urine or not.

15. Polysaccharides Made up of a large number of simple sugar units
Characteristics:
– Do not give a sweet        taste
– Insoluble or very slightly   soluble in water
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16. – Starch – the main form of carbohydrate storage in plants
Common examples:
– Starch – the main form of carbohydrate storage         in plants
– Cellulose – the main component of the plant         cell walls
Where comes the glucose for forming the starch and cellulose in plants?
– Glycogen – a common form of carbohydrate         storage in animals. In mammals, it is mainly         stored in the liver and skeletal muscles
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17. What processes are involved in building up and breaking down sugar molecules?
Condensation
2 C6H12O6
simple sugar
C12H22O H2O
Double sugar Water
Condensation
e.g. A large number of A polysaccharide
simple sugar molecules molecule
Condensation
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18. Hydrolysis C12H22O11 + H2O 2 C6H12O6 Double sugar Water Simple sugar
A polysaccharide A large number of
molecule simple sugar molecules
Hydrolysis
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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.
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20. Add a drop of starch solution on a spot tile.
Procedure
Add a drop of starch solution on a spot tile.
Add a drop of iodine solution to the starch solution.
Note any colour change of the mixture.
Design and perform a control experiment.
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21. From the results, what can you say about the use of the iodine test?
Analysis
From the results, what can you say about the use of the iodine test?
Ans: The change from brown to blue-black   colour of iodine solution indicates the   presence of starch
Further investigation
How would you perform the iodine test on solid food?
Ans: Just add a few drops of iodine solution   directly on solid starch and observe the colour   change
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22. Functions of Carbohydrates
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
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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 C54H110O3 where H:O d 37:1
Characteristics:
– Insoluble in water
– Readily soluble in organic solvents such as         alcohol, ether and chloroform
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24. Those which exist as liquid at room temperature are called oil
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
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25. The structure of a fat molecule
Note that the three fatty acid molecules may be the same or different
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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
Place a small drop of peanut oil on a small piece of filter paper.
Alongside the oil spot place a drop of distilled water.
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27. Hold the paper up against light to examine the oil spot.
Leave the paper in the air to dry for 10 minutes. Examine the oil spot against light.
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.
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28. 2. Describe the effect of ether on fat.
Analysis
1. Consider the results of the test, how do we know whether a liquid sample contains fat?
Ans: The presence of a translucent spot on   a filter paper after drying indicates the   presence of fat
2. Describe the effect of ether on fat.
Ans: Translucent spot disappears after   dipping in ether; because fat dissolves in   ether (an organic solvent)
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29. 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

30. To know more about fats, visit:
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:
Useful Website
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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
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32. Structure of an amino acid:
The side chains specify different amino acids
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33. Two amino acids condense to form a dipeptide
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34. Many amino acid molecules  polypeptide
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35. One or more polypeptide chains  a protein molecule
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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.
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37. Put a drop of egg white on a spot tile.
Procedure
Put a drop of egg white on a spot tile.
Dip a piece of Albustix paper into the egg white. Note any colour changes.
Repeat the above test with peanut oil and distilled water. Note any colour changes.
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38. 1. Why do we test distilled water with Albustix paper?
Analysis
1. Why do we test distilled water with Albustix paper?
Ans: As a control experiment
2. Why do we test peanut oil with Albustix paper?
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: The change from yellow to green   colour of Albustix paper indicates the   presence of protein
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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:
Useful Website
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40. – Enzymes: act as catalyst for chemical reactions in the cells
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?
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41. DNA stands for deoxyribonucleic acid Structure: double helix
What is DNA?
DNA stands for deoxyribonucleic acid
Structure: double helix
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42. What are the functions of DNA?
Contains the information that controls the activities of the cells
The information governs inherited characteristics
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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
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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
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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
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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
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47. The medium for transport of substances inside the body
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
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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
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49. Also needed by plants for healthy growth Required in small amounts
In plants
Also needed by plants for healthy growth
Required in small amounts
Land plants obtain minerals from soil water
Characteristics:
Absorbed from food in the gut
Have no energy value
Usually needed in small amounts
Some minerals are components of body structures
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50. 1. Carbohydrates and fats are the only energy-giving food substances.
Check Your Concepts
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.
Ans: Proteins are also 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.
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
3. Only fat or oil can form a translucent spot on a piece of filter paper.
Ans: Fat-containing substances can also form a translucent spot on a piece of filter paper
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