Grade 8 General Science Past Paper PDF 2022

Grade 8 UNIT THREE 3. CLASSIFICATION OF COMPOUNDS Learning Outcomes At the end of this unit, learners will be able to: ♻ explain the classification of compounds into organic and inorganic; ♻ write the formulas and name the first eight a...

Grade 8 UNIT THREE 3. CLASSIFICATION OF COMPOUNDS Learning Outcomes At the end of this unit, learners will be able to: ♻ explain the classification of compounds into organic and inorganic; ♻ write the formulas and name the first eight alkanes, alkenes and alkynes and list the uses of some important common organic compounds; ♻ classify oxides into different groups and give examples of each group; ♻ develop skills in identifying acidic, basic and neutral solutions; ♻ define, and apply the concept of neutralization; ♻ explain the safety precautions while working with acids and bases;and ♻ demonstrate scientific inquiry skills along with this unit: observing, classifying, comparing and contrasting, communicating, asking questions, designing experiment, drawing conclusion, applying concepts and problem solving. UNIT THREE : CLASSIFICATION OF COMPOUNDS 43  General Science | Student Textbook Main Contents 3.1 Introduction 3.2 Organic Compounds 3.3 Inorganic Compounds 3.4 Neutralization Reaction and Salts Start-up Activity Form groups and discuss the following and present to the class. Assume that you are given two compounds (water and alcohol) in two different containers. Explain how you could distinguish between these two compounds. Introduction In Grade 7, you have learned about elements, compounds and chemical reaction. You have distinguished elements from compounds and how they are represented by symbols and formulae. You are also familiar with naming compounds and writing their formulas. In this section you will learn about compounds and their classifications. 3.1. INTRODUCTION TO COMPOUNDS After completing this section, you will be able to: ♻ define organic compounds as carbon containing compounds;and ♻ define inorganic compounds as compounds of elements other than carbon. Compounds are classified into two classes; organic and inorganic. Compounds obtained from living things (plants and animals) are organic compounds and compounds obtained from the constituents of the earth are inorganic compounds. Organic compounds are carbon containing compounds where as inorganic compounds are compounds of elements other than carbon including carbonates (CO32-), hydrogen carbonates (HCO3-), carbonmonoxide (CO) and carbon dioxide (CO2). 44 Introduction to Compounds  Grade 8 Activity 3.1. Perform the following research activity and present to the class. From different science books, discuss the historical origins of organic and inorganic; and their relationship between organic chemicals and living things. Exercise 3.1 Answer the Following Questions 1. What are the differences between organic and inorganic compounds? 2. Classify each of the following compounds as organic or inorganic. a) Common salt (NaCl) b) Sugar ( C12H22O11) c) Carbon dioxide (CO2) d) Alcohol (C2H5OH) 3.2. ORGANIC COMPOUNDS After completing this section, learners will be able to: ♻ define hydrocarbons and mention at least one source of hydrocarbons; ♻ write the general formula of alkanes, alkenes and alkynes; ♻ write the specific chemical formulas of the first eight members of alkanes, alkenes and alkynes; ♻ describe a homologous series and its general characteristics; and ♻ identify some common uses of organic compound. UNIT THREE : CLASSIFICATION OF COMPOUNDS 45  General Science | Student Textbook 3.2.1. Hydrocarbons and its sources Activity 3.2. Form a group and perform the following activity. Share your opinion to the class. 1. Which elements are constituents of hydrocarbons? 2. How hydrocarbons are named? Is it based on certain rules or randomly? Hydrocarbons are organic compounds containing only hydrogen and carbon. The natural sources of hydrocarbons include coal, petroleum and natural gases which are formed from the remains of living organisms. The three major classes of hydrocarbons are alkanes, alkenes and alkynes. The name of a hydrocarbon is derived from the number of carbon atoms present (prefix) and the ending (suffix) that relate to their names. To find the base name of hydrocarbons (alkanes, alkenes and alkynes) use the following prefixes. Table 3.1 Prefixes of the first eight hydrocarbons No carbon atoms 1 2 3 4 5 6 7 8 Name Meth- Eth- Prop- But- Pent- Hex- Hept- Oct- Nomenclature of Alkanes, Alkenes and Alkynes Nomenclature of Alkanes Alkanes are hydrocarbons with the general formula of CnH2n+2, where n = 1, 2, 3, etc. and stands for the number of carbon atoms in each alkane. For example, if n=1, the formula of alkane is C1H2×1+2 = CH4. Any consecutive group of hydrocarbon differs from the next one in a series by a CH2 unit called homologues series. CH2 CH2 CH2 CH 4 C 2 H6 C 3 H8 C 4 H10 The names of alkanes end with the suffixes ‘-ane’. For instance, the formula of the alkane containing one carbon atom is CH4. Therefore, n=1 prefix is ‘meth-’ 46 Organic Compounds  Grade 8 and we add the suffix ‘-ane’ to the prefix. Thus, the name of the alkane becomes methane. 🔄 What is the formula and name of an alkane containing three carbon atoms (n=3)? Check point 3.1 Answer the Following Questions. 1. Write the formula and name of an alkane containing 2, 4, 5, 6 and 8 carbon atoms. 2. Give the formula and name for the alkane homologues coming before and after C7H16 and find their difference in the number of carbon and hydrogen atoms. Nomenclature of Alkenes Alkenes are hydrocarbons with the general formula of CnH2n, where n = 2, 3, 4, etc. For example, if n=5, the formula of the alkene is C5H2×5 = C5H10. The names of alkenes end with the suffixes ‘-ene’. The first member of alkene starts with two carbon atoms (n=2), C2H4. The prefix is ‘eth-’ and we add the suffix ‘-ene’ to the prefix. Thus, the alkene named as ethene. Similarly, the name of C5H10 is pentene. 🔄 What is the formula and name of an alkene containing three carbon atoms (n=3)? UNIT THREE : CLASSIFICATION OF COMPOUNDS 47  General Science | Student Textbook Check point 3.2 Answer the Following Questions. 1. Write the formula and name of an alkene containing 4, 5, 7 and 8 carbon atoms. 2. Give the formula and name for the alkene coming before and after C6H12; and find their difference in the number of carbon and hydrogen atoms. Nomenclature of Alkynes Alkynes are hydrocarbons with the general formula of CnH2n-2, where n = 2, 3, 4, etc. For example, if n = 4, the formula is C4H2×4-2 = C4H6. The names of alkynes are obtained by changing the suffix ‘-ane’ of alkanes to ‘-yne’. For example, the formula of alkyne containing four carbon atoms is C4H6. The prefix is ‘but-’ and the suffix is ‘-yne’. Combining the prefix and suffix gives butyne. 🔄 What is the formula and name of the first member of alkyne homologous series? Check point 3.3 Answer the Following Questions. 1. Write the formula and name of an alkyne containing 3, 4, 5, 6 and 8 carbon atoms. 2. Give the formula and name for the alkyne coming before and after C7H12; and find their difference in the number of carbon and hydrogen atoms. 48 Organic Compounds  Grade 8 Uses of Common Organic Compounds Activity 3.3. Perform the following activity in group and present your opinion to the class. List the sources of hydrocarbons that are found in Ethiopia and report to the class; and explain how they have made life more comfortable for human beings. Methane: Methane (CH4) is mainly used as a fuel gas for cooking, heating and generating light. Methane is the major component of natural gas (~85%), commonly called Biogas, which is used as a domestic fuel. Propane and butane: Both propane and butane are gaseous alkanes marked as bottled gas and commonly known as “buta gas”. It is mainly used for cooking and heating. Ethyne: One of the main uses of ethyne is to produce oxyacetylene flame, which is used in the cutting and welding of steel and iron at high temperature. Figure 3.1 Ethyne produces oxyacetylene flame UNIT THREE : CLASSIFICATION OF COMPOUNDS 49  General Science | Student Textbook Ethanol: is used in alcoholic beverages. Nowadays, ethanol is mixed with petrol for an automotive fuel. It is used in hospitals and clinics for cleaning wounds; and as a solvent for many substances and in making perfumes and paints. Ethanoic acid (Acetic acid): Vinegar (Ethanoic acid) is used as food flavoring agent and preserving vegetables. Formalin: is used for preservation of biological specimens. It is also commonly used as an industrial disinfectant, and as a preservative in homes and medical laboratories as antiseptics, medicines, and cosmetics. Exercise 3.2 Write your answers to the following questions. 1. Classify each of the following hydrocarbons as alkane, alkene or alkyne and write their names. a) C5H10 c) C4H10 e) C6H10 b) C3H4 d) C8H18 2. Write the molecular formulas of the following hydrocarbons and indicate their differences. a) Butane, butene and butyne b) Propane, propene and propyne 3. List common organic compounds and explain their uses. 50 Organic Compounds  Grade 8 3.3. INORGANIC COMPOUNDS After completing this section, students will be able to: ♻ classify oxides into metallic and nonmetallic; ♻ describe the properties of acidic oxides and basic oxides; ♻ predict the nature of common oxides; ♻ prepare sulphur dioxide in laboratory by burning sulphur in air; ♻ prepare magnesium oxide in laboratory by burning magnesium in air; ♻ define acid and base and describe their properties; ♻ name and write formulas for some common acids and bases; ♻ describe how indicators can be used to classify solutions as acidic or basic; ♻ investigate properties of bases/alkalis experimentally by preparing their own indicator by extracting the colour from a vegetable or flowers; ♻ investigate household chemicals using locally prepared indicators; ♻ explain the safety precautions while working with acids and bases;and ♻ create a safety booklet dealing with the handling of acids and alkali. Activity 3.4. Perform the following activity and share your opinion with your group. List some elements and inorganic compounds with which you are familiar in your daily activities. Inorganic compounds are compounds consisting of mineral constituents of the earth or generally found in non-living things. Inorganic compounds are mostly found in nature as oxides (O2-), carbonates (CO32-), sulphides (S2-), sulphates (SO42-), chlorides (Cl-) and nitrates (NO3-). Inorganic compounds can be classified into four groups according to their composition and their properties. These include oxides, acids, bases and salts. UNIT THREE : CLASSIFICATION OF COMPOUNDS 51  General Science | Student Textbook 3.3.1. Oxides Oxides are binary compounds containing oxygen and any other element. Binary compounds are those consisting of only two elements. Element + Oxygen → Oxide Some examples of oxides are calcium oxide (CaO), aluminium oxide(Al2O3), sulphur dioxide (SO2), carbon monoxide (CO), hydrogen oxide (water or H2O), etc. Types of Oxides Most oxides are classified as metallic oxides and non-metallic oxides. Metallic oxides are binary compounds containing only metal and oxygen. Some examples of metallic oxides are Calcium oxide (CaO), Sodium oxide (Na2O), Aluminium oxide (Al2O3), Magnesium (MgO), etc. Non-Metallic Oxides are binary compounds containing only non-metals and oxygen. Some examples of non-metallic oxides are Nitrogen dioxide, (NO2), hydrogen oxide (H2O), carbon dioxide (CO2), sulphur dioxide (SO2), etc. Based on their chemical behaviour oxides are classified in to acidic oxides and basic oxides. Acidic oxides: Acidic oxides are oxides of non-metals. They are also called acid anhydrides. Acid anhydride means acid without water. Most non-metals form oxides that exhibit acidic properties and dissolve in water to give acidic solutions. Examples of acidic oxides include; sulphur dioxide (SO2,) nitrogen dioxide (NO2,) carbon dioxide (CO2), etc. It is important to note that all non-metal oxides are not necessarily acidic oxides. 🔄 What is the nature of phosphorous pentoxide, P O ? 2 5 52 Inorganic Compounds  Grade 8 Basic oxides: Basic oxides are oxides of metals. They are also called basic anhydrides. Basic anhydride means base without water. Some metals form oxides which exhibit basic properties and dissolve in water to give alkaline (basic) solutions. Some examples of basic oxides are sodium oxide (Na2O), calcium oxide (CaO), magnesium oxide (MgO), etc. All metallic oxides are not necessarily basic oxides. 🔄 What is the nature of potassium oxide, K O? 2 Properties of oxides i. An acidic oxides (acid anhydride) reacts with water to form an acid. Acid oxide + Water → Acid Example: SO3 + H2O → H2SO4 Sulphur trioxide Water Sulphuric acid CO2 + H2O → H2CO3 Carbondioxide Water Carbonic acid ii. A basic oxide or basic anhydride reacts with water to produce a base (Alkaline). Basic oxide + Water → Base Example: CaO + H2O → Ca(OH)2 Calcium oxide Water Calcium hydroxide K2O + H2O → 2KOH Potassium oxide Water Potassium hydroxide Preparation of Oxides The common method for preparing oxides is direct combination of elements with oxygen. The following practical activity shows the preparation of oxides. UNIT THREE : CLASSIFICATION OF COMPOUNDS 53  General Science | Student Textbook Experiment 3.1 Title: Preparation of Sulphur Dioxide Objective: To prepare SO2 and test whether it is an acidic oxide or a basic oxide. Materials required: Sulphur, litmus paper (blue and red), gas jar, bunsen burner, deflagrating spoon. Procedure: 1. Put some powdered sulphur in a deflagrating spoon and ignite. 2. When it starts burning, put it into a gas jar. 3. When the burning stops, add 5 mL of water to the gas jar and shake. 4. Put blue and red litmus paper, one after the other, in the jar. 5. Record your observations. Figure 3.2 Burning sulphur in air Observation and Analysis: (f) What is the color of the flame when sulphur burns in air? What happens to the color of blue and red litmus papers in step 4? (g) Write the chemical equation for this combustion reaction. (h) Classify the oxide formed by the combustion of sulphur as acidic or basic. Write a laboratory report in groups and present your findings to the class. 54 Inorganic Compounds  Grade 8 Experiment 3.2 Title: Preparation of Magnesium Oxide Objective: To prepare magnesium oxide and test whether it is an acidic oxide or a basic oxide. Materials required: Magnesium ribbon, red and blue litmus papers, bunsen burner, tongs, crucible. Procedure: 1. Cut about 2 cm of magnesium ribbon. 2. Hold the ribbon with a tong and burn it over a flame from the Bunsen burner. 3. After burning, put the burning metal into a crucible and collect the product. 4. Add small amount of water to the resulting powder in the crucible and shake it.Test the solution with red and blue litmus paper and record your observations Observation and Analysis: (a) What is the color of the flame produced when magnesium burns in air? (b) Write the chemical equation for the reaction. (c) What happens to the color of the red and blue litmus papers? (d) Is the resulting solution basic or acidic? Figure 3.3 Burning of magnesium in air Write a laboratory report in groups and present your findings to the class. UNIT THREE : CLASSIFICATION OF COMPOUNDS 55  General Science | Student Textbook Exercise 3.3 Answer the Following Questions 1. Classify the following oxides as acidic or basic oxides. Give reasons for your classifications. a) SO3 c) N2O5 e) P2O5 b) K2O d) BaO 2. Complete the following reaction. a) CO2 + H2O → ? b) Na2O + H2O → ? 3. Identify the anhydrides of the : a) HNO3 c) H2SO4 b) Mg(OH)2 d) KOH 4. What products are formed when the following metals react with an excess Oxygen? a) Magnesium b) Zinc c) Lithium 3.3.2. Acids Activity 3.5. Form a group and perform the following activity. Imagine a taste experiment using orange, lemon, tomato and grape fruit. They all taste alike. In what way would they taste alike, and why? What is the name of the acid in lemon and orange? Acids are among the most familiar of all chemical compounds that we encounter every day. Citric acid in lemons, sour ‘Tella’ contains acetic acid, human 56 Inorganic Compounds  Grade 8 stomach contains hydrochloric acid and some insects such as bees and ants contain formic acid. It is important to remember that not all acids are harmful. 🔄 Can you mention the acids found in milk and soft drinks? Acids are compounds that release hydrogen ions (H+) when they are in aqueous solution. H2O Example: HCl (g) H+ (aq) + Cl– (aq) Hydrochloric acid, HCl, nitric acid, HNO3 and sulphuric acid, H2SO4 are the three common laboratory acids. These acids are called mineral acids. Rules for writing and naming common acids Acids are named based on their anion or the ion attached to the hydrogen. In simple binary acids, one ion is attached to hydrogen. Names for such acids consist of the prefix “hydro-“, the first syllable of the anion, and the suffix “-ic”. These anions usually have the ending “-ide”. For example, HCl, which is hydrogen (H) and chlorine (Cl), is called hydrochloric acid (HCl). Hydro + Base name of non-metal + ic acid Example: HBr, contains the anion bromide named as hydrobromic acid. 🔄 How do you name HI? Acids containing polyatomic ions are named as follows. If the polyatomic ion ends in –ate, change the ending to –ic acid If the polyatomic ion ends in –ite, change the ending to –ous acid Examples: a. HNO3, contains the polyatomic ion nitrate, is called nitric acid. b. HNO2, contains the polyatomic ion nitrite, is called nitrous acid. UNIT THREE : CLASSIFICATION OF COMPOUNDS 57  General Science | Student Textbook Check point 3.4 Answer the Following Questions. 1. Name the following acids. a) HF b) H2SO4 c) H2CO3 2. Write the formula of the following acids. a) Sulfurous acid b) Phosphoric acid c) Nitric acid. Acid- base Indicators An indicator tells us whether a substance is acidic or basic in nature by showing changes in colour. The common indicators available in laboratories are litmus, phenolphthalein, methyl orange or methyl red and universal indicators. The pH Scale Substances can be classified as acidic, basic, or neutral based on their pH values. pH (Power of hydrogen) is a measure of acidity or basicity of a solution. pH scale is ranging from 0 (very acidic) to 14 (very basic/alkaline). Acids have a pH value less than seven and bases have a pH value greater than seven. The pH of a neutral solution equals seven. Figure 3.4 The pH scale 58 Inorganic Compounds  Grade 8 Properties of Acids i. Acids have a sour taste: The sour taste of many unripe fruits, lemon, vinegar and sour milk is caused by the acids present in them. Never taste mineral acids because they are corrosive. ii. Acids change the colour of indicators: Indicators show the presence of an acid or a base with specific color changes when placed in a solution. Acids change blue litmus and methyl orange solution to red and in phenolphthalein becomes colourless. The following practical activity shows the effect of acids on indicators. Experiment 3.3 Title: Effect of acids on acid-base indicators Objective: To investigate the effect of dilute hydrochloric acid and sulphuric acid on the colors of litmus paper, phenolphthalein and methyl orange. Materials required: Blue and red litmus papers, phenolphthalein, methyl orange, test tubes, test tube rack, dilute HCl and H2SO4. Procedure: 1. Pour about 5 mL of dilute HCl into three test tubes. 2. Hold the first test tube in inclined position and put blue and red litmus papers turn by turn into it and see if there is any colour change. 3. Add few drops of phenolphthalein in the second and few drops of methyl orange in the third and observe if there is colour change. UNIT THREE : CLASSIFICATION OF COMPOUNDS 59  General Science | Student Textbook 4. Repeat the above procedure using dilute H2SO4 solution. Observation and analysis Record your findings on table. Write a laboratory report in groups. Table 3.2: Effects of acid on Indicators Color of the indicator in the acid solution Acid Litmus Phenolphthalein Methyl orange Dilute HCl Dilute H2SO4 iii. Reaction of Acids with metals: Dilute acids react with active metals like zinc, magnesium and aluminum to form salts and liberate hydrogen gas. Very active metals like sodium, potassium, and calcium react very violently with dilute acids, so care should be taken. Active Metal + Dilute Acid → Salt + Hydrogen Example: Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g) Calcium Hydrochloric acid Calcium chloride Hydrogen gas The following practical activity demonstrates the reaction of acids on metals. Experiment 3.4 Title: Reaction of an acid with a metal Objective: To investigate the reaction of zinc metal with hydrochloric acid. Materials required: A test tube, zinc granules, dilute hydrochloric acid, match box rubber stopper and a test tube holder. 60 Inorganic Compounds  Grade 8 Procedure: 1. Add a few zinc granules in a test tube. 2. Pour about 5 mL of dilute HCl into a test tube as shown in Figure 3.2. Figure 3.5 Reaction of zinc with hydrochloric acid 3. Remove the rubber stopper and introduce the lighted splint in to the mouth of the test tube and record your observations. Caution! Note that you should hold the test tube and the lighted splint away from Yourself and others! Observation and analysis: (a) What happens when you drop zinc metal into the test tube containing dilute HCl? (b) What is the colour of the gas? (c) What happens when the lighted splint is held inside the mouth of the test tube? (d) Write the chemical equation for the reaction between zinc and hydrochloric acid. Write a laboratory report in groups and present to the rest of the class UNIT THREE : CLASSIFICATION OF COMPOUNDS 61  General Science | Student Textbook iv.Reaction of Acids with Carbonates and Hydrogen Carbonates: Acids react with metal carbonates and hydrogen carbonates to form salts, water and carbon dioxide gas. Acid + Carbonate → Salt + Water + Carbon dioxide Example: 2HCl (aq) + Na2CO3(s) → 2NaCl (aq) + H2O(l) + CO2(g) Hydrchloric acid Sodium carbonate Sodium chloride Carbon dioxide Acid + Hydrogen carbonate → Salt + Water + Carbon dioxide Example: HCl (aq) + 2NaHCO3 (aq) → Na2CO3 (aq) + 2H2O (l) + 2CO2(g) Hydrchloric Sodium bicarbonate Sodiom carbon- Water Carbon diox- acid ate ide The following practical activity demonstrates the reaction of acids with carbonates and hydrogen carbonates. Experiment 3.5 Title: Reactions of acids with carbonates and hydrogen carbonates Objective: To investigate the reactions of carbonates and hydrogen carbonates with dilute hydrochloric acid and sulphuric acid. Materials required: test tube, boiling tube fitted with cork, thistle funnel, delivery tube, sodium carbonate, sodium hydrogen carbonate, dilute HCl and freshly prepared lime water (calcium hydroxide solution). 62 Inorganic Compounds  Grade 8 Procedure: 1. Take the boiling tube and add about 0.5 g sodium carbonate to it. 2. Take about 2 mL of freshly prepared lime water in a test tube. 3. Add about 3 mL dilute HCl to the boiling tube containing sodium carbonate. 4. Immediately fix the cork filled with a delivery tube. 5. Dip the other end of the delivery tube in the lime water. 6. Observe the lime water carefully. 7. Repeat the above procedure for sodium hydrogen carbonate and dilute H2SO4. Observation and analysis: (a) When dilute HCl is added to sodium carbonate or sodium hydrogen carbonate, what gas is evolved? (b) What happens to the lime water the gas passing to it? Why is that so? (c) Write the chemical equation that occurred on the reactions. Write a laboratory report in groups and present to the rest of the class. v. Acids neutralize bases: Acids react with bases to form salts and water. This reaction is called neutralization reaction. Acid + Base → Salt + Water Example: HCl + NaOH → NaCl + H2O Hydrchloric acid Sodium hydroxide Sodium chloride Water The following practical activity demonstrates the neutralizing effect of an acid on a base. UNIT THREE : CLASSIFICATION OF COMPOUNDS 63  General Science | Student Textbook Experiment 3.6 Title: Neutralizing effect of an acid on a base. Objective: To investigate the neutralizing effect of HCl on sodium hydroxide. Materials required: A test tube, dropper, methyl orange or phenolphthalein solution indicators, solution of sodium hydroxide and dilute hydrochloric acid. Procedure: 1. Take about 2 mL solution of sodium hydroxide in a test tube. 2. Add a drop of phenolphthalein indicator to it and observe the colour. 3. With the help of a dropper add dilute hydrochloric acid drop wise and stir the solution constantly till the colour disappears. 4. Now add a few drops of NaOH solution. The colour of the solution is restored. Figure 3.6 Reaction between NaOH and HCl 64 Inorganic Compounds  Grade 8 Observation and analysis (a) What colour appeared when phenolphthalein is added to the solution of NaOH? (b) Why does the colour disappear on adding HCl? (c) What will happen when sodium hydroxide has reacted with hydrochloric acid? (d) Write the balanced equation for the reaction that takes place in this experiment. Write a laboratory report in groups and present your findings to the class. Exercise 3.4 Write the Answer for the Following Questions. 1. Which ion is a characteristic of acids in water solution? 2. What will happen if you add the following on hydrochloric acid, HCl? a) Phenolphthalein b) Blue litmus c) Methyl orange 3. An acid reacts with a substance Z with the liberation of CO2 gas. What can be the nature of Z? 4. List the properties of acids. 5. Complete the following reaction a) Zn(s) + HCl (aq) → ? b) HCl (aq) + CaCO3 (s) → ? c) HNO3 (aq) + KOH(aq) → ? UNIT THREE : CLASSIFICATION OF COMPOUNDS 65  General Science | Student Textbook 3.3.3. Bases Activity 3.6. Perform the following activity and share your opinion with the class. When plants are partly burned, ash is formed. When the ash is dissolved in water, it gives a solution which tastes bitter and feels slippery when rubbed between the fingers. Why do you think this happens? Bases are chemical compounds that we encounter every day and used in industry and at home. Sodium hydroxide, NaOH, used in washing soaps and detergents; potassium hydroxide, KOH in bathing soaps, calcium hydroxide, Ca(OH)2 neutralizes acidic soil, etc. Bases are substances that react with acids to form salts. Bases which are soluble in water are called alkalis. An alkali is a substance that releases hydroxide ion (OH–) when dissolved in water. H2O For example: NaOH (aq) Na+(aq) + OH–(aq) Sodium Hydroxide Sodium ion Hydroxide ion Some of the example of bases include sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide. 🔄 What is the name of the base used to neutralize excess acidity in our stomach? Naming Bases The names of bases end with hydroxide. Start with name of the cation (metal ion or ammonium ion, NH4+) followed by name of the anion (hydroxide ion). Metal (cation) name + hydroxide (OH-) Example: Na+ + OH- → NaOH Sodium ion Hydoxide ion Sodium hydroxide 66 Inorganic Compounds  Grade 8 Check point 3.6 Answer the Following Qustions. 1. Name the following bases. a) Mg(OH)2 b) Al(OH)3 c) Ca(OH)2 2. Write the formula of the following bases. a) Potassium hydroxide b) Iron(III) hydoxide c) Ammonium hydroxide Properties of Bases i. Bases are slippery to the touch and have a bitter taste in aqueous solutions: Strong bases such as NaOH and KOH are very corrosive. So they should be neither brought in to contact with the skin nor tasted. ii. Bases change the colour of indicators: Bases turn red litmus to blue, methyl orange solution to yellow and Phenolphthalein to pink. The following practical activity demonstrates the effect of a base on indicators. Experiment 3.7 Title: The effect of a base on indicators Objective: To study the effect of a base on indicators Materials required: Red and blue litmus papers; phenolphthalein solution, methyl orange, calcium hydroxide, test tubes, test tube holder and rack. UNIT THREE : CLASSIFICATION OF COMPOUNDS 67  General Science | Student Textbook Procedure: 1. Take four clean test tubes. 2. Add about 5 mL calcium hydroxide solution in each of the test tubes and label the test tubes as 1, 2, 3, and 4 as shown in Figure 3.4. Figure 3.7 Testing the effect of base on indicator 3. Put red litmus paper, blue litmus paper, 2 drops of phenolphthalein solution and 2 drops of methyl orange solution in test tubes 1,2,3 and 4 respectively. Observe the colour change and record your observation. Observation and analysis: What happens to the colours of the red litmus paper, blue litmus paper,phenolphthalein and methyl orange solutions after the addition of calcium hydroxide (Lime water) solution? Write a laboratory report in groups and present your to the rest of the class. iii. Bases neutralize acids: Bases react with acids to form salt and water. Base + Acid → Salt + Water Example: KOH (aq) + HCl (aq) → KCl (aq) + H2O (aq) Potassium hydroxide Hydrchloric acid Potassium chloride Water 68 Inorganic Compounds  Grade 8 Experiment 3.8 Title: Neutralizing effect of a base on an acid. Objective: To investigate the neutralizing effect of NaOH on HCl. Materials: test tube, dropper, methyl orange or phenolphthalein solution indicators, solution of sodium hydroxide and dilute hydrochloric acid. Figure 3.8 Reaction between hydrochloric acid and sodium hydroxide. Procedure: 1. Take about 2 mL solution of HCl in a test tube. 2. Add a drop of methyl orange solution indicator to it and observe the colour. 3. With the help of a dropper add dilute NaOH acid drop wise and stir the solution constantly till the colour disappears. 4. Now add a few drops of HCl solution. The colour of the solution is restored. Observation and Analysis (a) What colour appeared when methyl is added to the solution of HCl? (b) Why does the colour disappear on adding NaOH? (c) Write the balanced equation for the reaction that takes place in this experiment. Write a laboratory report in groups and present your findings to the class. UNIT THREE : CLASSIFICATION OF COMPOUNDS 69  General Science | Student Textbook Investigation using local indicators Project Work The objective of this project work is to investigate household chemicals using locally prepared indicators. In group, with guidance, you should prepare your own acid-base indicators by extracting the colour from different plants (flowers, fruits, vegetables) and investigate the presence of acid and base in different house hold chemicals such as vinegar, baking soda, lemon, etc. found in your local areas and present your result to the class using a table (chart). Safety precautions while working with acids and Bases It is very important to avoid contact with acids and bases with any part of your body or clothing. The following safety precautions are useful in handling acids and bases in school laboratories or anywhere while working with them. ✅ If a concentrate acid is spilled or splashed on your skin, wash thoroughly the affected part with water, and then wash it with 10% Na CO solution. ✅ If an acid enters your eye, wash thoroughly with plenty of water. 2 3 ✅ If you accidentally drink corrosive acids, take a base such as Mg(OH). ✅ If you drink corrosive base, neutralize it by drinking 1 - 2% dilute solution 2 of acetic acid or lemon juice. ✅ Never add water into concentrated acids! Instead add acid to water. ✅ If a base is spilled on your skin wash the affected area with plenty of water and then treat the affected part with a weak acid such as dilute acetic acid. ✅ If a base comes into contact with your eyes, wash the eyes with cold water. Assignment In groups, conduct an investigation using science books or internet; search and develop a safety booklet on the correct ways of handling acids and alkalis. 70 Inorganic Compounds  Grade 8 Exercise 3.5 Answer the Following Questions 1. Indicate whether each of the following is a property of acids, bases, or both acids and bases. a) Have a sour taste b) Taste bitter c) React with metals d) Turns litmus paper red e) Feels slippery f) Turns litmus paper blue 2. What measures should you take if: a. an acid accidentally enters your eyes? b. you accidentally drink a base? 3. Write a least two important properties of bases. 4. What ion is a characteristic of all bases in water solution? 5. complete the following reaction a) NaOH (aq) + HCl (aq) → ? b) Mg(OH)2 (aq) + HNO3 → ? UNIT THREE : CLASSIFICATION OF COMPOUNDS 71  General Science | Student Textbook 3.4. NEUTRALIZATION REACTION AND SALTS After completing this section students will be able to: ♻ identify some everyday uses of neutralization; ♻ define salt and give its examples;and ♻ name and write formulas for some common salts. Activity 3.7. Discuss the following in groups and share your opinion to the rest of the class. What is the importance of neutralization in daily life? 3.4.1. Neutralization Reaction A neutralization reaction is the reaction between an acid and a base to form salt and water. Neutralization reactions are very useful in our daily activities. Some of the applications of neutralization in our daily activities are as follows. i. Neutralization at Home We use neutralization for most of the activities in our home for different purposes. Baking powder is usually used to help the dough rise to bake bread. Conditioner is used with shampoo to prevent small scales on hair. Toothpaste contains bases that neutralize the acid produced by bacteria in our mouth. 🔄 Can you mention other applications of neutralization reaction in home? ii. Neutralization in Health 72 Neutralization Reaction and Salts  Grade 8 Our stomach contains hydrochloric acid. The excess acid in the stomach is neutralized by taking antacid like milk of magnesia, Mg(OH)2. The sting of an ant and bee contains formic acid. When an ant or bee bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralized by rubbing moist baking soda (NaHCO3). Wasp stings are alkaline and can be neutralized with vinegar. 🔄 Can you mention other applications of neutralization reaction in health? iii. Neutralization in Agriculture Excessive use of chemical fertilizers results in increased acidity of the soil. When the soil is acidic, it is treated with powdered lime (CaO), limestone (CaCO3) or ashes of burnt wood. If the soil is basic, organic matter is added to it. The acidic gas from the decomposition of compost neutralizes the alkalis in basic soil. 🔄 Can you list other applications of neutralization reaction in agriculture? The ability of plants to take nutrients from the soil into their roots is affected by the pH content of the surrounding soil particles. When organic materials, such as dead leaves, animal wastes, decay, organic acids, etc are produced and these lower the pH of the soil so, over the years, soil naturally becomes more acidic. For the soil to produce good yields of crops, it is necessary to raise the pH by spreading lime in the form of limestone, CaCO3, quick lime, CaO or slaked lime, Ca(OH)2. 🔄 Why it is necessary to adjust the pH of the soil? In agriculture different crops require different nutrients in different proportions and, as a result each crop grows best in soil within a particular pH range. Maintaining proper soil pH is one of the most important aspects of soil fertility management. Soil pH is a measure of active acidity based on the concentration of hydrogen ions (H+) in soil solution. Soil pH directly affects the life and growth of plants because it affects the availability of all plant nutrients. Between pH 6.0 and 6.5, most plant nutrients are in their most available states. A nutrient must be soluble and remain soluble long enough to successfully travel through the soil solution in to the roots. UNIT THREE : CLASSIFICATION OF COMPOUNDS 73  General Science | Student Textbook The best pH ranges for growing different crops are for example: potatoes 5.5 – 6.5, oats 5.5 – 7.0 and beans 6.0 – 7.5. Practical Activity Perform the following activity in groups and present your work to the class. 1. Create a written or digital display to exhibit the use of neutralization reactions in daily life. 2. Using a pH meter in your school laboratory, perform a measurement on the pH of different soil samples taken from different locations. 3.4.2. Salts 🔄 What is a salt? Does common salt (sodium chloride) is the only salt? The term ‘salt’ does not refer only to the table salt (sodium chloride, NaCl) which we use to make our food. The word ‘salt’ applies to a large group of compounds. Salts are widely used as raw materials in chemical industries, as fertilizers, and building materials, etc. A salt is a compound consisting of the positive ion of base and the negative ion of an acid. Sodium sulphate (Na2SO4) is a salt that contains sodium ion (Na+), derived from NaOH and the sulphate ion (SO42–), derived from H2SO4. Some examples of salts are sodium chloride, (NaCl), calcium carbonate (CaCO3), potassium nitrate (KNO3) and Sodium bicarbonate, (NaHCO3). Naming and Writing Formula of Salts Salts are named by writing a prefix with a cation name followed by base name of an ion such as -ate, -ite and –ide. Name of Cation + Base Name of Anion + ide/ ate/ite 74 Neutralization Reaction and Salts  Grade 8 Example: The formula and name of the compound formed from Mg2+ and Cl− is: For each ion of Mg2+ ion one Cl- ions is needed; so write 2Cl- and deduce the formula as: Mg2+ + 2Cl- → MgCl2 (Magnesium chloride) For writing and naming a salt containing polyatomic ions, the positive ion is named first followed by the name of the polyatomic ion. Polyatomic anions end with –ate: includes NO3− (nitrate), PO43−(phosphate), CO32− (carbonate), and SO42− (sulphate). Examples: NaNO3sodium nitrate, Potassium carbonate, K2CO3, etc Polyatomic anions end in –ite: includes NO2−, nitrite and SO32−, sulphite. Examples: Potassium sulphite, K2SO3, Sodium nitrite, NaNO2,etc. Polyatomic anions with hydrogen attached use the prefix -hydrogen (or bi): HCO3−( hydrogen carbonate (bicarbonate)), HSO4− (hydrogen sulfate) and HPO4- (hydrogen phosphate). Example: (NH4)2HPO4, diammonium hydrogen phosphate (DAP) Uses of salts Activity 3.8 In this activity you are expected to perform the following tasks in groups by reading different Science reference books and present to the class. Prepare a table and write the formula and important uses of: a) sodium chloride d) potassium nitrate b) calcium carbonate e) diammonium phosphate c) sodium bicarbonate (DAP) UNIT THREE : CLASSIFICATION OF COMPOUNDS 75  General Science | Student Textbook Exercise 3.6 Answer the Following Questions. 1. Name the following salts. a) Na2SO4 c) Mg3(PO4)2 b) K2CO3 d) NaHCO3 2. Write the formula of the following salts. a) Calcium sulphate b) Sodium carbonate c) Ammonium phosphate d) Potassium nitrate 3. Name the base and the acid from which the positive and the negative ions are derived in each of the following salts. a) Sodium nitrate b) Calcium chloride c) Potassium sulphate 4. Mention and explain the importance of neutralization in daily activities? 5. How do you treat if the soil is too acidic and too basic? 🔒 🔑🔑 Acid KEY TERMS 🔑🔑 Metallic oxide 🔑🔑 Acidic oxide Alkane 🔑 Naming salts Neutralization 🔑🔑 Alkene Alkyne 🔑🔑 reactions Nomenclature 🔑🔑 Base (Alkali) Basic oxide 🔑🔑 Non metallic oxide Organic compound 🔑🔑 Homologous series Hydrocarbon Inorganic compound 🔑 Oxide Salt 76 Neutralization Reaction and Salts  Grade 8 UNIT SUMMARY ʯOrganic compounds are carbon-containing compounds except the oxides of carbon, carbonates, and hydrogen carbonates. ʯHydrocarbons are organic compounds that contain only carbon and hydrogen. ʯAlkanes are hydrocarbons with the general formula CnH2n+2 where ‘n’ is the number of carbon atoms in the molecule. ʯAlkenes are hydrocarbons with the general formula CnH2n where ‘n’ is the number of carbon. ʯAlkynes are hydrocarbons with the general formula CnH2n-2 where ‘n’ is the number of carbon. ʯInorganic compounds are classified as oxides, acids, bases, and salts. ʯOxides are classified as acidic and basic oxides depending on their properties. ʯAcids are compounds that release hydrogen ions in water solution. ʯSalts are mainly prepared by neutralization reactions. ʯNeutralization reactions have different applications in everyday life and industrial Processes. Neutralization reactions are very useful in our daily activities such as in home, health and agriculture. UNIT THREE : CLASSIFICATION OF COMPOUNDS 77  General Science | Student Textbook REVIEW EXERCISE I. Match the items under column ‘A’ with those under column ‘B’. Column “A” Column “B” 1. Bottled gas used as fuel. A. Ethyne 2. A fuel to produce flame used for cutting B. Formalin C. Methane and welding metals. D. Butane 3. A constituent of all alcoholic beverages. E. Ethanoic acid 4. Organic chemical used to preserve F. Octane biological specimens. G. Ethene 5. A chemical used as food flavoring agent. H. Ethanol 6. Major component of natural gas called Biogas II. Choose the correct answer from the given alternatives for each of the following questions. 1. A molecule with the formula C3H8 is a(an): A. propene C. propyne B. propane D. ethane 2. When a drop of vinegar solution is put on the blue litmus paper, it turns; A. red C. colourless B. blue D. no change 3. What must be added when the soil is too basic? A. Organic matter C. Slaked lime B. Quick lime D. Lime stone 4. The correct formula of octene is: A. C8H18 C. C8H16 B. C8H14 D. C8H20 5. Which of the following feel soapy on touching? A. Acid C. Salt B. Base D. None of these 78 Neutralization Reaction and Salts  Grade 8 6. The formula of sodium carbonate is: A. NaHCO3 C. Na2CO3 B. Na2SO4 D. NaHPO4 7. Which of the following salts is used as a baking powder? A. (NH4)2HPO4 C. CaCO3 B. NaHCO3 D. KNO3 8. Which one of the following pairs of compounds produces calcium sulphate? A. CaO and HCl. C. CaO and H2O. B. Ca(OH)2 and HNO3. D. Ca(OH)2 and H2SO4. 9. Which of the following are not the characteristics of a base? A. A base changes the colour of an indicator. B. A base produces hydrogen ions in water. C. A base has a bitter taste. D. A base can neutralize acids. 10. Which one of the following compounds is used as a fertilizer? A. Mg(OH)2 C. HCl B. NaCl D. NH4NO3 III. Give short answers for each of the following questions. 1. Deduce the molecular formula of: a) butyne c) hexane e) heptene b) propene d) octyne 2. Write the names and formulas of the acids and bases required to prepare each of the following salts. a) Potassium phosphate b) Sodium sulphate c) Magnesium carbonate 3. Write the name and the formula of a salt used in: a) our diet. b) making construction materials c) making gun powder UNIT THREE : CLASSIFICATION OF COMPOUNDS 79  General Science | Student Textbook UNIT FOUR 4. HUMAN BODY SYSTEMS AND HEALTH Learning Outcomes At the end of this unit, learners will be able to: ♻ list down the major organs that constitute the human body systems; ♻ explain the main functions of the major human body systems; ♻ list down the main diseases associated with the major human body systems;and ♻ discuss the effects of diseases of the major human body system. Main Contents 4.1 Integumentary System 4.5 Respiratory System 4.2 Muscular System 4.6 Circulatory System 4.3 Skeletal System 4.7 Reproductive System 4.4 Digestive System Introduction 80 Neutralization Reaction and Salts  Grade 8 In grade 7, you have learned about cells as the basis of life; their basic structures, functions and the level of organization. A human body is the result of coordinated activities and functions of different systems which are made up of several organs found in human body. In this unit you will learn about the body systems which include the integumentary, muscular, skeletal, digestive, respiratory, circulatory and reproductive systems. The aim of this unit is to introduce the major organs that constitute the human body systems and their functions in your daily life and to identify the diseases associated with the human body systems. The unit also deals with the causes or effects of major diseases or disorders of these body systems. Start-up Activity Discuss this activity in groups and present your discussions to the class. Identify and name of organs that form human body systems Figure 4.1 Human body systems UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 81  General Science | Student Textbook 4.1. INTEGUMENTARY SYSTEM At the end of this topic, learners will be able to: ♻ distinguish the major structural components of human integumentary system; ♻ describe the main functions of human integumentary system; and ♻ identify and discuss the main diseases or disorders and effects of human integumentary system. 🔄 How the human body is protected from foreign invaders? Integumentary system is a system that covers and protects the entire human body. It consists of skin and accessory organs to protect the body from the outside world. 4.1.1. Components of Integumentary System Activity 4.1. Discuss the following questions in a group and present your response to the class. 1. Name the structures that form human integumentary systems. 2. Identify and discuss the outer layer and inner layer of a skin, the outer and inner parts of hair. 3. Discuss about sweat and sebaceous glands with their ducts. 82 Integumentary System  Grade 8 Figure 4.2 Integumentary system 🔄 What are major layers that form skin? The integumentary system consists of the skin and its accessory organs such as hair, nails, and cutaneous glands. Skin is the largest organ in the body and composed of three layers of tissue: the outer epidermis, the middle dermis and the inner hypodermis (subcutaneous) layer. Epidermis is the outer layer of the skin made of stratified squamous epithelium. It has no blood supply. Dermis/true skin is strong, flexible, connective tissues of a mesh work of collagen, reticular and elastic fibers. Most part of the skin is composed of dermis. Hypodermis is a subcutaneous layer (under the skin) found beneath the dermis. It is composed of loose, fibrous connective tissue, which is richly supplied with lymphatic and blood vessels and nerves. Hypodermis is much thicker than dermis. 🔄 What are accessory organs of integumentary system? Accessory organs of integumentary system include the hair, nails, sebaceous and sweat (sudoriferous) gland, etc. UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 83  General Science | Student Textbook Hair is composed of keratinized threads of epithelial cells, which develops from the epidermis. Hair consists of two regions: the shaft part above skin (protruded through the epidermis to the outside) and the root embedded in the skin (dermis). Nails are scale-like modifications of epithelial cells in the epidermis. They are made of hard, flat, keratin on dorsal side of the distal segment of fingers and toe. Sebaceous (oil) glands are made of modified cuboidal epithelium and occur all over the body except in the palm and sole. They secret sebum (oily semi fluid substance, form entirely lipids). Sudoriferous gland is sweat gland that found all over the body, except the lips, nipples, and external genitalia. They are two types: eccrine and apocrine glands. Eccrine glands occur over most of your body and open directly onto the surface of skin. Apocrine glands open into the hair follicle, leading to the surface of the skin. 4.1.2. Functions of Integumentary System Activity 4.2. Perform this activity in a group and present your responses to the class. Discuss the roles of skin and accessory organ forming the integumentary system. 🔄 What are the functions of integumentary system? i. Protection: The integumentary system is used to protect physical, chemical and biological barrier against skin infection by secreting substances. ii. Excretion: Waste materials such as ammonia, urea and excessive salt are eliminated in the form of sweating. 84 Integumentary System  Grade 8 iii. Body temperature regulation: Sweating by the sweat glands promotes evaporation, resulting in a loss of excessive body heat. iv.Cutaneous sensation: Nerve receptors in the dermis (skin) layers detect sensations such as heat, cold, pain, pressure, and touch. v. Vitamin D synthesis: Radiation of the sunlight activates a series of chemical reactions in the epidermis layer, resulting in the synthesis of vitamin D. 4.1.3. Major Skin Diseases Activity 4.3. Discuss in groups and list as many skin diseases you know as possible from your personal experience and present your opinion to the class. Acne is a skin disease marked by pimples on the face, chest, and back caused by excessive amount of sebum into hair follicles at puberty. Blister is characterized by watery, clear, fluid-filled area on the skin. Hives are the familiar welts (raised, red, itchy areas) that can occur on the skin. They are an allergic response due to food, drug, insect bite, infection or stress causes. Actinic keratosis is caused by sun damage and lead to squamous cell carcinoma. Roscea is redness of skin around eyes and nose accompanied by rash like lesions. Carbuncle is red, painful and irritated lump under the skin and may be accompanied by fever, body aches and fatigue. It can cause skin crustiness/ oozing. Latex allergy is warm, itchy, red wheals at the site of contact that may take on a dry, crusted appearance with repeated exposure to latex. UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 85  General Science | Student Textbook Eczema is non-contagious, inflammatory skin disorder caused by allergen or irritant such as diet, make-up, soaps, medications, and emotional stress. Warts are small growths caused by a viral infection of the skin or mucous membrane. They are contagious and can easily pass from person to person. Chickenpox is clusters of itchy, red, fluid-filled blisters in all over the body. Rash is accompanied by fever, body aches, sore throat, and loss of appetite. 86 Integumentary System  Grade 8 Exercise 4.1 Choose the correct answer from the given alternatives. 1. Which of the following layer of the skin does not contain blood vessels? A. Epidermis C. Dermis B. Hypodermis D. Reticular layers 2. Which of the following is the proximal part of nail? A. Free edge C. Lunula B. Nail body D. Shaft 3. The glands that are found all over the skin except on the palms and soles are: A. Merocrine glands C. Apocrine glands B. Sebaceous glands D. Sweat glands 4. Which of the following sensations is not detected by nerve receptors in the dermis layers? A. Heat C. Pressure B. Pain D. Taste 5. What causes acne? A. Clogged merocrine glands B. Clogged apocrine glands C. Clogged sebaceous glands D. Clogged sweat glands UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 87  General Science | Student Textbook 4.2. MUSCULAR SYSTEM At the end of this topic, learners will be able to: ♻ distinguish the major structural components of human muscular system; ♻ describe the main functions of human muscular system;and ♻ identify and discuss the main diseases and effects of human muscular system. 🔄 What is muscular system? Muscular system is a system that allows movement of part of a body, the whole body or fluids such as blood via a blood vessel. It is composed of muscle fibers. 4.2.4. Components of Muscular System Activity 4.4. Discuss in group about the human muscular system and present your responses to the class. 1. Identify and name musles that form the muscular system. 2. What do you feel when you relax and contract your arm and leg muscles? 🔄 Can you mention the types of muscles? There are three types of muscles in human body. They are skeletal muscles, the smooth muscles and cardiac muscles. 88 Muscular System  Grade 8 Figure 4.3 Human muscular system Skeletal (voluntary) muscles are muscles attached to the bones of the skeleton by tissues called tendons. They are capable of permitting body movement. When these muscles contract, skeletal parts move. The contraction of the skeletal muscles is under conscious or voluntary control and occurs faster than other muscles. Smooth (involuntary) muscles are muscles found in the walls of viscera (intestine, stomach, and other internal organs) and blood vessels. Their contraction is involuntary and contract more slowly than the skeletal muscles. Cardiac muscle is found only in the walls of the heart. Unlike the skeletal muscles its contraction is involuntary for the most part. Its contraction pumps blood and accounts for the heartbeat. UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 89  General Science | Student Textbook 4.2.5. Functions of Muscular System Activity 4.5. Perform the activity in group of 5 or 6 and present your responses to the class. Explain the main functions of muscles and special property of muscle cell that allows movement. The functions of muscular system are: muscles produce movements of body as a result of contraction; muscles force or transport substances to move through visceral tracts; muscles enable quick response to changes in environment such as expression of emotions (facial and neck muscles); muscles maintain posture by overcoming gravity effects while sitting/standing; muscles are also needed to pump blood and maintain blood pressure; muscles produce body heat and regulate body temperature; muscles act as protection of internal organs. 🔄 How do muscles work? When muscles are involved in body movement, they actually work in pairs in antagonistic (opposite) manner. While one muscle in the pair contracts the other must relax. For instance, if you were to bend your arm at the elbow, the biceps contracts and bulges and at the same time the triceps relaxes. You can see the bulges in your arm as the biceps contract. The biceps relax while the triceps contract during lower the arm to the original position. In your heart also, when the upper chamber (auricles) contract, the lower chambers (ventricles) relax. 90 Muscular System  Grade 8 4.2.6. Major Muscle Disorders Activity 4.6. Discuss the activity in group and present your discussion to the class. Mention and explain any muscle disease you know from your personal experience. Muscle strain is an injury that affects the muscle or the tendon and ligament. Muscle strain is caused by general weakness and fatigue; challenges with flexibility; body not conditioned enough. Muscle dystrophy is inherited disorder characterized by muscle weakness and a loss of muscle tissue. Exercise 4.2 Choose the correct answer from the given alternatives. 1. Which type of muscle is contracted under conscious or voluntary control? A. Cardiac C. Smooth B. Skeletal D. A and B 2. Which one of the following muscle is found in the walls of stomach? A. Smooth C. Skeletal B. Cardiac D. Heart muscle 3. What would happen if you were to bend your arm at the elbow? A. The biceps contracts C. The triceps relaxes B. The biceps bulges D. All of the above UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 91  General Science | Student Textbook 4. Which of the following is not the function of muscular system? A. Movement of the body B. Maintain blood pressure C. Give response to environmental change D. Protect external structures of the body 5. Which one is inherited disorder characterized by loss of muscle tissue? A. Fibromyalgia B. Myasthenia gravis C. Muscle dystrophy D. Muscle strain 4.3. SKELETAL SYSTEM At the end of this topic, learners will be able to: ♻ distinguish the major structural components of human skeletal system; ♻ describe the main functions of human skeletal system; and ♻ identify and discuss the main diseases and effects of human skeletal system. 🔄 What is the skeleton and its importance in our body? The skeleton is the entire collection of bones inside our body. It can be defined as the hard framework of human body around which the entire body is built. Skeletal system is a system that supports our flesh or soft tissue giving us an erect posture as well as protection of major organs. 92 Skeletal System  Grade 8 4.3.1. Structural Components of Skeletal System Figure 4.4 The human skeleton Activity 4.7. Be in groups and discuss on the above figure 4.4 of the human skeletal system. Observe, record and investigate bones of the major body parts. 1. How many number of bones in the various body parts of human skeletal system? 2. Identify axial and appendicular skeletons and examine their types, sizes and shapes. UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 93  General Science | Student Textbook 🔄 What are structural components of skeletal system? Skeletal system is also the system of bones, associated with cartilages and joints. Bones are tough, rigid (strongest) and dense forms of connective tissues made up of living cells. The body of the baby has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults have. The bones of the skeleton can be categorized into two: the axial and appendicular. 🔄 What is the axial skeleton? The part of the skeleton along the axis of the body is the axial skeleton. The axial skeleton consists of skull, sternum, ribs and vertebral column. Skull is a bony outline of the head formed from cranial and facial bones. The cranium protects the brain. However, the facial bones provide structure for the upper and lower jaws, cheeks and nose. Sternum is the breast bone in the middle of the rib cage attached to it by cartilage. Ribs are twelve (12) pairs of thin and flat bones. They are slightly curved and connected to sternum in the middle of the chest. Vertebral column also referred to as the back-bone or spine vertebral column is extending from the end of skull to the pelvis (hip). 🔄 What is the appendicular skeleton? The appendicular skeleton supports the limbs and connects them to the axial skeleton. It is composed of all the bones of shoulder, hip and limbs or appendages. Shoulder bones are composed of clavicle and scapula. The clavicle or collar bone is connected to the sternum in front while the scapula bone is at the back. Hip bones are also known as hip girdle and composed of two hip bones. Fore limbs are the front limbs that refer to the arms, the forearms and the hands. It consists of various bones like humerus (upper arms), radius (inner lower arm), ulna (outer lower arm), carpals (wrists), metacarpals (hands) and 94 Skeletal System  Grade 8 phalanges (fingers). Hind limbs are the back limbs or appendages and consist of different bones like femur (upper leg or thigh), tibia and fibula (lower legs or shin), patella (kneecap) tarsals (ankles), metatarsals (feet), and phalanges (toes). 🔄 Do our bones have the same size and shape? Bones of the skeleton vary in shape and size so do in their structure. i. Long bones are compact bones with hollows or cavities filled with yellow bone marrow. Their ends contain spongy bones covered with cartilage for cushion. They are designed for strength. Example: Upper and lower limb bones. Bone marrow is soft structure in the bones where red blood cells are made. ii. Short bones are compact bones with chambers or partitions but without marrow. Example: Bones of fingers and toes. iii. Flat bones are compact bones that have no cavity or hollow. Examples are bones of ribs, sternum and scapula. Activity 4.8. Perform the activity in group and present your responses to the class. 1. Explain the type of movement allowed by each type of joint by giving example. 2. Your teacher may display charts and observe the types of joints and then cut the cardboard or any thick paper. 3. Construct models of types of joints by using cardboard, papers and glue. Joint is a junction between two or more bones, bone and cartilage as well as between two or more cartilages. It is a structure to permit movements in a hard and rigid skeleton. Joints keep bones apart and hold them in place as they move or rotate. Based on their function or movability, there are two different types of UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 95  General Science | Student Textbook joints; these are fixed (immovable) and movable joints. i. Immovable joint is joint in which the bones are fixed in place and do not move at all. It is made up of bones fused together with fixed joints. Example: skull bone. ii. Movable joints allow a person to twist and bend. Some movable joints allow us to move all direction and others only allow us to move one direction. 4.3.2. Functions of Skeletal System Activity 4.9. Form a group of 5 or 6 to discuss the following questions and share your discussions to the class. 1. Discuss and report the roles of the bones of the upper and lower extremities. 2. Why joints are important at articulations of two or more bones? The roles of skeleton in our body are: ✅ it protects vital organs, such as the brain, heart, and lungs, ✅ it supports the body and gives us our distinctive shape, ✅ it allows us to move in particular ways, ✅ it makes new blood cells within the marrow cavities of certain bones to maintain a healthy bloodstream. 4.3.3. Major Diseases of Skeletal System Activity 4.10. Perform the activity in a group and present your response to the class. Discuss and list various skeletal system diseases and their effects. 96 Skeletal System  Grade 8 The major skeletal disorders are osteoporosis, osteoarthritis and fracture. Osteoporosis is increased porosity or softening of the bones caused by hormone deficiency, prolonged lack of calcium in the diet, and sedentary lifestyle. Osteoarthritis is a chronic disease that usually occurs as a result of aging and affects the hips and knees. It leads joint pain, stiffness, aching and limited motion. Fracture is a broken bone due to high physical impact or other bone disorders. Exercise 4.3 Choose the correct answer for the following questions. 1. Which bone is axial skeleton? A. Skull C. Tibia B. Humerus D. Metatarsals 2. Which of the following bone is the appendicular skeleton? A. Vertebrae C. Sternum B. ribs D. Metacarpals 3. Which of the following bones are found in both fore and hind limbs? A. Wrist C. Ankle B. Phalanges D. Ribs 4. Which bones is wrongly paired with its example? A. Long bone - humerus C. Short bone-vertebrae B. Flat bone – ribs D. A and B 5. Which of the following skeletal disease is usually occurs as a result of aging? A. Osteoarthritis C. Fracture B. Osteoporosis D. Botulism UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 97  General Science | Student Textbook 4.4. DIGESTIVE SYSTEM At the end of this topic, learners will be able to: ♻ distinguish the major structural components of human digestive system; ♻ describe the main functions of human digestive system; and ♻ identify and discuss the main diseases and effects of human digestive system. 🔄 What is digestive system? The digestive system is a group of organs that break down food into smaller components so that nutrients can be absorbed and assimilated, providing energy to sustain the body. 4.4.1. Structural Components of Digestive System Activity 4.11. Perform the activity in group and present your responses to the class. Your teacher may display you a chart; observe and identify the various parts of alimentary canal and their associated accessory organs such as salivary glands, liver and pancreas. 98 Digestive System  Grade 8 Figure 4.5: Human digestive system 🔄 What are structural components of digestive system? Human digestive system consists of alimentary canal and associated glands. The alimentary canal consists of the following parts: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus. The associated glands of the digestive system are tongue, salivary glands, liver, gall bladder and pancreas. Mouth (oral cavity) is the beginning of the digestive tube where food is taken in. It consists of the teeth, tongue, salivary glands, cheek and palate form the mouth. Activity 4.12. Discuss the activity in group and present your discussion to the class. Look a teeth model and tell the types, numbers and roles of their teeth. Humans have two sets of teeth (dentitions) such as deciduous and permanent. i. Deciduous teeth (decidu- falling out) also called primary teeth, milk teeth, UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 99  General Science | Student Textbook or baby teeth begin to erupt at about 6 months of age, and approximately two teeth appear each month then, until all 20 are present complete by the age of 2 years. ii. Permanent teeth-the milk teeth drop out and replaced by permanent teeth. By age 7, 32 permanent or secondary teeth are developed & are divided into 4 types: Incisors (for cutting), Canines (for tearing), Premolars (for crushing) and Molars (for grinding). These teeth follow the human dental formula of 2-1-2-3. Pharynx (throat) is a tube running from the nose and mouth to esophagus. Epiglottis is a lid-like structure at the top of the windpipe. Esophagus is the muscular tube which leads from the pharynx to stomach. Stomach is a muscular bag which lies in upper abdomen on the left side. Liver is the largest gland situated in the abdominal cavity and has two lobes. Gallbladder is a pear shaped organ that stores bile until it is needed for digestion. Bile is a yellow-green, pasty material that contains water, bicarbonate ions, cholesterol, phospholipids, bile pigments and a number of bile salts. Pancreas is a soft, oblong, pale grey gland which consists of head, body and tail. Small intestine is a long and highly coiled and folded structure. It is divided into three regions such as duodenum, jejunum and ileum. Large Intestine is the terminal end of the alimentary canal runs from the appendix to the anus. It is divided into four regions: cecaum, colon, rectum and anus. 100 Digestive System  Grade 8 4.4.2. Functions of Digestive System Activity 4.13. Discuss the activity within a group and present your responses to the class. 1. Discuss how food moves and what moves it through the alimentary canal. 2. Differentiate physical and chemical digestion in mouth, stomach and small intestine. 🔄 What are the functions of digestive system? The digestive system performs the basic processes such as ingestion, propulsion, digestion (mechanical/physical and chemical), absorption, assimilation and defecation. These processes are takes place by the alimentary canal or gut and the accessory (associated) structures. Ingestion is the process of taking foods and liquids into the mouth (eating). Digestion is the process of breaking down food in to small particles. Digestion of food start in the mouth and end in small intestine. Digestion is divided in to two. These are physical or mechanical and chemical digestions. 🔄 How mechanical (physical) digestions take place in alimentary canals? Mechanical digestion is muscular movement of the digestive tract physically breaks down food into smaller particles. The process of mechanical digestion in the mouth which is performed by the teeth and the tongue with the help of saliva is called mastication. Teeth are adapted for cutting, grinding and masticating food in the oral cavity. Tongue is a freely movable muscular organ that moves swallow and holds food in place. Mechanical digestion of food takes place by emulsification and churning action due to muscular contraction of stomach and small intestine. UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 101  General Science | Student Textbook 🔄 How can food moves along the gut? Mixing and propulsion refers to the movement of food through the digestive tract. It includes both the voluntary process of swallowing (deglutition) and the involuntary process of peristalsis. Peristalsis is the wave like contraction and relaxations of smooth muscles pushing food along the gut. 🔄 How chemical digestions take place in alimentary canals? Chemical digestion in the mouth is performed by saliva which is produced by salivary glands. Saliva contains salivary amylase (ptyalin), mucus, water, chloride, bicarbonate and phosphate ions, and lysozyme enzymes and releases it to the oral cavity. The contents of saliva dissolve lubricate and facilitate food digestion. Starch Salivary Amylase at (pH = 6.8) Maltose Chemical digestion in the stomach is started by gastric juice which is secreted by gastric glands. The gastric juice consists of a lubricant called mucin, hydrochloric acid with a pH of 1-2 (too acidic) and enzymes like pepsin and rennin (in children only). Here mostly digestion of proteins is taking place. Proteins Pepsin Peptone (smaller polypeptides) Renin Milk proteins (milk casiens) Curdle of milk Chemical digestion in the small intestine by digestive enzymes (pancreatic amylase, pancreatic lipase and trypsin and chymotrypsin) secreted from pancreatic juice digest carbohydrates, fats and proteins respectively in the duodenum of the small intestine. Polysaccharides ^starchh Pancreatic Amylase Disaccharide Trypsin (Chemotrypsin) Proteins and Peptones Dipeptides Pancreatic Lipase Fats (triglycerides) Diglycerides Nuclease Nucleic acid (DNA and RNA) Nucleotides + Nucleosides Chemical digestion is also takes place in small intestine by producing intestinal juice consisting of the enzymes such as maltase, sucrase, lipase and peptidase convert maltose into glucose and glucose, sucrose into glucose and fructose, fats into fatty acids and glycerol and peptides into amino acids respectively. 102 Digestive System  Grade 8 Maltase Maltose Glucose + Glucose Lactase Lactose Glucose + Lactose Sucrase Sucrose Fructose + Glucose Dipeptidase Dipeptides Amino acids Intestinal Lipase Diglycerides and Monoglycerides Fatty Acid and Glycerol Nucleosidases Nucleosidases Mucleqtides Nucleosidises Sugar and Bases 🔄 What are the end products and wastes of digestion? Absorption is the process by which digestion end products (glucose, amino acids, fatty acids and glycerol) and other substances pass through the wall of alimentary canal. This is mainly takes place in small intestine. The inner wall of small intestine is covered with millions of tiny finger like projections called villi (villus) which increase the surface area for absorption. Assimilation is the process of utilization of absorbed food and converting it in to body cells and tissue. Egestion is the process of eliminating the undigested food (semi solid waste, feces) out of the body through the opening of anus. Most of the water is absorbed here. The process of digestion is summarized as follows: Ingestions " Digestion " Absorption " Assimilation " Egestion UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 103  General Science | Student Textbook 4.4.3. Major Diseases of Digestive System Activity 4.14. Discuss the activity in group and present your work to the class. List and explain some digestive system diseases and their effects. The major diseases of digestive system are as follows. Constipation occurs due to the slow movement of feces that promotes the water re-absorption and as a result feces become more solid. This leads to pain in the anus and difficulty in defecating. Hemorrhoids are painful, swollen blood vessels in the anal canal. Symptoms include pain, itching, and bright red blood after a bowel movement. Gastritis is a condition resulting inflammation of the stomach which can be due to excess secretion of HCl by glands of the stomach wall and leads damage to the mucosa, prolonged starvation and mental stress. Peptic ulcer Disease (PUD) is an open sore in the lining of the stomach or upper part of the small intestine. The causes and symptoms are similar with gastritis. Diarrhea is abnormal frequency of bowel movement and increased liquidity of faecal discharge. Absorption of food is reduced in case of diarrhea. 104 Digestive System  Grade 8 Exercise 4.4 Choose the correct answer from the given alternatives 1. Most of the water in the alimentary tract is absorbed through፡ A. Small intestine C. Stomach B. Large intestine D. Esophagus 2. Which of the following enzymes is correctly matched with its source? A. Amylase – stomach tine B. Peptidase – pancreas D. Maltase – small intes- C. Trypsin – small intes- tine. 3. The finger-like projections that increase surface area of wall of in the small intestine are: A. Bilirubin C. Sphincters B. Ileocecal D. Villi 4. The voluntary swallowing of food or fluid from the mouth to the esophagus is: A. Deglutition C. Ingestion B. Absorption D. Peristalsis 5. All of the following are substances found in pancreatic juice except: A. Amylase D. Trypsin B. Pepsin C. Lipase UNIT FOUR : HUMAN BODY SYSTEMS AND HEALTH 105