Focus On Science Grade 8

©Praxis Publishing_Focus On Science

CONTENTS About This Book iv Introduction to Cells 1 1.1 Cells and Microscopes 2 1.2 Animal and Plant Cells 5 1.3 Unicellular and Multicellular Organisms, and Cell Specialisation 9 Recall 12 Put on your Thinking Cap 13 Project 14 Structures and Functions of the Human Body Systems 15 2.1 Food and Digestive System 16 2.2 Circulatory System 38 2.3 Respiratory System 45 2.4 Excretory System 50 Recall 53 Put on your Thinking Cap 54 Project 55 Work, Energy and Simple Machines 56 3.1 Work 57 3.2 Power 58 3.3 Sources and Forms of Energy 59 3.4 Simple Machines 73 Recall 86 Put on your Thinking Cap 87 Project 88 Vibrations, Waves and Light 89 4.1 Vibrations 90 4.2 Waves 93 4.3 Light and Optical Instruments 107 Recall 122 Put on your Thinking Cap 123 Project 124 CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 ii ©Praxis Publishing_Focus On Science

Elements, Compounds and Mixtures 125 5.1 Atoms and Molecules 126 5.2 Elements 130 5.3 Compounds 138 5.4 Mixtures 143 Recall 153 Put on your Thinking Cap 154 Project 155 Acids and Alkalis 156 6.1 Acids and Alkalis 157 6.2 Neutralisation 176 Recall 181 Put on your Thinking Cap 182 Project 183 Structure of the Earth and Natural Disasters 184 7.1 Structure of Earth 185 7.2 Movement of Tectonic Plates 196 7.3 Earthquakes 202 7.4 Volcanoes 205 Recall 208 Put on your Thinking Cap 209 Project 210 CHAPTER 5 CHAPTER 6 CHAPTER 7 iii ©Praxis Publishing_Focus On Science

ABOUT THIS BOOK Focus-on Science is a pedagogy-driven series developed to provide a clear and effective learning trajectory for Grade 7 to Grade 9 students. The inquiry approach used in the Textbook assists students in acquiring scientific knowledge and science process skills through a variety of activities, experiments and projects. To make learning more engaging, photographs, infographics, diagrams and examples are used to present the content. In addition, animations, videos, simulations and Augmented Reality (AR) models are included to help bring science to life. Chapter Opener A short write-up with trigger questions based on a photo, as in the chapter introduction, to pique students’ interest. Experiment Engages and helps students to develop science process skills, manipulative skills and an inquisitive attitude through well-designed laboratory experiences. Our body is made of cells. Have you ever wondered how many cells are there in our body? Are all the cells of the same shape and size? Are there any other cells besides human cells in our body? Introduction to Cells CHAPTER 1 What will you learn? Understand what cells are Know the history of microscopes Differentiate between a light microscope and an electron microscope Proper handling of a light microscope including the preparation of specimen slides Compare animal and plant cells Compare unicellular and multicellular organisms Give examples of specialised cells and their functions Problem statement How does the length of a pendulum affect the period of the pendulum? Hypothesis As the length of the pendulum increases, the period of the pendulum increases. Manipulated variable Length of pendulum Responding variable Period of pendulum Constant variable Mass of the pendulum bob Materials and apparatus Thread, pendulum bob, retort stand and clamp, stopwatch, and metre ruler Procedure 1 Prepare a pendulum with a 20 cm long thread. B A Retort stand Thread Pendulum bob Diagram (a) Diagram (b) 2 Hang the pendulum on a retort stand clamp. 3 Pull the hanging pendulum to one side and release. 4 Record the time for the pendulum to make 20 complete oscillations. Repeat this step to obtain the second and third reading. 5 Repeat steps 1 to 4 using different lengths of thread (40 cm, 60 cm, 80 cm and 100 cm) for the same pendulum Result Record your result. Length of pendulum (cm) Time taken for 20 oscillations / s Period, T(s) Reading 1 Reading 2 Reading 3 Reading 4 20 40 60 80 100 Discussion What is the relationship between the length of the pendulum and the period of the pendulum? Conclusion Can the hypothesis be accepted? Write down your conclusion. 1 Experiment Investigating the effect of the length of a swinging pendulum on its period 95 Chapter 4 Vibrations, Waves and Light What will you learn? The chapter’s learning outcomes which provide an idea of what students will learn. iv ©Praxis Publishing_Focus On Science

Science Facts Provides additional information related to the topic taught in order to stimulate students’ interest in learning science. Activity Provides students with a total learning experience through learning by doing, encouraging them to reflect on the experience and think critically. 1.3 Unicellular and Multicellular Organisms, and Cell Specialisation Organisms are living things. Organisms can be divided into two groups, namely unicellular organisms and multicellular organisms. Unicellular and Multicellular Organisms Unicellular organisms are organisms that are made up of a single cell (‘uni’ means one). Most of them are invisible to the naked eye, hence, they are also called microscopic organisms. They can only be observed under the microscope. These organisms usually live in seas, rivers and lakes. They perform all the processes of life, such as respiration, response, digestion, excretion, reproduction and growth. Examples of unicellular organisms Multicellular organisms are organisms that are made up of many cells (‘multi’ means many) of different types. Each type of cell has a different structure and carries out a specific function. Like unicellular organisms, multicellular organisms perform all the processes of life. Humans, plants, animals and some fungi and algae are examples of multicellular organisms. Examples of multicellular organisms Give one similarity between unicellular and multicellular organisms. Think About It Amoeba Euglena Paramecium Chlamydomonas Bacteria viewed under microscope (Escherichia coli) Viruses are not classified as cells and therefore are neither unicellular nor multicellular organisms. They are not considered living things as they do not perform some processes of life such as breathing and growing. They infect all types of organisms, including animals and plants. Science Facts Hydra Millipede Spirogyra Mucor Cat Mushroom 9 Chapter 1 Introduction to Cells Introduction to Cells Activity 2 Observing onion cells Onion epidermis Forceps Onion epidermis Filter paper Iodine solution Mounting pin Cover slip Scalpel Scale of an onion leaf Caution Be careful when using the scalpel and forceps to avoid getting hurt. Aim: To observe onion cells Materials and apparatus: Onion, iodine solution, scalpel, glass slide, cover slip, filter paper, mounting pin, forceps and microscope Procedure: 1 Cut an onion bulb vertically and remove one of the inner scale leaves. Preparation of a slide of onion cells 2 Then, remove the inner epidermal layer from the scale leaf using a pair of forceps. 3 Spread out the epidermal layer on a drop of water in the middle of a slide. 4 Cover the specimen with a cover slip using a mounting pin. 5 Add a drop of iodine solution on one side of the slide. 6 Put a filter paper on the opposite side of the slide to draw the iodine solution over the specimen. 7 Observe the onion cells through the microscope with a low-power objective lens followed by a high-power objective lens. 8 Draw a few onion cells and label them. Observation: Draw what you observe. Discussion: 1 What is the purpose of using iodine solution? 2 What is the shape of the onion cells? Conclusion: Write down your conclusion. 6 How to Use a Light Microscope Although a microscope has several parts, its lenses are the most crucial parts. It is through the microscope’s lenses that the image of a specimen can be magnified and observed in detail. Follow the steps below to handle a microscope properly: 1. Place a microscope on a flat surface with the mirror facing a light source. 2. Select the low-power objective lens and position it above the hole of the stage. 3. Adjust the diaphragm and mirror so that there is sufficient light to view the specimen through the microscope. 4. Place the specimen slide on the stage and hold it with the clips. 5. Turn the coarse focus knob to lower the objective lens close to the specimen without touching it. 6. Look through the eyepiece. Turn the coarse focus knob anticlockwise until the object is in focus. Change to a high-power objective lens if necessary. 7. Adjust the fine focus knob until a sharp image is obtained. Eyepiece: used to look through the specimen and it magnifies the image formed by the objective lens to ten times (10×). Medium-power objective lens: magnifies the image of the specimen to 10 times. Tube: connects the eyepiece to the objective lenses. High-power objective lens: magnifies the image of the specimen to 40 times. Coarse focus knob: used to move the stage up or down in initial focusing. Low-power objective lens: magnifies the image of the specimen to 4 times. Fine focus knob: used to sharpen the focus quality of the image after it has been brought into focus with the coarse focus knob. Stage: the platform to place the slides. Clips: hold the slides in place on the stage. Mirror: reflects light towards the diaphragm. Arm and base: for holding and supporting the microscope. Condenser: focuses light from the mirror onto the specimen. Diaphragm: controls the amount of light that enters the condenser. Resource 4 Think About It Provides questions that encourage students to find the answers to support constructivist learning. Resource Helps students make learning more enjoyable and in a more engaging way via scanning QR codes to access fascinating videos, animations, simulations, AR models, etc. Resource v ©Praxis Publishing_Focus On Science

THINKING CAP Put on your 1 Explain how energy is transferred and transformed when an arrow is shot using a bow? 2 What can be done to increase the mechanical advantage of an inclined plane without changing its height? Give a reason. 3 A wheel and axle system has a mechanical advantage of 3 and the radius of the axle is 15 cm. What is the radius of the wheel? 4 Why are pulleys used to lift objects during the construction of buildings? 87 Chapter 3 Work, Energy and Simple Machines 1 The building blocks of an organism which can function on their own are called . 2 A typical cell is made up of cell membrane, a nucleus and . 3 The mitochondrion is a structure in the cytoplasm that produces for the cell. 4 is a British scientist who observed a slice of cork and showed that the plant tissue were made up of tiny, room-like structures. 5 made a single-lens microscope that could magnify objects up to 250 times and he discovered bacteria. 6 In an electron microscope, a beam of electrons is used to the image of specimens. 7 The light microscope is called a microscope because it contains two types of lenses to magnify an object, namely the eyepiece and the objective lens. 8 In a light microscope, the controls the amount of light that enters the condenser. 9 In the preparation of the slide for human cheek cells, the staining agent that is used is methylene solution. 10 A plant cell has a shape due to the existence of its cell wall. 11 Unicellular organisms are organisms that are made up of cell only. 12 Multicellular organisms are organisms that are made up of cells of different types. 13 A spider is an example of a organism. 14 Euglena is an example of a organism. 15 Cells that have different shapes and structures to carry out different functions are called cells. 16 cells contract and relax to produce movements. 17 Palisade cells contain lots of chloroplasts to enable them to carry out . 18 Nerve cells, red blood cells, muscle cells and epithelial cells are examples of specialised cells in . 19 The specialised cells in plants are cells, guard cells, root hair cells, xylem cells and phloem cells. RECALL Fill in the missing words. 12 Project Making a Periscope Activity objective: To design and create a periscope Problem statement: A periscope is an optical instrument people use to look at things over walls, corners, or other obstacles from a hidden position. Submarines have periscopes so that those who are inside the submarines can see objects above the surface while still underwater. We can demonstrate how a periscope works by making our own periscope. Concept applied: Reflection of light to enhance the ability to see objects over walls, corners or other obstacles Procedure: 1 Sketch a few designs of your periscope. 2 Prepare a variety of building materials (plane mirrors, shoe box/milk cartons). 3 Choose a design. Build the model that you have sketched. 4 Test your model by holding the periscope up to your eye and looking through it. 5 Think about improvements that you can make to your model such as adjusting the position of the plane mirrors to make the image clearer to the observer. Make the necessary changes to your model and test it again. You can choose another design, if required. Solution: Design of the model of periscope and its features Presentation: Compare your own model of periscope with your friends. Share the information with the class about what you learned about the application of the concept of reflection of light. 124 Put on your Thinking Cap Challenges students with questions that promote higher-order thinking skills. Recall Assists students in recalling concepts learned and serves as a summary of key points. Project Appears at the end of each chapter that helps students develop problem-solving and critical thinking skills, and to connect what students have learned to the real world. vi ©Praxis Publishing_Focus On Science

Our body is made of cells. Have you ever wondered how many cells are there in our body? Are all the cells of the same shape and size? Are there any other cells besides human cells in our body? Introduction to Cells CHAPTER 1 What will you learn? Understand what cells are Know the history of microscopes Differentiate between a light microscope and an electron microscope Proper handling of a light microscope including the preparation of specimen slides Compare animal and plant cells Compare unicellular and multicellular organisms Give examples of specialised cells and their functions ©Praxis Publishing_Focus On Science

1.1 Cells and Microscopes Organisms are made up of one or more cells. Cells are the most basic unit of organisms which can function on their own. They are the building blocks of an organism. Together they form tissues that themselves form organs, and eventually the entire organisms. Cells of living things exist in many sizes and shapes. A cell is like a factory, using material and energy resources to produce products. In the same way that each department in a factory carries out a specialised task, each organelle in a cell has one or more specific task to perform as well. In a factory, the main office controls the whole operation, similarly in a cell, the nucleus is the control centre of the cell. Cells in organisms are very tiny and cannot be seen with the naked eye but can be observed using a microscope. The average size of a human cell is about 100 μm in diameter. Anton van Leeuwenhoek’s unique microscope Brief History of Microscopes Robert Hooke, a British scientist, was the first person to study cells. Hooke used a compound microscope that has two lenses, and works like the microscopes we use today. His microscope enabled him to magnify objects up to 50 times. The microscope allowed him to observe the smallest of details in the natural world. He observed a slice of cork (dead oak tree bark) and showed that the tissue of the plant was made up of tiny, room-like structures. He called these structures “cells”. In 1665, Robert Hooke published Micrographia, a book illustrated with microscopic observations of his discoveries. A drawing of Robert Hooke’s microscope is shown on the right. A water lens is placed close to the microscope to focus light from an oil-lamp onto the specimen observed to make it look brighter. Another discoverer of cells is Anton van Leeuwenhoek. After coming across Hooke’s book Micrographia, he was inspired to take up microscopy. He learned to grind lenses and started building simple microscopes. Although Leeuwenhoek is a textile merchant by profession, with his intelligence and curiosity, he created his own version of a microscope, that could magnify objects up to 250 times. Leeuwenhoek used small, spherical lenses to make singlelens microscopes. It was he who discovered bacteria, sperm cells, blood cells and much more. A drawing of one of Leeuwenhoek’s microscopes is shown on the right. It is an extremely simple device about 3–4 inches long, which used only one lens, mounted in a tiny hole in the body of the device. The specimen to be observed was mounted on the sharp point that sticks up in front of the lens. The position of the specimen could be adjusted by turning the two screws. The device had to be held up close to the eye and required good lighting. Lens Specimen mounted here Focusing screw Elevating screw Cork cells as seen by Robert Hooke through his microscope. Compound microscope Robert Hooke’s microscope Water lens Flames Specimen Resource 2 ©Praxis Publishing_Focus On Science

Light Microscope and Electron Microscope The most common types of microscopes are the light microscope and electron microscope. In a light microscope, visible light and lenses are used to magnify the image of specimens while in an electron microscope, a beam of electrons is used. Some of the differences between a light microscope and an electron microscope are as follows. The light microscope is called a compound microscope because it contains two types of lenses to magnify an object. The lens closer to the eye is called the eyepiece or ocular, while the lens closer to the specimen is called the objective lens. The monocular light microscope is equipped with one eyepiece while the binocular light microscope is equipped with two eyepieces. Light microscope Smaller and lighter, easily moved around Uses a beam of light Lower magnification (500× to 1500×) Lower resolution (lesser clarity) Used to see dead and live specimens Specimen takes a few minutes to hours to be prepared Image is seen directly through the eyepiece Electron microscope Big and heavy, hard to be moved around Uses a beam of electrons Higher magnification (more than 100 000×) Higher resolution (higher clarity) Used to see only dead specimens Specimen takes a few days to be prepared Image is produced on a screen or photographic plate Electron microscopes are widely used by scientists in laboratories. The head of a fly observed under an electron microscope Monocular light microscope (left) and binocular light microscope (right) used in schools and colleges Epidermal cells of an onion as seen under a light microscope Chapter 1 Introduction to Cells 3 ©Praxis Publishing_Focus On Science

How to Use a Light Microscope Although a microscope has several parts, its lenses are the most crucial parts. It is through the microscope’s lenses that the image of a specimen can be magnified and observed in detail. Follow the steps below to handle a microscope properly: 1. Place a microscope on a flat surface with the mirror facing a light source. 2. Select the low-power objective lens and position it above the hole of the stage. 3. Adjust the diaphragm and mirror so that there is sufficient light to view the specimen through the microscope. 4. Place the specimen slide on the stage and hold it with the clips. 5. Turn the coarse focus knob to lower the objective lens close to the specimen without touching it. 6. Look through the eyepiece. Turn the coarse focus knob anticlockwise until the object is in focus. Change to a high-power objective lens if necessary. 7. Adjust the fine focus knob until a sharp image is obtained. Eyepiece: used to look through the specimen and it magnifies the image formed by the objective lens to ten times (10×). Medium-power objective lens: magnifies the image of the specimen to 10 times. Tube: connects the eyepiece to the objective lenses. High-power objective lens: magnifies the image of the specimen to 40 times. Coarse focus knob: used to move the stage up or down in initial focusing. Low-power objective lens: magnifies the image of the specimen to 4 times. Fine focus knob: used to sharpen the focus quality of the image after it has been brought into focus with the coarse focus knob. Stage: the platform to place the slides. Clips: hold the slides in place on the stage. Mirror: reflects light towards the diaphragm. Arm and base: for holding and supporting the microscope. Condenser: focuses light from the mirror onto the specimen. Diaphragm: controls the amount of light that enters the condenser. Resource 4 ©Praxis Publishing_Focus On Science

1.2 Animal and Plant Cells A typical cell is enclosed by a cell membrane which is a thin film that is partially permeable to the surrounding substances. Let’s carry out activities to observe how animal and plant cells look like under a light microscope, in this case human cheek cells and onion epidermal cells respectively. The preparation of both the cells are almost the same except for the type of staining agent used. Activity 1 Aim: To observe human cheek cells Materials and apparatus: Clean toothpick, methylene blue solution, filter paper, glass slide, cover slip, mounting pin and microscope Procedure: 1 Use the blunt end of a toothpick to scrape the inside of your cheek. Mounting pin Cover slip Toothpick Methylene blue solution Glass slide Preparation of a slide of cheek cells 2 Place the scraping on the glass slide and add a drop of methylene blue solution and water to it. 3 Lower the cover slip gently onto the glass slide using a mounting pin. 4 Use a filter paper to remove any excess methylene blue solution and water. 5 Observe the cheek cells through the microscope with a low-power objective lens followed by a high-power objective lens. 6 Draw a few cheek cells and label them. Observation: Draw what you observe. Discussion: 1 What is the purpose of using methylene blue solution? 2 What is the shape of the cheek cells? Conclusion: Write down your conclusion. Observing human cheek cells Caution Do not use dirty toothpicks or scrape too hard to avoid getting hurt. Generally, each animal cell is made up of protoplasm, surrounded by a cell membrane. Protoplasm is the living part of the cell and comprises the cytoplasm and nucleus. In the cytoplasm, there are mitochondria. Chapter 1 Introduction to Cells 5 ©Praxis Publishing_Focus On Science

Activity 2 Observing onion cells Onion epidermis Forceps Onion epidermis Filter paper Iodine solution Mounting pin Cover slip Scalpel Scale of an onion leaf Caution Be careful when using the scalpel and forceps to avoid getting hurt. Aim: To observe onion cells Materials and apparatus: Onion, iodine solution, scalpel, glass slide, cover slip, filter paper, mounting pin, forceps and microscope Procedure: 1 Cut an onion bulb vertically and remove one of the inner scale leaves. Preparation of a slide of onion cells 2 Then, remove the inner epidermal layer from the scale leaf using a pair of forceps. 3 Spread out the epidermal layer on a drop of water in the middle of a slide. 4 Cover the specimen with a cover slip using a mounting pin. 5 Add a drop of iodine solution on one side of the slide. 6 Put a filter paper on the opposite side of the slide to draw the iodine solution over the specimen. 7 Observe the onion cells through the microscope with a low-power objective lens followed by a high-power objective lens. 8 Draw a few onion cells and label them. Observation: Draw what you observe. Discussion: 1 What is the purpose of using iodine solution? 2 What is the shape of the onion cells? Conclusion: Write down your conclusion. The basic structure of plant cells is similar to that of animal cells, but all plant cells have a cell wall which gives them an almost fixed shape. Plant cells often have one large vacuole, whereas animal cells usually have many small ones. Most plant cells contain chloroplasts which are green. Animal cells do not have chloroplasts. 6 ©Praxis Publishing_Focus On Science

An animal cell observed under an electron microscope A plant cell observed under an electron microscope Do you know which part of a plant has the most chloroplasts and why? Think About It Cytoplasm: is a jelly-like substance, is a site where many chemical reactions take place and it stores dissolved material. Cell membrane: controls the movement of materials in and out of cells. Mitochondrion: produces energy from digested food. Nucleus: controls all cellular activities. It contains chromosomes that are made up of DNA which carries genetic information that determines the various traits of an organism such as eye colour. Cell wall: is an outer non-living layer of cellulose that supports and gives a fixed shape to the cells. Vacuole: is a fluid-filled sac containing cell sap. It holds useful substances, water and wastes. It supports the plant when it is full of water. Chloroplast: contains chlorophyll that absorbs light for photosynthesis to produce food and oxygen. Nucleus Cell membrane Mitochondrion Cytoplasm Chapter 1 Introduction to Cells 7 ©Praxis Publishing_Focus On Science

Comparison Between Animal Cells and Plant Cells The similarities and differences between an animal cell and a plant cell are shown in the chart below. Similarities Not fixed and may vary during life Shape Fixed shape Does not have a cell wall Cell wall Has a cell wall Generally smaller Size Generally bigger Does not have chloroplasts Chloroplast Has chloroplasts to make its own food Usually, it does not have vacuoles but if present, the vacuole is small Vacuole Often, has a large vacuole Usually, at the centre of the cell Position of nucleus Often, one side of the cell Glycogen granules Food storage Starch granules • Both have the cell membrane, cytoplasm, nucleus and mitochondria. • Both carry out life processes. The largest human cell in terms of volume is the egg cell (ovum). The smallest cell in the human body is the sperm cell. The ovum is about 1000 micrometres, or one millimetre, in diameter. The head of the sperm cell measures about 4 micrometres in length. Science Facts Sperm cell Egg cell Animal cell Plant cell Differences Aspects 8 ©Praxis Publishing_Focus On Science

1.3 Unicellular and Multicellular Organisms, and Cell Specialisation Organisms are living things. Organisms can be divided into two groups, namely unicellular organisms and multicellular organisms. Unicellular and Multicellular Organisms Unicellular organisms are organisms that are made up of a single cell (‘uni’ means one). Most of them are invisible to the naked eye, hence, they are also called microscopic organisms. They can only be observed under the microscope. These organisms usually live in seas, rivers and lakes. They perform all the processes of life, such as respiration, response, digestion, excretion, reproduction and growth. Examples of unicellular organisms Multicellular organisms are organisms that are made up of many cells (‘multi’ means many) of different types. Each type of cell has a different structure and carries out a specific function. Like unicellular organisms, multicellular organisms perform all the processes of life. Humans, plants, animals and some fungi and algae are examples of multicellular organisms. Examples of multicellular organisms Give one similarity between unicellular and multicellular organisms. Think About It Amoeba Euglena Paramecium Chlamydomonas Bacteria viewed under microscope (Escherichia coli) Viruses are not classified as cells and therefore are neither unicellular nor multicellular organisms. They are not considered living things as they do not perform some processes of life such as breathing and growing. They infect all types of organisms, including animals and plants. Science Facts Hydra Millipede Spirogyra Mucor Cat Mushroom Chapter 1 Chapter 1 Introduction to Cells Introduction to Cells 9 ©Praxis Publishing_Focus On Science

Cell Specialisation Humans, animals and plants which are multicellular organisms, are made up of different types of cells. These cells have different shapes and structures to carry out different functions. They are known as specialised cells. Here are some specialised cells in humans with their unique features and functions. Nerve cells have long, thin fibres that carry information in the form of nerve impulses to different parts of the body. Muscle cells contract and relax to produce movements. Star-shaped mature bone cells called osteocytes are involved with the maintenance of bone tissue. Epithelial cells that line the trachea have a thin layer of tiny moving hairs called cilia. They cover the outer surface of the body and line the surfaces of organs. Reproductive cells include the sperm (found in males) and the ovum or egg (found in females). Both cells carry genetic materials. Red blood cells have biconcave disc shapes without a nucleus in them. They contain haemoglobin (red pigment) which carries oxygen. They transport oxygen from the lungs to all parts of the body. Types of animal cells 10 ©Praxis Publishing_Focus On Science

There are specialised cells in all plants. They have developed certain structures or characteristics to perform functions. A cell can be specialised by having extra mitochondria or chloroplasts or no chloroplasts at all. It could be elongated or have extra-large vacuoles. The following are examples of some specialised plant cells. Palisade cells contain lots of chloroplasts that have chlorophyll to carry out photosynthesis. Guard cells are kidney-shaped cells, usually found on the underside of a leaf. They help to regulate gas exchange by controlling the opening and closing of stomata (the small pores between the two guard cells). Tracheids which are specialised cells found in xylem tissue, conduct water and minerals from the roots to the leaves and other parts of the plants. Sieve elements which are specialised cells found in phloem tissue, transport food from the leaves to other parts of the plant. Root hair cells have a long thin extension that absorbs water and minerals from the soil. Guard cells help to balance the amount of carbon dioxide absorbed versus the amount of water lost through evaporation. Science Facts Tracheids Types of Sieve elements plant cells Chapter 1 Chapter 1 Introduction to Cells Introduction to Cells 11 ©Praxis Publishing_Focus On Science

1 The building blocks of an organism which can function on their own are called . 2 A typical cell is made up of cell membrane, a nucleus and . 3 The mitochondrion is a structure in the cytoplasm that produces for the cell. 4 is a British scientist who observed a slice of cork and showed that the plant tissues were made up of tiny, room-like structures. 5 made a single-lens microscope that could magnify objects up to 250 times and he discovered bacteria. 6 In an electron microscope, a beam of electrons is used to the image of specimens. 7 The light microscope is called a microscope because it contains two types of lenses to magnify an object, namely the eyepiece and the objective lens. 8 In a light microscope, the controls the amount of light that enters the condenser. 9 In the preparation of the slide for human cheek cells, the staining agent that is used is methylene solution. 10 A plant cell has a shape due to the existence of its cell wall. 11 Unicellular organisms are organisms that are made up of cell only. 12 Multicellular organisms are organisms that are made up of cells of different types. 13 A spider is an example of a organism. 14 Euglena is an example of a organism. 15 Cells that have different shapes and structures to carry out different functions are called cells. 16 cells contract and relax to produce movements. 17 Palisade cells contain lots of chloroplasts to enable them to carry out . 18 Nerve cells, red blood cells, muscle cells and epithelial cells are examples of specialised cells in . 19 The specialised cells in plants are cells, guard cells, root hair cells, xylem cells and phloem cells. RECALL Fill in the missing words. 12 ©Praxis Publishing_Focus On Science

THINKING CAP Put on your 1 Why are cells the basic building blocks of life? 2 Are the cells in bigger animals such as crocodiles larger than the cells in smaller animals such as lizards? Give your opinion. 3 Initially when red blood cells are produced in the bone marrow, they have nuclei but as they enter the bloodstream for the first time, they lose their nuclei. Give a reason. Chapter 1 Chapter 1 Introduction to Cells Introduction to Cells 13 ©Praxis Publishing_Focus On Science

Project The Ethical Issues of Stem Cell Research Activity objective: Gather information on breakthroughs in stem cell research and the ethical issues related to them. Problem statement: Stem cells have the potential to develop into any part of the body. In other words, the cells can change into specialised cells such as heart muscle cells, red blood cells and liver cells. Stem cells can be used to cure diseases such as heart failure by using them to make new and healthy cells. What are the ethical issues that arise from stem cell research? Procedure: 1 Split the class into groups. Each group is tasked to look for information of the following: (a) What are stem cells? (b) What are the types of stem cells? (c) What are the breakthroughs so far in the use of stem cells? (d) Why do some people support stem cell research, while some reject the research? 2 Students in each group discuss, then search information on the Internet and books. List down all the references. Concept applied: Stem cell research Action plan: 1 Carry out this task in a group of five students. 2 Appoint a leader in each of the groups to delegate sub-tasks to the group members. 3 Have a discussion on how to present the information gathered. Solution: The information gathered must at least include the following aspects, and you are encouraged to add more. (a) Definition of human stem cells (b) Types of human stem cells (c) Some of the breakthroughs so far in stem cell research (d) Ethical issues with stem cell research Presentation: Present your findings creatively such as in the form of a poster. 14 ©Praxis Publishing_Focus On Science

Rina is breathing in fresh air at the park. Do you know what happens to the inhaled air? Do you know what are the structures involved in breathing? Structures and Functions of the Human Body Systems CHAPTER 2 What will you learn? Understand nutrients and balanced diet List the classes of food additives, their usage and the side effects that arise from their intake Identify the structures of the human digestive system Describe the processes of food digestion, absorption of digested food and defaecation Identify the structures and organs of the circulatory system and describe their functions Know the health issues related to the circulatory system Identify the structures and organs of the respiratory system Explain breathing mechanisms Identify the structures and organs of the excretory system and explain the excretion process Health effects of smoking, alcohol consumption and drug addiction ©Praxis Publishing_Focus On Science

2.1 Food and Digestive System Have you heard of the phrase “You are what you eat”? Well it is true! The food we consume daily plays an important role in our well-being. Food is the source of the nutrients we need. Nutrients Our body breaks down the food we eat into basic nutrients. The chart below shows the different types of nutrients that we can obtain from food. Types of Nutrients Carbohydrates Vitamins Fats Minerals Proteins Do you know why some people eat banana after a workout? Think About It 16 ©Praxis Publishing_Focus On Science

Apart from the nutrients shown, water is equally essential for our body. A combination of different nutrients is found in most types of food. However, some types of food contain more of a particular nutrient than others. Carbohydrates Carbohydrates are organic compounds that contain three elements: carbon, hydrogen and oxygen. All carbohydrates are made up of units of sugar molecules, also known as saccharides. There are two types of carbohydrates as shown in the chart below: simple carbohydrates and complex carbohydrates. Carbohydrates Simple Complex Monosaccharides • Glucose • Fructose • Galactose • Maltose • Lactose • Sucrose • Starch • Dietary fibre Disaccharides Polysaccharides Simple carbohydrates are small molecules that consist of one sugar unit (monosaccharides) such as glucose, fructose and galactose or two sugar units (disaccharides) such as sucrose, lactose and maltose. They are found in food such as fruits, table sugar and milk. Complex carbohydrates are much larger molecules that consist of thousands of sugar units bonded together. Complex carbohydrates include dietary fibre and starch. Starch is found in bread, cereal, pasta, potatoes, peas and corn. The body needs to break down starch into sugars that will then be used to provide energy. Dietary fibre is found in fruits, vegetables, nuts, beans, wholemeal bread and cereal. Consuming food rich in dietary fibre can help a person feel full and less likely to overeat because his body cannot break down most of the dietary fibre. A deficiency of dietary fibre can cause constipation, a condition that occurs when undigested food that move along the large intestine becomes hard and dry and the removal of faeces from the rectum becomes painful. Food rich in starch Food rich in dietary fibre What is the difference a person feels when he consumes wholemeal bread compared to white bread? Think About It Chapter 2 Structures and Functions of the Human Body Systems 17 ©Praxis Publishing_Focus On Science

The main function of carbohydrate is to provide energy so that life processes such as growth, reproduction and movement can be carried out. One gram of carbohydrate provides four calories of energy. Both simple and complex carbohydrates, except dietary fibre, are eventually converted by our body into glucose, also known as blood sugar. Glucose can be used immediately, serving as the main source of energy for cells, tissues and organs, or stored in the liver and muscles as glycogen to be used later. Simple carbohydrates provide bursts of energy as they are digested quickly. On the other hand, complex carbohydrates take longer to be digested and thus provide longer-lasting energy when compared to simple carbohydrates. Why do simple sugars found in table sugar or honey taste sweet to our tongue, but complex carbohydrates found in rice do not have a similar taste? Think About It Proteins Proteins are organic compounds. Protein molecules consist of long chains of smaller molecules called amino acids. The amino acids are composed of carbon, hydrogen, oxygen and nitrogen elements. Some amino acids contain sulphur and phosphorus elements as well. Our body needs 20 different types of amino acids to function well. These 20 types of amino acids combine in various ways to make proteins in our body. Out of the 20 types, 11 are non-essential amino acids and the other 9 are essential amino acids. Non-essential amino acids are synthesised by our body whereas essential amino acids are obtained from the food we eat. We can get proteins from many sources, including animals and plants. Proteins obtained from animal sources have all the essential amino acids whereas proteins obtained from plants only have some of the essential amino acids. The proteins we eat are digested into their basic units, which are amino acids. The main function of protein is to build and repair body tissues. Protein also supplies us with energy. One gram of protein provides four calories of energy. There are many other functions of proteins as follows. Meat, fish, cheese, eggs, milk and beans are good sources of proteins. 18 ©Praxis Publishing_Focus On Science

Why do babies and children need plenty of protein in their diet? Who else need plenty of protein in their diet? Give a reason. Think About It In a healthy person, protein contributes only a small amount of energy to the body. In a person whose diet does not contain enough carbohydrates and fats, the body will use amino acids to produce energy. The body cannot store protein, so once their needs are met, the excess protein consumed is usually stored as fat, while the surplus of amino acids will be converted to urea and removed from the body through the urine. Kwashiorkor is a severe protein deficiency disorder that affects mainly children in regions facing famine. Some of the symptoms of kwashiorkor are oedema (fluid retention in the belly), retarded growth and fatigue. Marasmus is a disorder caused by severe deficiency of protein and calories. It affects mainly children in regions of high poverty. Some of the symptoms of marasmus are severe weight loss and muscle wasting. If not treated properly, it can be fatal. Science Facts Bulging eyes Swollen face Thin limbs Thin upper arms Wrinkled skin Prominent ribs Protuding stomach Long and thin legs Curved legs A source of energy to our body Build new cells or replace dead cells Functions of proteins Synthesise enzymes, antibodies and hormones Required for growth Help repair worn-out or damaged cells and tissues Chapter 2 Structures and Functions of the Human Body Systems 19 ©Praxis Publishing_Focus On Science

Fat Fat is an organic compound that consists of carbon, hydrogen and oxygen elements. Fat is made up of glycerol and fatty acids. Fat is an energy source for our body. One gram of fat provides nine calories of energy which is two times the energy supplied by carbohydrates. Fat can come from plant or animal sources. There are three types of fat, namely saturated fat, unsaturated fat and trans fat. Most animal fat are saturated whereas most plant fat are unsaturated. Saturated fat exists in solid form whereas unsaturated fat exists in liquid form at room temperature. Trans fat is usually found in fried food. A small amount of fat is important for good health. Large amounts of fat can be harmful especially animal fat, which are saturated fat, as they can lead to obesity and problems in the circulatory system such as heart diseases. Unsaturated fat is healthier to be consumed compared to saturated fat. Therefore, it is advisable to have a diet low in saturated fat. Trans fat is the unhealthiest one among all the types of fat. Eating too much trans fat can cause weight gain, heart diseases and higher risk for type 2 diabetes. Meat Cheese Vegetable oil Avocado Nuts Animal fats are found in these food Plant fats are found in these food Butter 20 ©Praxis Publishing_Focus On Science

Examples of food containing saturated, unsaturated and trans fats Saturated fat Unsaturated fat Trans fat Beef Olive oil French fries Poultry Sunflower oil Cookies Butter Sesame oil Cholesterol is a fat-like substance found in the blood and it helps the body make cell membranes, hormones and vitamin D. The cholesterol in the blood comes from the food we eat and the liver. The cholesterol produced by the liver is enough to meet the daily requirement, therefore there is no need to get it from food. Cholesterol is carried in the bloodstream as lipoproteins, which is a combination of protein and fat found in the blood. There are two types of lipoproteins, namely the low-density lipoproteins (LDL) and high-density lipoproteins (HDL). When we consume a high amount of saturated fats, there will be an increase in the low-density lipoproteins (LDL), considered as the ‘bad cholesterol’. High levels of low-density lipoproteins (LDL) contribute to atherosclerosis, which is the fatty build-up in the walls of arteries making the arteries narrower, disrupting blood flow and increasing the risk for heart diseases such as heart attack and stroke. On the other hand, high-density lipoproteins (HDL), considered as the “good cholesterol” carry cholesterol from other parts of the body back to the liver to be removed from the body. A healthy level of HDL may protect a person against heart diseases. Apart from supplying energy to our body, fat plays several other roles as shown in the chart below. Functions of fat As an energy source Excess fat that is stored under the skin acts as a thermal insulator Protect internal organs such as the heart and kidneys Constituent of cell membranes and nerve cells Adds flavour to food and contribute to the sense of fullness Transports fat-soluble vitamins such as vitamin A, D, E and K to be effectively absorbed by the body Fried chicken Chapter 2 Structures and Functions of the Human Body Systems 21 ©Praxis Publishing_Focus On Science

Vitamins In addition to carbohydrates, proteins and fats, we need vitamins in tiny amounts for good health and growth. Vitamins are organic compounds that are absorbed directly from the food into our body with no digestion required. A lack of vitamins in our diet can lead to various deficiencies and diseases. On the other hand, vitamins must not be taken in excess because they can be toxic to the body. There are two categories of vitamins: water-soluble and fat-soluble vitamins. Water-soluble vitamins are vitamins B and C which cannot be stored in the body, thus they must be taken regularly from our diet. Fat-soluble vitamins are vitamins A, D, E and K which can be stored in the body. Green leafy vegetables Dairy products Yeast Vitamin B2 (riboflavin) Vitamin B2 releases energy from food and is required for the health of the nervous system and the heart. A deficiency of this vitamin can cause sore eyes, a swollen tongue, and skin lesions at the corners of the mouth, nose and ears. Liver Unpolished rice Nuts Vitamin B3 (niacin) Vitamin B3 releases energy from food and is required for the health of the nervous system, skin, intestines and heart. A deficiency of this vitamin can cause pellagra, a disease characterised by dermatitis, diarrhoea and dementia. Sources of Vitamin B1 , B2 , B3 and B12 Vitamin B1 releases energy from food and is required for the health of the nervous system. A deficiency of this vitamin can cause beriberi, characterised by weight loss and weakness in the limbs. Vitamin B1 (thiamine) Eggs Nuts Legumes Vitamin B12 (cobalamin) Vitamin B12 is required in the formation of red blood cells and for the health of nervous system. A deficiency of this vitamin causes anaemia, neurological disorders and weight loss. Red meat Eggs Dairy products Water-soluble vitamins 22 ©Praxis Publishing_Focus On Science

Vitamin A Vitamin A is for maintaining healthy skin and good eyesight. A deficiency of this vitamin causes night blindness and scaly skin. Sources of Vitamin A Carrots Green vegetables Dairy products Vitamin D Vitamin D is for the growth and development of teeth and bones. A deficiency of this vitamin causes rickets, a disease in children where their bones become soft and weak. Dairy products Eggs Sunlight Sources of Vitamin D Vitamin E Vitamin E acts as an antioxidant, helps in the formation of red blood cells, maintains the functions of reproductive system and strengthens the immune system. A deficiency of this vitamin causes anaemia and infertility. Sources of Vitamin E Nuts Green vegetables Olive oil Vitamin K Vitamin K helps in the blood clotting process. A deficiency of this vitamin causes prolonged and excessive bleeding. Sources of Vitamin K Egg yolk Milk Cabbage Fat-soluble vitamins Vitamin C Vitamin C helps to fight diseases, heals wounds, is required for the absorption of iron and maintains the health of gums and mouth. A deficiency of this vitamin can reduce the ability of the body to fight infections and may cause scurvy, a disease where the bleeding of the gum occurs. Sources of Vitamin C Citrus fruit Tomatoes Vegetables Chapter 2 Structures and Functions of the Human Body Systems 23 ©Praxis Publishing_Focus On Science

Minerals Minerals are non-organic substances required by our body. We need tiny amounts of minerals for proper growth and to stay healthy. The table below shows a variety of minerals, their sources, functions and symptoms of deficiencies. Mineral Sources Functions Symptoms of deficiency Calcium Milk, cheese, anchovies, green vegetables • Aids in blood-clotting • Strengthens bones and teeth • Delayed blood clotting • Rickets in children • Osteoporosis in elderly people Magnesium Green leafy vegetables, whole grains, meat • Regulates functions of muscles and nerves • Keeps the bones strong • Weak bones • Muscle weakness • Fatigue Sodium Table salt • Regulates body fluid • For the proper functioning of nerves • Muscle cramps • Fatigue Iron Green leafy vegetables, liver, meat, egg • For the formation of haemoglobin in red blood cells • Anaemia Iodine Seafood, seaweed, iodised salt, green vegetables • For the formation of hormones in the thyroid gland • Goitre (swelling of the thyroid gland) Phosphorus Milk, cheese, eggs • For the formation of healthy bones and teeth • For the contraction of muscles • Tooth decay • Weak muscles Potassium Bananas, potatoes, fish, meat, nuts • Regulates body fluid • For the proper functioning of nerves and muscles • Weak muscles • Fatigue Chlorine Table salt • Regulates body fluid • For the proper functioning of nerves • Muscle cramps • Loss of appetite Activity 1 1 Work in groups. 2 Make a poster of both the fat-soluble and water-soluble vitamins, their sources (other than the ones given above), importance and effects of deficiencies, including the factors that can cause vitamins to be destroyed. You may search on the Internet for the information. 3 Each group will then present their findings to the class. Understand vitamins 24 ©Praxis Publishing_Focus On Science

Water Water is essential in many life processes. Water makes up about 60% to 70% of our body mass. When proper water balance is maintained in the body, all the processes in the body can be carried out efficiently. The daily water loss through our sweat, urine, and the air we breathe out needs to be replaced. An average person needs to consume approximately six to eight glasses of water daily. Water can also be obtained from food with high water content. Water loss can affect the physiological processes and physical performance of the body. If the water that is lost is not replaced, dehydration occurs. An extreme water loss can be fatal. Examples of other sources of water apart from consuming water directly We need to consume about 2.5 litres of water daily. The functions of water Medium of transportation for respiratory gases and nutrients Medium for all cellular biochemical reactions Main component of cells and blood plasma Removes excretory waste through sweat and urine Dissolves nutrients and transports them throughout the body Enables the breakdown of food substances during digestion Regulates body temperature Functions of water Chapter 2 Structures and Functions of the Human Body Systems 25 ©Praxis Publishing_Focus On Science

A Balanced Diet A balanced diet fulfils all the nutritional and energy needs of the body. It consists of carbohydrates, fat, proteins, vitamins, minerals and water in the correct quantities and proportion. A balanced diet for a person varies based on his lifestyle, health conditions and specific nutritional requirements. In the latest recommendation by the USDA (United States Department of Agriculture) of the balanced meal known as the MyPlate guide, vegetables and fruit must form about half of the food plate serving since they are the healthiest food. The remaining food plate serving should contain proteins and grains accompanied by a small serving of dairy product with low-fat content. A person can be healthy and energised by eating the right food in the right amount. A balanced diet is required for the healthy growth and development of the body. Each food group plays a role, for example, carbohydrates and fat are sources of energy, proteins repair and build new tissues for growth, vitamins and minerals keep us healthy and dietary fibre prevents constipation. However, if a person overeats, the extra energy is stored as a layer of fat. Too much fat may lead to health problems such as heart diseases and diabetes. On the other hand, if a person eats less than what is required, he may suffer from malnutrition. Malnutrition can weaken the immune system, making the person susceptible to diseases. Therefore, by following the minimum daily energy requirements, health issues related to overeating and malnourishment can be prevented. Protein Grains Vegetables Fruits Dairy Nutrition Facts Label A nutrition facts label on packaged food product lists the types of nutrients found in the product, the serving size, and the calories per serving of the food product. This enables consumers to make the best decision on how much to eat, or how they can better balance their food choices throughout the day. They can choose food that are high in nutrients they need more of, such as protein and low in nutrients they need less of, such as fat. The value of energy on labels shows how much energy the food contains. It does not measure how much energy a person gets from it. This is because certain foods use a lot more energy to digest than others. Number of servings in the whole container (If everything in the container is eaten, you have consumed 6 times the amount of calories and nutrient values shown on the label) Calories per serving (Number of calories or the amount of energy one serving of the product contains) Size of one serving of this product (All of the nutrition information on the label is based on one serving of the product) Percent daily value (The intake of each nutrient per serving that contributes to a total daily 2000 calories diet of an average person - this enables consumers to estimate how much they need daily) MyPlate, the plate guide illustrating recommended proportions of food groups to be consumed in each meal. 26 ©Praxis Publishing_Focus On Science

Activity 2 1 Work in groups. 2 Each group must obtain two nutrition facts labels of the same type of food product but from different brands. 3 Compare the information on both labels. 4 As a consumer, determine which product you should choose by asking yourself these questions: • Which one has more nutritional values? • Which one is healthier to be consumed? 5 Present your findings to the class. Understand food labels Energy Content of Food All of us need energy to move around, grow and build new tissue and repair damaged tissue. Food is the source of energy for our body. In a calorimeter, a food sample is burned inside a closed, insulated container. As heat energy is released from the combustion, the temperature of the surrounding water rises. The equation to calculate the energy value of a food sample by using a calorimeter is as follows: Energy value of food (kJ g–1) = Water mass (g) × 4.2 J g–1 ºC–1 × Increase in water temperature (ºC) Food sample mass (g) × 1000 The amount of energy in a food can be determined by burning a sample of food in a calorimeter and measuring the amount of heat released. The amount of heat produced from the complete combustion of one gram of food is known as the energy value of the food. It is measured in kilojoules per gram (kJ g–1). The energy value can also be measured in calories. 1 kilojoule = 1000 joules 1 calorie (cal) = 4.2 joules 1 calorie or 4.2 joules is defined as the quantity of heat energy needed to raise the temperature of 1 gram of water by 1 degree Celsius at a pressure of 1 standard atmosphere. Food sample Water Ignition wires Thermometer Insulated container 70 60 50 40 30 20 10 80 90 100 Stirrer Chapter 2 Structures and Functions of the Human Body Systems 27 ©Praxis Publishing_Focus On Science

Example 1 A chicken burger contains 40 g of carbohydrate, 23 g of fat and 28 g of protein. Calculate the total energy, in kcal. Solution: Amount of energy from 40 g carbohydrate = 40 g × 4 kcal/g = 160 kcal Amount of energy from 23 g fat = 23 g × 9 kcal/g = 207 kcal Amount of energy from 28 g protein = 28 g × 4 kcal/g = 112 kcal Total amount of energy from the chicken burger = (160 + 207 + 112) kcal = 479 kcal Our body uses energy from food to perform daily activities such as walking, breathing and working. We need different amounts of energy from the food we consume, at various stages of our lives. The average amount of calories a person needs is about 2000 calories per day to maintain his current weight. However, the daily energy requirement or calory intake varies with individuals based on several factors such as work, size or body weight, condition or state of health, climate, age, gender and physical activity of a person. Factors that affect our daily energy requirement A person who does heavy work needs more energy than a person who has a sedentary job. For example, labourers, fishermen and construction workers need more energy compared to clerks and graphic designers. The quantity of energy in 1 g of each nutrient differs. Although the energy value of carbohydrates is not the highest, our body uses carbohydrates as a source of energy first and only when carbohydrates are used up will fat be used. The table shows the energy value of the three main classes of food. Food class Energy value (kJ /g) (kcal / g) Fat 37 9 Protein 17 4 Carbohydrate 17 4 A small-sized individual has a larger surface area per unit volume than a big-sized individual. The rate of heat loss in small-sized individuals is higher, thus they need more energy than big-sized individuals. Pregnant women require a lot of energy for the growing foetus and lactating women also need extra energy to produce milk for their baby. A person who is sick requires a lot of energy to recover from his illness. Work Size or body weight Condition or state of health 28 ©Praxis Publishing_Focus On Science

Consuming Healthy Meals Food contains the nutrients our body needs to build new cells and tissue as well as to repair damaged cells and tissue. Food provides us the substances needed to maintain good health and prevent diseases. Food provides us the energy to do work and carry out life processes. Although we love having a tasty meal, we must also consider its nutritional value. By neglecting the nutritional value of the food we consume daily, we are risking our overall health in the long run. Healthy meals consist of fruit and vegetables, whole grains, lean protein and nuts. These food are rich in nutrients and have a beneficial effect on our health. On the other hand, unhealthy meals such as fast food and snacks, have less nutritional value and are high in fat, salt and sugar. We should avoid or take unhealthy food in small amounts. People living in cold climate countries require more energy to maintain their body temperature compared to those living in hot climate countries. Climate Children and teenagers require more energy compared to adults. This is due to their higher metabolic rate as they are more active and are undergoing rapid growth. Age A male adult requires more energy than a female adult of the same age and body size. This is because the metabolic rate is higher in a male than a female. Gender Physical Athletes need extra calories for both their physical activities and their growth. activity Fruit salad Nasi pecel Gado-gado Healthy meals Fast food Instant noodle Sweet food Unhealthy meals For each food shown on the left, give a reason why it is considered healthy or unhealthy. Think About It Chapter 2 Structures and Functions of the Human Body Systems 29 ©Praxis Publishing_Focus On Science

Food Additives Food additives, which can be natural or synthetic, are substances added to food during food processing, packing or storing for specific purposes. Examples of food containing food additives are cakes, biscuits, ice cream, sweets, fizzy drinks, sausages and jelly. Here are the reasons why food additives are used. There are two main groups of additives: natural food additives and synthetic food additives. Synthetic food additives are synthetised in laboratories or industries from chemical substances. They are much cheaper to be produced on a large scale. They can withstand the heat involved in food processing. Purposes of using food additives Enable food to last longer by preventing growth of harmful microbes Maintain or improve quality of food texture Restore nutrients or colours of food that have been destroyed Change the appearance of food to make it more appealing Cater to the diet needs of specific consumers Some examples of natural food additives Turmeric Pandan leaves Palm sugar Table salt Garlic Lime leaves Synthetic food colourings are commonly used in the making of cakes, desserts and pastries commercially to make it look attractive to consumers. Natural food additives are substances that exist naturally in plants, animals or minerals and extracted to be used in another food product without any chemical reactions involved. There are not many choices of natural food additives and some are expensive. Therefore, a lot of food additives are synthetically manufactured. 30 ©Praxis Publishing_Focus On Science

Food additives are classified according to their usage: preservatives, colourings, sweeteners, flavourings, essence and antioxidants. Food additives Functions Examples of natural and synthetic food additives and food containing the additives Preservatives • Reduce food spoilage • Prevent growth of microorganisms to prolong the storage and shelf life of food Natural: • Salt (vegetables and seafood) • Sugar (fruit) Synthetic: • Vinegar (pickled food) • Boric acid (noodle) • Benzoic acid (ketchup) • Sodium nitrite (processed meat) • Propanoic acid (bread and cheese) Colourings • Add colours to food to make it more attractive Natural: • Pandan leaf, turmeric, carrot, caramel (kueh, drinks, candies, turmeric rice, ice cream) Synthetic: • Sunset yellow (reddish-yellow colouring in beverages, cereals and snack food) • Tartrazine (lemon yellow colouring in soft drinks, pastries and cotton candy) • Brilliant blue (blue colouring in icing and ice cream) • Erythrosine (red colouring in dried fruits, sauces and juices) Sweeteners • Add sweetness • Replace sugar (synthetic sweeteners) Natural: • Cane sugar, honey, palm sugar (beverages and biscuits) Synthetic: • Aspartame (beverages and jams) • Sorbitol (used in food for diabetic patients) • Saccharin (fruit juices, jellies and jams) Flavourings • Improve the taste of food • Enhance the flavour of food Natural: • Sugar, vanilla, salt (cakes and ice cream) Synthetic: • Monosodium glutamate/MSG (Instant noodle and processed meat) Essence • Make the food smell nice • Give fruity odours (synthetic essence) Natural: • Lime leaves (tom yam and laksa) • Vanilla (cakes and biscuits) • Pandan leaves (jellies and coconut milk rice) Synthetic: • Methyl butanoate (apple odour) • Ethyl butanoate (pineapple odour) • Amyl acetate (banana odour) Antioxidants • Inhibit the oxidation of fatty food • Prevent fruit and vegetables from turning brown Natural: • Tocopherol (margarine and mayonnaise) Synthetic: • Butylated hydroxyanisole (butter, cereals and snack food) Chapter 2 Structures and Functions of the Human Body Systems 31 ©Praxis Publishing_Focus On Science

Common side effects due to intake of food additives Monosodium glutamate (MSG) may cause dizziness and difficulty in breathing. Saccharin may cause allergic reactions such as itchiness. Synthetic colourings may cause hyperactivity. Nitrite salts can cause cancer, allergies, rapid breathing, seizures and hyperactivity. Benzoic acid may cause allergy and hyperactivity in children. Excessive consumption of food additives found in processed foods, for a prolong period of time can be detrimental to our health. These food additives also have lesser nutritional value. The chart below shows the common side effects that arise due to the intake of several food additives. Activity 3 Ingredients: Chicken Meat, Modified Tapioca Starch, Soya Protein, Spices, Salt and Sugar. Contains Food Conditioner, MSG as a Flavour Enhancer and Permitted Colouring. Ingredients: Water, Sugar, Seaweed Extract, Citric Acid, Permitted Flavour (Apple, Orange, Strawberry, Pineapple) Potassium Citrate, Potassium Sorbate, Sucralose and Colouring. 1 Work in groups. 2 Get three food labels of any type of packaged food similar to the examples shown above. 3 Study the information on the ingredients in the food products as shown above. 4 Identify all the synthetic food additives and find out their functions. 5 Paste them on a manila card and highlight all the synthetic food additives with their functions stated. 6 Present your findings to the class. Understand food additives Table salt (sodium chloride) is one of the most widely used natural food additives since ancient times. It is also used as preservatives in salted fish, meat and vegetables to make them last longer. How does salt preserve food? Think About It 32 ©Praxis Publishing_Focus On Science

The Digestive System Do you know how the nutrients from the food we consume are absorbed by our cells? This is made possible by our digestive system through the process of food digestion. Food digestion is the breakdown of food that are large, complex and insoluble into smaller, simple and soluble molecules that can be absorbed into the bloodstream and transported to different parts of the body. There are two types of digestion: physical digestion and chemical digestion. Both the processes involve the breakdown of food and occur in the digestive tract, also known as the alimentary canal. Food digestion starts in the mouth with the aid of the teeth, saliva and tongue. The Parts of the Digestive System Food digestion takes place in the alimentary canal that extends from the mouth to the anus. The alimentary canal is long and muscular. It consists of the mouth, oesophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine (appendix, caecum, colon, rectum) and anus. The total length of the alimentary canal is around 9 metres, and it is open at both ends, at one end is the mouth and at the other is the anus. The small intestine makes up two thirds of the total length of the alimentary canal. There are also other organs in the digestive system which are the liver, gallbladder and pancreas. Each part of the digestive system has its own specialised function. Types of Digestion Physical Digestion Breakdown of large pieces of food into smaller pieces by the grinding action of teeth with the aid of tongue and saliva (chewing) Wave-like contraction and relaxation (peristalsis) by the muscles in the walls of the oesophagus and the whole length of the digestive tract, pushes the food down the tract Squeezing and mixing of food by the muscles of the stomach lining (churning) Contraction and relaxation of segments of muscles in the small intestine (segmentation) • Occurs in the mouth, stomach and small intestine • Breakdown of complex food molecules into simple molecules with the aid of the enzymes • Does not involve peristalsis Chemical Digestion 1 2 3 4 Involves • Occurs in the mouth, oesophagus, stomach and small intestine • Does not involve any enzymes • Involves peristalsis Chapter 2 Structures and Functions of the Human Body Systems 33 ©Praxis Publishing_Focus On Science

The epiglottis plays an important role in both the digestive system and the respiratory system. What do you think happens if there is no epiglottis? Think About It Human digestive system Peristalsis, the wave-like pattern produced by the contraction and relaxation of muscles along the alimentary canal. Digestion in the Mouth The digestive process begins in the mouth. The chewing action of teeth cuts the food into smaller pieces to increase the surface area of the food for the digestive enzymes to act on. The presence of food stimulates the salivary glands in the mouth to secrete saliva. Saliva contains the digestive enzyme, salivary amylase, which breaks down starch into maltose. Starch + Water Maltose Salivary amylase The tongue then rolls the partially digested food into a small ball called bolus with the help of the saliva and pushes it into the oesophagus. The oesophagus is a long, narrow tube with strong muscles in its walls. The bolus is then pushed through the oesophagus into the stomach by peristalsis. Peristalsis is the rhythmic contraction and relaxation of muscles which pushes food along the alimentary canal. Oesophagus Salivary gland Stomach Pancreas Small intestine Rectum Anus Mouth Tongue Epiglottis Liver Gall bladder Large intestine Appendix Pharynx Resource Contracted muscle Relaxed muscle Bolus of food 34 ©Praxis Publishing_Focus On Science

Digestion in the Stomach The stomach is a sac-like muscular organ at the end of the oesophagus. The glands in the stomach wall secrete a liquid called gastric juice. Gastric juice consists of hydrochloric acid, mucus, and the digestive enzyme, pepsin. • Hydrochloric acid kills bacteria in the food that enters the stomach, creating an acidic environment for the enzyme, pepsin, and stopping the action of the salivary amylase. • Mucus protects the stomach wall from the hydrochloric acid and digestive enzymes. • Pepsin breaks down protein into polypeptides. Activity 4 Analyse the action of enzyme Aim: To study the action of the enzyme in saliva on starch. Materials and apparatus: 1% starch suspension, iodine solution, Benedict’s solution, Bunsen burner, glass rod, wire gauze, 250 ml beaker, boiling tubes, boiling tube holder, stopwatch, dropper, tripod stand, retort stand with clamp, thermometer Procedure: 1 Add 10 ml of starch suspension into two boiling tubes, J and K. 2 Rinse your mouth and collect some saliva. 3 Add 4 ml of saliva into boiling tube K. Stir with a glass rod. 4 Test the solutions in both the boiling tubes for simple sugar and starch immediately. Test for simple sugar: Take 2 ml of solution from each boiling tube and place them into different boiling tubes. Add a few drops of blue Benedict’s solution to each boiling tube and heat the tubes in a boiling water bath for a few minutes. Record the colour of the contents. If the solution contains sugar, it will change from blue to a red brick colour. Test for starch: Take 2 ml of solution from each boiling tube and place them into different boiling tubes. Add a few drops of iodine solution and record the colour of the contents. If the solution contains starch, iodine solution changes colour from yellow to blue-black. 5 Then, put both boiling tubes in a water bath at 37ºC and leave them for 10 minutes. Test the solutions in both the boiling tubes for simple sugar and starch. Observation: Record your observations. Boiling tube Beginning of activity End of activity Starch Sugar Starch Sugar J K Discussion: 1 The water bath must be maintained at 37ºC. Give a reason why. 2 What happens to the starch in boiling tube K at the end of the activity? Explain. Protein + Water Polypeptides Pepsin Chapter 2 Structures and Functions of the Human Body Systems 35 ©Praxis Publishing_Focus On Science

The stomach stores food for about three to four hours, enabling the food to mix with the gastric juice. From the stomach, the partly digested, semi-liquid mass called chyme moves into the small intestine when the sphincter muscle relaxes. Sphincter muscles are found at the connection between stomach and small intestine. Sphincter muscles control the flow of food out of the stomach and allow only small amount of food into the duodenum (first part of the small intestine) at one time. Digestion in the Small Intestine The small intestine consists of the duodenum, jejunum and ileum. Duodenum receives • chyme from the stomach • bile produced by the liver • pancreatic juice secreted by the pancreas. The liver produces a greenish liquid called bile and stores it in the gall bladder. Bile flows into the duodenum through the bile duct. Bile emulsifies fat into small droplets and creates an alkaline condition for the pancreatic enzymes to work. The pancreas secretes pancreatic juice into the duodenum through the pancreatic duct. The pancreatic juice contains digestive enzymes such as trypsin, lipase and pancreatic amylase. Unlike pepsin, these enzymes require an alkaline environment to function. • Trypsin further breaks down polypeptides into peptides. Polypeptides + Water Peptides Trypsin • Lipase breaks down fat molecules into fatty acids and glycerol. Fat + Water Fatty acids and glycerol Lipase • Pancreatic amylase breaks down starch into maltose. Starch + Water Maltose Pancreatic amylase Stomach Sphincter muscles Pancreas Liver Gall bladder Bile duct Duodenum Jejunum Ileum Resource 36 ©Praxis Publishing_Focus On Science

Digestion ends in the small intestine with fatty acids, glycerol, amino acids and glucose as the final products. Absorption of Digested Food in the Small Intestine The jejunum and ileum are adapted to enable simple molecules produced from the digested food to diffuse through its wall. The final breakdown of food occurs in the ileum. The glands on the ileum wall secretes intestinal juice which consists of the enzymes maltase, sucrase, lactase, erepsin and lipase. • Maltase breaks down maltose into glucose. Maltose + Water Glucose Maltase • Sucrase breaks down sucrose into glucose and fructose Sucrose + Water Glucose + Fructose Sucrase • Lactase breaks down lactose into glucose and galactose. Lactose + Water Glucose + Galactose Lactase • Erepsin breaks down peptides into amino acids. Peptides + Water Amino acids Erepsin • Lipase breaks down fat into fatty acids and glycerol. Fat + Water Fatty acids + Glycerol Lipase Digestion of carbohydrate Digestion of proteins Digestion of fat When nutrients enter the blood, they are carried away to the liver and then throughout the body. Nutrients travel through the bloodstream to feed all the cells in the body. There are some substances that cannot be absorbed by the villi. Thus, they are left in the small intestine. • The small intestine is long, enabling greater absorption of nutrients. • Their internal layer is highly folded and covered with many finger-like projections called villi. Villi play a major role in the absorption of digested food. • The villi wall is one-cell thick, which helps speed up nutrient absorption. • Each villus has many specialised epithelial cells with tiny projections called microvilli to increase the surface area for nutrient absorption. • The villi have a network of blood capillaries that ensures glucose, amino acids and water-soluble vitamins are absorbed easily. • Each villus contains a structure called lacteal to absorb fatty acids, glycerol and fat-soluble vitamins. Lumen of small intestine Folds of small intestine Microvilli Small intestine Villus Epithelial cells with microvilli Chapter 2 Structures and Functions of the Human Body Systems 37 ©Praxis Publishing_Focus On Science

Defaecation The digested food and most of the water we drink are absorbed into the body in the small intestine. The remaining food that cannot be digested, dead cells, fibre and water enter the large intestine. In the large intestine, some of the water is reabsorbed. The remaining semi-solid waste is called faeces. It moves slowly with the help of the peristaltic action. It takes between 12 to 24 hours to reach the rectum. When the faeces accumulates in the rectum, it puts pressure to the rectum and triggers the urge to expel the faeces out of the body. The rectum muscles will contract to pass the faeces out of the body from the anus. This process is called defaecation. The absorption of water from the large intestine into the blood The circulatory system The waste from a meal you consume should be expelled from your body within about 24 hours if your gut is working well. In people who suffer from constipation, the waste will remain in the large intestine for quite some time and almost all of the water will be removed. This causes the faeces to become dry and hard. The best way to relieve constipation is to add more fibre to the diet. 2.2 Circulatory System Our body has a system to transport materials to and from the cells. Nutrients and oxygen need to be transported to cells whereas carbon dioxide and waste need to be removed from the cells. The circulatory system transports useful materials to where they are needed, and waste materials to where they are to be removed. The main components of the circulatory system are the heart, blood vessels and blood. • Blood is the circulating fluid, and it transports both useful materials and waste materials. • The heart is the pumping device which pushes the blood around the body via muscular contractions. • The blood vessels which consist of arteries, veins and capillaries transport materials to the tissues and back to the heart. • Some of the blood vessels have valves to prevent backflow ensuring the blood flows in one direction only. The circulatory system is a closed system since the blood flows in blood vessels that are connected to one another. Heart Blood in the blood vessels Large intestine Small intestine Rectum Anus 38 ©Praxis Publishing_Focus On Science

Blood Blood is a body fluid in the circulatory system. Blood transports oxygen, water, and nutrients to the cells where they are needed. It transports waste materials such as carbon dioxide away from the cells to prevent build-up and problems arising from it. The chemical messengers or hormones produced in the body also circulate through the blood. They control and regulate growth, reproduction and many other processes in the body. The human blood consists of 55% plasma and 45% blood cells. In one drop of blood, there are millions of blood cells, namely red blood cells, white blood cells and platelets suspended in a pale yellowish liquid called the plasma. The plasma is made up of 90% water and 10% soluble substances such as hormones, mineral salts, glucose, acid amino and waste materials. The plasma leaks out through the capillary walls to fill the space between the cells close to the capillaries. This enables substances to be transported between the blood and the cells. Red blood cells • Red blood cells, also known as erythrocytes, carry oxygen around the body. • The cells are biconcave (both sides of the surfaces curve inwards), which provides a larger surface area to help in the transportation of oxygen. • They contain oxygen-carrying pigment called haemoglobin. Platelets • Platelets help clot blood at an injured site. • Platelets do not transport substances. White blood cells • White blood cells are bigger than red blood cells. • White blood cells come in different sizes and shapes. • They help defend the body from infections. They attack and destroy germs that cause diseases. Blood cells seen under the microscope Plasma (55%) Red blood cells (41%) White blood cells and platelets (4%) Chapter 2 Chapter 2 Structures and Functions of the Human Body Systems Structures and Functions of the Human Body Systems 39 ©Praxis Publishing_Focus On Science

Blood Vessels There are three types of blood vessels: arteries, veins and capillaries. Venule Valve Arteriole Arteries • Arteries are blood vessels that carry blood away from the heart to the rest of the body. • Arteries have thicker and strong walls compared to veins due to the higher blood pressure of blood flow. Capillaries • Capillaries are a network of tiny blood vessels that connects arteries to veins. • They have very thin walls to enable substances to get in or out of the capillaries easily. Veins • Veins are blood vessels that carry blood back to the heart. • They have thinner walls compared to arteries due to the lower blood pressure in the veins. • They have valves to prevent any backflow of the blood so that blood flows in one direction only. Why do arteries not have valves? Think About It Artery Vein Capillary As you can see in the diagram below, capillaries close to the cells allow substances to move in and out of the cells easily. Blood Body cells Blood out Venule Carbon dioxide and other waste products move into the blood Oxygen and nutrients move into the body cells Blood in Arteriole Capillary Exchange of materials in capillaries Blood flows slowly in the capillaries. Oxygen and nutrients in the blood move through the capillary walls into the body cells that need them. At the same time, carbon dioxide and other waste products that are not needed by the cells move out from the cells into the blood through the capillary walls. Substances usually move from the place where their concentration is higher to places where their concentration is lower. 40 ©Praxis Publishing_Focus On Science

The differences between the artery, vein and capillary are given in the table below. Artery Vein Capillary Diagram Smaller lumen Thick layer of muscles and elastic fibres Larger lumen Thin layer of muscles and elastic fibres Very small lumen One layer of cells Wall Thick, muscular and elastic wall Thin, less muscular and less elastic wall Very thin walls, one cell thick Valve Absent (except in the pulmonary artery) Present Absent Lumen Small Large Very small Colour Red Bluish-red Bluish-red Blood content Oxygenated blood (except in the pulmonary artery) Deoxygenated blood (except in the pulmonary vein) Oxygenated blood at the arteriole ends and deoxygenated blood at the venule ends Heart The heart is the size of a clenched fist and lies in the chest between the two lungs, towards the left side. The heart is a muscular organ with its walls made of cardiac muscles. The heart receives its own blood supply. Coronary arteries provide nutrients and oxygen to the heart muscles while the coronary veins remove wastes from the heart muscles. The heart has four chambers. The two upper chambers are called auricles or atria (singular: atrium) and the two lower chambers are called ventricles. The right and left atria receive blood returning to the heart. The left and right ventricles pump blood out of the heart. The septum divides the right and left sides of the heart. The left ventricle has a much thicker muscular wall than the right ventricle. This is because the right ventricle pumps blood to the lungs situated next to the heart whereas the left ventricle must pump blood from the heart to the whole body. The walls of the atria are thinner than the walls of the ventricles. Coronary arteries Chapter 2 Structures and Functions of the Human Body Systems 41 ©Praxis Publishing_Focus On Science

When the atria contract, blood is pushed into the ventricles. There are three valves in the heart: tricuspid, bicuspid and semilunar valves. The tricuspid valve connects the right atrium to the right ventricle. The bicuspid (or mitral valve) connects the left atrium to the left ventricle. Semilunar valves are located at the entrances of the aorta and the pulmonary artery to prevent the backflow of blood into the ventricles. All the valves prevent backflow of blood to ensure the blood flows the right way around the heart. The right-hand side of the heart receives blood low in oxygen and rich in carbon dioxide from around the body and pumps it into the lungs. This blood is called the deoxygenated blood. The left-hand side of the heart receives blood rich in oxygen from the lungs and pumps it around the body. This blood is called the oxygenated blood. Stethoscope is a device used by doctors to listen to the sound of the heartbeat. Before the invention of stethoscope, doctors had to place their ear directly onto a patient’s chest to listen to their heartbeat. Science Facts 1 Deoxygenated blood from the body (head and lower body) enters the right atrium through the superior and inferior venae cavae whereas oxygenated blood from the lungs enter the left atrium through the pulmonary veins. 2 Both the right and left atria contract and pump blood into the ventricles. Both the tricuspid and biscuspid valves close to prevent backflow of blood into the atria. 3 Both the right and left ventricles contract forcing the semilunar valves to open. 4 The left ventricle will pump oxygenated blood into the aorta and the rest of the body. The right ventricle will pump deoxygenated blood into the pulmonary artery and the lungs. The flow of blood in the heart Key: Deoxygenated blood Oxygenated blood Septum Bicuspid valve Pulmonary veins From lungs Pulmonary artery To lungs Aorta To head and body 2 From head and body Superior vena cava Semilunar valves Tricuspid valve Inferior vena cava From trunk and legs 1 1 1 4 4 3 2 2 3 Right atrium Right ventricle Left ventricle Left atrium Resource 42 ©Praxis Publishing_Focus On Science

The human circulatory system is known as a double circulatory system. This is because it has two separate circuits and blood passes through the heart twice. In one complete circulation, the heart pumps the blood twice - once to the lungs, known as the pulmonary circulation and once to the body, known as the systemic circulation. Pulmonary circulation • Deoxygenated blood in the right ventricle is pumped into the lungs through the pulmonary artery. This blood has a greater concentration of carbon dioxide than oxygen. • In the lungs, gas exchange occurs. Carbon dioxide molecules diffuse out into the lungs, while oxygen molecules diffuse from the lungs into the blood. The blood is now oxygenated. A Systemic circulation • Oxygenated blood from the lungs returns to the left atrium through the pulmonary vein. • The left ventricle will pump this blood into the aorta to be distributed to all parts of the body (except the lungs). In the tissues and organs, gas exchange occurs. The blood is now deoxygenated. • The deoxygenated blood then returns to the right atrium through the veins. B A double circulatory system makes sure that the cells of the body receive blood which is rich in oxygen. This system makes sure that our blood becomes fully oxygenated in the lungs before it is transported to the rest of the body. Every time our heart pumps or beats, a ‘lup-dup’ sound is heard. It is the sound of the heart valves closing. The heartbeat is called the pulse. The heart rate or pulse rate is the number of heartbeats per minute. A healthy adult normally has a resting heart rate of about 60 to 100 beats per minute. Activity 5 Determining the heart rate per minute at rest and after exercising Procedure: 1 By referring to the diagram on the right, use your index and third fingers of one hand to press lightly on the opposite wrist, just below the base of the thumb. 2 You will be able to feel the pulse in your radial artery between your wrist bone and the tendon on the thumb side of your wrist. 3 Count the number of beats in 15 seconds. Right atrium B A Pulmonary vein Left atrium Left ventricle Aorta Pulmonary artery Right ventricle Venae cavae Chapter 2 Structures and Functions of the Human Body Systems 43 ©Praxis Publishing_Focus On Science

4 Multiply the value by four and that is your heart rate per minute. 5 Now, run around the school field once and repeat steps 1− 4. 6 Sit still for 10 minutes, then repeat steps 1− 4. Observation: Record the heart rate per minute before exercising, immediately after exercising and after resting for a while. Discussion: Does the heart rate decrease or increase after exercising? Give a reason. Conclusion: Write down your conclusion. Blood pressure is the pressure exerted by the blood when it flows inside the blood vessels. When a doctor checks your blood pressure, it is the blood pressure in arteries that is measured. A healthy adult will have a blood pressure reading of around 120/80 mm Hg. Science Facts Health Issues Related to the Circulatory System We need to ensure that our circulatory system is healthy because it plays a major role in bringing nutrients and oxygen to all the cells in our body. Blood needs to flow freely through our arteries. 40 60 80 100 120 0 5 Time (min) Healthy Heart 10 Heart rate (bpm) 40 60 80 100 120 0 5 Time (min) Unhealthy Heart 10 Heart rate (bpm) An example of graphs showing the heart rate (beats per minute) of a healthy individual compared to that of an unhealthy individual. Cardiovascular diseases are diseases related to the heart and blood vessels such as atherosclerosis, hypertension, heart attack (myocardial infarction) and stroke. Your pulse is taken from an artery that passes close to your skin. You cannot take your pulse by pressing your fingers against a vein. Give a reason. Think About It Atherosclerosis is the build-up of plaque inside the arteries. Plaque is formed from cholesterol, dead tissues and other substances. Factors that contribute to plaque build-up include a high-fat diet, high cholesterol, smoking, obesity and diabetes. As plaque builds up, it narrows the arteries and disrupts blood flow. Atherosclerosis becomes a threat to health when the plaque build-up prevents blood circulation in the heart or the brain. Atherosclerosis Blood flow is restricted Plaque formed in the artery 44 ©Praxis Publishing_Focus On Science