Textbook PRIMARY 5 Consulting author: Giam Kah How SCAN ME fo r i... Online QuickQuiz
Textbook PRIMARY 5 ISBN 978-981-14-7010-3 First Published 2020 6001 Beach Road, #14-01, Golden Mile Tower, Singapore 199589. E-mail: [email protected] Printed in Malaysia by The Commercial Press Sdn. Bhd. Lot 8, Jalan P10/10, Kawasan Perusahaan Bangi, Bandar Baru Bangi, 43650 Bangi, Selangor Darul Ehsan, Malaysia. All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, photocopying, mechanical, recording or otherwise, without the prior permission of Praxis Publishing Singapore Pte. Ltd. © Praxis Publishing Singapore Pte. Ltd. 2020 This cover has been designed using resources from Freepik.com, image by BlueRingMedia. Consulting author Giam Kah How The URLs in this book were reviewed and deemed suitable at the time of publication.
Contents LIVING THINGS AND LIFE PROCESSES Chapter 1 Cells and Their Structures 1 1.1 Cells 2 1.2 Animal Cells and Plant Cells 4 1.3 Cell Division 10 Chapter 2 Air, Our Body Systems and the Plant Transport System 14 2.1 Air 15 2.2 Respiratory System 17 2.3 Circulatory System 22 2.4 Transport System in Plants 25 Chapter 3 Reproduction 29 3.1 Reproduction in Humans 30 3.2 Reproduction in Animals 38 3.3 Reproduction in Plants 40 Chapter 4 Energy and Photosynthesis 52 4.1 Energy from Food 53 4.2 Photosynthesis 58 ii
ENERGY AND THEIR CHANGE Chapter 5 Electricity 65 5.1 Electric Circuits 66 5.2 Open and Closed Circuits 68 5.3 Series and Parallel Circuits 71 5.4 Electrical Conductors and Insulators 77 Chapter 6 Simple Machines 83 6.1 Types of Simple Machines 84 6.2 Precautionary Measures in Using Simple Machines 96 MATTER AND THEIR PROPERTIES Chapter 7 Water and Its Changes of State 99 7.1 Changes of State in Water 100 7.2 The Water Cycle 106 7.3 Importance of Water 108 7.4 The Impact of Water Pollution 109 EARTH AND THE UNIVERSE Chapter 8 Changes in the Environment 113 8.1 Soil 114 8.2 Rocks 118 8.3 The Structure of Earth 120 8.4 Natural Disasters and their Effects 121 8.5 Human Activities that Change Earth’s Surface 123 STEM Activity 127 iii
Let’s Think Let’s Try! Let’s Scan What pupils already know Reflects what pupils have learned Challenges pupils with questions that promote higher-order thinking skills Presents extra information that is relevant to the concept learned What pupils would like to explore as they study the chapter Helps pupils to master their scientific knowledge and skills Provides direct access to the relevant information on the Internet by scanning the QR codes given A diagram to ‘map’ out all the concepts in the chapter An activity that engages in applying the knowledge of scientists, mathematicians and engineers Explain It Map It Out Provides direct access to extra questions by scanning the QR codes given Explains difficult terms used in the text Encourages pupils to find information and present their findings Let’s Find Out! STEM Activity Let’s Know More Online QuickQuiz Special Features Special Features iv
Chapter 1 What do I know about cells? 1. 2. 3. What do I want to know about cells? 1. Recognize that some living things are unicellular while others are multicellular. 2. Identify the different parts of a typical animal cell and a plant cell. 3. Relate the different parts of an animal cell and a plant cell to their functions. 4. Use the microscope to view animal and plant cells. 5. Describe how cells grow and divide by producing more cells. 6. Recognize that cell division occurs in unicellular and multicellular organisms. Cells and Their Structures The simplest living things such as bacteria are made up of cells. Complex living things such as animals and plants are made up of cells too. What are cells and how do the cells in animals and plants differ?
1.1 Cells A cell is the basic unit of life. It is the smallest part of a living thing. Cells come in different shapes and sizes. Some organisms are made up of a single cell, like bacteria. Others are made up of many cells. Cells work together to carry out life processes such as growth. They are the building blocks of life. Unicellular Organisms A living thing is called an organism. Living things that are made up of only one cell are called single-celled or unicellular organisms. Some examples of these organisms are amebas, paramecia, euglenas, bacteria and yeast. Euglenas can be found in moist soil and in water. Paramecia live in water. They can move, digest food and reproduce. Bacteria are found everywhere—air, soil and water. Some live in or on other organisms like humans, animals and plants. 2 Hands-on Science Primary 5
Multicellular Organisms Most living things are made up of more than one cell. They are called multicellular organisms. Some examples of these living things are human beings, animals and plants. We are made up of cells. Every part of our body consists of cells. Our body is made up of different types of cells. Other than nerve cells and red blood cells, there are other cells such as fat cells, skin cells, bone cells and muscle cells. The largest cell in the human body is the egg cell produced in the ovary of females. It is usually visible to the naked eye without a microscope. The size of the egg measures about 0.1 mm in diameter. Nerve cells in our brain. Our blood contains red blood cells that are made inside our bones. Cells in plant stems are responsible for transporting food and water to all parts of the plant. Cells in leaves contain a green pigment called chlorophyll. Cells and Their Structures Chapter 1 3
1.2 Animal Cells and Plant Cells Cytoplasm It is mostly liquid that fills up the rest of the cell. This is the place where the activities of the cell take place. Cell membrane It is a thin layer that surrounds the cytoplasm. It controls what goes in and out of the cell. It only allows small substances to pass through it. Thus, it is known as semipermeable. Nucleus It is found in the cytoplasm. It is the brain of the cell. It controls all the activities in the cell. Animal Cells A typical animal cell is made up of: • a nucleus • cytoplasm • a cell membrane All living things are made up of cells. The cells are made up of smaller parts. Animal cells and plant cells have some common parts. On the other hand, plant cells have parts that animal cells do not have. 4 Hands-on Science Primary 5
Vacuole It is found in the center of most plant cells. It contains a watery liquid called cell sap to keep the plant cell firm. It provides support to the cell. Cell wall It is found outside the cell membrane. It provides support and helps to maintain the shape of the plant cell. Chloroplast It is found in the cytoplasm. It contains the green pigment called chlorophyll that is responsible for making food for the plant. Plant Cells A typical plant cell is made up of: • a nucleus • cytoplasm • a cell membrane • a cell wall • chloroplasts • a vacuole Let’s Think What are plant cell walls made up of ? What will happen if the cell wall of a plant is damaged? Animal cells have vacuoles too, but are usually small and exist in large numbers unlike the vacuole in plant cells. Cells and Their Structures Chapter 1 5
Most cells are so small that they cannot be seen with the naked eye. They can only be seen with the help of a microscope. The parts of a microscope are shown as follows: Objective lens 1 2 Eyepiece This is where we look through to see the image of the specimen. It magnifies the image of the specimen. Focus knob 3 It is turned to get a sharp and clear image. Stage clips 4 They hold the slides in place. Stage 5 This is where the specimen slide is placed. Stage adjustment knob 6 It moves the stage up and down for focusing. Mirror 7 It reflects light from an external light source up through the bottom of the stage. 3 Base 8 It supports the microscope. 6 Hands-on Science Primary 5
An English scientist, Robert Hooke was the first person who discovered cells. He observed a slice of cork under a simple microscope he made. He found that the cork consisted of an arrangement of small units which were separated by walls. He named these units “cells”. In Latin, cells mean small rooms. Steps to use a microscope The steps below explain how to use a microscope. For safety reasons, we should never use a microscope in direct sunlight. This could hurt our eyes. When viewing a specimen, we need to keep both eyes open while looking into the microscope. This is to avoid eye strain. Place the microscope in a bright place. Use the low-power objective lens and ensure that it is clicked into position. Adjust the mirror so that there is sufficient light to view the specimen through the eyepiece. Place the slide on the stage and use the clips to hold the slide firmly. Look down the eye piece. Turn the stage adjustment knob to bring the specimen into focus. You may need to use the highpower objective lens if you want to observe a very fine detail. Ensure it is clicked into position. Turn the focus knob to get a sharp and clear image. Cells and Their Structures Chapter 1 7
Let’s Try! 1. Your teacher will prepare the sample slides of animal cells and plant cells, and set up the microscope. 2. Observe the slides of animal cells and plant cells under the microscope. Get help from your teacher if you cannot get a sharp and clear image to view. 3. Draw the cells that you observe in the space below. Then, label the parts of the cells. Animal cells Plant cells How do animal cells and plant cells look like? • Microscope • Slides of human cheek cells (animal cells) • Slides of onion skin cells (plant cells) Things needed: 8 Hands-on Science Primary 5
4. Compare the animal cells and plant cells in terms of the following: Aspect Animal cell Plant cell Shape of the cell Position of the nucleus in the cell Presence of cell wall Presence of chloroplast Presence of vacuole 5. (a) Which cell has a regular shape? (b) Why does it have a regular shape? 6. What is the similarity between animal cells and plant cells? 7. What is your conclusion from this activity? Cells and Their Structures Chapter 1 9
Let’s Think How do you relate the size of a living thing with the number of cells in it? Cell division occurs in multicellular organisms throughout their lives. We grow in size because more cells are formed. Thus, we grow bigger and taller. Cell division is important because it also produces new cells to replace the old or damaged cells. The cells in our body do not live forever. For example, our skin cells can only live about two to three weeks. Cells grow, or multiply, by dividing. When a cell grows to a certain size, the nucleus and cytoplasm will divide. First, there is only one cell, then it divides by a process called cell division to become two cells. 1.3 Cell Division Then each of those cells divides again, and there are four cells. Then those four cells repeat the same process, and there are eight cells. The process can be repeated to produce more cells. 10 Hands-on Science Primary 5
Cell division also occurs in unicellular organisms. They grow by dividing themselves. For example, paramecium goes through cell division and produces two daughter cells. Each of these daughter cells is identical to its parent cell. Each daughter cell will grow by dividing itself into two again. The process can continue until many cells are formed. After you have learned about cell division in multicellular organisms and unicellular organisms, • find out more about the reasons for cell division • compare cell division in multicellular and unicellular organisms • find out how other unicellular organisms such as bacteria and yeast multiply Share your findings with your friends. Let’s Find Out! Human cells take 24 hours to complete a cycle of birth and then division to form new cells. Cells and Their Structures Chapter 1 11
Fill in the blanks. Some words can be used more than once. 1. A is the basic unit of life. 2. Living things that are made up of only one cell are organisms. 3. Living things that are made up of more than one cell are organisms. 4. Animal cells and plant cells have a , and a . 5. Plant cells have a , and a that animal cells do not have. 6. The part that controls all the activities that happen in the cell is called the . 7. Cells that are too tiny can only be seen with the aid of a . 8. In a microscope, the knob that is turned to get a clear and sharp image is the knob, and the knob that is turned to move the stage up and down for focusing is the knob. 9. The process to divide cells to produce more cells is called . 10. The function of cell division is to produce cells or to replace the or damaged cells. new cytoplasm cell wall microscope cell division focus adjustment chloroplasts old nucleus cell membrane vacuole multicellular unicellular cell Let’s Scan 12 Hands-on Science Primary 5
A process by which new cells are produced by dividing Map It Out Living things that are made up of only one cell Unicellular organisms Living things that are made up of more than one cell Multicellular organisms Allows only small substances to pass through it Semipermeable Cell divison Online Explain It QuickQuiz Cells and their structures Cell division • Nucleus • Cytoplasm • Cell membrane • Cell wall • Chloroplast • Vacuole • For growth • To replace old and damaged cells • Nucleus • Cytoplasm • Cell membrane Organisms • Unicellular organisms • Multicellular organisms Animal cells Plant cells Cells and Their Structures Chapter 1 13
Chapter 2 What do I know about air, our body systems and the plant transport system? 1. 2. 3. What do I want to know about air, our body systems and the plant transport system? 1. Recognize that air is a mixture of gases such as nitrogen, carbon dioxide, oxygen and water vapor. 2. Identify the organs of the human respiratory and circulatory systems and describe their functions. 3. Recognize the respiratory system in some animals and plants. 4. Explain the path of blood from the heart to all parts of the body and from all parts of the body to the heart. 5. Relate the function of the circulatory system to that of the respiratory and digestive systems. 6. Explain how water and food are transported in plants. Air, Our Body Systems and the Plant Transport System Living things need air to survive. Without oxygen, humans and animals will die. Without carbon dioxide, plants cannot survive. How is air important to all living things and our body systems? How are water and food transported in plants?
2.1 Air Air is all around us, but we cannot see it because it is colorless. We can only feel it and hear it when it moves. Air contains different types of gases. It is made up of nitrogen, oxygen, carbon dioxide, water vapor and other gases as shown below. It is a mixture of gases that we breathe. Let’s Think How do astronauts in space get oxygen? Oxygen Nitrogen Oxygen Carbon dioxide and others 78% 1% 21% Oxygen is a colorless, odorless and tasteless gas. We take in oxygen from the air around us. Air can be in the form of dissolved oxygen in water and in the soil for the use of aquatic living things and things that live in the ground. For example, fish take in oxygen produced by plants that is dissolved in water. Air, Our Body Systems and Chapter 2 the Plant Transport System 15
Carbon Dioxide Carbon dioxide is produced by human beings when they breathe out. The air we breathe out contains more carbon dioxide and water vapor than the air we breathe in. When we breathe out, our lungs and mouth are moist. Each breath we exhale contains a little bit of water in the form of water vapor. During winter, we can see our breath because the water vapor in our exhaled breath comes in contact with the cold air outside. This will form tiny water droplets which appear as a thick cloud of breath. In the presence of light, green plants make food by taking in carbon dioxide from the air. At the same time, they release oxygen into the surroundings. Oxygen supports burning whereas carbon dioxide is used in fire extinguishers to put out fires. The presence of nitrogen in the air helps to slow down the burning process. Let’s Try! Does your breath contain carbon dioxide? Things needed: • Glass tube • Test tube • Limewater 1. Fill half the test tube with limewater. 2. Observe the color of the limewater. 3. Using the glass tube, blow air into the test tube containing limewater. 4. Observe what happens to the limewater when you blow air into it. 5. Compare your observations in no. 2 and no. 4. What is the change in terms of the color of the limewater? 6. What is your conclusion from this activity? 16 Hands-on Science Primary 5
We need oxygen to survive. Our respiratory system is a series of organs responsible for taking in oxygen and giving out carbon dioxide. The main organ in our respiratory system is the lungs which carry out this exchange of gases as we breathe. Breathing is a process of taking air into our lungs and then releasing it. Let us take a look at the parts of our respiratory system and how they function. 2.2 Respiratory System In the lungs, an exchange of gases occurs. When we breathe in, the oxygen from the air passes into the blood and is transported to all parts of the body. At the same time, the carbon dioxide that is carried in the blood is removed from the body when we breathe out. 3 Lungs Blood vessels Air sacs In the lungs, the air tubes branch into smaller tubes. These tubes end in clusters of thin-walled air sacs. The air sacs are rich in blood vessels. This is where gas exchange takes place. The windpipe provides a clear airway for air to enter and exit the lungs. It branches into two air tubes. One enters the left lung and the other enters the right lung. 2 Windpipe Air enters and leaves our body through the nose. Nasal hairs in the nose filter the dust from the air we breathe in. 1 Nose Air, Our Body Systems and Chapter 2 the Plant Transport System 17
Earthworms and leeches breathe through their skin. Many blood cells are spread on their skin. This is where the gas exchange process takes place because they have very thin and moist skin. They will die if their skin is dried up. Amphibians such as frogs use more than one respiratory organ during their life cycle. They breathe through gills while they are young. Mature frogs breathe with their lungs on land. When they are in water, the process of gas exchange takes place through their skin. Humans breathe all the time. They can breathe through their nose and mouth. What about animals? Do they use the same body parts as humans to obtain oxygen? They get oxygen through different parts of the body, for example, moist skin, openings in the body, lungs and gills. Insects such as butterflies, dragonflies, grasshoppers and cockroaches breathe through the openings in their body. Oxygen enters through these openings to reach every cell in the body. At the same time, carbon dioxide released from the cells comes out through the same openings. 18 Hands-on Science Primary 5
Birds, mammals and reptiles breathe through nostrils. Like humans, the process of gas exchange takes place in their lungs. Aquatic animals such as fish breathe through gills. To get the oxygen dissolved in water, fish swallow the water through the mouth and pump it over the gills. Gills contain blood vessels that help in the exchange of gases. They take in oxygen from the water and give out carbon dioxide. The water containing carbon dioxide then passes out through the gill opening. Gills Gill cover Air, Our Body Systems and Chapter 2 the Plant Transport System 19 Air, Our Body Systems and the Plant Transport System
Let’s Try! How do fish gills look like? • Fish • Magnifying glass Things needed: 1. Your teacher will prepare the fish. 2. Pull open the gill cover. 3. Use a magnifying glass to observe what is under the gill cover. 4. Draw your observation in the space below. 5. (a) What are these comb-like structures called? (b) What is the color of the structures? (c) Why are these structures in this color? (d) What is their function in a fish? (e) Why are the structures made up of many flaps? 6. What is your conclusion from this activity? 20 Hands-on Science Primary 5
Plants do not have lungs, so how do they respire? All parts of the plants respire. They take in oxygen and give out carbon dioxide. The plant parts above the soil get the oxygen directly from the air through tiny openings found on the lower surface of the leaves. These openings are pores that allow the exchange of gases to take place. The roots of plants also need oxygen which they obtain from the air spaces in the soil. A small part of the leaf has been magnified under a microscope to show a pore found on it. Green plants respire during the day and night, but they take in carbon dioxide and give out oxygen during the day in the process of making food. It is an opposite process compared to respiration. Give enough water to plants. If a potted plant is over watered, you could kill the roots by drowning them because the roots will not get enough oxygen to breathe. Compare how plants, animals and humans take in oxygen and give out carbon dioxide. Then, show how the respiration in plants is interrelated with the respiration in animals and humans. In groups, you may present your work in the form of a table or other creative ways. Let’s Find Out! Opening in the lower surface of the leaf viewed under a microscope Air, Our Body Systems and Chapter 2 the Plant Transport System 21
2.3 Circulatory System The circulatory system is the system that carries blood which contains digested food, oxygen and water to all parts of the body. It also carries waste materials and carbon dioxide away from them. Our circulatory system is made up of the heart, blood vessels and blood. Heart The heart is the main organ in the circulatory system. It is located in the center of our chest. Our heart is made of cardiac muscles. The muscles contract and relax to pump blood continuously to all parts of the body. Each cycle of contraction and relaxation is called a heartbeat. We cannot control our heartbeat. Heart 22 Hands-on Science Primary 5
Let’s Think Our heart beats every second even when we are asleep. Why does our heart beat faster when we exercise? Our blood consists of plasma, red and white blood cells, and platelets. Plasma is the fluid part of the blood. Red blood cells are produced by the bone marrow and have a lifespan of about three months. White blood cells are colorless and have a lifespan of one day. Platelets are made in our bone marrow along with our white and red blood cells. They help our body form clots to stop bleeding and have a lifespan of eight to ten days. Blood vessel Blood vessels carry blood • from our heart to all parts of our body, and • from other parts of the body back to our heart Blood Blood transports nutrients, oxygen and water to all parts of the body. Red blood cells play an important role by carrying fresh oxygen throughout the body. At the same time, they also remove waste materials such as carbon dioxide from our body, transporting it to the lungs for us to exhale. Air, Our Body Systems and Chapter 2 the Plant Transport System 23
Every system in our body is important for performing their own functions. The diagram below shows how the circulatory system works closely with the respiratory system and digestive system. Blood Circulation in the Systems Blood circulation from the lungs to the heart and to all parts of the body • In the lungs, the oxygen that we breathe in passes into the blood. The blood rich in oxygen is carried to the heart. 1 • The heart pumps the blood to all parts of the body. 2 – 3 Blood circulation from the digestive system to all parts of the body • Blood also transports nutrients and water from the digestive system to all parts of the body. Our body parts produce energy by using oxygen, nutrients and water to carry out their functions. Blood flow rich in oxygen, nutrients and water Blood flow rich in carbon dioxide and waste materials Blood circulation from all parts of the body back to the heart and lungs • As our body parts use oxygen, nutrients and water to carry out their functions, carbon dioxide is produced. • Blood carries carbon dioxide away from all parts of the body and back to the heart. 4 – 5 • The heart pumps blood back to the lungs where carbon dioxide is removed when we breathe out. In the lungs, the blood exchanges its carbon dioxide for oxygen when we breathe in, and the cycle is repeated. 6 Blood also carries other waste materials to the organs such as the kidneys and liver before they are removed from our body. Upper body parts Lower body parts Lungs Heart 4 5 6 1 3 2 24 Hands-on Science Primary 5
2.4 Transport System in Plants The transport system in plants extends from the roots, up through the stem to the leaves, flowers and fruits. The transport system of plants consists of two types of tubes which are water-carrying tubes and food-carrying tubes. These tubes are found in the stem. Leaves In the presence of sunlight, plants need water and carbon dioxide to make food. In the food-making process, water and minerals are transported from the roots up to the leaves and other parts of the plant through water-carrying tubes. Roots provide support by holding the plant firmly in the soil. The roots absorb water and minerals from the soil for the growth of the plant. They also store food that the plant uses to carry out other functions. 3 1 The stem provides support for the plant by allowing the leaves to get plenty of sunlight. It also holds up the flowers, fruits and seeds. This is the main part to transport food and water. 2 The food produced by the leaves moves to other parts of the plant through foodcarrying tubes. 4 Transports water and minerals from the roots to all parts of the plant Transports food from the leaves to all parts of the plant Air, Our Body Systems and Chapter 2 the Plant Transport System 25 Air, Our Body Systems and
After you have learned the transport systems in humans and plants, find out the information below and share it with your classmates. • In what ways are the transport systems the same for humans and plants? • In what ways are the transport systems different for humans and plants? • What are transported in the transport systems of humans and plants? • Why is a transport system important in humans and plants? Let’s Find Out! Let’s Try! How is water transported in plants? • Water • Food coloring • Water glass • Spoon • Cup • Celery stalk with leaves Things needed: 1. Fill a water glass with half a cup of water. 2. Add a small cup of food coloring into the water glass. 3. Stir the food coloring until it is evenly mixed. 4. Cut about 3 cm off the bottom of a celery stalk. 5. Then, put the celery stalk, with the leaves sticking up, into the water glass. 6. Observe it the next day. Pay attention to the leaves. What do you observe? 7. (a) Cut 2 cm off the bottom of the stalk, what do you observe? (b) What is this structure called? (c) What is the role of the structure you observed? 8. Why do we need to cut 3 cm off the bottom of the celery stalk at the beginning of the activity? 9. What is your conclusion from this activity? 26 Hands-on Science Primary 5
Fill in the blanks. Some words can be used more than once. 1. Air is made up of , oxygen, carbon dioxide, water vapor and other gases. 2. Aquatic animals breathe dissolved in the water. 3. Our respiratory system is made up of the nose, and lungs. 4. Our respiratory system allows an exchange of gases to occur in the . 5. The process of taking air into our lungs and giving it out again is called . 6. Animals breathe through their , , gills or openings in their body. 7. Plants take in and give out air through the found on their leaves. 8. Our circulatory system is made up of the , blood vessels and blood. 9. flows through the blood vessels from the heart to all parts of our body and back to the heart again. 10. The heart pumps blood containing , oxygen and to all parts of the body and removes waste materials from the body. 11. The circulatory system, system and system work closely to carry out their own functions. 12. Water-carrying tubes and food-carrying tubes are found in the of plants to transport food and water for the growth of the plant. heart oxygen windpipe stem breathing water pores blood nutrients respiratory lungs nitrogen digestive skin Let’s Scan Air, Our Body Systems and Chapter 2 the Plant Transport System 27
A system that is responsible for taking in oxygen and giving out carbon dioxide Map It Out Respiratory system A system that carries blood containing digested food, oxygen and water to all parts of the body Circulatory system A very small opening on the lower surface of the leaves Pore Space in the lung containing air Air sac Online Explain It QuickQuiz Air, our body systems and the plant transport system Air Our body systems Plant transport system • Nitrogen • Oxygen • Carbon dioxide • Water vapor • Other gases • Respiratory system for taking air in and out • Circulatory system for carrying blood to all parts of the body • Water-carrying tubes transport water and minerals from the roots • Food-carrying tubes transport food made in leaves 28 Hands-on Science Primary 5
Chapter 3 What do I know about reproduction? 1. 2. 3. What do I want to know about reproduction? 1. Identify the main organs of the male and female reproductive systems and their functions. 2. Describe the process of fertilization in the sexual reproduction of humans. 3. Describe the growth and development of humans from birth to old age, including the physical changes during puberty. 4. Identify the methods of sexual reproduction in animals. 5. Explain how flowering and non-flowering plants reproduce. 6. Describe the processes in the sexual reproduction of flowering plants such as pollination, fertilization, seed dispersal and germination. 7. Recognize the similarities in terms of fertilization in the sexual reproduction of flowering plants and humans. Reproduction A family grows when a mother gives birth to a child. Reproduction enables us to produce young to start a family. Reproduction also happens in the world of animals and plants to increase their numbers. How does reproduction differ in humans, animals and plants?
Reproduction is the process by which new individuals are generated. Living things reproduce to ensure continuity of their kind and to prevent becoming extinct. Subsequently, reproduction enables the characteristics of an individual to be passed on from the parents to their young, generation after generation. Male Reproductive System The male reproductive system consists of five parts as shown below. The main reproductive organ of a male is the testis (plural: testes). During puberty, the testes produce reproductive cells that are called sperms. Sperms Sperm duct Urethra Penis Testis Scrotum What are the characteristics of your parents that have been passed on to you? Do a family tree consisting of three generations, starting from your grandparents. Paste their photos and write down who they are. List out their characteristics such as looks, type of eyelid, hair type, eye color, teeth structure, appearance of dimples and others. Observe whether there is any similarity between you and them. Present your findings in a table. Let’s Find Out! 3.1 Reproduction in Humans 30 Hands-on Science Primary 5
Sexual Reproduction in Humans Sexual reproduction in humans involves a male and a female. For reproduction to occur, both the male and the female reproductive systems must work together. Reproductive cells are found in the male and the female reproductive systems. During mating, their respective reproductive cells come together so that the joining of these cells can take place. Female Reproductive System The female reproductive system consists of five parts as shown below. The main reproductive organ of the female is the ovary. During puberty, the ovaries produce reproductive cells that are called ova (singular: ovum). Fallopian tube Ovary Uterus Cervix Vagina Ovum Have you ever wondered how babies come about? You are learning this topic which means you are probably an older kid. You should learn to be more responsible in your activities with the opposite gender. Chapter 3 Reproduction 31
Fertilization and Pregnancy The birth of a baby starts with a process called fertilization and it is the first step of pregnancy. It takes about nine months for a baby to develop and be ready to be born. Walls of uterus Fertilized egg Ovum The male reproductive cells (sperms) enter the female reproductive system and reach the Fallopian tubes. Many sperms can swim to reach the ovum, but only one sperm is allowed to meet the ovum. At the Fallopian tube, when a sperm meets an ovum, They join together. This is called fusion. The fusion of a sperm and an ovum to form a fertilized egg is called fertilization. Life begins here and the woman is said to be pregnant. The fertilized egg from the fusion of the two cells starts to divide to form more cells. This ball of cells attaches itself to the wall of the uterus. It develops and grows until the shape of a baby is seen. 1 2 3 4 Fallopian tube Sperm 32 Hands-on Science Primary 5
Each month, only one ovary produces an ovum. Sometimes, the ovaries produce two ova at once. It is possible for the ova to be fertilized by two sperms. In this case, a woman becomes pregnant with non-identical twins because they come from two ova and two different sperms. 5The baby continues to grow. In the mother’s womb, the developing baby gets nutrients and all the life support from the mother’s blood through the umbilical cord. When all the organs are completely formed and the baby is fully developed, it is ready to be born. 6 Umbilical cord Chapter 3 Reproduction 33
The Growth of Humans Growth in humans involves six stages as shown below. Infancy (0 to 1 year old) An infant is a very young child between birth to one year of age. At this stage, the infant depends on his parents for everything. Crying is a major form of communication for infants. Slowly, the child will learn to smile, sit up, crawl, stand, walk and talk. An infant requires a lot of sleep. The number of hours will be reduced as he grows. When a child learns to walk, he becomes more mobile and starts to explore things that he can access. He also learns to talk more and to follow simple instructions. He imitates the people around him. As he gets older, he learns to express more feelings and emotions. He still needs a lot of sleep and may take a nap during the day. Toddler (1 to 3 years old) The child starts to explore the world. He can also learn in a school. He learns to read and write. He starts to do things on his own. He likes to make new friends through playing with others. He should be able to communicate with others using simple but complete sentences. Childhood (4 to 11 years old) 34 Hands-on Science Primary 5
Adolescence (12 to 18 years old) Adolescence is the period when the child experiences growth before adulthood. This period is also known as puberty as the reproductive organs of a child mature. During puberty, he will experience a series of changes in his body. In this stage, he wants independence from parents, while peer influence and acceptance become very important. He begins to develop self-identity. Now, he is more mature physically and mentally. He is responsible for himself and able to make his decisions independently. Later, he will settle down and start his own family. Once he has children, he will take on new roles and responsibilities as a parent. Although his growth has slowed down, he still needs a balanced diet. He should eat a wide range of food moderately and exercise regularly. Adulthood (19 to 65 years old) As he reaches old age, his body is not as strong compared to his young age. His hearing may be less sensitive and he needs hearing aids. His eyesight starts to decline. His muscles may be weak and he needs support and assistance to walk. Old people are at high risk of contracting diseases. Nevertheless, old people should not be forgotten and put aside. We should take care of them and respect them. We should shower them with love and warmth as they are part of the family. Old age (66 years old and above) Chapter 3 Reproduction 35
Reproductive system • Penis enlarges. • The testes produce sperms and hormones. Due to the changes in the level of hormones, acne or pimples can show up on the face. Emotional changes can occur due to these body changes. Physical Growth in Humans The process of growth in humans involves a lot of change. The changes are height, weight, body proportions, general appearance and changes that happen in the body. Height (cm) Age (years) Infancy and toddler Childhood Adolescence Adulthood Old age Rapid growth Growth occurs slowly Rapid growth Only a little growth occurs No growth happens Male Female Changes during Puberty in Boys General appearance • Facial hair grows on the face. Hair grows on chest, armpits and pubic region. • Body becomes more muscular and stronger. • Shoulders and chest broaden. • Voice box enlarges causing voice to become deeper. Let’s Think • As teenagers grow rapidly, they need to eat more nutritious food. What kind of food should be included in their diet? Why? • What kind of food should be avoided? Why? 36 Hands-on Science Primary 5
Physical Growth in Boys and Girls Boys and girls develop differently in a few ways, either in general appearance or internally. At the end of the rapid period of growth, the growth rate of boys becomes higher than that of girls. Changes during Puberty in Girls Reproductive system • Uterus enlarges. • The ovaries produce ova and hormones. • Start to experience menstruation. Menstruation is the discharge of blood from the vagina. Girls have their menstruation cycle once a month. General appearance • Hair grows on armpits and pubic region. • Breasts grow larger. • Hips become wider and rounder. During puberty stage, practice a high level of personal hygiene. Exercise can keep the growing body in good shape and it also helps to manage our emotions better. In addition, getting sufficient sleep and rest are important. Talk to your parents and teachers, and listen to their advice if you experience any physical or emotional changes. Chapter 3 Reproduction 37
3.2 Reproduction in Animals Like humans, animals need a male and a female to reproduce babies. For humans, we undergo internal fertilization. For animals, there are two ways, either internal fertilization or external fertilization. Internal fertilization Some animals such as tigers, lions and sheep give birth to their young. The male animal releases sperms inside the female’s body to fertilize the egg. The fertilization which takes place in the female animal’s body is called internal fertilization. The fertilized egg grows in its mother’s womb until it is fully developed to be born. Internal fertilization increases the chances of a successful reproductive cycle. This is because it has the advantage of protecting the fertilized egg in the body. Animals such as birds and reptiles undergo internal fertilization too. The difference is that females lay their eggs after they have been fertilized. The young hatch from the eggs after a few days or weeks. It takes about 42 days for ostrich eggs to hatch while for turtle eggs, they hatch anywhere from 45 to 90 days after being laid. Donkeys practice internal fertilization. After the fertilization is successful, the young is born alive. The young looks like its mother. 38 Hands-on Science Primary 5
Let’s Think What are the disadvantages of having external fertilization? External fertilization Some animals such as frogs and fish reproduce through external fertilization. These animals live in water, so the female animal lays its eggs directly into the water. Then, the male animal releases its sperms to fertilize the eggs. The fertilization which takes place outside the female animal’s body is called external fertilization. The benefit of external fertilization is the mother can lay many eggs at one time. A common frog can lay up to 1000 eggs at one time. This is to increase the chances of fertilization. Most fish release thousands of eggs in the water where the male fish can fertilize them. The fertilized eggs then develop into baby fish. Animals can reproduce in two ways, that is either sexual or asexual. • What is the main difference between sexual and asexual reproduction? • Give five examples of animals that practice sexual reproduction. Provide the photos, if possible. • Give five examples of animals that practice asexual reproduction. Provide the photos, if possible. • What are the advantages and disadvantages of asexual reproduction? Share your findings with friends. Let’s Find Out! Chapter 3 Reproduction 39
3.3 Reproduction in Plants Like humans and animals, plants reproduce to ensure the survival and continuity of their own kind. Most plants reproduce from seeds but there are some plants that reproduce in a different way. Let us learn how flowering plants reproduce. Reproduction in Flowering Plants Flowers are the reproductive organs of flowering plants. The male and female parts are found on the flowers. Male Parts 1. Anther It contains pollen grains. The pollen grains contain male reproductive cells. 2. Filament It supports the anther. Female Parts 1. Stigma Tip that receives pollen grains. 2. Style The stalk that connects the stigma to the ovary. 3. Ovary It contains ovules. It will develop into a fruit. 4. Ovule It contains egg cells. Ovary and ovules are at the lower end of the style. 40 Hands-on Science Primary 5
The sexual reproduction of flowering plants involves four processes—pollination, fertilization, seed dispersal and germination. Flowers that are pollinated by birds or insects usually have bright-colored petals or are larger in size. The flowers produce nectar and have a nice smell. These attract animals to come near them. Pollination Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Pollen grains from the same flower or from another flower can reach the stigma of the same flower or of another flower for fertilization to take place. Birds, insects or wind play an important role in carrying the pollen grains from the anther to the stigma of a flower. They are the pollinating agents. Let’s Think How does reproduction take place if the male and female reproductive organs in flowers mature at different times? Flowers that are pollinated by wind are generally dull-colored and smaller in size. The flowers do not produce nectar. They do not have a pleasant smell and usually face downwards. Chapter 3 Reproduction 41
Fertilization During pollination, pollen grains are transferred by pollinating agents from the anther to the stigma of a flower. After pollination, fertilization that involves sexual reproduction occurs in the ovule. When the pollen grains land on the stigma, each pollen grain produces a tube called the pollen tube. 1 Anther Pollen grain Stigma Pollen tube Style Ovary Ovule Egg cell (inside the ovule) Male reproductive cell Pollination The pollen tube carrying the male reproductive cells grow down from the stigma, through the style to the ovary. The ovary contains ovules. Each ovule contains the egg cell. 2 When the pollen tube reaches the ovule, the male reproductive 3 cell fuses with the egg cell. This is where fertilization takes place. 42 Hands-on Science Primary 5
Pollination is an important step in the fertilization of plants for the purpose of reproduction. Other than bees and birds, flies, beetles, wasps and mammals such as bats are common pollinators. About 75% of flowering plants depend on these pollinators for fertilization. These plants include those grown for food, spices and medicines. After fertilization, the ovary becomes a fruit while the ovules become seeds. If the flower contains more than one ovule, more than one seed will be produced. The tomato is an example of a fruit that contains many seeds. 1 After fertilization, the petals of flowers start to wither and drop off. 2 The ovary enlarges and begins to develop into the fruit. The ovules in it develop into seeds. The seeds continue to develop. The fruit grows bigger and protects the seeds. 3 Once the tomato has reached maturity, the fruit softens and ripens. The color has changed from green to red. 4 The ripe fruit which contains seeds allows for seed dispersal. Seeds Chapter 3 Reproduction 43
Seed Dispersal Plants produce seeds that can grow into new plants. If the seeds fall to the ground under the parent plant, they will compete with each other for sunlight, water and nutrients from the soil. To avoid this from happening, the dispersal of seeds far away from the parent plant is a must to give space for the young plants to grow well. Seeds or fruits of plants are dispersed by water, animals, wind and the explosive mechanism. Water Dispersal One way that plants disperse their seeds is through water. When the seeds fall in the water, they are carried away by the tide to grow somewhere else. Lotus seeds have a spongy part which has air spaces that help them to float on water. Pong pong fruits have a waxy skin which prevents water from entering the fruits. Coconut trees that grow near the beach disperse their fruits by releasing them into water. These fruits are covered with a waxy surface, have a husk and have air spaces that enable the fruits to float on water. The fruits are then carried by water out to distant locations. Fibrous husk 44 Hands-on Science Primary 5
Animal Dispersal Some plants have fleshy fruits that are eaten by animals. Animals eat the fruits and throw away the seeds. This can help to scatter the seeds away from the parent plants. If the seeds are eaten, they will be passed out with the feces of the animals onto the ground. Then, the seeds will germinate on the ground. The donkeys and squirrel shown are eating apples that are bright in color and have seeds in it. Let’s Think What are the characteristics of fruits that can attract animals for seed dispersal? Some seeds have bristles or hooks that can attach themselves onto the fur of animals. Humans can also help to spread the seeds if they get stuck to our clothing or shoes. Bristles Hook Chapter 3 Reproduction 45