Focus On Science Grade 7

Application of Heat Absorption and Emission Are you aware that the concept of heat absorption and emission is used in our daily lives? Consider some of the examples provided below. Petrol is highly flammable. Thus the petrol tank of a petrol tanker is painted silver and shiny because a bright surface does not absorb much heat and this can keep the petrol at a lower temperature. The car mechanic holding the manometer is filling gas in the car's air conditioning compressor. Heat radiators in cars, machines and air conditioners are painted black to provide a cooling effect by radiating most of the heat. The compressor at the back of the refrigerator is usually black to allow for rapid heat emission into the surrounding environment. Wearing light-coloured clothes during outdoor activities especially during hot weather can keep us cool because they are good reflectors of heat. Generally, the base of cooking utensils is black. The black surface absorbs heat well, and this can speed up the cooking process. 94 ©Praxis Publishing_Focus On Science

Green building technology incorporates heat concepts into buildings to reduce the impact of rapid development on the environment and human health. It involves designing a building with features like low energy consumption, excellent design flexibility and minimal maintenance costs. Green building technology incorporates some of the following features. The walls are painted with bright colours because bright surfaces are poor heat absorber. Windows are designed for maximum air circulation in the house. The roof surfaces are applied with a heat reflecting coating to keep the house cool and reduce electricity usage. More trees are planted in the surroundings to provide shade. Modern business buildings are fitted with glazed windows to cool the building. Chapter 3 Temperature and Heat 95 ©Praxis Publishing_Focus On Science

Green building technology also emphasises the importance of installing energy-efficient and self-sufficient home appliances. Refrigerators, washing machines, dishwashers and microwave ovens are examples of such technologies. These technologies are aimed at creating zero-energy homes and commercial buildings. Water conservation is another aspect of green building. Green buildings are environmentally friendly structures that conserve water. Thus, all water fixtures, such as faucets, toilets and shower heads are water efficient. Science Facts The use of glass in the roof or ceiling allows natural light to enter the house, which saves energy. A rainwater collection tank collects water that can be used to water plants or wash cars. The home has solar panels installed on the roof that absorb energy from the Sun and convert it into electrical energy. The solar water heater is a cost-effective way to generate hot water at home without the use of electricity. 96 ©Praxis Publishing_Focus On Science

3.8 Body Temperature Regulation The capacity of organisms to maintain their body temperature within specified ranges despite a change in the surrounding temperature is known as thermoregulation. Humans maintain a consistent body temperature regardless of changes in the outside temperature. Through metabolic processes, they produce heat. The hypothalamus in our body controls how warm or cold the body is. It senses changes in body temperature and carry out the changes through effectors like muscles, sweat glands, hair, and so on. Controlling heat production and heat loss from the body allows for the maintenance of a constant body temperature. When the body temperature is high The hypothalamus starts heat-releasing processes to increase body heat loss as below. • The widening of superficial arteries allow body heat to escape into the atmosphere via the skin. • The sweat gland produces sweat that evaporates on the skin, cooling down the body. • Controlling the release of thyroid hormones that lowers internal metabolism. When the body temperature is low The hypothalamus activates heat-generating processes to boost body heat generation as below. • The tightening of superficial arteries reduces heat lost from the body. • The smooth muscles shiver to produce heat. • Thyroid hormone is released to increase metabolism. When we are hot, we sweat to release our body heat to maintain our body temperature. Chapter 3 Temperature and Heat 97 ©Praxis Publishing_Focus On Science

Most animals must keep their internal body temperatures within a specific range. Some animals often produce heat from within to keep their bodies at a constant temperature. No matter what the situation, their body temperature remains constant. On the other hand, certain animals rely on outside heat sources, and the environment affects how hot or cold their bodies are. Therefore, we can classify animals into two groups: homeothermic and poikilothermic, based on how stable their deepbody temperature is. Animals that keep a relatively constant body temperature regardless of the outside temperature are said to be homeothermic. Birds and mammals make up the majority of homeothermic animals. Some animals, such as dogs and lions, are unable to sweat. Instead, they pant to allow the water in their mouths to evaporate, keeping them cool. Birds do not have sweat glands to lower their body temperature. They release heat through conduction (the contact with items that are colder than the skin), the radiation of heat through the surface of the skin, and the convection, or irradiation of heat in the surrounding air. Canaries should always be kept in well-ventilated areas because of this. Penguins live in colder climates than any other birds. However, they are able to keep a steady body temperature because of their plumage, which has a higher density of feathers and forms many layers on their skin. The average body temperature of polar bears is 37°C. Thick layers of hair, skin and oil allow them to keep their internal temperature isolated from the outside environment. 98 ©Praxis Publishing_Focus On Science

The green iguana regulates its body temperature by transferring heat from its head to its body or from its mouth, nose and eyes—areas where warm or cold blood is delivered—during the process of heat exchange between its head and body. Poikilothermic animals control their body temperature based on the surrounding environment. This occurs because they lack of the ability to control their body temperature by producing heat—which is why these kinds of animals are commonly referred to as cold-blooded animals. Take a look at the examples below. Desert lizards interact with their surroundings to regulate their body temperature. In order to maintain a constant body temperature, the lizards bask in the hot sun before retreating to the cold shade and burrows. A grasshopper that is long and thin increases its body heat by exposing its sides to the sun while a grasshopper with a broad, flat back would face the sun perpendicularly. While extending the legs cools it by raising it off a heated surface and allowing air to circulate around its body, crouching allows heat absorption from a warm surface into the abdomen. What happens to lizards in the cold? Think About It Butterflies can sunbathe and position themselves differently in the sun to absorb the most heat. Chapter 3 Temperature and Heat 99 ©Praxis Publishing_Focus On Science

1 A measurement of how hot or cold an object is using a thermometer is known as its . 2 In the Celsius scale, the two fixed points which are usually chosen are the point of ice and the point of water. 3 Mercury and alcohol thermometers using capillary tubes are known as thermometers. These thermometers work using the principle of expansion and contraction of liquid when the temperature changes. 4 Most matter when heated and when cooled. 5 When temperature increases, the atoms of a solid vibrate more vigorously to increase its , so the solid expands. 6 Mercury is used in a thermometer because it is a metal that can expand and contract when there is a change in temperature. 7 Heat causes air to expand, which makes it less than the air around it and causes the heated air to rise. 8 Heat is a form of that is measured in joules (J) and it is transferred from a hot area to a cold area. 9 The specific heat capacity, c, of a substance is the amount of heat required to increase the of 1 kg of the substance by 1°C. 10 The specific latent heat of vaporisation of a substance is the amount of heat needed to change 1 kg of the substance from the to the state without any change in temperature. 11 The specific latent heat of fusion of a substance is the amount of heat needed to change 1 kg of the substance from the to the state without any change in temperature. 12 Heat is transferred by conduction through , by movements of liquids and gases, and radiation that can transfer heat through . 13 Sea and land breezes are natural phenomena as a result of . 14 We can feel the warmth of the sunlight because it reaches us through . 15 A heat is a substance that allows heat to flow through it easily. A heat is a substance that prevents or slows down the rate of heat flow through it. 16 A and object is a better heat absorber and heat emitter than a white and shiny object. 17 is the capacity of organisms to maintain their body temperature within specified ranges despite a change in the surrounding temperature. 18 Humans regulate body temperature through the in their body to control how warm or cold the body is. RECALL Fill in the missing words. 100 ©Praxis Publishing_Focus On Science

THINKING CAP Put on your 1 Ms Annisa pours hot coffee into two porcelain cups. Porcelain cup X has an iron spoon in it and porcelain cup Y has a wooden spoon in it. After a while, the coffee in cup X is colder compared to that in cup Y. Explain why. 2 As compared to wearing a thick jacket in the winter, why do people who live in cold regions choose to dress in layers? 3 Explain why an air conditioner is usually fixed near to the ceiling of a room. Chapter 3 Temperature and Heat 101 ©Praxis Publishing_Focus On Science

Project Activity objective: Design and build a solar oven to heat up 100 ml of water in a cup. Problem statement: The heat energy from the Sun makes our Earth habitable for humans and other living things. Heat transfers better in the atmosphere by convection. There are a variety of ways we can harness the heat energy from the Sun to meet our needs. Concept applied: Conduction, convection and radiation Procedure: 1 Work in a group of five students. Appoint a leader in each group. Other members are the researcher, designer, builder and recorder. 2 Brainstorm on how to build a solar oven to heat up 100 ml of water in a cup using the Sun as the only source of energy. The temperature of water in the oven must increase by 10°C in 15 minutes. 3 Design a prototype of the solar oven. List the materials needed. 4 Build the oven and test it. 5 Record the initial temperature of the water and the final temperature of the water (after 15 minutes). 6 Improve your oven, if necessary. Suggested materials: A plain box, a box with a black bottom, a black-bottomed box coated with aluminium foil, a cup, plastic wrap Presentation: Present your design, the solar oven built and the recorded temperatures in a creative way. You can take pictures for your presentation. During your presentation, you may reflect on your solution design. Then, submit a complete report. A Solar Oven 102 ©Praxis Publishing_Focus On Science

Sudi fastens his seat belt before he starts to drive. What happens to Sudi when the brake is applied suddenly upon seeing a cat crossing in front his moving car? Why is it necessary to use the seat belt? Motion and Force CHAPTER 4 What will you learn? Describe motion in terms of distance, displacement, speed, velocity and acceleration Measure speed Understand the relation between force and motion Understand Newton’s Laws of Motion and their applications in daily life Demonstrate Newton’s Law of Motion ©Praxis Publishing_Focus On Science

4.1 Motion We can see various objects in motion around us daily such as children running in the playground, a butterfly flying towards a flower and vehicles travelling on the road. Activity 1 Work in groups. Research further about the differences between distance and displacement and tabulate the findings with examples. Understand the differences between distance and displacement B Jakarta Bandung A A bus travelling along the highway. Linear motion is described in terms of distance, displacement, speed, velocity and acceleration. Distance and Displacement Distance is the total or complete path travelled by an object from one location to another. Displacement is the shortest distance in a straight line between the initial position and the final position of the motion of the object. In other words, displacement is the direct distance between two points. Distance is a scalar quantity (has only magnitude) while displacement is a vector quantity (has both magnitude and direction). The movement around a circular path from a fixed point is called rotational movement. The movement in a straight line is called linear motion. A Ferris wheel which rotates on its axis. The road map shows the distance and displacement of the motion of a car driven from Jakarta to Bandung. This shows the distance travelled by the car, which is 149.3 km. This straight line shows the displacement of the car’s motion, which is 117.3 km. 104 ©Praxis Publishing_Focus On Science

Speed Speed refers to how fast an object moves. As the object moves faster, its speed increases. An object that is moving fast has a higher speed than an object that is moving slow. Speed is a scalar quantity that has magnitude only. It is the distance travelled per unit time. Speed = Distance travelled Time taken The SI unit of speed is metres per second (m/s). Speed can also be stated in kilometres per hour (km/h). A motorbike with an approximate speed of 25 m/s. A woman cycling with an approximate speed of 5 m/s. A plane with an approximate speed of 240 m/s. A stationary object has a speed of zero. This is because it is not moving and there is no distance travelled. The driver is waiting for passengers to board the bus. The bus is at rest because there is no change in the distance travelled over time. Chapter 4 Motion and Force 105 ©Praxis Publishing_Focus On Science

Instantaneous speed Speed limit signs are usually placed at the side of roads. The signs help motorists drive within the speed allowed in a particular area. For example, the maximum speed allowed in residential areas is 30 km/h. Wildlife found in Indonesia. The distances these animals can travel in 30 s are shown. What is the speed of each animal in m/s? Pak Budi is driving in a residential area. Look at his speedometer. Do you think he obeyed the speed limit? Why is it necessary to obey the speed limit? What are the maximum speed allowed in freeways, intercity roads and urban areas in Indonesia? Think About It Speedometers in vehicles help motorists monitor their speed. The speedometer shows instantaneous speed, which is the speed of the car at a particular instant. The clouded leopard can move 560 m in 30 s. The Komodo dragon can move 165 m in 30 s. The elephant can move 360 m in 30 s. The siamang can move 450 m in 30 s. 106 ©Praxis Publishing_Focus On Science

Average speed Average speed is the rate of change of distance travelled. It is the overall rate at which an object moves. Average speed is calculated by dividing the total distance travelled by the total time taken to travel the distance. Average speed = Total distance travelled Total time taken Example 1 Rina travelled by bus from city P to city R via city Q. The bus took 2 hours 30 minutes to travel 240 km from city P to city Q. At city Q, the bus stopped for 15 minutes to pick up and drop off some passengers. The bus continued its journey for 124 km and arrived 1 hour 15 minutes later. Calculate the average speed of the bus, in km/h, (a) from city P to city Q (b) from city Q to city R (c) from city P to city R. Solution: (a) Average speed = 240 km 2 hours 30 minutes = 240 km 2.5 hours = 96 km/h (c) Average speed = (240 + 124) km (2.5 + 0.25 + 1.25) hours = 364 km 4 hours = 91 km/h (b) Average speed = 124 km 1 hour 15 minutes = 124 km 1.25 hours = 99.2 km/h City P City Q City R From this calculation, you can see that the average speed of the whole journey (from city P to city R), which is 91 km/h is not the average of the speeds between city P and city Q, and between city Q and city R. The speed of light is 300 000 km/s. The estimated distance between the Earth and the Sun is 149 000 000 km. Therefore, the time taken for light to travel from the Sun to the Earth is 497 seconds or 8.3 minutes. If the estimated distance between the Earth and the Moon is 384 400 km, how long does moonlight take to reach Earth? Science Facts As you need your answer in km/h, your time must be “hours” instead of “hours and minutes”. Chapter 4 Motion and Force 107 ©Praxis Publishing_Focus On Science

Timing gate is linked to the timer Toy car Length of card Measuring speed using one timing gate Speed can be measured in the laboratory using miniature timing gates, also known as photogates. A light beam is used in the timing gates to start and stop the timer. The speed of a moving object can be measured accurately. Two timing gates or one timing gate can be used to measure the speed of a moving toy car. First timing gate is linked to the start terminal of the timer Second timing gate is linked to the stop terminal of the timer Toy car Distance between the timing gates Measuring speed using two timing gates When the car passes the first timing gate and breaks the infrared beam, the timer is started. When the car passes the second timing gate and breaks the infrared beam, the timer is stopped. The average speed of the toy car is calculated by dividing the distance between the timing gates by the time taken As the car passes the timing gate, the card breaks the infrared beam and the timer is started. As the car moves past the timing gate, the timer is stopped. The average speed of the toy car is calculated by dividing the length of the card by the time taken. The length of the card is equivalent to the distance travelled by the toy car. 108 ©Praxis Publishing_Focus On Science

Activity 2 Aim: To measure average and instantaneous speed of a toy car on the runway Materials and apparatus: Photogate (timing gate) system and electronic timer, toy car and runway Procedure: A Measuring average speed 1 Set up the apparatus as shown in the diagram. Distance between two timing gates Black strip to break infrared beam Transparent card First timing gate linked to the timer Second timing gate linked to the timer Toy car Runway Electronic timer 15 cm 2 Adjust the distance between two timing gates to 50 cm. 3 Release the toy car from the high end of the runway. 4 Catch the toy car once it passes the second timing gate. Record the time taken. B Measuring instantaneous speed 1 Set up the apparatus as shown. Transparent card Length of black strip that breaks the infrared beam Timing gate linked to the timer Toy car Runway Electronic timer 15 cm 2 Release the toy car from the high end of the runway. 3 Catch the toy car once it passes the timing gate. 4 Record the time taken. Results: Activity A Calculate the average speed of the toy car in m/s by dividing the distance between the timing gates by the time taken. Activity B Calculate the instantaneous speed of the toy car in m/s by dividing the length of the black strip by the time taken. Discussion: Why is it advisable not to place the timing gate too high on the runway or too close to the bottom of the runway? Measuring speed Caution • Do not place the timing gates too high on the runway. • Do not place the timing gates too close to the bottom of the runway. Chapter 4 Motion and Force 109 ©Praxis Publishing_Focus On Science

Velocity Velocity is the rate of change of displacement. It is a vector quantity that has both magnitude and direction. It is calculated by dividing displacement by the time taken. Velocity, v = Displacement, s Time taken, t Example 2 Adi runs from his house to the park along the route shown in the diagram and then back to a cafe. The total time taken is 120 s. Determine the velocity of Adi’s motion. 0 100 m 200 m 300 m 400 m 500 m House Cafe Park Solution: Velocity = Displacement Time taken = 300 m 120 s = 2.5 m/s (to the East) Example 3 A cyclist cycled from P to R via Q as the path shown in the diagram. The time taken is 3 s. What is the velocity of the cyclist? Solution: Q P R 1 m Displacement = straight line distance from P to R = PR = 82 + 62 = 10 m Velocity = Displacement Time taken = 10 m 3 s = 3.3 m/s (to the northwest) 110 ©Praxis Publishing_Focus On Science

Acceleration and Deceleration While driving a car along a straight road, the reading on the speedometer changes. At times the reading remains constant and at times, the reading varies. There are two types of motion involved as shown below. 25 m 15 m 0 s 1 s 2 s The car is moving at decreasing velocity. 15 m 25 m 0 s 1 s 2 s The car is moving at increasing velocity. Acceleration Its rate of change of displacement remains the same. Deceleration Non-uniform velocity The car moves at non-uniform velocity when it does not cover equal distances in the same direction in equal intervals of time. Uniform velocity The car moves at uniform velocity when it covers equal distances in the same direction in equal intervals of time. 15 m 15 m 15 m 0 s 1 s 2 s 3 s Motion of car travelling in a straight line Chapter 4 Motion and Force 111 ©Praxis Publishing_Focus On Science

Acceleration is defined as the rate of change of velocity and its SI unit is m s-2. Acceleration is a vector quantity. When the velocity increases, the acceleration is positive. Acceleration is in the same direction as motion. When the velocity decreases or the object slows down, the acceleration is negative, and this is known as deceleration. In this case, acceleration is in the opposite direction of motion. The formula for an object travelling with a uniform acceleration, a is as follows: Acceleration, a = Change of velocity Time taken = v – u t u = initial velocity of the object v = final velocity t = time taken Example 4 A train moves from rest and accelerates uniformly to a velocity of 20 m/s in 25 s. What is its acceleration? Solution: Acceleration, a = Change of velocity Time taken = v – u t = (20 − 0) m/s 25 s = 0.8 m s-2 Example 5 A car travelling at 20 m/s starts to decelerate uniformly. It stops completely in 12 s. Calculate its deceleration. Solution: Acceleration, a = Change of velocity Time taken = v – u t = (0 – 20) m/s 12 s = −1.7 m s-2 The negative value shows that the car is decelerating. Therefore, the magnitude of deceleration is 1.7 m s–2. A velocity-time graph can be used to understand the motion of an object. We can understand better the velocity of an object, the direction it is moving, its acceleration and the displacement of the object. The gradient is equal to the acceleration of the object and the area under the graph is equal to the displacement of the object. v / m s–1 0 t / s v / m s–1 0 t / s v / m s–1 0 t / s The object is moving with uniform velocity. The object is moving with uniform acceleration. The object is moving with uniform deceleration. 112 ©Praxis Publishing_Focus On Science

Activity 3 Aim: To determine the velocity and acceleration of a moving object Materials and apparatus: Ticker tape, adhesive tape, ticker timer, trolley, 12 V AC power supply, runway and wooden blocks Procedure: A Velocity of a moving object 1 Set up the apparatus as shown in the diagram. Adjust the runway for friction compensated by tilting the runway until the trolley, when given a gentle push, moves down the runway at a constant velocity. Trolley Runway Ticker timer Ticker tape Wooden block Power supply 2 Attach the ticker tape to the back of the trolley. Turn the ticker timer on and allow the trolley to move down the runway. If it does not move, give it a gentle push. 3 Observe the dots printed on the tape. Are the distance between the dots the same? 4 Ignore the first few dots if they are too close to each other. Mark and cut the tape into five strips in order. Each strip contains 10 dots as shown in the diagram below. 0 First 10-tick strip Second 10-tick strip Third 10-tick strip 10 20 30 5 Paste the five pieces of 10-tick strips vertically side by side on a piece of paper to make a tape chart. 6 Measure and record the length of each strip in the table provided. Calculate the velocity of the trolley for each strip. B Acceleration of a moving object 1 Tilt the runway used in Activity A by adding another wooden block so that the trolley moves down the runway with an increasing velocity. 2 Attach the ticker tape to the back of the trolley. Turn the ticker timer on and gently push the trolley so that it moves down the runway. 3 Observe the dots printed on the tape. Are the distance between the dots the same? 4 Cut the tape into five pieces of 10-tick strips and paste them vertically side by side. 5 Using the tape chart, measure and record the length of the first 10-tick strip and the fifth 10-tick strip in the table provided. Calculate the velocity of the trolley for these two strips. Velocity and acceleration Chapter 4 Motion and Force 113 ©Praxis Publishing_Focus On Science

Result: Distance (cm) Time (s) Ticker tape chart of Activity A Distance (cm) Time (s) Ticker tape chart of Activity B Guide to calculate time: 1-tick interval = 1 50 s = 0.02 s 10-tick interval =10 3 0.02 s = 0.2 s Activity A Strip Length (cm) Time (s) Velocity (cm s-1) = Length Time First 10-tick Second 10-tick Third 10-tick Fourth 10-tick Fifth 10-tick Activity B Strip Length (cm) Time (s) Velocity (cm s-1) = Length Time First 10-tick Fifth 10-tick Discussion 1 What is the meaning of each of the following terms? (a) Speed (b) Average speed (c) Velocity (d) Acceleration 114 ©Praxis Publishing_Focus On Science

2 Why must the runway be adjusted until the friction is compensated? 3 (a) Describe the pattern of dots produced on the ticker tape in Activity A. (b) What inference can you make based on the answer in 3(a)? (c) Calculate the average velocity of the trolley in Activity A. 4 (a) Describe the pattern of the dots produced on the ticker tape in Activity B. (b) What inference can you make based on the answer in 4(a)? (c) What is the time taken between the first strip and the fifth strip? (d) Calculate the acceleration of the trolley using the formula given. Acceleration = Final velocity − Initial velocity Time taken (e) What will happen to the acceleration of the trolley if the runway is tilted even more? 5 There are several patterns of dots on a ticker tape with varying velocities. Underline the correct answers. (a) Time Velocity Direction of movement (b) Time Velocity Direction of movement (c) Time Velocity Direction of movement Conclusion: Write down your conclusion. Velocity (increases, decreases) uniformly. The object (accelerates, decelerates). Velocity (increases, decreases) uniformly. The object (accelerates, decelerates). Velocity (varies, is uniform). The object (accelerates then decelerates, decelerates then accelerates). Chapter 4 Motion and Force 115 ©Praxis Publishing_Focus On Science

Gravitational force The force that acts towards the centre of the Earth causing objects to fall to the ground. Elastic force The force that is induced through the stretching or compression of a material. Buoyant force The force in fluids acting upwards on an object causing the object to float. Buoyant force Frictional force The force that opposes motion of an object when two surfaces are in contact with one another. Normal force The force that acts against an object when an object is in contact with a surface. Frictional force Direction of motion Normal force 116 4.2 Force and Motion Force and motion are interconnected with one another. Force can produce motion in an object. Force is a push or pull acting on an object. When there is an interaction between two objects, the objects experience force. Types of forces Most of our daily activities such as pushing a button on the remote control, inserting a plug into the socket, opening the fridge door and pulling a ring pull on a can involve force. Force is a vector quantity that has magnitude and direction. The SI unit for force is Newton, N. There are various types of forces as shown in the diagram below. Pushing Pushing Pulling Pulling ©Praxis Publishing_Focus On Science

Effects of Force Sir Isaac Newton was the first person who found out the relation between force and motion. He developed gravitational theory after observing an apple fall. He pondered why the apple fell straight to the ground, and not sideways or even upwards. He realised that the force that causes the apple to fall and keeps everyone on the ground and the force that holds the moon and planets in their orbits are the same. The apple insight inspired him to eventually develop his law of gravitation. What happens when we squeeze a lump of plasticine with force? How does this relate to the effect of force? Let’s take a closer look at the effects that force has on motion and other properties of an object. Effects of force Can move an object at rest or a stationary object Can stop an object from moving Can change the speed of a moving object, can increase or decrease the speed of a moving object Can change the direction of a moving object Can change the shape or size of an object Sir Isaac Newton (1643−1727) was an English mathematician and physicist who became well known for his work on gravity and his three laws of motion. Chapter 4 Motion and Force 117 ©Praxis Publishing_Focus On Science

Activity 4 Aim: To study the effects of force on the change in shape, position, speed and direction Materials and apparatus: Toy car and plasticine Procedure: Carry out the activities and complete the table. Activity Observation Effect of force A (a) Place a toy car on the floor and push the car softly. The toy car moves from rest and Force can move a static object and (b) While the car is still moving, (i) push the car forward with more force. The car moves Force can change the (ii) then push the moving car from the side. The car Force can change the (iii) obstruct the car with your hand. The car B Press a plasticine with your palm. Conclusion: Write down your conclusion. Plasticine Effects of force 118 ©Praxis Publishing_Focus On Science

Newton’s Laws of Motion Consider this scenario: when the car suddenly brakes, the passengers in the car are pushed forward. The top of their bodies are still moving at the same velocity as the car before it breaks and continues to move forward. Do you understand the function of a seat belt and an airbag in a car in the event of a sudden crash or break? It relates to the Newton’s laws of motion. Let’s take a closer look at the three Newton’s laws of motion. Newton’s First Law of Motion Newton’s First Law of Motion (Newton’s Law of Inertia) states that an object remains at its original state, whether it is at rest or moving at uniform velocity in a straight line, unless acted upon by an external force. Inertia is the tendency of an object to remain at rest or, if in motion, to continue moving in a straight line at uniform velocity. The concept of inertia was incorporated into Newton’s First Law of Motion by Sir Isaac Newton. If an object is at rest, its inertia tends to keep it at rest, and for a moving object, its inertia tends to keep it in motion. The inertia of an object varies with mass. The more mass that an object has, the more inertia it has. The following examples are situations involving inertia in daily life. The passengers in a bus initially in a stationary state will be thrown backwards once the bus moves forward with an acceleration. This is due to the inertia of the passengers which keeps them in their original state of rest. The passengers in a moving bus are thrown forward when the bus stops suddenly. This is due to the inertia of the passengers that keeps them in their original state of motion. When a bottle of chilli sauce is moved quickly downwards with a sudden stop, the chilli sauce flows out. This is due to inertia of the sauce that makes it continue being in its state of motion and flow out of the bottle. Activity 5 Work in groups. Do some research on the Internet to get more examples in daily life that involve inertia. Using some creativity, prepare a poster. Each group can present their findings by explaining the examples based on Newton’s First Law of Motion. Exploring daily life situations that involve inertia What do you think happens when the cardboard is flicked away? Does the coin move with the cardboard or resist motion? Explain your answer based on Newton’s First Law of Motion. Think About It Resource Chapter 4 Motion and Force 119 ©Praxis Publishing_Focus On Science

Problem statement What is the relationship between inertia and mass? Hypothesis When the mass of an object , the inertia of the object . Manipulated variable Responding variable Constant variable Length of hacksaw blade Materials and apparatus Plasticine, hacksaw blade, G-clamp and stopwatch Procedure 1 Set up the apparatus as shown. Plasticine Hacksaw blade G-clamp 2 Fix 30 g of plasticine to the free end of the hacksaw blade. 3 Pull the plasticine lightly to one side and then release. Record the time taken for 10 complete oscillations in the table provided. 4 Repeat step 3. Then calculate the average time, t, and the period, T, taken for one oscillation. 5 Repeat steps 2 to 4 with different masses of plasticine, m = 40 g, 50 g, 60 g and 70 g. Results Mass of plasticine, m (g) Time taken for 10 oscillations t1 (s) t2 (s) t1 + t2 2 Period, T = t 10 (s) 30 40 50 60 70 Experiment 1 Investigating the relationship between inertia and mass 120 ©Praxis Publishing_Focus On Science

Based on the result, draw a graph of period, T/s against mass, m/g. 0 10 20 30 40 50 60 70 0.70 0.60 0.50 0.40 0.30 m/g T/s Discussion 1 What can you infer from the graph drawn? (a) The greater the mass of the plasticine, the (longer / shorter) the oscillation period. (b) The greater the mass of the plasticine, the (greater / smaller) the inertia of the object. 2 Is the gravitational force affecting the oscillation period of the hacksaw blade? Conclusion Is the hypothesis accepted? Write down your conclusion. Newton’s Second Law of Motion Newton’s Second Law of Motion (Newton’s Law of Acceleration) describes the relationship between the mass of an object and the force needed to accelerate it. It is often stated as F = ma, that is a force, F acting on a moving object is the product of its mass, m and its acceleration, a. An object with a greater mass requires more force than an object with a smaller mass to accelerate by the same amount. The following examples show how Newton’s Second Law of Motion is applied in daily life. A racing car is built with a low mass so that its acceleration can be increased considerably to win the race. This is because the mass of an object is inversely proportional to the acceleration. Chapter 4 Motion and Force 121 ©Praxis Publishing_Focus On Science

Pushing an empty shopping cart is much easier than pushing a loaded one. A loaded shopping cart has a higher mass and moves slower when the same amount of force is applied. A force called thrust is required to overcome Earth’s gravitational pull so that a rocket can be launched into space. Force is proportional to acceleration, thus the magnitude of thrust is increased to accelerate the rocket fast enough to escape earth’s gravitational pull and enter space. The harder a ball is hit, the faster it moves. This is due to the acceleration of the moving ball which is directly proportional to the force applied to it. 122 ©Praxis Publishing_Focus On Science

Newton’s Third Law of Motion Newton’s Third Law of Motion (Newton’s Law of Action and Reaction) states that for every action, there is an equal but opposite reaction. This means when an object exerts a force on another object, the second object exerts a force of the same magnitude but in the opposite direction of the first object. The following are examples of the applications of Newton’s Third Law of Motion in daily life. A jet engine produces hot exhaust gases which exit from the back of the engine. In reaction, a thrusting force produced in the opposite direction pushes the jet forward. When a person walks, the foot exerts a force on the ground. In reaction, the ground exerts an equal force in the opposite direction that pushes the person forward. When a thrown basketball hits a board, it bounces back. The throwing action resulted in an equal force in the opposite direction from the board. When a person rows the boat with the paddle, water is pushed backwards. Water reacts by pushing the boat in its opposite When the cannon is fired, force is exerted by direction. the cannon on the cannon ball to accelerate it out from the barrel. In reaction, an equal force produced in the opposite direction causes the cannon to recoil backwards. When a person jumps on a trampoline, a downward force is applied on the trampoline. In reaction, the trampoline exerts upward force, throwing the person skywards. Chapter 4 Motion and Force 123 ©Praxis Publishing_Focus On Science

Activity 6 Balloon rocket Aim: To demonstrate Newton’s Third Law of Motion Materials and apparatus: Long balloon, drinking straw, string and tape Procedure: Caution Blow the balloon within its volume limit. 1 Place two chairs 3 metres apart. 2 Tie a string to one of the chairs. 3 Slide a straw onto the string and attach the other end of the string to the second chair. Make sure it is pulled tightly. 4 Fully inflate the long balloon to the maximum size, hold tightly onto the neck of the balloon to make sure no air escapes through it. 5 Using the tape, attach the balloon to the straw. 6 Pull the balloon rocket to one end of the string. 7 Release the balloon so that air rushes out of the balloon. 8 Observe what happens. Observation: Record your observations. Conclusion: Write down the conclusion based on Newton’s Third Law of Motion. How does a helicopter use Newton’s Third Law of Motion to get lifted off the ground? Think About It Chair Straw String Chair Balloon 124 ©Praxis Publishing_Focus On Science

1 The movement in a straight line is called motion while the movement around a circular path from a fixed point is called movement. 2 is the complete path travelled by an object between any two points. 3 is the shortest distance in a straight line between the initial position and the final position of the motion of the object. 4 Distance is a quantity (has only magnitude). 5 Displacement is a quantity (has both magnitude and direction). 6 refers to how fast or slow an object moves. 7 The SI unit for speed is . 8 The speed of a object is zero. 9 speed is the speed of an object at a particular instant. 10 speed is the overall rate at which an object moves. 11 is the rate of change of displacement. 12 Speed is a scalar quantity while velocity is a quantity. 13 When an object covers equal displacement in equal intervals of time, it is known as velocity. 14 When an object does not cover equal displacement in equal intervals of time, it is known as velocity. 15 is defined as the rate of change of velocity. 16 The SI unit for acceleration is . 17 is a push or pull acting on an object. 18 The SI unit for force is . 19 Newton’s First Law of Motion states that an object remains at rest or moves at velocity in a straight line, unless acted upon by an external force. 20 is the tendency of an object to resist any change in its state of rest or of uniform motion. 21 Newton’s Second Law of Motion states that a force acting on a moving object is the product of mass and . 22 Newton’s Third Law of Motion states that when one object exerts a force on a second object, the second object exerts back a force of equal and opposite direction on the first object. RECALL Fill in the missing words. Chapter 4 Motion and Force 125 ©Praxis Publishing_Focus On Science

THINKING CAP Put on your 1 Have you noticed that an electric fan continues to revolve for some time even after the current is switched off? How do you explain this? 2 How does swimming relate to Newton’s Third Law of Motion? Explain. 3 Why does a bird flap its wings shortly before it takes-off? 126 ©Praxis Publishing_Focus On Science

Project Activity objective: Introduce Newton’s First Law of Motion Problem statement: Newton’s first law of motion states that an object remains at its original state, whether it is at rest or moving at uniform velocity in a straight line, unless acted upon by an external force. Also known as the law of inertia, it has important applications in our daily life and this project will demonstrate the first part of the law: An object at rest stays at rest. Concept applied: Newton’s First Law of Motion Procedure: 1 Work in a group of five students. Each group is to build a tower of at least 60 cm tall. 2 Brainstorm the design of the tower and the role of each member in the group. 3 Determine the material to build the tower. The material used must be stackable and it is a set of identical material. For different testing, materials of different mass will be used to build the towers. 4 Build the tower. 5 Prepare notecards by punching a hole on one end and tying a string through the hole. Place the cards in the tower as shown in the picture. 6 Starting at the top, pull the first notecard quickly from the tower. Observe and record your result. 7 Continue to pull one or two more cards from top to bottom and observe what happens. 8 What improvements need to be done if the test is not successful? 9 If this was done successfully, get everyone in the group to pull the cards out at the same time. Would the result be the same as in steps 6 and 7? 10 What improvements need to be done if the test is not successful in step 9? 11 Now try to build a tower of the same height by using materials that has less mass. 12 Repeat steps 6 to 10 and record your result. 13 Alternatively, you can try another test where the cards are without the holes and string. Would this make the pull easier? Would this affect the result? Presentation: You may present your findings with a video or any method that is suitable. Share with the groups the improvements you had done for successful testing. Submit a report. Inertia Tower Chapter 4 Motion and Force 127 ©Praxis Publishing_Focus On Science

Take a look at that sparrow. When it wants to get to the tree nearby from the wooden fence, how does it get there? What is the purpose of it getting there? What other characteristics does it have? Living Things CHAPTER 5 What will you learn? Describe biodiversity, its importance and management Differentiate between living and non-living things Explain the characteristics of living things List the levels in the classification hierarchy of living things Explain that bacteria are living organisms Recognise and name protozoa Explain that yeasts and moulds are types of fungi Classify animals into vertebrates and invertebrates Classify plants into non-flowering plants and flowering plants ©Praxis Publishing_Focus On Science

5.1 Biodiversity Biodiversity originates from the word ‘bio’ which means living thing and ‘diversity’ which means variety. Biodiversity refers to the variety of organisms on Earth, comprising a variety of plants, animals and microorganisms. Biodiversity exists as the result of organisms adapting to a variety of habitats and climate. Elephants that live on land have very big and strong frames to support their body weight. Polar bears live in the Arctic region have a thick layer of fat and fur to trap heat and keep their bodies warm. Camels that live in hot and dry areas have humps to store food, fats and water. Cacti that grow in the desert have needle-shaped leaves. Mangroves have stilt roots that grow in soft and muddy habitats. Coconut trees grow near the water as they need water to disperse their seeds. Characteristics of organisms in a variety of habitats and climate Chapter 5 Living Things 129 ©Praxis Publishing_Focus On Science

A country rich in biodiversity, Indonesia is known for its endemic species but these species are almost extinct on Earth. The government has taken initiatives to protect these species by establishing preservation and conservation centres, enforcing laws as well as raising awareness among the public. You can find the Sumatran Rhinoceros and the Javan Rhinoceros in the Indonesian Rainforest. Sumatran rhinos are the only Asian rhinoceros with two horns. Cendrawasih or “The Bird of Paradise” is an endemic species. Cendrawasih’s feathers are ornate and attractive, with a long tail that hang delicately from its body. You can find the bird of paradise in Taman Nasional Teluk Cenderawasih, West Papua. Orangutans are protected in Tanjung Puting National Park, Central Kalimantan. Borneo and Sumatra island are the only places where you can see orangutans in the wild. Titan Arum can be found around the Sumatran forest. The plant, also known as the Corpse Flower, can grow up to more than 3.5 metres tall. There are fewer than 1000 left in the world. The largest endemic hornbill on Sulawesi Island is the knobbed hornbill. It is a colourful hornbill. 130 ©Praxis Publishing_Focus On Science

Importance of Biodiversity Have you ever wondered why certain measures have to be taken to protect biodiversity? The processes that sustain all on Earth, including humans, rely on biodiversity. We need to have a diverse range of animals, plants and microorganisms to maintain a healthy ecosystem that provide us with the air we breathe and the food we eat. Let us look at some of the reasons why biodiversity is important. Biodiversity is important in the recycling of nutrients. For example, plants take nutrients from the soil and the air, and these nutrients form the basis of the food chain that transfers energy and nutrients from one organism to another. The nutrient cycle and interaction between various species control the balance of organism population. Biodiversity is essential in agriculture that provides food to all organisms in an ecosystem. Other small organisms also obtain their food from the various food sources available in this ecosystem. Biodiversity allows scientific research to be carried out on a variety of plants and organisms in order to develop new crops and medicines. It also helps scientists in gathering information about the evolution of life in specific species. Thus, biodiversity enables humans to expand their knowledge by conducting scientific research on a variety of animals and plants. Importance of biodiversity Biodiversity is essential for maintaining a healthy ecosystem that provides oxygen, water, plant pollination, wastewater treatment and other ecosystem services. Photosynthesis is the process by which plants produce oxygen. Humans breathe in oxygen and emit carbon dioxide which trees absorb. This forms a cycle that demonstrates how all organisms in this ecosystem are interconnected. Chapter 5 Living Things 131 ©Praxis Publishing_Focus On Science

Effective Biodiversity Management Humans need to manage biodiversity effectively in order to ensure all flora and fauna are protected and do not become extinct. Humans must protect these wildlife from human activities which could destroy biodiversity. These activities include: • Logging which can destroy forests and lead to the loss of habitat and subsequent extinction of flora and fauna • Illegal hunting or poaching of animals for body parts, that can reduce the number of animals including endemic species like the Sumatran rhinoceros and orangutans. • Deforestation without control for the purpose of settlement and agriculture could cause a dwindling in numbers due to loss of habitat, emigration or death of wildlife. To protect biodiversity, some measures have been taken to keep such activities from worsening the situation. Creating national parks, forest reserves, marine parks and wildlife sanctuaries to protect flora and fauna habitats. Protecting endangered species by prohibiting the killing and trading of these species, and imposing penalties for the offence. Only cutting down trees that are large and mature. Prohibiting illegal logging by imposing severe penalties on the perpetrator. Replanting trees of the same species to replace those that were cut down in order to preserve the tree species. Establishing rehabilitation centres to care for and conserve endemic species. Conducting campaigns to raise public awareness on the importance of biodiversity in maintaining an ecological balance for the survival of different species, including humans that are present in the ecosystem. Steps to protect biodiversity 132 ©Praxis Publishing_Focus On Science

5.2 Living and Non-living Things From mountains and oceans to plants and animals, we can find a variety of things all around us. The world in which we live is made up of these things. These “things” can be divided into two categories: living things and non-living things. Living things are made of cells which are tiny. They grow and exhibit movement. All living things have common characteristics. Activity 1 1 Complete the checklist below. Characteristic You Cat Plant Doll Need food Obtain energy from food Able to move Can grow Produce and able to remove waste products Produce offspring Respond to changes in the surroundings 2 What are the common characteristics you can find based on the table above among yourself and the others? 3 Would the non-living things show the same characteristics like what you do? Compare yourself with the things around you The chart below shows the characteristics of living things. Respiration Movement Growth Responding to stimuli Nutrition Excretion Reproduction Characteristics of living things Chapter 5 Living Things 133 ©Praxis Publishing_Focus On Science

Respiration We use energy to move, grow, reproduce, excrete waste products and carry out the work in our daily life. Living organisms get energy from food. The process of releasing energy from food is called respiration. In the process, oxygen is used to break down the food to produce energy. Nutrition Living organisms need food for their life processes. Nutrition is the process by which they use food to support life. Humans and animals cannot make food. They eat plants and other animals to get the nutrients they need. Plants can make their own food using light, carbon dioxide and water. They take in minerals from soil as their nutrients. Movement Movement can be seen in both animals and plants. Animals move to look for food, shelter and a mating partner. At the same time, they move to run away from danger. For plants, they move certain parts for specific functions. The Venus flytrap is a carnivorous plant that eats meat. It moves quickly by shutting its trap to capture and eat insects. Morning glory twines around a support with twining stems to climb up for sunshine. 134 ©Praxis Publishing_Focus On Science

Excretion Excretion is a process in which waste products are removed from an organism. If the waste products remain in the body, the waste products will become poisonous and the organism will die. Examples of excretion processes are breathing, sweating and urinating. We remove carbon dioxide, water vapour, salt and urea through the lungs, skin and kidneys. Plants remove carbon dioxide and oxygen via stomata, the openings under the lower surface of the leaves. Growth and Reproduction Growth is an irreversible process whereby living organisms increase in body size, weight and the number of body cells over time. To support growth, organisms need food and nutrients. When the organisms are in the adult stage, they have the ability to produce offspring to ensure the survival of their population. This process is called reproduction. Growth and reproduction are actually two aspects of an organism’s life cycle. Opening in the lower surface of the leaf viewed under a microscope Chapter 5 Living Things 135 ©Praxis Publishing_Focus On Science

After you have learnt the characteristics of living things, can you do a comparison between living and non-living things? 5.3 Classification of Living Things Biodiversity is the variety of all organisms such as animals, plants and microorganisms that interact with one another. Considering that there is still so much biodiversity to discover, and scientists continue to make interesting discoveries, have you ever questioned how scientists classify their numerous discoveries? For instance, how do they classify crocodiles and tortoises? Taxonomic Hierarchy System Classifying living things with similar characteristics aids in the systematic organisation of scientific discoveries, making it easier for them to trace the origins of living things. Scientists can learn more about how living things are related to one another when they have a proper classification system. At the same time, people can study and gain a better understanding of what has been discovered. Responding to Stimuli Living organisms are sensitive to the changes in their surroundings. These changes could be temperature, water and light. The ability to sense and respond to these changes enables organisms to look for food and keep out of danger for survival. Sunflower plants grow towards sunlight. When a cat’s pupils receive too much light, they become smaller, and when there is not enough light, they become bigger. We scratch when we feel itchy. 136 ©Praxis Publishing_Focus On Science

Do tigers and cats belong to the same family? What is the Linnaeus’s taxonomy hierarchy system that shows the classification of cats? What are the two plants in the same family but with different species? Show their taxonomy hierarchies. Think About It Carl Linnaeus, also known as the Father of Taxonomy, is a botanist who developed a scientific method of naming and classifying organisms, which is still being used until today. Taxonomy involves a systematic classification, identification and naming of organisms. In Science, classification means the arrangement of organisms into groups based on similarities and common characteristics. What is the importance of classification? Carl Linnaeus was a botanist, physician and taxonomist. Importance of classification Can identify organisms easily and accurately Facilitate discussions at international level Avoid confusion in naming an organism Ensure that no two organisms have the same name Domain Kingdom Phylum Class Order Family Genus Species Eukarya Animalia Chordata Mammalia Carnivora Felidae Panthera P. tigris Increase in number of organisms General Specific Linnaeus’s taxonomy hierarchy system that shows the classification of Panthera tigris Linnaeus’s taxonomic hierarchy system classifies organisms based on their position in the hierarchy. There are different levels in this taxonomy hierarchy. Domain is the highest level, which is the most general, followed by kingdom, phylum, class, order, family, genus and species, which is the lowest level and the most specific. Chapter 5 Living Things 137 ©Praxis Publishing_Focus On Science

Different species with similar characteristics are classified into the same genus, and different genera with similar characteristics are classified into the same family. Families are grouped in a specific order. A class is formed by grouping orders, and a group of classes form a phylum. Phyla are grouped together to form kingdoms, which are then grouped to form domains. Binomial Nomenclature System Carl Linnaeus developed the binomial nomenclature system, also known as the Linnaeus binomial system in the 18th century. According to the system, each species is given a scientific name that consists of two Latin words. The first word is the genus (generic) name, and the second word is the organism’s specific name. Humans, for example, have the scientific name Homo sapiens. Homo is the genus name, whereas sapiens is the specific name. The genus name starts with a capital letter, while the specific name starts with a small letter. The scientific name (both words) is italicised. Both words must be underlined separately if written. A given scientific name normally refers to the name of person, place or characteristic of the organism. For example, the scientific name Escherichia coli is named after Theodor Escherich, a scientist who discovered the bacterium. The specific name coli shows that E. coli lives in the colon (large intestine). Although the common names of an organism may differ in different places, it can be identified based on its scientific name which is used internationally. After learning Linnaeus’s taxonomic hierarchy system and binomial nomenclature system, let’s learn about the five kingdoms of living organisms: monera, protists, fungi, animals and plants. Unlike animals and plants, there are tiny living organisms known as microorganisms, that can only be observed using a microscope. Examples of these mircroorganisms are bacteria, protozoa and fungi. Monera (bacteria) Bacteria are single-celled organisms that exist everywhere in the millions either inside or outside other organisms. They come in various shapes and sizes. Bacterial cells are different from plant cells and animal cells. They have no nucleus. They have cytoplasm which is a substance inside the plasma membrane that contains genetic material (DNA) and ribosomes. This DNA contains all the genetic information used in the development and function of the bacterium. Bacteria need food, will respire, grow, reproduce and excrete waste products. Some bacteria have flagella that are used for movement. The Bird’s Eye Chilli’s scientific name is Capsicum frutescens. The scientific name of papaya in written form is Carica papaya. 138 ©Praxis Publishing_Focus On Science

GOOD BACTERIA BAD BACTERIA Lactococcus Lactobacillus Salmonella Campylobacter Streptococcus thermophilus Propionibacterium Bifidobacterium Escherichia coli Staphylococcus Clostridium perfringens Normally, E. coli bacteria are found in both human and animal intestines. However, some of them can cause diarrhoea because they are pathogenic. How is this type of bacteria transmitted into the human body? Think About It There are good and bad bacteria. Did you know salmonella is a harmful bacterium that can cause food poisoning? However, there are some good bacteria in our gut that help to keep us healthy. Bacteria are used to make cheese, yogurt, bread and vinegar too. Check the list of ingredients on their packaging to find out the types of bacteria used to produce them. We can grow bacteria on agar plates in the laboratory. The agar will provide the nutrients that the bacteria need to reproduce quickly to form colonies which can be seen with the naked eye. Bacteria in our gut Chapter 5 Living Things 139 ©Praxis Publishing_Focus On Science

The amoeba is a single-celled organism that can change its shape. Ponds, lakes and slow-moving rivers are common places where it can be found. The structure of amoeba mainly consists of the cytoplasm, plasma membrane and the nucleus. Pseudopodia are projections created when the cytoplasm pushes the plasma membrane outward or inward, resulting in blunt, finger-like projections. Euglena is a single-celled flagellated microorganisms with a whiplike appendage. It is a microorganism with both plant and animal traits. Euglena can be found in fresh and brackish water that is rich in organic matter, as well as moist soils. Euglena has chlorophyll to make its own food. Paramecium is a single-celled protist that lives in aquatic environments. It is usually slipper-shaped, with short hairy projections called cilia covering them. Certain Paramecium strains are also easy to culture in the lab and can be utilised as model organisms. Protists (protozoa) Protozoa, like bacteria, are single-celled organisms. They range in size and shape. Some, like the amoeba can change its shape. Others, like the Paramecium has a fixed shape and complex structures. They can be found in wet habitats, such as fresh water, marine environments and soil. Some protozoa are parasites, which means they exist and can cause disease in other plants and animals including humans. Plasmodium, for example, causes malaria. It is a mosquitoborne infectious disease. The disease is seen in tropical and subtropical regions near the equator. Much of Sub-Saharan Africa, Asia and Latin America fall within this region. Fungi Do you know what grows on a rotten orange or a rotten bread? What causes this to happen? Mould grows on a decaying orange and a rotten bread. Mould is a type of fungi that lives on plant and animal matter, such as food to cause it to deteriorate and degrade. Mould takes in the nutrients provided by the food, which allows it to grow, reproduce and multiply. If you take in contaminated food by accident, you may develop food poisoning, with symptoms that includes stomachaches, vomiting and diarrhoea. Fungi can be single-celled organisms or multicellular organisms with a great deal of complexity. They can be found in almost any habitat, but the majority of them reside on land, primarily in soil or plant material, rather than in the sea or fresh water. Plasma membrane Nucleus Cytoplasma 140 ©Praxis Publishing_Focus On Science

Yeasts Yeasts are single-celled organisms. They can cause fermentation of various fruits, plants and plant by-products since they thrive on organic compounds such as sugars. Each yeast cell has a nucleus, cytoplasm and a membrane that is surrounded by a cell wall. A yeast cell can reproduce via budding as shown in the diagram below. These are fast-occurring phenomena that can easily be observed through a highpowered optical microscope. Yeasts can be used to make baked foods as well as alcoholic beverages like beer and wine. Yeast can also be dangerous and cause infections in a variety of ways. Moulds Moulds are multicellular cells. They are made up of hyphae, which are very fine threads. Hyphae form long, branching chains by growing at the tip and dividing periodically along their length. The hyphae continue to develop and intertwine until they form a mycelium, which is a network of threads. From the hyphal tip, digestive enzymes are released. These enzymes break down organic materials in the soil into smaller molecules that the fungus consumes as food. Animals The animal kingdom can be divided into two groups which are vertebrates and invertebrates as shown in the chart below. The two groups can be further divided into smaller groups based on common characteristics. Nucleus Vacuole Daughter yeast Parent yeast • Mammals • Fish • Reptiles • Amphibians • Birds • Arthropods • Cnidarians • Echinoderms • Nematodes • Annelids • Platyhelminthes • Poriferans • Molluscs Animals Invertebrates Invertebrates with jointed legs Invertebrates without jointed legs Vertebrates Hyphae Chapter 5 Living Things 141 ©Praxis Publishing_Focus On Science

Vertebrates Vertebrates have backbones. They are divided into five groups: mammals, amphibians, reptiles, fish and bird. Reptiles • They are covered with scales. • They breathe with lungs. • They lay eggs with leathery shells. Some species give birth to fullyformed young. • They are cold-blooded. • They have no legs or have four legs with clawed toes. • Examples: turtle, snake Amphibians • Generally, they have smooth, moist skin without any coverings. However, certain species of salamanders and newts have rough or bumpy skin. • Adults breathe with lungs and moist skin on land while the young breathe with gills in water. • They lay eggs, usually in a jelly-like mass in the water. • They are cold-blooded. • They have four legs without claws or nails on their toes. • Examples: salamander, frog, toad Mammals • They have hair on their body. • They breathe with lungs. • They give birth to live young and nurse their young. • They are warm-blooded. • They, except whales, have four limbs with claws, nails or hooves. • Examples: bat, whale, hippopotamus 142 ©Praxis Publishing_Focus On Science

Have you ever seen a duck waddling about in the snow? Ducks do not require anything to keep their feet warm, their feathers are only for keeping their body warm. Since their feet lack nerves and blood vessels, their webbed feet are unable to sense the cold. Science Facts Fish • They have fins, tails and streamlined bodies help them move in water. • They are covered with scales or smooth, leathery skin. • They live in water and breathe with gills. • They are cold-blooded. • Examples: stingray, shark, seahorse Birds • They have a beak or bill, two legs, hollow bones and two wings used for flying. • They are covered with feathers. • They breathe with lungs. • They lay eggs with a hard shell. • They are warm-blooded. • Examples: ostrich, penguin, owl Resource Chapter 5 Living Things 143 ©Praxis Publishing_Focus On Science