Invertebrates Invertebrates do not have a backbone. They may have shells outside their bodies or an external skeleton (exoskeleton) in the form of a hard outer covering of the body. They are divided into two groups, invertebrates with jointed legs and invertebrates without jointed legs. Arthropods are invertebrates that have jointed legs, segmented bodies and exoskeletons. Cnidarians, Echinoderms, Nematodes, Annelids, Platyhelminthes, Poriferans and Molluscs are invertebrates without jointed legs. Some of them are worm-like and some are not. Arthropods • They have jointed legs (three, four or more than four pairs of legs). Some have many legs. • They have segmented bodies. • They have exoskeletons. • Some of them have antennae and some do not. • Some have compound eyes and some have simple eyes or no eyes. • Examples: scorpion, crab, praying mantis, centipede Cnidarians • They have tentacles to catch their food. • They do not have true organs. • They have jelly-like bodies. • Examples: jellyfish, sea anemone Echinoderms • They have hard, spiny covering or skin. • Some feature a radial symmetry starshaped pattern. • They have organs but no brains. • Examples: starfish, sea urchin Nematodes • They have round, thin and unsegmented bodies. • They have organs. • Examples: roundworm, pinworm 144 ©Praxis Publishing_Focus On Science
Snail shells are a hard and firm structure made primarily of calcium carbonate that protects the snails’ internal organs. What other function does this structure provide to snails? Think About It Annelids • They are segmented worms. • They have organs. • Examples: earthworm, leech Poriferans • They have a spongy appearance. • They have tiny pores. • They do not have true organs. • Example: sponge Platyhelminthes • They have flat, unsegmented bodies. • They have organs. • Examples: flatworm, tapeworm Molluscs • They have muscular bodies that are usually protected by a hard shell either inside or outside their bodies. • Examples: snail, octopus, squid Chapter 5 Living Things 145 ©Praxis Publishing_Focus On Science
Plants In the plant kingdom, plants are divided into non-flowering and flowering plants. Non-flowering Plants The most primitive plants on the Earth are non-flowering plants. They can be divided into Bryophytes, Filicinophytes and Coniferophytes. Mosses and liverworts are examples of Bryophytes. They do not have true leaves, stems and roots. The leaves and stems are usually small and simple. They are usually found in damp places because they do not have a transport system for water and food. They do not produce seeds or flowers, instead they reproduce by spores. Ferns are an example of Filicinophytes without seeds. They have strong stems, roots and leaves. They have a transport system for water and food. Ferns reproduce by making spores. These spores can be found on the underside of the leaves. Conifers are an example of Coniferophytes that produce seeds which are formed inside the cones. They have true roots, stems and needle-like leaves. They also have a transport system for water and food. They do not produce flowers or fruit. Moss capsules containing spores The spores are produced in the sori located on the underside of the fern leaves. The cones of conifers and their seeds. 146 ©Praxis Publishing_Focus On Science
• Monocots are not usually woody. Most of them are herbaceous plants. • They have leaves of parallel veins. • They have fibrous roots. • They produce seeds that have one cotyledon. • Examples: maize plant, banana tree, pineapple plant, coconut tree • Dicots are usually woody. • They have leaves of a network of veins. • They have taproots. • They produce seeds that have two cotyledons. • Examples: mango tree, tomato plant, sunflower plant, rose plant Flowering Plants Flowering plants are plants that bear flowers and fruits. They have a system for water and food. They are angiosperms. They reproduce by flowers. The flowers produce fruits which contain seeds. The seed consists of three parts, namely the plumule (embryonic shoot), the radicle (embryonic root) and the cotyledon (seed leaf). A cotyledon is the part of a plant embryo that is the first to emerge from a seed. Monocotyledons and dicotyledons are two groups of flowering plants, named based on the number of cotyledons in their seeds. Rafflesia is a parasitic flowering plant found in Indonesia, Malaysia, Thailand and the Philippines. It is the largest flower in the world and can grow as large as 100 cm across and weigh up to 7 kg. Science Facts Dicots Leaf of parallel veins Fibrous root Leaf of a network of veins Two cotyledons Taproot Monocots One cotyledon Chapter 5 Living Things 147 ©Praxis Publishing_Focus On Science
Dichotomous Key A dichotomous key is a tool for identifying organisms or things found in nature, such as plants and animals, based on their common characteristics. Dichotomy means division into two, hence a dichotomous key always provides two choices based on the main characteristics of organisms in each couplet series. A dichotomous key can be built based on a set of paired statements or clues concerning features or characteristics that serve as a step-by-step guide to identifying each organism or in the form of a flowchart. The clues steadily narrow down the list of possible organisms as the user progresses from one step to the next, until all are identified. The chart below shows a guide for building a dichotomous key for plants. 1 Create a list of physical characteristics, such as flowers to identify plants. 2 Start with one characteristic. Divide the plants into two groups; Group 1 possesses that characteristic while Group 2 does not. 3 Look at the plants in Group 1. Choose a characteristic and divide further the plants into two groups, one group possesses that characteristic while the other group does not. 4 Look at the plants in Group 2. Choose a characteristic and repeat the same as in Group 1. 5 Each group is then further divided into two groups based on a different characteristic, until each plant is differentiated from all of the other plants. 1 (a) Have flowers..................go to 2 (b) Do not have flowers.......go to 3 2 (a) Monocotyledon.....paddy plant (b) Dicotyledon..................hibiscus 3 (a) Vascular.............................ferns (b) Non-vascular................. mosses Rules to build a dichotomous key Let’s take a look at an example of a dichotomous key for plants using a series of statements. 148 ©Praxis Publishing_Focus On Science
1 (a) Has a long neck...........go to 2 (b) No long neck...............go to 3 2 (a) Has horns.....................gazelle (b) No horns.......................giraffe 3 (a) Has floppy ears.........elephant (b) No floppy ears.............go to 4 4 (a) Has stripes......................zebra (b) No stripes.................crocodile Monocotyledon Vascular Paddy plant Ferns Dicotyledon Non-vascular Hibiscus Moss Plants Have flowers Do not have flowers This is an example of a dichotomous key for animals using a series of statements. We can present the dichotomous key for plants in the form of flowchart. Chapter 5 Living Things 149 ©Praxis Publishing_Focus On Science
Activity 2 1 Take a look at the photos below. 2 Name the plants. 3 Make another statement that pairs each of the statements below to aid in building a dichotomous key. (a) Flowering (b) Has parallel veins (c) Has roots 4 Build a dichotomous key for plants based on 2 and 3. Make a dichotomous key for plants Gazelle Has floppy ears Giraffe Elephant Animals Has long neck No long neck Has stripes Zebra No stripes Crocodile Has horns No horns The dichotomous key for animals is presented in the form of flowchart. No floppy ears 150 ©Praxis Publishing_Focus On Science
1 Biodiversity refers to the variety of on the Earth and it is essential for providing food to all organisms in this ecosystem. 2 We get from food. The release of energy from the food in our body is called . 3 Carbon dioxide, water vapour, salt and urea are removed via breathing, and urinating through the process of . 4 The increase in body size, weight and the number of body cells are called . 5 A process whereby an organism is in adult stage and able to produce young is called . 6 Living organisms are to the changes in their surroundings, such as light and temperature. 7 Linnaeus’s hierarchy system categorises organisms based on their position in the hierarchy. 8 Bacteria such as Lactobacillus and E. coli are organisms that can exist inside our body. 9 Examples of , such as amoeba and Paramecium, can be found in a range of wet habitats. 10 Moulds are a type of fungi which are multicellular cells that are made up of that grow on a rotten bread. 11 Animals that have backbones are while animals that do not have backbones are . 12 The five main groups of vertebrates are mammals, amphibians, , birds and . 13 The two groups of warm-blooded vertebrates are and . 14 Arthropods are invertebrates that have jointed legs, segmented bodies and an . 15 Annelids, Nematodes and Platyhelminthes are invertebrates without jointed legs. 16 Non-flowering plants are plants that do not produce flowers but they reproduce by or seeds. 17 Flowering plants are angiosperms that produce flowers and . 18 A is a part of the embryo within the seed of a plant. 19 Monocots have leaves of veins, roots and can produce seeds of one cotyledon. Dicots have leaves of a of veins, and can produce seeds of two cotyledons. 20 A key is a tool that made up of a set of paired statements concerning characteristics that serve as a guide to identifying organisms. RECALL Fill in the missing words. Chapter 5 Living Things 151 ©Praxis Publishing_Focus On Science
THINKING CAP Put on your 1 What will be your basis to classify living things and non-living things? Discuss. 2 The animal kingdom consists of vertebrates and invertebrates. Other than having backbones, how do vertebrates differ from invertebrates in terms of physical characteristics? 3 Artificial Intelligence (AI) systems have the ability to learn and reason for themselves, allowing them to build skills as they practise and accumulate experience. Their purpose is to support and enhance human activities. They can move, sense, respond, communicate and perform certain tasks like humans. Are they living things? Explain. 152 ©Praxis Publishing_Focus On Science
Project Classification of Living Things Activity objective: Explore how classification shows the relationships between organisms Concept applied: Classification in animal kingdom and plant kingdom Procedure: 1 Work in groups of four to research the classification for the organisms chosen. 2 Choose two organisms from the animal kingdom. One invertebrate, while the other a vertebrate. 3 Choose two organisms from the plant kingdom. One non-flowering plant, while the other a flowering plant. 4 Identify the characteristics for each of the organisms chosen. Create a creative mini-poster to compare and contrast the two organisms in the animal kingdom. Do the same for the two organisms in the plant kingdom. 5 Once all the mini-posters are created, compare and contrast the classification of your organisms with other groups in class. Presentation: Stick your posters on the wall during the comparison and hold discussion with other groups in class. You can take photos of your complete work and write a report based on the reflection section below. Reflection: 1 What have you learned from the classification of other groups? 2 Do you need to improve the work that you have done? If yes, in what aspects? 3 What are the new skills or knowledge that you have achieved through the task completed? Chapter 5 Living Things 153 ©Praxis Publishing_Focus On Science
This is the habitat where zebras live in order to obtain food. What other animal populations live in this habitat? What animal makes the zebra its prey? A food chain can show the food relationship between predator and prey. How many food chains can be linked to form a food web? Interactions Among Organisms and the Environment CHAPTER 6 What will you learn? Differentiate biotic factors from abiotic factors Draw simple food chains Differentiate a food chain and a food web Describe energy flow and nutrient cycles in an ecosystem Differentiate the types of interactions between organisms Explain the factors that affect organisms and the environment, and as well as the roles of humans in maintaining a balanced nature ©Praxis Publishing_Focus On Science
6.1 Biotic and Abiotic Components There are over a million different species of animals and plants on Earth many of which live in groups. They are dependent on one another and the environment to obtain food, shelter and protection. A habitat is an organism’s natural surrounding where it obtains its food, shelter and protection. It is also the place where the organism reproduces. Some examples of habitats are a pond, a rice field and a rocky shore. There are different kinds of animals that live in the same habitat. A group of organisms with common characteristics that can breed among themselves to produce fertile offspring is called a species. Can you suggest a species that lives in the ocean? A great variety of organisms live in the ocean. Do you know what organisms live in this habitat? A population is made up of a group of organisms of the same species that lives and breeds in the same habitat. When many populations of different organisms live together in the same habitat, a community is formed. Once a few communities living together in one habitat interact with each other including with non-living components, we refer to this as an ecosystem. Chapter 6 Interactions Among Organisms and the Environment 155 ©Praxis Publishing_Focus On Science
Activity 1 1 Work in a small group. 2 Observe the rice field habitat. 3 Think of as many different populations of organisms that live in this habitat. 4 List them. 5 Name another habitat and the organisms that live there. 6 Share your list with the class. Organisms in a habitat Both living and non-living components coexist in an ecosystem. Organisms are the living components in an ecosystem which are interdependent on each other; they are biotic components. Abiotic components are the non-living components that affect how organisms live. Biotic Components The biotic components include plants, animals, and microorganisms like bacteria and fungi, all living things found in an ecosystem. For example, a marine ecosystem’s biotic components include algae, plankton, bacteria, coral, plants, fish, sharks and other organisms. These organisms and the abiotic components of the ecosystem interact with one another. Biotic components can be further classified into producers, consumers and decomposers. Plants are producers. They obtain sunlight, water and minerals from the soil to make food through the process of photosynthesis. Animals that eat plants or other animals are called consumers. Animals that live in the same habitat will compete for food among themselves. When plants and animals die, they become food for other living things such as bacteria and fungi, which are called decomposers. They break down dead or decaying matter into simpler substances that are returned to the soil as nutrients for the use of producers. Biotic components Producers Consumers Decomposers 156 ©Praxis Publishing_Focus On Science
Abiotic Components The abiotic components such as air, soil, water, sunlight and temperature are non-living things of an ecosystem. Without these components, organisms would not be able to grow and reproduce. There are different gases in the air. Organisms breathe in oxygen to release energy from the food they eat. Plants take in carbon dioxide to make food. Some soil bacteria transform nitrogen gas into nitrates to get the energy they need. The soil provides water and minerals to most plants. The type of organisms living in a soil habitat is determined by the type of soil. A healthy soil is rich in living organisms such as earthworms, insects, fungi and bacteria. It also contains humus that makes the soil fertile. Water is required for life processes such as seed germination, digestion and photosynthesis. Water also provides a home for some animals and plants. For example, desert regions have less vegetation due to a lack of water. On the other hand, a wide range of plants and animals can thrive in areas with excessive rainfall. Sunlight is the main source of energy for all organisms on Earth. Plants use sunlight to produce food and this stored energy in plants will be passed on to other living organisms through nature’s food chain. Animal behaviour is also affected by sunlight. Some animals are active during the day while others are more active at night. Many living organisms have special characteristics that allow them to adapt to extreme climates. For example, in the desert, where temperatures are extremely high and water is limited, most plants have long roots that grow deep into the soil to absorb water. Some animals that cannot stand the cold will hibernate throughout the winter. Chapter 6 Interactions Among Organisms and the Environment 157 ©Praxis Publishing_Focus On Science
A Effect of temperature towards the distribution of organisms Problem statement What is the effect of temperature towards the distribution of woodlice? Hypothesis Woodlice are more likely to gather in areas with a lower temperature. Manipulated variable Temperature Responding variable Woodlice distribution Constant variables Humidity, light and number of woodlice Materials and apparatus Woodlice, hot water, water at room temperature, petri dish, glass cover, wire gauze and stopwatch Procedure 1 Pour 20 ml of hot water into petri dish J and pour 20 ml of water at room temperature into petri dish K. Wire gauze Glass cover Woodlice Hot water Water (Room temperature) Petri dish J Petri dish K The set-up of apparatus 2 Place the wire gauze across petri dish J and K. 3 Then, let in 10 woodlice on the wire gauze. 4 Cover the wire gauze with a glass cover. Leave the apparatus in an exposed area in a laboratory for 20 minutes. 5 Record the number of woodlice in the area every 5 minutes. Observation Record your observations. Time (minutes) The number of woodlice J (hot) K (room temperature) 5 10 15 20 Conclusion Is the hypothesis accepted? Write down your conclusion. Experiment 1 Investigating the influence of temperature and light on the distribution of organisms 158 ©Praxis Publishing_Focus On Science
B Effect of light towards the distribution of organisms Problem statement What is the effect of light towards the distribution of woodlice? Hypothesis Woodlice are more likely to gather in dark areas. Manipulated variable The presence of light Responding variable Woodlice distribution Constant variables Humidity, temperature of surroundings and number of woodlice Materials and apparatus Woodlice, black cloth, petri dish, glass cover, wire gauze and stopwatch Procedure 1 Pour 20 ml of water at room temperature into petri dish L and M. 2 Place the wire gauze across petri dish L and M. 3 Then, let in 10 woodlice on the wire gauze above petri dish L and M. 4 Cover the wire gauze with a glass cover. Cover petri dish L with a black cloth as shown below. Black cloth Glass cover Woodlice Water (Room temperature) Water (Room temperature) Petri dish L Petri dish M The set-up of apparatus 5 Leave the apparatus in an exposed area in a laboratory for 20 minutes. 6 Record the number of woodlice in the area every 5 minutes. Observation Record your observations. Time (minutes) The number of woodlice L (covered with black cloth) M (not covered) 5 10 15 20 Conclusion Is the hypothesis accepted? Write down your conclusion. Chapter 6 Interactions Among Organisms and the Environment 159 ©Praxis Publishing_Focus On Science
Producers are organisms that produce their own food from the non-living components in their environment. Green plants are producers. They can produce sugars and starch from carbon dioxide and water, using energy from sunlight in a process called photosynthesis. Decomposers are organisms that break down dead animal and plant materials into simpler substances which can be used again by green plants. Examples of decomposers are bacteria and fungi. 6.2 Food Chains and Food Webs One of the common causes of interaction between organisms is the need for food. Organisms can be classified into three groups: producers, consumers and decomposers according to their roles in the ecosystem. Food Chains Have you ever thought about the complex web of relationships that exist between the various organisms in an ecosystem? How does the survival of one organism depend on the actions of others? A food chain is the feeding relationship between organisms in a habitat. The feeding relationship between producers and consumers can be written in a series of levels as below. Producer primary consumer secondary consumer tertiary consumer Consumers are organisms that eat other organisms or their products. Animals cannot make their own food. They depend on plants or other animals for food. Therefore, all animals are consumers. A primary consumer is a herbivore and it feeds directly on plants. An animal which feeds on a primary consumer is a secondary consumer. Secondary consumers can be carnivores or omnivores. These animals are bigger in size. Tertiary consumers are even larger animals which feed on the secondary consumers. DEATH 160 ©Praxis Publishing_Focus On Science
Food Web In an ecosystem, feeding relationships among organisms are complex. Most organisms eat more than one type of food. Therefore, food chains are interconnected. When food chains interlink, a food web is formed. A food web helps to maintain a balanced ecosystem by controlling the number of organisms at each level of a food chain. Oil palm Rat Snake Hawk Owl Sparrow Caterpillar Bacteria and fungi Grasshopper Study this food web. (a) Name the producer, primary consumers, secondary consumers, tertiary consumer and decomposer. (b Write two other food chains. Think About It Chapter 6 Interactions Among Organisms and the Environment 161 ©Praxis Publishing_Focus On Science
Pyramid of Numbers The food relationship between organisms in a food chain can be represented in the form of a pyramid of numbers. A pyramid of numbers is a diagram that shows the relative number of organisms at each level of a food chain. As you can see in the diagram, there is a progressive drop in the number of organisms as you move from a lower level to a higher level. The animals at the higher levels tend to be larger in size. 5 snakes Tertiary consumer 150 frogs Secondary consumer 3000 grasshoppers Primary consumer Producer 3 000 000 blades of grass An example of a pyramid of numbers Energy Flow in a Food Web Have you ever considered how energy flows through a food web, from producers to consumers to decomposers? How does the transfer of energy between different organisms impact the overall health and sustainability of an ecosystem? A food chain or a food web shows how the energy is transferred from one organism to another. In an ecosystem, the main source of energy is sunlight. Green plants trap and change solar energy into chemical energy which is stored as food during photosynthesis. When a primary consumer eats the producers, some of the chemical energy stored in the plants is passed on to the primary consumer, which would later pass its energy to a secondary consumer. In this way, energy flows through a food web and the pyramid of numbers. However, not all of the energy is passed on at each level. Some energy is lost as heat. Food webs are not permanent in any community. Some animals and plants may die from other causes. Some animals may leave the community while some new ones may move into the community. Hawk Snakes Rats Paddy plants Energy flow When a whole population in a food web is missing or decreases greatly in numbers, this will affect other organisms. The food web becomes imbalanced. If new organisms are introduced into a food web, the food web will become imbalanced too. It would take a long time for the ecosystem to become balanced again. If the snakes in the diagram move out of the paddy field, the number of rats will increase because there are fewer predators (snake). A trophic pyramid that shows the relationships between different levels of organisms in an ecosystem 162 ©Praxis Publishing_Focus On Science
The number of hawks that feed on the snakes will decrease because there is less food for them. After some time, we can predict that the growing number of rats will eat up most of the paddy plants. As a result, there will be little food left for the rats in the long run. So, the rats will eventually have to leave the community or they will die of starvation. Therefore, it is important to maintain a balanced number of organisms at each level of a food chain so that there is sufficient food supply. When one population of the organisms is missing or disturbed, it will affect the other populations in the food web and the balance of the entire ecosystem. A balanced ecosystem is one which does not appear to change very much over a period of time. It also provides organisms with all their daily needs such as food, nutrients, water, shelter and mates. Slight changes in the number of one species will offset the number of other species. The ecosystem would take time to become balanced again. In order to maintain a balanced ecosystem, the following factors need to be maintained: • The number of individuals in the different populations • The number of populations in the different communities • The quality of the air • The availability of water, soil and nutrients 6.3 Nutrient Cycles in an Ecosystem Energy is transferred from one organism to another in an ecosystem. This transfer occurs in a food network and the nutrients are eventually returned to the environment by the decomposer to be reused. The nutrient cycle is a cycle of non-organic chemical elements that includes mineral sources (in the soil), water, oxygen, nitrogen, hydrogen and carbon dioxide, from the physical environment to living organisms and back to the environment. In a balanced ecosystem, all biotic and abiotic components are in a state of balance. This balance is obtained through nutrient cycles such as the carbon cycle and nitrogen cycle. Carbon Cycle Carbon is an essential element for all life on Earth. It moves through a variety of processes such as photosynthesis, fossil fuel combustion and respiration. The carbon cycle describes the movement of carbon in the atmosphere. Carbon can be stored in plants or animals. During photosynthesis, green plants absorb carbon dioxide from the atmosphere and release oxygen. Plants make their own food for the growth of leaves and stems, which are then digested by animals when they eat plants. During respiration, plants and animals use oxygen and release carbon dioxide as well. Fungi and bacteria use oxygen and release carbon dioxide during the decomposition of dead organisms, which happens when the dead parts of plants rot or when animals die. Their remains gradually decompose into sediment, which traps the carbon in layers that eventually transform into rock or minerals underground. Some of the sediment may eventually turn into fossil fuels like coal or natural gas which release carbon back into the atmosphere when burned. Chapter 6 Interactions Among Organisms and the Environment 163 ©Praxis Publishing_Focus On Science
Nitrogen Cycle Nitrogen is constantly moving from the air, through the soil, into the bodies of plants and animals and eventually back to the air. This whole process is called the nitrogen cycle. All living things need nitrogen to grow. Nitrogen cannot be directly pulled from the air. It has to be converted by bacteria into nitrites and nitrates which are then absorbed by plants. Nitrogen-fixing bacteria are found in the roots of legumes in special structures called root nodules which can extract nitrogen from the air. Then nitrogen-fixing soil bacteria convert nitrogen to become ammonia through ammonification. Then, nitrifying bacteria will convert ammonia into nitrites or nitrates which dissolve in the soil through the process of nitrification. It is then absorbed by plants to make amino acids that are used to produce plant proteins. Animals get their nitrogen by eating plants or by eating other animals. Once the animal or plant dies, decomposers in the soil convert the nitrogen found in animal waste and the remains of dead plants into ammonia. Again, nitrifying bacteria convert the ammonia into nitrates. Some of the nitrates is then converted by denitrifying bacteria into nitrogen gas which is released into the air. CARBON CYCLE CO2 Transportation and factory emissions Organic carbon Animal respiration Photosynthesis Sunlight Dead organisms and waste products Root respiration Fossils and fossil fuel Carbon cycle 164 ©Praxis Publishing_Focus On Science
Other than the nitrogen-fixing bacteria, lightning helps in converting atmospheric nitrogen into nitrogen dioxide which is soluble in water to form nitric acid which falls back on land with rain. These are then utilised by various life forms. All these different steps form a massive cycle. Over time, bacteria in the soil return almost the same amount of nitrogen to the air as other bacteria take from the air. This keeps the nitrogen content of the earth and its atmosphere in balance. 6.4 Interactions between Organisms Organisms interact with each other in many ways. The main cause of interaction between organisms is the need for food, shelter and protection. How important are interactions between organisms in controlling the size of populations in a community and creating a balanced and stable environment? Let’s explore the types of interactions between organisms as shown below. Types of interactions Competition Predator-prey • Intraspecific competition • Interspecific competition Atmospheric nitrogen (N2) Decomposers (aerobic and anaerobic bacteria and fungi) Ammonium (NH4 + ) Nitrites (NO2 – ) Plants Nitrifying bacteria Nitrogen-fixing soil bacteria Nitrogen-fixing bacteria living in legume root nodules Assimilation Denitrifying bacteria Nitrates (NO3 – ) •Commensalism •Parasitism •Mutualism Symbiosis Nitrogen cycle Nitrification Ammonification Nitrifying bacteria Chapter 6 Interactions Among Organisms and the Environment 165 ©Praxis Publishing_Focus On Science
Symbiosis Symbiosis means living together in a relationship between two different organisms through which one of them benefits. The other organism may also benefit, be unaffected, be harmed or even be killed. There are three main types of symbiosis, namely commensalism, parasitism and mutualism. Competition Competition is a type of interaction among organisms living in the same habitat in which there is competition for basic needs. Organisms compete with each other for food, minerals, light, water, shelter and mates. Competition occurs when resources are limited. The consequence of competition is unfavourable to the weaker organism. Competition may exist between individuals of the same species or of different species. Intraspecific competition is the competition between individuals of the same species while interspecific competition is the competition between individuals of different species. The males fight with each other for a female mate—this shows intraspecific competition. Commensalism Commensalism is a relationship between two organisms in which one organism (the commensal) benefits from another (the host) without damaging the host. Commensalism generally occurs between a larger (host) organism and a smaller one (commensal). For example, barnacles that attach themselves to whale skin feed on plankton that is drawn to the whale’s movements. This relationship benefits the barnacles by providing an easy source of food and transportation, while the whale is not affected by the barnacles in any significant way. The staghorn fern (commensal) lives on a tree (host) to obtain sunlight. 166 ©Praxis Publishing_Focus On Science
Parasitism Parasitism is a relationship between two types of organisms in which one organism benefits while the other is harmed. Parasites benefit by living in or on the host. On the other hand, the host is harmed by the parasites. Tapeworm is a parasite that obtains food and shelter from humans. Humans (the host) are harmed by losing nutrients to the parasite. The host loses weight and becomes weak. Other examples of parasites are fleas, ticks and lice. These animals live off the blood of the host. Aphids or plant lice are tiny insects that feed on plant sap. Rafflesia (parasite) grows on a tree trunk (host) and absorbs nutrients causing the tree to die. Mutualism Mutualism is an interaction between two different organisms that benefit both. Neither species can survive without the other under natural conditions. For example, lichen consists of fungi and algae living together. The algae produce food and the fungi provide shelter. Bacteria that live in our large intestine produce vitamins that we cannot make for ourselves. In return, we provide food and shelter to the bacteria. Flowers provide honey to butterflies. At the same time, the butterfly serves as a pollinator. Tapeworms are parasites that live in the intestines of several animals, not just human beings. They vary in length from 1 cm to 10 metres. Each tapeworm has both male and female sex organs. Therefore, it does not need a mate to reproduce. Science Facts Chapter 6 Interactions Among Organisms and the Environment 167 ©Praxis Publishing_Focus On Science
6.5 Factors that Affect the Organisms and Environment Have you ever wondered why Indonesia is well-known for its biodiversity? Could it be because of its strategic location on the equator, surrounded by two continents and oceans, and receiving plenty of rain and sunlight throughout the year? As a result of these favourable conditions, Indonesia has the world’s second highest terrestrial biodiversity after Brazil and the world’s highest marine biodiversity. Among the many examples of flora in Indonesia are the Rafflesia Arnoldi, damar, pitcher plant and black orchid. We can also find animals, such as Sumatran Tigers, Indonesia Orangutans, Indian Tapir and Sun Bear in Indonesia. You know that animal populations can be influenced by the populations of their prey or predators. What are other factors that might cause the population size to change or eventually go extinct? Let’s look closely at some of the factors that impact not only the animals and plants but also humans and the environment. The animal eaten by a predator is its prey. Prey can be either carnivores, omnivores or herbivores. They have special adaptations such as monoscopic vision and the ability to move fast. In a predator-prey relationship, the predator benefits and the prey loses. Examples of predator-prey relationships are tiger (predator) and deer (prey), snake (predator) and chicken (prey), and eagle (predator) and fish (prey). Predator-prey Predator-prey interaction is one of the common relationships within a community. A predator is an animal that captures and eats other animals. The predators are usually bigger than the prey. They are carnivores or omnivores. They have special adaptations such as powerful jaws, sharp teeth, sharp claws, good vision or strong beaks. Tapir and pitcher plants in Indonesia 168 ©Praxis Publishing_Focus On Science
Change of Climate Extreme weather such as droughts, floods, snowstorms and tropical storms will reduce population size. Ongoing drought makes the soil infertile for planting due to limited water supply. When there is a drought, the paddy population decreases and disrupts the food chain in the paddy field. On the other hand, frequent floods can result in the loss of plant and animal habitat, and their population shrinks. Also, animal migration, or the movement of animals from one location to another due to a change in season or climate, can have an impact on an ecosystem. For example, the migration of great cattle egrets affects the size of the insect population in that area during certain months of a year. Diseases Disease can reduce the size of a species population. It has the potential to lead to the extinction of the species. For example, a pandemic of bird flu reduces the chicken population. Similarly, banana plants wilt and dry up as a result of the Panama disease. Veterinary vaccine is injected to chickens in order to prevent poultry diseases. Food Shortage Animals need food to survive. If there is a shortage of food supply, animal populations will decrease to the edge of extinction. Deforestation is one of the main factors that causes food shortage. When forests are cleared for farming, building roads or other purposes, the producers in the food chain are destroyed. This will reduce the source of food for wildlife. Many birds are forced to migrate due to the cold weather. Chapter 6 Interactions Among Organisms and the Environment 169 ©Praxis Publishing_Focus On Science
Air Pollution Many human activities such as open burning, forest fires, industrial emissions and agricultural activities are the main source of air pollution. Air pollution occurs when pollutants such as gases, smoke, smog and dust are present in high concentrations in the atmosphere. These substances are toxic to humans, animals and plants, and have great impact on organisms and environment. Acid Rain When air pollutants such as sulphur dioxide and nitrogen dioxide dissolve in rainwater, acid rain is formed. When acid rain flows into the water systems, it turns water acidic which is not suitable for aquatic plants and animals. Acid rain pollutes water sources with heavy metals such as iron and lead, which are toxic and not suitable for drinking. It also reduces the pH value of soil and causes the soil to be acidic and infertile for growing crops. Global Warming Air pollutants such as smoke and dust from factories, motor vehicles and open burning cause haze. Smoke and haze reduce the amount of sunlight that reaches Earth’s surface, which in turn slows down the pace at which green plants synthesise oxygen. The increased concentration of greenhouse gases in the atmosphere, such as carbon dioxide, methane, nitrogen oxide, water vapour and chlorofluorocarbon, prevents heat from escaping into space. Thus, this causes the greenhouse effect and global warming. Global warming causes an increase in the Earth’s temperature and results in climate change. Some locations may experience habitat loss, droughts, rising sea levels, floods and the spread of diseases which affect the existence of flora and fauna. Before After Acid rain kills trees in the long term. 170 ©Praxis Publishing_Focus On Science
Depletion of the Ozone Layer in the Atmosphere The increase of chlorofluorocarbons (CFCs) in the atmosphere causes depletion of the ozone layer. This allows more harmful ultraviolet (UV) rays to reach the Earth. This has harmful effects on our health and other organisms. UV rays can cause sunburn or damage tissues on organisms. To lessen the negative consequences of air pollution, numerous measures for prevention and management must be done. Some steps to prevent and control air pollution are as below. • Educate the public on the practices to reduce air pollution especially in schools. • All motor vehicles should have catalytic converters installed. • Use biological methods to control pests. • Factories must have their smokestacks at least 30 metres tall and equipped with electrostatic filters. • Issue fines to people who engage in open burning, smoke in prohibited areas and breach the rules concerning automobile emission standards. Animals living in the polar regions lose their habitats as ice continues to melt due to rising global temperatures. Droughts can occur in some areas due to global warming and climate change. The ozone layer is a thin layer of the Earth’s atmosphere that absorbs nearly all of the sun’s ultraviolet rays. Since the 1970s, the ozone layer has been observed by NASA and the National Oceanic and Atmospheric Administration (NOAA) from the ground using a range of instruments on satellites and balloons. Scientists predict that the ozone hole phenomenon which started to occur in the early 1980s would not return to its early levels until 2050. Science Facts Ozone layer UV C UV A UV B Chapter 6 Interactions Among Organisms and the Environment 171 ©Praxis Publishing_Focus On Science
Water Pollution Some human activities have resulted in toxic pollutants entering water sources such as rivers, ponds, lakes and seas. The hazardous compounds pollute the water, affecting the species that live in those aquatic ecosystems. Disposal of Industrial Waste Industry is a major source of water pollution since it emits pollutants that are exceedingly hazardous to people, organisms and the environment. Some industrial plants use freshwater to transport waste away from the plant into rivers, lakes and oceans. There are heavy metals (copper, mercury, arsenic and lead) in industrial waste that can create health and environmental issues, as lead is a non-biodegradable material, thus it is difficult to remove once it has contaminated the environment. Mercury is also hazardous to animals and human health since it can lead to sickness due to mercury toxicity. Toxic chemical waste and radioactive waste from nuclear power plants can be harmful to marine life and ecosystems. Sewage Waste (Domestic and Industrial) Sewage refers to waste water that usually contains faeces, urine and laundry waste. It may contain toxic chemical flushed down the toilet. Untreated sewage water can pollute the environment and cause diseases such as diarrhoea if it is released directly into water sources. Waste water released into the river sometimes contains heavy metals that can bring negative impacts to our health, organisms and environmental issues. Ecologists are taking samples of water to determine level of contamination and pollution. 172 ©Praxis Publishing_Focus On Science
Oil Spills Oil pollution of the oceans occurs as a result of oil spills from ships and tankers, fuel leaks from speed boats, run-offs from land, and dumping of oil drilling wastes. An oil spill from a tanker is a major issue because a large amount of oil is poured into one location and it can be disastrous to local marine wildlife such as fish and birds. The Use of Chemical Fertilisers, Pesticides and Fungicides in Agriculture The uses of chemical fertilisers are increasing in agricultural sectors. Rainwater will carry these excess chemical fertilisers into water systems. These chemicals contain nitrate and phosphate salts which encourage algae growth. An excessive growth of aquatic algae, and its decay, increases the usage of dissolved oxygen in water. As a result, aquatic organisms will die due to the lack of oxygen in the water. Other than this, pesticides and fungicides also pollute water sources when they dissolve in rainwater. Water pollution has caused the excessive growth of aquatic algae. A bird stuck in polluted water with tar. Sea water is polluted due to oil leaks from passing tankers. Chapter 6 Interactions Among Organisms and the Environment 173 ©Praxis Publishing_Focus On Science
Trash should be disposed of properly so that solid nonbiodegradable materials, such as plastics, do not end up polluting beaches and river banks. Contaminated water can be treated using biological treatment and microorganism processing by anaerobic digestion of food waste. Food waste, such as fruit peel and vegetables, can be used to create effective microorganism mud balls containing helpful bacteria that can break down organic compounds that pollute water. Do not flush tablets or medications down the toilet. Use the suggested disposal methods instead. Ensure the water is safe to drink by treating it with chlorine to kill bacteria before allowing it to enter pipes. Water can also be made safe to drink by boiling it. Use less herbicides, pesticides, fertilisers, bleach and detergents. We can utilise organic approaches to control pests, weeds and diseases. Continue to use phosphatefree detergents and soaps to significantly reduce water pollution. Steps to reduce water pollution Water treatment plants play an important role to safeguard public health, provide clean, drinkable water, and protect the environment. These are some of the steps to reduce water pollution. Proper sewage treatment programmes and management can be upgraded so that human waste is processed and proven safe before entering the water supply. Cooking oil, fat and grease should not be poured down the kitchen sink. Instead, retain a jar that gathers all fats, grease or oil, and then dispose of it in solid garbage. 174 ©Praxis Publishing_Focus On Science
Soil Pollution Do you realise that all soil have substances that are toxic or harmful to humans and other organisms? These substances do not threaten the local ecosystem when they are present in unpolluted soil in low concentrations. When one or more of these toxic substances are present in the soil in amounts that could endanger organisms, it is considered polluted. Therefore, when abnormally high amounts of harmful substances are present in the soil, it is referred to as soil pollution. A wide range of unfavourable effects caused by soil contamination harm humans, animals, plants and the environment as a whole. Let us take a look at the human activities that cause soil pollution. Agriculture (Overuse or Incorrect Use of Pesticides) Pesticides are chemicals used to either kill or stop the growth of pests. Pesticides that are frequently applied in agriculture include herbicides, insecticides and fungicides. Herbicides are used to manage weeds and other unwanted plants, insecticides are used to kill insects and fungicides are substances that either kill or stop the growth of parasitic fungi. However, there are a number of health risks for people that result from the unintentional release of these chemicals into the environment. Industrial Activity Soil pollution can happen when industrial waste, such as scrap metals and chemicals are dumped on ground. The petroleum sector produces a lot of waste materials made of petroleum hydrocarbons. Some of these pollutants are recognised to have cancer-causing tendencies. Soil degradation is increasing along with the mining and industrial industries. Soil fertility is impacted by the mining of minerals from the earth. No matter if it is iron ore or coal, the byproducts are contaminated and disposed of in an unsafe manner. Due to the industrial waste’s prolonged stay on the soil’s surface, it is no longer appropriate for other uses. Poor Trash Management or Ineffective Waste Disposal The improper disposal of plastics and other solid waste results in soil pollution, and the presence of hazardous substances in batteries and other electrical waste has a negative impact on the soil. For instance, batteries contain heavy metals and chemicals that could leak into the environment and pollute water sources and soil if they are improperly disposed of. Rubbish in a landfill Chapter 6 Interactions Among Organisms and the Environment 175 ©Praxis Publishing_Focus On Science
Regular application of chemical fertilisers, inorganic fertilisers and pesticides will reduce soil fertility and change the soil’s structure. This will result in a decline in soil quality and poor crops. Slowly declining soil fertility makes land unusable for farming and affect the survival of any local vegetation. Through a process called bioaccumulation, plants grown in polluted soil may collect large amounts of soil pollutants. When herbivores eat the plants, the pollutants may become toxins, move up the food chain and eventually appear as diseases in humans. Soil is an important habitat for various living organisms, such as microorganisms, birds and insects. Thus, changes in soil can have a negative impact on the lives of living organisms and may result in the death of many organisms over time. The impact of soil pollution on human health is serious. Respiratory conditions, skin conditions and other health issues can result from living, working or playing in polluted soil. Infections brought on by soil pollution include skin and eye irritation, headaches, motion sickness, coughing, chest pain and wheezing. The following shows some of the effects due to soil pollution. 176 ©Praxis Publishing_Focus On Science
Soil is one of the important natural resources. It is our responsibility to prevent and reduce soil pollution. The following are some methods for reducing soil pollution. • Polluted soils are gathered up and transported to far-off, unpopulated areas. • Recycle and reuse products Recycling waste materials will help reduce soil pollution brought on by landfills. • Reduce use of chemical fertilisers Whenever possible, the use of harmful compounds in industrial processes should be avoided. Reducing the amount of chemical fertilisers applied to agricultural soils can be accomplished by promoting healthy agricultural practises such as the use of organic manure and organic farming techniques. It is also necessary to promote the efficient and restricted use of chemical pesticides. • Encourage volunteers to help with the environmental effort to remove trash from public spaces and maintain a clean environment. What other types of pollution exist besides air, water and soil pollution? Explain two different types in terms of cause and effect. Think About It Activity 2 1 Work in a small group. 2 Gather information about other ways to conserve our environment. 3 You may classify the solutions if they are specific to the types of pollution. 4 Create a report that includes photos to make it more visually appealing. Ways to conserve our environment Chapter 6 Interactions Among Organisms and the Environment 177 ©Praxis Publishing_Focus On Science
1 A is an organism’s natural surroundings where it obtains its food, shelter and protection. 2 A group of organisms with common characteristics that can breed among themselves to produce fertile offspring is called . 3 A is made up of a group of organisms of the same species that live and breed in the same habitat. 4 A is formed when many populations of different organisms live together in the same habitat. 5 When a few communities living together in one habitat and interact with each others including non-living components, this is called an . 6 In an ecosystem, biotic components such as the producer, consumer and coexist with abiotic components such as air, sunlight, water, and temperature. 7 A food chain is the feeding relationship between living organisms in a habitat while a is formed when food chains interlink. 8 A consumer in a food chain is usually a herbivore and the consumers can be carnivores or omnivores. 9 A pyramid of numbers is a diagram that shows the relationship between organisms in a food chain, it also shows how is transferred from one organism to another. 10 Interactions between organisms are important because they control the of populations in a community, and create a balanced and stable environment. 11 is a type of interaction among organisms living in the same habitat in which each competes for its basic needs. 12 is a relationship between two organisms in which one organism benefits from another without damaging the host. 13 is a relationship between two types of organisms in which one organism benefits while the other is harmed. 14 is an interaction between two different organisms that benefit both. 15 A is an animal that captures and eats other animals, and is usually bigger than the prey. 16 Factors that influence population size are , source of food, change of climate, animal migration and human activities. 17 Human activities such as logging, waste disposal and industrialisation bring negative effects to the ecosystem. 18 Human activities such as biological control in , law enforcement, awareness campaigns and the implementation of the 5R Project have a positive impact on the ecosystem. RECALL Fill in the missing words. 178 ©Praxis Publishing_Focus On Science
THINKING CAP Put on your 1 How does a parasite differ from a predator? Explain. 2 The information below is used to construct a food web. • Tadpole eats algae. • Large fish eats snail, small fish and tadpole. • Snail eats water plant and algae. • Small fish eats algae, snail and water plant. How does removing the population of snails in a habitat affect the population of water plants, fish and algae? 3 What would happen to plants in an ecosystem if all herbivores went extinct? Relate it to the abiotic components. Chapter 6 Interactions Among Organisms and the Environment 179 ©Praxis Publishing_Focus On Science
Project Activity objective: Identify threats to the biodiversity in Indonesia and solutions to overcome the issues Problem statement: After Brazil, Indonesia has the world’s second-richest biodiversity. However, Indonesia is facing a number of major challenges, including natural disasters, biodiversity loss, increased pollution, and other issues. These are some of the threats to biodiversity and solutions are needed to overcome these problems. Concept applied: Biodiversity in Indonesia Procedure: 1 Students work in groups of five. Appoint a leader in each group and each member is given a task. 2 Each group search information on the Internet and books, remembering to list down all the references. 3 The information gathered must at least include the following aspects, and students are encouraged to add more relevant information. (a) Types of flora and fauna found in Indonesia (i) Types of flora and fauna in different regions (ii) Their photos (iii) Their classifications (b) Threats to biodiversity (i) Types of threats (ii) How each of the threats has a negative impact on the flora and fauna (c) Solutions to solve the problems (i) What are the efforts to conserve the endangered flora and fauna? (ii) What are the parties involved? (iii) What can you contribute as part of the solution? Presentation: Group sharing and presentation. Each group submits a report. Threats to the Biodiversity in Indonesia 180 ©Praxis Publishing_Focus On Science
The Sun is visible during the day, while the moon is typically visible at night. However, occasionally we can also observe the Moon during the day. Why? What other celestial bodies are there in our Solar System other than the Earth, the Moon and the Sun? Earth and the Solar System What will you learn? Describe the characteristics of the eight planets and the Sun Describe some other objects in the Solar System Describe why we experience days, nights and seasons Explain why the Moon’s shape changes over the period of a month Explain how lunar and solar eclipses happen Explain how the Moon influences the tides Explain the use of space technology CHAPTER 7 ©Praxis Publishing_Focus On Science
7.1 The Solar System The Solar System is made up of the Sun and eight planets that orbit it. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Sun is the central focus of the Solar System. Other objects in our Solar System include dwarf planets, meteors, asteroids and comets. While orbiting the Sun, the planets rotate on their own axis and their distance to the Sun varies depending where they are in their orbit. Mercury • The planet closest to the Sun. • The smallest planet in the Solar System. • Mercury’s diameter is 40% smaller than that of the Earth. • Mercury’s sky is always dark because it lacks a layer of atmosphere to scatter sunlight. • Due to the lack of an atmosphere to burn up meteoroids, Mercury’s surface is pockmarked with craters and rocks from countless impacts, much like the Moon. • During the day, the temperature on its surface is extreme. It is approximately 480°C during the day, and at night, approximately –170°C. Earth • The third planet in the Solar System. • The fifth largest planet in the Solar System. • Earth is the only planet in the universe that is home to life. • Earth is surrounded by a layer of atmosphere made up of nitrogen gas, oxygen, carbon dioxide, argon and water vapour. • Water covers 71% of the Earth’s surface, while land covers the remaining 29%. Venus • The second planet closest to the Sun. • Venus has a layer of atmosphere with a high carbon dioxide content. Due to the high carbon dioxide content, the temperature on its surface is around 460°C. • Unlike the Earth, this planet rotates from east to west. This means that the Sun rises west. • According to astronomers, Venus is the “Earth’s twin” because it has about the same age, mass and volume as the Earth. Mars • The fourth planet from the Sun. • It is also known as the Red Planet. • It has two moons which are Phobos and Deimos. • Its surface is covered in reddish sand dust, craters, volcanoes and canyons. • It has a thin atmosphere and an extremely high carbon dioxide content (96%). 182 ©Praxis Publishing_Focus On Science
Planets in the Solar System A planet is a massive sphere-shaped body that revolves around the Sun. The planet is an opaque object, thus it can reflect light rather than illuminate it like the stars. Let’s take a look at the eight planets in the Solar System. The four planets that are closest to the Sun, namely Mercury, Venus, Earth and Mars are made up of solid rocks. They are terrestrial planets. The four planets further away from the Sun, namely Jupiter, Saturn, Uranus and Neptune are much larger. They are made up of swirling layers of cold gases like hydrogen or helium and super-cold liquids like ammonia. Saturn • The sixth planet from the Sun. • After Jupiter, it is the second largest planet. • It is made up of gases and is classified as a gas giant planet. • Saturn has a density that is 30% less dense than water. • Saturn has at least 82 moons, the largest of which is Titan. • It has a ring system made up of ice with small amounts of rocky material and dust. Neptune • The eighth planet from the Solar System. • Neptune is blue because of methane. • It takes the longest time to orbit the Sun, 165 years (Earth time). • It is the most distant planet in the Solar System, thus the temperature on its surface is extremely cold, about –201°C. Jupiter • The fifth planet from the Sun. • It is the largest planet in the Solar System, with a diameter 11 times that of Earth and a mass 320 times that of Earth. • It has at least 79 moons orbiting it and the largest moon is Ganymede. • Jupiter has a massive gravitational pull that is nearly 2.53 times that of Earth. Uranus • The seventh planet from the Sun. • It is the third largest planet in the Solar System. • It is made up of ice and rocks. It has a ring like Saturn, but thinner and darker. • Its axis of rotation is tilted, almost parallel to its orbit around the Sun. • It has 27 moons orbiting the planet. Chapter 7 Earth and the Solar System 183 ©Praxis Publishing_Focus On Science
Characteristics Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Average distance from the Sun (million km) 57.9 108.2 149.6 227.9 778.3 1427 2871 4497 Relative mass (× earth) 0.055 0.815 1 0.107 317.8 95.159 14.536 17.147 Diameter (km) 4879 12 104 12 756 6 794 139 822 116 460 51 118 49 528 Density (g/cm3) 5.4 5.2 5.5 3.9 1.3 0.7 1.27 1.6 Gravitational pull (m/s2) 3.7 8.87 9.8 3.71 24.79 10.44 8.87 11.15 Surface temperature (°C) 430 462 15 –63 –108 –139 –197.2 –201 Time taken to orbit the Sun (time on Earth) 88 days 224.7 days 365 days 687 days 11.9 years 29.5 years 84 years 164.8 years Time taken for one complete rotation on its axis (time on Earth) 59 days 243 days 24 hours 25 hours 10 hours 11 hours 17 hours 16 hours Velocity of rotation on axis (km/h) 10.89 6.52 1 674.4 868.2 45 300 35 500 24 800 23 500 Number of natural satellites or moons 0 0 1 2 at least 79 at least 82 27 14 Main atmospheric contents No atmosphere 96.5% carbon dioxide, 3.4% nitrogen, 0.1% argon, helium, neon, sulphur dioxide, water vapour 78% nitrogen, 21% oxygen, 1% argon, carbon dioxide, water vapour 96% carbon dioxide, 1.9% nitrogen, 1.9% argon, 0.2% oxygen, carbon monoxide 89.6% hydrogen, 10.1% helium, 0.3% methane, ammonia, ethane, water 96% hydrogen, 3% helium, 0.4% methane, ammonia, ethane, water 83.3% hydrogen, 15.5% helium, 2.4% methane 80% hydrogen, 19% helium, 0.1% methane, ethane Condition of planet’s surface No colour, craters covered in fine dust, has plains, mountains and valleys. Orange in colour, sandy and rocky, with big plains, volcanoes and huge craters. Water on 71% of the surface, with plains, mountains and volcanoes Red, sandy and rocky, with big plains, volcanoes and wide craters. Does not have a hard surface. Covered only in gas. Gas changes to liquid and solid as it approaches the core of the planet. General characteristics of planets in the Solar System 184 ©Praxis Publishing_Focus On Science
Activity 1 1 Working in groups of four, use the data from the table of ‘general characteristics of planets in the Solar System’ and look for the sizes of the eight planets. 2 Find out the size of the Sun in this chapter or via the Internet. 3 Using modelling clay and sports balls or any other things that you think are suitable to make a set of planets including the Sun. 4 Use a suitable scale to size down the size of the planets and the Sun, and the distance of the planets from the Sun. 5 Add important notes for each of the planets. 6 Use your creativity to design and display the planets around the Sun. Write down the scales in your display. Model of Solar System Other Objects in the Solar System In our Solar System, there are many celestial objects with the Sun is at the centre. The eight planets in our Solar System all orbit the Sun in elliptical orbits. Other than the eight planets, there are many other objects in the Solar System. Let us look at a few of these objects. Satellites Satellites are celestial bodies that orbit other celestial bodies with a higher mass. The moon is an example of a satellite. It is the only naturally occurring satellite of the Earth. Mercury and Venus do not have natural satellites, while Mars has two, Phobos and Deimos. There is a vast network of natural satellites orbiting the big planets like Saturn and Uranus. With at least 79 moons, Jupiter has the greatest number of naturally occurring satellites. The four largest moons of Jupiter are Io, Europa, Ganymede and Callisto. Besides the naturally occurring satellites, there are artificial satellites that are man-made and launched from Earth. Jupiter and its moons. Chapter 7 Earth and the Solar System 185 ©Praxis Publishing_Focus On Science
Dwarf Planets Dwarf planets, like the eight major planets, are round in shape and orbit the Sun. Unlike planets, they do not have a clear path around the Sun. The path of a dwarf planet around the Sun is scattered with other objects such as comets and asteroids. A dwarf planet is significantly smaller than any of the eight major planets. Ceres, Pluto, Eris, Makemake and Haumea are the first five recognised dwarf planets. Pluto is located in the Kuiper Belt, a donut-shaped region of icy objects beyond the orbit of Neptune. It was long considered to be the ninth planet in our Solar System. However, the International Astronomical Union (IAU) confirmed in 2006 that Pluto shares its orbital neighbourhood with other icy Kuiper Belt objects. Pluto was thus reclassified as a dwarf planet. Eris is located in the Kuiper Belt. It is similar in size as Pluto, but it is three times farther away from the Sun. Given that Eris’s surface is extremely cold, it appears unlikely that life could exist there. Makemake is located in the Kuiper Belt. Slightly smaller than Pluto, it is the second brightest object in the Kuiper Belt as seen from Earth. Haumea is a dwarf planet located in the Kuiper Belt that orbits the Sun much further out than Neptune. It is roughly the size of Pluto and has two moons. Its rapid rotation on its axis is one of its outstanding features. Ceres is the largest object in the asteroid belt between Mars and Jupiter, and it is the only dwarf planet in the inner Solar System. It was the first object in the asteroid belt to be found in 1801. Ceres became the first dwarf planet to host a probe when NASA’s Dawn arrived there in 2015. 186 ©Praxis Publishing_Focus On Science
Comets Comets are rocky objects that orbit the Sun and are composed of a mixture of gas, ice and frozen dust. Most of the comets originate from the Kuiper Belt and Oort Cloud. The structure of the comet is divided into two parts: the head and the tail. The head part can reach a length of 250 thousand kilometres, while the tail part can reach a length of 150 million kilometres. They have their own elliptical orbits around the Sun. Their average speed ranges between 10 and 70 km/s depending on their distance from the Sun, and they can be either periodic or non-periodic. Asteroids Asteroids are large rocky and metal objects that orbit the Sun in the Solar System. Larger asteroids are also known as planetoids. The size of asteroids vary significantly, ranging from 1 m to 1000 km in diameter. The average temperature on the asteroid’s surface is –73°C and the average speed is 25 km/s. Asteroids are mostly found in the asteroid belt between Mars and Jupiter. Ceres, Pallas, Juno, and Vesta are the four largest asteroids. Collisions can happen between asteroids and the Earth if the asteroids and the Earth are at an intersection point at the same time or are located extremely close to each other. Comet Asteroid Kuiper Belt Asteroid belt Halley’s Comet was last seen across the Earth in 1986 and is expected to be seen again in 2061. Science Facts The asteroid belt and Kuiper Belt are two distinct regions in the Solar System. Chapter 7 Earth and the Solar System 187 ©Praxis Publishing_Focus On Science
Meteoroids, Meteors, Meteorites Meteoroids are rock and metal fragments formed by the debris of asteroids or comets that orbit the Sun. Its size ranges from as fine as sand to a maximum of one metre. Its surface temperature in space is close to 0°C. Meteoroids are free to move in space and are influenced by the gravity of the planets and moons that surround them. Meteoroids enter the Earth’s atmosphere at very high speeds, ranging from 11 km/s to 72 km/s, depending on their size and trajectory. When a meteoroid enters the Earth’s atmosphere, the meteoroid is known as a meteor. Molecular friction between the air and the meteor produces heat until it burns, resulting in a streak of light. The meteor usually burns up completely in the atmosphere. When many meteors enter the Earth at a time, they are known as meteor showers or meteor rain. The meteor that does not completely burn up in the atmosphere and falls to the surface of the Earth is known as the meteorite. Craters form as a result of being hit by these meteorites. 188 ©Praxis Publishing_Focus On Science
7.2 Earth and Its Satellite Our home planet, Earth, is the third planet from the Sun and the only planet where living things can be found. It has one natural satellite that we know as the Moon. It is the only planet in our Solar System with liquid water covering 71% of its surface. Earth’s atmosphere is mostly nitrogen with plenty of oxygen. Earth’s atmosphere protects us from ultraviolet radiation from the Sun as well as incoming meteoroids. It also regulates global temperatures, allowing life to grow and thrive. Movement of Earth in the Solar System There are two major ways the Earth moves in our Solar System. The Earth rotates on its axis, making a full rotation each day, and the Earth orbits around the Sun once each year (revolution). Day and Night We have seen the Sun’s daily path across the sky when it rises in the morning and sets at night. Do you realise that it is the Earth’s rotation on its axis that causes these things to happen? The axis of the Earth is the imaginary line passing through its centre with the North Pole and South Pole located at either end of the axis. As the Earth rotates on its axis and revolves around the Sun, it is slightly tilted at an angle of 23.5 degrees. Since it rotates slowly, smoothly and consistently at the same speed, we are not conscious of this movement. The Earth takes 24 hours to make a complete rotation on its axis, and this results in day and night. Half of the Earth faces the Sun as it rotates, and the other half faces away. Can the day and night have different duration? As the Earth rotates, different regions on the Earth face the Sun and receive sunlight at different times. This can occur in different regions of the same country. There are three time zones in Indonesia, one for each of West Indonesia, Central Indonesia and East Indonesia. Which region experiences sunshine first? Sunlight Sunrise Axis The South pole is the point on Earth’s surface that is furthest south. The North pole is the point on Earth’s surface that is furthest north. Day Night Chapter 7 Earth and the Solar System 189 ©Praxis Publishing_Focus On Science
Calendar Year The Earth makes one complete revolution around the Sun. The common year on the Gregorian calendar, often known as the modern calendar, has 365 days, whereas a leap year has 366 days. This is because the Earth rotates on its own axis and takes 365¼ days to complete one revolution around the Sun. If it is a leap year, it takes the Earth 366 days to complete one revolution. Every four years, there is a leap year. The diagram below shows the rotation and revolution of Earth on its own axis. Seasons The tilt of the Earth on its axis and the movement of the Earth around the Sun are two key factors that determine the climate of the Northern and Southern Hemispheres. While the Earth orbits the Sun, its axis is tilted at an angle of about 23.5 degrees relative to its orbital plane. This tilt causes the Earth’s axis to precess, which leads to a gradual change in the direction in which it points over time. As a result, the angle at which sunlight strikes various locations of the Earth changes throughout the year. Locations that are struck perpendicular by direct sunlight receive more heat energy and are hotter, whereas the indirect sunlight locations receive less energy from the Sun, and they are cooler. The variations in temperature produce the four seasons in Earth: spring, summer, autumn and winter. 365 1 4 days 24 hours Moon Sun Earth How does the Gregorian calendar differ from Julian calendar in terms of leap year calculation? Think About It The Gregorian calendar, which is the most widely used calendar in the world today, was introduced by Pope Gregory XIII in 1582. It replaced the Julian calendar, which had been in use since ancient Rome. Science Facts 190 ©Praxis Publishing_Focus On Science
The diagram below shows the occurrence of four seasons. Summer occurs in the Northern Hemisphere in June because the northern section of the Earth is tilted towards the Sun, whereas winter occurs in the Southern Hemisphere because these parts are tilted away from the Sun. After three months, the Northern Hemisphere will transition to autumn, while the Southern Hemisphere will transition to spring. Six months later, the Northern Hemisphere of the Earth begins to tilt away from the Sun. As a result, winter will be experienced in the Northern Hemisphere, while summer will be experienced in the Southern Hemisphere. In the fourth quarter of the year, the Northern Hemisphere will transition to spring, while the Southern Hemisphere will transition to autumn. Countries such as Indonesia, Malaysia and the Philippines are positioned near the equator and receive almost the same amount of sunlight throughout the year. These countries do not have four seasons, although they have rainy and dry seasons. Summer Winter Winter Summer September 22 Spring Autumn June 21 December 22 March 21 Spring Autumn In polar regions such as Finland, Greenland and Alaska, the Sun remains visible in the sky for 24 hours around summer solstice. This phenomenon is known as the midnight Sun, and they also experience polar night when the night lasts for 24 hours. This occurs around winter solstice. Science Facts Chapter 7 Earth and the Solar System 191 ©Praxis Publishing_Focus On Science
Moon as Earth’s Satellite The Moon is about 363 300 km away from Earth. The Moon rotates in the same way that the Earth does. However, the Moon takes approximately 27 days to complete one rotation on its axis. The Moon also revolves around the Earth in its orbit and it takes an approximate time of 27 days as well. As a result, the same surface of the Moon always faces towards the Earth at all times. As the Moon continues to revolve, we can see a greater portion of its bright face. Currently, the Moon appears as a semicircle, which is known as the First Quarter Moon. As time passes, the First Quarter Moon transitions into the Waxing Gibbous Moon, with over half of the Moon’s visible side illuminated by the Sun. At this stage, the Moon is entirely visible to us as its illuminated portion faces the Earth directly, which is referred to as the Full Moon phase. The Earth is positioned between the Sun and the Moon, forming a straight line, allowing us to see the Moon as a complete circle. As the Moon continues to revolve, a lesser portion of its illuminated side is facing the Earth, which is known as the Waning Gibbous Moon phase. As time progresses, we are only able to view half of the illuminated portion of the Moon, which is referred to as the Third Quarter Moon phase. Phase 3 Phase 4 Phase 5 Phase 6 Phase 7 Earth Resource 192 ©Praxis Publishing_Focus On Science
The final phase is the Waning Crescent Moon, during which we can only observe a small section of the illuminated side of the Moon. The whole cycle starts with a New Moon, where the Moon is between the Sun and the Earth. The dark side of the Moon is facing us, making the Moon ‘invisible’ in the night sky. This is why we do not see the Moon at night during this phase. As the Moon orbits around the Earth, a small part of it that is illuminated by the Sun can be seen from the Earth. We see the illuminated part of the Moon as a crescent. This phase is known as the Waxing Crescent Moon. Phase 8 Phase 1 Phase 2 Sun Moon Day 1 Day 14 to 16 Day 28 Day 30 New Moon Full Moon Waning Crescent Moon Phases of the Moon at different times in a month Phases of Moon The Moon does not emit its own light, but rather appears visible to us on Earth because it reflects sunlight. However, the Moon appears to change shape as we observe it each day due to different portions of its surface being illuminated during its orbit around the Earth. These alterations in appearance are known as the phases of the Moon. The lunar cycle, which repeats itself, takes approximately 29.5 days for the Moon to reach the same visual phase. Movement of the Moon around the Earth Chapter 7 Earth and the Solar System 193 ©Praxis Publishing_Focus On Science