CHAPTER 2 1 The Cycles of Matter SECTION Cycles in Nature BEFORE YOU READ After you read this section, you should be able to answer these questions: Why does matter need to be recycled? How are water, carbon, and nitrogen recycled? National Science Education Standards LS 1c, 4b, 4c, 5a Why Is Matter Recycled on Earth? The matter in your body has been on Earth since the planet formed billions of years ago. Matter on Earth is limited, so it must be used over and over again. Each kind of matter has its own cycles. In these cycles, matter moves between the environment and living things. What Is the Water Cycle? Without water there would be no life on Earth. All living things are made mostly of water. Water carries other nutrients to cells and carries wastes away from them. It also helps living things regulate their temperatures. Like all matter, water is limited on Earth. The water cycle lets living things use water over and over. In the environment, water moves between the oceans, atmosphere, land, and living things. Eventually, all the water taken in by organisms returns to the environment. The movement of water is known as the water cycle. The parts of the water cycle are explained in the figure below. STUDY TIP Mnemonic As you read, create a mnemonic device, or memory trick, to help you remember the parts of the water cycle. Say It Identify Describe to the class all the things you and your family do in a day that use water. Can you think of any ways you might be able to use less water? Precipitation is rain, snow, sleet, or hail that falls from clouds to Earth's surface. Most precipitation falls into the ocean. It never touches the land. Condensation happens when water vapor cools and changes into drops of liquid water. The water drops form clouds in the atmosphere. Evaporation happens when liquid water on Earth's surface changes into water vapor. Energy from the sun makes water evaporate. 1. Describe How do clouds form? Groundwater is water that flows under the ground. Gravity can make water that falls on the land move into rocks underground. Runoff is water that flows over the land into streams and rivers. Most of the water ends up in the oceans. Transpiration happens when plants give off water vapor from tiny holes in their leaves. Interactive Textbook 19 Cycles in Nature
SECTION 1 The Cycles of Matter continued STANDARDS CHECK LS 4c For ecosystems, the major source of energy is sunlight. Energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis. That energy passes from organism to organism in food webs. 2. Analyze Explain the role of photosynthesis in the carbon cycle. What Is the Carbon Cycle? Besides water, the most common molecules in living things are organic molecules. These are molecules that contain carbon, such as sugar. Carbon moves between the environment and living things in the carbon cycle. PHOTOSYNTHESIS AND RESPIRATION Plants are producers. This means they make their own food. They use water, carbon dioxide, and sunlight to make sugar. This process is called photosynthesis. Photosynthesis is the basis of the carbon cycle. Animals are consumers. This means they have to consume other organisms to get energy. Most animals get the carbon and energy they need by eating plants. How does this carbon return to the environment? It returns when cells break down sugar molecules to release energy. This process is called respiration. DECOMPOSITION AND COMBUSTION Fungi and some bacteria get their energy by breaking down wastes and dead organisms. This process is called decomposition. When organisms decompose organic matter, they return carbon dioxide and water to the environment. When organic molecules, such as those in wood or fossil fuels, are burned, it is called combustion. Combustion releases the carbon stored in these organic molecules back into the atmosphere. The Carbon Cycle Carbon dioxide in the air Photosynthesis 3. Complete Carbon dioxide in the air is used for 4. List What three processes release carbon dioxide into the environment?. Decomposition soil and rock Respiration living things Combustion fossil fuels Interactive Textbook 20 Cycles in Nature
SECTION 1 The Cycles of Matter continued What Is the Nitrogen Cycle? Nitrogen is also important to living things. Organisms need nitrogen to build proteins and DNA for new cells. Like water and carbon, nitrogen cycles through living things and the environment. This is called the nitrogen cycle. NITROGEN FIXATION About 78% of Earth s atmosphere is nitrogen gas. Most organisms cannot use nitrogen gas directly. Bacteria in soil can change nitrogen gas into forms that plants can use. This is called nitrogen fixation. Other organisms can get the nitrogen they need by eating plants or by eating organisms that eat plants. Critical Thinking 5. Apply Concepts How is nitrogen fixation important to animals? The Nitrogen Cycle Nitrogen in the air Lightning causes some nitrogen fixation. Animals get nitrogen from plants. Plant roots take up nitrogen from soil. Dead animals and plants Bacteria in soil convert nitrogen back to gas. Decomposition releases nitrogen into soil. Bacteria in soil and plant roots perform most nitrogen fixation. 6. Identify What process releases nitrogen into the soil? How Are the Cycles of Matter Connected? Other forms of matter on Earth also cycle through the environment. These include many minerals that living cells need, such as calcium and phosphorus. When an organism dies, every substance in its body will be recycled in the environment or reused by other organisms. All of the cycles of matter are connected. For example, water carries some forms of carbon and nitrogen through the environment. Many nutrients pass from soil to plants to animals and back. Living things play a part in each of the cycles. READING CHECK 7. Explain What happens to the substances in an organism s body when the organism dies? Interactive Textbook 21 Cycles in Nature
Section 1 NSES LS 1c, 4b, 4c, 5a SECTION VOCABULARY combustion the burning of a substance condensation the change of state from a gas to a liquid decomposition the breakdown of substances into simpler molecular substances evaporation the change of state from a liquid to a gas precipitation any form of water that falls to Earth s surface from the clouds 1. Identify In the water cycle, what makes water evaporate? 2. Summarize Draw arrows to show how carbon cycles through the environment and living things. Plants Air Animals Decomposers 3. Explain Why does matter need to be recycled? 4. Explain Why is water so important to life on Earth? 5. Define What is nitrogen fixation? 6. Define What are organic molecules? Interactive Textbook 22 Cycles in Nature
E Environmental Science Answer Key continued 1. Possible answers: food, water, sunlight, shade, shelter 2. Individuals will die or will have to move to a new area. This will cause the population to decrease. 3. No, some species may use more resources than others. Some species may be more affected than others by a limiting factor. 4. First row, left to right: parasitism, parasite (flea) Second row, left to right: both, none Third row, left to right: commensalism 5. Commensalism; the pollinator is not harmed, but the plant still benefits. Chapter 2 Cycles in Nature SECTION 1 THE CYCLES OF MATTER 1. Water vapor cools and changes into drops of liquid water. The water drops form clouds. 2. Photosynthesis uses carbon dioxide from the air. When the sugars that a plant makes during photosynthesis are broken down, carbon returns to the environment. 3. photosynthesis 4. respiration, combustion, decomposition 5. Animals need to get nitrogen from plants or other animals. Plants get their nitrogen from nitrogen fixation. 6. decomposition 7. They are recycled in the environment or reused by other organisms. 1. energy from the sun 2. There should be arrows from air to plants to animals to decomposers to air, and from plants to decomposers. 3. Matter on Earth is limited, so it needs to be used over and over again. 4. Living things are made mostly of water. Water carries nutrients to cells and carries wastes away. Water also helps organisms regulate their body temperatures. 5. Nitrogen fixation is the process in which bacteria in soil change nitrogen gas into a form that plants can use. 6. molecules that contain carbon SECTION 2 ECOLOGICAL SUCCESSION 1. 34% 2. the first species to live or grow in an area 3. Lichens don t have roots. They get their water from the air, so they do not need soil. 4. tall trees 5. in places where living things already exist 6. weeds 7. conifers 1. Abiotic factors are the nonliving parts of the environment. They include water, light, and space. 2. Primary succession is the change from bare rock to a community of organisms. Secondary succession is a change in a community where other living things already exist. 3. In secondary succession, there is already soil for new plants to use. In primary succession, soil has to develop before species other than lichens can grow. 4. There is little grass in a mature forest, because the tall trees prevent the light from reaching the ground. Nuts grow on many kinds of trees. Therefore, there would be more nut eaters than grass eaters. 5. Tall trees need deep soil. Pioneer species are the first species to live or grow in an area. There usually would not be soil in an area where no living things had been before. 6. the variety of species that live in an area 7. pieces of rock that have been broken down and remains of dead lichens Chapter 3 The Earth s Ecosystems SECTION 1 LAND BIOMES 1. Biomes are made of many related ecosystems. 2. Africa, South America 3. plenty of rain, moderate temperatures 4. deciduous trees and shrubs 5. in cones 6. The evergreen conifers shade the forest floor, but the deciduous trees of the temperate forest allow light to reach the ground. Interactive Textbook Answer Key 30 Environmental Science