CHAPTER 2 2 Cell Energy SECTION The Cell in Action BEFORE YOU READ After you read this section, you should be able to answer these questions: How do plant cells make food? How do plant and animal cells get energy from food? National Science Education Standards LS 1c, 4c How Does a Plant Make Food? The sun is the major source of energy for life on Earth. Plants use carbon dioxide, water, and the sun s energy to make food in a process called photosynthesis. The food that plants make gives them energy. When animals eat plants, the plants become sources of energy for the animals. Plant cells have molecules called pigments that absorb light energy. Chlorophyll is the main pigment used in photosynthesis. Chlorophyll is found in chloroplasts. The food plants make is a simple sugar called glucose. Photosynthesis also produces oxygen. Photosynthesis STUDY TIP Compare As you read this section, make a Venn Diagram to compare cellular respiration and fermentation. READING CHECK 1. Identify In which cell structures does photosynthesis take place? 6CO 2 6H 2 O light energy C 6 6O 2 Carbon Water Glucose Oxygen dioxide Plant cell Chloroplast 2. Identify What two materials are produced during photosynthesis? Photosynthesis takes place in chloroplasts. Chloroplasts are found inside plant cells. Interactive Textbook 23 The Cell in Action
SECTION 2 Cell Energy continued STANDARDS CHECK LS 1c Cells carry on the many functions needed to sustain life. They grow and divide, thereby producing more cells. This requires that they take in nutrients, which they use to provide energy for the work that cells do and to make the materials a cell or an organism needs. Word Help: function to work Word Help: energy the capacity to do work 3. Identify Name two ways cells can get energy from food. How Do Organisms Get Energy from Food? Both plant and animal cells must break down food molecules to get energy from them. There are two ways cells get energy: cellular respiration and fermentation. During cellular respiration, cells use oxygen to break down food. During fermentation, food is broken down without oxygen. Cellular respiration releases more energy from food than fermentation. Most eukaryotes, such as plants and animals, use cellular respiration. What Happens During Cellular Respiration? When you hear the word respiration, you might think of breathing. However, cellular respiration is different from breathing. Cellular respiration is a chemical process that happens in cells. In eukaryotic cells, such as plant and animal cells, cellular respiration takes place in structures called mitochondria. Recall that to get energy, cells must break down glucose. During cellular respiration, glucose is broken down into carbon dioxide (CO 2 ) and water (H 2 O), and energy is released. This energy is stored in a molecule called ATP (adenosine triphosphate). The figure below shows how energy is released when a cow eats grass. 4. Identify What two materials are needed for cellular respiration? Cellular respiration C 6 6O 2 6CO 2 6H 2 O energy (ATP) Glucose Oxygen Carbon Water dioxide Mitochondria 5. List What three things are produced during cellular respiration? Animal cell The mitochondria in the cells of this cow will use cellular respiration to release the energy stored in the grass. Interactive Textbook 24 The Cell in Action
SECTION 2 Cell Energy continued The Connection Between Photosynthesis and Cellular Respiration Light energy Cellular respiration Cellular respiration releases carbon dioxide and water. These are used by plant cells in photosynthesis. (ATP) Critical Thinking 6. Apply Concepts What would happen if oxygen were not produced during photosynthesis? CO 2 H 2 O Mitochondrion Chloroplast C 6 O 2 Photosynthesis Photosynthesis uses carbon dioxide and water and produces glucose and oxygen. Plant and animal cells use glucose and oxygen to make ATP in cellular respiration. Plant cell Animal cell 7. Complete Plant and animal cells use glucose and oxygen to make. How Is Fermentation Different from Cellular Respiration? During fermentation, cells break down glucose without oxygen. Some bacteria and fungi rely only on fermentation to release energy from food. However, cells in other organisms may use fermentation when there is not enough oxygen for cellular respiration. When you exercise, your muscles use up oxygen very quickly. When cells don t have enough oxygen, they must use fermentation to get energy. Fermentation creates a byproduct called lactic acid. This is what makes your muscles ache if you exercise too hard or too long. Say It Research Use the school library or the Internet to research an organism that uses fermentation. What kind of organism is it? Where is it found? Is this organism useful to humans? Present your findings to the class. Interactive Textbook 25 The Cell in Action
Section 2 NSES LS 1c, 4c SECTION VOCABULARY cellular respiration the process by which cells use oxygen to produce energy from food fermentation the breakdown of food without the use of oxygen photosynthesis the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to make food. 1. Identify What kind of cells have chloroplasts? 2. Explain How do plant cells make food? 3. Explain Why do plant cells need both chloroplasts and mitochondria? 4. Apply Concepts How do the processes of photosynthesis and cellular respiration work together? 5. Compare What is one difference between cellular respiration and fermentation? 6. Explain Do your body cells always use cellular respiration to break down glucose? Explain your answer. Interactive Textbook 26 The Cell in Action
C Cells, Heredity, and Classification Answer Key continued 2. No. Organs are made of tissues, so to have organs, an organism must have tissues. 3. Function is the purpose of a part, or the job the part does. Structure is the arrangement of parts in an organism. 4. Specialization of cells means that, in multicellular organisms, different cells perform different functions to help keep the organism alive. 5. An organ has to have two or more tissues. Tissues have to work together for an organ to do a job. 6. The life span of a multicellular organism is not limited to the life span of any one of its cells. Chapter 2 The Cell in Action SECTION 1 EXCHANGE WITH THE ENVIRONMENT 1. the movement of particles from areas of high concentration to areas of low concentration 2. by diffusion 3. The 200 molecules of water have a higher concentration of water because 100% of the molecules are water. 4. Water moves into it by osmosis. 5. by osmosis 6. energy 7. The vesicle in the third picture should be labeled. 1. Both involve moving large particles across the cell membrane. In endocytosis, particles move into the cell. In exocytosis, particles move out of the cell. 2. Osmosis is the diffusion of water across a semipermeable membrane. 3. During passive transport, particles move from areas of high concentration to areas of low concentration. During active transport, particles move from areas of low concentration to areas of high concentration. Active transport uses energy from the cell, and passive transport does not. 4. channels 5. An arrow should point from the pure water to the water mixed with sugar. SECTION 2 CELL ENERGY 1. chloroplasts 2. glucose and oxygen 3. cellular respiration, fermentation 4. glucose and oxygen 5. carbon dioxide, water, energy (ATP) 6. Plants and animals wouldn t have oxygen for cellular respiration. They couldn t use cellular respiration to get energy. 7. ATP 1. plant cells 2. Plant cells use carbon dioxide, water, and energy from the sun to make food by photosynthesis. 3. Chloroplasts make food for the plant, and mitochondria break down the food to release energy. 4. Each process gives the other the materials it needs. Cellular respiration uses oxygen and glucose and produces carbon dioxide, water, and ATP. Photosynthesis uses carbon dioxide, water, and sunlight and produces glucose and oxygen. 5. Cellular respiration uses oxygen to break down food. Fermentation does not. Cellular respiration produces more energy than fermentation. 6. No, if cells don t have enough oxygen, they break down glucose using fermentation. When you exercise, for example, your muscle cells use up oxygen quickly. When there is not enough oxygen left, the muscle cells use fermentation. SECTION 3 THE CELL CYCLE 1. The cell must make a copy of its DNA. 2. binary fission 3. Chromatids are copies of chromosomes that are held together at the centromere. 4. interphase, mitosis, cytokinesis 5. eight more 6. prophase, metaphase, anaphase, telophase 7. cell plate 1. In prokaryotic cells, the DNA is on a single, circular chromosome. The DNA of eukaryotes is stored on many chromosomes. Interactive Textbook Answer Key 14 Cells, Heredity, and Classification