Classifying and Exploring Life

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1 Classifying and Exploring Life Characteristics of Life What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After 1. All living things move. 2. The Sun provides energy for almost all organisms on Earth. Key Concept What characteristics do all living things share? Characteristics of Life Your classroom is full of nonliving things and living things. Desks, books, and lights are nonliving things. Your classmates, teacher, and plants are living things. What makes people and plants different from desks and lights? People and plants, like all living things, have all the characteristics of life. All living things are organized. They grow and develop. All living things reproduce. They respond to their environment. All living things maintain certain internal conditions and use energy. Nonliving things do not have all these characteristics. Books might be organized into chapters. Lights might use energy. But only those things that have all the characteristics of life are living. Things that have all the characteristics of life are called organisms. Organization Your school has organization. The classrooms are for learning and the gym is for sports. Living things are also organized. Their organization involves cells. A cell is the smallest unit of life. An organism might be made of just one cell or of many cells. All organisms have structures with specific functions, or jobs. Make Flash Cards Write each boldface word on one side of a flash card. Write the definition on the other side. Use the cards to quiz yourself. 1. Identify How do living things differ from nonliving things? Reading Essentials Classifying and Exploring Life 1

Make a half-book and use it to organize your notes on the characteristics of living things. Characteristics of Life 2. Apply You are a multicellular organism.

2 Make a half-book and use it to organize your notes on the characteristics of living things. Characteristics of Life 2. Apply You are a multicellular organism. Name one function that groups of your cells carry out. Unicellular Organisms Living things that are made of only one cell are called unicellular organisms. A unicellular organism has structures with specialized functions. Some structures control cell activities. Some take in nutrients. Other structures enable the organism to move. Multicellular Organisms Living things that are made of two or more cells are called multicellular organisms. Some multicellular organisms only have a few cells, but others have trillions of cells. The cells of a multicellular organism usually do not all do the same things. Instead, groups of cells have specialized functions. These functions might include digestion or movement. Growth and Development Think about the tadpole in the figure below. The tadpole does not look like the frog it will become. The tadpole will lose its tail and grow legs. Like all organisms, the tadpole will grow and develop. Stage 2: Fertilized frog eggs are hatched into tadpoles. Stage 4: The adult frog can live on land. Stage 1: Amphibian eggs are laid and fertilized in water. Visual Check 3. Identify the characteristics of life that you see in the figure. Stage 3: Tadpoles begin to grow into adults. 2 Classifying and Exploring Life Reading Essentials

3 How do organisms grow? When an organism grows, it increases in size. A unicellular organism grows as its one cell gets bigger. A multicellular organism grows when more cells are produced. How do organisms develop? The changes in an organism during its lifetime are called development. A multicellular organism develops as cells become specialized into different cell types, such as skin and muscle cells. Some organisms have amazing developmental changes over their lifetimes. An example is a tadpole developing into a frog. Reproduction Reproduction is the process by which one organism makes one or more new organisms. Organisms must reproduce, or they will die out. Not all organisms reproduce, such as family pets. But if a type of organism is going to survive, some organisms of that type must reproduce. 4. Explain What is development? Organisms reproduce in many ways. Some unicellular organisms divide and become two new organisms. Each new organism is just like the original cell. Some organisms must have a mate to reproduce. Other organisms can reproduce without a mate. Organisms produce different numbers of offspring. Humans usually produce only one or two offspring at a time. Other organisms, such as frogs, can produce hundreds of offspring at one time. Responses to Stimuli Organisms live in environments that change all the time. These changes are called stimuli (STIHM yuh li). One change is called a stimulus. All organisms respond to stimuli. Internal Stimuli Internal stimuli are changes inside an organism. They include hunger, thirst, and pain. If you feel hungry and look for food, you are responding to an internal stimulus hunger. The feeling of thirst that causes you to look for water is another internal stimulus. External Stimuli External stimuli are changes outside an organism. They are usually changes in the environment that the organism lives in. Light and temperature are examples of external stimuli. 5. Name two internal stimuli. 6. Contrast How do external stimuli differ from internal stimuli? Reading Essentials Classifying and Exploring Life 3

4 7. Apply What word explains why you go to the bathroom more when you drink a lot of water? 8. Explain Why is maintaining homeostasis important to organisms? 9. Generalize What conditions might be too harsh for an organism to maintain homeostasis? Light Many organisms respond to changes in light. Many plants will grow toward light. You respond to light, too. If you spend time in sunlight, your skin s response might be to darken, turn red, or freckle. Temperature How does your body respond to changes in temperature? Like many animals, your body responds by increasing or decreasing the amount of blood flow to your skin. If the temperature gets warmer, your blood vessels respond by widening. Then more blood can flow to your skin. You feel cooler. Homeostasis All organisms are able to maintain some internal conditions. Homeostasis (hoh mee oh STAY sus) is an organism s ability to maintain steady internal conditions when outside conditions change. Have you ever noticed that if you drink more water than usual, you have to go to the bathroom more often than you usually do? Your body is keeping your internal conditions steady. The Importance of Homeostasis Cells need certain conditions to function the way they should. Homeostasis makes sure cells can function. If cells cannot function the way they should, an organism might get sick or die. Methods of Regulation Humans cannot survive if their body temperature changes more than a few degrees from 37 C. When your outside environment becomes too hot or too cold, your body responds. It sweats, shivers, or changes the flow of blood to maintain the body temperature of 37 C. Both unicellular and multicellular organisms have ways to maintain homeostasis. Some unicellular organisms have a structure called a contractile vacuole (kun TRAK tul VA kyuh wohl). It collects and pumps extra water out of the cell. There is a limit to the amount of change that can occur inside an organism. For example, you could live for only a few hours in very cold water. Your body could not maintain steady internal conditions, or homeostasis, in this environment. Your cells could not function. 4 Classifying and Exploring Life Reading Essentials

Energy All organisms use energy. Digesting food, thinking, reading, and sleeping use energy. Cells use energy to transport substances, make new cells, and perform chemical reactions.

5 Energy All organisms use energy. Digesting food, thinking, reading, and sleeping use energy. Cells use energy to transport substances, make new cells, and perform chemical reactions. All of the characteristics of life use energy. Energy s Origin Where does this energy come from? The energy that most organisms use originally came to Earth from the Sun, as shown below. The energy goes from one organism to another. Energy in the cactus comes from the Sun. The squirrel gets energy from the cactus that it eats. The coyote gets energy from eating the squirrel. Key Concept Check 10. State What characteristics do all living things share? Visual Check 11. Interpret Diagrams From which food sources does the badger get energy? California myotis bat Mountain lion Northern harrier hawk Ants Big sagebrush Longnose snake Pronghorn Desert paintbrush Sagebrush lizard Badger Prickly pear cactus Coyote Golden-mantled squirrel Reading Essentials Classifying and Exploring Life 5

6 Energy for Life There are six characteristics of life. From the chart below you will learn how each characteristic depends on energy from the Sun. Visual Check 12. Apply In the chart, add another example for each characteristic of life. Characteristics of Life Characteristic Definition Example Organization Living things have structures with their own functions or jobs. In living things with more than one cell, groups of cells work together. These living things have a higher level of organization than living things with only one cell do. a leopard running Growth and Development Living things might grow by increasing cell size. They also might grow by making more cells. Living things develop when cells get specialized functions. a tadpole changing into a frog Reproduction Living things make more living things by reproducing. a mother duck and her ducklings Response to Stimuli Homeostasis Use of Energy Living things respond to changes in their internal and external environments. Living things keep their internal environment stable. Living things use energy for everything they do. They get their energy by making, eating, or absorbing food. a plant leaning toward the sunlight coming in a nearby window a girl drinking water after exercising a squirrel eating a nut 6 Classifying and Exploring Life Reading Essentials

7 Mini Glossary cell: the smallest unit of life homeostasis (hoh mee oh STAY sus): an organism s ability to maintain steady internal conditions when outside conditions change multicellular: describes a living thing that is made of two or more cells organism: a thing that has all the characteristics of life unicellular: describes a living thing that is made of only one cell 1. Review the terms and their definitions in the Mini Glossary. Write one or two sentences to explain the difference between multicellular and unicellular organisms. 2. Fill in the table below to identify the six characteristics all living things share. Then add an example for each characteristic from your life or the life of someone you know. Characteristic of Life Personal Example 3. How did making flash cards help you learn the important terms in the lesson? What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? ConnectED Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. END OF LESSON Reading Essentials Classifying and Exploring Life 7

8/25/13. What are living things, and how can they be classified? Characteristics of Life. What do you think? Do you agree or disagree?

8/25/13. What are living things, and how can they be classified? Characteristics of Life. What do you think? Do you agree or disagree? 8/25/13 Chapter Introduction Characteristics of Life Lesson 2 Classifying Organisms Lesson 3 Exploring Life Chapter Wrap-Up What are living things, and how can they be classified? Steven P. Lynch Lesson