Classifying Organisms PDF

# Classifying Organisms In Chapter 4, you learned about the characteristics of living things. Living things are often called **organisms**. Organisms are living systems composed of smaller parts working together to carry out the processes of life. Despite its small size, a cell is an organism whos...

# Classifying Organisms In Chapter 4, you learned about the characteristics of living things. Living things are often called **organisms**. Organisms are living systems composed of smaller parts working together to carry out the processes of life. Despite its small size, a cell is an organism whose organelles work together to keep the cell alive. An organism that is made up of only one cell is called a **unicellular organism** (Figure 1). Almost all unicellular organisms are so small that they can only be seen using a microscope. Organisms can also be made up of many cells working together. An organism that is made up of more than one cell is called a **multicellular organism**. Most of the living things that you see every day are multicellular organisms. Humans and dogs, for example, are multicellular organisms made up of trillions of cells. Scientists classify living things into groups based on their characteristics. Every organism may be classified into one of five smaller groups: plants, animals, fungi, protists, and bacteria. ## Plants Plants are multicellular organisms. Trees, grasses, flowers, bushes, vines, mosses, and herbs are examples of plants. All plants make their own food by photosynthesis. Plants can live on land or in water. Water lilies and Elodea are examples of plants that live in the water. ## Animals Animals are also multicellular organisms. Animals may be further divided into vertebrates and invertebrates. **Vertebrates** are animals with a backbone, such as a moose, salmon, or blue jay (Figure 2). **Invertebrates** are animals without a backbone, such as a spider, shrimp, or snail (Figure 3). In general, there are more types of invertebrates than there are vertebrates. ### Figure 1 - A diatom is an example of a unicellular organism. ### Figure 2 - A blue jay has a backbone and is therefore a vertebrate. ### Figure 3 - A snail does not have a backbone. It is an invertebrate.