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Grouping Organisms Classifying Organisms When you look for socks to wear, you probably go to your sock drawer. Your shirts might be in a different drawer. The clothes are grouped so that you can find them. When you group things by the ways they are alike, you classify them. Scientists classify organisms by using a system with seven levels, or groups. Each level is smaller and less general than the one before it. The most general level is the kingdom. All animals make up one kingdom. All plants make up another kingdom. There are other kingdoms too. The next classification level after the kingdom is the phylum. The smallest, lowest level of classification and the most specific is the species. There are enormous numbers of kinds of organisms. Classifying organisms helps us to describe and compare them. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The Animal Kingdom What makes an animal an animal? An animal is made up of many cells. It moves from place to place for at least part of its life. Animals cannot make their own food but must eat other organisms to get energy. Animals can be further classified. Vertebrates A vertebrate is an animal with a backbone. A backbone is actually many small bones next to each other. The backbone protects a spinal cord. You are a vertebrate. You can feel your backbone running down the center of your back. Fish Most but not all fish have backbones. A shark is a fish with no backbone. Instead, a stiff tissue called cartilage covers its spinal cord. The same kind of tissue makes your ears stiff. Most kinds of fish have scales on their bodies, and most kinds of fish lay eggs. Fish live only in water, and they use gills to breathe the oxygen in water. Amphibians Frogs, toads, and salamanders are amphibians. They spend part of their lives in water and part on land. Many amphibians have skin that is smooth and moist. Young amphibians are a lot like fish. They hatch from eggs in water and breathe with gills. Older amphibians grow lungs. Adults can live on land, but they come back to water to lay their eggs. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Reptiles Turtles, snakes, lizards, alligators, and crocodiles are reptiles. Like fish, they have scales. Unlike fish, reptiles breathe with lungs. Sometimes it can be hard to tell reptiles from other animals. Some reptiles live on the land, but others spend a lot of time in water. Some reptiles lay eggs, but others give birth to live young. Some reptiles have legs, but others have no legs at all! Birds Birds are the only animals that have feathers and wings. Feathers help birds stay warm and dry. Feathers also help birds fly, though not all birds can fly. Birds that fly have hollow bones, which make the birds light in weight. Birds breathe with lungs and hatch from eggs. Their eggs have hard shells. Some birds live only on land, while others spend a lot of time in water. How can you tell where a bird spends most of its time? Look at its feet! Mammals Did you know that you are a mammal? All mammals have at least a little bit of hair or fur, and almost all are born live. Mammal mothers make milk in their bodies and feed the milk to their young. No other group of animals does this. All mammals, even those that live in water, breathe air with lungs. Whales and dolphins are mammals that live in the ocean. They must come to the water’s surface, though, to breathe air. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Invertebrates Invertebrates, or animals with no backbones, come in a huge range of sizes and shapes. Some have hard shells, while others have very soft bodies. Some live on land, but others live in water. Some invertebrates fly, some swim, and others crawl. The largest group of invertebrates is arthropods. Insects, spiders, and lobsters are all arthropods. Each arthropod has a thin, hard covering and legs that bend in many places. A Dichotomous Key You can use a dichotomous key to identify an organism. The key asks a series of questions, and each answer leads to another question. You answer questions until you get to the name of the organism. A dichotomous key about mammals asks different questions from those asked by a dichotomous key about birds. The Plant Kingdom Plants make up a large group of organisms. They form the plant kingdom. Like animals, plants may be made up of many cells. Plants have different structures, or parts, from those that animals have. Plants make their own food. Scientists classify plants by how they carry food and water. In vascular plants, food and water move through tiny tubes. Not all plants are vascular. Scientists also classify plants by how they reproduce. Some plants make seeds from flowers. Other plants make seeds but do not have flowers. Still others do not even make seeds to reproduce. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Mosses and Ferns Mosses and ferns do not make seeds. Instead, they make tiny cells called spores. Each spore may grow into a new plant. Conifers Conifers are vascular plants that make seeds with cones instead of with flowers. Conifers have both male and female cones. The seeds grow inside closed female cones. When the cones open, the seeds are ready to grow into new plants. Conifers have thin leaves called needles. The leaves of most conifers stay green all year. That is why people call them evergreens. Flowering Plants You may already know that seeds grow inside parts of flowers. Flowering plants are not all the same, however. Some plants’ flowers have both male and female parts. Other plant types make separate male and female flowers on the same plant. Still other plant types make only male or female flowers on an individual plant. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary classify to group things by how they are alike dichotomous key a tool that uses a series of questions to identify an organism an animal without a backbone kingdomthe highest and most general invertebrate group of organisms phylum the classification level below kingdom species the lowest classification level; the most specific group of organisms carrying food and water vascular through tiny tubes vertebrate an animal with a backbone Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
