Animal and Plant Classification

Transcription

1 Animal and Plant Classification The Building Blocks of Living Things Think about the building blocks you played with when you were younger. You started with just one block. If you put a few blocks together, you could build a house. If you put many blocks together, you could build something complicated, like a castle with towers. All living things plants and animals are made of cells. A cell is the smallest unit of a living thing. You can think of cells as building blocks. Some living things are made of just one block, or cell. Most plants and animals are made by putting thousands, millions, or even billions of cells together. Cells can have many jobs. Some cells help a living thing to be healthy. Other cells help it to adapt to its environment. Microscopes make objects appear larger than they really are. By looking at cells under a microscope, scientists can see inside them and learn how they work.

2 The Parts of a Cell Cells have different parts, and each part has a specific job to do. The nucleus is like the brain of the cell. The instructions for the cell s job are stored in the nucleus. The cell membrane is a thin covering all around the cell. It has two jobs. It separates the cell from things around it. It also acts as a guard that decides what can come into and go out of the cell. Cytoplasm holds everything a cell needs to carry out its life processes. It is a material similar to jelly that fills the cell. The nucleus floats in the cytoplasm. Plant cells have the same parts as animal cells plus some extras. The cell wall is outside of the cell membrane. The walls of all the cells help hold up a plant. Chloroplasts are the parts of a cell that trap energy from sunlight so a plant can make its own food.

3 From Cells to Organisms Cells have different shapes, depending on the kinds of jobs they do. For example, nerve cells are very thin. They act like wires that send messages through the body. Nerve cells can be as long as your arm or as short as the period at the end of this sentence. Cells that look alike and have the same shape do the same job. These cells combine to build tissue. For example, nerve tissue is made of nerve cells. Tissues of the same type combine to form organs. For example, the brain is an organ that is made of nerve tissue. Organs that work together form an organ system. Two organs the brain and the spinal cord build the central nervous system in your body. An organism is the complete living thing that is made when all the parts are combined. An organism is made of many cells. Unlike an organism, a virus is a very tiny particle with similarities to both living and nonliving things. It uses plant and animal cells to make more viruses.

4 Sorting Living Things Into Groups There are more than a million organisms. Who keeps track of them all? Biologists! In order to identify, compare, and study all these organisms, biologists use a classification system. Using this system, they place every kind of organism into a group. All the organisms in a group have common characteristics. Biologists would ask questions like these to help them decide if a shark and a dolphin belong in the same group. Do sharks and dolphins have one cell or many cells? They have many cells. That is a common characteristic, so they belong in the same group. Where do sharks and dolphins live? They live in the ocean. That is another common characteristic, so they still belong in the same group. How do sharks and dolphins get oxygen? Sharks get oxygen from the water. Dolphins get oxygen from the air. That is a different characteristic, so they belong in different groups.

5 Kingdoms The Largest Group Kingdoms are the largest groups in the classification system. Many scientists divide organisms into six kingdoms. The kingdom that an organism belongs to depends mostly on how many cells it has, what cell parts it has, where it lives, and how it gets its food. Dividing the Kingdoms Sorting living things into six kingdoms is only the beginning! Next, scientists divide the members of each kingdom into smaller and smaller groups. They use organisms features to decide which organisms are in each group. After kingdoms, the groups are divisions, classes, orders, and families. The last two groups are genus and species. Scientists use these last groups to name animals. A genus is a group of animals that are similar in many ways. For example, a dog and a wolf are members of the same genus. Their genus is Canis. The genus group is divided one more time into groups of species. A species is a group of animals whose members can reproduce. The species name often describes where the animal lives or what color it is. The first part of an animal s scientific name is the genus. The second part is the species. So, although you might name your pet dog Max, his scientific name would be Canis familiaris.

6 How Scientists Classify Plants To sort plants into groups, scientists look at two main characteristics. One is the way that a plant transports water and nutrients. The other is how a plant reproduces. Moving Water and Food Some plants, called vascular plants, have parts that look like tubes. Water and nutrients from the soil move up and down these tubes to the roots, stems, and leaves. Vascular plants are all around you. You may have stepped on some this morning, if you walked on grass. If you had celery with your lunch, you ate one! The tissue that makes up the tubes supports a plant s stems and leaves. Because of this, vascular plants can grow to be very tall. Plants without these tubes are called nonvascular plants. These plants pass water and nutrients through cell walls, from one cell to the next. This process is very slow, so nonvascular plants usually grow close to the ground. That way, water and nutrients do not have to travel so far. Some nonvascular plants are mosses, lichen, and algae.

7 Reproduction The second way that scientists classify plants is by how they reproduce, or make new plants. One group reproduces by making seeds. A seed is a structure with a protective covering. Inside the seed is a young plant. In plants with flowers, the seeds are in the flowers. Conifers are plants that make seeds but do not have flowers. In conifers, the seeds are in the cones. Some plants have no seeds at all. They use spores to reproduce. A spore is a single cell surrounded by a cell wall. It can grow into a new plant if it falls on a place where it can get the water and food it needs. Ferns and mosses have spores.

8 How Scientists Classify Animals The animal kingdom is divided into two main groups. One group is vertebrates, or animals with a backbone. The other group is invertebrates, or animals without a backbone. Vertebrates Scientists have divided vertebrates into five smaller groups. This group includes mammals, birds, reptiles, amphibians, and fish. Reptiles Let s take a closer look at one group of vertebrates reptiles. Reptiles include lizards, snakes, turtles, crocodiles, and alligators. These animals live in the water and on land. As you can see from the chart, reptiles breathe air with their lungs. Many people are very surprised when they touch a reptile for the first time. They expect them to be wet and slimy, but they have dry skin covered with scales. People often confuse crocodiles and alligators because the bodies of these reptiles are similar in many ways. An easy way to tell them apart is to look at their mouths. You can see a crocodile s teeth when its mouth is shut, but you cannot see an alligator s teeth in that position.

9 The Life Cycle of a Reptile Sea turtles spend most of their time underwater, where they swim, sleep, and eat. Like all reptiles, they have to come to the surface to breathe air with their lungs. If they are swimming, they need to come up for air about every five or ten minutes. However, if they are asleep, they can stay underwater for hours. Male sea turtles rarely come on land, but female sea turtles come on land about six times each nesting year to lay their eggs. Scientists are not sure how old female sea turtles are when they nest for the first time. But they do know that they swim back to the same area where they were hatched as babies even if that place is miles and miles away. A female sea turtle lays her eggs on land. Baby turtles hatch from the eggs between forty-five and seventy days later, and they make their way to water. The turtles grow to be adults who will reproduce.

10 Animals Without a Backbone Animals without a backbone are called invertebrates. You might be surprised to learn that most animals in the world are invertebrates. Arthropods are the largest group of invertebrates. This group includes ticks, spiders, bees, shrimp, scorpions, and centipedes. At first, these animals seem very different because some swim, some fly, and some crawl. However, they have two common characteristics that cause scientists to group them together. The first characteristic is that all arthropods have legs and a body that are divided into sections. The second is that all arthropods are covered with a lightweight, hard skin that protects them. This hard skin is called an exoskeleton. The second largest group of invertebrates is mollusks. This group includes scallops, oysters, squid, and snails. Mollusks have soft bodies. Some have a hard shell and some don t. Most mollusks live in water, but some live on land in damp places. Most mollusks are only a few inches long, but a few kinds are huge! Giant clams, for example, can grow to more than four feet long and weigh more than five hundred pounds!

11 The Life Cycle of a Mollusk When octopuses are ready to mate, the male fertilizes the female s eggs. The female attaches the fertilized eggs to a rock or places them in a hole. Over the course of several days, a female may lay more than 100,000 eggs! If the female has laid her eggs in a hole, she will often seal up the hole to protect the eggs and ensure that they are not harmed. Females guard the eggs constantly. Depending on temperature, the eggs hatch anytime between four weeks and seven months later. A short time after the baby octopuses emerge from their eggs, the female octopus dies. When the baby octopuses emerge from their eggs, they float to the top of the water. They stay there until they grow larger and can return to the bottom of their water habitat.

12 Animal Adaptations Adaptations are physical features or behaviors passed on from parents. Adaptations help animals get food, protect themselves, move, and reproduce. Animals with the best adaptations have a better chance at getting the resources they need, so they have a better chance of reproducing. Adaptations That Help and Protect Many animals have physical adaptations that help them move. Did you know that birds have hollow bones to make them lighter? Did you know that fish have bags of air in them that help them float? Or that flamingoes have long necks so they can submerge their heads in water and find food in the muddy bottom? What about snails? They have a flat foot that oozes a sticky liquid. They move by sliding along paths of their own slime. Shapes and colors can provide protection by making animals nearly invisible. When the long, thin razor fish holds itself straight up and down in the water, it looks like a piece of floating grass. Features such as claws, tusks, and horns protect some animals. Chemicals are another kind of adaptation. Some chemicals give animals a nasty smell or taste so other animals won t eat them. Others poison their victims. An octopus can use its sharp teeth to drill a hole in a clamshell. It then injects poison through the hole. After the clam is poisoned, its shell can be opened easily.

13 Animal Instincts Instincts are behaviors that are inherited from parents. These natural behaviors tell young animals how to move, how to hide, and how to catch food. They will remember these things all their life. Remember the baby turtles that find their way to the sea? That is an instinct. Migration and Hibernation Migration is an instinct. Many animals migrate to find food as seasons change. Arctic terns leave the Arctic Ocean in the fall, when the ocean begins to freeze and fish are scarce. They fly to Antarctica, where fish are plentiful. In the spring, when the ice in the Arctic Ocean begins to melt, the terns fly home to nest. Another natural behavior that does not need to be learned is hibernation. Some kinds of mammals, reptiles, and amphibians hibernate, or become inactive, when the weather is very cold and food is hard to find. Chipmunks, for example, eat a lot in the fall. The food is stored as body fat that gives them energy during winter, when they hibernate. They don t sleep straight through the winter but wake for short periods to move around and snack on saved food.

14 Animals Learn Not all animal behaviors are instincts. Many animals learn behavior from their parents. Mother bears teach their cubs to fish. And wolves have a way of teaching their young to avoid traps! All living things, from the smallest cell to the largest organism, can be classified. Knowing the classification of living things gives us information about what they are made of and how they adapt.

15 Glossary cell chloroplast cytoplasm genus invertebrates nucleus species vertebrates the smallest unit of a living thing that can carry out all life functions the part of a plant cell that traps energy from sunlight so the plant can make its own food the substance in a cell that contains what the cell needs to carry out its life processes a group of closely related animals animals without a backbone the control center of a cell a group of animals whose members can mate and produce offspring that can also produce offspring animals with a backbone