Classifying living things

Transcription

1 Classifying living things Classifying means sorting, or organising into groups. In this lesson, you are going to classify living things into two groups plants and animals. You will examine the characteristics that scientists use to separate plants from animals. That is, you will learn about what makes a plant different from an animal. Why classify? A study of living things allows you to better understand yourself and how you fit into your environment. To make this understanding possible, it helps if we sort out, or classify, living things into groups. Classifying all the living things is a bit like when you get dressed in the morning it's much quicker if all the things you wear are already sorted into groups. Your socks, undies, shirts, jeans and shoes are grouped together so you can find them easily, rather than all being in one big box. Imagine how long it would take you to get dressed in the morning if all your clothes were in one big pile? You'd probably feel just like Laura does, in the following drawing. Lesson 6/20 What are plants and animals? 1

2 Sorting out clothes Scientists would feel pretty confused when they tried to study living things if they were in just one big group. Classifying in our daily lives What other things in your daily life do you classify? Classification systems are not only used in science but in everybody s daily life as well. The following diagram is another example of how things are classified in the home. 2 Living things

3 Classifying in the kitchen This makes it a lot easier to find the things you are looking for and to communicate with other people in your family. Activity: Why classify? Make a list of things in your daily life that you classify. Well done! You have realised how important classification is. You will probably agree that classifying things makes it easier to find them. Lesson 6/20 What are plants and animals? 3

4 Are there any other reasons to classify? There are also other reasons for classifying things. Classifying makes it easier to communicate. For example, when you say knife you mean a tool for cutting, with a handle and a long, sharp metal blade. It is easier to say knife than go into a long description of the object. This is the same in biology. When you say that a cat is a mammal you mean that the animal is covered with fur, is warm-blooded and suckles its young on milk. Once again, one word has saved a lengthy explanation. Classifying also makes it easier to identify or name unfamiliar objects. For example, can you identify the object in the drawing below? Unknown object Even if you have never seen this object before, you can classify it as a type of knife from its features, or characteristics. You could also predict that it can be used for cutting. In fact, it is a scalpel used by doctors for operating. You have just read about the three benefits of classifying objects. Activity: Are there any other reasons to classify? List the three benefits of classifying objects. Check your response by going to the suggested answers section. When you classify, you put things into groups. How do you do this? 4 Living things

5 How do you classify? First you need to carefully observe the things that you want to classify. Then you can compare them. When you compare things, you are looking for similarities and differences. Things that are similar are put into the same group. A B Two groups of living things The living things in Group A are a pine tree and a gum tree. What are the similarities? Lesson 6/20 What are plants and animals? 5

6 Activity: How do you classify? List how the living things in Group A are alike. They both have a trunk, leaves, branches, roots and seeds. The living things in Group B are a snail and a gibbon. A snail is more like a gibbon than a gum tree. Snails and gibbons both move around a lot, need to breathe in oxygen and eat food. Gum trees are rooted to the spot and make their own food. These are reasons why a snail is in the same group as a gibbon but in a different group from a gum tree. Once you have established your groups and the reasons for grouping in that way, you have built a classification system. Classifying plants and animals Look at the following diagrams and decide whether they are plants or animals. Wheat Caribou 6 Living things

7 Butterfly Dandelion Grass Bee Gum tree Pine Cockroach Sea urchin Lesson 6/20 What are plants and animals? 7

8 Look closely at the diagrams and then do the activity. Activity: Classifying plants and animals Classify the things in the photographs as plants or animals. Plants Animals Check your response by going to the suggested answers section. You probably had no trouble deciding that a dandelion is a plant and a caribou is an animal. But what are your reasons for classifying in this way? How is a plant different from an animal? You have probably noticed that it is not that easy to say why plants and animals are different. This is especially true when you investigate some of the weird and wonderful living things that exist on the Earth. For example, is a green praying mantis a plant or an animal? What about a Venus fly trap that eats insects? 8 Living things

9 Venus flytrap praying mantis Plant or animal? These living things are not easily recognisable as plants or animals. A praying mantis is an animal. A Venus flytrap is a plant. Activity: How is a plant different from an animal? What do you think makes plants different from animals? You may have thought of things like: plants don t move as much as animals do; plants are green; plants have leaves and animals don t; plants don t feel things like animals do. Take a look at two of these ideas and see how useful they are for classifying plants and animals. Animals move more than plants When animals respond to changes in their environment, it is often obvious immediately. Animals usually move away from things like heat whereas plants don t move much at all. Plant movement is usually only fairly slow growth. Animals may move from place to place whereas plants may not. Is this really true? Lesson 6/20 What are plants and animals? 9

10 Sea anemones, sponges, oysters and barnacles are examples of animals that are unable to move their entire bodies. They are fixed to a particular place. barnacle mussel sea anemone Three fixed animals But you can say that most animals are able to move from place to place. But what about plants? In the ocean, there are tiny plants called phytoplankton. This word comes from the Greek language. Phyto- means plant. Plankton means drifting. So, phytoplankton are drifting plants, able to move from place to place. Phytoplankton However, you can say that most plants are not able to move from place to place. 10 Living things

11 Plants are green but animals are not Plants are green. Well, what about wheat in the summertime, fruit trees in the autumn? Most plants are green but some are not. What makes plants green? There is colouring matter called chlorophyll present in plants. Chloro- means green in Greek and -phyll means leaf. Therefore, chlorophyll means green leaf. Chlorophyll is present in any parts of plants that are green, such as leaves and stems and flowers. Are there animals that are green? You may have thought of animals like tree frogs, caterpillars, grasshoppers, tree snakes, praying mantis, sea horse or grass parrots. mantis frog Green animals sea horse There are quite a number of green animals, but most animals are not green. Animals do not generally contain chlorophyll even the green ones do not contain chlorophyll. Chlorophyll is generally only present in plants. Some marine animals such as giant clams and corals do contain some cells with chlorophyll in their bodies. But this is a special case and its more like these animals have plants living within their bodies. By now you probably have realised that identifying the differences between plants and animals is not as easy as you might have thought. In fact, the scientific community has used many different methods of sorting, or classifying, living things over the years. For example, writings from ancient China suggest that this culture used movement and growth to classify plants and animals. Lesson 6/20 What are plants and animals? 11

12 The classification system that is used by biologists today has developed from the ideas of other cultures. Additionally, the modern classification system has been greatly influenced by two technological developments. These are: the development of the printing press in 1440, because this enabled descriptions of living things to be communicated more easily between scientists the development of the microscope, because this enabled biologists to study living things more closely. So now, look at how modern biologists decide if a living thing is a plant or an animal. How do biologists classify plants and animals? Can you remember the name of the green chemicals in plants? This simple question leads into a way of classifying living things as plants or animals. Activity: Plants, animals and food Plants are green because they contain. The missing word is chlorophyll. Chlorophyll is an amazing substance. It can trap energy from sunlight. Plants take in carbon dioxide and water. These are the raw materials plants need to make their own food. Energy trapped by chlorophyll drives this process. The process is called photosynthesis. The word photosynthesis also comes from the Greek language. Can you deduce (work out) what it means? Remember photo- means light. Synthesis means to make or to put together. 12 Living things

13 What is photosynthesis? Photosynthesis means to make using light. This is how biologists group plants and animals. Plants make their own food using sunlight. On the other hand, animals cannot make their own food. Is this the only way that plants and animals could be classified? No. But this is the way scientists have decided to group plants and animals. Over the next few lessons, you'll learn more about what it means to call a plant a plant, and an animal an animal. Now that you have a list of the characteristics of living things you can further investigate the work of biologists. Are you making good progress? Try completing this summary in the exercise to find out. Go to the exercises section and complete Exercise Classifying living things. What did you achieve? Tick what you can do. list some benefits of classifying classify living things as either plants or animals list some differences between plants and animals Lesson 6/20 What are plants and animals? 13

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15 Suggested answers Check your responses against these suggested answers. Are there any other reasons to classify? Three benefits of classifying objects are that: it makes objects easier to find it is easier (and quicker) to communicate it is easier to identify or name unfamiliar objects. Classifying plants and animals Plants wheat dandelion grass pine gum tree Animals caribou butterfly bee cockroach sea urchin Lesson 6/20 What are plants and animals? 15

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17 Exercise Living things Name Teacher Exercise Classifying living things Fill in the blanks on this summary using the following words: food living things animals plants can be classified as plants or animals. Most can move from place to place. Most are green. Plants make their but animals cannot. Lesson 6/20 What are plants and animals? 17