2. LIVING THINGS 2.1 THE CHARACTERISTICS OF LIVING THINGS

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1 2. LIVING THINGS 2.1 THE CHARACTERISTICS OF LIVING THINGS The study of living things is called biology. In biology, living things are often called organisms. There are more than different kinds of living organisms - kinds like grasses and ants, seaweeds and sharks, palm trees and people. But how do we know whether something is living or not? When we observe animals moving and feeding, it is obvious that they are alive. But plants are alive too. We can see that plants grow. Plants also make seeds that grow into new plants. All living organisms move, feed, grow and reproduce their own kind. Movement, feeding, growth and reproduction are four characteristics of all living things. Three more are respiration, excretion and sensitivity. Each of these seven characteristics is explained below. Movement Most animals can move freely from place to place. They can also move different parts of their bodies. Plants do not move from place to place, but some of their parts can move slowly. The leaves and flowers of many plants turn to face the sun every day. Buds open and flowers open and close. Roots, stems and branches grow out in different directions. Feeding Animals eat plants or other animals to stay alive. Plants also need food, but they make their own. To make food, the leaves take in carbon dioxide gas from the air, and the roots take in water and other materials from the soil. Growth All living things grow. Most organisms change in various ways as they grow. Reproduction All living things produce young ones of their own kind. This is called reproduction. Some animals reproduce by laying eggs but others produce live young. Many plants make seeds or spores from which young plants grow. In other cases, new plants may grow from the roots or stems of a parent plant. Excretion All living things have to get rid of waste products. This process is called excretion. Many animals excrete by urinating and in other ways. Excretion also takes place in plants but is more difficult to observe. Respiration All living things need oxygen from the air, as well as food, to obtain energy. This process is called respiration. We can see part of this process in many animals when they breathe. But in some animals, and all plants, it is much harder to observe. (We will study respiration in Chapter 6). Sensitivity All living things react to the world around them. Reacting to things is called sensitivity. Animals react quickly to things they see, hear, smell or feel. Plants also respond to things around them, but only very slowly and in a more limited way. 12

2 2.2 INTRODUCING PLANTS There are more than different kinds of plants. The biggest plants are the giant redwood trees in North America. These trees can grow over 100 m tall and weigh more than 6000 tonnes. Some plants called duckweeds are so small that we need a microscope to study them. One of the most important characteristics of plants is that they make their own food. This happens in green leaves, which take in carbon dioxide gas from the air. The carbon dioxide is combined with water and other materials that are taken from the soil by roots, and then passed up a stem to the leaves. The diagram below shows the structure of a typical plant and the names of its main parts. Pull up a small weed. Observe your plant carefully and make a simple labelled drawing of it. The other pictures on this page give some idea how different plants can be. Palm trees and pandanus Apple of Peru (a common weed) Forest trees and vines Bamboo forest Savannah grassland Water lilies and pond weeds 1. Which of the following are organisms? grass, people, clouds, flies, rocks, trees, fish, moon, snakes, rivers, birds. 2. What are (i) reproduction, (ii) respiration, (iii) excretion, and (iv) sensitivity? 3. How many different plants are named on this page? Make a list of them all. 4. List as many differences as you can between animals and plants. 13

3 2.3 INTRODUCING ANIMALS Animals can differ from one another even more than plants. In fact, there are probably over two million different kinds of animals. The largest is the blue whale, which can grow up to 30 m long and weigh about 200 tonnes. On land, the tallest is the giraffe, which can be over 6 m tall, and the heaviest is the African elephant, which can weigh over 12 tonnes. The smallest animals are some tiny creatures less than 0.2 mm long. You would need a microscope to see one properly. Animals cannot make their own food. Some animals eat plants and some eat other animals. The diagrams below show a few common kinds of animals with the names of some important parts. If you can, try to observe and draw some animals yourself. D.G.Mackean Bird Antelope Fish Lizard D.G.Mackean Insect Snail 1. Which are the biggest, the biggest animals or the biggest plants? 2. On this page, what has (i) wings, (ii) four legs, (iii) six legs, (iv) a foot but no legs, (v) hooves, (vi) scales, (vii) eyes on stalks, (viii) compound eyes, (ix) horns, (x) antennae? 3. What do each of the following have instead of front legs? (i) a human being, (ii) a bird, (iii) a fish, (iv) a snail, (v) a snake. 4. What do the deer, bird, fish and lizard all have, that the insect and snail do not have? (Hint: It is something inside!) 14

4 2.4 CLASSIFICATION AND KEYS Classification means putting things into different sets or classes. This is an important part of summarising our observations. Look at the eight objects on the right. How would you put them into two sets? There are many ways, but most students choose FOOD for one set, and the regular shapes for the other. The regular shapes are models of CRYSTALS. How can you divide the food into two sets? One way is to choose FRUIT and VEGETABLES. The orange, lemon and banana are fruit, and the sweet potato is a vegetable. Then we could divide the fruit into two sets. For example the orange and lemon are very similar inside and come from very similar trees. They are called CITRUS fruits. The banana is quite different inside and comes from a very different kind of tree. The model crystals can be divided into sets too. For example cubic crystals and diamond shaped crystals - or white crystals and coloured crystals. Keys are instructions for sorting things out into sets or classes. A key can be drawn as a diagram, or written as a list of instructions. The diagram below is a key for the objects we have just been classifying. Study it carefully. Start at the top and follow the instructions step by step as you go down. At each step are instructions for dividing the objects into smaller and smaller classes. You will also find the name for each class in capital letters. Right at the end of the key, is the name for each object. ALL THE OBJECTS Biological kingdoms There are more than three million different kinds of living organisms. Biologists start by classifying most of these into two huge sets called the animal kingdom and the plant kingdom. Three smaller kingdoms are also recognised by most biologists: fungi (mould, mushrooms and similar organisms) monera (tiny organisms called bacteria and blue-green algae) protista (seaweeds and many tiny organisms) things we can eat FOOD regular geometrical shapes CRYSTALS has seeds in it no seeds in it shaped like a shaped like a FRUIT VEGETABLE CUBE DIAMOND sweet potato round shape long shape white black white yellow CITRUS banana rock salt lead ore alum sulphur orange/lemon 1. Name 5 kingdoms of living organisms. To which kingdoms do each of these belong: insect, grass, mushroom, cassava, fish, mould, seaweed? 3. In the key above what is: (i) something we can eat that has no seeds in it, (ii) a regular geometrical shape, shaped like a diamond, and white? 2. (i) In the key above, to what class do the orange and lemon belong? (ii) Extend the key to distinguish between these two. 4. How does the key above describe the differences between (i) the crystals and the food, (ii) the fruit and the vegetable, and (iii) the rock salt and the lead ore? 15

5 2.5 CLASSIFYING PLANTS A key for classifying plants is shown on the next page. The same key is given in written form in the box below. Study both versions of the key before you read on. Biologists classify plants into four main divisions: bryophytes, ferns, conifers and flowering plants. The flowering plants are divided into two classes, monocots and dicots. Mosses are plants that have no proper system of roots and stems. Because they have no stems to carry water, they must grow close to a wet surface. The most common examples are green mosses that grow on damp soil, on rocks close to streams, and on the bark of well shaded trees. A simple key to plants 1. Plant has a system of roots and stems GO TO 2 Plant has no proper roots and stems MOSS 2. Plant has fruits GO TO 3 Plant has no fruits FERN 3. Plant has flowers GO TO 4 Plant has no flowers, fruit is woody cone CONIFER 4. FLOWERING PLANT Spear-shaped leaves with parallel veins Variable leaves with a network of veins MONOCOT DICOT Ferns are plants that have proper roots and stems, but do not bear fruits. There are many different kinds of ferns. They often grow in damp places, and have very beautiful leaves with many parts. Mosses covering stones Ferns Conifers are plants with no flowers, but they have fruit in the form of woody cones. Almost all conifers are trees with tough, needleshaped leaves. The most common conifers are the many different kinds of pine trees. They often form huge forests, especially in cold countries. Pine trees are used for timber and for making paper. Pine tree Flowering plants are much the most common kinds of plants. Almost all the plants we will study in this book are flowering plants. They are divided into two classes: monocotyledons (or monocots for short) and dicotyledons (or dicots). Monocots have spear-shaped leaves in which the veins are nearly parallel to one another. The seeds contain only one fleshy seed-leaf (cotyledon). We will talk more about seeds in Chapter 5. The monocots include our cereal crops, grasses and bamboos, palm trees and bananas, and a group of plants called lilies. Dicots have leaves of many different shapes in which the veins form a network. Their seeds contain two fleshy seed-leaves (cotyledons). Many common bushes and trees are dicots; so are most of the plants we get our fruits and vegetables from. 1. Do all monocots have fruit? (Clue: use the key). 2. What plants have (i) roots and stems but no fruits, (ii) roots, stems and fruits but no flowers, (iii) two cotyledons? 3. Is a fern a monocot or a dicot? 4. Use the key to list as much information as you about all plants that are dicots. 16

6 A simple key to plants PLANTS plants have a system of roots and stems plants have no proper system of roots and stems MOSSES eg mosses plants have fruits plants have no fruits FERNS eg ferns plants have no flowers, fruit forms woody "cones" CONIFEROUS PLANTS eg pine trees plants have flowers FLOWERING PLANTS leaves spear-shaped with parallel veins, seeds have one cotyledon MONOCOTS eg grasses. lilies, bananas, palms leaves variable with network of veins, seeds have two cotyledons DICOTS eg yams, tomatoes, hibiscus and many bushes and trees Pine tree and cone 17

7 2.6 CLASSIFYING ANIMALS - INVERTEBRATES Biologists classify animals into many large sets called phyla (singular phylum). Animals with backbones belong to the phylum vertebrates. We will look at vertebrates in Module 2-7. Animals in other phyla have no backbones and are called invertebrates. The keys below and on the next page show three important phyla of invertebrates called molluscs, annelid worms and arthropods. Molluscs are invertebrates like snails and seashells. They have soft bodies and usually carry hard shells which they can hide inside. There are about different kinds of molluscs. The largest are squid which swim in the oceans. Squid have long tentacles to catch their food and their shells are inside their bodies. Some grow up to 45 m in length. Many molluscs are edible and their shells are often used to make beautiful ornaments. A simple key to animals 1. Animal has a backbone (Vertebrate) GO TO MODULE 2.7 No backbone (Invertebrate) GO TO 2 2. Soft body and hard shell MOLLUSC Soft, round, long, thin body, segments ANNELID WORM Hard covering, jointed legs (Arthropod) GO TO 3 3. Six legs INSECT Eight legs ARACHNID More than eight legs GO TO 4 4. Four antennae, body segments all different CRUSTACEAN Many body segments and legs, all the same MYRIAPOD Annelid worms include earthworms, which live in the soil. There are about 9000 different kinds. They all have soft, round, long, thin bodies divided into many segments, and they have no legs. (Worms with flattened bodies, and worms with no segments, belong to quite different phyla. They are not annelid worms). Earthworms help to make the soil more fertile and better for growing crops. Leeches are annelid worms that feed by sucking the blood of larger animals, including human beings. In the past, doctors used leeches to try to cure fevers! They believed that people with fevers needed to loose some of their blood. Arthropods have bodies with several segments, each covered with a hard outer casing. The name arthropod comes from two Greek words, arthron (joint) and pod (foot). Arthropods have bent legs with movable joints. They are divided into four main Classes: insects, arachnids, crustaceans and myriapods. Insects have six legs and three segments, head, thorax and abdomen. All insects have two antennae and most also have wings. Insects are very successful animals. There are more than different kinds and billions and billions of individuals. Although each one is not very big, the total mass of all the insects in the world is greater than the mass of all the other animals put together! Although some insects like houseflies, cockroaches and mosquitos are pests, many are useful to us, either directly or indirectly. Arachnids have eight legs and only two segments, head and abdomen. They have no antennae and no wings. Common examples are spiders, ticks and mites. Ticks and mites live on the blood of larger animals and may spread diseases. Many spiders are useful because they catch and eat insects. Crustaceans are like crabs and scorpions. They have more than eight legs and four antennae. All their segments are different from one another. Some of their legs may be different too, and some may end in claws. Lobsters, crabs and prawns are eaten by many people. Scorpions have a powerful sting in their tails. D.G.Mackean A scorpion Myriapods include centipedes and millipedes. Their bodies have many, identical segments. Centipedes have two legs on each segment, but millipedes have four legs on each segment. 1. What are (i) invertebrates, (ii) phyla, (iii) squid, (iv) leeches, (v) myriapods. What does the word myriapod mean? 2. What animal has eight jointed legs? 3. State one way each of these is useful: (i) crab, (ii) earthworm, (ii) spider, (iv) mollusc, (v) insect. 4. List all you can find out from the keys about crustaceans. 18

8 A simple key to animals (invertebrates) ANIMALS animals have no backbone INVERTEBRATES animals have a backbone VERTEBRATES (See Module 2.7) animals have a soft body animals have a soft, round, long, thin animals have segments with hard and (usually) a hard shell body, divided into many segments outer covers, and jointed legs MOLLUSCS ANNELID WORMS ARTHROPODS eg snails, seashells eg earth worms, leeches Snail Earthworm animals have more than 8 legs animals have 4 antennae; animals have many identical animals have 6 legs animals have 8 legs body segments all different body segments and legs INSECTS ARACHNIDS CRUSTACEANS MYRIAPODS eg house fly, beetles, butterflies eg spiders, ticks eg scorpions, crabs, prawns eg centipede, millipede D.G.Mackean 19

9 2.7 CLASSIFYING ANIMALS - VERTEBRATES Vertebrates are animals with backbones. There are over different kinds of vertebrates and more than half of them are fish. The other main classes are amphibians, reptiles, birds and mammals. The keys below and on the next page show how we can sort them out. Fish are covered in scales and have fins. They live in water and breath through gills. They range in size from certain sharks, which can grow up to 18 m long, to tiny fresh water fish called gobies, which measure only a few mm. Most fish are good to eat, so fish like Tilapia and Carp are farmed in many countries. Reptiles are also covered in scales but have no fins. All reptiles except snakes have four legs. Most reptiles live on the land including many kinds of A simple key to animals 1. Animal has a backbone (Vertebrate) GO TO 2 Animal has no backbone (Invertebrate) GO TO MODULE Body covered in scales GO TO 3 Body not covered in scales GO TO 4 3. Animal has fins FISH Animal has no fins REPTILE 4. Body covered in feathers BIRD Body not covered in feathers GO TO 5 5. Animal has hair or fur MAMMAL Animal has smooth skin AMPHIBIAN lizards. Turtles live in the sea, but come to the land to lay their eggs. Reptiles are generally harmless, but a few are dangerous. Crocodiles may attack and eat people and some snakes have very poisonous bites. Some large snakes such as pythons squeeze their prey to death. D.G.Mackean Blue whale Birds are covered in feathers except for their legs, which are scaly. They have a beak for a mouth and wings instead of front legs. Most birds can fly, except for a few very large ones like the ostrich and the emu. Ostriches can be over 2½ m tall, but some humming birds are less than 6 cm long. Peregrine falcons are the fastest fliers. They can reach speeds of 290 km/h when diving on prey. We Toad keep the domestic fowl for food and for its eggs, which are good to eat. Amphibians have smooth skins that they like to keep cool and damp. They have four legs and webbed feet, and lay their eggs in water. Frogs and toads are amphibians. They have very strong back legs. Some frogs can jump over 5 m. Mammals usually have hair or fur covering all or part of their skin. Female mammals have milk glands for feeding their young. Most mammals live on land and have four legs, or two legs and two arms. A few mammals such as whales and dolphins live in the sea and have flippers instead of legs. We keep mammals such as sheep, goats and cattle for food and we sometimes use their skin for clothing. Some mammals are also used for riding or pulling loads. 1. From the key, what three things do all fish have? scales? toad, centipede, snake, goby, hen, whale. 2. Do each of the following have (i) a backbone, (ii) 3. Try to list all the ways people use mammals. 20

10 A simple key to animals (vertebrates) ANIMALS animals have backbones VERTEBRATES body covered in scales body not covered in scales animals have no backbones INVERTEBRATES (See Module 2.6) animals have fins animals have no fins body covered in feathers body not covered in feathers FISH REPTILES BIRDS eg shark, tuna, Tilapia eg snake, lizard, turtle eg vulture, parrot, hen, finch animals have fur or hair MAMMAL eg cow, dog, rat, whale animals have smooth skin AMPHIBIAN eg frog, toad 4. What kind of animal is this? 21

11 2.8 FOOD CHAINS Living organisms depend on one another in many ways. One way they depend on one another is for food. Only plants make their own food. Animals must eat either plants or other animals. Plants use energy from sunlight to change carbon dioxide from the air, and water from the soil, into the food they need. This process is called photosynthesis. The word photosynthesis comes from two Greek words, phot (light) and synthesis (putting together, making). So photosynthesis means making with light. Animals that eat only plants are called herbivores. Sheep, goats and cattle are domestic animals that are herbivores. Many invertebrates are herbivores too. For example earthworms eat dead leaves, and snails and many insects eat the leaves of living plants. Animals that eat other animals are called carnivores. Lions, tigers, wolves and birds of prey are carnivores, and so are the domestic cat and dog. Carnivores mostly eat herbivores, but they sometimes eat other carnivores too. But even carnivores depend on plants. If there were no plants, there would be no herbivores for them to eat! The way in which living organisms depend on one another for food is called a food chain. A basic food chain eaten by eaten by eaten by PLANT HERBIVORE CARNIVORE CARNIVORE eaten by eaten by grass goat humans eaten by eaten by eaten by leaf insect bird cat Biologists call plants producers, because they produce food for all other living things. Herbivores are called primary consumers. They are the first to consume the food made by plants. Carnivores are called secondary consumers because they consume the food made by plants at second hand. 1. What are (i) producers, (ii) herbivores, (iii) secondary consumers, (iv) food chains? 2. Humans are omnivores. (i) What does this mean? (ii) Are humans primary or secondary consumers? 22

12 2.9 ADAPTATION Living things are everywhere. Many animals and plants live on top of the ground as we do. But some live under the ground and even in the soil. Others live in ponds, rivers and lakes. The sea is full of living things and so is the air. Organisms live even in the hottest and coldest and driest places on Earth. The kind of place where any organism lives is called its habitat. Water is the habitat of fish and trees are the habitat of monkeys. Every organism has to be fit for its own habitat. A fish cannot live in trees and monkeys cannot live under the water! The ways in which different organisms vary, so that they can live in different ways, in different habitats, are called adaptations. A fish is adapted to living in water. It has gills, which enable it to breathe under water, and fins for swimming. The gills and the fins are two of its adaptations. They help to make the fish fit for its watery way of life. Every living organism is adapted to its own special habitat and way of life. Some adaptations in plants. The funny looking tree on the right is called a baobab. Some people say it was planted upside down! The baobab grows in parts of Africa where rainfall is uncertain. It stores water in its huge trunk and fat branches. This enables it to survive a long drought. We can say that its fat shape adapts it for the climate. A baobab tree All plants need sunlight for making their food (by photosynthesis). They are adapted to expose their leaves to the sun in different ways. Trees have long trunks and branches that push their leaves high up towards the light. The stems of vines have special roots, suckers or tendrils. These adapt them so they can climb over other plants to reach the sunlight. Plants such as grasses and creepers are adapted to catch sunlight by spreading out and covering large areas of ground. Birds and their beaks Some adaptations in birds. Birds provide some good examples of adaptation. They are adapted for flying in several ways. Compared to other vertebrates, their bodies are very light. They have wings instead of front legs, and very big chest muscles for flapping them. These muscles are the breast meat we enjoy when we eat roast chicken! The beaks of different birds are adapted for eating different kinds of food. Look at the drawings and decide what each bird eats. The eagle is a carnivore. It has a strong, hooked beak for tearing flesh. The parrot has a powerful beak for cracking nuts. The kingfisher uses its long, sharp beak to spear small animals or fish. The honeyeater drinks nectar from flowers with its long thin beak. The duck's broad beak is adapted for pulling up weeds from the bottom of ponds or streams. And the mynah bird, which eats many different kinds of food, has a medium sized, all purpose beak. 1. What do we mean by (i) habitat, (ii) adaptation? 2. How are (i) fish adapted for living in water, (ii) birds adapted for flying and feeding, (iii) monkeys adapted for living in trees? 3. Think about any different birds you know. How are their feet adapted for the different ways in which they use them? 4.Say how one plant and one animal you know are adapted to their habitats and ways of life. 23