My Science School

            Those animals with backbones have a much more developed skeletal structure and tend to be stronger than invertebrates. Therefore, invertebrates have to look for other means to protect themselves from danger.

           Many invertebrates have strong shells that substitute for a backbone. These external structures play an important role in their survival. The shells protect the invertebrates from predators. They also prevent their bodies from drying up when they are out of water.

          Other invertebrates have developed various ways to defend themselves. Some brightly coloured sea slugs taste so terrible that other animals do not want to eat them. Sea anemones possess numerous stinging tentacles, and sharp spines shield the sea urchins body. These are just some of the ways by which invertebrates survive.

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              What, do you think, would happen if we had no backbone? Our backbone not only supports our body, but also enables us to walk erectly. Without a backbone, vertebrates in general would not be able to survive in nature.

              However, as we have already seen, not all animals have backbones. Then, how do they survive? Internal and external skeletons help an animal to survive without a backbone. Some invertebrates have internal skeletons that support and protect their internal tissues. These skeletons are made up of different materials. Sponges have a framework of silica or other substances that stiffen their bodies. Others have external skeletons in the form of shells. Invertebrates belonging to the molluscs group have shells made of calcium carbonate, while those that are anthropods have external skeletons made up of a substance called chitin.

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              Have you seen the picture of the skeleton of a man? A strong backbone system supports our body. Man is able to stand erect or walk because of his backbone. Invertebrates are animals without a backbone. Of the millions of species of animals on the planet, 97 per cent are invertebrates. Common examples of invertebrates include snails, clams, insects, spiders, worms and molluscs.

              Do you think that all animals on Earth have the same body structure? Do insects such as caterpillars and bees have backbones like mammals such as bears and sloths? Even though they are all animals, insects and mammals have very different body structures! Caterpillars and bees are invertebrates.

              In the animal kingdom, invertebrates are actually the largest group. They make up 97 per cent of all animals on the planet. The total number of invertebrate species could be over 30 million. This number is much higher than that of the vertebrates, which is about 60,000. Invertebrates are also very diverse. They include animals living on the land and those living in the sea. Some examples are earthworms, centipedes, flies, sea stars, jellyfish and crawfish!

             Invertebrates have a long history of existence on Earth. Fossil records show that invertebrates even existed 600 million years ago. Invertebrates also have a big impact on other animals’ lives. They are a major food source for other animal species such as birds and fish. In agricultural production, some of them act as pests and parasites. This includes bugs like grasshoppers and ladybugs.

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              Classifying animals into groups was based entirely on observation initially. Our observation has a limited scope because we rely exclusively on our senses, which can sometimes deceive us. However, today, with modern equipment with more precision and accuracy, Man is able to do this job better.

              Animal classification now uses sophisticated scientific methods to identify relationships among species. Since the methods used to classify animals are continuously changing, there is the probability that the groups in which species are placed may change too. Occasionally, new species are identified!

               For example, until recently, elephants were classified into two species: African and Asian elephants. But DNA studies conducted in 2010 revealed that African elephants actually are of two distinct species- African bush elephants and African forest elephants. This, there are three species of elephants in the world now!

                                                                                                               

              Do you know that all the animals that we know have separate scientific names? Sometimes, it is very difficult to recall these names too. However knowledge of their scientific names would help us categorize animals according to their similarities and differences.

              The system of naming that we follow today is called the binomial system. It is the formal method of naming different species. Under the binomial system, each species is given a scientific name that is formed by the combination of two terms: the genus name and the specific descriptor.

              The genus is the major subdivision into which organisms are classified. The descriptor is the category into which the organism falls. For example, the scientific name for man is ‘Homo Sapiens’. ‘Homo’ is the genus name for animals that have large brains and use tools. ‘Sapiens’ is the category that pertains to modern humans.

              Here is a list of the binomial name of some common animals: Dog - Canis lupus, Cat - Felis catus, Horse - Equus caballus, Goat - Capra aegagrus hircus, Donkey - Equus asinus, Cow- Bos Taurus, Tiger-Panthera Tigris, Lion - Felis Leo, Indian Elephant- Elephas maximus indicus.

 

 

                 From the time language originated, Man starter naming animals. His scientific temper prompted him to order and categorize all living and non-living things for easier understanding. Man observed, named and compared animals and plants.

                 Aristotle, an ancient Greek philosopher, was the first known man to introduce the classification of animals. He classified species according to various characteristics, including whether they gave birth or laid eggs, or whether they were warm or cold-blooded.

                 The Roman naturalist Pliny the Elder wrote Naturalis Historia, a large work in which many plants were described. Naturalis Historia is also considered the first encyclopedia.

 

                 Over the years, animal classification became more scientific. The 16th century Italian philosopher Andrea Cesalpino classified plants according to their fruits and seeds.

                 The English naturalist John Ray published works on botany and zoology in the 17th century. He classified species according to the similarities that he observed, and was the first person to offer a scientific definition of the word species.

                 The Swedish botanist Carl Linnaeus of 18th century is known as the father of modern taxonomy. He popularized the binomial naming system, and introduced the use of kingdoms, classes, orders, genera and species. The Linnaean system is still in use today.

            When you are going to appear for an important examination, how would you prepare? If you try to read everything that comes your way, you would not be able to secure the best results. Studying something in a structured and orderly fashion makes it easier for comprehension. Ordering and classifying animals makes it easier to study them. Animal classification is the process of identifying, naming and organizing animal species into groups. The branch of science that deals with animal classification is known as taxonomy.

            Animals can be classified into two main groups: vertebrates and invertebrates. Vertebrates have backbones, while invertebrates do not. In all, there are more than 8 million animal species in the Kingdom Animalia and most of them are invertebrates.

            Each living organism is classified into Kingdom, Phylum, Class, Order, Family, Genus, and Species. There are five kingdoms. The two main kingdoms are animals and plants. Animalia includes animals and plantae, plants. The other kingdoms are Protista that includes single-celled organisms, Fungi that includes yeast, moulds, mushrooms etc., and Monera that include Bacteria.

            Some scientists say that there are five kingdoms, while for some others there are six. Other than Animalia, Plantae, Fungi, and Protista, they consider Archaea and Bacteria as other different kingdoms. For some other scientists, Monera is the fifth one, which includes Archaea and Bacteria.

 

 

 

 

 

 

 

 

 

 

 

 

 

          How many kinds of animals do you know? If you start writing down the names of the animals that you know, the list would be very long. There are innumerable animals in the world. However, we have found ways to classify them too.

          There are a million different kinds of animals, belonging to different species. Scientists have divided them into two main groups – those that have a backbone or vertebrates, and those that do not have a backbone or invertebrates. Some vertebrates are cats, dogs, horses and humans. Jellyfish, sponges, octopuses and squids are some examples of invertebrates.

          Within the vertebrate group, there are five different classifications. These classifications are mammals, fishes, amphibians, birds and reptiles.

          Of the millions of species of animals on Earth, 97 percent are invertebrates. Common invertebrates are insects, spiders and worms. Some of the major invertebrate groups are Porifera, Cnidaria, Platyhelminthes, Nematoda, Mollusca, Annelida, Echinodermata and Anthropoda.

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Science was never satisfied with the creation myths of various religions that explained the origin and development of life on Earth. Charles Darwin, an English naturalist, provided a solution in the form of a theory called the Evolution Theory in 1859.

            According to Darwin, the living things we see today have evolved gradually over millions of years. This theory also says that different species may show some similarities because they have evolved from a common ancestor. Charles Darwin explained that different species evolve by a process known as natural selection.

            The characteristics of each individual are determined by extremely small pieces of genetic material called genes. Genes are present in the nuclei of the body’s cells. Sometimes, certain changes, known as mutations take place in the genes. These mutations cause the formation of new characteristics in individuals. Some mutations are harmful, and make it difficult for the babies to survive. Animals that possess these harmful mutations may not be able to compete with other animals for food and space to live. Therefore, they will gradually die. Other mutations make animals more fit and able to survive in new conditions. These animals will gradually increase in number. In this way, Nature selects those animals and individuals who are best suited to survive in a changing environment. This is called natural selection.

            The giraffe is an excellent example of natural selection. Animals that had longer necks than others were able to reach up higher and get more food. They survived, while those with shorter necks could not compete with them and, therefore, died.

 

 

 

 

 

 

 

 

 

 

 

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          While the oceans provided the most conducive atmosphere for the occurrence of life, the dry lands offered further opportunities for growth and development. In the process of evolution, the movement of animals from the oceans to land was an important milestone.

          In the earliest stages of life on earth, organisms lived only in the sea. Single-celled organisms gradually developed into multi-celled organisms. The first forms of plant life were algae, lichens and mosses. These plants provided food for the early forms of animal life in the sea.

          In the course of time, in fact, millions of years, new forms of plant life developed. These new plants were more complex. They had some new features such as roots, stems and leaves, which made it possible for them to survive on land as well. Giant horse-tail plants and tree ferns started growing on land, mostly in wet, swampy areas on land.

         When there was food available on land as well, animal life gradually began to evolve in order to survive on land. The availability of food was an important factor in the movement of animals to land. The first animals to move to land were probably worms and other soft-bodied invertebrates. They were followed by certain fishes that developed limbs to crawl and lungs for breathing. Reptiles that could live on both land and water came next. Such animals, as you know, are called amphibians.

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            We cannot travel to the past to see how life began on Earth. All we can do is to speculate and hypothesize. Some scientists tried to recreate the prehistoric past when life was non-existent and the earth had just started cooling down. Stanley Miller, an American chemist, conducted many experiments in this regard and tried to prove how life came into existence.

             Miller conducted an experiment in 1953, which shed light on the sprouting of life on Earth. He filled a laboratory flask with a mixture of gases.

            These gases were similar to those that made up the atmosphere of the earth billions of years ago. He then fired electrical sparks through the gases for a week. The electrical sparks had the same effect on the gases in the flask that bolts of lightning had on the earth’s atmosphere before the appearance of life.

            The results were revelatory. Miller discovered that a variety of substances had formed in the flask, including amino acids and sugars, which are necessary for life to occur. From Miller’s experiment, scientists concluded that the fierce flashes of lightning  that were common during the early days of the earth reacted with the gases in the atmosphere to produce the substances necessary for introducing life on Earth.

 

 

 

 

 

 

 

 

 

 

 

 

              Have you tried to stay underwater holding your breath? We cannot live in a sea or river like a fish, because our body cannot take oxygen from water. However, there are innumerable organisms in oceans. In fact, life began in water.

              Two-thirds of the surface of the earth is covered with water. Oceans and seas were formed very long ago, long before there were any plants, animals or people on Earth. The earth was made up of red-hot rocks then. When they cooled, they gave off steam. This steam became rain, which fell and filled up the hollows and deep holes in the earth’s surface to become oceans.

              The first life was not as complex and developed as it is found now. It probably was one-celled organisms. The first plants that appeared on this planet were microscopic, single-celled organisms floating in the world’s oceans, billions of years ago. That is why we say that life began in water, and not on land.

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               From time immemorial, the question of how this Universe came to be has haunted Man’s mind. While ancient Man chose to believe in the easiest answer that everything came into existence-through an act of God, modern science persisted with rational enquiries that proved otherwise. Have you ever wondered what it must have been like millions and millions of years ago, when the earth first came into existence? Were there plants and animals then?

               When the earth was first formed, there was no life on it. Its surface was extremely hot and had giant volcanoes that threw fiery rocks, dust, and gases into the air. Scientists estimate that the first life forms on Earth were primitive, single-celled organisms. They must have appeared about three billion years ago in the oceans. They had no bones or shells, so they looked more like worms and jellyfish. These one-celled organisms gradually became multi-cellular organisms. As time passed, more complex forms of life began to fill up oceans. One of the first forms of life was a very simple plant called algae. Different types of plants came later on. And so, yes, animal life appeared only after the appearance of plant life.

            You must have observed huge trees in your own backyard that have been staying in the same place for years, without any explicit signs of movement. Unlike animals, trees cannot move about, eat through the mouth, express emotions and communicate their needs. Plants and animals are as different from each other as a rose is from a rabbit!

            Generally, plants, with a few exceptions like the swimming algae, cannot move about from place to place, while animals can move freely. One of the most distinguishing features of plants is that they can make their own food with the help of their green colouring, which is called chlorophyll. On the other hand, animals must rely on plants for their food, or hunt other animals. Animals have a nervous system, which makes them sensitive to touch, heat, cold, pain, and other stimuli. Plants lack such a nervous system. However, as you must have observed, some plants such as the touch-me-not, do fold their leaves when touched. Others sense that a support is near, and twine themselves around it.

            The cell structure of plants and animals is different too. Most plants have rigid cell walls and contain cellulose. Animal cells do not have cellulose. The development of animals and plants is different too. While animals stop growing when they reach maturity, plants do not stop growing until they die!

 

 

 

 

 

 

 

 

 

 

 

            Life is what makes our planet different from the rest of the known universe. There are diverse forms of life on our planet. Living beings such as ants, beetles, fishes, sparrows, cats, dogs and cows have always fascinated us in several ways. Green plants like grass, shrubs, bushes and tall trees have also caught our imagination. While trees and plants are stationary, animals can move around.

            The word animal comes from the Latin word ‘anima’. It means ‘life’ or ‘breath’. Animals are living organisms, often belonging to a family or herd. They eat food, move about, and are capable of taking care of themselves. However, the simplest animals are very much like the simplest plants. Sometimes it is difficult to differentiate between the two.

            There are some telling differences between plants and animals. These are very clear when you look at the more highly developed animals. Plants have the ability to prepare their own food. However, animals eat plants or hunt down other animals. This characteristic of animals means that they have to be able to move about.

            On the other hand, things are not so clear-cut when you look at organisms that are made of only one cell. Sometimes, it is hard to tell if they are animals or plants. Bacteria, for example, can have characteristics of both animals and plants.

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