My Science School

            The kingdom of animals has always been a source of fun, amusement and entertainment for man. We often discover very amazing and interesting features and characteristics in some animals that are peculiar and unique to those animals only. Now when we say there exists a type of bear which wears spectacles, it sounds amazing. But is it true?

            The truth is that the visual appearance of its face gives the spectator an impression that it has put on a pair of glasses. In reality, lines of lighter fur of white colour encircle its eyes and these circular markings around the eyes look like spectacles from a distance. 

            This ‘spectacled bear’ is found in tropical South America. It is very small in size. An interesting pattern is made on its facial area when a creamy yellow snout with fur of the same colour runs down from the nose and sometimes it makes a ring around the eyes and then cross the nose. These rings are the so-called ‘glasses’. It is also called the Andean bear. Some of them have only the bottom half of their glasses, whereas, some have the eye-rings so thick that they completely fill the face.

            Although there is only one species of the spectacled bear, Tremarctos ornatus, there are different kinds of facial markings within the same species. Though all bears can climb trees, the spectacled bear is particularly expert at clambering through the branches to feed on leaves, fruits and nuts.

             The ‘spectacled bear’ is the smallest among the bears. The adult is up to 64 cms 2 feet at the shoulders, 120 to 180 cms (4-6 feet) in total length, with about a 7 cm long (3 inch) tail. The colour of its shaggy coat varies from dark brown to black. It weighs less than 135 kg. Although it may feed on small mammals, deer, guanacos and vicunas, its diet mainly consists of fruits and leaves. It usually lives in cool mountain forests.

            Litters of one to three cubs have been born in captivity after a gestation period of 8-8 months. 

               The twittering of birds usually produces a pleasant sensation, especially in the spring in countryside. Some birds produce very sweet sounds while others produce harsh and unpleasant sounds. Do you know why birds sing?

               The songs and calls are important methods of communication among birds. They sing to attract mates in the mating season, to warn other birds of any incoming danger from predators, and to establish their home territories or nesting area. The bird calls are usually distinctive and vary from species to species. This distinction helps the birds to identify the calls meant for them.

               Among all the species of the singing birds, the male bird is usually the singer. It sings to attract the female bird. The songs of nightingale produce the best musical effects and other birds do not match it in comparison. The mocking bird has its own harsh call but can imitate the songs of other birds. Crow has a very crude voice.

                Apart from singing, birds make other types of calls — call for sending alarm signals, for food or calling their parents, call in an aggressive or hostile mood etc. A few birds, such as pelicans and cormorants, are voiceless.

               The singing birds belong to the suborder oscines. Their vocal cords are located in a special box, the syrinx, at the base of the windpipe where it divides into two bronchi. The syrinx has a bony structure and forms a sound-box within which membranes vibrate when the bird exhales. This produces varying notes in the bird’s voice. The structure of syrinx varies from species to species and till now seven different types have been recognized.

               The songs of the birds have a pitch of about 4300 Hertz, which is above the highest note of a piano. Intensity of the calls of any single bird varies from the deep-pitched hoot of owls to the very high notes of small birds which are scarcely audible to the human ear. 

            There are several species of birds on earth which cannot fly because they stopped using their wings for flying many thousands of years ago. Perhaps neither the environment around them nor their living conditions required them to fly. Generally birds fly either to protect themselves from enemies or in search of food. These flightless birds either lived in places where there were no enemies to prey on them, or were so big that they could rely on their legs to carry them out of trouble. As a result, their wings almost fell into disuse and gradually they became flightless. Do you know which are the birds that cannot fly? 

   

 

        First of all we have the Penguins. They turned their wings into paddles or flippers. As a result they cannot fly but they are excellent swimmers. These birds mainly live in the southern hemisphere – mostly at the edge of Antarctica. 

 

 

 

            

 

                The Kiwis of New Zealand took to living by night, finding its food by smell and almost ceased flying. Gradually the bird became flightless. Also it almost stopped using its eyes and today it has very poor eyesight. Now these birds have small wings which are hidden by hair-like feathers that cover the body. 

Continue reading "Which birds cannot fly? "

               The most surprising fact about fishes is that you cannot hear them but, they can certainly hear you. Fishes are very well-equipped for hearing. They have a pair of ears. These ears do not have an outer projection as we have, but are simply tiny holes on either side of the head, leading to the inner ear. Since there is no external ear to direct the sound, these ears are probably not as effective as our own. But the fishes have other ways of picking up sounds of vibrations in the water. 

              Along each side of the fish’s body is a line of little holes or pores, which can also pick up vibrations and changes in pressure inside water and pass on the message to the brain. This line of pores is called the lateral line, and can be seen quite easily.

               By using this lateral line a fish can avoid all obstacles when it is extremely sensitive to pressure changes caused by the vibrations of another fish or some other objects. A fish’s lateral line contains sensory cells which provide the fish with all the information of events going on around it.

                   Some other teleost fishes such as catfish that lives in rather muddy water have barbells — long sensitive feelers on their mouths.

                   The fishes of the ‘carp’ family have tiny bones in the head which are linked to the swim bladder. The swim bladder keeps the fish upright in water and also acts as a sounding board which can pick up and magnify the tiniest vibrations, and then pass them along the bones directly to the inner ear.

                   These are the different mechanisms in the fishes by which they can even hear very feeble sounds. 

                There are certain peculiar types of bugs called ‘Back Swimmers’ (Greater-water Boatman) that can swim upside down. These back-swimmers are also called boat bugs. Although they spend most of their lives in water, they are able to fly long distances. These insects are small, usually 3 to 17 mm (0.13 to .63 inch) in length. Instead of wings they use their legs to swim. They swim on their backs and make use of their hind legs to paddle through the water. These flat ‘paddles’ are ideal for swimming, and are often made even more efficient by a fringe of hairs which runs down each side. This makes a broader surface to push against the water. The insect uses its short front legs for holding the prey.

                Back swimmers hold a bubble of air between their wings and body. This air is used for breathing when they are underwater. This lets them stay underwater for as long as six hours. In winter, back swimmers bury themselves in the mud at the bottom of a pond or stream.

                They have sharp beaks which they use for stabbing fish and other small water animals and suck out their juices. Back swimmers sometimes even bite human beings.

                These creatures belong to Notonectidae family which has in all about 200 species. They are found generally all over the world. They cause great harm to fishes and tadpoles. They deposit their eggs in the plant tissue of pond vegetation. 

                    When a cat wants to express contentment or pleasure, it purrs. Purring of a contented cat results in a low vibrating noise. It is a kind of low, continuous rattling hum and has nothing to do with a cat’s real voice. A mother cat purrs when it wants to call her kittens for feeding. At birth the kittens cannot see, hear or smell. So in the initial stages after birth, it is the purring of their mother that helps them to communicate with her. Once the kittens start feeding themselves, the mother stops purring. It implies that purring began as a kind of homing device.

               Now the question arises how a cat produces the purr? 

               Purr is caused by the vibrations in a cat’s vocal cords. When a cat takes air into its lungs, the air passes through the voice-box that contains the vocal cords. If the cat then wants to express its satisfaction about something, it will allow the vocal cords to vibrate as the air passes in and out of the lungs during breathing. When it chooses not to purr, the passing air does not affect the vocal cords and thus doesn’t produce any such sound.

                Although there are many other members of the cat family such as lion, tiger, leopard, cougar, jaguar, ocelot and lynx, their throat structure is quite different from a cat and hence they cannot purr. However, they can make other kinds of sound.

               It is said that only man has highly developed reasoning faculties and hence can think and act accordingly. But there are animals that sometimes, with their superior senses excel man in certain activities. For example, dog has an excellent power of smell and often helps man in his day-to-day life. Like man there are some animals who take reasonable care of their offspring. But how do these animals recognise their young ones?

               Among the animals where parental care is prevalent, it is important for the mother and her young ones to recognise one another, so that they do not lose contact. This is done through one of their four senses: smell, sound, sight or touch.

               Most of the mammals recognise their offspring by smell. It is a common practice among dogs, deer, sheep, horses and seals.

               It's interesting to note that among a flock of sheep every mother can recognise her own young ones by smell and ignore others. Among some other animals, when a young one is born, its mother sniffs it and the smell remains in her memory. Thereafter the mother easily locates her baby by sniffing all the babies around until she finds her own.

               Among the birds recognition is more by sound. Each parent bird has her own special ‘mother call’ which the baby immediately recognizes on hatching. An Austrian naturalist, Dr. Konard Lorenz, has made a special study of geese. He conducted his study just before some gooslings were about to hatch. He immediately removed the mother goose and sat by the eggs himself. As the babies hatched he gave the ‘mother call’. As a result, they followed him everywhere believing him to be their mother as they recognized only the sound. But since he was too big for the young geese they got confused when he stood up. However they were quite happy to follow him when he crawled about on hands and knees.

               To some animals, shape and size also matter as the sense of touch also plays an important role in the recognition of young ones.

 

                           The botanists study the internal structure of plants mainly by examining their cross section under a microscope. These thin slices can tell us a lot about the structure of the cells that make up the plant and how they vary in different parts of the plant. In 1665, a scientist named Robert Hooke looked at a piece of cork (a material from the thick outer part of certain trees) under a microscope and saw that it was made up of many tiny compartments. He named them cells and this term has been in use since then. The equipments needed for obtaining the sections include a sharp razor, a small fine brush and a number of watch glasses and microscopic slides. The razor is stroked across the top towards the body, cutting off thin slices as required. Cross-sections as well as the longitudinal pieces are obtained in the same manner. To obtain best results the razor and the material must be kept moist with water in case of fresh material or alcohol if the specimen is a preserved one. To prevent shrinkage the sections shaved off are brushed into water or alcohol. For quick examination the sections are placed on a slide with a drop of glycerine. The thin ones that show the cells clearly can be stained for permanent use. In fact staining is a process of adding dyes to show the different tissues in different colours. Many stains are dissolved in alcohol and before staining the sections must be placed in alcohol. After a certain period in the stain(s) the section is transferred to a series of watch glasses full of alcohol. This removes water and the excess stain. The alcohol is removed by dipping the sections in clove oil or benzene. The section is then placed on a clean glass slide with a drop of Canada Balsam (a resinous glue). A thin glass is added as a cover-slip and sealed by warming the balsam to harden it. The slide, properly labelled, can then be kept and examined whenever necessary. Details of time exposure for staining varies with the stain and material used. The information can be collected from a text-book or worked out by practice. In laboratory analysis many modern techniques are being adopted for in-depth studies on the subject.

 

     

              When Darwin propounded his theory of ‘Survival of the fittest’, it created a great deal of controversy during those days. But gradually it started receiving a wider acceptance as many species were found to be either extinct or facing extinction for the reasons best explained by Darwin. Since the evolution of plant and animal lives, quite a few of them have faced complete extinction and others are facing the dangers of extinction. Hence the conservation of certain species that face extinction has drawn the worldwide attention. These species have been categorized as ‘endangered species’. 

                    Factors responsible for endangering the existence of these species are both natural and man-made. Firstly, the increasing human population is encroaching more and more land, and thus creating a scarcity of land for the wildlife to survive. Forests and heaths have been removed to make way for farming. Large-scale deforestation for wood and industrialization is another cause of the loss of wildlife. Secondly, man has hunted down many animals to extinction — auk and dodo are distinct examples of it. Pollution is also affecting the lives of many animals. Every year millions of sea-birds die unpleasant deaths as their feathers get covered with sticky, black oil waste. The natural causes are the unsuitable conditions of temperature and pressure, lack of proper food material, natural calamities etc. 

 

 

Continue reading "Why do plants and animals become extinct? "

            An affirmative reply to this question is amazing but true. It is a fact that many trees can produce the fruit of another kind of tree by a simple method called ‘grafting’. It is an artificial method or technique of vegetative reproduction in which a small branch or bud of any desired plant is inserted into another rooted plant. This is called plant propagation. If a bud from a twig of pear tree is carefully inserted in a slit made in the bark of a quince bush, a pear twig will grow. The quince bush will bear both pears and quinces.

            In the same way, an almond tree can be made to produce both peaches and almonds. Although sometimes grafting is used to produce freak trees and bushes, this technique is of immense importance in agriculture. Lots of experiments in this field are still being carried on to produce better and new varieties of fruits, flowers and corns etc.

            The greatest advantage of grafting is that it can be used to better the quality and quantity of a particular product. It is possible for a nurseryman or gardener to be sure that his young trees or shrubs will bear the same quality and variety of fruit as the parent tree. A twig taken from a tree and grafted into another tree will produce the same type of fruit borne by the tree from which it was taken.

            There are many methods for inserting the budded twigs or scions, as they are called, into the stock of another plant, but two rules must always be followed. First, only related species of trees or shrubs can he grafted. This implies that apples can be grafted onto pear and quince trees, and peaches can be grafted onto apricot, almond, plum or other stone fruit trees. It is impossible to graft apples on a peach tree. Secondly, the cambium layer (a layer of actively dividing cells) which carries the vital sap of scion must touch the cambium layer of the stock on which it is grafted. Otherwise the grafted twig cannot grow.

            There are different techniques of grafting. It can range from inserting a single bud under the bark to grafting long twigs across the wound of a tree in order to heal wide wounds in the bark. Tissue culture is popular these days in which cells from a plant are removed to propagate in another plant to obtain a hybrid product or the product of the original plant.

            The technique of grafting is now widely applied in case of animals as well as human beings. There have been surgical operations in which a bone taken from the ribs has actually been grafted onto the nasal bone to form a new nose. But the best application is in cases of severe burning where the healthy skin from one part of the body is grafted onto the burnt tissues to remove scars.

               One of the fundamental differences between plants and animals is that animals can move from place to place whereas plants lack mobility. But inconsistent with this general distinction, there are some plants which move on their own. For example, slime molds have amoeba like movement whereby they ‘coze’ from one place to another. Some types of algae have whip like flagellas, they use to paddle themselves through water. Many plants particularly, the lower ones, produce mobile male gametes which swim about in order to find eggs to fertilize. Englena is a protozoa which is capable of swimming. Apart from these exceptions, the movement of plants is usually confined to the movement of some parts of it while the plant itself remains fixed at one place.

               There are three basic types of plant movements: tropisms, nutations and nastic movements. 

               A tropism is a growth response towards or away from something caused by a specific environmental stimulus. The direction of growth is determined by the stimulus. When it is towards the stimulus, it is caller positive tropism and when away from it, it is called negative tropism.

               Tropisms are caused by special growth hormones called auxins. In most of the cases, the stimulus causes the auxins to collect on one side of an affected organ. This causes the cells on that side to grow and divides more quickly than the cells on the other side. As a result, the organ bends away from the side with the most auxins.

               Tropism is of several types. Phototropism is a growth response to the stimulus of light and auxins are concentrated on the side away from the light. This causes stems and leaves to grow towards light and roots grow away from light. Geotropism is the growth towards the gravity of earth. Roofs show positive geotropism while stems show negative geotropism. Hydrotropism is the growth response to the stimulus of water. Roots grow towards water and often move great distances to areas of moist soil. 

Continue reading "Do some plants also move? "