My Science School

            It is a well-known fact that trees and plants are also living beings like humans. They need food, water and air for survival. It is interesting to know how they take their food.

            Plants derive their food both from the earth and the air. If you minutely look at their roots, you will find that the ends of these roots are like fine fibres. We call them root-hairs. They absorb water and minerals and transport them upwards to the leaves through the trunk and the branches. It is the leaves which prepare the food.

            The leaves have pores which are filled with air. They also have a green colouring matter called chlorophyll. This chlorophyll acts as a catalyst, and uses carbon of the carbon dioxide and the hydrogen of the water present in the leaves to make carbohydrates (sugars). In this process oxygen and water are given out which are excreted by the leaves of plants.

            Sugar is further converted into starch. From these carbohydrates, the plant can build up complex substances as foods which it needs for its life and growth. These substances include proteins, juices, oils (fats) etc. The water from which the plants take hydrogen for photosynthesis contains dissolved minerals needed in building various parts of the plant body. These are chiefly the compounds of nitrogen, sulphur, phosphorous, sodium, calcium, magnesium, iron etc.

            Food not immediately needed for growth is stored in the plant including its seeds, fruits, tubers or bulbs. This accumulated food in the seed is used in its germination.

 

Every spring millions of birds migrate from their winter quarters to the temperate regions of the world to breed. These regions abound with food on which the parents can rear their hungry chicks.

The biggest migrations are to the northerly parts of North America, Europe and Asia. But there is some migration to the southern hemisphere too. For example the double-banded dotterel flies from Australia to New-Zealand to breed. The American golden Plover undertakes a non stop flight of 3325 km between Alaska and Hawaii. In the northern hemisphere wild geese fly north to their breeding grounds in the spring and fly south in the autumn.

Migration is mainly triggered off by changes in the length of the day, which cause a change in the bird’s hormone balance.

Now the question is how do the birds find their way while migrating from a place and then returning to their original place?

Some birds may learn from their parents. They make the first migration with the older birds which have made the trip before. These younger birds teach their young the migration route the next year. Some birds may guide themselves by landmarks, such as mountains, lakes and coast-lines. Others may use the sun and stars to navigate by, because when the sky is cloudy, they often get hopelessly lost. Scientists still do not know how all migratory birds find their way.

Birds are not the only animals that migrate. Many fish, mammals, flying insects, locusts, and eels also migrate. 

            Due to the scarcity of water and particular climatic conditions (hot, dry, windy) prevailing in the desert, it is very difficult for animals as well as plants to survive. Nonetheless, we do find some of these. These are adapted to the desert conditions. Let us see what types of vegetation and animals are found there and how do they survive.

           The vegetation of a desert is mainly thorny shrubs, cacti and palm (especially date) trees. Cacti and other desert plants have adapted themselves to live in desert conditions. They have evolved ways to store water in their fleshy stems. The leaves have squeezed themselves into tiny thorns to reduce the loss of water. The roots go deep into the ground and are wide spread to collect every drop of water available. The stem stores the water and slowly gets thinner as the water gets used up. In some cacti the thorns are pointed towards the earth. The dew drops deposited on the ends fall on the earth hence moisture is maintained below the cacti. There are quite a few animals found in deserts such as snails, pack rat, jerboa, etc. Most desert animals sleep during the day to escape the day temperature and they come out in night in search of food. Some animals sleep during the hottest part of the year. Animals such as kangaroo, rat and gerbil can survive with little or no water. Reptiles adjust their body temperatures to cope with heat and cold. The Australian desert toad stores water in its body. Some lizards, ants, owls and snakes also live in deserts. 

             You must have heard the sound of conch (shankh) blowing in the temples. You must have also seen big and small conches at sea-shores and on the river banks. Some conches are so small that they can be seen only with the help of a magnifying lens, whereas there are others as big as measuring up to 120 cm.

              Do you know what these conches are and how they are formed? They are the body shells of aquatic creatures. These creatures are called mollusks. Some 60,000 species of the mollusks have so far been studied by the scientists. As the size of the mollusk increases, the outer shell also increases and becomes harder. They are made up of calcium carbonate (lime). The mollusk collects lime from the sea water and deposits it in its outer shell. When the mollusk dies, the shell floats and comes to the surface of water.

              The shell of the mollusk has three main layers. The outer layer of the shell is made up of smooth material like the oyster and contains absolutely no lime. The layer below this i.e. the second layer is made up of calcium carbonate. The lowest layer that is the third layer is a group of many thin layers, which are made up of oyster-like material and calcium carbonate. The conches are of many colours. They have many stains and stripes. These stains, colours and stripes have their origin in some colourful materials present in the glands of the mollusk. These colours, stripes and stains enhance the beauty of the conches.

              The conches not only protect the mollusk, but they are also very useful for us. In ancient times people used mollusk shells as coins. Small conches are even used as part of necklaces. They are used as decoration pieces in homes. Buttons are made from small shells. Aquatic animals with shells have been existing for billions of years. After their death these shells deposit themselves on the sea-bed which forms rocks of limestone. 

             Majority of people believe bamboo to be a kind of shrub or plant. In fact, it is neither. It is a type of grass. It can reach a height of about 35 metres and upto a thickness of about 30 cm. It has many varieties. About 600 species of bamboo have been studied. All kinds of bamboos have smooth, hard and strong trunks. The rate of their growth is very fast. It can grow up at the rate of 40 cm a day. One bamboo reportedly grew 90 cm in 24 hours. Some bamboos blossom only once in 30 years. Others may take 100 years to blossom. A bamboo plant dies after it blooms. The seeds from these blossoms grow into new plants.

            It is only the stem of the bamboo grass that is of most use in the construction of roofs, huts, walls, houses, etc. It is used to make mats, baskets, musical pipes, paper, as a fishing rod and weapon for defence; it is cooked as vegetable and pickle is also made of them; some medicines are made from a fluid in the stem joints of bamboo branches. Its hollowed stems are used as water pipes especially in Japan.

            It is found in abundance in South-East Asia, Indian subcontinent and the islands of the Pacific Ocean.

 

Would it not be wonderful if people who lost an arm or a leg or even a finger in an accident could simply grow another one in its place? But in reality it does not happen so in case of human beings. However, you will be surprised to know that there are some living beings in which a new limb develops at the same point from where the original limb has been lost. Development of a new body part in place of a lost one is known as regeneration.

If a small arm of a starfish is cut off or destroyed, it is regenerated. The hydra, lizards, sponges, newts and earthworm also possess this capability of regeneration.

The ability of regeneration is different in different creatures. Living beings with complicated structures have lesser ability of regeneration. Man and other mammals have a complex constitution. That is why they have lesser ability of regeneration. Mammals can replace hair, nails and skin. Mammals can also repair broken bones and other damaged tissues. Regrowing of the wings of birds is another example of regeneration.

In some species new tissues grow from the surface of the wound replacing the lost or damaged tissues. Sometimes, the tissues that an organism regenerates are different from the original ones. The regenerated structure may be smaller and weaker than the original one.  

               Bacteria belong to the lowest category of plants. They are unicellular micro-organisms. They are as small as 25,000th part of an inch. Some of them are even smaller and cannot be seen with the help of an ordinary microscope. They reproduce through the process of cell division (fission) i.e. one cell divides itself into two. Under favourable circumstances the rate of their reproduction increases. Within twenty minutes the cells of the new bacterium divide into two, in forty minutes one bacterium multiplies to four and to sixty four in two hours. In this way, in twenty-four hours, one bacterium multiplies into 4,000,000,000,000 bacteria. If the rate of the reproduction of bacteria remains the same, the weight of the bacteria produced within 72 hours will become 33,000 times more than the weight of the earth. But this is impossible because in the struggle for food and water only one percent of them can survive. They may live in soil, water, air or in any other organisms.

               Bacteria can be broadly classified into four types. Some bacteria are round, they are called coccus. The rod-shaped are called bacillus, spiral-shaped the spirillum and the comma-shaped vibrio.

               Bacteria are both harmful and useful. They spread many diseases in human beings, animals and plants. Typhoid, tetanus, T.B., cholera, diphtheria, dysentery, whooping cough etc. are some of the well-known diseases which are spread by bacteria. But, on the other hand, some bacteria are very useful for mankind. Conversion of milk into curd is done by bacteria. They destroy the dead plants and animals by setting decay in them. Vinegar is also prepared by them. It is the bacteria which make yeast for bread, and colours the hides (animal skin). Certain antibiotics are also prepared by using them. Thus, bacteria are both useful and harmful to us. Antibiotics and sulpha drugs are used to control bacterial diseases. 

 

 

 

 

 

 

 

              In rainy season, you must have seen the growth of soft, white, cottony and velvety patches of mould on stale bread, pickles, damp cloth, leather, food, leaves, fruits and vegetables. These are called fungi and are classified flowerless plants having no roots, no stems and no leaves and are without chlorophyll - the green colouring matter. Due to the lack of chlorophyll, fungi depend for their food either on a living organism (parasite) or on the dead organic matter (saprophyte). When we examine the fungi under a microscope, we see that they consist of a large number of black, green, yellow or blue fibres. These fibres have two parts - one part is mycelium which spreads like roots and takes food from the material on which it grows. The other part is round, ball-like lymph, which contains spores. Always present in the air, they start multiplying whenever they get bread, fruits and other eatables in hot and humid places.

Continue reading "What is Fungus? "

                Viruses are micro organisms which cause various diseases in all types of living bodies, so much so that even bacteria are affected by viruses. There is a helpful virus called bacteriophage which eats bacteria and can not be seen by necked eye. One can only see them with the help of an electron or ultra microscope. Strangely enough, viruses are considered both as living and non-living objects. They grow and multiply in living cells and therefore are treated as living organisms. Since they do not grow outside living cells. They are classified as non-living objects also. Consequently, they are treated on the border line of living and non-living matter.

                  Viruses were first discovered by Mayer in 1888. He found them on tobacco leaves. There are many kinds of viruses. They are of varying shapes and sizes. Some are long as rods, some are hexagonal. The smallest viruses are of the size of a millionth part of an inch. They are found in the cells of plants, animals and human beings. They are born in these cells, multiply there and spread diseases.

Continue reading "What is a Virus? "

              Kangaroos are marsupials (animals with pouches) that live in Australia and New Guinea. Most of them live on grassy plains and feed on plants. They move about in troops, springing along on their big, powerful hind legs and large feet. Their long tails help them to balance.

              There are five species of kangaroos. Red and grey ones are the largest. A red kangaroo may be taller and heavier than a man. Grey kangaroos can bounce along at 40 kilometres per hour if chased. Wallaroos are smaller kind of kangaroo.

              A full grown kangaroo stands about six feet tall. Its front legs are short while the hind legs are very long. The powerful hind legs enable the kangaroo to take long jumps of 3 to 5 metres at a time. If a hunter or hunting dog chases a kangaroo, it runs very fast making long jumps. It can cover a distance of 7 to 9 metres just in one jump. When a kangaroo is cornered by hunting dogs, it can seize a dog with its forelegs and kill it with one swing of its hind legs.

             The female kangaroo has a pouch in its belly in between the hind legs in which it keeps its young ones till they grow up. When a baby kangaroo is born, it is a tiny, pink, naked mass of about 2.5 cm in length and about 1 gm in weight. Not only the infant kangaroo, but even young kangaroos need the protection of their mothers. A kangaroo lives on the mother’s milk until it leaves the pouch at the age of 6 to 8 months. A kangaroo lives for about 6 to 8 years. Finding the young ones in danger, the mother kangaroo lifts them with its mouth and places them inside its pouch.

           The kangaroo is a mild animal like the sheep and goats. Like the hare, it is unable to see an object just in front of it. But its power of smelling and hearing is quite strong.

           Have you ever seen a cat sitting in the dark? Though its body is not visible, yet its yellow eyes shine in the darkness. The eyes of tiger, leopard, lion etc. also shine in the darkness or night just like the eyes of a cat. Besides these, there are many other animals whose eyes shine in the dark.

           The eyes of these animals have a thin layer of a special crystalline substance which reflects the light falling on it. This reflected light is the cause of the shine. In the night, even the smallest amount of light falling on this crystalline surface gets reflected and thus we see the shining eyes. Animals with such eyes that can see things clearly in darkness are called nocturnal animals.

           Studies made on cats have shown that behind the retina of eyes, there is a crystalline layer called the ‘luminous tapetum’, which reflects light. Due to this layer the cat can see clearly in dim light and its eyes shine in the dark when the light is directed on them. Many animals do not have this crystalline layer; hence their eyes do not shine in the dark.

          It has been observed that the colour of the shine is different in different animals. It depends upon the number of blood vessels present in their eyes. If the number of blood vessels is large, the colour of the shine is red and if the number of blood vessels is small the colour of the shine is white or pale yellow.

 

Dog is regarded as a faithful animal. But when it goes mad it becomes very dangerous. If a mad dog bites someone, it leads to his death if not treated properly.

              A dog goes mad when it suffers from a disease called ‘rabies’. This disease is caused by a virus which is carried by air or by some wild animals and enters the dog’s body through a wound in its skin. The virus is bullet shaped having a diameter of about 70 milli-microns and a length of about 210 milli-microns. It moves from the saliva to the infected wounds and through sensory nerves to the central nervous system, multiplies there and then destroys brain cells. The dog becomes lazy, suffers from fever and loses all interest in food. In about 4-6 weeks, when these viruses affect the dog’s brain, the dog gets excited. It growls and barks and saliva froths from the mouth. During this period, the dog can bite anybody. This is the stage when the dog is said to be mad. After these symptoms appear, it is likely to die within 3 to 5 days. Some infected dogs do not go mad but show signs of paralysis, called ‘dumb rabies’.

             When a mad dog bites a man, the virus present in its saliva enters man’s body through the wound. Initially the victim experiences mental weakness and uneasiness which is followed by fever. He suffers from lack of sleep and feels frightened. The muscles in his throat get slackened and he faces difficulties in swallowing food or liquid. He is afraid of water. That is why this condition is also called ‘hydrophobia’ which means ‘fear of water’. These signs appear in the victim within one to three months after dog’s bite. In cases of dog-bite, the affected portions should be immediately cleaned and anti-rabies injections should be given to the victim within three days of the bite, the number of injections varying from 3 to 14 depending on the location and number of bites.

             The virus of rabies also attacks foxes, jackals, monkeys, cats and rats because they have the least contact with us. 

            Ants are insects that belong to the order Hymenoptera. More than two thousand species of ants have been studied by scientists. Ants are found in most parts of the world. Most ants are smaller than an inch.

            Ants are social animals and have their own kingdoms. This means that they live together in large colonies or groups. Some colonies may contain millions of ants. Most colonies make nests in the ground or in dead trees.

            There are three kinds of ants in each colony - queens, laying eggs; males who do not work; and a corps of female workers. An ant colony contains too many cells or chambers for different purposes. The queen lives in one, laying eggs. Next door is the hatching room, from which the grubs as they turn into pupae are carried into another room to develop. The other rooms are used for special purposes such as storing food etc. An ant colony may contain several queens each with its own suite of rooms. Worker ants collect food, feed the young ants and build the nest. Some species of ants also have female soldier ants. They protect the nest. 

Continue reading "Do Ants also have their kingdoms? "

           An owl is a bird of prey with large head and eyes, short neck, broad wings and sharp claws. About 130 species of owls are found around the world. In some countries, they are treated as in auspicious birds, while in others; they are regarded as symbol of wealth and wisdom. What is peculiar about owl is that they can see more clearly at night than during the day. In fact they “come to life” at night and are an apt example of ‘nocturnal’ birds. Birds which can see more clearly at night rather than during the day are known as nocturnal birds. On the other hand, birds which have a clearer vision along the day time than during night are called ‘diurnal’.

             You must be very curious as to how nocturnal birds in general and owls in particular can see so clearly at night.

             To understand this, it is essential to know how we see things. Light scattered by an object is focused on to the screen of the eyes by the lenses inside the eyes. This screen of the eyes is called the retina. An inverted image of the object is formed on the retina which is carried to the brain by optic nerves. This is erected by the brain and thus we see the object.

                 The owl’s eyes have four special features due to which it can see more clearly at night. Firstly, the distance between the lens of its eye and the retina is more than the distance in the case of human eyes. Due to this, the image formed on the retina is bigger in size. Secondly, the number of ‘rods’ and ‘cones’ (special cells which help in the vision) in the retina is very large - almost 10,000 per sq mm compared to 2,000 per sq mm in our eyes. Thus, the owl can see five times more than us. Thirdly, its eyes have a red coloured material, chemically a protein, which makes its eyes more sensitive to light. Fourthly, the pupils of its eyes can dilate more, thus allowing even the smallest amount of light to enter into the eyes. Because of these four factors, the owl can see more clearly in darkness. Due to the extreme sensitivity of their eyes to light, objects appear too bright and uncomfortable to the eyes in the bright light of the day. Surprisingly enough, an owl can rotate its head by 180° i.e. it can see at the back of his head. 

                Antibiotics are special kind of medicines which inhibit the growth of or destroy Bactria and some other disease producing micro-organisms. They help our body to fight against diseases hence they are used in the treatment of many diseases.

                The word ‘antibiotics’ is derived from ‘antibiosis’. ‘Anti’ means ‘against’ and ‘biosis’ means ‘life’. Antibiotics act only against certain types of micro-organisms like bacteria. In fact, ‘antibiotics’ are chemical substances derived from the bodies of micro-organisms such as bacteria, moulds or some plants.

            The antibiotic era began around 1928 with the discovery of a species of Penicillium by Sir Alexander Flemming. Flemming named the substance Penicillin. This antibiotic was effective in the treatments of pneumonia, cough, inflammation of throat, boils, sores etc. Streptomycin is another antibiotic which is used in the treatment of Tuberculosis. In addition to these, Ampicillin, Tetracyclin, Chloromycetin and many other antibiotics are used for curing various diseases. In fact there are more than 80 known antibiotics. Some antibiotics are effective against just some micro-organism while some other are effective against a large range of micro-organisms. Those which cover a large range are called broad-spectrum antibiotics. When an antibiotic is brought into the body either by injection or capsules, it kills the disease spreading micro-organism.

                   Do you know how antibiotics are made? Most of the antibiotics are made from bacteria and fungi. Scientists have not been really able to know the complete mechanism by which antibiotics kill the germs of diseases. Some scientists think that antibiotics prevent oxygen from reaching the germs of diseases and in the absence of oxygen they die. Some other scientists say, antibiotics prevent the germs from taking food from the body and they die for want of food. Whatever may be the mechanism of the action of antibiotics, it is an established fact that these medicines have proved very useful for mankind. Every year millions of people in the world suffering from various diseases are saved by these medicines. In 1930, 20% to 85% of total deaths in America were due to pneumonia. In 1960, this figure came down to 5%. Similarly, the deaths due to typhoid have come down from 10% to 2%. Infectious diseases can also be checked with their help. They are also useful in preventing diseases like throat infection, rheumatic fever, venereal diseases etc.

                   They have their adverse effects also, such as reaction of the body to them, rashes and other symptoms may develop or they may cause other diseases. An extreme reaction may even lead to death. Sometimes, they are ineffective on the germs of the diseases.