My Science School

          Amongst the thousand kinds of insects, there are some who bite us and are our great enemies. When they bite us, they inject germs of many dangerous diseases into our body. Do you know which insects are our enemies?

          Dangerous among the insects which spread various diseases through bites are mosquitoes, tse tse flies, lice, rat fleas, bed bugs etc. When these insects bite any sick person, and suck the blood, the germs of the disease pass into the bodies of the insects. When these insects bite a healthy person, they pass on to him the germs of that disease along with the saliva through a needle-shaped hollow organ. These germs infect the healthy person and make him sick. 

Continue reading "Why insect bites are dangerous? "

          Mammals are vertebrates or animals with back bones. They have large brains and a keen awareness of their surroundings. They are warm-blooded and have their skin covered with hair. The young are born alive except for egg laying platypus and sping anteater and suckle milk from the milk glands of female. You will be surprised to know that many animals which are otherwise very different from one another come under this category. For example the cow, seal and bat have nothing in common, yet they come under the category of the mammals. Man is a mammal too.

          Many of the mammals are very peculiar. Some of these live on the land, some on trees while some others inside the earth. There are some which live in water also.

          Some of them are carnivorous while others are herbivorous. Some mammals are both carnivorous and herbivorous.

          Monkey, gorilla, chimpanzee, baboon, etc. are the mammals with resembling features. Cow, pig, camel, horse, rhinoceros, elephant, rabbit, rat, squirrel etc., are some other mammals. Most of the time they live on the ground. The dugong, dolphin, whale etc., are mammals which live in water. Amongst the flying mammals are the bat and colugo. The kangaroo is a peculiar mammal that has a pouch on its belly for keeping its young ones.

          Platypus is another peculiar mammal which does not give birth to its young but lays eggs. Generally it is found in Australia. Pangolin does not have teeth. It lives on ants. The wolf, lion, cheetah, bear, cat, seal - all are mammals. There are about 4000 distinct species of mammals. It is not possible to describe all of them. Only important ones have been described here.

          The web made by a spider is a fascinating thing, but spider itself is more amazing in many other respects. It is a peculiar creature found in all seasons and at all places - air, water, land and also inside the earth. Its size varies from that of a small dot to 20 cms. There are some spiders which can live without water for a year. A giant spider called tarantula feeds on birds and can live for as long as 15 years. In February 1985, Charles J. Seiderman of New York City captured a female bird-eating spider near Paramaribo, Surinam, which weighed a record peak of 122.2 grams. Generally most of the spiders live only for one year. The spider has 8 legs and 8 eyes. Its body has only two parts - head and trunk. 

          The silk that spiders fabricate for making their webs is produced in certain abdominal glands. A liquid in the form of fine thread comes out from a small hole at the top of its abdomen, which solidifies after coming in contact with air. These threads are of various types. Some of them are sticky while some others are dry and soft. The sticky thread helps the spider in catching its prey. As soon as a fly or a small insect touches or falls on the web it gets entrapped in it. Now the question arises: why doesn’t the spider itself get caught in its web?

          It is interesting to note that the spider itself does not get trapped in it because it has a kind of oil on its legs. In fact, when the spider moves across the web, it uses the dry-soft threads and is careful to avoid touching the sticky threads with its legs. Even if it did, the oily secretions on its feet would prevent it from sticking and it moves along those threads easily. In England and Wales there are more than 2,000,000 spiders in every acre of meadow land. It has been estimated that in one year the spiders in the country eat a weight of insects that exceeds the total weight of the human population of England and Wales.

           The spiders make many kinds of webs. Some of these are wheel-shaped while some are shaped like a funnel. The sticky threads which are meant for trapping the prey are separately located.

 

          Most of the trees and plants shed their leaves during autumn and new leaves sprout on them during spring. After the defoliation they appear quite barren. The trees which shed leaves every year are called ‘deciduous trees’. However, there are other trees which do not shed all their leaves at one time, and thus always appear green. Such trees are called evergreen trees. Do you know why this happens so?

          In fact, all the trees shed leaves. But the leaves of the trees which undergo defoliation every year live only for one year. On the other hand leaves of the evergreen trees last for two to three years. As soon as a leaf withers it falls down and a new leaf sprouts in its place. Thus all leaves are not shed at a time. As a result the tree always retains a large number of leaves and this cycle continues. 

          Among the well-known evergreen trees are pines and firs. Besides these, there are many other trees which always remain green. The Italian cypress found in Europe is one such tree. The olive plant also comes under the category of evergreen plants. Its oil is very useful for us. The magnolia plants are used for decoration because their white flowers are very beautiful and do not have defoliation. Perfumes are extracted from the evergreen plants of the rosemary. The juniper plants, having short and bitter leaves which are found in North Britain, are famous for their greenness. In addition to these, other evergreen plants and trees are myrtle of Britain, oleander of North Africa, oak tree, ivy creeper, orange tree and tall palm tree. The tea plant also comes under the category of the evergreen plants.

 

          Camel is called the ‘ship of the desert’ because it has the ability to survive in the desert without food and water for six to ten days. They are able to withstand the loss of about one-third of their body fluid without danger. Its nose, ears and eyes are formed in such a way that they are least affected by the dust of the desert. It is a very useful animal for the desert travellers and can carry enormous loads.

          It is commonly believed that a camel does not require food very regularly but this notion is not correct. Because of the peculiarity of its body constitution, it can store food and water for many days.

          Camel has a big hump on its back. As a matter of fact, this hump is a storehouse of fats. The camel uses the fat so stored as a source of energy during its long journey in the desert. Inside its belly it has two flask-shaped bags for storing water. When it does not get water it uses this stored water. It is on the strength of the fat and the water stored in the hump and the bags respectively that it can go without food for a long time.

          In fact, before starting on a long journey, a camel takes large quantities of food and water so that enough fat and water get stored in the body. After a long journey, the hump of the camel becomes loose because the fat stored in it is almost exhausted. Even the water stored in the bags gets consumed. After the journey it becomes so exhausted that it lies down on the ground for a long time. With the gradual intake of food and water, it becomes strong and healthy again.

          Camel has been man’s companion for a long time. The people of Egypt tamed the camel around 3,000 years ago. Camels are mainly found in Africa and Asia. In Africa the one-humped camel is found while the two-humped or Bacterian camel is found from Asia Minor to Manchuria and there are still a few, living wild in Gobi desert.

 

          Whenever we pass through a garden during the spring the fragrance of flowers enchants us. Nature has endowed flowers with beauty, attractive colours, nectar and fragrance. Insects and flies get attracted towards the flowers and sit on them. And when they leave they carry with them pollen grains to other flowers. This dispersing of pollen grains helps in the pollination of flowers, as a result of which, seeds are produced. In this way plants and trees multiply on their own.

          Different flowers contain different oils which give specific fragrance to flowers. As these oils gradually keep on evaporating, the fragrance of the flowers spreads in the air. In fact, perfumes are prepared from the oils extracted from these flowers. There are various processes of making perfumes. In one process, flowers are kept in a pot through which steam is passed. The outgoing steam brings oil with it. This steam is passed through water. Thus the oil brought out by the steam starts floating on the water surface. This is then separated from water. There are other methods of making perfumes also. France produces the maximum amount of perfumes. It has been found that one ounce of rose perfume is extracted from 110 kgs of rose flowers.

           Flowers like rose, Raat Ki Rani, Pandarus, lavender, jasmine etc., are generally used for making perfumes.

           The anthocyanin pigment is responsible for producing red, blue and violet colours. The plastid pigment causes other colours. These pigments remain mixed in the juice of the flowers. The presence of chlorophyll and carotene make some flowers green. There are at least 200,000 kinds of flowers, ranging in size from the microscopic duckweed blossom with a diameter of 0.4 mm to the tropical Rafflesia with a diameter of 90 cm. 

          On the basis of age, plants are divided into three categories: annuals, bi-annuals and perennials. The annuals are those plants which take birth, grow up, give fruits and die within a year. Wheat, barley, gram, peas, tomato - all live for one year only. The bi-annual plants live for two years. In the first year they bear only leaves, and in the second year - flowers and fruits, and after that they die. Plants like the ‘fox-glove’ and the ‘hollyhock’ come under this category. The perennial plants live for more than two years. Generally they are called trees or bushes. They blossom and bear fruits many times. The trees of the neem, mango, jamun (black plum), guava etc. come under this category. Some perennial trees have a life of more than 4000 years. The great sequoia trees found in California are reported to have a life of more than 4000 years. The yew trees live for 3000 years. The chestnut and the oak trees live for 2000 and 1500 years respectively.

          Now the question arises: how is the age of any perennial tree determined? Scientists have devised a very simple technique to do this. This technique refers to the number of rings present in the trunk of a tree. If you cut off a slice from the tree trunk, you will notice many concentric rings in it. These rings are the record of the tree’s age. In fact, the trunk, underneath the bark, keeps on growing thicker with age. However, the wood which grows in winter and autumn is denser and harder as compared to that grown in spring and summer. This results in the formation of a ring in the trunk every year. These rings are of brown and cream colours alternatively. Thus the number of rings counted from the centre of the trunk of a tree tells its age in years. Its central portion is called the ‘path’.

          Some fruits like watermelon, guavas, grapes, apples, mangoes etc. are sweet in taste while lemon, orange, raw mango, etc. are sour. Each fruit has a distinct taste which differs in some way from the taste of any other fruit. The question arises: why does every fruit have a characteristic taste?

         In fact, the taste of any fruit depends on the compounds present in it. In general a fruit contains fructose (natural sugar), organic acids, vitamins, starch, proteins, minerals and cellulose. All these materials are in a mixed state inside the fruit and are found in different proportions in different fruits. Fruits having more fructose content taste sweeter, while those having more acids taste sour. Orange is a fruit which has almost equal quantities of fructose and acids hence it tastes both sweet and sour.

          In general, raw fruits contain more acids but on ripening, the quantity of acid in them decreases and the amount of sugar increases. Hence raw mangoes are sour, but ripe ones are sweet. Raw bananas contain more of starch, but it gets converted into fructose when the fruit ripens.

          During the process of ripening, chemical changes take place inside the fruit by which the quantity of sugar increases thus adding to the sweetness of the fruit.

          You will notice a difference of taste even in two fruits of the same kind. Two apples or two mangoes do not always taste alike. This is so because there are many varieties of the same fruit and also the variations in the quality of soil, climate, growing technique, manure, water etc. change the proportion of the compounds inside the fruit resulting in the difference of taste.

          Sour fruits like lemons; do not taste sweet even after they are ripe, because of the presence of excessive amounts of acids.

          Elephant is the largest land animal of the present day. It is a mild and peace-loving animal. That is why it can be more easily domesticated and trained. An elephant can weigh up to 5 tons. It has four legs which are thick and short. It is easier to balance a heavy weight with the help of short legs. It has two ivory tusks which protrude outside from the upper jaw. These tusks are used by them as weapons for defence. However for chewing food it has teeth inside its mouth.

          The elephant lives in herds. A group has ten to fifty elephants. These groups of elephants keep on moving about in the jungles. In general the elephant has the colour of catechu with a blackish shade. Some elephants are white also. Today there are two classes of elephants - African and Asiatic and are found in the tropics of Africa and Asia. The African species are bulky with bigger ears whereas the Asiatic ones have high, doned forehead. 

          Elephant’s trunk is a very important organ, without which it cannot exist. It may be called as the lifeline of an elephant. It is as essential for the elephant as the hands are for us. It is an extension of the nose and upper lip. For elephant it performs the functions of hands, nose and lips. They have also developed a heavy head. Since a heavy head cannot be carried on a long neck, so the elephants need long trunks to reach their food. The trunk has about 40,000 muscles. Because of such high number of muscles, it is flexible and strong. It can lift very huge wooden poles with its trunk. The tip of the trunk is just like a finger and is so sensitive that it can even lift a needle. It carries its food to the mouth with its help. It also drinks water with the help of the trunk. To take baths it fills water in it, curls it up and pours that over its back. Thus, we can see how the trunk is very useful for the elephant.

          The average life of an elephant is 90 years. Elephants are herbivores, eating a wide range of plants. It is a very useful animal for us. Elephants are used in jungles for carrying heavy wooden logs from one place to another. They entertain us in the circus. 

          Like us the bees also have colonies. No other class of wild species can match their organized way of life. The honey-bee colony consists of three main divisions: the workers, who provide food and protection for the colony; the queen who lays eggs, and the drones, who mate with the queen. An average honey beehive contains one queen, 100 drones and 60,000 workers. The workers are female bees while drones are male. The queen bee lays more than 2,000 eggs in a day, and about 250,000 eggs in a season, it lays more than 1,000,000 eggs in its lifetime. Most of the bees live for one to two years. One bee colony can have a grouping of up to 60,000 bees. The worker bees have many duties. In the beginning they clean and polish the hives. After some days, they look after the larvae of the bees. Eventually, they go out to collect the nectar from flowers. Do you know how these bees make honey?

          In fact, honey is the food of these bees. As such, for the bees, making of honey is like gathering food for themselves. And this they collect from flowers. The flowers contain a sweet liquid called the nectar. The bees drink this nectar and carry it to the beehive in their honey sacs. A bee must visit about 1000 flowers to fill its honey sac. The honey sac is located near the belly of the bee. A valve separates it from the belly. The sugar present in the nectar undergoes a chemical reaction. The water present in the nectar evaporates. And after this evaporation the honey can remain in the hive for a very long time without getting spoiled. This honey is stored as the food for future.

          There are many ways of extracting honey from the hive. The comb can be squeezed to yield honey. A machine is also available for removing honey from the combs. It is called the ‘honey extractor’. The colour and taste of various kinds of honey vary depending upon the flowers from which the nectar has been collected. Honey contains many substances which include two kinds of sugar-laevulose and dextrose, maltose, dextrins, minerals, enzymes, many vitamins, small amounts of proteins and acids. That is why honey is very useful for our health and fitness. 

A few years ago, the American scientist and explorer Roy Chapman Andrews came to India as the leader of an expedition team. One day he was driving a jeep near the India-Nepal border. He saw a cheetah there. He steered his jeep towards the cheetah. On seeing the jeep, the cheetah started running. Andrews decided to make a test of its speed. He accelerated the speed of his jeep towards the cheetah at a rate of 80 kms per hour but still the jeep remained behind the cheetah. Even at the speed of 100 kms per hour the animal was ahead of the jeep till it disappeared into the Jungle. From this incident one can conclude that the speed of the cheetah was more than 100 kms per hour.

Over a short distance, (i.e. upto 550 metres or 600 yds) the cheetah or hunting leopard of the open plains of East Africa, Iran, India, Turkmenia and Afghanistan has a maximum speed of 96-101 km per hour (60-63 miles) on level ground. Speeds upto 145 km per hour (90 miles) have been claimed for this animal, but these figures are considered to be exaggerated. Black buck comes next. It is a kind of deer. The third place goes to Mongolian gazelle and the pronghorn - the two species of deers. They can run at a speed of 95 kms (60 miles) per hour. Lion occupies the fourth place. It can run at a speed of 88 kms (55 miles) per hour.

Rabbit and fox can run at a speed of about 75 kms (47 miles) per hour. Horse, zebra and grey-hound can run at the speed of 64 kms (40 miles) per hour. Buffalo and hare can run at the speed of 55 kms per hour while giraffe and wolf at a speed of 50 kms per hour. The speed of elephant is 40 kms per hour. Kangaroo and sheep can run at a speed of 64 and 25 kms respectively while camel and pig can run at 18 kms per hour. The speeds of the four-legged animals given above are based on the tests conducted by a large number of researchers.

These animals cannot run at these speeds for a very long time. At the most they can cover a distance of a few kilometers at these speeds.

 

          Scientists have already studied more than 8 million kinds of animals. From these animals we get many useful things like meat, eggs, milk, skins, wools etc. We get many medicines from animals which are also used in the treatment of various diseases. Do you know which are these medicines obtained from different animals?

          Most of the hormonal medicines are obtained from the animal glands. Epinephrine, used in the treatment of heart ailments, is extracted from the adrenal glands of cats and pigs. This is also known as ‘adrenaline’. It was discovered in 1904 and is also used by asthmatic patients.

          The medicine, thyroxine, is obtained from the thyroid glands of the cat. It is used in the treatment of diseases relating to the thyroid glands. Insulin, the common medicine for the treatment of diabetes, is prepared from pancreatic secretion of cats and pigs.

          Sex hormones obtained from many animals are used for curing many sexual diseases of men and women. Snake bites are treated by anti-venom serum obtained from snakes.

          Vaccines for many diseases are also obtained from animals. For example, the polio vaccine is prepared by taking polio virus out of the kidneys of monkeys. In 1790s Edward Jenner, the British pioneer of vaccination, inoculated cowpox materials into non-immune persons who then showed resistance to small pox.

          Apart from these medicines, animals prove very useful in the medical sciences. The efficacy and toxicity of medicine are first tested on animals. And when it is found to have the desired curative effect on them, it is put in the market for human use.

          Through the dissection of different animals, students of biology are taught about various parts of human body. The studies of these animals have provided us with ample information to control many kinds of viruses and bacteria. Diseases like rabies, small-pox, malaria, typhoid, diphtheria etc. have been controlled only because of the knowledge obtained from the study of animals.

          In addition to these medicines, things like silk, lac, honey, pearl etc. are also obtained from the animals. Thus, we see that the animals are immensely useful for us in many respects. 

          Chameleon is a variety of lizard which often changes its colour to match with its surroundings. This is possible because of the colour-containing cells beneath the skin. But how do these cells help it to change its colour?

           The upper layer of a chameleon’s skin is transparent but the layer just underneath it has cells containing yellow, black and red pigments. These pigments are granular in structure and the granules can easily move from one point to another in its body. When these cells contract, the concentration of granules increases at one point turning the colour of the skin into black. And when they get scattered throughout the body, different colours are produced. This implies that the contraction and expansion of its cells are responsible for change in the colour of its skin. The cells contract or expand due to several factors as described below.

          First, emotions play a role in changing its colour. When a chameleon gets enraged or frightened, its colour turns into black. Also in a state of excitement yellow spots appear on its skin making it yellow. Secondly, light brings a change in colour, for example when exposed to the sunlight; its cells turn black due to the heat of the sun. Thirdly, heat is also a contributory factor. When it is in a hot and dark atmosphere, its colour becomes green and at lesser temperatures in darkness, the skin becomes light yellow.

          The ability to change its colour provides the chameleon with many advantages like protection from enemies and catching of insects for its food. Among the other traits of chameleon the most remarkable one is that it can move one eye independently of the other. One eye can be looking forward while the other looks behind. This enables them to look at two things at a time and helps in catching the insects on which they feed.

          Generally the edible-fleshy part with seeds which develops from the flowers of any plant is called a fruit, whereas trunks, leaves and flowers of herbaceous plants used as food are called vegetables. But scientifically speaking, the above definitions are not correct.

           According to botanists the part of the plant that carries seeds and produced by the ovary of a flower plant is called fruit and the remaining part used for food is called vegetable. Scientists have divided fruits into three categories (i) fruits with pulp and seeds such as apple, orange, watermelon etc. (ii) fruits with stones, such as plum, cherry, peach, etc., (iii) dry fruits such as almonds, walnuts etc.

          According to botanists, beans and peas also fall under the category of fruits. Cucumbers and marrows are also fruits. But cabbage, turnip, radish, cauliflower - all are vegetables. Onions, potatoes etc., are also vegetables.

          In USA a controversy over tomato went on for a long time. Finally the U.S. Supreme Court had to decide the issue. According to botanical sciences, tomato is a fruit but generally it is used as a vegetable. Keeping both the views in mind, the Supreme Court ruled in 1893 that tomato is a vegetable from commercial point of view. In science, however, this can be treated as a fruit. In reality, the scientific definitions of fruits and vegetables do not agree with the general usage. In our common language we treat some fruits as vegetables such as brinjal, peas etc. and some vegetables as fruits, such as raw banana. 

          Today we see innumerable varieties of insects, birds and animals besides human beings on the earth. Similarly there are various kinds of trees, plants and bushes. All of them come under the category of living beings. Do you know how life started on the earth?

          To study the origin of life on the earth, the scientists study the fossils of those animals, trees and plants which lived on the earth millions of years ago. Excavations carried out at various places on the earth have made available fossils, rocks and bones which throw a significant light on the existence of living beings of ancient times.

          There are many theories about how life began on earth. Almost all religions teach that all forms of life were created by some divine or supernatural being or force. Another theory states that life originally came to earth from outer space through micro-organisms. Many biologists and bio-chemists believe that life developed from non-living materials. 

          However, scientific studies have revealed that life on the earth started with the unicellular organism called amoeba. This happened some 570 million years ago. From this very unicellular amoeba evolved the multi-cellular life on the earth. The first 345 million years saw the development of marine life. The subsequent 160 million years had the development of reptiles. In the last 65 million years, the evolution of mammals took place. Man’s birth is a phenomenon only one million year old.

          It is observed from the study of the cells of plants and animals that they are made of proteins, carbohydrates, fats and many other substances. All these things must have been existing on the earth much before the origin of the unicellular life. Now the question arises: how did these substances which are so essential for life come to the earth? Recent studies have shown that these were formed by electric discharge.

          Around 3500 million years ago, the earth’s atmosphere was full of ammonia, methane, hydrogen, water vapour etc. At that time the earth was very hot and the sky was overcast with clouds. Lightning and thunder were common occurrences. The electric discharge during the lightning led to the chemical combination of the molecules of these gases resulting in the formation of proteins, carbohydrates etc. which finally gave birth to the unicellular amoeba.

          Even though we have been able to solve many mysteries relating to the origin of life on the earth, there are many more which are still needed to be looked into. For example, when atoms and molecules are lifeless, how come their combination creates life? What is it which enables a unicellular amoeba to produce a multi-cellular creature? We still have to find answers too many such complex questions.