My Science School

            When a wall lizard is attacked by an enemy it often flees, leaving behind some portion of its tail. The detached tail keeps wagging for some time. This confuses the enemy and the wall lizard escapes. This is how it protects itself from its enemies.

            The wall lizard can detach a portion of its tail at its will. The bones in its tail are joined together loosely, so that any portion of the tail separates easily from the main body. When the tail is separated, it does not lose much blood because the ends of the blood vessels are almost sealed. It is, therefore, possible for the wall lizard to get rid of its tail. Soon it grows a new tail.

            Scientists have studied more than 3,000 species of lizards till today. It has been found that their bodies are usually divided into three distinct parts: head, trunk and tail. Most species have four legs. Although most lizards are hatched from eggs, a few are directly born. Most lizards feed on insects; a few of the larger species are more than 3 metres long. They are quite frightening in sight. They can easily kill a fairly large animal with one blow of their long, strong tails. They are mostly found in tropical countries. A number of African species live in tropical forests where they climb trees. Some of them have flattened flaps of skin which can be stretched down between hind and fore limbs to jump from tree to tree. Lizards can run fast, and some can swim or even glide through the air.

            Crabs and lobsters are also able to get rid of their legs in a similar fashion. When a fish catches the leg of a lobster, it jerks away its leg and escapes. These are the defence mechanisms which enable some animals to survive.

               On the basis of body temperatures, all the living beings have been classified into two categories: the cold-blooded and the warm-blooded. Cold-blooded creatures are those whose body temperature does not remain constant. Their body temperature changes according to the surroundings. It becomes high during the summer and low during the winter. Interestingly it changes even during the day - being less in the cool morning than in the hot moon. Frogs, tortoises, snakes, skunks, and some variety of fishes are the cold-blooded creatures. During the winter their temperature falls down to such a proportion that in order to survive they go into their holes inside the earth. If they do not do so, their blood would freeze and they would die. During winter they keep on sleeping in their holes inside the earth. This is called the ‘hibernation’ period. They do not take food during this period. Even their physical processes get slowed down. When they come up on the earth’s surface after this period, they remain very weak.

                On the other hand warm-blooded creatures are those whose body temperature remains almost constant in winter or summer. The surroundings do not affect their body temperature. Man, bat, dog, cat, cock, cow, etc., come under this category. For example, the normal body temperature of man is 98.4°F. And of some other creatures it is as follows: bat, 104°F; dog, 102°F; cow, 101°F; cat, 101.6°F; cock, 101°F. They need more energy to maintain a constant body temperature. That is why the warm-blooded creatures need to consume more food. Their physical processes continue normally all round the year. There are special organs like hypothalamus in their bodies that control the temperature and do not allow it to go beyond or below a certain level. In these animals there is a balance between the heat lost and the heat produced.

          We know that animals can see things like us. But can they distinguish between different colours like human beings? To find an answer to this question, scientists have conducted a number of experiments on many animals like cats, dogs, apes, bees, etc.

          It has been found that dogs cannot distinguish between different colours. Some dogs were given eatables of different colours. The variation in colours had no effect on them. This has proved that dogs cannot identify different colours. Some experiments of this type were also conducted on cats. Even they were found to be colour-blind.

          Besides man, ape is the only mammal which can differentiate between different colours. All other mammals are colouring blind.

          The honey bee is also endowed with this unique property of colour discrimination. 

          However, it cannot identify the red colour. It appears black to it. It is on the basis of identification of colours that these bees are attracted towards the flowers of different colours from which they collect honey. The honey bee is capable of seeing the ultraviolet rays which even human beings cannot see.

          To test their power of colour vision, they were shown two cards - blue and red. A little syrup was placed on the blue card, whereas the red card was without it. The honey bees gathered on the blue card. Now the blue card, without any syrup on it, was kept at a different place. The bees reached there also. This proved that they can distinguish between different colours.

          Even birds can differentiate between different colours. The colours of the male birds are more attractive than those of the females. Thus the females are attracted towards them because of their colours. It has been observed that birds can identify all the colours of the rainbow.

          Generally animals have no need to distinguish between colours because most of them hunt by night and do not depend on colour. However, they have a greater power of smell and as such their colour blindness does not handicap them.

 

          Lion is the largest and most powerful of the wild cats. It is regarded as the symbol of power and strength in all the countries of the world. We often hear strong people being referred to as ‘lion-hearted’. Also, the figure of the lion, as a symbol of strength, is engraved on many shields awarded to players. Even some flags carry the picture of a lion. The ancient Egyptians believed lion to be a sacred animal.

          It is generally believed that lion is the most powerful animal in the jungle. It is called the ‘King of the beasts’, because it attacks so swiftly that the victim does not get any time to defend itself. It attacks animals bigger than itself like giraffe and wild buffaloes from behind and then tears them apart with the help of its powerful paws and teeth. They often hunt as a team.

          Lions were found in many parts of Europe some 2000 years ago, but gradually they were wiped off. Now they are found only in the jungles of Africa and north-west India. A few, not more than 200 live in India’s Gir forest.

          Lion is a carnivorous animal which kills wild animals and lives on their flesh. It is a member of the cat family. The average length of an adult lion is about 3 metres and its weight varies from 180 to 225 kgs.

          The female species is smaller in size and does not have mane. Lioness generally hunts and kills the prey. Its cubs hop and jump like kittens. The roar of a male lion is a territorial proclamation. Unlike the cat it cannot climb the trees.

          Lions live in family groups called ‘prides’ of 4 to 30 in the forest. It rests during the day and kills at night. It does not attack elephants and hippopotamus. The main animals of its prey are zebra, deer, bear, jackal etc. If it is not disturbed it does not attack anybody. But on being teased or attacked, it turns extremely ferocious. Some lions which get the taste of human flesh become man-eaters and start living in the nearby jungles around villages. Whenever they get an opportunity, they kill man, sheep, goats etc. A lioness, after a gestation period of 110 days, gives birth to one to six spotted cubs.

          Lion can be domesticated and we can see them in the circus performing tricks. Lions have a potential lifespan of 20 to 30 years. 

          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.

 

          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.

 

          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. 

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.

          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. 

          Our body is like a furnace. The food we eat acts like fuel inside the body. It produces heat energy by the process of oxidation. Through this process about 2500 calories of heat is produced every day which can boil 25 kgs of water at 0°C. But what happens to this heat in the body?

          In our body certain metabolic activities are constantly taking place which do not normally allow the temperature to go beyond 98.4° F. Perspiration is one of the means through which the body furnace keeps its temperature normal. In fact, the body temperature is controlled by the ‘temperature centre’ located in the brain. This centre has three parts: control centre, heating centre and cooling centre.

          If the temperature of the blood falls below the normal due to some reason, the heating centre starts operating immediately. At the same time some special glands produce certain combustible chemicals which are used by our muscles and liver to raise the internal temperature of the body to the normal degree.

          On the other hand if the body temperature rises for some reasons the cooling centre goes to work. The process of oxidation slows down. Sweat glands start excreting sweat. Water, urea and some salts come out with the sweat. The sweat glands work fast only when the internal temperature of the body goes up. Sweat evaporates with the help of the body heat and this produces a cooling effect in the body. This process is similar to that of cooling of water in a pitcher during summer. Evaporation always causes cooling. Sweat, therefore, is a very effective process of controlling the body temperature. It also cleanses the internal parts. Many substances, harmful to the body, are excreted out through the millions of pores of the skin in the form of sweat. When the humidity is high, sweating causes uneasiness because the rate of evaporation under humid conditions decreases.

          A cat produces a cat and a rat, a rat only. The neem tree does not bear mangoes and the mango tree does not bear guavas. The children of human beings resemble their parents. This is a universal truth that the offspring of all the living beings have close resemblance to their parents. Do you know why it is so?

          The answer to all these questions can be had from the genetics - the science of heredity. It deals with all those factors which are responsible for the close resemblance of the offspring to their parents. With the help of genetics we also come to know what traits in the young ones would be different from those of the parents. 

          Heredity is another name of the transmission of characteristics from parents to the offspring. These are inherited from the parents through very minute particles, called ‘genes’. The term ‘Gene’ was coined in 1909 by the Danish geneticist Wilhelm Johannsen (1857-1927). It is a part of the cell. There are some 20,000 genes in the nucleus of every cell. Out of these, some ten thousand of them are inherited from the mother and the other ten thousand from the father. All these genes are contained in 46 chromosomes in the nucleus having a diameter of .01 mm. At the time of conception 23 chromosomes come from the father and 23 from the mother. Thus there are 23 pairs of chromosomes in every cell. The gene is the unit of heredity. In every plant and animal, some genes come from the male and some from the female. 

          Gregor Mendel (1822-1884) a Christian priest and biologist from Austria, is called the father of genetics. He conducted many experiments on the pea-plants and formulated certain rules of heredity. These are known as Mendel’s Laws. He showed through experiments that the dominating genes of parents dominate the traits of the children also. For example, if the eyes of one parent are brown, and those of the other blue, then the eyes of the child would be brown since the brown colour has dominance over the blue. If the eyes of both the parents are blue then the eyes of the children will also be blue. Similarly children of tall parents tend to be tall and those of short parents short. In this way genes are responsible for the close resemblance of offspring to their parents.