Category Science

Why insect bites are dangerous?

          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. 

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What are mammals?

          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.

Why don’t spiders get caught in their own webs?

          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.

 

Why do trees shed their leaves?

          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.

 

Why do camels have humps?

          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.

 

Why do flowers have fragrance?

          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.