Category Biology

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. 

How do we estimate the age of a tree?

          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’.

Why are some fruits sweet while others are sour?

          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.

Why do elephants have trunks?

          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.