Category Biology

Why do trees change colour in autumn?

               On the basis of autumn defoliation (shedding of leaves) trees and plants can be divided into two groups. The first includes those plants and trees which undergo defoliation every year and are called deciduous trees, while the other includes the evergreen plants or trees which defoliate very slowly and remain green throughout the year. Evergreen plants also undergo defoliation but at one time only a small portion of their leaves fall off.

               Every year with the approach of autumn the trees begin to have their period of rest. In autumn the leaves fall and eventually rot down to give the leaf-mould and humus, which are essential to support rich vegetation. During this period gradually their leaves turn yellow and then curl up and fall on the ground. The tree then remains almost completely inactive until the arrival of spring. The denuded or defoliated trees or plants are a sad sight but at the same time very useful to plants because after it plants get a new life and look. Before defoliation the leaves take yellowish, brownish and reddish hues.

               But why do the trees shed leaves? We know that plants are living organisms which need food to survive. This food is obtained by utilizing the organic substances provided by the leaves. Just like animals, plants also produce waste materials and have to get rid of them, but they do it in a different way. They have to retain waste materials in their tissues until autumn. When the time comes for trees to shed their leaves, the plants extract all the useful products from them, and shake off the waste materials behind. Due to the presence of these waste materials the leaves turn yellow, brown and red. When the leaves are shed a layer of dry needles is left on the tree and it is visible in winter.

               Autumn is thus the period in which the trees get rid of their waste materials.

 

Why do animals have a tail?

            All vertebrates except man have a tail. According to scientists, there was a time when man also had a tail. But when he stopped using it, it fell into disuse and became extinct. We still have a mark of a tail on our body. Do you know what the usefulness of a tail in different animals is?

            The tail is found in the post-anal part of the body. It has different uses in different animals. In fishes it is surrounded by a tail fin and plays an important part in providing forward thrust. They have different types of tails. These help them in swimming and providing the upward movement.

            In crocodiles and whales the tail acts as a powerful organ for locomotion. In frogs and toads the tail and tail-fin are present only in the larval states and absent in the adult. Crocodiles use their tails for defence and also to attack their enemies. 

               All reptiles possess a well-developed tail. The length of these tails is different in different reptiles. Tortoises and turtles have short tails while lizards have long ones. If somebody attacks a lizard, it can break a part of its tail. It is a defence mechanism. Reptiles perform wriggling movements with the help of their tails. Lizards after sometime regenerate a new tail. In chameleon the tail is quite long. It can be rolled downwards to coil round the branches for extra grip. The tail of snake is small in size. It acts as a storehouse of fat. The tail of the sea snake is small in size and oar-shaped, and helps it in swimming.

               Real tail in birds is extremely short and stumpy. It gives a support for the feathers. Feathers help birds in flying.

               Most mammals have well developed tails. With these they can get rid of flies. Men and apes do not have such tails. Whales have two lobes of tail fin of which one is at right and one, at left. It helps it in swimming. The tails of kangaroos and squirrels act as a balancing organ during walk and leap. During winter season when squirrels hibernate, the hairy tail acts as a blanket. Rabbits use their tails for providing warning signals. Peacocks display their tails to attract the opposite sex. In this way we see that different vertebrates make use of their tails for some purpose or the other.

 

Why is it said: An apple a day keeps the doctor away?

          The age-old maxim, ‘An apple a day keeps the doctor away’ was a polite way of saying that this habit would help to prevent constipation and other related ailments. Since it was believed that the juice of a raw apple aided the fermentation of undigested foods.

          Although one might question such a sweeping statement in the highly advanced modern times, none can deny that apples are good for health because of their high nutritious value. Some people have modified this statement and suggested that ‘it keeps the dentist away more than the doctor’. According to the dentists, biting on a crisp apple is an effective way of removing food particles from between the teeth. Eating an apple after meals and cleaning the teeth in the night and morning is the best way to keep the teeth healthy. 

          Apples contain Vitamins A and C. They are rich in cellulose and carbohydrates. They also contain some minerals. This implies that apples also help in the prevention and cure of several deficiency disorders, e.g. scurvy, night blindness etc. as well as in purifying blood. They also aid in healing, protection against cold and building of healthy bones, teeth and gums.

          The presence of these food sources and their utility in keeping the body fit and healthy justifies the old adage.

          Apples are eaten raw, both for taste as well as its beneficial values. An apple contains about five-sixths water and the remaining one-sixth consists of sugar, ascorbic acid (Vitamin C) and other acids, and rough indigestible matter. Apart from their nutritious value, apples are also used for cooking sweet dishes, and cider is brewed from fermented apples.

          Apples belong to the family of Rosaceae. In the ripen state they are usually red, yellow or green. Apples grow in temperate zones, in relatively cold weather. By the end of 300 A.D, a Roman writer named 37 varieties of apple and today hundreds of varieties are available with varying sweetness. 

What is a rain forest?

          A rain forest is a warm and rainy place with a thick growth of trees. Because of heavy rains, the trees grow tall and close together. The tree tops are so thickly branched that they almost block the passage of the wind. The air is still and uncomfortable. The thick tree top also prevents sunlight from reaching the ground. It is difficult to walk through these areas. Along with a large number of trees, it also has many different kinds of animals. These include noisy birds, hungry crocodiles, lizards, snakes and jaguars. Thousands of insects of different types are also found in the rain forests. There is an ant called ‘army ant’     that eats anything that would not move out of its way. There are certain mosquitoes whose bite is fatal; sweat bees which crawl into people’s ears and noses, and ticks and flies bite their skin.

          Most rain forests are located near the equator. The largest rain forest is the Amazon basin in South America. The temperature ranges from about 20 to 34°C. Thunderstorms occur about every three days. Areas of rain forests experience heavy rains upto 250 cms (100 inches). The tallest trees of rain forest form a covering of leaves called the upper canopy. The upper canopy may be 30 to 46 m above the ground. Smaller trees form lower canopies. The shade from the trees prevents about 99 percent of the sunlight from reaching the ground. Thus there is not much plant life on the forest floor. Dense vegetation close to the ground occurs in clearings and along rivers. These areas are sometimes called jungles.

          There are different kinds of plant and animal life in rain forests. Tropical rain forests contain the greatest variety of wild life including the wealth of insect life. Many of these insects have wonderful forms of camouflage. Also more different species of trees are found in tropical rain forests than in any other kinds of forests in the world. The soil layer in the tropical rain forests is very good for farming. 

What are pesticides?

            Any plant or animal that occurs in such abundance as to pose a distinct threat to man or his interests is called a pest. And the chemicals used for mitigation, control or elimination of such plants or animals are known as pesticides. Today we have algaecides, defoliants, herbicides, plant growth regulators and fungicides in use to control the growth of undesirable plants which compete with crops or other useful plants. Attractants, insecticides, miticides or acaricides, molluscicides, nematocides, repellents and rodenticides are used to reduce parasitism and disease-transmitting organisms in animals, crops, plants, foods, textiles and human beings.

            Most of the pesticides are chemical compounds and act in a similar fashion, i.e. by blocking some metabolic process. They, however, differ in composition, potency, mode of action, speed of effect. So different pesticides are used at different stages of infection. 

Continue reading “What are pesticides?”

Why are crocodiles so dangerous?

          A crocodile is a large reptile with a long cigar-shaped body, short legs and a powerful tail and jaws. They have a heavy body covered with bony scales. Its pointed snout and long partially exposed sharp teeth distinguish it from an alligator (another species of the same family). A crocodile is generally more aggressive than an alligator and may attack large animals such as deer or even human beings. Caymans and Gavials are the largest living reptiles of this family.

          All the crocodiles are carnivores and live in water. Since their eyes and nostrils are located a little higher than the rest of their head, they can hide in water staying almost completely submerged and still able to breath and watch the movement of their prey. They are particularly successful in catching smaller animals because they can float closely up to their prey without being seen. Once they catch their prey they slowly tear it apart in bits by gripping with the teeth and turning it over and over again. The crocodiles have been seen mysteriously more aggressive when protecting a nest or when the water is drying up. They usually feed on fish, birds and small mammals.

          The crocodiles live in tropical areas throughout the world, usually in swamps or marshes, or along slow-moving rivers. They have webbed feet which help them walk on wet or muddy ground.