My Science School

          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. 

          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. 

            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. 

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          Bonsai is the art of developing and growing dwarf trees. The bonsai specimens are ordinary trees and not hereditary dwarfs. They are dwarfed by a system of pruning the roots and branches and training the branches by typing with wire. Any tree or shrub would be called a bonsai if grown in a suitable container and kept dwarf by special horticultural techniques.

          This art originated in China about 1000 years ago, but it was pursued and developed by the Japanese in the 12th century. In fact, bonsai is a Japanese word which means ‘tray planted’.

          The inspiration for bonsai, in fact, comes from the nature itself. The trees grown in rocky crevices of high mountains or overhung from the cliffs remain dwarfed throughout their lives.

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                    Almost every plant and animal in the world has enemies that threaten its existence. So to protect itself every living being has developed some defence mechanism. Sensing the danger some organisms hide, others run, while others just fly away. 

                 Some organisms can even hide without moving. They use ‘camouflage colouring’. That means that their skin colour blends in with the matching colour of the surrounding area so well that the enemies cannot see them. Chameleon has the capacity of changing its body colours. If it is on a green leaf, it turns green; if on a brown twig, it turns brown. Some rabbits change colour with the season. The snowshoe hare is brown in summer and white in winter. The white fur camouflages the rabbit in the snow. Another phenomenon called counter-shading is a common type of camouflage among the fishes. The underside of their body is of lighter shade than the top. This helps the fish to blend in with many shadows it might make. Some other animals have a remarkable ability to take the form and colour of some other object around them. Camouflage also helps some animals catch their food. Since they can blend in with their surroundings, their victims can’t spot them immediately, and thus get caught.

                    Then there are other animals such as antelope who can run very fast. Others may dodge back and forth, like a rabbit. Birds can escape most predators by flying away. 

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          Ever since the evolution of languages different plants and trees have been given names to distinguish one variety from the other. The nomenclature is essential for general use, for a gardener’s catalogue and for botanists. The source of their names is often very interesting and hence worth-knowing.

          Some names have simply been borrowed from other languages, while some others take the name of the places of their origin. Some plants have been named according to their shapes and colours while still others owe their names to some unique features of the plants. Some may have come after the names of their discoverers. Over the time even the names have undergone changes. The origin of names of some important plants and trees are discussed below. 

          The pine tree got its name from the Latin word pinus which means ‘a point’. The spruce tree should really be called the Prussia Tree because it was long thought to be a native of Prussia. The name gradually got corrupted to ‘spruce’.

          A butter cup is a flower which has the shape of a cup and the colour of butter. Lady’s mantle was the name given when ladies wore collars that were pleated and with serrated edges like the leaves of the plant. Honeysuckle has flowers rich in nectar and is, therefore, popular with bees collecting substance for making honey.

          The magnolia has been named after Pierre Magnol of France who was a professor of Botany. The cypress is called so because it was first brought from the island of Cyprus. In Madagascar, there is a tree called, ‘The Travellers Tree’. It has large, fan-shaped leaves that catch the rain water and the passing travellers sometimes quench their thirst with this water.

          The barber plant has been named so because the natives of Orient used to rub its leaves on their faces to check the beard from growing. The names dandelion comes from the French dent de lion because the leaves of this plant resemble the teeth of a lion. Thyme comes from the Latin word Thymus which means to sacrifice and the Romans used to burn this plant on their altars. 

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               One of the major differences between animals and plants is that animals can move whereas plants cannot. They remain static at one place even though they grow vertically horizontally depending on their growth pattern. But how do these plants spread their seeds to grow at different places? It is interesting to note that nature helps them in this activity and this process is termed as dispersion of seeds. 

               There are mainly four agents responsible for the dispersion of seeds, viz. air, water, birds and animals, and the plants themselves.

               When the dispersion is carried out by the plants themselves the process is called dehiscence. In dehiscence (or dispersion by explosion), a seed-containing structure such as a pod, bursts shooting the seeds into the air. These seeds land up at a distance depending upon the weight of the seed and the force with which they are thrown. Some of the plants that disperse their seeds in this manner include plants of the pea, mustard, and balsam family.

               Air is also an effective dispersing agent for the seeds. Lightweight seeds fly from one place to another along with the wind. Some grass seeds have been detected at heights of more than a thousand metres. Lightweight orchid seeds are carried away by air to great distances from their parent plants. Seeds of some plants, such as dandelion and cattail, have puffy hair that helps them float through the air and land up elsewhere. The seeds of maple, ash and box elder have wing like structures to move like small helicopters in the wind and thus get dispersed. 

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                           The botanists study the internal structure of plants mainly by examining their cross section under a microscope. These thin slices can tell us a lot about the structure of the cells that make up the plant and how they vary in different parts of the plant. In 1665, a scientist named Robert Hooke looked at a piece of cork (a material from the thick outer part of certain trees) under a microscope and saw that it was made up of many tiny compartments. He named them cells and this term has been in use since then. The equipments needed for obtaining the sections include a sharp razor, a small fine brush and a number of watch glasses and microscopic slides. The razor is stroked across the top towards the body, cutting off thin slices as required. Cross-sections as well as the longitudinal pieces are obtained in the same manner. To obtain best results the razor and the material must be kept moist with water in case of fresh material or alcohol if the specimen is a preserved one. To prevent shrinkage the sections shaved off are brushed into water or alcohol. For quick examination the sections are placed on a slide with a drop of glycerine. The thin ones that show the cells clearly can be stained for permanent use. In fact staining is a process of adding dyes to show the different tissues in different colours. Many stains are dissolved in alcohol and before staining the sections must be placed in alcohol. After a certain period in the stain(s) the section is transferred to a series of watch glasses full of alcohol. This removes water and the excess stain. The alcohol is removed by dipping the sections in clove oil or benzene. The section is then placed on a clean glass slide with a drop of Canada Balsam (a resinous glue). A thin glass is added as a cover-slip and sealed by warming the balsam to harden it. The slide, properly labelled, can then be kept and examined whenever necessary. Details of time exposure for staining varies with the stain and material used. The information can be collected from a text-book or worked out by practice. In laboratory analysis many modern techniques are being adopted for in-depth studies on the subject.

 

     

              When Darwin propounded his theory of ‘Survival of the fittest’, it created a great deal of controversy during those days. But gradually it started receiving a wider acceptance as many species were found to be either extinct or facing extinction for the reasons best explained by Darwin. Since the evolution of plant and animal lives, quite a few of them have faced complete extinction and others are facing the dangers of extinction. Hence the conservation of certain species that face extinction has drawn the worldwide attention. These species have been categorized as ‘endangered species’. 

                    Factors responsible for endangering the existence of these species are both natural and man-made. Firstly, the increasing human population is encroaching more and more land, and thus creating a scarcity of land for the wildlife to survive. Forests and heaths have been removed to make way for farming. Large-scale deforestation for wood and industrialization is another cause of the loss of wildlife. Secondly, man has hunted down many animals to extinction — auk and dodo are distinct examples of it. Pollution is also affecting the lives of many animals. Every year millions of sea-birds die unpleasant deaths as their feathers get covered with sticky, black oil waste. The natural causes are the unsuitable conditions of temperature and pressure, lack of proper food material, natural calamities etc. 

 

 

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            An affirmative reply to this question is amazing but true. It is a fact that many trees can produce the fruit of another kind of tree by a simple method called ‘grafting’. It is an artificial method or technique of vegetative reproduction in which a small branch or bud of any desired plant is inserted into another rooted plant. This is called plant propagation. If a bud from a twig of pear tree is carefully inserted in a slit made in the bark of a quince bush, a pear twig will grow. The quince bush will bear both pears and quinces.

            In the same way, an almond tree can be made to produce both peaches and almonds. Although sometimes grafting is used to produce freak trees and bushes, this technique is of immense importance in agriculture. Lots of experiments in this field are still being carried on to produce better and new varieties of fruits, flowers and corns etc.

            The greatest advantage of grafting is that it can be used to better the quality and quantity of a particular product. It is possible for a nurseryman or gardener to be sure that his young trees or shrubs will bear the same quality and variety of fruit as the parent tree. A twig taken from a tree and grafted into another tree will produce the same type of fruit borne by the tree from which it was taken.

            There are many methods for inserting the budded twigs or scions, as they are called, into the stock of another plant, but two rules must always be followed. First, only related species of trees or shrubs can he grafted. This implies that apples can be grafted onto pear and quince trees, and peaches can be grafted onto apricot, almond, plum or other stone fruit trees. It is impossible to graft apples on a peach tree. Secondly, the cambium layer (a layer of actively dividing cells) which carries the vital sap of scion must touch the cambium layer of the stock on which it is grafted. Otherwise the grafted twig cannot grow.

            There are different techniques of grafting. It can range from inserting a single bud under the bark to grafting long twigs across the wound of a tree in order to heal wide wounds in the bark. Tissue culture is popular these days in which cells from a plant are removed to propagate in another plant to obtain a hybrid product or the product of the original plant.

            The technique of grafting is now widely applied in case of animals as well as human beings. There have been surgical operations in which a bone taken from the ribs has actually been grafted onto the nasal bone to form a new nose. But the best application is in cases of severe burning where the healthy skin from one part of the body is grafted onto the burnt tissues to remove scars.

               One of the fundamental differences between plants and animals is that animals can move from place to place whereas plants lack mobility. But inconsistent with this general distinction, there are some plants which move on their own. For example, slime molds have amoeba like movement whereby they ‘coze’ from one place to another. Some types of algae have whip like flagellas, they use to paddle themselves through water. Many plants particularly, the lower ones, produce mobile male gametes which swim about in order to find eggs to fertilize. Englena is a protozoa which is capable of swimming. Apart from these exceptions, the movement of plants is usually confined to the movement of some parts of it while the plant itself remains fixed at one place.

               There are three basic types of plant movements: tropisms, nutations and nastic movements. 

               A tropism is a growth response towards or away from something caused by a specific environmental stimulus. The direction of growth is determined by the stimulus. When it is towards the stimulus, it is caller positive tropism and when away from it, it is called negative tropism.

               Tropisms are caused by special growth hormones called auxins. In most of the cases, the stimulus causes the auxins to collect on one side of an affected organ. This causes the cells on that side to grow and divides more quickly than the cells on the other side. As a result, the organ bends away from the side with the most auxins.

               Tropism is of several types. Phototropism is a growth response to the stimulus of light and auxins are concentrated on the side away from the light. This causes stems and leaves to grow towards light and roots grow away from light. Geotropism is the growth towards the gravity of earth. Roofs show positive geotropism while stems show negative geotropism. Hydrotropism is the growth response to the stimulus of water. Roots grow towards water and often move great distances to areas of moist soil. 

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