My Science School

            The holes in a piece of bread are made by bubbles of gas. In bread-making flour and water are mixed to form dough. Then a small amount of yeast is added to the mixture. Yeast is a type of fungus which grows very quickly when it is warm an damp. While growing, it gives off a gas which bubbles up through the dough, making it expand. It is yeast which gives bread its particular flavor and appetizing  smell.

            No one knows when yeast was first used to make bread, but it must have been many thousands of years ago. According to one story, the idea was the result of an accident. Some yeast is said to have got into the dough by chance and made it rise. Because this loaf was twice as big as normal, people thought it must be magic. But as the bread tasted better than the usual flat, heavy loaves, they soon used yeast to make all their bread.

            Cakes also have holes in them made by bubbles of gas. But these are made by a different substance which leaves practically no flavor. This substance is baking-powder, which is a mixture of tartaric acid and bicarbonate of soda. When these two chemicals are mixed together, wetted and heated, they react to produce carbon dioxide. This gas bubbles through the cake mixture to make I rise while being baked.

               After extensive us as a pesticide, DDT was found to have many harmful after-effects on human beings and animals. The control of insects was revolutionized by the introduction of DDT after the Second World War. It was employed to combat a wide range of insects which attacked food crops and was also instrumental in bringing the world malaria problem under control. But by the 1960s it was found the DDT affected the metabolism of many birds so much that their eggs became too fragile to survive. As a result many species have nearly become extinct. Several kinds of fish have also been seriously affected. Large numbers of insects which served as food for the both fish and birds have been destroyed.

               The effects of DDT on food for human consumption have been extremely serious. Food becomes poisonous if the amount of DDT in it exceeds a certain limit. However, such pesticides are now heavily restricted b most governments.

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            Photosynthesis is the process by which green plants make food for themselves and indirectly, for all animals, including human beings.

            In photosynthesis plants combine water and salts in the soil, and carbon dioxide in the air to build up organic compounds, such as sugar starch and proteins. To do this they use the energy of sun light, which is absorbed with the help of the green dye in their leaves called chlorophyll.

            This process of manufacturing food from what they absorb through their roots and leaves make green plants the primary food producers in the world. All animals draw their nourishment from them, either by feeding on plants themselves or by eating other animals that do so. During photosynthesis, which takes place only in daylight, excess oxygen is produced and released into the atmosphere for animals to breathe.

            After the Second World War, the American scientist Melvin Calvin wrote a book about how plants capture the carbon dioxide in the atmosphere. In 1961 he received the Nobel Prize in chemistry in recognition of his work.

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          Vampire bats are dangerous because they carry rabies and other diseases and infect their victims as they suck the blood which is their only food.

          Vampire bats (Desmodontidae) are found only in South and Central America. They have extremely sharp teeth and pierce the skin of their prey so gently that the victim does not awaken. Blood is drawn into the mouth by the almost tubular tongue and the vampire bat’s whole digestive system is specially adapted for his diet of blood.

            You would find a Red Giant on the Sierra Nevada Mountains of California in North America. It is a huge redwood tree, called a giant sequoia. These trees, members of the conifer family, are the largest in the world and grow to a height of 300 feet. They have a very hard, reddish brown wood and a thick, very rough bark. The giant sequoias were believed to be the oldest living things in the world. The ring marks on the stumps of the oldest trunks have been carefully counted and it is now known that some of the biggest are about 4,000 years.

              Many of these trees were cut down for their timber, which is resistant to attacks by fungus, and termites and other insects. To preserve the remaining groves of these huge redwoods, a reservation called the Sequoia National park was set up in 1890. The largest tree there is 272 feet high and has a circumference at the base of its trunk of 101(1/2) feet. Its weight has been estimated to be over 6,000 tons.

           Some of the other trees are taller but do not have such large trunks. A tunnel has been cut through the base of one of these giant trees which is big enough to drive a car through.

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          Fossils are the remains, moulds, traces or impressions of prehistoric animals and plants found in the ground. The word comes from the Latin fodere meaning to “to dig”, and originally meant any old, curious object dug out of the earth. But since about the middle of the 16th century, fossils have been regarded specifically as hard objects showing evidence of earlier forms of life, often many millions of years old.

       There are many kinds of fossils. Some are footprints which strange prehistoric animals left behind in mud long since turned to rock. Others are stones which were ones soft substances, but still preserve the outlines of extinct plants, or of seashells, or of the bodies of animals. Sometimes even the bones of creatures have survived.

      The study of fossils, which is called palaeontology, has enabled scientists to fill many vital gaps in the history of the world and its inhabitants. For example, fossils have shown that rocks in great mountain ranges like the Alps or the Rocky Mountains were once below the surface of the sea. They have indicated that the United States and Europe were once covered by tropical forests. Also, they provide evidence of the common ancestry of animals which today differ widely in appearance.

      The subject can be rewarding hobby for amateurs. Many important contributions to the world’s great collections have been made by people who looked for fossils in their spare time or even came across fossils by sheer accident.

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Trap-door spiders are to be found just under the surface of the earth. They belong to the class of spiders called mygalomorphae which includes the bird-eating spiders of the tropics. All these spiders tend to be rather large. They have four lungs instead of two, and their jaws work vertically instead of sideways.

     The trap-door spider has perfected the art of burrowing underground. Its jaws are provided with a special row of teeth with which to dig out its home. It lines its burrow with silk and makes a trap-door consisting of layers of silk and earth. The outside of this door is coated with moss or some other form of camouflage. The spider lies in weight behind its trap-door, darting out to seize its prey.

    Trap-door spiders are wide-spread throughout the hottest regions of the world, with comparatively few in the temperature zones. Specimens of up to four and a half inches have been found. It is estimated that some may live up to 20 years.

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The shape of a bird’s bill or beak is closely related to the kind of food it eats and the way in which it collects or catches this food.

    A crow or jay has a strong all-purpose bill, capable of killing small mammals but fine enough at the tip to pick up small insects. Many songbirds have slender bills for picking up insects from leaves or out of cracks; others have wide flat ones for catching flies or strong thick one for cracking seeds and nuts.

    Birds which dig for worms usually have long bills with sensitive tips while many water birds have broad dredging bills. Divers and grebes have straight spear-like bills and the birds of prey have strong hooked bills for tearing flesh.

    Birds which catch insects on the wing (nightjars, swallows etc.) have tiny beaks but an enormous “gape” by comparison.

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Frogs’ eggs become tadpoles within two weeks of being laid in the water, but tadpoles may take anything from two months to three years to change completely into frogs.

      The time taken seems to depend on the environment. Tadpoles will generally develop faster in warmer waters. Also the more advanced species of frog have simplified and shortened the process of transformation.

    Tadpoles, like fish, breathe through gills. They develop lungs during the change-over, gain legs and loose their tails. Their diet changes, too-tadpoles live on plants in the pond, but frogs live on very small insect.

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Termites are soft-bodied insects belonging to the family Isoptera. They are sometimes called “white ants” but they are like ants only in that both species live in social colonies. They live in the tropics and temperate. Countries and make various kinds of nests below the ground, but the most spectacular are large structures built above ground called “termitaria”. They are built from earth excavated below ground and cemented together by saliva. Some of these nests are 20 feet high and almost too hard to break open even with a pickaxe.

      The termite community is divided into four groups, but only two can breed. Each colony is founded by a “royal pair” and the queen’s life is devoted to laying eggs.

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Blue whales are the largest living animals. They are cosmopolitan creatures and are found in most of the seas, from the polar caps to the equator. Normally those which inhabit the colder seas will migrate to warmer waters in winter.

    Their dimensions are almost beyond belief. Although figures can never be quite accurate, a blue whale can weigh more than 200 tons and many have been found measuring over 100 feet in length. The tongue alone, of a female whale found in Antarctica, weighted well over four tons.

      It has been estimated that in the 1930s there were nearly 40,000 blue whales in the world. But by the end of the 1960s there were fewer than 1,000 alive. This was because for the misdirected efforts of over-zealous hunters.

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The sepals of a flower protect it while it is in bud. The flower is really a kind of shoot, In which the leaves have been altered so that they can take on the task of producing seeds.

    In a simple flower these leaves are arranged in circles, called whorls. The outermost are five green, leaf-shaped sepals. Inside these are five petals, usually heart-shaped, each with a small flap at its base where nectar is produced to attract bees and other insects.

     Both the sepals and the petals are attached at their bases to the “receptacle”, the swollen end of the flower-stalk, which looks like a cone in the middle of the flower.

    Above the sepals and petals are the parts of the flower used in reproduction. These are the stamens, which contain the yellow pollen, and the carpels, which contain the ovules.

   Most flowers are built on this plan but there are wide variations in size, shape and colour, and in the numbers of the different parts of the flowers.

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The coccyx is the lower end of the spinal column of man and consists of four nodules of bone, like tiny vertebrae, corresponding to the tail, which is found in lower animals. The bones are deeply buried in muscle tissue, but occasionally they jut backwards and are surrounded by a fold of skin, so as to form an actual tail.

    The name coccyx was given by the Greek physician Galen (c. A.D. 130-200) and free comes from the Greek word for “cuckoo”, as the bone rather resembles a cuckoo’s bill.

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The dodo was rather a stupid bird. Indeed, it was so stupid that it was named dodo by the Portuguese when they discovered Mauritius-its home-in 1507. The Portuguese word doudo means stupid.

    Mauritius is an island, 720 square miles in area and lying 500 miles to the east of Madagascar in the Indian Ocean. Until the arrival of man, with his attendant creatures such as the cat and dog, the dodo had been able to live in peace. It had no enemies, which was fortunate because it was big and clumsy and was completely unsuited to fleeing from danger. Its short legs were almost incapable of supporting the weight of the fat, round bocy (about the size of a swan’s) and the ridiculously inadequate, stubby wings were of no use for flying.

    Within 180 years of its discovery by the Portuguese, the dodo was extinct. Over the intervening years several were brought to Europe alive, and one was to be seen in London in 1638. By 1680 the dodo had succumbed.

   With the help of drawings and by the collection of bones gathered in Mauritius has been made of the poor bird. It can be seen at the Natural History Museum in London.

    Mauritius is the only place in the world where the bird is known to have existed. A similar Island of Rodriguez, but this also has become extinct.

    The phrase “as dead as the dodo” is used to mean that something is very dead indeed.

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Many Japanese trees are small because they are dwarfed by the Japanese art of bonsai. This art consists in training and growing dwarf trees as symbols of the Japanese ideal of the immersion of the self in nature. This ideal also finds expression in their poetry, the tea ceremony and flower arranging.

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