My Science School

Many varieties of seals live beyond the Arctic Circle. All these animals have short necks and no external ears. It is this latter feature that distinguishes true seals from sealions which have prominent ears.

Seals range in size from the little fresh-water seal of Siberia, about one metre long, to the enormous sea elephant of the subantarctic regions, which can grow to 6 meters in length.

The most common type of seal, however, grows to a length of just over 2 metres. Its fur is brown or yellowish with dark patches. The seal’s hind legs are part of its tail and cannot its body along in a clumsy manner when on land.

On the ice the animal is not awkward and it slides along for considerable distances. But the seal’s true element is the sea for this animal is an extremely skilful swimmer and dives at the slightest sign of danger.

 

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In zoos the popular names of the animals on display are written on a label in front of their cages. The label also carries the animal’s scientific name in Latin. For example, on a lion’s cage, the Latin name is Panthera leo; on a tiger’s cage of a leopard the name is Panthera pardus.

Latin is the language accepted by scientists and zoologists throughout the world to avoid confusion. The Latin name for any animal consists of two words because the scientific classification of animals still follows the basic principle laid down by the botanist Carolus Linnaeus. In the examples we have already quoted the first part of the names is the word Panthera: this refers to the genus of the animal. The second part of the name refers to the species. Members of an animal species that have many features in common come together in a genus. The Panthera genus, for example, includes the large cats which are unable to purr. Smaller cats, which can purr but do not roar, belong to the genus Feils. Both genera are in the family Felidae. A number of genera from a family and several families form an order. The orders come together under classes and the classes fall into types. The total of all these forms the animal kingdom.

 

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Dates are used in many ways. Those with a soft, pulpy flesh provide a syrup known as date honey which can be made into a jam. Hard-fleshed dates can be preserved in sugar or made into flour. The juice of dates can be fermented and turned into an alcoholic drink called arrack. The leaves of the date palm can be used for making mats or cord. The seeds or stones of the dates can also be made into buttons.

Dates are full of nutrition, especially dry dates. Dry dates are high in calories particularly carbohydrates (74 grams). It also contains several essential vitamins and minerals with fibres. Dates are famous for their rich concentration of antioxidants which can be beneficial for your cardiac and pulmonary health.

 

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Oil of cedar is a precious substance which the ancient peoples used to, embalm dead bodies. It was also once used to coat books to preserve them from insects and damp. The oil is obtained by distilling it from the African cedar and is essential oil, that one that gives a plant, flower or fruit its distinctive odour or flavor. These oils are used for the scenting or flavoring of numerous products, such as perfumes, cosmetics and soaps.

The African cedar grows in the north of that continent, especially on the Atlas Mountains. It is a very imposing conifer that bears many leaves and grows to a height of more than 40 metres. It closely resembles the more famous cedar of Lebanon which was also highly prized by the ancient peoples.

Cedar wood is soft and rich in resin. It can be worked easily and is used extensively in building and furniture-making.

 

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The holly bush can often look like a tree and grow to a height of more than 7 metres. Usually it is a shrub which in winter stands out in contrast with its glossy, green leaves against the dead, brown foliage all around it. The leaves of holly are intended to keep animals away. The leaves on the lower 'branches of the plant are very prickly as this is the part most likely to be attacked by hungry animals. The leaves nearer the top of the plant are not so prickly because they are out of the reach of leaf-eating animals.

Holly usually grows in oak and chestnut woods. In winter the plant has bright red berries and is widely used in Christmas decorations.

 

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If we examine the trunk of a tree that has been chopped down, we will see first of all the outer ring of the bark which acts as a sort of waterproof coat for the tree. Inside the outer covering come a number of concentric rings. Each one of these rings represents a year in the life of the tree. The space between the rings is the wood which the tree produced during one year.

 

By counting the number of rings we can tell when the tree was born. These rings also indicate the dry periods the tree lived through as well as wet periods. In dry times the rings are very thin. In heavy rainfall years the rings are thicker.

Slender cores of wood can be taken from a tree, from the bark to the centre of the trunk; these samples reveal the same information and are taken with a borer that does no, significant damage to the tree.

 

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The prickly pear grows wild in warm Mediterranean regions. It anchors itself to rocky, barren slopes and forms large areas of scrub that grow to about 3 meters high. On cultivated land the prickly pear is often cultivated as a hedge. It is enough to plant just one leaf for a whole bushy shrub to start growing.

‘Leaf is not really the correct word to describe the green, fleshy vegetation of this plant. The leaves are really parts of the plant's trunk which measure from 15 to 40 centimeters long and 15 centimeters wide.

The actual leaves of the prickly pear are very small and are shed almost as soon as they have appeared on the plant. They leave behind them thick tufts of thin needles. One of these needles grows outwards and becomes very sharp.

Since the prickly pear has no leaves the task of producing chlorophyll, without which no plant can live, is carried out by the trunk.

The prickly pear was introduced into Australia at the end of the eighteenth century as a food plant for cochineal insects. It spread and by 1870 had become a pest in Queensland and New South Wales. Its growth was controlled by the introduction of a little moth, the cactoblastis

 

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By using water, air and some mineral substances obtained from the soil, plants produce sugar and starch which are the basis of all organic matter. This transformation is made possible by chlorophyll which takes the energy of sunlight. Chlorophyll then uses this energy to separate the atoms of oxygen, hydrogen and carbon which make up air and water and rejoins them to produce organic matter and oxygen gas.

This process of photosynthesis is an extremely delicate and complicated operation. Scientists have succeeded in producing artificial photosynthesis.

 

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Every plant has to feed itself in order to carry out its vital functions. Usually the raw materials are extracted from the surrounding soil through the roots. In this way the roots supply the leaves of the plant, which are really small chemistry laboratories, with water and the necessary minerals to produce organic substances.

There are two basic' types of roots: the taproot which consists of a single large axis from which fine hairs grow, such as the radish or the turnip, and the fasciculate root which is composed of several axes each of the same size as in the dahlia.

In each type of root there is a root-cap at the end of each root. This cap protects the growing part of the root organism and helps it to dig into the soil. When viewed through a powerful magnifying glass these caps are seen to be covered in very fine hairs. It is through these hairs that the roots suck in water and certain mineral salts from the soil.

 

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Everything inside a flower is arranged to make pollination possible. This operation involves the transfer of pollen from the anthers of the stamens to the pistil.

It is very rare, however, that the pollen produced by one flower is used to fertilize the pistil in the same flower. Instead, flowers are designed to obtain pollen from other plants and their flowers. This enables better seeds and fruits to be produced and is known as cross-pollination. Its usefulness was demonstrated by the great naturalist, Charles Darwin, in 1859.

Cross-pollinating flowers occasionally have their pollen waiting on the stamens before the pistil is ready to take it, or the pistil may be ready but the stamens have produced no pollen. Some plants produce flowers with' stamens only (male flowers) while others produce flowers with only pistils (female flowers). These plants are pollinated with the help of the wind which blows the pollen grains through the air.

Such plants produce huge amounts of pollen because much of it is lost in the air and only a small quantity finally reaches its proper destination.

 

 

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A flower consists, first of all, of a pedicle, or stem, that joins it to the plant. The stem broadens out into a hollow cup known as the receptacle. This is surrounded by green sepals which form the calyx. The flower's petals grow from the calyx in all kinds of shapes and colours.

At the centre of the flower there is a part that resembles a long necked bottle. This is the pistil. The top of the pistil is called the stigma, the neck is called the style and the bottom, which is wider than the rest, is the ovary. Inside the ovary lie several tiny grains called ovules. Each one of these grains will become a seed. The ovary around the seeds will grow larger and turn into a fruit. The pistil is surrounded by several thread-like filaments, the stamens. At the top of each stamen there is a bag-like structure called the anther which contains the pollen.

 

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Bacteria are tiny organisms that can be seen only through a microscope. They live alone as solitary individuals or in groups that are linked like chains. They vary in shape according to their species.

Bacteria are responsible for many diseases in people, plants and animals. These diseases are infectious because they can be passed on whenever the bacteria move to a new place. In plants, over 150 different species of bacteria cause three main types of disease: vascular, parenchymatous and hyperplasic.

In vascular diseases the bacteria attack the vessels and main channels of a plant. This causes a blockage of vital food supplies and the plant dies.

In parenchymatous diseases, the bacteria attack the active tissues of the plant which then rots and dies.

In hyperplasia, the bacteria cause the cells of the plants to multiply wildly and produce swellings or tumours on the stem, the roots and sometimes even on the leaves.

Plants can also catch serious diseases from viruses. There are many kinds of virus, each different from the other and each capable of causing several disorders. It has been found that viruses are carried from one plant to another by insects. These insects act as carriers by sucking the juices of a diseased plant and then injecting them into a healthy one.

A number of viruses are soilborne and some of these are spread by eelworms that feed on plant roots.

Man, too, can spread viruses by handling diseased plants and then touching healthy ones.

One disorder caused by viruses is dwarfism when the plant is stunted. Other virus infections attack the leaves and make them dried and crumpled or cause blisters on the plant's tissues.

 

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Some plants are killed by the frost when winter arrives but the seeds they dropped on the ground in the autumn ensure that new plants grow to replace them in the spring. Other plants spread out their leaves and flatten them against the ground in order to obtain whatever warmth is left in the soil. The violet is a plant that does this.

Myrtle and heather allow their upper plant to wither and die, but the lower part of the stem stays alive and produces buds when the growing season comes.

Many other plants escape from the cold weather by hiding under the soil. These plants are tubers, bulbs and roots which have stored up all the food they need. When the warm weather returns they are ready to push out green leaves and new buds.

Sometimes mechanical means are used to protect plants from frost. In regions where citrus fruits are grown oil heaters, called smudge pots, are placed in the groves and huge fans are also used to keep the air moving and prevent the cold air from settling on the fruit trees.

 

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There are some seventy different varieties of Nepenthe, most of which grow in the tropical forests of Africa. These are rather strange plants which have clever traps to catch insects and other small creatures who are unwary enough to venture close to them.

The Nepenthe is a climbing plant which produces flowers in bunches. The plant’s insect-traps are located at the tip of the leaves. These traps are an extension of the main vein of the leaf and look like stems with a small bladder on the end. This bladder is known as the ascidium and insects are attracted by its colour and its sugary contents. The insects go inside the ascidium but they cannot get out again because of hundreds of little stiff, downward-pointing hairs. Below these is a highly polished area, without hairs, which is like a greased slide. The more the insect struggles, the farther down it slips until it drowns in an evil-smelling liquid.

 

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Early in the summers pretty little bunches of golden yellow flowers about a centimeter across appear floating on the water of ponds and ditches. This is the bladderwort, or Utricularia, a planet that keeps most of its body under water and looks very innocent. However underneath its leaves the Utricularia has lots of little bladders which turn into deadly traps should any unwary insect go too near them.

These bladders have a small opening surrounded by short hairs. When an insect explores the opening the plant swallows the insect and closes the opening with a special little lid. The plant then digests the captured animal through millions of microscopic tubes in its tissue.

This plant grows all over the world, on land as well as on the water, but the bulk of the species are found in tropical regions and only about four occur in Europe.

 

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