My Science School

          Do you know that there are certain plants which cannot produce their own food because of the absence of chlorophyll? Such plants, therefore, depend on other plants or dead animals for their food.

          Plants which feed on dead organic matter are called ‘saprophytes’ and those which feed on plants are called ‘parasites’. Saprophytes play an important role in the decay process. They clear the land of dead animals by digesting and absorbing nutrients from the dead material. For instance, all fungi and bacteria which do not contain chlorophyll fall in this group.

          Parasitic plants feed on other plants. They obtain water and food from the host through specially developed organs called ‘haustoria’ which secure the parasite to the host and grow into the host’s tissue. Parasitic plants do not give any benefit to their hosts in anyway. In some cases, they cause harm to their hosts.           

          The extent to which a parasite is dependent on its host largely determines its vegetative form. True parasites such as dodders, cuscuta and cassytha are entirely devoid of chlorophyll and rely entirely on the host as a food source. The dodder, which is a well-known parasitic plant, looks like a tiny slender snake. Its colour varies from bright yellow to red. When a dodder seed germinates, the young plant begins to grow in a circular fashion, searching for the mother plant. Once it gets a host, the thin stem of this plant twines around the host’s stem and starts taking food from the host.

          Other parasites such as the toothwort and the broom are parasitic on the roots of other plants, rather than their stems. Correspondingly, these plants are less conspicuous than dodders because their vegetative parts are underground.

          A well-known example of a partial parasite is mistletoe which grows as a cluster of branches hanging from trees. It produces a haustorium which connects with the host’s stem and extracts water and mineral nutrients. It can produce food by photosynthesis but needs water and minerals from trees.

          Mosses and lichen are also parasitic in nature. They cover the bark of the trees and take food from them. Rafflesia Arnoldi of Sumatra is also a famous parasitic plant.

 

          Insect is such a tiny creature that it is difficult to believe that it has a circulatory system and has blood in its body. But interestingly insects have a heart, blood and other organs.

          Insects are found everywhere in the world, except in the deep seas. Fossils indicate that they have existed on earth for more than 400 million years. They have been able to adapt quickly and efficiently, to environmental and climatic changes.

          The body of an insect is divided into three sections: head, thorax and abdomen. The head has one pair of antennae which serve to convey the senses of touch, taste and smell. There are usually two compound eyes which provide proper vision and two or three simple eyes (ocelli) which detect light or darkness. The mouth may have biting or chewing jaws or piercing and sucking structures. The head also contains a brain which connects with nerve cords in all parts of the body.

          The thorax or middle part of the body has three pairs of jointed legs. These legs are equipped with sticky pads or claws at the end. Insects are the only invertebrates with wings. Although most insects have two pairs of wings, some have only one pair or no wings at all.

 

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            In cold countries, when the temperature falls below the freezing point, water, lakes and rivers get frozen. Under such conditions, how do aquatic plants and animals survive?

            Generally all liquids expand on heating, but water is an exception. At 0°C, if water is heated gradually, its volume decreases and this contraction continues till the temperature rises to 4°C. Above 4°C water starts expanding and keeps on expanding with further rise in temperature. This shows that at 4°C, the volume occupied by a given mass of water is minimum. In other words, the density of water at 4°C is maximum. This irregular expansion of water is known as anomalous expansion.

            This anomalous expansion of water plays an important role in nature. Due to this only the upper layers of water in the ponds and lakes in cold countries get freezed. Lower layers remain as water, and as a result aquatic animals survive.

            In cold countries, during winter when the atmospheric temperature is very low, the upper layers of water in the lakes and ponds start cooling. When the temperature of the surface layer falls to 4°C, the water acquires maximum density and sinks down. The lower layers of water then rise up. This water also gets cooled to 4°C and again sinks down. The process continues till the temperature of the whole water falls to 4°C. As the temperature falls below 4°C, the density of water decreases and as a result water at the surface becomes lighter and does not sink down. The surface water finally freezes while the lower layers remain at 4°C. As ice is a bad conductor of heat, freezing in the lower layers is a very slow process. Thus underneath the frozen layer, fish and other aquatic animals and plants survive. Had the expansion of water been uniform, the lakes or ponds would have been completely frozen, along with the aquatic plants and animals. In this situation no plant and animal would have survived.

 

               According to ornithologists, the hearing abilities of birds are similar to those of man. Birds have ears for hearing which are in many respects similar to those of reptiles. The outer ear consists of a short external passage or meatus, ordinarily hidden under the feathers at the side of the head. Most birds have a muscle in the skin around the meatus that can partially or completely close the opening. The tympanic membrane bulges out. From the inner surface of the tympanic membrane, an ocular chain transmits vibrations of cochlea. The chain consists of an osseous inner element, the columella and a cartilaginous extra-columella that extends the columella peripherally and connects with the tympanic membrane. 

               It has been observed experimentally that most of the birds respond over a frequency range from 100 to 12,800 Hz. The frequency range of human ear is from 20 Hz to 20,000 Hz. Birds can separate sounds which appear as continuous to the human ear.

              Birds use their hearing power to guard themselves against enemies and other kinds of danger. Some birds also use vocalizations to identify their mates or group member. Owls locate and catch their prey by auditory cues.

               Birds are warm-blooded animals of the class ‘Aves’. Like mammals they are vertebrates. They do not bear their young but lay eggs from which they are hatched.

               Birds have feathers, wings and beaks that make them different from other animals. They don’t have any teeth. They mainly feed on insects, seeds and animal flesh. Their sight is well-developed and highly efficient, but their sense of smell is rather poor.

               There are about 9000 species of birds. They range in size from the tiny humming bird of about 5 cm in length, to the ostrich, which can grow 2.5 metres in height and can weigh as much as 136 kg!

          Do you know any animal that washes its food before eating it?

          Raccoon is such an interesting animal. Most raccoons wash their food, and there have been instances when not finding water to wash their food, they refused to eat. However, they have also been known to eat food even when they could find water nearby. Some racoons have been observed to eat without ever washing their food.

          Nobody really knows why raccoons wash their food. They do not seem to wash it in an attempt to clean it, since they even wash it in muddy water. Besides they would even wash food caught in the water which certainly does not need washing. So the reason is probably that water makes food tastier for them.

          The name ‘raccoon’ comes from the American Indian word arakhuman. They are furry mammals and belong to the family Procyonidae. They are found in the stretch from Southern Canada to Panama, except in the high Rockies.

          Raccoon is usually gray in colour, sometimes tinged with yellow or brown. It has a bushy, ringed tail which is about 25 cm long, dark brown in colour with four to six yellowish rings. The eyes are covered with black marks. They have pointed snouts and strong, sharp claws. They use their paws to find food.

          Raccoons live in places where there is water and trees for dens. Their food, which they hunt at night, is mainly crayfish, clams, fish and frogs. They find their prey in muddy water. They also feed on nuts, berries, fruits and particularly young corn.

 

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               There are about 600 marine organisms which produce light from their bodies. The main groups of marine luminescent organisms include protozoans, coelenterates, polychactes, molluscs, crustaceans and fishes. Many sea bacteria are also luminescent. Sponges, jellyfish, beetles, flies and earthworms also produce light. This type of luminescence is called bio-luminescence.

               Careful studies on fishes and other organisms have revealed that this light is the result of a series of chemical reactions taking place in the organisms. In this contest luminescence is basically of two types: Intracellular and Extracellular. Animals which produce luminescence by intracellular mechanism have luminescent glands. The others which produce luminescence by extracellular mechanism have unicellular or multi-cellular organs in some particular regions of their body. There are two substances (Iuciferin and luciferase) whose interaction produces luminescence. Intracellular light flashes range in duration from a fraction of a second to several minutes. Light producing organs in different sea animals are located in the skin on the ventral musculature and within the abdomen. Light is emitted only from the parts where they have these organs.

               Lantern fish and angler fish are two well-known luminescent sea animals. The angler fish has its lighted baits placed in the mouth. Lantern fish produces definite patterns of light.

               Luminescence produced by sea animals is helpful in locating fish shoals because the movement of a large number of fishes produces light which can be detected by light sensors. In the last two decades, significant progress has been made in the detection of fish shoals.

 

          All snakes fall into the category of reptiles. Scientists have so far studied more than 2,400 different kinds of snakes. Only about 8% of them are poisonous. They live on land, under the earth, in the water and on the trees. They are found in almost all parts of the world except in Polar Regions, New Zealand and in some other islands. Snakes are of different sizes and shapes.

          The constrictor snakes such as boa and pythons strike their prey with their teeth, and if the prey is large, then they wrap their bodies around it and squeeze until it suffocates.

          A snake can swallow large animals without chewing them, because its jaws are loosely attached to the skull and the two halves of the lower jaw are connected only by elastic ligaments (tissues). The mouth can therefore open very wide. By using its many backward pointing teeth the snake can gradually widen its mouth over its prey. In the meantime it breathes by bringing the wind pin opening forward to the front of the mouth. Swallowing and digestion of a large animal may take a long time and some larger snakes probably have only a few meals every year.

          The giant 100 kg anaconda snake of the boa family found in South America can swallow a whole pig or deer. In length it is about 10 metres. Due to the huge weight and length, it cannot move much. When some victim passes nearby, it coils its body around and constricts it. It takes several hours to digest the animal. The stomach of snakes produces powerful digestive juices that can break down even big bones of the victim.

          For over 150 million years, the Earth was ruled by some of the most extraordinary creatures, the giant reptiles, popularly known as the dinosaurs. The age of the dinosaurs was the Mesozoic Era which lasted from about 225 million years ago to 65 million years ago. The term dinosaur was coined in 1842 by the English zoologist Richard Owens, from two Greek words deinos and sauros meaning ‘monstrous lizard’ or ‘terrible lizard.

          Dinosaurs were short-legged animals; most of them had gigantic bodies. Most of the giant reptiles were vegetarians, but the few flesh-eaters were indeed terrible. They were able to live both on land and in water. Some walked on two feet, others on four. Many dinosaurs had smooth skin while others had scaly skins and still others were armoured with large bony plates. Their mental development was quite slow and hence they had small brains.

          Dinosaurs are divided into two classes based on the difference between the structures of the hip bone: the saurischians or lizard hipped and the ornithischians or bird hipped. 

The Saurischians: The lizard hipped saurischians are further subdivided into two groups: the sauropods or plant eaters and the theropods or meat eaters.

         The sauropods (plant eating quadrupeds) were the largest dinosaurs. They include the massive brontosaurus. This huge creature grew to lengths of 24 m and weighed about 32 metric tons. The brontosaurs probably spent much of its time eating in the huge swamps that existed then. All of the sauropods had long necks and tails and walked on all four legs. Even larger than the brontosaurs were the brachiosaurs, largest of all the dinosaurs. The brachiosaurs weighed 77 metric tons and was 21 m long.

         The meat-eating theropods walked on their hind legs. They used their very short front legs for grabbing and tearing food. The tall and terrible theropods hunted the plant eating sauropods. The tyrannosaur was the largest meat eating animal ever to live on the Earth. It was 6 m tall and had teeth that were 15 cm long. Its head was larger than that of most dinosaurs and its front legs were too small to be of any use. 

The Ornithischians: The bird hipped ornithischians included both the armour plated dinosaurs and the duck billed dinosaurs. They were divided into four groups: ornithopods which walked on two legs and included some with bills like a duck’s; stegosaurs - which had great bony plates for protection; ankylosaurs - which were even more heavily armoured and ceratopians or horned dinosaurs.

          The disappearance of dinosaurs 65 million years ago remains a mystery. Several theories have been put forward to explain this.

          One theory suggests that dinosaurs became extinct due to the changing climate and want of food. Another theory suggests that the development of egg-eating mammals may have been the chief cause. Some scientists even think that certain harmful bacteria may have evolved and wiped out most of the dinosaurs. Only the first of these theories could receive general acceptance.

 

          The strange sea creatures, with large heads resembling the horse’s head, are in fact bony fish that belong to the family of Syngnathidae. Because of its head it has been rightly named as a sea-horse. Its body is covered with rough bony plates. Its tail is just like that of a snake.

         Sea-horses vary in size (10 cm to 30 cm) and colour, but they all have the same basic shape. They are found in all the oceans of the world. There are 100 species, which may be white, yellow, red or blue. When resting, a sea-horse wraps its tail round a piece of seaweed. Even when they want to feed, they hold on to seaweed with their tails and pick food out of the water as it floats by. 

          The sea-horse swims in an upright position, using its dorsal (back) fin to drive it along. The fin vibrates very rapidly (up to 35 times a second), yet it is the slowest moving fish. It hovers in the water propelling itself and even at top speed it would take a sea-horse about 2.5 days to cover a distance of 1 kilometre!

          The sea-horse is unusual in another way. The female seahorse has a long egg-laying organ which is used to place the eggs in sea-horse’s pouch on the male belly. During courtship the female places her eggs into this pouch and the male then fertilizes them. The male sea-horse can take care of up to three broods every year, with as many as 50 eggs in each brood. The eggs hatch in the pouch of the male and then the tiny young sea-horses leave the pouch about five weeks after the eggs are laid.

           Sea-horses face the least danger from its enemies because other sea fishes do not like to eat them at all.

          Banana is a popular fruit and an important part of our diet today. It originally belongs to South-East Asia and the Indonesian region where it used to grow wild in the forests. Over the years, proper selection and cultivation of different varieties yielded the ‘edible’ banana. By the beginning of the Christian era it had already become a popular fruit in the Asian and Mediterranean countries. When the Spaniards settled in South America, they planted it there and being a tropical plant, it grew well. 

          The banana tree grows round the year in hot and moist climate. Bananas are picked when they are still green and left to ripen while being transported.

          Banana is a wholesome food. It is made up of water (75%), sugar (20%), proteins (2%), fats (1.5%), cellulose (1%), and other substances (1%). It also contains vitamins such as A, C, B1 and B2. It is quite a nourishing and easily digestible fruit. Half a kilo bananas contains 460 Calories and are more nourishing than any other fruit. A type of flour is also made of dried banana. In American and Asian kitchens bananas are used uncooked in salads and with ice creams. In Africa people thatch roofs of their huts with the banana leaves. 

          The plant yields a kind of fibre which is used to make ropes.

          There are over 200 varieties of banana belonging to about 30 species. They are never grown from the seed but are produced by planting of rhizome pieces. The new plants grow up amazingly fast from the buds. Its height varies between 5 to 30 ft. Each plant has about 10 large leaves and bears a single bunch of fruit. The banana leaves are about 6 to 7 ft. long and 1 to 2 ft. wide.

          Today, the United States is the greatest buyer of bananas, consuming more than 60 million bunches every year. 

          Insects are found all over the world. They are small creatures which fly, buzz around on a variable number of legs. They are by far the most numerous of all animal species. About 7,000 new insect species are classified each year. More than 850,000 different kinds of insects are already known to scientists. Roughly eight out of ten of the creatures on earth are insects. Insects range in size from tiny fleas which can be seen only through a microscope, to beetles as big as your palm.

          All insects have a similar body plan with three main parts: head, thorax and abdomen. On its head is a single pair of antennae or feelers, a pair of compound eyes, usually three small simple eyes, and a set of mouth parts which work sideways rather than up and down. The middle part or thorax carries three pairs of jointed legs and sometimes wings. The abdomen contains the stomach, reproductive organs and breathing tubes which open to the air through tiny holes called ‘spiracles’. Inside the insects body the tubes, called ‘tracheae’, branch repeatedly and end in the muscles. Normally oxygen passes through the tracheae into the tissue. Larger insects, such as bees and wasps, have air sacs in the muscles which can take in extra air as the muscles expand and contract. This increases the supply of oxygen to the muscles. These tubes work in the same way as man’s wind pipe. An insect breathes just like us, except that it may have hundreds of breathing tubes in its belly to take in the air. Among smaller insects these tubes do not take up much space.

           The rate of breathing depends upon the size of the animal. The larger the size, the slower is the rate of breathing. While the big animals like the elephant breathe about 10 times a minute, a mouse has to breathe about 200 times per minute. The oxygen taken in by the insects is needed to oxidize certain food materials for the body. Waste products, including water and carbon dioxide, are eliminated from the body by exhaling.

 

          All plants and animals need water for their survival. However, there is one creature which does not drink water in its entire life. It is the tiny kangaroo rat found in the South Western deserts of the United States.

          Kangaroo rats are an important part of desert life. They are often eaten by other animals for the water in their bodies! The rats can run very fast, covering 6 metres in one second, to avoid their enemies. They use their long tails as rudders (broad flat piece of wood) when jumping and can even change their course in mid-air.They move about by leaping, but with such an accuracy that they can jump over a cactus and land on top of a grass-hopper. Because of their long, powerful legs and the strong tail which resemble those of the kangaroo they are called the kangaroo rats. They grow to about 38 cm long, including a tail of 20 cm. They have short front legs, large heads and big eyes. Their silky fur is yellow or brown on the upper parts and white on the lower parts.

          How does the kangaroo rat survive without water? The physiological structure of desert plants and animals is such that they need very little water to survive. So efficient are the kidneys of the Kangaroo rat that it never has to drink water. All the liquid it needs is extracted from the plants, roots and seeds it eats. Yet it is enough to keep the kangaroo rat alive. It lives near bushes by making holes in the ground.

          The kangaroo rat’s legs are proportionately very long as compared with other parts of the body. When two kangaroo rats fight, it appears as though they were fighting with sticks. 

           Man has been using the red corals in the jewellery since ancient times. Romans used to hang pieces of coral around their children’s necks believing that it could prevent and cure diseases. In some parts of Italy, it is still worn to ward off the ‘evil eye’. Indians also use coral pieces as jewels in their rings and other ornaments. But what is a coral?

          Coral is the hard dried skeleton composed mainly of calcium produced by colonies of small animals known as ‘coral polyps’. They are small invertebrate organisms. The polyps of living coral live in tiny cups in the skeleton formed beneath and around their outer body. The polyp first attaches itself to a rock beneath the surface of water. The young ones are born as small buds from its body. When the old polyp dies, the living polyps remain attached to its skeleton and produce more buds. In this way, corals gradually build up into colonies of many millions. As layer upon layer of coral is built up they actually form reefs and islands in the ocean.

          Corals can be found in most seas, but the reef-forming ones prefer warm, shallow water. A coral reef begins as a fringing reef along the shore of a continent or island. Corals are found mainly in the warm tropical waters of the Pacific, the Indian Ocean and the Mediterranean Sea. We get red and pink corals from polyps found in the Mediterranean Sea off the coast of Africa and Italy. Corals begin to shine when they are polished. These are mainly used in ornaments. 

          The squirrel is a familiar animal seen most everywhere. It is an animal found in every part of the world, except Australia. There are about 320 kinds of squirrels all over the world. They may be as large as cats or as small as mice. They can be divided into two general groups – the ground squirrel and the tree squirrel. Apart from these, there are flying squirrels too.

          Most people think of squirrels as a kind of rodent that is good at climbing. The tree squirrels have a long bushy tail that helps them to steer and keep their balance. They can leap 3 metres to reach from one tree to another. The woodchuck, marmot, chipmunk and prairie dog are the tree squirrels.

          Flying squirrels jump 10 times farther than that. These little creatures have flaps of skin between their front and back legs. These flaps form a parachute when a flying squirrel jumps and spreads its limbs. This helps it to glide through the air. If attacked in the mid-air by an enemy like the owl it turns back immediately to the tree and protects itself by hiding in the tree trunk. They have soft fur and large eyes and are 8 to 60 cm (3 to 24 inches) in length exclusive of tail. They live on trees and unlike other squirrels they seldom come to the ground. They are nocturnal animals and can see clearly in the dark. They can glide up to 60 m. The flying squirrel, like the tree squirrels, feed on leaves, twigs or seeds.

          There are about 35 species of flying squirrels known to man today. They are found in North America, Africa, Europe and some parts of Asia. We scarcely get to see them because they usually sleep during the day.

 

          Man has been using garlic since ancient times to add flavour to food. Garlic has a powerful smell and a pungent taste. The Roman soldiers believed that it helped them in being more courageous and stronger so they made it a point to include it in their regular diet. In the Middle Ages garlic was eaten as a defence against the plague. It was also worn on the body to ward off evil spirits.

          It is only a few years ago that man discovered its medicinal importance. Its bulb contains an antibiotic called allium.

          It has antiseptic properties and is used for curing intestinal disorders. It is highly effective in controlling high blood pressure. It is also being used as an effective remedy for heart ailments and cough.

          Some people crush it and rub it on the skin as a cure against insect bites and stings. Some people make syrup out of it and drink it to cure cold. Gardeners put garlic in the soil around peach trees, to discourage borer from entering and damaging the trees.

          Garlic plant is native to Europe and Asia but it also grows wild in Italy and Southern France. Garlic produces two types of bulbs or bulbets. The aerial bulbets produced on the flower stalk are used as seeds to new plants. It is grown as an annual crop. The underground bulbs, called cloves, are the one sold in shops. They are formed at the base of the plant much like an onion. One bulb encloses up to 20 bulbets. Garlic contains about 0.1% essential oil, the principal components of which are diallyl disulfide, diallyl trisul-fide and allyl propyl disulfide.