My Science School

            Anything exposed to the sunlight for some time becomes very hot, especially during the summer months. A scrap of paper or a piece of metal kept in the sunlight may even become too hot to touch after a while. But have you ever wondered why the leaves of trees and plants, which are exposed to the sun the whole day, don't get so hot?

            This fact may be understood as follows: a plant leaf is made up of several layers of cells. The upper epidermis covers the top surface of the leaf and the lower epidermis covers the underside. The lower epidermis has many openings called stomata, which act as valves. They regulate the exchange of gases between the leaf and air. When they are open, they allow carbon dioxide to go into the leaf. They also release oxygen and water vapour. When the stomata are closed, inhaling or exhaling cannot take place.

            Each stomata is surrounded by two sausage-shaped guard cells, which control the size of openings. The stomata are usually open during the day and closed at night. The water vapour that is lost by the leaf through the stomata is replaced by water from the roots. This process is called transpiration.

            So when water evaporates, it cools the leaf. Hence this enables the plant to keep cool in the sunlight.   

         Scientists have studied more than 800,000 species of insects. Do you know how they reproduce and develop?

          Reproduction in insects is usually sexual, the male inserting sperm into the female’s body. The fertilized eggs are usually not tended by the insects, but they develop near or in a source of nourishment and protection. In some cases, fertilization is external. This means that the female lays the eggs and then the male fertilizes them. Some insects produce eggs which develop into adults without being fertilized. This is a type of asexual reproduction and is known as parthenogenesis.

          As an egg develops, it goes through several stages before becoming an adult. Some primitive insects develop directly from the eggs. Most of them, however, go through several stages of development called metamorphosis. In complete metamorphosis, there are four stages of development: egg, larva, pupa and adult. In incomplete metamorphosis there are three stages: egg, nymph, adult. The nymph is like a small adult. As the insect goes through its development, it moults several times. The entire process of metamorphosis may take a few days or several years depending on species and environmental conditions. Many insects lay eggs which can survive the winter or other unfavourable conditions.

        

Continue reading "How do insects reproduce and develop? "

The name ‘rhinoceros’ has Greek origin. In Greek rhino means ‘nose’ and keros means ‘horned’. The animal has one or two curved horns on its long nose. The horns grow throughout its life. Rhinoceros belong to the ‘odd-toed’ group of ungulates. Rhinoceros are found in Africa and South-East Asia.

The animal carries its large body on its four stout, short legs. It has three toes on each foot, each toe ending in separate hoof. Each front foot actually has a fourth toe, too, that is no longer used.

The skin of the rhinoceros is very thick and has little hair. They look as if they are wearing heavy armour plating held together with rivets. The horns are composed entirely of hair like growths set above thickenings of the nasal bones and frontal bones. They are not attached to the skull and may even be torn off in fighting. When this happens, they quickly grow again. The horn may be upto 107 cm in length.

There are five different kinds of rhinoceros existing today — two from Africa and three from Asia. The Sumatran rhinoceros have two horns whereas the other two Asian species — Indian and Javan — have only one. They are all in danger of extinction but the most endangered is the Javan rhinoceros, which survives only in one small reserve.

The largest of all these is the white rhinoceros from Africa. It stands 1.8 m (6 ft) high at the shoulder and can weigh over 3 tons. An interesting difference between the white and the black rhinoceros lies in the shape of their lips. The white rhinoceros has a wider, square-mouth which is very suitable for cropping grass. The black rhinoceros is more of a browser and has a pointed upper lip for grazing and plucking leaves and shoots from shrubs and bushes. The other two-horned species, the Sumatran rhinoceros, is the smallest of all, standing only about 4.5 ft at the shoulder and weighing less than a ton. 

Rhinoceros feeds on grass, twigs and shrubs. They do not hunt other animals for food. During the afternoon heat, the rhinoceros usually buries itself in muddy water. And from here it emerges with a layer of mud on its skin. This dries and forms a protective coating against insect bites.

This huge animal is usually quiet and retiring. But if it is cornered, it can become very fierce and dangerous. A rhinoceros can charge at a speed of 30 miles an hour, and use its strong, pointed horns to attack its enemy. In captivity the rhinoceros may live upto fifty years.

A female bears only one young at a time. The calf is born about eighteen months after the mating season and remains with the mother for several years.

Now unfortunately the rhinoceros is a rare species. Over the centuries they have been hunted by man for their horns. This is because according to an ancient belief, its horn imparted magical properties to its owner. However, now this second largest land mammal is being protected by law to prevent it from becoming extinct.

          The cassowary is the most dangerous bird in the world. Its inner toe has a long dagger-like claw that acts as a weapon and can slash open a man’s stomach!

          The cassowary is found in New Guinea and Northern Australia. It is a secretive forest dweller and is seldom seen, but often heard croaking and bellowing. It cannot fly, but runs at a great speed on its powerful legs. On each foot it has three toes, the inner one having a long straight claw. It can often be seen giving furious kicks at the trunk of trees without any apparent reason. Because of this strange habit the cassowary is regarded as having a very bad temper. In dense forests it can even speed upto 50 km an hour. It can grow upto a height of 6 ft and weigh as much as 180 pounds. When it gets annoyed, it jumps in the air and delivers a vicious kick.

          It is a bony-headed bird. Its naked blue head is protected by a bony helmet. Its body is covered with coarse hair-like feathers. It is the only member of the family casuariidae. Unlike other birds, the male incubates eggs. At a time three to six eggs are laid. The eggs are green in colour and 13 centimetres long. They are incubated for 50 days in a leafy nest and on the ground. The adult provides parental care for the young ones.

          Cassowaries live in family groups or in pairs. They like to be near water, for they swim readily. They are also good fishers.

          According to zoologists, the cassowary’s ancestors were able to fly. But in the process of evolution, it became flightless. It has adapted itself to make the most efficient use of its environment. Emu, kiwi weka and takahe are also flightless birds. Most of the flightless birds are found in Australia and New Zealand. 

          

    A woodpecker is a bird which gets its name as it pecks the wood of trees, looking for insects to eat. The woodpecker is a great help to the trees because quite often, the insects and worms are harmful for the trees. These grubs and insects remain hidden deep in the crevices of the bark of trees. The woodpecker can find them instinctively even when they cannot be seen outside. Then he drills a deep hole and straight gets down to them. Sometimes woodpeckers make two openings, like a front and back door. This is to enable them to get away if an enemy shows up.

           The woodpecker has a chisel-like beak which can drill holes into dead or unhealthy trees. The structure of the head and neck of a woodpecker is adapted for driving its beak powerfully forward into the tree bark and absorbing the shock of the blow. It then uses its long tongue to capture and eat worms and insects. They can bore holes in the trees. Most woodpeckers nest in large holes that they dig in the branches or tree trunks. 

 

             

 

 A woodpecker is a member of the family picidae. There are 24 species of wood-peckers found in North America. These include the flickers and sapsuckers. The downy woodpecker can grow upto a length of 14 cm. The pileated woodpecker, found in the Eastern and North-Western United States and in parts of Canada, often reaches a length of 34 cm. The pileated woodpecker chisels large, deep, oblong holes into tree trunks.

               The European green woodpecker is green with red crown and yellow rump. The greater and lesser spotted woodpeckers are the British species. They have black, red and white plumage. There are about 210 species of woodpeckers worldwide except in Australia.

 

 

               Most insects live only for a short span of time compared to other living creatures on earth. Do you know which insects have the longest lifespan? 

The longest living insects are the Splendour Beetles (Buprestidae), some of which remain in the larva stage for more than 30 years. They pass through a complete metamorphosis. In the young larval forms they are very varied and include some of the largest and smallest of all insects. The largest is ‘Hercules Beetle’ of South Africa which is 15 cm long. The smallest is only 0.05 cm. Queen Termites (lsoptera) previously thought to live 50 years or more, are now known to have a maximum lifespan of 15 years.

Apart from these two insects, there is one insect called cicada that actually lives for 17 years. Its lifecycle is very interesting. The female cicada lays eggs on the twigs of trees. When the young one (nymph) hatches, it drops down to the ground. Then it burrows itself into the ground and attaches itself to the roots of plants and trees. Here it remains motionless for about 17 years, sucking at the sap of the roots. After this long burial, it is driven by some mysterious instinct towards light. It climbs the tree trunks and its skin splits open and the mature cicada emerges.

For about five weeks, it leads an active life in the sunlight. After this it just dies. So it takes 17 years to develop for just five weeks of active life.

The male cicada makes a shrill sound which can be heard in the countryside. It is well known for the monotonous, whining songs of males. This sound is probably a mating call. According to scientists, the noise-producing organ of the cicada is probably the most complicated musical organ to be found in nature. The male cicacta has little drum-like plates which constantly vibrate by muscles that never seem to get tired.

There are more than 800 species of cicada and 100 of these are found in North America. But the 17-year cicada is found only in the United States. Most of the other species live only for two years.

          A peacock displaying its feathers provides one of the most spectacular sights. Do you know the reason behind it? 

          Peacock has a beautiful train of feathers which he displays during the breeding season. It usually attracts several females by such display, but as soon as any of them approaches, it turns its back. The reason for this peculiar behaviour is not clear. But it is certain that this is done to woo the female. In Greek mythology the pattern of the peacock’s tail feathers represents the eyes of Argus – a giant with 100 eyes.

          Peacock is the national bird of India. It belongs to the family phasianidae. Strictly speaking, the male is a peacock and the female is a peahen. Both are together known as peafowl. There are two species of peafowl. One is found in India and Sri Lanka and is blue in colour. The other species is found in South-East Asia which is green in colour. In fact, peacock is a native of Asia and the East Indies, from where it has been brought to other parts of the world.

          The male of both species has a 75 cm long body and 150 cm long tail. The female is smaller than the male. The tail is made up of beautiful feathers. In display, the peacock lifts its tail, brings it forward, enveloping his body as he struts and quivers, audibly rattling the quills and uttering loud screams. Generally, a peacock has a train of upto 150 tail feathers, which are erected by it in display to form a showy fan.

          The blue peacock’s body is metallic blue green. The green peacock has a green and bronze body. The hens of both species are green and brown. They do not have the train of feathers or ‘crown’ on them.

          In the wild, they live in open lowland forests, flocking by day and roosting high in trees. The male usually has a harem of one to five hens each of which lays four to eight buffy or white eggs. Peafowls are omnivorous, i.e. they eat both plants and animals. They can eat young snakes.

 

          You must have seen insects buzzing around a glowing lamp or bulb in your homes. The surprising aspect is that it is only the male insects that get attracted towards light. Moreover, insects are not attracted equally to all sources of light. Do you know why this happens? 

          The attraction of insects to light has been a subject of interest to researchers since Aristotle’s time. In the late nineteenth century, this phenomenon was studied in great detail by S.W. Frost of Pennsylvania University, U.S.A. Later, from an extensive study of this subject, a French entomologist, J.H. Fabre was able to provide a proper explanation.

          Fabre put forth the theory that certain radiations coming out from the light source are responsible for the attraction of insects. This has now been confirmed by some experiments that a series of narrow bands of infrared radiations emitted by the source of light, produce the attraction for insects. This study was conducted on moths.

          There is a gland at the tip of the female’s abdomen from which it releases some acetate molecules. These are called pheromone or sex scent. This chemical emits some infrared radiations which spread through air. The male moth, flying at some distance from the female, picks up these radiations and gets attracted towards the female.

          The most acute sense of smell exhibited in nature is that of the male emperor moth (Eudia pavonia) which according to German experiments in 1961, can detect the sex attachment of the female at a distance of almost 11 km. Some moths get attracted towards light under the impression that some female moths are there. Thus the search for the female leads it to the light.

          Candle lights emit sufficient amount of such radiations, thus attracting a lot of male insects. Insects are also attracted to street lights for the same reason.

          It has been found from different studies that the pheromones of different insects are not alike. That is why all insects are not equally attracted towards light. Similar is the case with different light sources. If a light source does not produce these infra-red radiations, insects will not be attracted towards it. This process of insect communication is very complicated and needs sophisticated equipment for study.

The roots of certain plants get swollen with stored food. They can be eaten as vegetables. The plants that produce such roots are called root crops.

Root crops have long been cultivated as a food source all over the world. Since they extract different chemicals from the soil, as against grain crops, they have proved useful in crop-rotation systems.

The roots of beet are consumed mainly in cooked form and are usually served with a main course or in soups. Beet powder is used as a red colouring agent in sauces.

Carrots are bright orange-coloured roots. They contain high percentage of carotene. They are consumed in fresh or cooked form and are sometimes dehydrated.

 

Continue reading "Which are the roots we eat? "

          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.

 

Continue reading "Do insects have organs and blood? "

            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.

 

Continue reading "Does any animal wash its food? "

               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.