Category Science

Why do flies rub their legs together?

            Fly is a two-winged insect that has some 90,000 different species of it. The housefly (musca domestica) is one of tie most common of all flies. You must have seen flies rubbing their legs together. Do you know why they do so?

            The housefly has a dull gray, bristled body that is about 7 mm in length. It has large reddish compound eyes. Its mouth cannot bite but consists of a spongy pad. It has a peculiar system of feeding itself. At first it releases saliva and digestive juices over food and then sponges up the resulting solution. In this way, flies contaminate large amounts of food with germs, and cause millions of deaths every year. Hence it is widely considered as a major health hazard.

            The whole body of the housefly, including claws and padded feet, is covered with bristles. Even its tongue is coated with sticky glue. A fly rubs its legs together just to clean itself. In the process of rubbing the legs, it scraps some of the material that has gathered on the bristles and thus drops germs of dangerous diseases on the food. When we eat this food, we may get infected. Some of the most common diseases spread by the housefly are typhoid, tuberculosis and dysentery. Flies gather such germs from garbage and sewage.

            Houseflies usually live and breed in or near garbage or organic wastes. The female lays about 100 eggs at a time and as many as 1000 during her life. The eggs hatch into larvae in 12 to 30 hours. The larvae moult several times before becoming pupae. Within a few days, the pupae become adult and the cycle begins again. Most houseflies have a lifespan of about 30 days during summer and longer when the weather is cooler. Cold weather usually kills the adults; but larvae and pupae are able to survive the winter.

 

Which is the world’s deadliest animal?

          The world’s deadliest animal is the sea wasp. It is a kind of jellyfish known as chironex fleckeri. Its tentacles are loaded with hundreds of thousands of microscopic stinging cells which inject cobra-like venom with poisonous barbed threads into any unfortunate creature that happens to brush against them closely. This venom is highly toxic and kills anybody in a few minutes. Pain and burning sensation caused by its venom are insufferable.

          The sea wasp is a colourless creature and has a bell-shaped body which consists of 95% water. It is so elusive that only careful eyes can spot it drifting in shallow tropical waters of seashores and beaches. 

          The size of a sea wasp varies from 4 cm to 20 cm across and 10 cm long. It has purple or blue tentacles which can be seen coming out of the bell. These may reach up to a length of 120 cm. One wasp may have upto 50 tentacles and one such tentacle may have 750,000 individual stinging cells, capable of injecting venom. They are mainly meant for securing food, and also to serve as a defence mechanism.

          Chironex fleckeri is found in great numbers in waters of Northern Australia. They are also found in the United States, waters off the Atlantic coast from North Carolina to the south of Florida Keys. They have also been discovered in West Africa and Indian Ocean.

          Scientists have not yet been able to devise any effective remedy for its venom. So one must be very careful while swimming in tropical waters!

          There are also some very poisonous sea-snakes that live permanently in the sea and are fully adapted to an aquatic existence. They swim with a sculling action of the paddle-shaped tail. They feed on fishes after immobilizing them with potent, fast-acting venom. 

Which are the different oils extracted from seeds?

          The oil that we use in our kitchen or for the manufacture of margarine and other goods is obtained from the seeds of many plants. The world production of major oilseed crops (in millions of metric tons) is Soyabeans 46.5, Peanuts 18.1, Cottonseed 22.1 and Copra 3.4. The other sources of vegetable oils are mustard, rapeseed, sunflower etc.

          The basic process for extracting oil is essentially the same for all oilseeds. It involves either pressing or solvent extraction or a combination of both. The material that remains after removal of the oil contains primarily fibres, carbohydrates and proteins. This may contain protein upto 50%. This material is discarded and used as fertilizer or animal feed.

          Most of the world’s supply of coconut oil comes from West Africa. It is taken from the dried kernel of the nut called copra which contains 70% oil. Palm oil also comes from West Africa and from South-East Asia. These oils are produced in a hard fatty form called stearine, which is used in the manufacture of chocolate, cooking fats and medicines. Crude oil is used in soaps and shampoos.

         Cottonseed provides about 37% oil. The cotton plant is grown commercially in the United States, India and Egypt. The fruit of the plant splits open to reveal fluffy white fibres and a number of seeds – each about six millimeters long. Cottonseed oil is used in margarine, cooking fat, and salad oil. It is also used in soaps, resins, grease and lubricants.

         Linseed is the seed of the flax plant which is grown primarily in the United States, Russia, Argentina, India and Canada. Flax fibres are woven into linen cloth and the seeds are used for extracting oil. Linseed oil is used in paints, varnishes, printing and lithographic inks, linoleum, oil cloth and as a water-proofing agent. The residue is a valuable cattle food.

         Groundnut or peanut is the seed of the plant Arachis Lypogea. The seeds of this plant yield oil and are cultivated mainly in China, West Africa, the United States and South-East Asia. It is mainly used as a cooking medium.

         Soyabean is the most important of all the oil seeds. It is extensively grown in China and the Far East. Soyabean oil is used for cooking and as a base for paints, plastics, adhesives, etc. It is a rich source of protein. The seeds can be ground into protein-rich flour which can be used in many foods.

          Sunflower is becoming increasingly popular in European oil markets, and so is rapeseed in Canada and Northern-Europe. Sunflower is now grown in countries like Mexico, Russia, erstwhile Yugoslavia, Turkey and South Africa.

 

 

Why don’t leaves get heated in sunlight?

            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.   

How do insects reproduce and develop?

         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?”

What are the different types of rhinoceros?

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.