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.