My Science School

            Leeches, carnivorous or bloodsucking worms, live as external parasites attaching themselves to a host and sucking blood. Actually, land leeches feed only on the blood of mammals. These flattened ringed worms, measure from 5mm to 46cm in length and are equipped with sucking disks at both the anterior and posterior ends. In some leeches, the anterior mouth contains three toothed plates with which the animal pierces the skin of its prey.

            First, with its 3 jaws set with sharp teeth, it makes a Y-shaped incisor in the flesh. Its saliva contains substances that anaesthetize the wound area, dilate the blood vessels to increase blood flow and at the same time prevent the blood from clotting.

            Hence the victim is often unaware that he has been bitten until blood is discovered running from the wound. Also the site of bite is directly connected to the crop of the leech through its buccal system.

            In the crop or pouch, food can be stored for several months. Land leeches await their victim in damp vegetation poising one end in the air.

            Leeches were once used by physicians and barbers for bloodletting and are still used for this purpose in some regions of the world. In modern medicine, bloodletting is no longer practiced, but leeches continue to be used to relieve blood congestion in certain delicate operations, where such use is less likely to cause infection than other techniques, according to the encyclopedia.

Blood ingested by leeches is mixed with salivary juices containing an anticoagulant substance known as hirudin (which can be extracted and has been used in medicine to prevent blood clotting. It is employed as an anticoagulant in surgical operations and has been recommended for the prevention of phlebitis and post-operative pulmonary inflammations.

            Hirudin has been synthesized by recombinant DNA technique. The blood passes into a dilated, branched stomach, or crop, where it is stored for several months before being completely digested. A leech consumes about 3 times its weight in one feeding and then subsists for months on the stored food.

  Clotting is a remarkable property of blood. Certain substances promote coagulation (procoagulants) and others inhibit coagulation (anticoagulants). Clotting depends on the balance between procoagulants and anticoagulants in the blood. While the anticoagulants normally predominate, the procoagulants get activated and cause clotting when a blood vessel ruptures. Injury to a blood vessel causes a complex cascade of reactions leading to the formation of a clot. The control of clotting is a major medical concern. Heparin, the most frequently used natural anticoagulant, is administered before and after surgery to retard clot formation.

 The prevention of clotting is also a concern of blood-sucking organisms, such as leeches which have been used (and misused) in the medical profession for centuries. The active agent responsible for the anticoagulative effect is a protein called hirudin secreted from the salivary glands of Hiduro Medicinalis.

   Hirudin is a small, highly active protein with a molecular weight of 7000 Daltons. It specifically binds to thrombin, the enzyme that catalysis the final step of clotting. It forms a stable 1:1 non-covalent complex with thrombin thereby inactivating it and preventing clot formation. Consequently, leech bite, though a minor wound bleeds quiet freely. It is the most potent thrombin inhibitor known because of exceedingly low dissociation constant of hirudin-thrombin complex. The x-ray structure of the complex of hirudin with human thrombin has revealed that numerous interactions are responsible for hirudin’s tight binding to thrombin.

  Hirudin is of great medical interest, not only because of its high specificity for thrombin, but because it possesses a number of characteristics which make it superior to the currently used blood anticoagulants such as heparin.

The breeding season of house fly, Musca nebulo, is from March to October in most of India. In the course of the breeding season, a single female may lay eggs 4 to 6 times and each time each female lays 120 to 160 eggs. They lay their eggs in clusters on compost, waste heaps, manure and dung. The conditions required for laying eggs are moisture and favourable temperature. The eggs hatch in 8 to 24 hours depending on the temperature. The whitish larvae moult twice to become the familiar white maggots in 5 to 7 days.

The maggots transform into quiescent reddish brown pupa from which the adult flies emerge after 5 days if the temperature is optimum. Summer provides all the favourable conditions. So the flies mate and lay a number of eggs and suddenly increase their population within 15 day.

    Firefly also known as lightning bug is the common name for about 100 species of insects found throughout the tropical and temperate regions. Fireflies are soft-bodied insects measuring` from a few centimetres to about a few tens of centimetres. They have generally dark brown sheath-like front wings covering the flying wings at rest, yellow or orange markings and luminescent glands located on the underside of the rear abdominal segment. Both sexes emit intermittent light signals often seen in meadows on late-spring and summer nights, to attract mates. The luminescent larvae and females of some species are also called glowworm. The firefly emits light by allowing oxygen, breathed through its abdominal tracheae, to combine with a substance called luciferins. The fly also controls the timing and duration of the flashes, for example, to attract its mates. The unique characteristic of the fly is that it emits light without producing heat.

            The process of emission of ‘cold’ light by living beings by various enzymatic reactions is termed bioluminescence or chemiluminescence. The glowworms, Lampyris noctiluca, are bioluminescent insects. The light produced may either be extracellular (outside the cells) or intracellular (inside the cells). Luciferin, a substance present in glowworms gets oxidized in the presence of an enzyme called luciferases to give light and carbon dioxide. Emitted light may be blue, green, yellow, red, orange or a combination of these colours.

            The intensity of the colour also differs among various animals. It is said that when 10 Phyrophorus noctilucus are kept in a glass bulb, one can read printed pages comfortably.

            The animals use this cold light to procure food, to escape from predators, as warning signal and as mating signal. During photosynthesis radiant energy (light) is converted into chemical energy (starch) by plants. But during bioluminescence the chemical energy in the body is converted into radiant energy, without raising the temperature in the process.

            In glowworms, a combination of adenosine tri phosphate (ATP) and oxidative energy is used in a set of reactions that convert chemical energy into light energy. Generation of light flash requires activation of luciferins by an enzymatic reaction with ATP in which a pyrophosphate cleavage of ATP occurs to form luciferyl adenylate. This compound is then acted upon by molecular oxygen luciferases to bring about the oxidative decarboxylation of luciferins to yield oxyluciferin. The intermediate step of this reaction is accompanied by emission of light. Luciferin is then regenerated from oxyluciferin subsequently.

            Many factors are involved in hair loss. The exact cause is not known but scientists think that stress and severer illness, can cause hair to fall out (Chemistry in Britain). Iron deficiency or pregnancy can cause hair loss in women. Some cases are potentially reversible. For example, hair may re-grow once the illness has been cured.

            Scientists also know that the largest cause of hair loss in men is genetic in origin. Alopecia androgenetica, which creates male pattern baldness in men and general thinning of the hair in women, is an ageing phenomenon. They do know that the mechanisms involved in hair loss are complex and mediated to some extent by the male hormone (androgen).

            There are also suggestions that genetic hair loss is just an ageing process where the chronological age of an affected individual becomes desynchronized with that of the hair follicles.

            The male hormone, testosterone, is pivotal in the physiology of balding. It includes any hairs that are predestined to stop growing. Treating suffers with testosterone can stimulate dormant hair follicles into growth, but giving testosterone to men cause unwanted side-effects.

            In genetic hair loss, changes occur in all three fundamental hair variables; hair density (number of hairs per square centimetre0; the proportion of hair follicles in the active growth phase and the hair diameter per unit area. Initially, there is a reduction in the period of active growth, which results in an increase in the number of hairs being shed from scalp. This is followed by a reduction in hair diameter as the hair follicle gradually becomes smaller. Finally, the number of productive hair follicles decreases, reducing the meaningful hair density.

            The principle mechanism of genetic hair loss appears to be “localized tissue sensitivity to normal androgen concentrations.” While the metabolic processes are far from clear, an important candidate is the enzyme 5-alpha-reductse inhibitor, which catalyses are reduction of testosterone to dihydrotestosterone (DHT).

 The object of blinking of our eyelids is to keep the front of the eyeball clean. Blinking is done by means of muscles in the eye lids and the cleansing by tears. The tears are secreted in a little gland and carried along to the eye and when our eyelids open and close the tears are poured over the front of the eye and they wash away any particles of dust or any other harmful substances.

            Some animals like the snake for example, do not have eye lids and hence cannot blink. But there is a hard film or scale over the eyes to protect them from dust and injury.

    Parrot’s vocal expressions are a result of imitation, not a part of its specific vocabulary.

            Man and birds share one thing in common: much of their behaviour depends on vocal and visual signals. Bird’s behaviour depends largely on vocalization and visual stimuli.

            It has been shown that birds’ syrinx (the functional equivalent of our larynx or voice box) is much simpler than that of humans. Some birds with more rudimentary syrinx can become more proficient in creating sound.

            In birds, the syrinx is located at the bottom of the trachea. Sound is produced at the syrinx as flows and the volume is controlled by muscles in the trachea. The sounds are then emitted with little or no modulation.

            Myna is also talkative: it can learn to speak more than 50 words and, in some cases, utter as many as 20 sentences. Males of almost all singing bird species are principal vocalizers and the male’s forebrains (which control their song output) have been found to be larger than those of females.

            Human vocalizations originate from the larynx at the top of the trachea. The larynx is more complex and produces relatively simple sounds.

            In addition, important changes in timbre are caused by the position and movement of the tongue, cheeks, mouth and lips.

         

 

 

 

 

 

  The energy is gathered from nectar, and the butterflies that make the trip, those born in the early fall, are able to convert nectar into fat.

            “Those born in September know to tank up on nectar,” said Dr. David Marriott, founder of the Monarch Program, a nonprofit research and education organization based in Encinitas, Calif. “Their abdomens get really large.”

            Unlike the other generations, these monarchs, he explained, have a little area of fatty tissue where the sugar of the nectar is converted into fat. They can live off this cushion in winter and need only water to rehydrate their bodies.

            Monarchs born in September or late August live seven or eight months, sometimes nine, Dr. Marriott said. Their children, grandchildren and great-grandchildren live just a month.

            “By the time you get to the great-great-grandchildren it puts us back to September again,” Dr. Marriott continued. The butterflies also feed while migrating, he said.

 

The snakes are the only vertebrates which have efficiently overcome the handicap of absence of limbs making them survive with relatively long, slender body and a cosmopolitan habitat bestowed on them by nature. This achievement was basically by adapting different modes of locomotion fulfilling the need of the environment (terrestrial, water and arboreal) in which the animals lives.

The most common mode of progression which is generally employed by all species and is characteristic to them is the ‘serpentine type of locomotion’ better named as ‘undulatory motion’ in which the animal forms a zigzag track.

The basic necessity and attribute of this motion is some form of maximum provided by any projections or depressions on the substratum like rocks, branches, twigs, dust, sand or pebbles. This roughness in real sense resists the long, slender body to move on a straight line owing to which the body assumes a position of a series of s-shaped horizontal loops or curves.

 Each loop or curve which faces some resistance in turn delivers an equal and opposite thrust against the resistance leading to the formation of a series of  lateral or horizontal waves produced by a flow of muscular  contraction and relaxation passing from head to tail, resulting in the , propulsion of the  body in the forward direction.

 This kind of a zigzag motion is undergone only when the surface is rough enough to offer maximum resistance. It is of no use when they move on a really smooth surface, where they are offered least resistance. 

 

            Fireflies are not really flies and glow worms are not really worms. Fireflies are soft bodied beetles in the family of Lampyridae and glow worms are actually young fireflies (larvae).

            Although the luminescent molecule in many organisms is yet undetermined, in most organisms the light producing reaction is mediate by the action of a class of enzymes called luciferases on their substrate called luciferins.

            Some organisms do not make use of luciferases but instead use calcium activated photo proteins in their bioluminescent reaction involves the oxidative decarboxylation of luciferins in the site of special cells called photocytes present on their lower abdomen segments to attract mates. It appears that male fireflies flashing patterns are mating signals and females seem to prefer the most rapidly flashing males.

            Since glow worms do not mate, no one knows exactly why they glow. But glow worms are carnivorous and probably use the light to lure or locate its prey.

            There are over 2000 species of fireflies inhabiting the tropical and temperate regions. Fireflies of the same species recognize each other by number of flashes used the frequency of flashes and colour of the light. Fireflies’ eggs are also reported to glow.

     Ants are social insects. Many ant species go out of their nests in groups in search of food. Initially, a few worker ants, called scouts, go out of the nest in search of food. Once an abundant source of food is found to the nest, it presses its abdomen to the ground and at frequent intervals extrudes its sting, the tip of which is drawn lightly over the ground surface, much like a pen drawing a thin line.

            As the sting touches the surface, a volatile chemical (trail pheromone), flows out of a gland (Dufour’s gland), associated with the sting. In this way the worker draws an invisible chemical line from the source of food to the nest. As soon as it returns to the nest, it contacts a couple of workers, antennates them and makes quick looping movements on the line for short distances. This excited movement attracts the attention of more workers and they start following the scout, which leads, initially, to the food. These workers return to the nest with more samples, and reinforce the chemical line while returning.

            This results in recruitment of more and more workers and soon one will find a never ending line of ants moving up and down the line bringing back food. Since the chemical is highly volatile, the trait remains only for a short time. Hence, all the worker ants constantly draw the line over and over again.

 

            Ants manage to float on water due to an interesting property, known as surface tension, of liquids. In any liquid, the constituent molecules are in constant motion. They slide over one another, maintaining some freedom of motion while exhibiting enough attractive force to hold the molecules close to each other. This enables the liquid to flow.

            But the attractive forces in a column of liquid are not the same at all points. Molecules at the centre of the liquid are subjected to uniform forces all around. But a molecule at the surface is subjected to unbalanced forces. Strong attractive forces exerted by the molecules amongst themselves pull the liquid inwards. That means, the molecules at the surface feel an excessive force pulling inwards. The net result is that the liquid behaves as though it has an invisible elastic ‘skin’ which always tries to contract and decrease the surface area. This contractive force on the surface of the liquid is called surface tension.

            Now let us come to the actual question: Ants are so light that their weight is not sufficient to overcome the surface tension and break the contracting forces. If the weight of an ant is, then it will break the elastic membrane and sink. Similar observations can be made by placing a greased needle on a blotting paper which in turn is placed on water. The blotting paper will absorb the water and sink. But the needle floats.

            The fall of a body is controlled mainly by gravitational attraction of the Earth. The gravitational force depends on the mass of the falling object-a heavier object is attracted more than a lighter object. This attractive force is opposed by an upward thrust (resistance) offered by air on the body. This resistance also depends on the surface area of the object. That is, if the surface area is more, the resistance is also more. Thus in any falling object, these two forces compete with each other.

            In the case of an ant, the force of gravity is almost balanced by air resistance and so it is able to land safely. If there is a wind blowing, ants also float away. However, if a cluster of ants or a big ant is forcibly hurled to the ground, they will get hurt. Anyway, it will be difficult to know whether the ant gets hurt or not.

            Antennae, the two hair-like structures on the head of the ants, help them in locating sweets. These chemoreceptor’s help them to perceive smell and taste through minute sensilla, or sensory cells.

             These sensilla can detect accurately the smell in the air. It points towards the origin of the smell by detecting accurately the changes in the concentration of the odoriferous particles. If the sweets are wrapped in paper bags or any other wrappers having minute holes, the odour carried by the air will be sensed by the sensilla. If the antennae are removed, ants cannot identify the smell and distinguish them from other foods.

           

 

 

 

 

 

 Birds have nifty tendon arrangement in their legs. The flexor tendon from the muscle in the thigh reaches down the leg, round the ankle and then under the toes. This arrangement means that, at rest, the bird’s body weight causes the bird to bend its knee and pull the tendon tight, so closing the claws. Apparently this mechanism is so effective that dead birds have been found grasping their perches long after they have died.

            Yes, birds do sleep. Not only that, some do it standing on one leg. And even more surprising, may be hypnotized into sleep at will. To try it, we will have to bring our eyes close to the cage, and use the hypnotist’s principles on our eyes. If we act as if we are gradually falling asleep the bird will follow us, finally holding one leg up under its belly, tucking its head under its wing and falling into a deep sleep.

            What’s more most pet bird owners know that all we need to do make the pet fall asleep is to cover the cage with a blanket to simulate night.

            Birds do sleep, usually in a series of short ‘power naps’. Swift are famous for sleeping on the wing. Since most birds rely on vision, bedtime is usually at night, apart from nocturnal species, of course. The sleeping habits of waders, however, are ruled by the tides rather than the Sun. some other species are easily fooled by artificial light. Brightly lit city areas can give songbirds insomnia.