My Science School

Jean Baptiste Lamarck believed that all bodies had ‘subtle fluids’. These were weightless fluids pervading all space and bodies. Two good examples of eighteenth – century subtle fluids were electricity and heat. Lamarck believed that subtle fluids were responsible for both movement and change. For example, Lamarck pointed out that snails have poor vision because the feelers on their heads acted as their eyes. According to him, the ancestors of snails did not have feelers. They groped about with their heads to find their way around. This groping sent subtle fluids to the front of the head, and the constant presences of moving subtle fluids eventually brought about the development of feelers, and these feelers were passed from generation to generatio 

Butterfly Evidence

         Lamarck supported his theory of evolution with the example of butterflies. According to him, you find different species of butterflies in different places because butterflies in one place acquire certain characteristics to survive in their environment, and pass on these characteristics to the next generation.

 

 

 

Lost Worlds

        The duck billed platypus of Australia is a strange looking bird that was discovered only in 1799. This made several people believe that there might be many other weird animals alive in some remote corner of our planet and that animals that were thought to be extinct might still exist in some unknown place.

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The Cambrian explosion is a brief time when most major groups of animals that have bilateral symmetry first appear in the fossil record. Do you know what a bilateral animal is? It is one whose body has two mirror-image halves. Modern examples are lobsters, people, dogs, and butterflies. The event is referred to as an ‘explosion’, because a rich diversity of species appeared in a relatively short amount of time. There is growing evidence that these different groups had a common ancestor that lived during the Cambrian Period. Evidence is growing to support this theory, at least from the fossils that date back to this period. After the Cambrian Period, very few additional animal phyla, or large animal categories, arose.

 

The Tasmanian tiger is one of the most fabled animals in the world. European settlers in Tasmanian were puzzled by it, feared it, and killed it when they could. After only a century of white settlement, the animal had been pushed to the brink of extinction. The Tasmanian tiger look like a large, long dog, with stripes, a heavy stiff tail, and a big head resembling that of a wolf. That is why it is sometimes called the Tasmanian wolf. It was shy and secretive, and always avoided contact with humans. It was a meat-eater. When the European began settling in Tasmania, the animal started killing the sheep and poultry raised by the settlers.As a result, Tasmanian tigers were hunted down relentlessly, and rewards were given to those who killed them.Another major factor that contributed to the Tasmanian tiger’s decline is the dingo, or wild dog population. These wild dogs hunted in packs, unlike Tasmanian tigers which hunted in small numbers or alone. Dingoes competed with these Tasmanian tigers for food and shelter. Climate changes and deforestation are also believed to have been contributing factors to their extinction. By 1936, the last captive Tasmanian tiger has died. 

A Chance for Rebirth

Although the Tasmanian tiger has been officially declared to be extinct, there have been unconfirmed reports of it being sighted. However, there is no hard evidence that the animal still exists. Efforts are being made to clone a specimen that has been preserved in alcohol. A team of Australian scientists has succeeded in replicating the DNA of the extinct Tasmanian tiger, and plan on reviving the species soon.

In the year 1507 AD, Portuguese sailors landing on the shores of the island of Mauritius discovered a strange looking bird. It was large and stubby, and could not fly. It had a hooked black beak, short yellow legs, grey-blue plumage, and tuft of pale coloured feathers for its tail. Since this bird had never seen humans before, it was very friendly and trusting. In fact, the sailors mistook its gentle nature for stupidity, and called it ‘dodo’, which meant simpleton in Portuguese.The dodo was an easy source of fresh meat for the Portuguese - and later, the Dutch who came to the island in 1598- because it could be easily captured due to its friendliness. Dodos were killed in large numbers by the new inhabitants of the island. Those that survived Man had to face new enemies like dogs and pigs that were introduced by these inhabitants. The dodo had no natural enemies on the island, but these new animals, together with Man, hastened its extinction. By the year 1681, the last dodo had died, and today, the term ‘as dead as a dodo’, means something that has disappeared entirely from the face of the Earth.

Dodo Tree

The extinction of the dodo almost led to the extinction of yet another species, a certain type of tree in Mauritius, which was known as the dodo tree. The seeds of this tree could only germinate after passing through the digestive tract of the dodo. When the dodo became extinct, no new trees grew on the island. However, the tree was saved from extinction when botanists fed its seeds to turkeys. The seeds passed through the turkey’s digestive system, and were propagated in the same way as when dodos were alive.

 

Fingerprint formation is like the growth of capillaries and blood vessels in angiogenesis. The pattern is not strictly determined by the genetic code but by small variables in growth factor concentrations and hormones within the tissue. There are so many variables during fingerprint formation that it would be impossible for two to be alike. However it is not totally random, perhaps having more in common with a chaotic system than a random system.

It is believed that the development of a unique fingerprint ultimately results from a combination of gene-environment interactions. One of the environmental factors is the so-called intrauterine forces such as the flow of amniotic fluid around the fetus. Because identical twins are situated in different parts of the womb during development (although they are not static), each fetus encounters slightly different intrauterine forces from their sibling, and so a unique fingerprint is born.

            Your genes specify only your biochemistry and through it, your general body plan. The pattern of your fingerprints forms rather in the way that wrinkles form over cooling custard. At most you may predict, say, the fineness of the wrinkles and their general pattern. Fingerprints are just one example. Many of your features could mark you out from any clone. Your genome only controls gross characteristics such as the rates at which the skin and its underlying attachments develop and grow. Even if there is no way for genes to specify everything exactly, there is no way the genome could carry enough information for the details. If our genomes had to specify everything, we would not be here. But, while the consequences of imperfect specification are usually trivial, they may have more serious effects. A minor distortion of a blood vessel could give poor blood flow or an aneurysm, and the branching and interconnection of brain cells affect mental aptitudes. That is why, though bright parents tend to have bright children, dimmer ones may have a child genius and vice versa.

The turtle lives ‘twixt’ plated decks

Which practically conceal its sex?

I think it’s clever of the turtle

In such a fix to be so fertile

            The poet Ogden Nash was right about the turtle’s external ambiguity and fertility, according to Grzimek’s Animal Encyclopedia (Van No strand Reinhold). Turtles are not only enthusiastic breeders; they also have external sexual characteristics that often make it hard for creatures other than turtles to determine which is which. The male is sometimes distinguishable by an indentation or curvature in its plastron, or lower shell, which fits over the back of the female; females have a flat or convex plastron.

To fertilize female's eggs, the male turtle conceals a sexual organ inside the cloaca, or waste removal chamber. The male positions itself over the female and often grasps the upper shell, or carapace, with its claws, then curves its tail until the vent contacts the female's vent; the penis emerges for often fertilization. The often dozens of eggs develop internally and are then usually laid and buried in sandy soil.

Fertilization is sometimes preceded by elaborate courtship rituals, with hours of demonstration followed by a few minutes of copulation. The female can store sperm to fertilize its eggs, sometimes years later. 

A thin coating of oil on the surface of the spider's legs prevents them from sticking to their own web.

Spiders have 3 pairs of spinnerets (silk spinning apparatus) located beneath the hind tip of their abdomen. Silk, made up of proteins, secreted by the silk glands, and are made into fibres as thin as a thousandth of a millimetre. The threads we see are actually a bundle of these fibres. The proteins are water soluble when secreted, but when made into a fibre, some Physical and chemical changes take place, and so, after a while the fibre becomes tough and does not dissolve in water. In fact, it becomes stronger than a steel wire of the same thickness. Hence, the spider silk is also used to make bullet proof vests.

To construct a web, the spider first lays the radical threads. These resemble the spokes on a wheel and they radiate from the centre or hub of the web. The radial fibres are then connected by spiraling threads. There may be 10-60 turns in a web. To capture the insects, spiders scatter small glue droplets throughout. The glue droplets remain sticky by absorbing moisture from the air. They also increase the capacity of the web to resist wind forces.

While some spiders do not place glue droplets around the central area of their web so that they can wait there for the prey, a few others attach a separate 'signal thread' from the web’s centre to a nearby place (not on the web) where it can conveniently relax. When the insects get stuck to web, spiders sense the vibrations and leap on the prey.

To help avoid being caught in their own webs, the spiders secrete oil and coat it on their toes. One can test this by dipping a spider’s legs in ether, an organic solvent, which dissolves the oil. If the spider is returned to the web after the dip, it will be caught in its own web.

Scorpion’s venom acts on the nerve tips and roots whereas snake’s poison acts on dendrites and axons of the nerves. As defence and prey capture are the sole aim of these and other animals and insects, it is the purpose on hand that determines venom’s composition and type.

 Cobra venom consists of 10 different enzymes, several different types of neurotoxins, cardio-toxins, cytotoxins, dendrotoxins and fasciculins (for example, lysocephalins, lysolecithins which are phospholipids). Snakes of the elapidae family (for example cobras, kraits and mambas) have venoms that kill primarily through neuro-muscular paralysis. It contains 60-75 amino acids and target nicotinic cholinoceptors in the muscle cell membranes which are sensitive to a chemical transmitter, acetylcholine. (Acetylcholine is released from nerve endings in response to an electrical impulse in the nerves.) The amino acids in snake’s venom block the junction between the nerves and the muscle. Scorpion’s venom consists of an arsenal of toxic compounds which contain 37 amino acids called charybdotoxin.

            When a scorpion stings these acids incapacitate the nerve cells causing severe pain, by rigidly binding with sulphur bonds unlike the snake’s toxin which binds by a ligand series. Moreover snake’s venom is digestible, but scorpion’s venom is not          

Snakes are stone deaf, yet they respond to charmers’ mahudi. Though this appears a contradiction the fact is that snakes actually respond to vibrations produced on the ground and not to the sound waves produced by the mahudi, in the air. Snakes do not have ears; instead they have a long bony rod called columella auris that extends from fenestra oval is to the quadrate bone. It is this bone which helps the snake to detect the vibrations.

One would have noticed that charmers first hit the ground with the pipe before playing it. The snake picks up the vibrations on the ground thus caused and comes out. When the snake charmer sways his pipe as he plays, up, down and forward, the snake too sways its body in the direction of the mahudi, only considering it as an object to be targeted and not because it follows the music. In some experiments, snakes have responded even without the ground tap because in these cases the tin in which the snake is housed is made to vibrate by the music (air waves) generating from the pipe. 

The subject is being studied by Dr. Julian Vincent of Reading University’s Biomimetics Centre, southern England, who hopes to learn the secret and adapt it for clothing.

 The idea of looking to nature for such answers is steadily becoming a science itself. The bones in a bird’s wing are powerful but incredibly light while spider silk is as strong as steel (in proportion) but enormously elastic and recyclable. “In nature the good designs eat the bad”, said Dr. Vincent.

            In Antarctica where temperatures reach minus 40 degrees Celsius, emperor penguins congregate to breed and produce a single egg which the male incubates. The penguins huddle together not eating for four months until the egg hatches.

            During that time they lose almost half their body weight. About 80 per cent of their insulation comes from their feathers which, it has been discovered, grow all over their body leaving no skin exposed.

            On land the birds use tiny muscles to erect the feathers forming a barrier of still air around their bodies. At the base of the feather is down, in which air is trapped close to the skin in small pockets. Each fiber has along its length a number of spikes, or nodes. When fibers from neighbouring plumes push into each other, the nodes buckle into loops producing a dense structure of tiny air pockets. By trapping the air, the penguin’s heat loss is drastically reduced.

            Dr. Vincent hopes to copy the essential features of the penguin’s insulation system and reproduce it in clothing.

Stings of insect group animals like mosquito cause skin lesions by direct effects of the insect parts or secretions which cause irritation. When the insect parts or secretions are retained for some time they tend to cause hypersensitivity responses. The immediate itching effect on the site of the bite is the appearance of urticaria or inflamed papules. Histologically the lesion shows a wedge shaped per-vascular infiltrate of the lymphocytes, histocytes and eosinophils within the dermis. The first event of the inflammation is an increased blood flow to the bite area. This results mainly due to the arteriolar dilation. Another event is the increased vascular permeability which results in the accumulation of protein rich extra vascular fluid.

The major chemical mediator of inflammation is the histamine. It is widely distributed in the tissue, the richest source being the mast cells that are normally present in the corrective tissues adjacent to the blood vessels. Preformed histamine is present in mast cell granules and is released by mast cell de-granulation process which in response to the stimulus caused due to irritation at the site of the bite. This histamine causes dilation of the arterioles and increase vascular permeability of venules. This in turn causes venular endothelial contraction and widening of the interendothelial cell Junctions, where the extra-vascular fluid accumulates causing, inflammation.

 There are more than 1,200 species of mosquitoes but all of them do not feed on the blood of mammals. The three important blood feeders found throughout the world are Culex, Anopheles and Aides. Even in these species, only the female mosquitoes suck blood, while the males thrive on plant sap and honey from flowers. The blood when drawn enters the highly dilatable stomach of the female which uses it for reproductive purposes. At least one-fifth of a drop of blood is sucked at a time. If these female mosquitoes are killed, they bleed.  Unfed females and males do not bleed when killed.

Some sleep out of the water, and some may not sleep at all. The furred or hairy aquatic mammals in the Pinniped order (like seals) have a variety of interesting adaptations that permit them to spend a comparatively long time under water sometimes at considerable depths, according to the Encyclopedia of Mammals.

            However they rise frequently to breathe and emerge from the ocean to sleep, relax, molt, mate and reproduce on a sandy beach or rock above the water.

            The situation is less clear for cetaceans (whales) and sirenians (sea cows and manatees). The whales evolved from land animals that returned to the sea, millions of years ago.

Though whales come to the surface to breathe air into their lungs, they can spend a long time between breaths, up to an hour in   some species, and spend nearly all their lives under water. However, whales learned to hold their breath so well that they lost their involuntary breathing mechanism and must be conscious to continue to breathe. Not only would a reflex have to take care of breathing, he said, it would have to take them to the surface for air.

Also, the blow hole automatically closes and must be opened voluntarily by the whale. Whales would drown if they fell asleep or were knocked unconscious. Sea cows and manatees tend to live in warm, calm, shallow, vegetation-rich waters where they can float lethargically at or near the surface.   They have an extremely low metabolic rate, do not expend much energy to regulate body temperature and require little oxygen.

Manatees may sleep or rest supported by the bottom. When they hold their breath, large blubber deposits and natural buoyancy let them float at the surface and engage in a resting behaviour, though not an unconscious sleep. 

            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.