My Science School

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.

The truth is that the glow is only the reflection of light from some other source. The reason that reflection takes place is that there is a layer of crystalline substance in the eyes of many animals. This substance has the ability to reflect light. This reflecting layer also helps the animal to see in the dark, which is why they can see better at night than man can.

The difference in the colour of the light reflected from the eyes of the animals is due to the different number of blood vessels in their eyes. An animal that has many blood vessels in its eyes will reflect a reddish glow. If it has fewer numbers of blood vessels, it will have a whiter glow.

            Bees live in colonies called hives. Each colony has one queen bee, few drones (males) and thousands of workers (females). The queen manipulates the behavior of the workers through various pheromones. A successful forager bee communicates information about the source of food discovered by them to the others upon returning home. This they do by means of a round dance or a waggle dance.

            During a round dance, the forager runs in small circles clockwise and anticlockwise, alternately. In the case of waggle dance the bee dances tracing a figure of eight. The round dance is performed if the food is far away. The waggle dance is said to convey information on the distance between the colony and the food, the direction in which the food is located and the quantity available. The dancer also carries the smell of the pollen and/or nector that it recently came across.

            Thus by this peculiar dance the bees find their way to the sources of food and the way back to the hive. This dance was first found by an Austrian zoologist Karl Von Frisch which got him the Nobel Prize in 1973.

            Besides the dance, the bees are also said to have various other ways of remembering their way home. They are said to possess excellent mathematical instinct. They return to their hives by remembering the angles of the triangle formed by the position of the hive, the sun and the bee though this may vary with time. As a result, they cannot spend more than half an hour at their target. When there is no wind they fly high but remember the angles. When the sky is cloudily or when there is a strong wind they fly at low levels remembering a few permanent marks on fields. They can identify almost all different geometrical forms and colours, scent and sound.          

            According to Frisch, the bees can perceive polarization of sunlight and thus use the sun as a compass. Even on overcast days they do not lose their sense of perception. Its sense of smell is also close to that of humans and they can distinguish all colours except red, it is said.

      In humans hair is present in the skin of nearly every part of the body excepting the palms of hands, the soles of the feet, and the flexor surface of the digits. The structural components of the skin alone decide the generation of the appendages of the skin. Structurally the skin has two layers: the Epidermis and Dermis. Among these two layers, the epidermis has a high capacity for regeneration after damage. It continually replaces the outer dead cells and also generates the appendages of the skin, like hairs, nails, sweat and sebaceous glands.

            In the two parts of the hair, namely the root and shaft, the root is the structure which emerges first during development and is called the hair follicle. It is set in between of the epidermis and the superficial part of the dermis. Each hair follicle commences on the surface of the skin with a funnel shaped opening. From this opening the follicle passes inwards in an oblique or curved direction.

            At the deep end of each here follicle there is a small conical vascular eminence called papilla, which is continuous with the dermal layer of the skin. The capillaries of the papilla provide nutrients to the hair.

            When any one of the layers of epidermis and dermis gets abnormal development it affects the formation of the hair follicle and also becomes an unfit layer to support the hair.

            For example, in the skin of palm and soles the stratum cornium of the keratinization zone of epidermis and reticular layer of dermis are comparative thicker than in the skin of other parts of our body.

            Such a thick keratinization zone will not allow the formation of hair follicles and the thick dermis is not the ideal structure to support the germinal matrix of the hair follicles. That is why hairs do not grow on our palm of the hands and the soles of the feet.

  The difference between mammalian hair and fur is chiefly one of arrangement, not structure. Hair tends to come individual strands that are fairly coarse, as well as being patchy in concentration.

            In people, for example, there is little in the genital area and underarms and some on the male face and chest, plus a dusting of individual, visible separated hairs on the rest of the body.

            Fur on the other hand, tends to coat the body of the animal in a closely packed arrangement, so that the naked eye finds it difficult to distinguish the individual hair roots. Fur is also usually finer in texture than hair.

            Typically, fur has two or more layers: a short, dense, soft undercoat of barbed hairs and longer guard hairs. Fur’s function is to trap pockets of dead air, providing warm insulation for the wearer.

         

 

 

 

 

  Generally animals and plants are attracted towards light. This tendency is termed phototropism or photo taxis. Animals which towards the source of light are known as positively phototropic and others that shun light are called negatively phototropic. Most of the insects are positively phototropic but the degree of attraction differs. And some are negatively phototropic. Bed bug shows negative phototropism. Mosquitoes shun intense light, but in dim light they display positive phototropism. This behaviour differs in different species of insects with the exhibition of the following traits.

            Insects without eyes also exhibit phototropism. The photosensitivity is distributed or diffused throughout the dorsal surface of insects so photo stimulation can occur even if the insect does not possess any eyes. Some insects are more sensitive to light rays. Their surface cells and eyes are more refined to perceive and follow light sources.

            Some are attracted towards yellow light and some towards mercury light etc. well illuminated areas are used as mating grounds by male insects, full of matured sperms and females with matured eggs.

Adult females (about 6 mm long) of the mango nut weevil Sternochetus mangiferae Fabr puncture the tender fruits just under the rind and lay about 12-30 eggs singly. These punctures leave black or brown marks on the skin.

            A gum-like secretion oozes out of the punctures and cover the eggs. These punctures heal in due course as a result of which the ripe fruits appear unaffected. However, the black marks can be seen sometimes even on ripe fruits.

            Legless fleshy larvae emerge out of the eggs after a week. They tunnel through the developing un-ripened pulp and enter the tender nut which is soft. The nut hardens later as the fruit matures. The larvae thrive on the cotyledons of the nut. They pupate there after three weeks and dark brown adults emerge. Their life cycle lasts for 35-50 days.

            The adult weevil rarely comes out of the ripened fruit. Their attack increases the number of fallen fruits. They hibernate in the crevices and bark till the next fruiting season. The weevil uses the oxygen present in the fruit for respiration.

            The beetle generally attacks soft-pulped varieties such as neelam, mulgoa, banglora, Romani, jehangir, surangudi and padhiri.

            

            Eagles adopt an energy-saving flight mode called gliding. Their broad wings and broad rounded tail enable them to exploit thermals in the air. (Thermals are upward air currents in the atmosphere caused by the absorption of heat, from the sun or land, by the air.)

            The birds flap their wings slowly and laboriously in the air in wide circles, but once they catch the rising air they begin to soar effortlessly without even a single beat up to a point where the warm air has cooled and stopped rising.

            From this point, they start gliding down to another thermal, which they spot by seeing other groups of rising raptors or perhaps by their delicate sensitivity to even minute changes in air currents. Their primary feathers are spread out to obtain the maximum advantage from the rising air. The wing tips are broadly splayed or ‘fingered’ to reduce turbulence in the air surrounding it. They also assist in gaining speed when the bird glides downwards.

            Sea birds such as albatrosses, fulmars, gannets and Manx shearwater also adopt gliding but a slightly altered version. As thermals do not form over the sea, they take a shallow downward glide across the wind then turn into the wind and climb steeply until they resume gliding in their original directions. They thus use relative wind speeds to power both the climb and control the long, downward glide over the sea. These birds can cover thousands of kilometers without expending much energy.

To keep our torsos stable and conserve energy, we swing our arms backwards and forwards while walking. When you swing, say, your right leg forward to take a step, you provide a rotational moment about the central vertical axis of your torso. By the principle of conservation of angular momentum, an opposite reactionary moment is felt by your torso. By swinging your right arm backwards and your left arm forwards, you counterbalance this moment. Just try running without swinging your arms at all. Or worse still, try running while swinging your arms in the opposite directions to normal: that is, swing your left arm forward when you swing your left leg forward and so on. You will find that your torso rotates from side to side in an uncomfortable and unnatural manner.

            Of course, legs are heavier than arms, so as to ensure that the moments are the same; evolution has ensured that our arms are further from the central axis of our bodies than our legs are. This allows the moments from our legs and our arms to be roughly equal.

            Going back a few steps (pun intended), Serge Gracovetsky hypothesized in the 1980’s that the spine, rather than the legs, is the primary source of power for gait, and this is now accepted by most, if not all, researchers in this fields.

            Many bilateral amputees, for example, can walk successfully. The mechanism works because the spine is curved. Any attempt to straighten such a structure will result in a twisting action.

            The lumbar muscles acting on the lumbar spine cause such a twist and provide the main impetus for placing one foot in front of the other.

.swinging one’s arms while walking assists in this twisting motion, increase efficiency, and reduces the physiological cost of walking. Indeed, nearly everything that we do naturally when moving is done purely to reduce the amount of energy that is expended in order to achieve the desired result.

            Other two-legged walking animals balance themselves by synchronizing the movement of the backbone to the side of the leg that stays in contact with the ground.

            This keeps their gravitational centre close to the standing leg. It is seen in chickens and, to better effect, in penguins.