Category Science

  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.

  There are many theories explaining this capability of birds. According to one of them, the Sun’s rays and the direction of winds help them to navigate. Birds’ extra sensory capabilities assist them in this task and direction them with the help of the Earth’s magnetic field.

            Another theory suggests that these winged wonders understand star-maps so well that it helps them to rack their way. But no one answer has been put down for this as of now.

            Birds have the capability to detect changes in atmospheric pressure, weather and earth’s magnetic field. Based on these they locate specific regions and find their home. But the most important navigational aid is said to be “internal magnetic compass” that they are said to posses in their brain. The compass works in relation to the earth’s magnetic field. The magnetic currents generated here are turned into flight paths.

            As a result, disturbances in Earth’s field can seriously affect bird’s judgment. In July, 1998, 3000 homing pigeons that set off for their return journey from northern France to southern England could not reach their destination because an explosion on the surface of the Sun, a few days prior to their journey, had sent radiations that disrupted the Earth’s magnetic field. As a result their internal magnetic compass picked up confusing signals and the birds lost their way.