My Science School

            Like any living organism, plants need, besides air and sunlight, water and nutrients for growth and survival which they take up through their roots. For land plants, the soil provides the moisture and nutrients. The soil also protects the roots from rapid fluctuations in temperature, as just below the surface the temperature scarcely changes from day to night. But more importantly, soil provides the firm support which holds the plants on the ground. Some plants, like the water hyacinth which grow in water, and orchids which grow on trees do not need soil to grow on as they can get their nutrients from water or the host                                                                                              plant.

            All plants respond to touch, but Mimosa pudica, or the “touch-me-not” plant is more sensitive than the others. Whenever touched, the leaves of the mimosa plant close and drop immediately, appearing like a dead plant. Possibly it is a defense mechanism by which the plant protects itself against its enemies.

   The opening and closing of the leaflets and the entire leaf are controlled by fluid-filled sac-like structures found at the base of not only the compound leaf but of each leaflet as well. When the leaf is touched, a chemical signal immediately moves to the base of each leaflet making the fluid drain away from the sac which makes the leaflet fold. When the signal reaches the base of the whole leaf, it makes the entire leaf drop. If left untouched for some time, the sacs fill up and the leaflets open again.

When your mother frowns at you without saying a word, you know that you have displeased her. Her displeasure is expressed through her   body language. In this way, other emotions too, are reflected through When you cross your arms, and lean away from another person to you are telling him that you want him to keep a distance, though of course, it may also mean that your arms are cold. If you look at a person in the eyes while speaking, it is a sign of honesty and straight forwardness. Looking away can mean you are lying, or that you don’t like the person. A person who shakes his legs constantly, or wets his lips is under stress. A person who leans towards you with clenched fists is quite likely to attract you! So you see, understanding body language helps you to understand the emotions of other people better.

 

 

Some species of animals are especially clever at detecting human body language, both voluntary and involuntary. There is the instance of a horse called Hans, who seemed to be able to add, subtract, multiply, divide, work with fractions and do other intellectual tasks. If you asked him a question, Hans would reply by tapping his foot till the correct

Han’s abilities amazed the world, but a formal investigation showed that the horse was not really calculating the answers, but was responding to the questioner’s body language. As the horse’s taps approached the right answer, the questioner’s posture and facial expression

            The peculiar smell is produced by the soil inhabiting bacteria called streptomycetes. Streptomycetes are abundant in dry warm soil – a million of them are present in a pinch of soil. They release compounds such as geosmin and 2-methyl isoborneol, which vapourize easily, when wetted by rain water after a dry spell. That is why we get the musty odour only after the first rain of the rainy season. The smell can be detected in a newly ploughed field also.

            Vultures are scavenger birds which feed on the carcasses of large animals and search out their food by flying in circles at a height. Hovering at a height gives them the advantage of surveying a large area. This is because the effective area which they can survey is the base of a cone at the tip of which the birds fly. Greater the height of this cone, larger is the area of the base. Thus, birds flying in small circles at great heights can keep a watch on a large tract of land below to look for a meal. That is why vultures and other birds of prey like kites, hawks and raptors circle at great heights. Of course, picking up tiny animals from such distances requires sharp eyesight, which all these predatory birds have.

 

   The wings of butterflies and moths are covered with small scales. These tiny scales produce the magnificent colours and patterns by optical interference of light. The tiny scales reflect and disperse light producing brilliant colours. When we touch the wings, these tiny scales come out in the form of powder, thereby leaving the surface of the wings colourless.            

            The direction in which roots and shoots move after germination of a seed is guided by two opposing properties. On germination, the roots emerge first. They are guided downwards by the action of hormones which sense gravity. This property is called geotropism. The shoots, on the other hand, are guided upwards by hormones that sense light. This property is called phototropism. Together these two properties ensure that the roots and shoot grow the right way irrespective of the position of the germinating seed in the soil.

            Most birds produce sounds in their throats using a voice organ called the syrinx. But not all birds’ calls can be described as ‘songs’. Males of only about 5000 species of birds are known to produce organized patterns of sounds that can be called melodious and described as songs. Male birds sing to attract females and to warn off other males. Although no two individuals sing alike, the song of each species is distinct. Most birds usually sing in the morning or evening and are quiet at midday. During winter most birds don’t sing, but they burst out into myriads of melodies with the onset of the spring, the time for                                                                                             courtship and breeding.

         In animals belonging to the cat family and other nocturnal animals the back of the eye ball – the retina, has a layer called “tapetum lucidum”. This layer is made of special cells which reflect light falling on the retina. It is this layer which makes the eyes of these animals glow in the dark. The tapetum layer also helps the animals in gathering all the available light to see in near darkness    

            The camel’s hump is filled largely with fat, accumulated at times when food and water are available. This fat is digested to meet the energy needs of the animal. Camels can go for a week or more without water and for 10 days without food. During such periods the accumulated fat is used up. The hydrogen released as a by-product by the breakdown of fat combines with the oxygen the camel breathes in to produce water. By utilizing this metabolic water the camel can keep going for many days. In this process, it may lose up to 100 kg of body weight. But as soon as it arrives at an oasis, it is capable of rapidly drinking some 120 litres of water.

            Most of the birds that we see around us are perching birds. They have four toes on each foot, three of which point to the front and one point backwards. This enables the birds to perch on leaf stems, telephone wires and even thick branches. The tendons in the feet of perching birds make the toes flexible and allow the birds to bend their toes to grasp the perch tightly. If any movement disturbs the balance of the birds, even while sleeping, their feet automatically tighten their grip on the perch thus preventing the bird from falling off.

            The buzzing sound made by the bees is due to the rapid beating of their wings. The rapid beating of the wings creates ripples in the air which produces the sound. All insects fly by beating their wings. But some insects, like the butterfly whose wings beat slowly- 6 to 10 times every second do not produce a buzzing sound. Other insects such as the mosquitoes with very small wings produce very little sound which can be heard only when it is close to our ears. However, the wings of bees are large and they beat very fast – 300 to 40 times every second. This produces the buzzing sound that is clearly audible.

 Snakes are unable to sniff the air through their noses quickly enough to follow the scent of their prey. To do that, they depend on a special organ called Jacobson’s organ located deep inside the upper surface of mouth, which detects odours. By flicking the forked tongue in and out rapidly, the snake picks up odours and puts it on to the Jacobson’s organ. The amount of odour picked up by each tip of the forked tongue also provides information about the direction of the prey.

 Bats are flying mammals. However, unlike birds which can fly and walk as well, bats have lost the ability to stand on their feet or walk. Evolution has modified their forelimbs to support them in air. At rest, the easiest posture for them to adopt is the ‘head down’ posture. They hang on to branches by means of special claws at the end of their limbs.