An igloo is comfortable because ice is a bad conductor of heat. It does not allow the heat generated by oil lamps to escape. The concave inner surface of the igloo reflects all the heat falling on it so there is almost no loss of heat. Besides, the entrance is usually through a narrow tunnel so that any snow adhering to the occupant’s clothes is brushed off before they enter the igloo.
Most medicines, which are chemical compounds and their combinations, degrade with time. This process is usually accelerated by heat and exposure to light. So the stability of every new formulation has to be checked over a period of time to evaluate its effective shelf-life. Ideally this should be done by storing the medicine at room temperature for some time. However, this method is time consuming. So what is done instead is that the medicine is stored at four different temperatures and under controlled conditions of light and humidity. The rates at which the medicine deteriorates are monitored. The compound’s stability at room temperature is calculated from the accelerated degradation tests made at higher temperatures. This allows scientists to fix a date beyond which the medicine may not be effective.
Herbicides are chemicals used to destroy weeds without harming the useful crops. This is possible because of the different rates at which herbicides are absorbed by the weeds and crop plant.Some crops have a dormancy period during which there is very little physiological activity. Herbicides can be safely used during this time. Some weeds have chemicals called enzymes that break down apparently harmless compounds into toxic products. Peas and other pod bearing plants, which do not contain this enzyme, remain unaffected. Such compounds are used as herbicides in legume fields. On the other hand, some crops contain compounds which convert the toxic herbicides into harmless compounds; most weeds lack this compound and are therefore killed. Factors like soil type, leaf shape, and method of application also affect the action of herbicides.
Seeds sprout when favourable temperature (15.38°C), enough oxygen and moisture are available. They absorb large amounts of water and swell. The moisture content of cells rises from 10 per cent to 90 per cent or more. The plant growth hormone, indole acetic acid which controls and promotes various stages of growth, sets into action the various life processes. Cells at the growing tips of the embryo within the seed divide rapidly and the primary root emerges through the soft seed coat. Further changes follow leading to emergence of the shoot Soil is not always necessary for the sprouting of seeds. Seeds will sprout in moist sand; saw dust, peat mosses, cloth or even paper if favourable conditions are available.
Lakes which appear frozen from the top never freeze completely. Only the top layer freezes and a thick layer of ice floats on water which remains liquid below and in which fishes and other aquatic animals survive. With the onset of winter water starts cooling. As it cools, it shrinks in volume and become denser, but only until it reaches 4°C. Below that temperature water expands and its density drops. This comparatively lighter water moves up and finally at 0°C turns into ice. Since the density of ice is less than that of water, the ice floats. Also, ice being a very poor conductor of heat, further cooling of the water below it stops. Thus the temperature of water below the ice layer remains at 4°C and fishes survive in it.
No animal can see in total darkness. However, some animals are capable of making use of faint light of the surrounding. Members of the cat family, like the tiger and cat or other nocturnal animals can see in near darkness because of the presence of large number of cells called rod cells in the retina. These cells are sensitive to dim light and help the animal to see in near darkness.Other nocturnal animals like owl and loris have very large pupils which allow more light to enter the eyes. In addition, the retinas of these animals have a layer called ‘tapetum lucidum’. This reflects inwards the light falling on retina and thus helps in gathering all the light available in dark surroundings.
The feet of lizards are adapted for walking on rough as well as smooth surfaces. The lizards have slits on their toes and these functions like suction disks helping them to cling to smooth areas such as a glass pane.
The claws present on toes help the lizard to hold on to and walk on a rough surface. In this way a lizard can even walk upside down across a plastered ceiling or on a glass roof without trouble.
Spiders spin webs as a means of trapping insects. They have special organs called spinnerets located in their abdomen. Spinnerets are muscular organs which release the thread, independently of one another. Most spiders are equipped with three pairs of spinnerets. Each pair is fed by several silk glands which produce a sticky liquid that can be drawn into fine threads. The sticky liquid turns into a thread by solidifying on exposure to air.
Besides chemicals called pheromones, bees use a kind of dance language to tell other bees in a hive where the food is. When a worker bee locates a source of food such as a tree in bloom, it returns to the hive and performs a ‘dance’. If it is a round dance, that is, if the bee just goes round and round, it only says that food is nearby. A more complicated waggle dance, in which the bee executes a kind of ‘figure of eight’ movement, gives information not only about the distance and direction of the source of food but also the quantity of food expected. It is now known that the bees use gravity and not the sun as the reference point while dancing. That the dance language really works has now been demonstrated beyond doubt by using robot bees.
Honeybees suck nectar from a wide variety of flowers. But each bee usually keeps to a particular kind of flower until its supply diminishes. The nectar is collected by the forager bee in an organ called the honey sac. Here the nectar is broken down to two sugars, fructose and dextrose, by the action of a special enzyme. On returning to the hive the bee empties the nectar load by disgorging it onto the mouth parts of the younger bees. They evaporate some of the water and concentrate the nectar. Glandular secretions further transform it. After this, the nectar is deposited in an empty storage cell in the honeycomb, where the nectar gradually thickens into honey by evaporation. To speed up evaporation bees in the hive fan their wings (26,400 times a minute) to set up additional air currents. After the cells are filled with honey these are sealed with wax by the bees.
Camels can survive for days in deserts with little food and no water due to their unique physiology. Contrary to the common belief, a camel does not store water in its stomach or its hump. Instead the hump stores fat which serves as a reserve for energy and a source of water when in need. When the fat is utilized by the camel’s body, hydrogen is released which combines with oxygen to form water. Camels also use water from other body tissues in a similar way. As body tissues dehydrate, it can lose as much as 25 per cent of its body weight without suffering any permanent damage. But when it does find water, a thirsty camel may drink up to 150 litres in 15 minutes. The water passes rapidly into its body tissues, making the animal fit for another desert crossing.
Electricity in fish is generated by the normal functions of nerves and muscles together with a chemical reaction. The electricity is produced in modified muscle tissue called electric organs. The nerves from these organs are joined to the brain. The electricity is produced by the passage of a stimulus along a nerve and a contraction in a muscle. The discharge goes from the belly to the back. It is a defensive mechanism in most cases, but is also used to kill the prey. Fishes are immune to their own shocks because of the insulating layers of fat.