The naphthalene balls used for keeping away harmful insects from damaging clothes are basically volatile chemicals having a strong odour. These compounds include a wide variety of aromatic chemicals which are mainly derived from petroleum and coal tar. These chemicals are toxic. As they are highly volatile, they produce vapours which repel insects such as moths and silverfish which damage clothes during storage.
Wool fibres are made of a particular protein (Keratin) which is a bad conductor of heat and as a result does not allow body heat to escape. This helps us in keeping warm during winter. These fibres are wavy in structure, the property commonly known as crimp. Crimp imparts resilience to the fibre due to which fibres quickly recover from wrinkling and crushing. Because of this wavy structure the fibres do not come perfectly close and as a result a large number of air pockets are formed. The air entrapped within these pockets acts as an insulator and traps body heat inside.
Hail is formed in thunder clouds when ice pellets formed near the freezing level in the atmosphere are caught in air currents. They are tossed up and down by air currents within the thundercloud where these pellets collide and fuse with one another. Further deposition of water or ice, causes them to grow into hailstones. Certain conditions such as vertical upward air currents help prevent hail falling too quickly and results in the increase in the size of hailstones.
Plants have special structures called root hairs for absorbing water and other nutrients from the soil. The root-hairs are thin-walled extensions of the outer layer of cells in the root. Deep underground they are surrounded by solutions of various minerals and nutrients in the moist soil. Some of these nutrients such as the nitrogen compounds simply pass through the root-walls when they are present in high concentrations in the soil. The process can be likened to the natural flow of water from the high hills to low valleys. Other nutrients such as minerals which are present in lesser quantities in the soil than inside the cells are transported into the root hairs by special proteins located on the cell-walls, a process which can be likened to pumping of water from wells to tanks higher up.
The annular rings or the alternating dark light circles seen in a cross section of a tree are produced because of differences in the rate of growth in different seasons. As it happens, the entire tissue in the trunk of a tree does not divide or grow to increase the girth of the tree. There is a layer of dividing tissue called the cambium sandwiched between the fibrous xylem (the water carrying tissue) and the phloem (the food carrying tissue). However, the cambium divides at different rates in different seasons. In winter, its growth is slower than in other seasons, say in spring, when conditions for growth are fairly favourable. Thus, the relatively small number of cell produced in winter remain compacted together producing a dark band while the cells produced during the spring season spread out into a broader light band. These growth patterns are repeated at annual intervals and hence the name. The annular rings thus indicate the age of a tree as well as the changes in climate that might have occurred in the tree’s life time.
Cells in the root hairs of plants contain dissolved sugars and salts. Water surrounding the root moves into them to equalize the pressure. This is called osmosis. The increased water pressure in root hairs forces water upward, cell by cell through the roots and trunk to reach the leaves.In addition to this, during the growing season, a tree passes tonnes of water into the atmosphere from its leaves through transpiration.
This creates a partial vacuum that is quickly filled by the water being pushed up from the roots. Water molecules stick together, and as water is lost during transpiration, this cohesion causes a chain reaction that is transmitted all the way down.
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.