Category Chemistry

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.

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.