There is a close link between the sense of taste and the sense of smell. Much of what we think of as taste has a big smell component. The taste buds in the tongue monitor relatively crude sensation of the four basic tastes – sweet, salty, sour and bitter. Faint vapours of whatever we eat drift into the nasal cavity where the smell receptors add more detail to the information given by the taste buds.

When we have a cold our nose becomes blocked and the sensation of smell ceases. The gas and vapours from the food cannot be sensed by the smell receptors; consequently we cannot perceive the smell or aroma of the food, which in turn makes the food appear tasteless.

            Tears produced by the tear glands keep the eyes moist and are normally drained off through the nose. Onions contain a number of water soluble volatile substances containing sulfur. On cutting the onion these substances quickly spread into the air and cause irritation in eyes. The tear glands start secreting more and more tears to wash out the irritants. The tears are produced so rapidly that they cannot be drained out through nose and so run down the eyes.

Potato is a living plant tuber (a modified stem specialized for storage of food). There is a lot of difference in the cellular structure and chemical nature of the potato peel and that of the flesh. The flesh is made up of parenchyma cells, specialized to store starch. The walls of these cells are made up of cellulose and they are joined together by a sort of glue called pectin. The peel or the skin of potato is made up of cork cells, the walls of which have a lot of lignin and suberin deposits. These substances give a greater mechanical and structural strength to the corky cells and hence are easy to remove as a continuous peel. In un-boiled potato the corky skin and the flesh of potato are sealed together by pectin. Hence peeling is difficult. During boiling, little change occurs in the corky peel, but the fleshy parenchyma becomes soft. Also the glue-like substances present between the cells, swell up and break down. As a result, the adhesion between the peel and the flesh is reduced and the effort required to separate the peel from the flesh is highly reduced. Hence it is easier to peel a boiled potato.

            Spoilage of foodstuffs is caused by microorganisms which decompose them to produce acid, alcohol, etc. Bacteria are always present in the atmosphere. When freshly prepared food is kept in the open for long periods it gets contaminated. The bacteria then act upon the foodcomponents such as proteins, carbohydrates and fats and break them down to products which due to their off-odours or bad-taste are not suitable for consumption. Factors such as high temperature and humidity help the bacteria to grow.

    Spoilage of food can be prevented by treatments like heat sterilization, refrigeration, deep-freezing and desiccation.

  Flowering is a natural mechanism by which the majority of plants perpetuate their species through the production of seeds. All the parts of a flower take part in one way or another in the reproductive process. The stamens consist of thread-like stalks supporting sac-like anthers which produce the pollen. The central pistil contains the ovary and a sticky stigma. The colourful petals serve as signals to attract insects and other pollinators. When pollinating insects or birds visit the flowers for nectar, they help transfer pollen to the stigma which leads to fertilization of the egg cells in the ovary. The ovary then grows into a fruit containing seeds that would, if planted, grow into new plants thus perpetuating the species.

            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.

            Lightning occurs when a massive electrical discharge takes place between two oppositely charged clouds or between a charged cloud and the ground. The charges develop in thunder clouds due to the friction of water droplets with air as the droplets move up and down with the rising and descending air currents within the cloud. During a bolt of lightning, thousands of amperes of electricity flows through the air in a fraction of a second. This rapidly heats up the air along its path which expands very fast producing shock waves which we hear as thunder. Although the lightning and thunder are produced at the same instant, we hear the thunder later because light travels faster than sound.

    The reason lies in the water cycle. The total quantity of water in the lakes, rivers and oceans of the world remains almost the same always; only the distribution changes periodically. The water cycle begins as the Sun evaporates water from oceans, lakes, rivers and soil. The vapour forms clouds which precipitate as rain or snow, 75 per cent of which falls on the oceans. The remainder falls on land. Some of this water seeps into the earth as groundwater while some is returned to the oceans by the rivers. Thus there is constant balance between water flowing into the oceans and water evaporating from them. That is why the oceans do not overflow.