My Science School

          The oil that we use in our kitchen or for the manufacture of margarine and other goods is obtained from the seeds of many plants. The world production of major oilseed crops (in millions of metric tons) is Soyabeans 46.5, Peanuts 18.1, Cottonseed 22.1 and Copra 3.4. The other sources of vegetable oils are mustard, rapeseed, sunflower etc.

          The basic process for extracting oil is essentially the same for all oilseeds. It involves either pressing or solvent extraction or a combination of both. The material that remains after removal of the oil contains primarily fibres, carbohydrates and proteins. This may contain protein upto 50%. This material is discarded and used as fertilizer or animal feed.

          Most of the world’s supply of coconut oil comes from West Africa. It is taken from the dried kernel of the nut called copra which contains 70% oil. Palm oil also comes from West Africa and from South-East Asia. These oils are produced in a hard fatty form called stearine, which is used in the manufacture of chocolate, cooking fats and medicines. Crude oil is used in soaps and shampoos.

         Cottonseed provides about 37% oil. The cotton plant is grown commercially in the United States, India and Egypt. The fruit of the plant splits open to reveal fluffy white fibres and a number of seeds – each about six millimeters long. Cottonseed oil is used in margarine, cooking fat, and salad oil. It is also used in soaps, resins, grease and lubricants.

         Linseed is the seed of the flax plant which is grown primarily in the United States, Russia, Argentina, India and Canada. Flax fibres are woven into linen cloth and the seeds are used for extracting oil. Linseed oil is used in paints, varnishes, printing and lithographic inks, linoleum, oil cloth and as a water-proofing agent. The residue is a valuable cattle food.

         Groundnut or peanut is the seed of the plant Arachis Lypogea. The seeds of this plant yield oil and are cultivated mainly in China, West Africa, the United States and South-East Asia. It is mainly used as a cooking medium.

         Soyabean is the most important of all the oil seeds. It is extensively grown in China and the Far East. Soyabean oil is used for cooking and as a base for paints, plastics, adhesives, etc. It is a rich source of protein. The seeds can be ground into protein-rich flour which can be used in many foods.

          Sunflower is becoming increasingly popular in European oil markets, and so is rapeseed in Canada and Northern-Europe. Sunflower is now grown in countries like Mexico, Russia, erstwhile Yugoslavia, Turkey and South Africa.

 

            Anything exposed to the sunlight for some time becomes very hot, especially during the summer months. A scrap of paper or a piece of metal kept in the sunlight may even become too hot to touch after a while. But have you ever wondered why the leaves of trees and plants, which are exposed to the sun the whole day, don't get so hot?

            This fact may be understood as follows: a plant leaf is made up of several layers of cells. The upper epidermis covers the top surface of the leaf and the lower epidermis covers the underside. The lower epidermis has many openings called stomata, which act as valves. They regulate the exchange of gases between the leaf and air. When they are open, they allow carbon dioxide to go into the leaf. They also release oxygen and water vapour. When the stomata are closed, inhaling or exhaling cannot take place.

            Each stomata is surrounded by two sausage-shaped guard cells, which control the size of openings. The stomata are usually open during the day and closed at night. The water vapour that is lost by the leaf through the stomata is replaced by water from the roots. This process is called transpiration.

            So when water evaporates, it cools the leaf. Hence this enables the plant to keep cool in the sunlight.   

The roots of certain plants get swollen with stored food. They can be eaten as vegetables. The plants that produce such roots are called root crops.

Root crops have long been cultivated as a food source all over the world. Since they extract different chemicals from the soil, as against grain crops, they have proved useful in crop-rotation systems.

The roots of beet are consumed mainly in cooked form and are usually served with a main course or in soups. Beet powder is used as a red colouring agent in sauces.

Carrots are bright orange-coloured roots. They contain high percentage of carotene. They are consumed in fresh or cooked form and are sometimes dehydrated.

 

Continue reading "Which are the roots we eat? "

          Do you know that there are certain plants which cannot produce their own food because of the absence of chlorophyll? Such plants, therefore, depend on other plants or dead animals for their food.

          Plants which feed on dead organic matter are called ‘saprophytes’ and those which feed on plants are called ‘parasites’. Saprophytes play an important role in the decay process. They clear the land of dead animals by digesting and absorbing nutrients from the dead material. For instance, all fungi and bacteria which do not contain chlorophyll fall in this group.

          Parasitic plants feed on other plants. They obtain water and food from the host through specially developed organs called ‘haustoria’ which secure the parasite to the host and grow into the host’s tissue. Parasitic plants do not give any benefit to their hosts in anyway. In some cases, they cause harm to their hosts.           

          The extent to which a parasite is dependent on its host largely determines its vegetative form. True parasites such as dodders, cuscuta and cassytha are entirely devoid of chlorophyll and rely entirely on the host as a food source. The dodder, which is a well-known parasitic plant, looks like a tiny slender snake. Its colour varies from bright yellow to red. When a dodder seed germinates, the young plant begins to grow in a circular fashion, searching for the mother plant. Once it gets a host, the thin stem of this plant twines around the host’s stem and starts taking food from the host.

          Other parasites such as the toothwort and the broom are parasitic on the roots of other plants, rather than their stems. Correspondingly, these plants are less conspicuous than dodders because their vegetative parts are underground.

          A well-known example of a partial parasite is mistletoe which grows as a cluster of branches hanging from trees. It produces a haustorium which connects with the host’s stem and extracts water and mineral nutrients. It can produce food by photosynthesis but needs water and minerals from trees.

          Mosses and lichen are also parasitic in nature. They cover the bark of the trees and take food from them. Rafflesia Arnoldi of Sumatra is also a famous parasitic plant.