My Science School

           Since ancient times, man’s curiosity has led him to explore the dark, mysterious world of the deep seas. Diving has therefore developed to be an important sport over the years. But how do men stay under water for long periods of time?

          The first practical diving apparatus was devised by a German scientist, named Augustus Siebe in 1819. It comprised a metal helmet with a shoulder plate attached to a waterproof leather jacket. A tube running from the helmet was attached to an air pump. This was the first of many major experiments he carried out in trying to perfect a safe method of staying and working under-water. In 1830 he designed and developed a complete suit and helmet with air valves. Although many improvements have since been made, Siebe’s principles remain in universal use. 

          Deep sea divers, such as those who search shipwrecks for treasure, are divided into groups. They are skin divers who wear rubber suits that fit tightly like the skin, and divers known as ‘hard hats’ who wear heavy diving dress.

          A deep sea diver should use seven essentials: (a) An air pump for pushing air downwards to him. (b) A helmet, usually of steel, with glass windows to see. (c) A flexible waterproof suit fitting closely at wrists and ankles. (d) A length of air tubing that must be flexible, but must not collapse under the pressure of water. (e) A pair of heavy boots to keep the feet on the bottom. (f) Lead weights, hooked to chest and back, to prevent floating up to the surface. (g) A life-line to communicate with the surface by a system of jerks. One jerk may mean danger, and so on!

          Some divers also have a telephone so that they can talk to the ship. The wires for these telephones are built into the lifelines.

          Water pressure is a big problem for deep sea divers. The deeper a diver goes, more becomes the pressure of water around him. So the air pumped down must enable him to breathe properly and also balance the water pressure outside.

          In the past, deep sea divers used to breathe ordinary air, which contained nitrogen.

          This was very dangerous because when the pressure was very high, nitrogen would dissolve in the blood. When the diver surfaced, the pressure quickly returned to normal, which caused the nitrogen to bubble out of the blood. This led to a very painful illness which could even kill the diver, called as ‘Bends’ or ‘Caisson disease’. To avoid this, divers now breathe a mixture of oxygen and helium. Helium does not dissolve in the blood, so it is safer to use. But breathing helium makes divers speak with a high, squeaky voice because sound travels three times as fast as it does in air!

          In recent years, diving has not only become a popular sport, but is also useful in performing important jobs. Divers are needed for the construction and repair of bridges. They study plant and animal life beneath the surface of water. They aid in finding drowned people, and they also help in the search for buried treasure! 

 

          Sahara is the world’s largest desert covering an area of 9 million sq km. in northern Africa. It extends from the coast of Atlantic Ocean in the west to the Red sea and Iraq. It includes parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Sudan and Tunisia. One third of the desert is covered by sand dunes and the rest consists of rocky uplands and stony plains. Crude oil and natural gas have been discovered beneath the Sahara and now being extracted. But there was a time when this great desert was covered by ice. Do you know when?

          The first clue of ice was discovered when geologists found evidence of glaciations in the bedrock of the Algerian desert. The approximate time of the ice covering was calculated to be about 450 million years ago. The location of the desert at that time, as research studies have found out was near the South Pole. The size, shape and position of the continents or landmasses of the earth have been constantly changing over the years. This happens due to the movement of plates in the earth’s crust. When these giant plates move they carry the continents along with them. As per the available evidences, 200 million years ago there was a supercontinent called Pangaea. It was formed when separate continental plates drifted together but later Pangaea also broke apart. But geologists are not sure about the continental locations before the formation of Pangaea. But rock studies provide some clue to the then location of Sahara. They suggest that Sahara was situated near the South Pole which eventually leads us to believe that it was covered by ice during that period of history. This period, according to geological classifications, is called the Ordovician period when North Africa was at South Pole ice-cap and the equator ran diagonally across today’s North America.

 

          Our atmosphere contains about 78% of nitrogen. A certain amount of this nitrogen is constantly being removed, and an approximately equal amount is being returned. This continuous circulation of nitrogen among the soil, water, air and living organisms is known as the Nitrogen cycle. Let us see how the percentage of nitrogen in the air remains constant.

          All living things need nitrogen. It is part of proteins and nucleic acids, both of which are vital for life. How nitrogen is removed from atmosphere and again returned to the atmosphere is given below.

          A part of the atmospheric nitrogen is removed from the air by lightning. The sudden discharge of electricity causes some of the nitrogen and oxygen components in the air to combine, forming the oxides of nitrogen. When these nitrogen oxides are dissolved in water, they combine with other elements to form nitrogenous compounds.

          Some nitrogen is removed, from the air by certain bacteria and algae in a process called nitrogen fixation. Symbiotic bacteria present in the nodules of roots of some plants, such as peas, beans, gram etc. take up atmospheric nitrogen directly, and pass it on to the plants. Plants take up nitrogen compounds and convert them into proteins. These proteins are assimilated by animals. Some other plants, like rice, have symbiotic blue-green algae which fix atmospheric nitrogen.

          As a result of death, decay and excretion by plants and animals, the organic matter is converted into ammonium salts in the soil. Special nitrifying bacteria convert ammonia into nitrogenous compounds that are used up by plants. Animals get their nitrogenous compounds by eating plants, or other animals that eat plants.

          Thus an approximately equal amount of nitrogen is also being constantly returned to the atmosphere. Denitrifying bacteria change some of the nitrogenous compounds in the soil, back into gaseous form of nitrogen. These gases then return to the air.

          Thus nitrogen from the atmosphere passes into the soil, plants and animals and finally returns to the air. It may take thousands or millions of years, but every molecule of nitrogen eventually returns to the air.

 

          Proteins are very important chemical compounds contained by all plants and animals. Probably life would not exist without proteins.

          The word ‘protein’ originated from a Greek word which means ‘first’, because proteins are considered to be the most essential part of the living matter. These chemical compounds are made up of chains of amino acids. There are more than 21 amino acids. Each amino acid has carbon, nitrogen, oxygen and hydrogen as its constituents. The different amino acids combine in different ways to form thousands of proteins.

            Proteins work in many different ways in the body. An important group of proteins, called enzymes act as catalysts in many biochemical reactions. Enzymes are essential for metabolic activity of the body. Some hormones, such as insulin, are also proteins. They are called regulatory proteins because they regulate blood pressure and blood glucose level. Immune proteins protect the body against infection. Transport proteins such as haemoglobin carry vital substances to different parts of the body. Movement of the muscles is helped by proteins called contractive proteins. Thus proteins are vital for the body. 

Continue reading "What are proteins? "

          Litmus is used in chemistry to detect the presence of alkalis and acids. Litmus is a dye made from small plants called lichens. It is either red or blue in colour and is used in the form of a solution which is sometimes on a test paper.

          When lichen called Rocella Tincotoria is allowed to react with ammonia, potassium carbonate or lime, it gives a blue colour material. The paper is dipped into it and dried. This is known as a blue litmus paper, and is used to test acids. Acids turn blue litmus red.

          Orchil or cudbear is a red dye obtained from another species of lichens. This is used to make red litmus paper. Alkannet or alkanna is another dye obtained from the root of the plant Alkanna Tinotoria. The colouring ingredient, alkannin, is soluble in alcohol, benzene and others. When white paper is impregnated with an alcoholic solution of alkannet, it becomes red. This red paper is turned blue or deep violet by alkalis. 

          Neutral solutions (neither acid nor base) do not change the colour of litmus.

          When a chemist wishes to neutralize an acid solution, he first adds litmus solution. This changes its colour to red. The base is then added, until its colour changes to violet. The solution then becomes neutral, i.e. neither base nor acid and one more drop of base turns the solution blue.

          When acids and bases react, they produce salts by neutralization. For instance, the common salt that we use in our food is produced by the reaction of caustic soda and hydrochloric acid.

          Nowadays, litmus paper is made from several substances such as azolitmin, crysthrolitmin, spaniolitmin etc. These are apparently mixtures of closely-related compounds that were identified in 1961 as derivatives of the heterocyclic compound phenoxazine.

 

          Before the discovery of anaesthetics, an operation used to be an agonizing experience for the patient. Even though different agents like herbs, gases, oils and drugs were used for relieving pain, the patient sometimes died from pain and shock. It was only with the discovery of modern anaesthetics that a major break-through was achieved in the field of surgery.

          An anaesthetic is a substance that causes a loss of sensation or feeling in the body. The history of its discovery is very interesting. In 1799, the British chemist, Sir Humphry Davy inhaled some ‘laughing gas’ (nitrous oxide) and found that it produced unconsciousness. Davy published this experience and in 1844 in the United States Horace Wells performed the first dental operation using nitrous oxide as an anaesthetic. Two years earlier, i.e. in 1842, the first painless operation had been carried out by Craw Ford W. Long, using ether as an anaesthetic. In 1847, chloroform was reported to have similar anaesthetic effect. At last surgeons had found a method of overcoming pain to carry out lengthy operations without undue haste. 

          Today, many new types of anaesthetics have been developed. Their application is of two types: local and general. Local anaesthetics are used to numb a particular part of the body. They act by blocking the transmission of electrical impulses along nerve cells, and are usually injected around the nerves that normally carry impulses from the area to be operated upon. The first of these anaesthetics was cocaine. This was superseded by another drug called procaine in 1905. Numerous drugs related to procaine such as lignocaine are nowadays used.

            General anaesthetics render the entire body unconscious. Nitrous oxide, ether and chloroform are included in this category, together with a more recently developed drug, halothane. Once inhaled, they act within seconds but recovery starts immediately after the drug is withdrawn. Halothane has been found to have side effects on liver. Now it has been replaced by ethrane.

          Under general anaesthesia, the patient’s respiration may be controlled externally. There are two reasons for this. First, general anaesthesia depresses the area of the brain that controls respiration. Second, for many operations the patient’s muscles need to be released which is achieved by giving a drug called curare.

          A person called an anaesthetist is trained to give proper amounts of anaesthetic to patients being operated for different ailments. At least one anaesthetist is always present in the operation room during the surgery.

 

            The human body is a machine that needs energy to work. This energy is obtained from food materials through metabolism. These metabolic processes are carried on by activating agents or catalysts called enzymes. Let us see what enzymes are and what they do in our body.

             An enzyme is an organic catalyst produced by a living cell. All enzymes are proteins made up of long chains of amino acids. They combine with the substrate to form an intermediate compound. This intermediate compound is an unstable complex, and breaks down to yield the reaction product, plus the original enzyme.

             Enzymes are themselves synthesized by other enzymes derived from nucleic acids. An average cell contains about 3000 different enzymes. In order to function correctly, many enzymes require the assistance of related substances known as co-enzymes which are produced from vitamins in the diet.

             The human body literally contains hundreds of different enzymes. Many are contained within the cells, but some others, such as those used for digestive purposes, act outside cells in the gut itself. Enzymes are involved in almost every chemical reaction taking place in our body.

             Many physiological activities such as digestion, building up and breaking down of tissues, cellular respiration and muscle contraction depend on their action. The activity of an enzyme depends on the temperature, the degree of acidity or alkalinity (pH) and the substance upon which the enzyme acts. A single enzyme molecule is capable of bringing about the required changes on hundreds of molecules of the substrate in a few seconds.

             Enzyme action can be blocked by some poisonous substances such as mercury, lead or arsenic. The presence of such substances hinders the enzymes from forming intermediate complex with the substrate. Normal metabolism is thus prevented.

            Enzymes are classified into six major groups: Oxidases which bring about oxidation, transferases which bring about group transfer; hydrolases which speed up the process of hydrolysis; lyases that bring about group removal. Isomerases enzymes are responsible for isomerization and ligases for joining of molecules.

           Enzymes are not only important for our body, but are also very useful in industry, medicine and analytical chemistry. Although enzymes normally work inside living cells still they are capable of working outside the cell. They are used to convert starch into glucose and glucose into fructose. They are also used in cheese-making industry and for the production of semi-synthetic penicillin. Artificial sweeteners are also produced with their help.