FST - 1

4th Part

Q.  Describe the origin of life through chemical evolution as explained by Oparin and Haldane. 

A. Soviet biochemist, Oparin, and the British biologist, Haldane proposed that "life could have arisen from non-living organic molecules". 

            In the early stages of development with the hot gases condensing and the molten matter was solidifying to form rocks, the Earth acted as the huge factory, producing many kinds of compounds. The sources of energy available for the formation of numerous types of molecules were cosmic rays, ultraviolet radiations, electrical discharges such as lightning, radioactivity, and heat from volcanoes and hot springs. The lighter gases of the atmosphere such as hydrogen, helium, oxygen, nitrogen, etc.. escaped into space unless they could combine with other elements to form liquids or solids. In such cases, they remained on the earth. In particular, oxygen could not remain as free oxygen. It combined with other elements to form compounds. For example, hydrogen and oxygen combined to form water vapor and remained in the Earth's atmosphere. Similarly, oxygen combined with calcium and carbon to form calcium carbonate, i.e. limestone. Again, nitrogen, hydrogen, and oxygen combined together to form ammonium nitrate. Compounds of carbon and hydrogen were also formed sometimes along with nitrogen or oxygen. These compounds are, today, called "organic compounds".

          The Earth had at the same time started cooling down. As the Earth cooled sufficiently, there were torrential and prolonged rains taking place which were caused due to condensation of steam. The rains began to accumulate in the depressions on the earth and so the oceans were formed. These hot bodies of water contained abundant and varied organic compounds washed down from the atmosphere. Continued interaction among these compounds in the warm waters resulted in the formation of yet more compounds. The water in the oceans at this stage of the Earth's development has been referred to as "hot dilute soup", which amongst other things also contained "amino acids" having a composition of carbon, hydrogen, nitrogen, and oxygen. The molecules of amino acids combined together to form large complex molecules, the "proteins" which are the building blocks of life.

         It is from this accumulation of complex organic molecules that the first extremely simple self-replicating molecular systems accidentally originated. Because of the property of self-replication, they are called living organisms.

Q.  Briefly explain the impacts of Miller's experiment on the classical theories of the origin of life.           

A.  The origin of life through chemical evolution was proved through Miller’s experiment. It was tested by recreating the conditions in the laboratory on a small scale, the conditions which must have existed when life originated on the earth.

       Miller through his experiment has proved that life might have accidentally originated from the non-living organic molecules. Miller, an American biologist subjected a gaseous mixture of methane, ammonia, water vapour, and hydrogen in a closed flask at 80°C to electric sparking for a week. This mixture with its temperature, and electric discharge through it, represented a situation that might have prevailed during the early stages of the development of the earth before life came into existence. When the contents of the flask were examined a week later, they were found to have amino acids which are essential for the formation of proteins. As we have said before, proteins are the essential building blocks for living organisms. Thus with the help of the Millers experiment, the credibility of the Oparin-Haldane theory of chemical evolution greatly increased. Many amino acids have been obtained, since then by this method. So also some sugars and nitrogenous bases which are otherwise found in the nucleus of a cell, which is a unit of living organisms. Miller's experiment thus forms a turning point in our approach to understand the problem of the origin of life on Earth.

           The evidence, we get from Miller's experiment, is supported by evidence of similar chemical reactions occurring in space even today. Chemical analysis of a meteorite that fell near Murchi Murchison in Australia, in 1969, showed the presence of organic molecules. These organic molecules were very similar in type to the products that were formed in Miller's experiment.

Q.  Write the life story of a star.                       

A.  A young star is largely composed of hydrogen gas. Hence, the most likely place for a star to be born is in one of the numerous clouds of hydrogen gas that exist in the interstellar space. Stars are also formed inside large dense interstellar clouds of gas. Under the influence of the gravitational pull of the gas, a gas cloud starts contracting. As gravity pulls in the clouds, the pressure, and temperature in the cloud increases. This stage is called a protostar.

        When the temperature becomes sufficiently high (about 4 million degrees centigrade), a nuclear reaction starts in the protostar, in which the hydrogen nuclei fuse together to make helium nuclei. In this process, a large amount of energy is released. The energy travels to the surface of the star and is radiated in the form of light, heat and other electromagnetic radiation. This energy creates an outward pressure and force. The contraction of the star stops only when the inward pull of gravity is balanced by the outward force of this radiant energy. At such a time the star becomes stable in size and temperature. 

        As the star consumes a significant percentage of the hydrogen fuel in its core, the nuclear reaction decreases and the out force of the radiant energy weakens. The core of the star further contracts because its gravitational pull becomes more than the out-force of radiant energy. But this raises the temperature of the core. Meanwhile, the hydrogen nuclei 'burn' in the outer layer or shell surrounding the core. The extra heat from the core as well as the heat generated in the outer layers causes the star's outer region to 'boil' and expand. The star becomes big and its brightness increases. But, as the outer layer expands farther away from the nuclear furnace, its temperature falls. The puffed-up star looks red and cool. If it is many times more massive than the Sun, it becomes a red supergiant. If it is sun-sized or only slightly more massive than the Sun, it becomes a slightly swollen red giant.

        The red giant stage of a star is a relatively short stage. In this stage, the star consumes its hydrogen at a very fast rate, piling up helium in its core. As the fuel burns, the core contracts further, producing temperatures as high as 100 million C. At this point, the helium nuclei in the core fuse together in another nuclear reaction to form carbon nuclei. This is a critically unstable moment in a star's life with two layers of the star burning at the same time-an outer layer where hydrogen is being turned into helium and inner core where helium is being turned into carbon. Hereafter the fate of the star depends on the mass of its core.

            If the mass of the core is less than 1.4@ where M, is the Sun's mass, the contraction of the core halts when it is about the size of the Earth. This limit of 1.4M is known as the Chandrasekhar limit. Such a star is known as a white dwarf.

           If the core mass of the star is in the range 1.4M,--3Mo, or the star mass is between 8M, to 15 M,, the core shrinks to a radius of about 10 km and a neutron star is formed.

           If a star starts with a mass of more than 20 M,, its contraction continues. Then the core of the star collapses to become a black hole. Its gravity is now so strong that nothing, not even light, can leave it.

          Sometimes, massive stars (with the core mass between 3 M, and 15 M,) explode, releasing a tremendous amount of energy. Such explosions are called 'supernova'.

Q.  Differentiate between quasar and pulsar.       

A. Radio telescopes have led to the discovery of hundreds of cosmic objects that emit radio waves. Most of these cosmic objects can be identified by the optical

telescopes. With the help of radio telescopes, pulsars were discovered. Pulsars are stars that send out pulses of light and radio waves in regular bursts of energy. For example, a pulsar in the center of the Crab nebula at a distance of 6000 light-years from the Earth sends outbursts of light and radio waves 30 times a second.

      Quasar an abbreviation of 'quasi-stellar radio source', is a star-like object situated billions of light-years away, are the radio sources. Not all quasars are radio sources. Since the electromagnetic waves from quasars are being detected on the Earth, and after observation, it shows they send out huge amounts of energy. Quasars are comparatively small in size but it emits 100 times more energy than the entire Milky Way Galaxy.

Q.  What is the difference between a red giant and a neutron star?   

A. During the life cycle of a star, as the star consumes a significant percentage of the hydrogen fuel in its core, the nuclear reaction decreases and the out force of the radiant energy weakens. The core of the star further contracts because its gravitational pull becomes more than the out-force of radiant energy. But this raises the temperature of the core. Meanwhile, the hydrogen nuclei 'burn' in the outer layer or shell surrounding the core. The extra heat from the core as well as the heat generated in the outer layers causes the star's outer region to 'boil' and expand. The star becomes big and its brightness increases. But, as the outer layer expands farther away from the nuclear furnace, its temperature falls. The puffed-up star looks red and cool. If it is many times more massive than the Sun, it becomes a red supergiant. If it is sun-sized or only slightly more massive than the Sun, it becomes a slightly swollen red giant.

         The red giant stage of a star is a relatively short stage. In this stage, the star consumes its hydrogen at a very fast rate, piling up helium in its core. As the fuel burns, the core contracts further, producing temperatures as high as 100 million C. At this point, the helium nuclei in the core fuse together in another nuclear reaction to form carbon nuclei. This is a critically unstable moment in a star's life with two layers of the star burning at the same time-an outer layer where hydrogen is being turned into helium and inner core where helium is being turned into carbon. Hereafter the fate of the star depends on the mass of its core. If the core mass of the star is in the range 1.4M--3Mo or the star mass is between 8M to 15 M,, the core shrinks to a radius of about 10 km and a neutron star is formed. If a neutron star is born rotating very fast, it emits electromagnetic radiation, which astronomers detect as pulses of radio waves. Such stars are called pulsars.

                  

Q.  With the help of a suitable example, describe the concept of the systems view of life.                                 

A.  The characteristics which we recognize as life are, in fact, an expression of the coordinated working of various parts of an organism. Various parts in an organism, whether plant or animal are not haphazardly put together rather organized to perform certain specific tasks or work and together they are organized into systems. The parts work together and the entire combination forms one unit. An animal or a plant is also made up of numerous parts that represent a well-defined system. For example, in an animal body, there are parts concerned with the intake of food and digesting it, the bones arranged as a skeleton to support the body, the heart circulating blood to different parts of the body through the arteries and veins and the brain receiving signals and giving orders of various kinds, together all these parts compose the system.

          The idea that an organism is a system, consisting of various parts, that function to maintain its internal environment throughout its lifetime. In its lifetime, an organism passes through certain recognizable stages like birth, growth, reproduction, and death. We see around us plants sprouting from seeds, growing, bearing fruit and ultimately drying up. Children are born, grow to adulthood, marry, have children of their own, grow old and die. The series of events that occur from the time an organism is born to the time it dies, constitute a life cycle.

                 Aging is an integral part of the life cycle of an organism. Even if an individual meets no fatal accident, or is not eaten up by other organisms or does not suffer a killing disease, death still comes as the natural final result of old age. Aging simply means the process of growing old or the process of progressive deterioration in the structure and function of the cells and organs of the body.

          Another example of a system is the planet Earth. The assemblage of all plants and animals in an environment along with the land, air, and water, which are dependent on each other and works collectively constitutes different parts of a system Earth. The way these diverse forms of life depend on each other makes this planet itself as a huge system. Looking at it in another way, the life and environment of the earth are a well-coordinated system, within which there are sub-systems like individual Organisms exist. And within each of these sub-systems, a single plant or animal, one would find a complex multicellular system. Similarly, industrial, agricultural or educational systems can be visualized as the sub-systems in the society.

Q.  What is aging? Discuss different symptoms of aging.           

Q.  Give different factors for aging. How we can slow down this process.   

A. Aging is an integral part of the life cycle of an organism. Even if an individual meets no fatal accident, or is not eaten up by other organisms or does not suffer a killing disease, death still comes as the natural final result of old age. Aging simply means the process of growing old or the process of progressive deterioration in the structure and function of the cells and organs of the body.

            Symptoms of aging in man include dry and wrinkled skin, brittle bones, reduced blood circulation, reduction of the body’s immune system against diseases and a thin shriveled body. These outward signs of aging are the result of changes taking place inside the body, within the cells and the loss of the ability of cells to divide. During a lifetime, millions of cells are destroyed and replaced rapidly by the process of cell division. When more cells are destroyed than are replaced, aging takes place. The ability of cells to divide depends on an organism. This explains why some animals age more rapidly than others and have a shorter life span than others.

              The division rate of different body cells is also specific. In human beings, the cells forming the skin are continually destroyed and rebuilt, while the cells constituting the brain undergo no division at all from a time about 5-6 years after birth. 

     In recent years, much attention has been paid to study the process of aging, and how to slow it down. Physical exercises that counter sluggish blood circulation and other body processes are known to be of some help. Some drugs, which can slow down aging, are also being experimented with.

Q.  Describe Pasteur's experiment that disproved the theory of spontaneous generation. Support your description with suitable diagrams.      

A.  If we look around in our everyday environment, we observe that straw, soil, mud, dirt, indeed any kind of garbage or rotting matter is infested with a large number of different kinds of living organisms. Such observations led people to believe that life originated spontaneously from non-living matter. Aristotle (384-322 B.C.), known as the father of biology, maintained that not only worms and insects, but also fish, frogs and mice could spring from suitable breeding materials like filth and moist soil. This theory of spontaneous generation was disproved by the experiments of the French microbiologist Louis Pasteur in 1862. Pasteur performed his experiment before a gathering of biologists to test his hypothesis, that only "life begets life".

                For his experiment, Pasteur took two flasks, half-filled them with yeast infusion containing a little bit of sugar and heated them so as to kill any living organisms. He sealed the mouth of one of the flasks and left the other open to the air. After a few days, he invited His friends to observe what had happened. To their surprise, they found that the closed flask was still free of any living organism while the open one was infested with living organisms. In fact, one of this sealed flask is still kept at the Academy of Sciences in Paris. Even after more than a hundred years, there are no living organisms in it.  Pasteur had, thus, shown by these simple experiments that living organisms do not arise spontaneously.