FST -1

7th Part

Q.  What is meant by the cycling of materials in an ecosystem? Describe the carbon cycle in detail with the help of a suitable diagram              

A.   Cycling of materials - Living organisms require four nutrients in relatively large amounts, these are carbon. oxygen, nitrogen, and hydrogen. They also require phosphorus and sulphur. These elements are present in our environment in a fixed quantity, therefore they must be recycled in order to sustain life. Also, these elements must move efficiently, from the living to non-living components and vice versa. For example, plants take in carbon as carbon dioxide to produce food. As the herbivores eat plants, carbon is passed on to them, which in turn is passed on to carnivores, and so on. Carbon is eventually returned to the nonliving pool in the ecosystem, through the excretory processes of the producers, the herbivores. the carnivores, and also through the activity of the decomposers. Through such cyclic processes, these nutrients are used over and over again by the organisms. This aspect of the ecosystem function is called the cycling of materials.

Carbon is one of the essential elements of all organic substances and it enters the ecosystem through the process of photosynthesis. Carbon is present as carbon dioxide in the atmosphere. Carbon dioxide forms 0.03 to 0.04% of the atmosphere. The oceans also have carbon dioxide dissolved in their water. There are 12 basic steps of the Carbon cycle.

1. Carbon dioxide enters the food chain through the plants by the process of photosynthesis.

2. Some of the carbon dioxide captured by the plants and converted into organic molecules are returned to the atmosphere via respiration.

3.  Some portion of the carbon is incorporated into the plant body, which is later passed on to the herbivores, etc.

4.  The living beings release carbon dioxide into the air during breathing.

5.  (i, ii) carbon dioxide is also returned to the atmospheric reservoir by the death and subsequent decay of the dead bodies and wastes of animals and plants.

6)  Formation of fossil fuels, like coal. oil. gas is a part of the carbon cycle, wherein carbon is trapped for millions of years. Fossil fuels are the remains of ancient plants and animals that were subjected to high temperature and pressure over millions of years. Man has been using wood, peat, coal, and petroleum as sources of energy, for running transport such as motorcars, airplanes, etc.: for industries. for cooking food and various other purposes. The burning of fossil fuels returns carbon back into the atmosphere. 

7)  Since air is in direct contact with the sea, the carbon dioxide from the air dissolves in the upper layers of water resulting in the formation of carbonates.

8) The plants that grow in seawater, do not get atmospheric carbon dioxide. Therefore, they utilize carbonates present in water as a source of carbon dioxide during photosynthesis.

9)   Food produced by water plants passes through the aquatic food chain. For example, when fish feed on the water plants, carbon passes on from plants to the fish, and ultimately to the other organisms that feed on fish.

10)  Some of the carbon dioxide produced by marine plants and animals during breathing gets dissolved in seawater and can be re-utilized by the plants.

II )  However, some of the carbon dioxides thus evolved escapes to the atmosphere.

12) Organisms like snails, oysters, etc. extract carbon dioxide dissolved in water and combine it with calcium to form calcium carbonate from which they construct their shells. Shells of these dead animals collect in undersea deposits and may eventually be converted to limestone.

Q.  Define by diagram Nitrogen cycle and the Water cycle

A.  

Nitrogen is a vital part of many essential organic compounds especially nucleic acids and proteins. It also forms a major part (79 percent) of the atmosphere. In fact, the atmosphere is the chief reservoir of nitrogen, where it is present in the gaseous form, which, unfortunately, cannot be directly used by plants and animals. Plants actually obtain their nitrogen from nitrates and ammonium salts in the soil to build up proteins, from which animals derive some of their proteins. The amount of nitrates and ammonium salts in the soil, is limited, at a given time, and their supply would quickly exhaust, if it were not for the renewal of supply of nitrogen which goes on continuously.

1) During thunderstorms, some of the oxygen and nitrogen in the air are converted into oxides of nitrogen by the high temperature of lightning. The oxides of nitrogen dissolve in rain water, reach the soil and get converted into nitrates. These nitrates are taken up by plants.

2) Certain bacteria can utilize nitrogen available in the atmosphere and convert them into nitrates. They are called nitrogen-fixing bacteria. Some of these bacteria live freely in soil, others live in small knots or nodules on the roots of certain plants such as beans, peas, peanuts, clover, and alfa etc. These plants have these bacteria carrying nodules on their roots. Farmers make use of some of these plants, to make fodder, and then plough the rest of the plant into the soil, to increase the nitrates in the soil.

3)  Nitrogen fixation by bacteria, i.e., the process of putting nitrogen in a form that plants can absorb, is rather slow, compared with the rate at which plants need nitrogen. In such a situation the demand for nitrogen is fulfilled by adding nitrogen-containing fertilizers to the soil.

4) Nitrogen in the form of nitrates is consumed by plants and is converted into amino acids, which are the building blocks of proteins.

5) Nitrogen enters the food web through plants and passes on to animals which feed on them.

6) Nitrogen eventually returns to soil in the following ways: (i) During excretion, nitrogenous wastes in the form of various ammonium compounds are returned to the soil or water. (ii, iii) Nitrogen trapped in plants and animals returns to the soil by death and subsequent decay of their bodies by the action of bacteria and fungi.

7) In soil, the nitrogen-containing matter is acted upon by bacteria and are converted to ammonium compounds, then eventually to nitrates.

8) Some soils, particularly the ones in bogs. estuaries, lakes, and parts of the seafloor contain denitrifying bacteria that produce the opposite effect of nitrogen fixation. They act on nitrates and release nitrogen to the atmosphere.

9) Volcanoes are one of the important sources of nitrogen. They have been emitting small quantities of nitrogen for centuries and contribute significantly to the nitrogen reservoir of the atmosphere.

Water Cycle -

The ocean is the major reservoir of water which covers about seventy percent of the earth's surface. Ocean water is salty. Freshwater is mostly found in rivers, glaciers and in between rocks below the surface of the earth.

         The water cycle is driven by the sun's heat energy, which causes water to evaporate while gravity draws the water back to earth in the form of rain, snow etc after water vapour condenses. The water cycle is divided into 4 basic steps.

1) All water, which is used by mankind for personal and industrial purposes, is plain or freshwater, which is derived largely from the ocean water through evaporation and precipitation.

2) As the precipitation reaches the earth, some of the waterfalls directly on the ground, some falls on vegetation, on buildings, and on streets. A part of the water that falls on the ground, seeps through the soil, to an impervious layer of clay or rock where it is collected as groundwater. The rate of downward movement of water in the soil is dependent on the type of soil, its slope, type of vegetation and the amount of rainfall. The underground water is utilised by human beings for domestic, agricultural or for industrial purposes.

3) Some of the water falling on the ground runs down the gutters and drains to be carried off to rivers. Some surface runoff water may also get collected in small ditches, lakes, etc.

4) So far we have been discussing the various ways in which water, in different forms, reaches the earth. Now let us understand as to how water reaches back to the

atmosphere.

i) Some amount of rainwater never reaches the ground as it evaporates back into the atmosphere.

ii) Plants also give out large amounts of water back to the atmosphere through their leaves.

iii-v) The water remaining on the surface of the ground and on vegetation as well as the water in the surface layers of streams, lakes mad oceans evaporates and goes back to the atmosphere. As the water vapors in the atmosphere form clouds and drift with the wind,'they eventually meet cold air and condense, this leads to rainfall, snowfall, etc. and thus the water cycle continues. 

Q.  "Land is the most precious resource." Discuss this statement.     

A.  The land is the most precious resource because it produces supports the human population and other living beings on Earth. Soil, which forms the uppermost layer of the land, is the most precious of all resources because it supports the whole life system on Earth. It provides food and fodder in the form of vegetation and stores water essential for life. The land is important to us as around, nearly 44% of land in India is used for agricultural purposes, of which 11-14% is covered with forests that include good as well as degraded forests, and 4% of the land is used as pastures and grazing fields. The remaining 8% is used for various other purposes such as housing, agroforestry, the establishment of industries, the development of roads and reservoirs, etc.. About 14% of our land is barren i.e. it cannot be used for the cultivation of crops. Nearly 1/3 of the barren land has lost its productivity due to alkalinity or salinity of the soil and waterlogging, etc. Soil erosion causes great harm to the productivity of our land because in this process soil is broken up and washed away by water or swept away by the wind. These facts indicate careless and unwise use of land and are a reflection of the mismanagement of our land resources.

Q.  Why is soil considered a basic resource for agriculture? How can saline and alkaline soils be reclaimed (or how to treat soil sickness)?                       

A.  Soil, which forms the uppermost layer of the land, is the most precious of all resources because it supports the whole life system on Earth. It provides food and fodder in the form of vegetation and stores water essential for life. It contains sand, silt and clays, mixed with air and moisture. It possesses rich organic and mineral nutrients which are required for agriculture. The type of soil varies from place to place. Those soils which are rich in organic matter are fertile. Fertility is also dependent on the capacity of the soil to retain water and oxygen. For ex., Deep red soil is good for cultivation of potatoes, bananas, pineapples and rubber etc. Black soil supports crops of sugarcane, groundnut, soyabean, cotton and rice etc.

             (Due to overuse without rest, the soil becomes deficient in the required nutrients and loses its fertility. Rotation of crops and vegetables, such as peas and beans, helps to remove the deficiency of nutrients. Plants such as peas add nitrogen to the soil and thus increase its binding property as well as productivity. The roots and off-shoots of the crops and their remains are left in the field for a certain period of time to protect the soil from erosion.)

                      Excessive irrigation causes complete saturation or waterlogging of the soil. As a result of it, soil loses its productivity, partially or completely. As a consequence of over-irrigation in some areas, salinity and alkalinity of the soil increase, making it "sick". This kind of soil sickness can be controlled by, first of all, sealing off all points of leakage from canals, reservoirs, tanks and ponds, and use of only the required amount of water. Alkalinity and salinity of the soil can also be reduced by the application of some chemicals like gypsum (chalk-like substance, from which Plaster of Paris is made), phosphogypsum (gypsum with phosphates), pyrites (sulfides of copper, iron, etc.) in addition to organic manures and fertilizers. Cultivation of salt-resistant plants such as barley, millets, soya, cotton, spinach, date palm is another way of overcoming the problem of salination of the soil.

Q.  Describe the various non-conventional renewable resources of energy.        

A.  Solar energy - Solar energy can be used directly to give us hot water during winter or for producing electricity to run electric appliances. It can be used for heating rooms in colder regions. It can also be used, with the help of a "photocell" to produce electricity for driving vehicles and illumination of streets. In a desert-like Rajasthan, the earth's surface receives solar energy at a rate of 200 watts per square meter per hour. Since this is an unfailing source of energy, it would be a great advantage to develop cheap and efficient photocells or photovoltaic devices to harness solar energy. A feature of using solar energy is that it can be generated where needed. Solar cookers are being used in many homes to cook food. Photocells are also becoming common for generating electricity.

Wind energy - Like solar energy, wind flow can also be harnessed to obtain mechanical energy for fetching water from the wells or from rivers. Once the windmill is turning due to the force of the wind, it may as well run a generator to get electrical energy. In the coastal and hilly regions, where the wind blows at high speed, a windmill can be used for the supply of electricity to a small town. Windmills have been used for long in many countries, but in India, they have only been recently introduced.

Wave and tidal energy

Waves and tides are other sources of energy which are perpetual and can be converted into electric energy, particularly where seawater can move into a narrow cut, such as cuts provided naturally where rivers flow into the sea. The long flow of water has been widely used in India's hilly regions, where a strong stream of water is made to fall on pedals of motor generating electricity on a small scale. Flour mills of small size built on this principle were used in Kashmir for a long time. In fact, large "hydroelectric" power stations work on the same principle. A natural or artificial waterfall is made to turn a modem kind of pedal wheel, called a turbine, which rotates and causes electricity to be generated.

Geothermal energy

Hot water and superheated steam of hot springs are a natural phenomenon and can be used to generate electricity. In our country there arc 46 hydrothermal areas where the temperature of the spring water exceeds 15D°C. These hot springs can be used to generate electricity for heating homes, or glass-houses to grow vegetables.

Biogas - Cattle dung was used for the production of biogas which is used for cooking. Water weeds like water hyacinth, water lettuce, Salvinia, hydrilla, duckweeds, and algae are found to be a useful supplement to cattle dung. Biogas can be used not only as cooking gas, but it can also be used to raise steam, which can be used for running engines or machines in the factories or for running turbines to generate electricity. It has been found that large biogas plants can supply the needs of a number of families or even small villages. What is left over after generating the gas, can be used as manure. Hence this is also an economical way of getting more energy.

Q.  Eutrophication       

Q. What is an algal bloom                             

A.  Materials such as sewage or organic wastes from milk plants, canneries, slaughterhouses, paper mills, starch factories, and fish processing plants, and runoff from agricultural lands greatly increase the productivity of waters and cause algae to grow in abundance so that sometimes water surface gets entirely covered by algae. This is called 'algal bloom'. In general, the entire water body becomes a green nourishing soup. Eventually, the death of his algae promotes the growth of a very large 'decomposer' population. The decomposers break down the dead algae using a lot of oxygen present in the water. In addition, the living algae also consume oxygen from water at night for their respiration. The action of decomposers, and the algae cause decreased amounts of oxygen available to fishes, ultimately causing them to die. The problem of eutrophication or excessive nourishment leading to loss of life in water bodies mainly occurs in ponds and lakes and not in flowing water.

FST - 1

6th Part

Q.  What is carbon dating? How is the age of fossils determined?   

A.  With the developing knowledge of radioactivity more accurate dating of fossils and certain types of rocks has become possible. Radioactive substances can be easily detected using certain instruments. The method most commonly used, now, for estimating the age of fossils is radio-carbon dating. Radioactive isotope of carbon is commonly known as carbon- 14. Since carbon- 14 is chemically the same as ordinary carbon, both arc absorbed by plant and animal tissues in the same proportion as they are present in the atmosphere as carbon dioxide. Plants use this carbon dioxide in making their food. Animals eat plants. Hence, the proportion of carbon- 14 in the tissues of plants and animals is the same as in the atmosphere, as long as the plant or the animal is living. But as soon as it dies, no more carbon can enter its body as photosynthesis or food intake stops. Following death, the carbon-14, already present in the body, decays steadily into ordinary carbon. So the smaller the number of carbon-14 atoms remaining, the older is the fossil. Thus, if we take a piece of ancient wood or bone and measure the amount of carbon-14 present in it, we can estimate the age of the material. This technique has been applied to materials of known age, and thus its accuracy was tested giving confidence in the method to determine the age of unknown objects. The carbon-14 method is applicable only to organic materials which still contain carbon. It cannot be used for fossils in which all organic matter has decayed. In that case, the age of the fossil can be estimated by determining the presence of other radioactive elements like fluorine, or phosphorus.

Q.  Role of radioisotopes in dating the past. 

A.  With the developing knowledge of radioactivity more accurate dating of fossils and certain types of rocks has become possible. Radioactive substances can be easily detected using certain instruments. They have built-in "clocks" in the form of 'radioactive isotopes' that change or decay at a constant rate into non-radioactive form. If this rate of conversion is known, then it is easy to estimate the age of a fossil by measuring the quantities of the radioactive isotopes and the non-radioactive ones into which they have changed in the rock. For example, Uranium is transformed into certain isotopes of lead which are not radioactive. So, the age of uranium-containing rocks can be determined by determining the amount of Uranium left or decayed into lead.

Q.  Name in a sequence the four main stages of human evolution. Which out of these showed bipedal posture for the first time?         

A. The main stages of human evolution are as follows - 

Hominids - The earliest human-like or hominid remains come from two separate East African sites (3.5 million years ago) Ethiopia and Tanzania (3.75 million years ago). It is concluded that these earliest hominids were built with an ape's head on top of a man-like body. They show hominid characteristics to place them firmly within human ancestry. There is evidence that they walked on two feet. 

'Homo Habilis-The First Tool Makers - One of the most important developments in human evolution was the dramatic expansion in brain size. Certain specimens recovered from deposits in East Africa apparently have brain capacities in excess of 650 cm" and close to 800 cm3. These specimens represent the first appearance of our own kind and were termed Homo habilis. The species name Homo habilis, means, literally, handyman. Homo habilis walked upright. The bones of the hand, while displaying many characteristics of modern humans, are somewhat curved in places and more robust than in modern man, i.e. Homo sapiens. The leg and foot bones have characteristics that are both ape-like and human-like, but overall, they are much closer to those of modern humans than to apes. The leg and foot were those of a habitual two-footed animal. The simultaneous occurrence of Homo habilis fossils and crude flakes and stone tools indicate that they used tools.

Homo Erectus

Homo erectus or the erect man first arose at least 1.6 million years ago and continued to live for more than a million years before the transition to Homo sapiens occurred. Homo erectus had a large brain measuring 800 to 900 cm" Fossils of Homo erectus have been discovered throughout Africa, Europe, and Asia. Signs that Homo erectus hunted animals and ate meat are available from the stone tools they used and the marks which these tools left on the bones of animals which have been recovered near their own dwelling areas. There is evidence, that the life of Homo erectus must have been fairly complex and these individuals are considered as intelligent, socially interacting beings. One can even imagine that a relatively complex spoken language may have evolved. The prehistoric record is, of course, silent on this point.

The Neanderthals

These were the first human-like fossils found. The Neanderthals existed throughout western Europe and across into the near east and central Asia from about 100,000 years ago to 40,000 or 35,000 years ago, depending on the precise locality. There are, striking structural similarities between Neanderthals and modern humans. Although the posture, range of movements and manipulation skills were the same in Neanderthals as in modem humans, the skeleton was substantially more robust. Neanderthal's brain was on average slightly larger than normal for modern humans, measuring about 1400 cm3. Neanderthals were proficient hunters, skilled toolmakers and they used hides for protecting their bodies. For the first time in human history, ritual burial became common.

Homo Sapiens-Modern Human Beings

Discoveries of a number of fossils of Homo sapiens suggest that modern humans arose in Africa and migrated to the rest of the old world via the Middle East. It should be noted that these modern humans of the early upper stone age, 40,000 years ago, were distinctly more robust or sturdy as compared with the population today.

Q.  Describe the evidence that supports the various theories proposed for the evolution of modern man.                                   

A.  The general theory of evolution of man is based on evidence that is provided from different sources, such as the fossil records of animals which lived in the past, similarities found in the developing embryos of primates and of other animals, the archaeological remains of the past and their dating and more recently from biochemical studies. Cave paintings and other artifacts left by the early human beings speak of their social and cultural life.

Palaeontological - Palaeontological evidence, of their existence, is left in the form of skeletons and bones buried in the rocks. These are known as fossils. Crucial evidence of human evolution is provided by the study of these fossils. Sometimes, the buried body and the skeleton of an animal disintegrate entirely. If the surrounding material is sufficiently firm, a cavity may remain, having the exact outlines of the structures that disappeared. Such a cavity is called mold, Similar to molds are the impressions. These are left by extinct objects or parts of the body upon the surrounding material. The impression is made while the surrounding material is soft, like footprints in clay or lava. Footprints of extinct animals are also impressions giving valuable information about the animals that made them.

Archaeological Evidence

The study of human antiquities, especially of prehistoric period is known as archaeology. The biological and cultural evolution of man proceeded side by side and the two influenced each other. Like the physical remains of man, his cultural remains also lie buried in the ancient deposits. Often, the two categories of evidence are found together in the same layers of the rock. With the passage of time and the increasing capacity of his brain and development in other bodily organs, man's culture became more and more varied and complex. He learned the use of new materials for making tools and developed new techniques for improving them. The use of tools had a tremendous impact on increased access to food and therefore on cooperative living in colonies. In many areas, archaeological remains show reindeer to be the principal source of meat they ate.

Anthropological Evidence

Modern humans arose at a time when the Earth was going through a very cold and icy period called the Ice Age, which began about 75,000 years ago and ended about 10,000 years ago. The Ice Age was at its most severe about 18,000 years ago, the time which coincides with the development of prehistoric art. This art is represented by colourful images painted on cave walls and rock shelters. Many thousands of carved and engraved pieces of bone and ivory have also been discovered from the same period. A large majority of images are of animals which we can recognize, especially images of reindeer and bisons are plentiful; while paintings of people are strangely absent.

Biochemical Evidence -

Biochemical studies show us that, as evolution proceeds and the species get differentiated, they accumulate changes in the structure of their proteins and DNA. Longer the separation time, the greater the changes. These changes are expressed in terms of percent genetic distance which indicates the proportional difference between the DNA of the two species. Comparative studies of the proteins of the African apes and humans showed that chimpanzees, gorillas, and humans are closely related to one another.

Q.  Who is lucy             

A. The partial skeleton of a 20 years old hominid who lived more than three million years ago was found by Dr. Donald Johanson in Ethiopia. The fossil remains, are known as 'Lucy'.

Q.  List five astronomical methods being used to explore the universe.   

A.  Optical Astronomy - The easiest method of studying light from a cosmic object is to collect it through a telescope and record it on a photographic plate. Photographic films are exposed for long periods of the time-sometimes night after night-to the light being collected by a telescope aimed at distant stars. This method of collecting and investigating light from the cosmos is called optical astronomy.

 Radio Astronomy - Radio astronomy, i.e. the study of cosmic objects through radio waves emitted by them. The radio telescope, a basic tool of radio astronomy, collects radiations from space in the radio wave region. One of the largest radio telescopes in the world was designed and set up by Indian astronomers at Ootacamund. The other radio telescopes in India are stationed at Gulmarg, Ahmedabad, Gauribidanur near Bangalore.

Meteorites - Meteorites entering the Earth's atmosphere from time to time. They bring us many messages about the cosmic objects from which they were chipped off.

Observatories in Space

With the coming of the Space Age, observatories equipped with telescopes and cameras could be placed right in space, beyond the Earth's atmosphere. An observatory in space may be in the form of an orbiting satellite like the Unmanned Orbiting Solar Observatories, Orbiting Astronomical Observatory, Skylab, Einstein Observatory, IRAS (Infra Red-Astronomy Satellite) and many others. An observatory may also be stationed on the Moon or any other planet having suitable temperature and other conditions. Instruments are also put aboard high flying balloons, rockets and aircraft are to record observations. These observatories can record radiation from a cosmic object in the regions of the spectrum such as the IR, UV, gamma rays and X-rays do not penetrate the Earth's atmosphere.

Visiting the Neighbouring Worlds

As space research came of age, it became possible for us to send spacecraft to other planets & even land men & instruments on the Moon. These ventures also provided a rich stock of information about the Solar System. For instance, astronauts of the Apollo mission to the Moon brought back lunar rocks & soil samples, photographs of the lunar surface and Ieft several instruments there for further study.

FST - 1

5th Part 

Q.  With the help of a neat labeled diagram describe the 'feedback' mechanism which checks the loss of water from kidneys in the human body. What is it technically known as? 

Q.  Define homeostasis with example

A. Living organisms have a remarkable capacity to regulate their own lives according to the changes in the environment around them. They maintain a normal external and internal structure and environment in spite of the changes taking place in the outside surroundings. This state of constant structure which is vital for life is known as 'homeostasis'.

            One example of the feedback system in the human body is the availability of the right amount of water in the blood due to the functioning of kidneys. Kidneys are able to control or check the loss of water from our bodies. For this, water is reabsorbed by the collecting tubes in the kidneys so as to prevent its undue loss in the form of urine. This absorption of water is under the control of a chemical called Antidiuretic Hormone (ADH) which is produced by specialized nerve cells in one of the parts of the forebrain. If more water begins to be lost by the body due to greater evaporation during summer, a decrease of water in the blood will take place. It denotes the changes in the internal environment for which our body is very sensitive. At the time of need, a positive signal to the brain causes the production of this particular chemical (ADH) which increases the absorption of water in the kidneys and reduces excretion of urine. The absorbed water gets back into the blood to maintain the normal concentration of the fluid.

Q.  Why is Mars called red planet and in what ways is it similar to earth?    

A.    Mars is often called the 'Red Planet' because it appears in the sky as an orange-red star. The reason for the red color of Mars is because, about 16 percent of the Mars soil is made up of iron oxide, giving it its red color.

         Mars seems very earth-like. There are ice-caps on its poles, drifting white clouds, and raging dust storms in its atmosphere. Seasonally changing patterns also occur on the red planet. There are large dark areas on its surface called maria (meaning 'seas'). It even has a twenty-four-hour day. Mars experiences summer and winter seasons, each of which lasts for almost six earth months.

         The atmospheric pressure on Mars is very low. It is comparable to what it is on the Earth at a height of 32 km from sea level. Thus, Mars has a very thin atmosphere. It is made up of 95 percent carbon dioxide. The rest is nitrogen, argon and a small amount of water vapor. Tiny amounts of hydrogen, oxygen, and ozone have also been detected. Though the Martian atmosphere has clouds of frozen water, carbon dioxide and of reddish dust, it does not contain enough gases to trap the Sun's heat. This makes Mars a very cold planet. The surface temperature may rise to 21°C or 27°C near its Equator, at noon. But, during the night, it becomes as low as-84°C. The present conditions on Mars-cold, extreme dryness, intense ultraviolet light and little oxygen-are hostile to the familiar forms of life. The Viking space probes, send by U.S.A.did experiments on Mars which showed no signs of life.

           Like Earth, the Martian surface has deep ridges and valleys. Pictures also show islands made where water once flowed and river beds which are dry for hundreds of millions of years. The surface features indicate that Mars may have had both the atmosphere and ocean in the past. Martian surface has craters of sizes, ranging from 5 km to 121 km in diameter, created by meteorite impact. It also has enormous volcanoes. The largest volcano on Mars Mount Olympus is nearly three times as high as Mount Everest. Martian soil is mostly like the Earth's soil made up mainly of silicates. 

Q.  Write any five features of the planet Jupiter. How would you differentiate it from the Red Planet?                               

A. #  Jupiter is the largest planet of the Solar System.

#  It weighs more than twice as much as all the other eight planets put together. It has sixteen known satellites. Jupiter is not only the biggest planet but also the liveliest.

#  Its highest clouds are mainly crystals of frozen ammonia gas at a temperature of about -140C. It is veiled in a turbulent, gaseous atmosphere made up of hydrogen and helium with significant amounts of ammonia and methane.

#  At its center, Jupiter has a small rocky core where temperatures reach 20,000"C, about three times the temperature of the Sun's surface. There are iron, silicon and other heavy elements in the rocky core. Jupiter seems to be more like the Sun in its composition than the other planets.

#  Jupiter is mainly a quick-spinning ball of gas and liquid with no solid surface. It also emits radio waves. Its composition, size and the number of moons gave rise to the idea that Jupiter is not a planet but rather a star with a "solar system" of its own, that did not start 'burning'. It is estimated that if Jupiter, were just ten times heavier, it could have started to produce its own energy like the Sun.

Q.  Differentiate between chemical evolution and biological evolution.     

A.  Chemical evolution -  the formation of organic molecules from inorganic molecules is referred to as chemical evolution. Chemical evolution describes chemical changes that took place on primitive earth that give rise to first life forms. Around 4 Billion years ago, the earth's atmosphere consisted of chemicals such as water vapour, Methane, Ammonia, and hydrogen. The waters of this stage of the Earth's development have 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.

Biological Evolution -  the enzymes proteins once formed during the chemical evolution process leads to self-replicating molecular systems which further evolved over a period of time, into membrane-bound protocells and finally transformed into living cells. This process is called biological evolution. Biological evolution thus refers to the slow and gradual process by which living organism has changed from the simplest self-replicating molecular systems form to the most complex multicellular forms that exist today. Biological evolution primarily involves modifications in the existing organisms and the inheritance of these modifications. During this stage, first cells capable of using carbon dioxide and energy from light, to make their own food through photosynthesis emerged.

Q.  Comets                   

A.  The cold outer areas beyond Pluto are the regions of comets. When the solar matter was churning and the Sun had just been ignited, its heat drove, the lighter elements into the outer reaches of the Solar System. Hydrogen, oxygen, nitrogen, and carbon collected into something like snowy cotton balls and they still float as a "cloud", at a distance of 100.000 times the distance of the Earth from the sun. Comets are made mainly of 'ices', that is ordinary water mixed with frozen gases such as methane, carbon dioxide, and ammonia. The ices are mixed with specks of dust that makes them look like dirty snowballs. While still in this cloud, comets do not shine. Once in a while, the gravity of a passing star attracts this cloud. A few comets then move into interstellar space and are lost to the Solar System. Others move towards the Sun.

             As a comet moves towards the Sun, its surface is heated up by the strengthening sunlight. Some of its frozen material turns into gas, forming a rapidly growing cloud around its center which is called its head or coma. On getting nearer to the Sun, more gas evaporates and its head becomes bigger and brighter. Also, a brilliant tail, made of dust and gas, is pushed out of the head by the pressure of the sunlight and the solar wind. This tail extends in a direction away from the Sun. One of the most famous comets is Halley's Comet which returns once every 74 to 79 years. It was last seen in 1986. Sometimes fragments from the comets fall on the Earth producing meteors. Comets returning repeatedly lose their gases each time. When all their ices melt, comets disintegrate, leaving a stream of small particles that spreads out thinly and loses its identity.

Q.  Write a brief note about Neptune and Pluto                     

A. Neptune - The eighth planet of the solar system, Neptune, was discovered in 1846 by astronomer Johann Gottfried Galle. Neptune's atmosphere has methane but no detectable ammonia. Its cloud temperature is about -237°C. Neptune is orbited by Triton, one of the biggest satellites in the Solar System. It orbits Neptune in a clockwise direction, i.e. opposite to the planet's own rotation. It has an atmosphere of nitrogen and methane. It may even have an ocean of liquid nitrogen. Triton is accompanied by a smaller satellite, Nereid. In 1989, Voyager 2- passed within 35,000 km of Neptune and within 40,000 km of Triton.

Pluto - Pluto is the ninth and the farthest planet from the sun. In 1916, Pluto was discovered however, its mass is even less than our Moon. Small, cold and dark, Pluto is about one-fifth of the size of the Earth. Its surface is coated with frozen methane. In 1938, a satellite of Pluto was discovered and named Charon. Not much is really known about Pluto. Pluto's orbit crosses that of Neptune's. No other planetary orbits cross in this way, and it is possible that Pluto is an escaped satellite of Neptune.

Q.  What observations led to the discovery of planet X still on?   A. Pluto was earlier supposed to make for deviations in the orbit of Uranus. Even after the influence of Neptune had been accounted for, an American astronomer Professor of Physics, detected that the orbit of Uranus was still disturbed. Neptune's orbit too showed similar disturbances. Scientists calculated and predicted the mass and radius of the orbit of Planet X which was supposed to cause these disturbances. Pluto's discovery had led astronomers to believe that it was Planet X. But now calculations show that the mass of Pluto is too low to cause irregularities in Uranus' orbit. Thus, the search for the elusive Planet X goes on.

Q.  Explain Darwin's theory of Natural Selection. Why was it not acceptable to most people of that time?                       

A. Darwin’s theory of Natural selection was based on two observations. First. more organisms are born in nature than can survive to reproduce themselves. This is because the environment has limited resources for subsistence. This overproduction results in a struggle for existence and ultimately leads to the survival of the fittest. Plant and animal species compete within and among themselves for food, water, air, light-everything that enables organisms to survive and reproduce. The second observation is that offspring, i.e, children differ slightly from their parents and from each other in characteristics that they inherit. This we now call genetic variations. Darwin held the view that these variations are a source of evolutionary change. According to him in any group both plants and animals, individuals with characteristics that enable them to adapt best to their environment survive and reproduce, while those who lack these characteristics have a poor chance of survival. Thus, Nature selects and preserves the favorable characteristics or useful variations in a changing environment, Darwin called this natural selection. Darwin's theory of evolution through natural selection was based on observations as well as the other existing information of that time. Through his analysis, he not only gave the theory of evolution but was able to give us a mechanism for evolutionary change.

               Darwin's theory of Natural Selection was not acceptable to most people of that time including the Church as it was a radical theory and spoke against special creation or the theory of divine creation by god which was proposed by Church and is uniformly accepted by the society. In fact, Darwin was very severely criticized for his views. However, he got support from scientific circles. The debate went on for quite a few years and continues even today between the men of science and those of religion.

Q.  Write about the most important current theory for the origin of the universe. Describe any two pieces of evidence that support this theory.         

Q.  What is the 'Big bang' theory regarding the origin of the universe? Explain the various evidences favoring this theory.      A. The most important current theory for the origin of the universe is the Big Bang theory. According to this theory, the universe started with a huge explosion. It was not an explosion like the ones with which we are familiar, which start from a definite center and spread out. It was an explosion that occurred everywhere in space at the same time. It filled all space from the beginning, with every particle of matter rushing apart from every other particle. This was not an explosion of matter into space but rather an explosion of space itself. Every particle of matter rushed away from every other particle. It is so far impossible to 'picture' the first moment of the 'creation' of the universe.

Evidence Favouring the Big Bang

The first evidence comes from the expanding universe which suggests that the matter was packed much more densely in the early stages of the universe. The proof for this also comes from distant objects called quasars. When we 'look' at quasars situated 6 to 8 billion light-years away, we are looking at them as they existed then. If the universe were more dense in that epoch, we should be able to see some evidence of that density in the quasars. We do see such high density among the quasars which proves the Big Bang theory.

      Another evidence for the Big Bang theory comes from the cosmic background radiation. For many years the astronomers believed that if there was a cosmic explosion long ago, radiation from that event should still exist within the universe. This radiation may be weak, it may have lost its energy due to the expansion and cooling of the universe, but it should exist. Radio-astronomers have successfully discovered faint signals -a constantly present radio noise in the background that pervades all space. Calculations done by astrophysicists show that this radiation, called the cosmic microwave background radiation, is a relic of the ancient past when the universe went through the Big Bang.

       An additional discovery made by astronomers in the past two decades is that of the primordial abundance of elements, i.e. the elements hydrogen and helium which are firstly created in the aftermath of Big bang. These elements are found to be most abundant in the universe. By examining the light coming from the various parts of the universe, astronomers have found out that, out of every 100 atoms, almost 93 are hydrogen atoms and seven are helium atoms. Elements heavier than helium are present in traces only. This suggests that the universe started out with a Big Bang from a very hot and dense state and quickly cooled as it expanded. The hot and dense conditions lasted long enough for some hydrogen to fuse into helium. But they did not last long to allow other heavier elements to form in significant amounts. These were made much later in the interior of massive stars. 

Q.  Explain the steady state theory.

A. There is another theory about the origin of the universe known as the steady-state theory. This theory holds that the universe has always been just about the same as it is now. As it expands, new matter is created continuously to fill up the gaps between the galaxies. Thus, the problem of the origin and early moments of the universe is banished there was no early universe. However, the Big Bang theory is the most favored by astronomers and astrophysicists.

Q.  Describe Kepler's laws related to planetary motion.          

A.  Kepler's three laws of planetary motion can be described as follows:

#  The path of the planets around the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses). Kepler's first law states that - all planets orbit the sun in a path that resembles an ellipse, with the sun being located at one of the foci of that ellipse.

#  An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas). Kepler's second law - sometimes referred to as the law of equal areas. It describes the speed at which any given planet will move while orbiting the sun. The speed at which any planet moves through space is constantly changing. A planet moves fastest when it is closest to the sun and slowest when it is furthest from the sun

#  The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies).Kepler's third law - sometimes referred to as the law of harmonies - compares the orbital period and radius of orbit of a planet to those of other planets.

Q.  State the differences between paleontology and archaeology.      

A. Archaeology - The study of human antiquities, especially of prehistoric period is known as archaeology. The biological and cultural evolution of man proceeded side by side and the two influenced each other. Like the physical remains of man, his cultural remains also lie buried in the ancient deposits. Often, the two categories of evidence are found together in the same layers of the rock. With the passage of time and the increasing capacity of his brain and development in other bodily organs, man's culture became more and more varied and complex. He learned the use of new materials for making tools and developed new techniques for improving them. The use of tools had a tremendous impact on increased access to food and change in socio-economic conditions which has been discovered in archaeology.

Paleontology - Palaeontology is a branch of earth sciences, which is essentially a study of plant and animal life in the past geological periods, millions of years ago. It deals with the successive plants and animals which have inhabited the earth since the earliest times. Evidence of their existence is left in the form of skeletons and bones buried in the rocks. These are known as fossils. Crucial evidence of human evolution is provided by the study of these fossils.

                Sometimes, the buried body and the skeleton of an animal disintegrate entirely. If the surrounding material is sufficiently firm, it leaves a cavity having the exact outlines of the structures that disappeared. Such a cavity is called mold, Similar to molds are the impressions. These are left by extinct objects or parts of the body upon the Surrounding material. The impression is made while the surrounding material is soft, like footprints in clay or lava. Footprints of extinct animals are also impressions affording valuable information about the animals that made them.

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.