There will be many food chains in an ecosystem. Some organisms will be involved in several food chains at the same time. A number of food chains get interwoven into a complex food web. The actual feeding relationship within a given ecosystem is called food web.
The most commonly used method for estimating the age of fossils is radio-carbon dating. Carbon 14 is the radio active isotope of carbon. It is absorbed by plants and animals in the same proportion as they are present in the atmosphere as CO2. Plants use CO2 to make food and animals eat it. Hence the proportion of Carbon 14 in tissues of plants and animals is the same as in the atmosphere, as long as they are living. As soon as it dies, more carbon can enter its body as photosynthesis or food in take stops. After death, Carbon 14 decays steadily into ordinary carbon. Smaller the number of carbon 14 atoms remaining, older is the fossil.
1. Hominids : The First Human Fossil
It was discovered in Ethiopia and lived between 3 and 3.6 million years ago. It was also discovered in Tanzania about 3.75 million years ago. They had Ape's head and human like body. Evidences are there that they walked on two feet. They were good tree climbers.
2. Australopithecus : The Transitional Human Forms
They lived about 2 million years ago. Brains were small, they were ape like with shorter faces than apes. Enamel of the teeth indicated they ate fruits. Bipedal posture is strong as the back bone shows strong hominid curvature. Hip bones are shorter than apes but not as short as modern humans.
3. Homo Habilis : The First Tool Makers
They had a dramatic expansion of brain size up to 800cm cube. They walked up right. Bones of the hand were robust than modern man. Leg and foot bones were much closer to modern man than apes. They used tools.
4. Homo Erectus
They lived about 1.6 million years ago. They had large brain up to 900cm cube. They hunted animals and ate meat and used stone tools.They were socially interactive and may have spoken a complex language.
5. The Neanderthals
They existed throughout Western Europe and Central Asia about 1 lakh - 35000 years ago. The skeleton was more robust than modern humans. Brain size was larger than modern humans at 1400cm cube. They were proficient hunters, skilled tool makers and they used hides for protecting their bodies. The ritual of burial became common.
6. Homo Sapiens
They arouse in Africa and migrated to other parts of the the world via Middle East about 40000 years ago.
No. Only vehicles that are over 1 year old, needs to produce smoke pollution certificate. The certificate can be obtained from any Government authorized smoke testing centres. The fee is Rs.70 for 4 wheel vehicles and Rs.50 for 2 wheelers.
The theory began with two observations. First, more organisms are born than can survive to reproduce themselves. Because the environment only had limited resources. This over production results in a struggle for existence and ultimate survival of the fittest. Plant and animal species compete within and among themselves for food, water, air and everything that enables them to survive and reproduce.
The second observation is that the offsprings differ slightly from their parents and from each other in characteristics they inherit. This is called genetic variation. Darwin told that these variations are a source of evolutionary change. According to him, in any group, individuals with characteristics which enable them to adapt the 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 useful variations in a changing environment. Darwin called this natural selection. Darwin's theory is a scientific theory. He developed it taking into account his own observations as well as other existing information.
Kidneys are able to check water loss from our body. Water is reabsorbed by the collecting tubes in the kidneys to prevent loss in the form of urine. This absorption of water is under the control of anti-diuretic hormone (ADH), which is produced by specialized nerve cells in fore brain. If more water is lost through sweating during summer, it will decrease the water in blood. The brain will send signals to produce ADH which increases the absorption of water. The absorbed water gets back into the blood to maintain the normal concentration of the fluid.
Oparin and Haldane proposed that "life could have arisen from non-living organic molecules". With hot gas condensing and molten matter solidifying to form rocks, the earth acted as a huge factory producing many kinds of compounds. The sources of energy for formation of molecules were cosmic rays, UV rays, electrical discharges such as lightning, heat from volcanoes and hot springs. Lighter gases escaped into space unless they could combine with other elements to form liquids or solids. Hydrogen and oxygen combines to form water vapour. Oxygen combined with calcium and carbon to form limestone. These compounds were called organic compounds.
Earth slowly started to cool down. Prolonged rains accumulated to form oceans. These hot bodies of water had several organic compounds washed down from atmosphere. Their interaction resulted in the formation of more compounds. The water was like a 'hot dilute soup' then, which also contained amino acids. Amino acids combined to form proteins, the building blocks of life. First self replicating molecular systems accidentally originated from these complex molecules. They are called living organisms for the property of self-replication.
They remained under water as Sun's UV rays would destroy them if they came to the surface. It remained so, for millions of years. Then random combinations may have led to the formation of chlorophyll containing organisms which could produce their own food by photosynthesis. Due to photosynthesis, the atmosphere grew rich in oxygen. Oxygen when acted upon by UV formed ozone, which resulted in the formation of ozone layer 25Kms above the earth. Ozone layer protected the organisms from UV radiation. This allowed them to come to the surface of water and then land. Slowly life flourished and thrived.
Biological evolution began with the formation of first true cells. They lived at the expense of organic molecules in the water, they did not want oxygen. As nutrients depleted, cells capable of doing photosynthesis emerged. These simple cells were the forefathers of life on earth. All the life forms are inter-related and also that the higher forms have evolved from the lower ones. Today there are 5 categories or kingdoms of living organisms.
1. Monera : Primitive single celled organisms. About 2 billion years ago. They had no nuclei. Eg: Bacteria
2. Protista : 1.5 billion years ago. Single celled organisms containing a nucleus. Eg: Algae, Protozoans.
3. Fungi : Complex organisms that feed on decaying matter.
4. Plants : 600 million years ago. Has chlorophyll for photosynthesis.
5. Animals : Multi-cellular organisms that survive on food produced by plants. Divided into vertebrates and invertebrates.
NB: Draw the diagrams given on study material.
Miller subjected a gaseous mixture of methane, ammonia, water vapour and hydrogen in a closed flask at 80 Degree Celcius to electric sparking for a week. This mixture represented the condition of the earth before life. After a week, there were amino acids essential for the formation of proteins. Proteins are the building blocks of living organisms. With the making of molecules related to life, the credibility of chemical evolution greatly increased. Many amino acids were since obtained. Sugars and nitrogenous bases found in nucleus of a cell are also obtained.
Various compounds which form many kinds of fats and important natural pigments have also been produced through similar experiments. The evidences of Miller's experiment is supported by the chemical analysis of a meteorite which fell in Australia in 1969, which showed the presence of organic molecules. The types and relative proportions of these molecules were very similar to the products formed in Miller's experiment. The presence of organic molecules like methane, ethane, formaldehyde, acetylene etc has been shown in interstellar space by radio astronomy as well.
NB: There is a diagram which shows the experiment, draw that too.
Pasteur performed the experiment before a gathering of well known biologists, commissioned by the Academy of Sciences of France to test his hypothesis that only 'Life Begets Life'. Pasteur took 2 flasks, half filled them with yeast infusion containing a little bit of sugar and heated them 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, it was found that the closed flask was still free of living organisms while the open one was infested with living organisms.
To further remove any doubt that organisms did not grow in sealed flask due to lack of oxygen, Pasteur repeated the experiment with swan necked flasks which were left open. The swan neck would enable air to get in, but would prevent any living organisms from getting into the infusion. Again, no organism grew in the flasks. Pasteur thus proved that living organisms do not arise spontaneously.
By 1845 the paths of all planets were calculated. All planets except Uranus were observed to follow calculated paths. Adams and Leverrier reasoned that the deviation in the path of Uranus could be due to an unknown outer planet beyond it. Using Newton's law of universal gravitation, they predicted its size and exact path. In 1846 Galle discovered Neptune at almost the predicted position. Pluto's existence was also proposed to account for deviations in the orbit of Uranus.
Even after the influence of Neptune had been accounted for, Lowell detected that the orbit of Uranus was still disturbed. Neptune's orbit also showed similar disturbances. Lowell and Pickering did some calculations to predict the mass and radius of the orbit of the Planet X which was supposed to cause these disturbances.
In 1916 Pluto was discovered. Pluto's orbit crosses that of Neptune's. No other planetary orbits cross in this way. Pluto could be an escaped satellite of Neptune. Astronomers believed that the Planet X was Pluto, but now calculations show that the mass of Pluto is too low to cause irregularities in Uranus' orbit. Thus the search for Planet X is still on.
There are ice caps in Mars' poles. There are drifting white clouds and raging dust storms in its atmosphere. Mars has a 24hrs day. Summer and Winter are six months long. Martian surface has huge craters ranging from diameter of 5Km to 121Km. It has enormous volcanoes. The largest volcano in Mars is Mount Olympus (3 times higher than Mount Everest). There are deep ridges and valleys. Pictures show islands made by water, river beds that dried out millions of years ago.
Surface features indicate that Mars may had both atmosphere and ocean in the past. Viking space probes send by USA did find evidence that liquid water once flowed on the planet and atmosphere was also more dense than what it is now. Martian soil, like Earth's soil is mainly made up of silicates. However, 16% of the soil is made up of iron oxide, giving its red colour. Mars has a thin atmosphere. Temperature may rise to 21-27 Degree Celsius near equator at noon, but during night it goes as low as -84 Degree Celsius. Phobos and Deimos are the natural satellites of Mars.