Q.19. What is meant by biomagnification? How
pesticide will deteriorate the ecosystem? (AKTU. - 2013 - 14)
Ans. Biomagnification,
also known as bioamplification or biological magnification, occurs when the
concentration of a substance, such as DDT or mercury, in an organism exceeds
the background concentration of the substance in its diet. This increase can
occur as a result of:
Persistence – where the
substance can't be broken down by environmental processes
Food chain energetics –
where the substance concentration increases progressively as it moves up a food
chain
Low or non-existent rate of
internal degradation or excretion of the substance – often due to
water-insolubility
The following is an example showing how
bio-magnification takes place in nature: An anchovy eats zoo-plankton that have
tiny amounts of mercury that the zoo-plankton has picked up from the water
throughout the anchovies lifespan. A tuna eats many of these anchovies over its
life, accumulating the mercury in each of those anchovies into its body. If the
mercury stunts the growth of the anchovies, that tuna is required to eat more
little fish to stay alive. Because there are more little fish being eaten, the
mercury content is magnified.
Biological magnification often refers to the process
whereby certain substances such as pesticides or heavy metals move up the food
chain, work their way into rivers or lakes, and are eaten by aquatic organisms
such as fish, which in turn are eaten by large birds, animals or humans. The
substances become concentrated in tissues or internal organs as they move up
the chain. Bioaccumulants are substances that increase in concentration in
living organisms as they take in contaminated air, water, or food because the
substances are very slowly metabolized or excreted.
Q.20. What is solar pond. (AKTU. - 2013 - 14)
Ans. A solar
pond is a pool of saltwater which acts as a large-scale solar thermal energy
collector with integral heat storage for supplying thermal energy. A solar pond
can be used for various applications, such as process heating, desalination,
refrigeration, drying and solar power generation.
A solar pond is simply a pool of saltwater which
collects and stores solar thermal energy. The saltwater naturally forms a
vertical salinity gradient also known as a "halocline", in which
low-salinity water floats on top of high-salinity water. The layers of salt
solutions increase in concentration (and therefore density) with depth. Below a
certain depth, the solution has a uniformly high salt concentration.
There are 3 distinct layers
of water in the pond:
The
top layer, which has a low salt content.
An
intermediate insulating layer with a salt gradient, which establishes a density
gradient that prevents heat exchange by natural convection.
The bottom layer, which has a high salt
content.
If the water is relatively translucent, and the
pond's bottom has high optical absorption, then nearly all of the incident
solar radiation (sunlight) will go into heating the bottom layer.
When solar energy is absorbed in the water, its
temperature increases, causing thermal expansion and reduced density. If the
water were fresh, the low-density warm water would float to the surface,
causing a convection current. The temperature gradient alone causes a density
gradient that decreases with depth. However the salinity gradient forms a
density gradient that increases with depth, and this counteracts the
temperature gradient, thus preventing heat in the lower layers from moving
upwards by convection and leaving the pond. This means that the temperature at
the bottom of the pond will rise to over 90 °C while the temperature at the top
of the pond is usually around 30 °C. A natural example of these effects in a
saline water body is Solar Lake in the Sinai Peninsula of Egypt.
The heat trapped in the salty bottom layer can be
used for many different purposes, such as the heating of buildings or
industrial hot water or to drive an organic Rankine cycle turbine or Stirling
engine for generating electricity.
Q.21. What do you mean by the term fossils and
fossil fuels? What type of different types of fossils fuel based energy?
Briefly explain them. (AKTU. - 2013 - 14)
Ans. Fossils
(from Classical Latin fossil is; literally, "obtained by digging") are
the preserved remains or traces of animals, plants, and other organisms from
the remote past. The totality of fossils, both discovered and undiscovered, and
their placement in fossiliferous (fossil-containing) rock formations and sedimentary
layers (strata) is known as the fossil record.
The study of fossils across geological time, how they
were formed, and the evolutionary relationships between taxa (phylogeny) are
some of the most important functions of the science of paleontology. Such a preserved
specimen is called a "fossil" if it is older than some minimum age,
most often the arbitrary date of 10,000 years. Hence, fossils range in age from
the youngest at the start of the Holocene Epoch to the oldest from the Archaean
Eon, up to 3.48 billion years old. The observation that certain fossils were
associated with certain rock strata led early geologists to recognize a
geological timescale in the 19th century. The development of radiometric dating
techniques in the early 20th century allowed geologists to determine the
numerical or "absolute" age of the various strata and thereby the
included fossils.
Like extant organisms, fossils vary in size from
microscopic, even single bacterial cells one micrometer in diameter, to gigantic,
such as dinosaurs and trees many meters long and weighing many tons. A fossil
normally preserves only a portion of the deceased organism, usually that
portion that was partially mineralized during life, such as the bones and teeth
of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates.
Fossils may also consist of the marks left behind by the organism while it was
alive, such as animal tracks or feces (coprolites). These types of fossil are
called trace fossils (or ichnofossils), as opposed to body fossils. Finally,
past life leaves some markers that cannot be seen but can be detected in the
form of biochemical signals; these are known as chemofossils or biomarkers.
Fossil fuels are fuels formed by natural processes
such as anaerobic decomposition of buried dead organisms. The age of the
organisms and their resulting fossil fuels is typically millions of years, and
sometimes exceeds 650 million years. Fossil fuels contain high percentages of
carbon and include coal, petroleum, and natural gas. They range from volatile
materials with low carbon:hydrogen ratios like methane, to liquid petroleum to
nonvolatile materials composed of almost pure carbon, like anthracite coal.
Methane can be found in hydrocarbon fields, alone, associated with oil, or in
the form of methane clathrates. The theory that fossil fuels formed from the
fossilized remains of dead plants by exposure to heat and pressure in the
Earth's crust over millions of years (see biogenic theory) was first introduced
by Georg Agricola in 1556 and later by Mikhail Lomonosov in the 18th century.
The Energy Information Administration estimates that
in 2007 the primary sources of energy consisted of petroleum 36.0%, coal 27.4%,
natural gas 23.0%, amounting to an 86.4% share for fossil fuels in primary
energy consumption in the world. Non-fossil sources in 2006 included
hydroelectric 6.3%, nuclear 8.5%, and others (geothermal, solar, tidal, wind,
wood, waste) amounting to 0.9%. World energy consumption was growing about 2.3%
per year.
Strictly speaking, fossil fuels are a renewable
resource. They are continually being formed via natural processes as plants and
animals die and then decompose and become trapped beneath sediment. However,
fossil fuels are generally considered to be non-renewable resources because
they take millions of years to form, and known viable reserves are being
depleted much faster than new ones are being made.
The use of fossil fuels raises serious environmental
concerns. The burning of fossil fuels produces around 21.3 billion tonnes (21.3
gigatonnes) of carbon dioxide (CO2) per year, but it is estimated that natural processes
can only absorb about half of that amount, so there is a net increase of 10.65
billion tonnes of atmospheric carbon dioxide per year (one tonne of atmospheric
carbon is equivalent to 44/12 or 3.7 tonnes of carbon dioxide). Carbon dioxide
is one of the greenhouse gases that enhances radiative forcing and contributes
to global warming, causing the average surface temperature of the Earth to rise
in response, which the vast majority of climate scientists agree will cause
major adverse effects. A global movement towards the generation of renewable
energy is therefore under way to help reduce global greenhouse gas emissions.
