1. Organisms and Environment
1. The CO2 has crucial role in global warming. Explain.
Ans: i. Carbon dioxide is produced by many activities of human beings
such as destruction of forests, combustion of fossil fuels, cement plants and
other industries, burning and respiration by all living organisms.
ii. This CO2 forms a layer in the upper atmosphere.
iii. When solar energy reaches the earth surface, the infrared
radiations from this are trapped by the layer of CO2.
iv. Along with CO2 other gases such as methane, CFCs and nitrogen
oxides also form a blanket in the atmosphere which traps the reflected infrared
rays.
v. This results in greenhouse effect and global warming. CO2 alone
can increase the temperature by about 50%. During the last 50 years the
average temperature of the earth has increased due to
steadily increasing CO2 concentration. Thus CO2 plays a crucial role in global
warming.
2. Write about the effects of agrochemicals.
Ans: i. Most of the agrochemicals are not species-specific pesticides,
therefore, they kill the entire microbial fauna of the soil. Many useful microbes

2. such as nitrogen fixing bacteria, cyanobacteria which act as
biofertilizers, are also eradicated. This affects the productivity of the soil.
ii. Pest organisms develop resistance to some of the pesticides and
thus they survive causing more damage. More amount of pesticides is then
required to kill such resistant varieties.
iii. Many pesticides such as organochlorines are persistent and
nonbiodegradable. They pollute the environment and enter the food chain.
iv. Organochlorines are lipophilic and hence remain accumulated in
the fatty tissues of the animals. This creates serious problem of
bioaccumulation. The amount of such pesticide goes on
increasing as they travel through the food chain. The highest concentration
occurs in the top level consumers which causes toxicity.
v. Pesticides being toxic, handling them in industries or fields can
cause various health hazards such as skin diseases, blindness, respiratory
diseases, nervous disorders, etc.
vi. Agrochemicals also contaminate the soil and ground water. Only
15% hits the target organisms, rest gets sprayed in nearby areas causing
pollution.
3. Comment in details on the carbon cycle.
Ans: i. Carbon is an important element as it forms 49% of the dry weight
of all organisms. 71% of global carbon is present in the oceans. Therefore,

3. ocean is the major reservoir of carbon. Carbon is also present in all
fossil fuels.
ii. Respiration and photosynthesis are the events that keep the carbon
in cyclic circulation.
iii. During respiration, oxygen is used for combustion of carbohydrate
as a result of which carbon dioxide and water are formed with the release of
energy.
iv. On the contrary photosynthesis utilizes carbon dioxide and water
vapour liberating oxygen and producing carbohydrates at the same time.
v. Solar energy is stored in the carbon – carbon bonds of
carbohydrates during photosynthesis whereas respiration releases the same
stored energy.
vi. The main reservoirs for carbon dioxide are in the oceans and in
rocks. Carbon dioxide is highly soluble in water and form mild carbonic acid
upon dissolving.
vii. This dissolved carbon dioxide precipitate as a solid rock or
limestone which is calcium carbonate.
viii. This reaction in the seas is aided by corals and algae which in turn
builds the coral reefs made up of limestone.
ix. Autotrophic green plants on land and in water take up carbon
dioxide and manufacture carbohydrates by the process of photosynthesis.

4. x. The carbon stored in plants has three different fates, viz. liberation
into atmosphere, consumption by animals upon feeding, storage in the plant till
the plant dies.
xi. Animals get their carbon requirement through their food. When
autotrophs are consumed, the heterotrophs obtain carbon. Carbon in animals
also has three fates, viz. release back into the atmosphere in the
process of respiration, release of stored carbon from the body by the action of
decomposers, or conversion into fossil fuels if buried intact.
xii. Fossil fuel such as coal, oil, natural gas, etc. can be mined and
burned for energy purposes. This burning releases carbon dioxide back into the
atmosphere.
xiii. Carbon from limestone can also be released if pushed to the
surfaces and slowly weathered away. Subducting and volcanic eruptions can
also release the stored carbon from sediments.
xiv. Through burning of fossil fuels, there is great human interference
with carbon cycle.
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