Wednesday, December 26, 2012

CBSE solved Questions Chapter - 15 Our Environment Class - X Biology

Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Removal of all the organisms of a trophic level will affect the entire ecosystem of that area. Its impact on different trophic levels will be different because of the organisms of a trophic level are directly dependent on them while the organisms of other trophic level are indirectly depend on them for their food. For example, killing of herbivores will increase the number of carnivores and killing of carnivores will increase the number of herbivores. Most of the organisms will die of starvation.
How do flows of energy occur in tropic level?
Energy is used and conveyed from one trophic level to another is a food chain. This is called flow of energy. Green plants capture about 1% of the solar energy during photosynthesis. A part of this trapped energy is used by plants in performing their metabolic activities and some energy is released at heat into the atmosphere. The remaining energy is chemical energy stored in the plants as ‘carbohydrates’.
                                 When plants are eaten up by herbivores, the chemical energy stored in the plants is transferred to these animals. These animals (herbivores) utilize some of this energy for metabolic activities, some energy is released as heat and the remaining energy is stored.
What are the characteristics of energy transfer in the biosphere?
The following are the characteristics of energy transfer in the biosphere:
(i) Energy is supplied by the sun and it is not created in the biosphere. Energy is only converted from one form to another in the biosphere.
(ii) There is a continuous transfer of energy from one trophic level to the next in a food chain.
(iii)At each trophic level, some of the energy is utilized by the organisms for their metabolic activities.
(iv)  At each trophic level, some amount of energy is utilized for the composition of decomposers.
(v) At each trophic level, there is loss of energy, which goes into the environment and remains un-utilized.
(vi) At each trophic level, the amount of energy available is less than that available at the previous level.
Why is energy flow considered as unidirectional?
The flow of energy is unidirectional and non cyclic. The energy captured by the autotrophs does not return to the sun, and the energy which passes to the subsequent levels does not come back to autographs. The amount of energy goes on successively decreasing from the producers to the carnivores.
How much energy is lost in transferring from one trophic level to other in a food chain?
Ans.  90%.
What is biomass?
The amount of organic matter present in an organism is called biomass.
What will happen if we kill the organisms in one trophic level?
The balance in ecosystem will be disturbed because in an ecosystem every trophic level is interlinked with the other. Thus, absence of any one trophic level will surely create problems for the other trophic level dependent on the previous one.
Define biomagnifications.
The increase in concentration of a chemical per unit weight of the organisms with successive rise in trophic level is called biomagnifications.
How does a food web an important factor of our environment? Describe its four benefits.
Importance of food web
(i) Starvation: Food web does not allow any population to starve when members of lower trophic level decrease in number.
(ii) Checking Overpopulation: Food web does not allow a species to overgrow as increased availability will increase the chance of higher number of its predations.
(iii) Endangered Population: It allows endangered population to grow in size.
(iv) Stability: Food webs provide stability to ecosystems.
What is 10% Law?
The energy available at each successive trophic level is only 10 percent of the previous level.
How much energy will be available to hawks in the food chain comprising hawk, snake, paddy and mice, if 1,000 J of energy is available to wheat plants from the sun?
Wheat plants represent the producer level. They trap only 1% of the sun’s energy falling on them. So, the energy available in wheat will be 1% of 1,000 J which will be 10 Joule. We can now show the food chain and apply ten per cent law to it.
Wheat plant (10J) --10%--> Mice (1J)---10%---->Snake(0.1J)--10%-->Hawk(0.01J)
Thus, the energy available to the hawk will be 0.01 J.
Differentiate between food chain and food web?
Food chain                                                                             
1. Food chain consists of a single series of food relations.
2. It has maximum 4-6 trophic levels of different species.
3. Each organism uses a particular food.
4. Starvation is observed whenever the members of lower trophic level decrease in number.
Food web
1. Food web is a complex network of several series of food chains or food relations.
2. It has a number of trophic levels or populations of different species.
3. Each organism can use different types of type of food.
4. Food webs do not allow starvation and help in increasing the population of endangered species.
Why is damage to the ozone layer a cause of concern? What steps are being taken to limit this damage?
 Ozone layer has become a cause of concern because depletion of ozone layer can cause serious effects on human body and other organisms of the environment like —
(i) Cancer in human beings.
(ii) Loss of immunity in humans.
(iii) Destruction of aquatic life and vegetation.
(iv) Temperature changes and rainfall failures.
Steps being taken to reduce it are :
(i) by reducing the use of CFCs — Many countries have already banned the use of CFCs.
(ii) by developing substitutes of CFCs — Scientists have already developed some substitutes which are ozone-friendly.
Which compounds are responsible for the depletion of ozone layer?
 Ozone depleting substances like chlorofluorocarbons, hydrocarbon, N2O, chlorine, etc. are responsible for the depletion of ozone layer.
Which disease is caused in human being due to depletion of ozone layer in the atmosphere?
Ozone layer is located in the atmosphere as a part of stratosphere. Skin cancer is caused in human being due to depletion of ozone layer in the atmosphere
Why is ozone layer getting depleted at higher levels of the atmosphere?
 Due to the release of CFCs in the environment the ozone layer is getting depleted at higher levels of
How is ozone formed in the upper atmosphere? Which compounds are responsible for the depletion of ozone layer?
The ozone layer occurs naturally in the stratosphere. The ozone layer is formed when intense UV radiation from the sun reacts with ordinary molecules of oxygen (O2) in the stratosphere to dissociate into single oxygen atoms (O). Single oxygen atoms are very reactive they combine with O2 to form O3.
The CFCs (chlorofluorocarbons), halons, nitrous oxide, methane, carbon tetrachloride and chlorine are responsible for the depletion of ozone layer.
When is World Ozone Layer Preservation Day celebrated?
World Ozone Layer Preservation Day is celebrated on September 16.
What is green house effect?
The gases like CO2 and methane absorb infra red radiations of the sun and cause heating of the earth. It is known as green house effect.
Suggest activities in our daily life which are eco friendly.
 (i) Cloth bags should be used in place of plastic bags or polythenes.
(ii) Domestic wastes and kitchen wastes can be made use of as manures or compost for plants.
(iii) We should reduce the wastage of foods, water, or any other thing.
(iv) We should not use the electronic equipments using the ozone depleting gases or chemicals.
(v) From biodegradable waste, biogas can be prepared which costs much less than other fuels.
(vi) Separation of biodegradable and non-biodegradable wastes of our house.
How can you help in reducing the problem of waste disposal? Give any two methods.
Every individual should play a role in reducing the problem of waste disposal. They can do that by-
(i) Improved packing methods.
(ii) Increased use of disposable items.
(iii) Use of compost in the field
What is the importance of phytoplankton?
The phytoplankton supply dissolved oxygen to the organisms living in water. They are food for fish.
Which pollutants are contributed by airplanes?                              
Aerosols  and CO2.
How is ozone layer formed in the atmosphere? What is the function of this layer?
The ozone layer occurs naturally in the stratosphere. The ozone layer is formed when intense UV radiation from the sun causes ordinary molecules of oxygen (O2) in the stratosphere to dissociate into single oxygen atoms (O). Single oxygen atoms are very reactive and combine with O2 to form O3.
O2 + UV radiation O + O
O + O2  O3 (ozone)
Function: Ozone absorbs UV radiation from the sun, thus shielding the earth’s surface from the harmful effects of this radiation e.g.: skin cancer. 
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