1. Acid rains are produced by

(a) excess NO2 and SO2 from burning fossil fuels

(b) excess production of NH3 by industry and coal gas

(c) excess release of carbon monoxide by incomplete combustion

(d) excess formation of CO2 by combustion and animal respiration. (1988, 89)

Answer and Explanation:

1. (a): Acid rain refers to the precipitation with a pH of less than 5. It is a mixture of H2SO4 andHNO3, the ratio of the two acids vary depending on the relative quantities of sulphur oxides andnitrogen oxides present in the atmosphere. These oxides are mainly produced by combustion offossil fuels, smelters, industries, power plants, automobile exhausts etc

 

2. Which one is not a pollutant normally?

 (a) hydrocarbon

(b) carbon dioxide

(c) carbon monoxide

(d) sulphur dioxide.

Answer and Explanation:

2. (b): The common gaseous pollutants are oxides of carbon (CO and CO2), oxides of nitrogen(NO and O2) oxides of sulphur (SO2 and SO3), all these together contribute 90% of the global airpollution. Out of all these CO2 is not a pollutant normally, the green plants, by photosynthesisbalance the CO2 and O2 ratios in the air to a great extent, whereas others like carbon monoxide,NO2 etc are poisonous gases.

3. Upper part of sea/aquatic ecosystem contains

 (a) plankton

(b) nekton

(c) plankton and nekton

(d) benthos.

Answer and Explanation:

3. (a): Planktons are passively floating in upper water, nektons are actively swimming whilebenthos lead sedentary life upon the sea bottom. Planktons are producers and are present inlarge number.

4. Competition for light, nutrients and space is most severe between

 (a) closely related organism growing in different niches

(b) closely related organisms growing in the same area/niche

(c) distantly related organisms growing in the same habitat

(d) distantly related organisms growing in different niches. (1988)

Answer and Explanation:

4. (b): Competition is rivalry for obtaining the same resource. Competition of light, nutrients andspace is most severe between closely related organisms growing in the same area/niche, due tooverproduction of population in the same area/niche.

5. A mutually beneficial association necessary for survival of both partners is

 (a) mutualism/symbiosis(b) commensalism(c) amensalism(d) both A and B.

Answer and Explanation:

5. (a): Mutualism is an association between individuals of two species, both of which arebenefitted but cannot live separately under natural conditions e.g. instances of mutualism existbetween animals and plants and also in between plants e.g. lichens. Ammensalism is aninteraction in which one species causes harm to another spices with its toxic secretion oftenwithout gaining any benefit from the interaction. Commensalism is the relationship betweenindividuals of two species of which one is benefitted and the other is almost unaffected i.e.; neitherbenefitted nor harmed.

6. What is true of ecosystem?

 (a) primary consumers are least dependent upon producers(b) primary consumers out-number producers(c) producers are more than primary consumers(d) secondary consumers are the largest and most powerful.

Answer and Explanation:

6. (c): An ecosystem may be defined as a structural and functional unit of the biospherecomprising living organisms and their non-living environment that interact by means of food chainsand chemical cycles resulting in energy flow, biotic diversity and material cycling to form a stable,self supporting system.The organisms in an ecosystem are classified into 3 main categories-producers, consumers anddecomposers. The consumers utilize materials and energy stored by the producers. Decomposersobtain their food molecules from the organic materials of dead producers and consumers. In a trueecosystem, producers are more than consumers (herbivores and carnivores).

7. in an ecosystem, which one shows one-way passage

 (a) free energy(b) carbon(c) nitrogen(d) potassium.

Answer and Explanation:

7. (a): The behaviour of energy in ecosystem can be termed energy flow due to unidirectional flowof energy, Flow of energy is only in one direction i.e., from solar radiation—> producers—> heribivorous—> carnivores. This energy cannot pass in the reverse direction. There is decreasein the content and flow of energy with rise j in tropic level.

8. Green house effect is warming due to

 (a) infra-red rays reaching earth(b) moisture layer in atmosphere(c) increase in temperature due to increase in carbon dioxide concentration of atmosphere(d) ozone layer of atmosphere.

Answer and Explanation:

8. (c): The mean global temperature rise by 2° –  6°c and the concentration of carbon dioxideincreases in the troposphere upto 600 ppm. Hence, the surface of the earth becomes warm whichcauses global warming. The phenomenon is similar to that of green house in which the glassenclosed atmosphere gets heated up due to its insulation from the rest of the environment. Hence,global warming is also known as green house effect and the gases responsible for it are calledgreen house gases e.g CH4, CO2 etc.

9. Soil conservation is

 (a) conversion of sterile soil into fertile one(b) aeration of soil(c) erosion of soil(d) protection against loss.

Answer and Explanation:

9. (d): Soil conservation is to conserve fertile soil from the losses like heavy rainfall, drainage, highwind, flood, draught etc. Soil is the top cover of the earth in which plants can grow. The rotation ofcrops, contour ploughing and use of proper fertilizers help in maintaining the fertility of soil.Plantation of trees, controlled grazing of grasslands, reforestation, prevention of forests fires willprotect the erosion of top soil. The regulation of water resources to prevent flood will help not onlyin soil conservation but also supply an adequate water supply in the period of drought.

10. The relation between algae and fungi in lichen is

 (a) symbiosis(b) parasitism(c) commenalism(d) protocooperation.

Answer and Explanation:

10. (a): Algae and fungi in a lichen show symbiotic relationship. Fungi give support to the algae,give protection and help in absorption of water while algae provide food to fungi which isachlorophyllous. No one is harmed but both are benefitted by each other.