Environmental Issues Class 12th Biology CBSE Solution

Class 12th Biology CBSE Solution

Exercises
Question 1.

What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.


Answer:

Various constituents of domestic sewage are:


(i) Solid wastes such as faecal matter, detergents etc. dissolved/suspended in water from the kitchen, toilets, bathrooms and laundry.


(ii) Harmful pathogens including disease causing microbes- bacteria, viruses, fungi etc.


(iii) Dissolved minerals such as phosphates, nitrates, sodium ions, ammonia etc.


Discharge of untreated sewage in water bodies leads to:


(i) Contamination of water in the water bodies with the faecal matter rendering it unfit for future usage.


(ii) Accumulation of various pathogens in the water bodies that can cause water borne diseases.


(iii) Increase in the Biological Oxygen Demand (BOD) of the water body thereby deteriorating the quality of water.


(iv) Excessive accumulations of minerals causes accelerated aging of the water bodies due to rapid growth of algae, called eutrophication.


(v) Negative impact on the flora and fauna of the particular water body. Number of fishes are found to be less in water bodies with high BOD.



Question 2.

List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?


Answer:

We generate a lot of waste during our day to day activities such as:


(i) Vegetable, fruit peels and leftover foods.


(ii) Plastic containers, polythene bags, the wrappers of various goods, leftover tinned food, foils, disposable utensils etc.


(iii) Wrapping papers, electronic wastes, sewage, etc.


Yes, most of the waste generation can be minimised or controlled such as:


(i) Usage of proper utensils which can be reused over a period of time rather than disposable items.


(ii) Using the organic wastes developed in the kitchen i.e. vegetable peels, food leftovers for making compost.


(iii) Buying fresh vegetables rather than canned goods.


(iv) Avoiding the usage of polythene bags and taking your own cloth bag to buy various products.


Some wastes which can be very difficult to reduce include sewage, waste water from washing clothes, electronic wastes etc.



Question 3.

Discuss the causes and effects of global warming. What measures need to be taken to control global warming?


Answer:

Global warming is defined as the overall increase in the temperature of the Earth.


Causes of global warming:


(i) It is caused due to increase in the concentration of greenhouse gases in the atmosphere. The greenhouse gases trap the infrared heat reflected back by the earth’s surface and does not let the heat escape the atmosphere thereby increasing the temperature. Examples of greenhouse gases are-Methane, Carbon dioxide, CFS’s, etc.


(ii) Over exploitation of fossil fuels releases excessive amounts of CO2 in the atmosphere along with oxides of Nitrogen and sulphur.


(iii) Usage of CFC’s in aerosols, refrigerator coolants etc.


(iv) Deforestation of a very large scale causes disturbance in the CO2-O2 balance I atmosphere created by pants through photosynthesis.


Effects of global warming:


(i) Global warming has caused change in the seasonal patterns, rainfall etc. making the occurrence of floods, droughts more rapid.


(ii) Melting of polar ice caps.


(iii) Rise in the sea level which has caused submerging of various islands and low lying areas.


(iv) Many species of organisms (plants, animals and microbes) sensitive to temperature change may vanish leading to loss of biodiversity.


Various measure to control global warming:


(i) Usage of alternative sources of energy- renewable sources such as solar, wind energy, over traditional fossil fuels will decrease the CO2 emissions.


(ii) Afforestation may increase the taking in of CO2 by the plants thus reducing its levels in the atmosphere.


(iii) Reduce the usage of CFC’s and instead use its alternatives.



Question 4.

Match the items given in column A and B:





Answer:

A-(ii)


B-(i)


C-(iii)


D-(iv)



Question 5.

Write critical notes on the following:

Eutrophication


Answer:

(i) Eutrophication is the natural aging of a lake (or any standing water source) by nutrient enrichment of its water.


(ii) The accumulation of nutrients such as nitrogen and phosphorus leads to excessive growth of aquatic plants, algae and animals thereby increasing the organic content of the lake.


(iii) Eutrophication is both natural and man-made. The natural one is a slow and gradual process which spans over thousands of years.


(iv) On the other hand, pollutants and wastes from man-made activities such as industries, excessive use of fertilizers, dumping of sewage into water bodies without treatment causes a sudden increase in the nutrient content in the water bodies. This causes excessive growth of algae over the surface of lakes in a very short period of time and hence is also called Cultural or Accelerated Eutrophication.



Question 6.

Write critical notes on the following:

Biological magnification


Answer:

(i) Biological magnification or Biomagnification refers to the increase in concentration of the toxicant at successive trophic levels.


(ii) This caused due to the inability of the organisms to metabolise or excrete the particular toxic substance and hence it keeps on accumulating at each level.


(iii) As the biomass passes forward in the food chain, the toxicant concentration in the body of organisms increases at each trophic level.


(iv) E.g. Accumulation of DDT, mercury.




Question 7.

Write critical notes on the following:

Groundwater depletion and ways for its replenishment


Answer:

(i) Groundwater has served as one of the major water sources in villages as well as in cities for quite a time.


(ii) Groundwater table is the level of water collected after the seepage of water through the top layers of soil and their collection somewhere in between voids and cracks in rocks.


(iii) Due to overexploitation of the groundwater, the water table has depleted over the years. Also because of the laying down of water impervious cemented floors and roads, rain water cannot seep in and replenish the groundwater level, thus, further contributing to depletion.


(iv) The groundwater table can be replenished by letting the rain water run into the soil, by leaving small gaps of un-cemented pavements, putting restrictions on the over-usage of ground water, etc.



Question 8.

Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?


Answer:

(i) Ozone layer present in the stratosphere absorbs the harmful UV rays from the sun. The ozone molecule (O3) is continuously degrading and forming in the atmosphere.


(ii) Lately, due to the usage of CFCs (Chlorofluorocarbons), the balance between the formation and degradation of ozone has been disturbed. The CFCs release Cl on reacting with UV rays in the atmosphere and Cl then further breaks down ozone molecules.


(iii) Since Cl only acts as catalyst and is not actually utilised in the reaction, hence the damage due to the current present CFCs in the atmosphere is permanent and continuous.


(iv) Although ozone depletion is widely spread all through the stratosphere, it is particularly present over the Antarctic region. The ozone layer over the area is particularly thinned and hence is also referred to as Ozone hole.


Enhanced exposure to ultraviolet rays is harmful as:


(i) Excessive exposure to UV rays might cause mutations in the cells and can be extremely harmful.


(ii) It can cause skin aging, damage to skin cells and various types of skin cancers.


(iii) In human eye, cornea absorbs UV-B radiations and prolonged exposure might cause inflammation of cornea, called snow blindness, cataract etc. It can also cause permanent cornea damage in extreme cases.



Question 9.

Discuss the role of women and communities in protection and conservation of forests.


Answer:

Peoples’ participation has been very crucial in the protection and conservation of forests. A few of the examples of the active participation includes:


(i) The daring act by a Bishnoi woman- Amrita Devi in 1731 who hugged a tree to protect it from getting cut down by king’s men for procuring wood for the construction of new palace. She along with other villagers lost their lives protecting the trees from being cut down.


(ii) In the memory of Amrita Devi, government has instituted Amrita Devi Bishnoi Wildlife Protection Award for individuals or communities from rural areas whohav show enormous courage and dedication to protecting wildlife.


(iii) In 1974, local women in Garhwal, Himalayas showed enormous courage in protecting the trees by hugging them. This started the very famous Chipko Movement.


(iv) Government has initiated Joint Forest Management (JFM) so as to work closely with the local communities in protecting and managing forests.



Question 10.

What measures, as an individual, would you take to reduce environmental pollution?


Answer:

As an individual, we can take certain steps to reduce environmental pollution such as:


(i) Using CNG instead of petrol, diesel. Opting more for either public transport or encouraging more and more carpooling.


(ii) Minimising the solid waste generation and recycling the plastic, metal and glass commodities.


(iii) Using the biodegradable waste generated in the kitchen to prepare compost.


(iv) Avoiding the usage of plastic bags wherever possible and opting for the jute or cotton bags.


(v) Avoiding tinned food products.


(vi) Celebrating a cracker-free Diwali and encouraging others to follow it as well.


(vii) Using catalytic converters in the automobiles. Getting them checked for pollution on a regular basis.


(viii) Educating everyone and encouraging them to opt for renewable sources of energy.



Question 11.

Discuss briefly the following:

Radioactive wastes


Answer:

Radioactive wastes


Radioactive wastes are generated as a waste/side product in the utilisation of nuclear energy. The radiations given off by nuclear waste in extremely damaging to organisms due to its high rate of causing mutations.


In lower doses, it can cause mutations leading to severe cancers while in heavier doses, the exposure to such radiations is lethal.


Therefore, radioactive waste is considered a very potent pollutant. Its disposal has to be dealt with utmost care as lenient handling can be very harmful.


It is stored in suitably shielded container within the rock after extensive pre-treatments, buried about 500m deep into the ground.



Question 12.

Discuss briefly the following:

Defunct ships and e-wastes


Answer:

Defunct ships and e-wastes


Defunct ships are the abandoned or broken down ships which are in no longer use. These ships are a pool of scrap metal, along with other things, and disposing of such ships is quite a troublesome task. The sunken ships too add up to the waste. Proper techniques to utilise and dispose them should be adopted.


Irreparable computers and electronic goods come under the category of electronic wastes. E-wastes are either dumped into the landfills or incinerated. Developed countries have specific facilities to take care of such wastes whereas developing countries adopt manual segregation. Recycling is the only option available for the treatment of electronic wastes.



Question 13.

Discuss briefly the following:

Municipal solid wastes


Answer:

Municipal solid wastes


Municipal solid waste refers to any waste that comes from schools, offices, homes, stores, and hospitals etc. that are collected by the Municipality. It comprises of food wastes, paper, plastic, glass metal, rubber, leather etc.


It has to be dealt with proper care as the municipal waste has been observed to be increasing every passing day.


Burning of such waste reduces the volume but produces large amounts for polluting gases. Landfills or sanitary landfills were adopted to cope with the ever increasing waste generation. The waste are buried in a depression or trench after compaction and covered with dirt.


The best way to cope with the waste is to promote the 3R strategy- reduce, Reuse, Recycle. Also, segregating the waste based on whether they are biodegradable or non-biodegradable and then utilising the specific measures for each category can help reduce a lot of the municipal waste generated.



Question 14.

What initiatives were taken for reducing vehicular air pollution in Delhi?

Has air quality improved in Delhi?


Answer:

(i) In the 1990s, Delhi ranked fourth among the 41 most polluted cities in the world. Government of Delhi was asked by The Supreme Court to take strong actions, in a limited time frame.


(ii) All the buses of Delhi were converted to run on CNG (Compressed Natural Gas) by the end of 2002. CNG burns more efficiently than diesel or petrol. Also CNG is cheaper than any of the liquid fuels.


(iii) CNG can also not be adulterated or siphoned by the thieves.


(iv) The other steps included:


a) phasing out of old vehicles,


b) use of unleaded petrol,


c) use of low sulphur petrol and diesel,


d) use of catalytic converters in automobiles,


e) Application of stringent pollution-level norms etc.



Question 15.

Discuss briefly the following:

Greenhouse gases


Answer:

Greenhouse gases


(i) The gases present in the atmosphere that trap the sun’s heat and are responsible for the heating of earth’s atmosphere are called greenhouse gases. E.g. Methane, CO2 etc.


(ii) These gases are responsible for the greenhouse effect. The sunlight contains infrared radiations which are responsible for the heating. Earth reflects the radiations back into the atmosphere but not all the radiations escapes as some part of it is absorbed by the greenhouse gases.


(iii) This helps in maintaining a hospitable temperature of the earth’s surface (average temperature being 15⁰C) as it provides balance in the temperature during day and night.


(iv) But recently due to excessive pollution and releasing of CO2 and other greenhouse gases in the atmosphere, more heat is being trapped in the atmosphere leading to an overall increase in the temperature of the Earth known as Global Warming.



Question 16.

Discuss briefly the following:

Catalytic converter


Answer:

Catalytic converter


(i) Catalytic converters are devices fitted in automobiles to reduce the emission of harmful and poisonous gases.


(ii) They contain metals such as platinum, palladium and rhodium as catalysts that convert the unburnt hydrocarbons, carbon monoxide(CO) and nitric oxide passing through them into less harmful Carbon dioxide(CO2), water and nitrogen respectively.


(iii) Automobiles fitted with catalytic converters should use unleaded petrol because lead in petrol inactivates the catalysts.



Question 17.

Discuss briefly the following:

Ultraviolet B


Answer:

Ultraviolet B


(i) Ultraviolet B has shorter wavelength than the visible light and is extremely harmful for humans.


(ii) UV-B penetrates deep into the skin and can cause mutations in the exposed cells.


(iii) It causes aging of skin cells and various types of skin cancers.


(iv) It can also cause inflammation in cornea called snow-blindness, cataract etc. Prolonged exposure is extremely harmful and can leave permanent damage to the cornea.


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