CBSE Class 12 Biology Environmental Issues Notes

Download CBSE Class 12 Biology Environmental Issues Notes in PDF format. All Revision notes for Class 12 Biology have been designed as per the latest syllabus and updated chapters given in your textbook for Biology in Standard 12. Our teachers have designed these concept notes for the benefit of Grade 12 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 12 Biology for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 12 Biology given our website

Environmental Issues Class 12 Biology Revision Notes

Class 12 Biology students should refer to the following concepts and notes for Environmental Issues in standard 12. These exam notes for Grade 12 Biology will be very useful for upcoming class tests and examinations and help you to score good marks

Environmental Issues Notes Class 12 Biology


1. What is meant by algal blooms? What is its significance?

Ans. Excess growth of certain phytoplankton due to excess nutrients in water causes Deteriorates water quality, leads to fish mortality.

2. Define eutrophication.

Ans. Nutrient enrichment in water bodies leading to depletion of oxygen and loss of life supporting Environment.

3. What is bio magnification?

Ans. Increase in the concentration of certain toxic chemicals at successive trophic levels.

4. What is BOD?

Ans. Biological Oxygen Demand is the measure of organic matter in any water sample.

5. What is the effect of DDT in birds?

Ans. DDT disturbs calcium metabolism in birds, thinning of egg shell and premature breaking of Eggs lead to decline in bird population.

6. What do you understand by ‗Ecosan‘?

Ans. Ecosanare the toilets which use compositing method for ecological sanitation.

7. Why are nuclear wastes called potent pollutants?

Ans.Are lethal even at lower doses and cause damaging disorders.

8. What is Jhum cultivation?

Ans Farmers cut down the tress, burn, use cattle for grazing and then allow the land to recover.

9. Mention two problems that have arisen due to green revolution.

Ans. Water logging and soil salinity.

10. What is snow blindness?

Ans. Inflammation of cornea caused by a high dose of UV-B radiation.

11. Which is the world‘s most problematic weed, also known as ―terror of Bengal”?

Ans. Eichornia crassipes(Water hyacinth).

12.. What is the effect of DDT in birds?

Ans. Disturbs Calcium metabolism Thinning of egg shells and premature breakage of eggs, Decline of bird population.

Important Questions for NCERT Class 12 Biology Environmental Issues

Ques. High value of BOD (Biochemical Oxygen Demand) indicates that
(a) water is less polluted
(b) consumption of organic matter in the water is higher by the microbes
(c) water is pure
(d) water is highly polluted. 

Answer: B


Ques. Rachel Carson’s famous book “Silent Spring” is related to
(a) population explosion
(b) ecosystem management
(c) pesticide pollution
(d) noise pollution. 

Answer: C


Ques. In an area where DDT had been used extensively, the population of birds declined significantly because
(a) birds stopped laying eggs
(b) earthworms in the area got eradicated
(c) cobras were feeding exclusively on birds
(d) many of the birds eggs laid, did not hatch.

Answer: D


Ques. Measuring Biochemical Oxygen Demand (BOD) is a method used for
(a) estimating the amount of organic matter in sewage water
(b) working out the efficiency of oil driven automobile engines
(c) measuring the activity of Saccharomyces cerevisiae in producing curd on a commercial scale
(d) working out the efficiency of RBCs about their capacity to carry oxygen. 

Answer: A


Ques. Eutrophication is often seen in
(a) deserts (b) fresh water lakes
(c) ocean (d) mountains. 

Answer: B


Ques. When domestic sewage mixes with river water
(a) small animals like rats will die after drinking river water
(b) the increased microbial activity releases micronutrients such as iron
(c) the increased microbial activity uses up dissolved oxygen
(d) the river water is still suitable for drinking as impurities are only about 0.1%.

Answer: C


Ques. Biochemical oxygen demand (BOD) in a river water
(a) has no relationship with concentration of oxygen in the water
(b) gives a measure of Salmonella in the water
(c) increases when sewage gets mixed with river water
(d) remains unchanged when algal bloom occurs.

Answer: C


Ques. DDT residues are rapidly passed through food chain causing biomagnification because DDT is
(a) moderately toxic
(b) non-toxic to aquatic animals
(c) water soluble
(d) lipo soluble. 

Answer: D


Ques. A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this.
A. Lots of urea and phosphate fertilizer were used in the crops in the vicinity.
B. The area was sprayed with DDT by an aircraft.
C. The lake water turned green and stinky.
D. Phytoplankton populations in the lake declined initially there by greatly reducing photosynthesis.
Which two of the above were the main causes of fish mortality in the lake?
(a) A, C (b) A, B
(c) B, C (d) C, D 

Answer: A


Ques. In which one of the following the BOD (Biochemical Oxygen Demand) of sewage (S), distillery effluent (DE), paper mill effluent (PE) and sugar mill effluent (SE) have been arranged in ascending order?
(a) SE < PE < S < DE (b) PE < S < SE < DE
(c) S < DE < PE < SE (d) SE < S < PE < DE

Answer: B


Ques. Which one of the following statements is correct?
(a) Both Azotobacter and Rhizobium fix atmospheric nitrogen in root nodules of plants.
(b) Cyanobacteria such as Anabaena and Nostoc are important mobilizers of phosphates and for plant nutrition in soil.
(c) At present it is not possible to grow maize without chemical fertilizers.
(d) Extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies. 

Answer: D


Ques. Which one of the following is not a bioindicator of water pollution?
(a) Blood-worms (b) Stone flies
(c) Sewage fungus (d) Sludge-worms 

Answer: B


Ques. Limit of BOD prescribed by Central Pollution Control Board for the discharge of industrial and municipal waste waters into natural surface waters, is
(a) < 30 ppm (b) < 3.0 ppm
(c) < 10 ppm (d) < 100 ppm. 

Answer: A


Ques. Which one of the following is not used for disinfection of drinking water?
(a) Chlorine (b) Ozone
(c) Chloramine (d) Phenyl 

Answer: D


Ques. Common indicator organism of water pollution is
(a) Lemna pancicostata
(b) Eichhornia crassipes
(c) Escherichia coli
(d) Entamoeba histolytica. 

Answer: C


Ques. Escherichia coli is used as an indicator organism to determine pollution of water with
(a) heavy metals (b) faecal matter
(c) industrial effluents (d) pollen of aquatic plants.

Answer: B


Ques. Which of the following is absent in polluted water?
(a) Hydrilla (b) Water hyacinth
(c) Larva of stone fly (d) Blue green algae

Answer: C


Ques. What is B.O.D.?
(a) The amount of O2 utilised by organisms in water.
(b) The amount of O2 utilised by microorganisms for decomposition.
(c) The total amount of O2 present in water.
(d) All of the above 

Answer: B


Ques. The Minamata disease in Japan was caused through the pollution of water by
(a) cyanide (b) methyl isocyanate
(c) lead (d) mercury. 

Answer: D


Ques. D.D.T. is
(a) not a pollutant
(b) an antibiotic
(c) a non-degradable pollutant
(d) a biodegradable pollutant. 

Answer: C


Ques. Which of the following organism is likely to have more concentration of D.D.T. in its body?
(a) Top carnivores (b) Primary producers
(c) Herbivores (d) Carnivores 

Answer: A

Please refer to attached file for CBSE Class 12 Biology - Environmental Issues

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