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NCERT Exemplar Class 8 Science Chapter 1 Crop Production and Management are part of NCERT Exemplar Class 8 Science. Here we have given NCERT Exemplar Class 8 Science Chapter 1 Crop Production and Management. https://www.cbselabs.com/ncert-exemplar-problems-class-8-science-crop-production-management/

NCERT Exemplar Class 8 Science Chapter 1 Crop Production and Management

Multiple Choice Questions
Question . 1 Which one of the following conditions is not essential to grow maize?
(a) High temperature (b) Humidity
(c) Low temperature (d) Rainfall
Answer. (c) Maize is a kharif crop, which requires high temperature, rainfall and humidity to grow, while rabi crops require low temperature for their growth,

Question. 2 Propagation of ginger is generally done using
(a) seed (b) stem (rhizome)
(c) root (d) leaf
Answer. (b) The ginger is a modified underground stem, which is propagated vegetatively by stem (rhizome) cultivation. It does not propagate by roots, leaves or seeds.

Question. 3 Which of the following statements is not true for organic manure?
(a) It enhances water holding capacity of soil
(b) It has a balance of all plant nutrients
(c) It provides humus to soil
(d) It improves texture of soil
Answer. (b) Organic manures are obtained from decomposition of plant and animal wastes that are rich in nutrients and humus.
But all nutrients might not be present in a proportionate amount in it, thus will not solve : the problem if soil is particularly deficient in one or more specific nutrient.

Question. 4 The term used for the process of separation of grains from chaff is
(a) sieving (b) winnowing
(c) threshing (d) hand picking
Ans. (c) The process of separating the edible part of the harvested grains (crop) by loosening and removing the scaly, inedible chaff surrounding the grain.
The process utilises a machine called ‘combine’ which is a combination of harvester and a thresher.

Question. 5 Read the statements given below.

1. Seeds require moisture for germination.
2. Plants can absorb nutrients mostly in dissolved form.
3. Irrigation protects crops from both frost and hot air currents.
4. Irrigation improves soil texture.

Choose combination of statements which indicate need to irrigate crops.
(a) (1) and (2) (b) (1), (2) and (3)
(c) (1), (2), (3) and(4)-,(d) (1) and (3)

Answer. (a) The combination of statements (1) and (2) indicate need for irrigation.
Irrigation is the supply of water to crops at regular intervals as water or moisture is necessary for seed germination, growth and other physiological processes. Moreover, the plants readily absorb nutrients in dissolved form along with water through root hairs of roots.
It does not protect crops from frost and hot air currents and manure not irrigation improves soil texture.

Question. 6 Which of the following tools would a farmer use to remove weeds from the field?
(a) Hoe (b) Plough (c) Axe (d) Cultivator
Answer. (a) Hoe is a simple tool used for removing weeds from the field and loosening of soil, it works like a blade, pulled by the animals In the field. Plough is used for tilling of soil, axe is used for cutting trees and cultivator is another tool implemented for ploughing,

Question. 7 Which of the following is not true for fertilisers?
(a) They increase the yield
(b) Their excessive use disturbs the balance of nutrients in soil
(c) They are generally used in small quantity
(d) They are environment friendly
Answer. (d) Fertilisers are not environment friendly as they are chemical substances rich in particular nutrient, Though, they increase the crop yield, the repeated and excessive use of fertilisers in the same field reduces the soil fertility, It also pollutes water bodies as they get dissolved and washed away by rain and also seeps in the water table posing threats to humans.

Question. 8 Given below are statements about the harmful effects of weeds on crop plants.

1. They interfere in harvesting.
2. They help crop plants to grow healthily.
3.  They compete with crop plants for water, nutrients, space and light.
4. They affect the plant growth.

(a) (1), (3) and (4)
(b) Only (3)
(c) (3) and (4)
(d) (1), (2), (3) and (4)

Answer. (a) Statements (1), (3) and (4) are correctly suggesting the harmful effects of weeds. Weeds are the undesirable plants that grow along the main crops.
Removal of weeds is necessary because they interfere and affect the major crop’s growth, by competing for light, water, nutrients and space.They also interfere during harvesting procedure.
Weeds do not help in healthy growth of crop plants.

Question. 9 The process of loosening and turning of soil is called
(a) irrigation and manuring
(b) digging and winnowing
(c) tilling and ploughing
(d) harvesting and storage
Answer. (c) The process of loosening and turning of soil is called tilling and ploughing . It is the first step in preparation of soil for cultivation of crop. Ploughing is done using a plough, made of wood or iron.

Question. 10 The monsoon season in our country is during the months
(a) April-December
(b) June-September
(c) November-March
(d) January-May
Answer. (b) The monsoon season in India is during the months June to September, The crops grown in this season are called kharif crop, e.g. paddy, maize, cotton, etc.
The kharif crops sown in June are harvested towards the end of rainy season (October-November).

Question. 11 The system of irrigation where water is supplied drop by drop near the roots of plants, is called
(a) pulley system
(b) drip system
(c) sprinkler system
(d) lever system
Answer. (b) Drip system is the method of irrigation which conserves water and avoids wastage as water is made to fall drop by drop at the position of roots. It is best technique for watering fruit plants, trees and gardens.
Sprinkler system is also a modern method of irrigation that efficiently uses water in the form of sprinklers. It is useful for uneven lands, while pulley and lever system are traditional methods of irrigation where a lot of water is wasted.

Very Short Answer Type Questions
Question.12 Pick out the odd one from the following words given in the box and give reason for it. Plough, Seed drill, Hoe, Chain pump. Sickle
Answer. Seed drill is the odd one in the above given set of tools as it is a modern agricultural tool used to sow seeds at uniform distances and to properly cover them with soil.
Rest of the tools, i.e. plough (used for tilling), hoe (for removal of weeds and loosening of soil), chain pump (irrigation method) and sickle (tool for removing weeds) are all traditional implements used in agriculture.

Question. 13 If you are given a dry piece of land for cultivation, what will you do before sowing the seeds?
Answer. If the field is dry for cultivation of crops, the soil preparation is done accordingly before sowing of crops. Preparation of dry soil includes adequate watering to restore the moisture content and then tilled and ploughed to allow growth of microbes and aeration, Finally, the soil is turned and its crumbs are levelled and manures are mixed. The soil is ready for sowing of crops in the field.

Question. 14 State whether the following statements are True/False

1. Using good quality seed is the only criterion to get high yield.
2. Growing different crops in different seasons in the same field will deplete the soil of nutrients.
3. Ail crop plants are sown as seeds in the field.
4.  Cells of root nodules of leguminous plants fix nitrogen.
5. Freshly harvested grains must be dried before shoring.

Answer.

1.  False, apart from good quality seeds, using appropriate agricultural practices are important for getting higher yield.
2. False, it actually enriches the soil. Different crops utilises different nutrients which permits the replenishment of used nutrients. This method is also called as crop rotation.
3. False, some crop plants need transplantation.
4. False, Rhizobium (bacteria) present in the cells of root nodules of leguminous plants fix nitrogen.
5. True, the freshly harvested grains must be dried. The moisture content in them can spoil the grains or microbial infection may occur.
   Drying reduces’ the moisture content in grains, thus preventing the attack of different organisms.

Question. 15 During which months do farmers grow mustard in India?
Answer. Farmers grow mustard during the months from October-March. Mustard is a rabi crop that is sown in beginning of winters (October-November) as they need low temperature and harvested at the end of winter (April-May).

Question. 16 Which activity of the farmer can promote growth of earthworms and microbes in the field?
Answer. Ploughing of the soil during soil preparation creates spaces in the soil thus, leading to aeration and the soil also loosens which promotes the growth and survival of earthworms and microbes and release of nutrients in the soil

Short Answer Type Questions
Question. 17 Beera wants to practice crop rotation in his field. Suggest a rabi crop and a kharif crop which will replenish his field with nitrogen. Which crop replenishes nitrogen and why?
Answer. Rabi crops are wheat, pea, mustard while kharif crops are maize, paddy (rice) or soyabean, These are grown in different seasons and therefore, can very well be rotated alternatively. Pea and soyabean are leguminous plants which harbour bacteria, i.e, Rhizobium in their nodules, thus help in fixing nitrogen.
These nitrogen fixing plants can replenish nitrogen in the field and hence, Beera can easily practice crop rotation.

Question.18 Match the agricultural implements given in column A with their use given in column B.

Answer. The correct matching is as given :
(a) —(iii), (b)—(i), (c)—(ii), (d)—(iv)
(a) Harvesting is the process of cutting matured crops from close to the ground. It is done manually using a sickle.
(b) Ploughing is the process of loosening and turning of soil. It is done with hoe, made of wood or iron.
(c) Sowing is the process of adding seeds of the crop to be grown in field using the seed drill.
(d) Irrigation is the process of watering the fields which favours the germination and growth of seeds, A sprinkler is one method used to water the field.

Question. 19 What are organic foods?
Answer. The crops that are cultivated using organic substances like manures, etc and prohibit the use of harmful chemical substances like fertilisers, pesticides, weedicides, etc., are called organic foods.

Question.20 Crossword Puzzle From the word puzzle given as figure. Find at least eight words which are ‘farmer’s friends’. Classify them into living and non-living.

Answer. From the given puzzle, the farmer’s friends are:
Living Seed, Earthworm, Rhizobium, Microbes, Ox. Living components like seeds, microbes earthworm, etc., helps in growth of crops, enrichment of soil nutrients, etc,, microbes like Rhizobium fix the nitrogen in soil, earthworms loosens the soil.
Non-living Plough, Urea, NPK, Manure, Hoe. Non-living components support the living components and help in better yield of crops. Plough and the hoe are instruments used in ploughing and harvesting.
Manure and urea are used for enrichment of soil in nutrients.

Question. 21 (a) Name the tool used with a tractor for sowing seeds in a field.
(b) What are the advantages of using this tool?
Answer. (a) The tool used with a tractor for sowing seeds in a field at uniform distances is seed drill. Before the introduction of seed drill, the process was manual.
(b) The advantages of seed drill are:

1. Seeds are sown at a uniform distance and depth to avoid over crowding.
2. After sowing, seeds are covered by soil which prevent them from being eaten by birds.
3.  It saves time and labour.
4. Improves the ratio of crop yield by as much as nine times.

Question. 22 (a) Name the practice followed for large scale rearing of farm animals.
(b) What facilities are provided to farm animals?
Answer. (a) The science of rearing, caring, breeding and improvement of domesticated animals is known as animal husbandry. It is the practice of breeding and raising livestock like cows, buffaloes, pigs, horses and sheep, etc. This practice requires good care and management of livestock.
(b) The animals or livestock in animal husbandry practice should be provided with:

1. Appropriate shelter facilities
2. Food and water
3. Good hygienic practices
4. Medical facilities, etc.

Question. 23 Classify the following crops into kharif and rabi crops and write in the tabular column given below: Maize, paddy, mustard, pea, gram, wheat, groundnut, cotton

Answer.The crops which are sown in the rainy season, i.e. from June to September are classified as kharif crops.
The crops sown in the winter season, i.e generally from October to March are called as Rabi crops. From the above given crop list, the kharif and rabi crops can be grouped as

Long Answer Type Questions
Question. 24 Despite favourable climatic conditions, a farmer’s crop failed to give
good yield. Give the possible reasons for this.
Answer. If despite favourable climatic conditions, farmer’s crop failed to give good yield, the possibilities may be

1. selection of crops was not done correctly.
2. he did not use good quality and healthy seeds.
3. his field was not well irrigated.
4. manures/fertilisers were not timely and properly applied.
5. weeds were not removed.
6. seeds were not sown at appropriate distance.
7. the soil was not ploughed and levelled properly.

Question. 25 As a part of eco-club activity, students were asked to raise a kitchen garden in the school premises. They were provided with some materials given in the box. List the other materials you would require. How will you plan the garden? Write the steps.
Khurpi, water-can, spade, shovel
Answer. Besides the given tools, the other items required for raising a garden are seeds and seedling of vegetables, plants from nursery, kitchen waste, manure, water, soil.
Steps for raising the garden:

1. Kitchen waste will be collected and composted in a pit.
2. A patch of land will be identified for the garden, with adequate sunlight available.
3. Soil will be dug up and levelled with the help of a spade.
4. Sowing of seeds/ transplanting of seedlings will be done. Seeds should be uniformly placed with adequate spacing,
5. Select seeds/seedlings as per the season. Water the plants regularly with a water-can.
6. Compost will be applied.
7. Weeds will be removed periodically with the help of khurpi.

Question. 26 Paddy is a major cereal crop in our country.
(a) In which season is paddy cultivated?
(b) Discuss the method of sowing.
(c) What measures must be taken to prevent spoilage and insect attack of harvested grains?
Answer. (a) Paddy is cultivated in rainy season as it is a kharif crop.
(b) For sowing paddy, seeds are first grown in a nursery and later after selecting healthy seed plant lets, they are transplanted in the field. This allows us to select seedling which can survive in harsher environmental conditions for cultivation.
(c) Measures taken to prevent spoilage or damage of harvested crops from insect attack are:

1. Exposing them in sunlight for drying as freshly harvested crops have moisture.
2. Dried neem leaves are added to stored grains, so as to prevent damage from pests.
3. Specific chemical treatments are also available for preventing crops from pest
   infestations.
4. Fumigation of the storage area to remove its insects.

Question. 27 Unscramble the words related to crop production and its management and write in the boxes given beneath them.

Now, using the circled letters, form one word which is an activity carried out in fields, after maturation of crops.
Answer.

1. SILOS Used for storing of harvested grains.
2. THRESHING The process of harvested grains being separated from the chaff.
3. IRRIGATION The process of supplying water to a crop field at different intervals is called irrigation.
4. RIVER The source of water.

The letters in circles are I S HR GATVE Which forms HARVESTING.
Harvesting is the activity carried out in fields after the maturation of crops, i.e. the cutting of matured crop from close to the ground.

Question. 28 Given below is a conversation between two farmers Heera and Beera.
Heera Brother Beera, your maize crops look beautiful. They have grown pretty fast.
Beera Yes, I have sprayed urea this time. What about you?
Heera Well, I am still relying on good old cow dung. I am saving money for buying a tractor. Beera That’s good. Tractor saves a Lot of time and labour.
Heera Yes, it’s been very labour intensive for me and now these weeds have come up.
Beera Try weedicides, they are very effective.
Now, answer the following questions.

1. List the practices which are not environment friendly and why?
2. What is the advantage of modern agricultural implements over traditional ones?
3. Name one weedicide and the precaution, farmers must take during its application.

Answer.

1.  The practices used in field which are not environment friendly are use of fertilisers, pesticides, weedicides and other chemical substances that pose health hazards.
   Tractor though saves labour and time but contributes to air pollution.
2. Modern agricultural implements save both time and labour as compared to traditional equipments.
   They import more efficiency and accuracy in different agricultural procedures like sowing of seed.
3. The example of weedicide is 2,4-D. The precaution taken by farmers, while spraying it on crops is they should properly cover their nose and mouth, so as to avoid inhaling of these chemicals.
   Excessive use is harmful, hence they should limit the application of such chemicals.

Question. 29 For discussion
Despite being one of the growing economies, our country still has a large section of population going hungry and malnourished. Do you think an efficient crop production mechanism is the only solution to this? Discuss in the class what else needs to be done to root out hunger and malnutrition from our country.
Answer. India, a growing economy with agriculture is a main contributor in its growth.
Agriculture is science of cultivating plants, animals and other life forms for food and other sources, Despite large production of crops by agricultural practices, people still go hungry and malnourished. This happens because of inefficient crop production and management.
In India, an increase in production of food grains has been observed from 1960 to 2004. With efficient management, the crop production can be enhanced and improved to feed the country’s poor.
A few steps in this direction can be:

1. Selection of high field seeds for planting The seeds with increased yield and reduced growth period.
2. Management of crop production The financial aspects of agriculture should be made more approachable to farmers at all levels.
3. Information regarding Use of chemicals, manures, cropping patterns, nutrient quality and irrigation facilities should be discussed and propagated among farmers.
4. Protection of crops The agricultural produce should be shared efficiently to reduce the microbial, pest or other organisms from infesting the produce.Pest and weed control measers should be adopted.

A large amount of crops get spoiled during storage by different living and non-living factors.
Living factors include rodents, microbes and insects.
Non-living factors are moisture, temperature and hygiene of storage place.
Keeping these factors in mind, we can reduce the economic losses, increase the marketability and feed the country’s poor.

Question. 30 Terms related to agricultural practices are given below. Rearrange them in the correct sequence, harvesting, sowing, manuring, tilling and ploughing, irrigation, weeding.
Answer. The correct sequence in the series of agricultural practices is:
Tilling and ploughing ——–> Sowing ——> Manuring ——–> Irrigation ———> Weeding —–> Havesting

1. Tilling and ploughing It is the turning and loosening of soil to encourage growth of earthworms and microbes. It is the first step in preparation of soil.
2. Sowing After soil preparation, good and healthy seeds are selected and sowed to considerable depths in soil by either traditional or modern methods.
3. Manuring It is done to add humus, improve texture of soil as well as to replenish nutrients in soil.
4. Irrigation Crop fields are watered at regular intervals to provide moisture for growth and germination of seeds.
5. Weeding Weeding is removal of weeds that grow naturally between crops and compete with them for sunlight, space, water and nutrients. They should be removed before weeds mature, i.e. produce flowers and seeds,
6. Harvesting It is the process of cutting and gathering mature crops. It can be done manually by sickle or by harvester machine.

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NCERT Exemplar Class 8 Maths Chapter 7 Algebraic Expressions, Identities and Factorisations are part of NCERT Exemplar Class 8 Maths. Here we have given NCERT Exemplar Class 8 Maths Chapter 7 Algebraic Expressions, Identities and Factorisation. https://www.cbselabs.com/ncert-exemplar-problems-class-8-mathematics-algebraic-expressions-identities-factorisation/

NCERT  Exemplar Class 8 Maths Chapter 7 Algebraic Expressions, Identities and Factorisation

Multiple Choice Questions
Question. 1 The product of a monomial and a binomial is a
(a) monomial (b) binomial
(c) trinomial (d) None of these
Solution. (b) Monomial consists of only single term and binomial contains two terms. So, the multiplication of a binomial by a monomial will always produce a binomial, whose first term is the product of monomial and the binomial’s first term and second term is the product of monomial and the binomial’s second term.

Question. 2 In a polynomial, the exponents of the variables are always (a)’integers (b) positive integers (c) non-negative integers (d) non-positive integers
Solution. (c) In a polynomial, the exponents of the variables are either positive integers or 0. Constant term C can be written as C x°. We do not consider the expressions as a polynomial which consist of the variables having negative/fractional exponent.

Ncert Exemplar Class 8 Maths Algebraic Expressions
Question. 3 Which of the following is correct?
(a) \({{\left( a-b \right)}^{2}}={{a}^{2}}+2ab-{{b}^{2}}\) (b) \({{\left( a-b \right)}^{2}}={{a}^{2}}-2ab+{{b}^{2}}\)
(c) \({{\left( a-b \right)}^{2}}={{a}^{2}}-{{b}^{2}}\) (d) \({{\left( a+b \right)}^{2}}={{a}^{2}}+2ab-{{b}^{2}}\)
Solution.

Ncert Exemplar Class 8 Algebraic Expressions
Question. 4 The sum of -7pq and 2pq is
(a) -9pq   (b) 9pq
(c) 5pq   (d) -5pq
Solution.

Algebraic Expressions Class 8 Exemplar
Question. 5 If we subtract \(-3{ x }^{ 2 }{ y }^{ 2 }\) from \({ x }^{ 2 }{ y }^{ 2 }\), then we get

Solution.

Ncert Exemplar Class 8 Maths Factorisation
Question. 6 Like term as \(4{ m }^{ 3 }{ n }^{ 2 }\) is
(a)\(4{ m }^{ 2 }{ n }^{ 2 }\) (b) \(-6{ m }^{ 3 }{ n }^{ 2 }\)
(c) \(6p{ m }^{ 3 }{ n }^{ 2 }\) (d) \(4{ m }^{ 3 }{ n }\)
Solution. (b) We know that, the like terms contain the same literal factor. So, the like term as \(4{ m }^{ 3 }{ n }^{ 2 }\) , is \(-6{ m }^{ 3 }{ n }^{ 2 }\), as it contains the same literal factor \({ m }^{ 3 }{ n }^{ 2 }\).

Ncert Exemplar Class 8 Factorisation
Question. 7 Which of the following is a binomial?

Solution.

Factorisation Class 8 Exemplar
Question. 8 Sum of a – b + ab, b + c – bc and c – a – ac is

Solution.

Ncert Exemplar Class 8 Maths
Question. 9 Product of the monomials 4p, -7\({ q }^{ 3 }\), -7pq is

Solution.

Ncert Exemplar Class 8 Maths Factorisation Solutions
Question. 10 Area of a rectangle with length 4ab and breadth 6\({ b }^{ 2 }\) is

Solution.

Class 8 Factorisation Exemplar
Question. 11 Volume of a rectangular box (cuboid) with length = 2ab, breadth = 3ac and height = 2ac is

Solution.

Question. 12 Product of 6\({ a }^{ 2 }\) -7b + 5ab and 2ab is

Solution.

Ncert Exemplar Class 8 Maths Solutions Algebraic Expressions
Question. 13 Square of 3x – 4y is

Solution.

Ncert Exemplar Class 8 Maths Solutions Chapter 7
Question. 14 Which of the following are like terms?

Solution.

Algebraic Expressions Identities And Factorization Class 8
Question. 15 Coefficient of y in the term of \({ -y }^{ 3 }\) is
(a)-1 (b)-3 (c)\({ -1 }^{ 3 }\) (d)\({ 1 }^{ 3 }\)
Solution.

Ncert Exemplar Class 8 Maths Chapter 9 Algebraic Expressions
Question. 16 \({ a }^{ 2 }-{ b }^{ 2 }\) is equal to

Solution.

Maths Exemplar Class 8
Question. 17 Common factor Of 17abc, 34a\({ b }^{ 2 }\), 51\({ a }^{ 2 }\)b is
(a)17abc (b)17ab (c)17ac (d)17\({ a }^{ 2 }\)\({ b }^{ 2 }\)c
Solution.

Maths Class 8 Exemplar Solutions
Question. 18 Square of 9x – 7xy is

Solution.

Question. 19 Factorised form of 23xy – 46x + 54y -108 is

Solution.

Question. 20 Factorised form of \({ r }^{ 2 }\)-10r + 21 is
(a)(r-1)(r-4) (b)(r-7)(r-3) (c)(r-7)(r+3) (d)(r+7)(r+3)
Solution.

Question. 21 Factorised form of \({ p }^{ 2 }\) – 17p – 38 is
(a) (p -19)(p + 2) (b) (p -19) (p – 2) (c) (p +19) (p + 2) (d) (p + 19) (p – 2)
Solution.

Question. 22 On dividing 57 \({ p }^{ 2 }\) qr by 114pq, we get

Solution.

Question. 23 On dividing p(4\({ p }^{ 2 }\) – 16) by 4p (p – 2), we get
(a) 2p + 4 (b) 2p – 4 (c) p + 2 (d) p – 2
Solution.

Question. 24 The common factor of 3ab and 2cd is
(a) 1 (b) -1 (c) a (d) c
Solution. (a) We have, monomials 3ab and 2cd Now, 3ab = 3xaxb 2cd =2 x c x d
Observing the monomials, we see that, there is no common factor (neither numerical nor literal) between them except 1.

Question. 25 An irreducible factor of24\({ x }^{ 2 }\)\({ y }^{ 2 }\) is
(a)\({ a }^{ 2 }\) (b)\({ y }^{ 2 }\) (c)x (d)24x
Solution. (c) A factor is said to be irreducible, if it cannot be factorised further.
We have, 24\({ x }^{ 2 }\)\({ y }^{ 2 }\) =2 x 2 x 2 x 3 x x x x x y x y Hence, an irreducible factor of 24\({ x }^{ 2 }\)\({ y }^{ 2 }\) is x.

Question. 26 Number of factors of \({{\left( a+b \right)}^{2}}\) is
(a) 4 (b) 3 (c) 2 (d) 1
Solution. (c) We can write \({{\left( a+b \right)}^{2}}\) as, (a + b) (a + b) and this cannot be factorised further.
Hence, number of factors of \({{\left( a+b \right)}^{2}}\) is 2.

Question. 27 The factorised form of 3x – 24 is
(a) 3x x 24 (b)3 (x – 8) (c)24(x – 3) (d)3(x-12)
Solution. (b) We have,
3x – 24 = 3 x x – 3 x 8= 3 (x – 8) [taking 3 as common]

Question. 28 The factors of \({ x }^{ 2 }\) – 4 are
(a) (x – 2), (x – 2) (b) (x + 2), (x – 2)
(c) (x + 2), (x + 2) (d) (x – 4), (x – 4)
Solution.

Question. 29 The value of \((-27{ x }^{ 2 }y)\div (-9xy)\) is
(a)3xy (b)-3xy (c)-3x (d)3x
Solution.

Question. 30 The value of \((2{ x }^{ 2 }+4)\div (2)\) is

Solution.

Question. 31 The value of \((3{ x }^{ 3 }+9{ x }^{ 2 }+27x)\div 3x\) is

Solution.

Question. 32 The value of \({{\left( a+b \right)}^{2}}+{{(a-b)}^{2}}\) is

Solution.

Question. 33 The value of \({{\left( a+b \right)}^{2}}-{{(a-b)}^{2}}\) is

Solution.

Fill in the Blanks
In questions 34 to 58, fill in the blanks to make the statements true.
Question. 34 The product of two terms with like signs is a term.
Solution. Positive
If both the like terms are either positive or negative, then the resultant term will always be positive.

Question. 35 The product of two terms with unlike signs is a term.
Solution. Negative
As the product of a positive term and a negative term is always negative.

Question. 36 a (b + c) = a x ——– + a x ———-
Solution. b,c
we have , a(b+c)=a x b + a x c [using left distributive law]

Question. 37 (a-b) ————- =\( { a }^{ 2 }-2ab+{ b }^{ 2 }\)
Solution.

Question. 38 \({ a }^{ 2 }-{ b }^{ 2 }\)=(a+b)—————-
Solution.

Question. 39 \({{(a-b)}^{2}}\)+—————-=\({ a }^{ 2 }-{ b }^{ 2 }\)
Solution.

Question. 40 \({{(a+b)}^{2}}\)-2ab=————- + ———–.
Solution.

Question. 41 (x+a)(x+b)=\({ x }^{ 2 }\) + (a+b) x + ———–.
Solution.

Question. 42 The product of two polynomials is a ————–.
Solution. Polynomial
As the product of two polynomials is again a polynomial.

Question. 43 Common factor of ax2 + bx is——————.
Solution.

Question. 44 Factorised form of 18mn + 10mnp is —————–.
Solution.

Question. 45 Factorised form of 4\({ y }^{ 2 }\) – 12y + 9 is———– .
Solution.

Question. 46 \(38{ x }^{ 2 }{ y }^{ 2 }z\div 19x{ y }^{ 2 }\) is equal to———–.
Solution.

Question. 47 Volume of a rectangular box with length 2x, breadth 3y and height 4z is ——.
Solution. 24 xyz
We know that, the volume of a rectangular box,
V = Length x Breadth x Height = 2x x 3y x 4z = (2 x 3 x 4) xyz = 24 xyz

Question. 48 \( 6{ 7 }^{ 2 }-3{ 7 }^{ 2 }\) =(67 -37) x ———–=————.
Solution.

Question. 49 \( { 103 }^{ 2 }-{ 102 }^{ 2 }\)=————- x (103-102)=————–.
Solution.

Question. 50 Area of a rectangular plot with sides 4\({ y }^{ 2 }\) and 3\({ y }^{ 2 }\) is————–.
Solution.

Question. 51 Volume of a rectangular box with l = b = h = 2x is ———-.
Solution.

Question. 52 The numerical coefficient in -37abc is————–.
Solution. -37
The constant term (with their sign) involved in term of an algebraic expression is called the numerical coefficient of that term.

Question. 53 Number of terms in the expression \({ a }^{ 2 }\) and + bc x d is –.
Solution.

Question. 54 The sum of areas of two squares with sides 4o and 4b is————-.
Solution.

Question. 55 The common factor method of factorisation for a polynomial is based on————-property.
Solution.Distributive
In this method, we regroup the terms in such a way, so that each term in the group contains a common literal or number or both.

Question. 56 The side of the square of area 9\({ y }^{ 2 }\) is————.
Solution.

Question. 57 On simplification, \(\frac { 3x+3 }{ 3 }\) =————.
Solution.

Question. 58 The factorisation of 2x + 4y is————-.
Solution. 2 (x + 2y)
We have, 2x + 4y = 2x + 2 x 2y = 2 (x + 2y)

True/False
In questions 59 to 80, state whether the statements are True or False
Question. 59 \({{(a+b)}^{2}}={{a}^{2}}+{{b}^{2}}\).
Solution.

Question. 60 \({{(a-b)}^{2}}={{a}^{2}}-{{b}^{2}}\).
Solution.

Question. 61 (a+b) (a-b)=\({{a}^{2}}-{{b}^{2}}\)
Solution.

Question. 62 The product of two negative terms is a negative term.
Solution.False
Since, the product of two negative terms is always a positive term, i.e. (-) x (-) = (+).

Question. 63 The product of one negative and one positive term is a negative term.
Solution.True
When we multiply a negative term by a positive term, the resultant will be a negative term, i-e. (-) x (+) = (-).

Question. 64 The numerical coefficient of the term -6\({ x }^{ 2 }{ y }^{ 2 }\) is -6.
Solution. True
Since, the constant term (i.e. a number) present in the expression -6\({ x }^{ 2 }{ y }^{ 2 }\) is -6.

Question. 65 \({ p }^{ 2 }\)q+\({ q }^{ 2 }\)r+\({ r }^{ 2 }\)q is a binomial.
Solution. False
Since, the given expression contains three unlike terms, so it is a trinomial.

Question. 66 The factors of \({ a }^{ 2 }\) – 2ab + \({ b }^{ 2 }\)are (a + b) and (a + b).
Solution.

Question. 67 h is a factor of \(2\pi (h+r)\).
Solution.

Question. 68 Some of the factors of \(\frac { { n }^{ 2 } }{ 2 } +\frac { n }{ 2 }\) are \(\frac { 1 }{ 2 } n\) and (n+1).
Solution.

Question. 69 An equation is true for all values of its variables.
Solution. False
As equation is true only for some values of its variables, e.g. 2x – 4= 0 is true, only for x =2.

Question. 70 \({ x }^{ 2 }\) + (a+b)x +ab =(a+b)(x +ab)
Solution.

Question. 71 Common factors of \(11p{ q }^{ 2 },121{ p }^{ 2 }{ q }^{ 3 },1331{ p }^{ 2 }q\) is \(11{ p }^{ 2 }{ q }^{ 2 }\)
Solution.

Question. 72 Common factors of 12 \(11{ a }^{ 2 }{ b }^{ 2 }\) +4a\({ b }^{ 2 }\) -32 is 4.
Solution.

Question. 73 Factorisation of -3\({ a }^{ 2 }\)+3ab+3ac is 3a (-a-b-c).
Solution.

Question. 74 Factorised form of \({ p }^{ 2 }\)+30p+216 is (p+18) (p-12).
Solution.

Question. 75 The difference of the squares of two consecutive numbers is their sum.
Solution.

Question. 76 abc + bca + cab is a monomial.
Solution. True
The given expression seems to be a trinomial but it is not as it contains three like terms which can be added to form a monomial, i.e. abc + abc + abc = 3abc

Question. 77 On dividing \(\frac { p }{ 3 }\) by \(\frac { 3 }{ p }\) ,the quotient is 9
Solution.

Question. 78 The value of p for 5\({ 1 }^{ 2 }\)-4\({ 9 }^{ 2 }\)=100 p is 2.
Solution.

Question. 79 \((9x-51)\div 9\) is x-51.
Solution.

Question. 80 The value of (a+1) (a-1)(\({ a }^{ 2 }\) +1) is \({ a }^{ 4 }\)-1.
Solution.

Question. 81 Add:

Solution.

Question. 82 Subtract

Solution.

Question. 83 Multiply the following:


Solution.

Question. 84 Simplify

Solution.

Question. 85 Expand the following, using suitable identities.


Solution.

Question. 86 Using suitable identities, evaluate the following:

Solution.

Question. 87 Write the greatest common factor in each of the following terms.


Solution.

Question. 88 Factorise the following expressions.

Solution.

Question. 89Factorise the following, using the identity,\({{a}^{2}}+2ab+{{b}^{2}}={{(a+b)}^{2}}\)

Solution.

Question. 90 Factorise the following, using the identity,\({{a}^{2}}-2ab+{{b}^{2}}={{(a-b)}^{2}}\)

Solution.

Question.  91 Factorise the following

Solution.

Question.  92 Factorise the following using the identity ,\({{a}^{2}}-{{b}^{2}}\)=(a+b)(a-b).

Solution.

Question. 93 The following expressions are the areas of rectangles. Find the possible lengths and breadths of these rectangles.

Solution.

Question. 94 Carry out the following divisions:

Solution.

Question. 95 Perform the following divisions:

Solution.

Question. 96 Factorise the expressions and divide them as directed.

Solution.

Question. 97 The area of a square is given by 4\({{x}^{2}}\)+ 12xy + 9\({{y}^{2}}\). Find the side of the square.
Solution.

Question. 98 The area of a square is  9\({{x}^{2}}\) + 24xy + 16\({{y}^{2}}\). Find the side of the square.
Solution.

Question. 99 The area of a rectangle is \({{x}^{2}}\) + 7x + 12. If its breadth is (x + 3), then find its length.
Solution.

Question. 100 The curved surface area of a cylinder is \(2\pi ({ y }^{ 2 }-7y+12)\) and its radius is (y – 3). Find the height of the cylinder (CSA of cylinder = \(2\pirh\))
Solution.

Question. 101 The area of a circle is given by the expression \( \pi { x }^{ 2 }+6\pi x+9\pi \). Find the radius of the circle.
Solution.

Question.102 The sum of first n natural numbers is given by the expression \(\frac { { n }^{ 2 } }{ 2 } +\frac { n }{ 2 }\) Factorise this expression.
Solution.

Question.103 The sum of (x + 5) observations is \({ x }^{ 4 }\) – 625. Find the mean of the observations.
Solution.

Question.104 The height of a triangle is \({ x }^{ 4 }\) + \({ y }^{ 4 }\) and its base is 14xy. Find the area of the triangle.
Solution.

Question.105 The cost of a chocolate is Rs (x + 4) and Rohit bought (x + 4) chocolates. Find the total amount paid by him in terms of x. If x = 10, find the amount paid by him.
Solution.

Question.106 The base of a parallelogram is (2x + 3) units and the corresponding height is (2x – 3) units. Find the area of the parallelogram in terms of x. What will be the area of a parallelogram of x = 30 units?
Solution.

Question.107 The radius of a circle is 7ab – 7be – 14ac . Find the circumference of the circle,\( (\pi =\frac { 22 }{ 7 } )\)
Solution.

Question.108 If p + q = 12 and pq = 22, then find \({ p }^{ 2 }\) + \({ q }^{ 2 }\) .
Solution.

Question.109 If a + b = 25 and \({ a }^{ 2 }\) + \({ b }^{ 2 }\) then find ab.
Solution.

Question.110 If x – y = 13 and xy = 28, then find \({ x }^{ 2 }\) + \({ y }^{ 2 }\).
Solution.

Question.111 If m – n = 16 and \({ m }^{ 2 }\) + \({ n }^{ 2 }\) = 400, then find mn.
Solution.

Question.112 If \({ a }^{ 2 }\) + \({ b }^{ 2 }\) = 74 and ab = 35, then find a + b ?
Solution.

Question.113 Verify the following:

Solution.

Question.114 Find the value of a, if

Solution.

Question.115 What should be added to 4c (-a + b + c) to obtain 3a(a + b + c) – 2b (a – b + c)?
Solution.

Question.116 Subtract b(\({ b }^{ 2 }\) + b – 7) + 5 from 3\({ b }^{ 2 }\) – 8 and find the value of expression obtained for b = – 3.
Solution.

Question.117 If x – \(\frac { 1 }{ x }\) = 1, then find the value of \({ x }^{ 2 }+\frac { 1 }{ { x }^{ 2 } }\) .
Solution.

Question.118 Factorise \({ x }^{ 2 }+\frac { 1 }{ { x }^{ 2 } } +2-3x-\frac { 3 }{ x }\).
Solution.

Question.119 Factorise \({ p }^{ 4 }+{ q }^{ 4 }+{ p }^{ 2 }{ q }^{ 2 }\).
Solution.

Question.120 Find the value of

Solution.

Question.121 The product of two expressions is \({ x }^{ 5 }\) + \({ x }^{ 3 }\)+ x . If one of them is \({ x }^{ 2 }\) + x + 1, find the other.
Solution.

Question.122 Find the length of the side of the given square, if area of the square is 625sq units and then find the value of x.

Solution.

Question.123 Take suitable number of cards given in the adjoining diagram [G(x x x) representing \({ x }^{ 2 }\), R (x x 1) representing x and Y (1 x 1) representing 1] to factorise the following expressions, by arranging to cards in the form of rectangles: (i) 2\({ x }^{ 2 }\) + 6x + 4 (ii) \({ x }^{ 2 }\) + 4x + 4. Factorise 2\({ x }^{ 2 }\) + 6x + 4 by using the figure.

Calculate the area of figure.
Solution. The given information is incomplete for solution of this question.

Question.124 The figure shows the dimensions of a wall having a window and a door of a room. Write an algebraic expression for the area of the wall to be painted.

Solution.

Question.125 Match the expressions of column I with that of column II

Solution.

NCERT Exemplar Solutions

We hope the NCERT Exemplar Class 8 Maths Chapter 7 Algebraic Expressions, Identities and Factorisation help you. If you have any query regarding NCERT Exemplar Class 8 Maths Chapter 7 Algebraic Expressions, Identities and Factorisation, drop a comment below and we will get back to you at the earliest.

NCERT Exemplar Class 12 Biology Chapter 16 Environmental Issues are part of NCERT Exemplar Class 12 Biology. Here we have given NCERT Exemplar Class 12 Biology Chapter 16 Environmental Issues. https://www.cbselabs.com/ncert-exemplar-problems-class-12-biology-environmental-issues/

NCERT Exemplar Class 12 Biology Chapter 16 Environmental Issues

Multiple Choice Questions
Single Correct Answer Type

1. Non-biodegradable pollutants are created by
(a) Nature (b) Excessive use of resources
(c) Humans (d) Natural disasters
Answer. (c) Non-biodegradable pollutants are created by humans.

2. According to the Central Pollution Control Board, particles that are responsible for causing great harm to human health are of diameter
(a) 2.50 micrometers (b) 5.00 micrometers
(c) 10.00 micrometers (d) 7.5 micrometers
Answer. (a) According to CPCB (Central Pollution Control Board) particulate size 2.5 micrometer or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health.

3. The material generally used for sound proofing of rooms like a recording studio and auditorium, etc. is
(a) Cotton (b) Coir (c) Wood (d) Styro foam
Answer. (d) Styro foam is a kind of expanded polystyrene used especially for making food containers used for sound proofing of rooms like a recording studio and auditorium, etc.

4. Compressed Natural Gas (CNG) is
(a) Propane (b) Methane (c) Ethane (d) Butane
Answer. (b) Compressed Natural Gas (CNG) is methane.

5. World’s most problematic aquatic weed is
(a) Azolla (b) Wolffia (c) Eichhomia (d) Trapa
Answer. (c) The world’s most problematic aquatic weed is water hyacinth (Eichhornia crassipes) also called Terror of Bengal. It were introduced into India for
their lovely flowers (mauve coloured) and shape of leaves. They grow abundantly in eutrophic (nutrient rich) water bodies. Eichhornia caused havoc by their excessive growth by causing blocks in our water ways and lead to an imbalance in the ecosystem dynamics of the water body. They grow faster than our ability to remove them.

6. Which of the following causes biomagnification?
(a) SO₂ (b) Mercury
(c) DDT (d) Both (b) and (c)
Answer. (d) Biomagnification refers to increase in concentration of the toxicant at successive trophic level. This phenomenon is well known for DDT and Hg. In an aquatic food chain concentration of DDT is 0.003 ppb (parts per billion) in water but it can ultimately reaches 25 ppm in fish eating birds through biomagnification. Highest DDT deposition shall occur in birds or sea gull. High concentration of DDT disturb calcium metabolism in birds which causes:
1. Thining of egg shell.
2. Their premature breaking of egg shell.
Thus eventually causing decline in bird population.

7. The expanded form of DDT is
(a) Dichloro diphenyl trichloroethane
(b) Dichloro diethyl trichloroethane
(c) Dichlorodipyrydyltrichloroethane
(d) Dichloro diphenyl tetrachloroacetate
Answer. (a) The expanded form of DDT is dichloro diphenyl trichloroethane.

8. Which of the following material takes the longest time for biodegradation?
(a) Cotton (b) Paper (c) Bone (d) Jute
Answer. (c)

9. Choose the incorrect statement.
(a) The Montreal protocol is associated with the control of emission of ozone depleting substances
(b) Methane and carbon dioxide are greenhouse gases
(c) Dobson units are used to measure oxygen content
(d) Use of incinerators is crucial to disposal of hospital wastes
Answer. (c) The thickness of ozone is measured in terms of Dobson Units (DU). In stratosphere ozone gas is continuously-formed by the action of ultra violet rays on molecular oxygen & also degraded into molecular oxygen.

10. Among the following which one causes more indoor chemical pollution?
(a) Burning coal (b) Burning cooking gas
(c) Burning mosquito coil (d) Room spray
Answer. (a) Burning coal causes more indoor chemical pollution.

11. The green scum seen in the fresh water bodies is
(a) Blue green algae (b) Red algae
(c) Green algae (d) Both (a) and (c)
Answer. (d) The green scum seen in the fresh water bodies is due to blue green algae and green algae.

12. The loudness of a sound that a person can withstand without discomfort is about
(a) 150 dB (b) 215 dB (c) 30 dB (d) 80 dB
Answer. (d) Green muffler is related to pollution of noise. Noise pollution is measured in decibels (dB). Intensity level of whispering sound is 20-40 dB. Intensity of sound in normal conservation 30-60 dB. Day time sound level in silent zone is 50 dB. Noise become uncomfortable above 80 dB. Sound become hazardous noise pollution at level above 80 dB.

13. The major source of noise pollution, worldwide is due to
(a) Office equipment
(b) Transport system
(c) Sugar, textile and paper industries
(d) Oil refineries and thermal power plants
Answer. (b) The major source of noise pollution, worldwide is due to transport system.

14. Match correctly the following and choose the correct option:

The correct matches is
(a) i—C, ii—D, iii—A, iv—B (b) i—A, ii—C, iii—B, iv—D
(c) i—D, ii—A, iii—B, iv—C (d) i—C, ii—D, iii—B, iv—A
Answer. (a)

15. Catalytic converters are fitted into automobiles to reduce emission of harmful gases. Catalytic converters change unburnt hydrocarbons into (a) Carbon dioxide and water (b) Carbon monoxide (c) Methane (d) Carbon dioxide and methane.
Answer. (a) Catalytic converters are fitted into automobiles for reducing emission of poisonous gases.’ Catalytic converters have expensive metals namely platinum—palladium and rhodium (Pt—Pd and Rh) as catalysts. As the exaust passes through the catalytic converter :
1. Unburnt hydrocarbons are converted into CO₂ and H₂0.
2. Carbon monoxide is changed to CO₂.
3. Nitric oxide (NO) is changed to N, gas.
Vehicles equipped with catalytic converters should use unleaded petrol because lead in the petrol inactivates the catalyst.

16. Why is it necessary to remove sulphur from petroleum products?
(a) To reduce the emission of sulphur dioxide in exhaust fumes.
(b) To increase efficiency of automobiles engines.
(c) To use sulphur removed from petroleum for commercial purposes.
(d) To increase the life span of engine silencers.
Answer. (a) To reduce the emission of sulphur dioxide in exhaust fumes is necessary to remove sulphur from petroleum products.

17. Which one of the following impurities is easiest to remove from wastewater?
(a) Bacteria (b) Colloids
(c) Dissolved solids (d) Suspended solids
Answer. (d) Suspended solids impurities is easiest to remove from waste water.

18. Which one of the following diseases is not due to contamination of water?
(a) Hepatitis-B (b) Jaundice (c) Cholera (d) Typhoid
Answer. (a) Sewage from our homes as well as from hospitals are likely to contain many undesirable pathogenic micro-organisms and its disposal into a water without proper treatment may cause outbreak of serious diseases such as:
1. Dysentry, 2. Typhoid, 3. Jaundice, 4. Cholera

19. Nuisance growth of aquatic plants and bloom-forming algae in natural waters is generally due to high concentrations of
(a) Carbon (b) Sulphur (c) Calcium (d) Phosphorus
Answer. (d) Nuisance growth of aquatic plants and bloom-forming algae in natural waters is generally due to high concentrations of phosphorus.

20. Algal blooms impart a distinct colour to water.due to
(a) Their pigments
(b) Excretion of coloured substances
(c) Formation of coloured chemicals in water facilitated by physiological degradation of algae.
(d) Absorption of light by algal cell wall. 
Answer. (a) Algal blooms impart a distinct colour to water due to their pigments.

21. Match the items in column 1 and column II and choose the correct option:

The correct match is:
(a) A—ii, B—i, C—iv, D—iii (b) A—iii, B—ii, C—iv, D—i
(c) A—iii, B—iv, C—i, D—ii (d) A—iii, B—i, C—iv, D—i
Answer. (c)

22. In the textbook you came across Three Mile Island and Chernobyl disasters associated with accidental leakage of radioactive wastes. In India we had Bhopal gas tragedy. It is associated with which of the following?
(a) CO₂ (b) Methyl Iso-Cyanate
(c) CFC’s (d) Methyl Cyanate
Answer. (b) In the textbook we came across Three Mile Island and Chernobyl disasters associated with accidental leakage of radioactive wastes. In India we had Bhopal gas tragedy. It is associated with Methyl Iso-Cyanate (MIC).

Very Short Answer Type Questions
1. Use of lead-free petrol or diesel is recommended to reduce the pollutants emitted by automobiles. What role does lead play?
Answer. Anti knocking agent

2. In which year was the Air (Prevention and Control of Pollution) Act amended to include noise as air pollution?
Answer. 1987.

3. Name the city in our country where the entire public road transport runs on CNG.
Answer. Delhi.

4. It is a common practice to undertake desilting of the overhead water tanks. What is the possible source of silt that gets deposited in the water tanks?
Answer. The soil particles carried by water from the source of supply.

5. What is cultural eutrophication?
Answer. Pollutants from man’s activities like effluents from the industries and homes can radically accelerate the aging process. This phenomenon has been called Cultural or Accelerated Eutrophication.

6. List any two adverse effects of particulate matter on human health.
Answer. When particulate matter inhaled deep into the lungs they cause:

1. Breathing and respiratory symptoms
2.  Irritation
3.  Inflammations
4. Damage to the lungs and premature deaths.

7. What is the raw material for polyblcnd?
Answer. Plastic waste.

8. Blends of polyblend and bitumen, when used, help to increase road life by a factor of three. What is the reason?
Answer. Blends of polyblend and bitumen, when used to lay roads, enhanced the bitumen’s water repellant properties, hence helped to increase road life by a factor of three.

9. Mention any two examples of plants used as wind breakers in the agricultural fields.
Answer. Acacia and Neem.

10. Name an industry which can cause both air and thermal pollution and as well as eutrophication.
Answer. Fertiliser factory.

11. What is an algal bloom?
Answer. Presence of large amounts of nutrients in waters causes excessive growth of planktonic (free-floating) algae, called an algal bloom.

12. What do you understand by biomagnification?
Answer. Biomagnification refers to increase in concentration of the toxicant at successive trophic levels.

13. What are the three major kinds of impurities in domestic wastewater?
Answer. 1. Suspended solids, e.g., Sand, silt and clay.
2. Colloidal materials, e.g., Fecal matter, bacteria, cloth and paper fibres.
3. Dissolved materials, e.g., Nutrients (nitrate, ammonia, phosphate, sodium, calcium).

14. What is reforestation? 
Answer. Reforestation is the process of restoring a forest that once existed but was removed at some point of time in the past.

15. What is the best solution for the treatment of electronic wastes?
Answer. Recycling.

Short Answer Type Questions
1. Is it true that carpets and curtains/drapes placed on the floor or wall surfaces can reduce noise level. Explain briefly.
Answer. Yes, carpets and curtains/drapes placed on the floor or wall surfaces can reduce noise level because these are sound absorber substances.

2. What is hybrid vehicle technology? Explain its advantages with a suitable example?
Answer. Vehicles running on dual mode like petrol and CNG are hybrid vehicle. As CNG is a green fuel there is conservation of fossil fuels and reduction in the environmental pollution.

3. Is it true that if the dissolved oxygen level drops to zero, the water will become septic? Give an example which could lower the dissolved oxygen content of an aquatic body.
Answer. Yes, the water become septic if the dissolved oxygen drops to zero. Organic pollution (biodegradable) is an example.

4. Name any one greenhouse gas and its possible source of production on a large scale. What are the harmful effects of it?
Answer. CO₂ and Methane. CO₂ levels are increasing due to burning of fossil fuels, leading to Global Warming.

5. It is a common practice to plant trees and shrubs near the boundary walls of buildings. What purpose do they serve?
Answer. The plants growing near the boundary wall act as barriers for sound pollution and act as dust catchers.

6. Why has the National Forest Commission of India recommended a relatively larger forest cover for hills than for plains?
Answer. The National Forest Commission of India recommended a relatively larger forest cover for hills than for plains to reduce the chances of landslides.

7. How can slash and bum agriculture become environment friendly?
Answer. Slash and bum agriculture, commonly called as Jhum cultivation in the north-eastern states of India, has also contributed to deforestation. In slash and bum agriculture, the farmers cut down the trees of the forest and bum the plant remains. The ash is used as a fertilizer and the land is then used for farming or cattle grazing. After cultivation, the area is left for several years so as to allow its recovery. The farmers then move on to other areas and repeat this process. In earlier days, when Jhum cultivation was in prevalence, enough time-gap was given such that the land recovered from the effect of cultivation. With increasing population, and Treated cultivation, this recovery phase is done away with, resulting in deforestation.

8. What is the main idea behind “Joint Foregt Management Concept” introduced by the Government of India?
Answer. Realising the significance of participation by local communities, the Government of India in 1980s has introduced the concept of Joint Forest Management (JFM) so as to work closely with “the local communities for protecting and managing forests. In return for their services to the forest, the communities get benefit of various forest products (e.g., fruits, gum, rubber, medicine, etc.), and thus the forest can be conserved in a sustainable manner.

9. What do you understand by Snow-blindness?
Answer. In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow-blindness.

10. How has DDT caused decline in bird population?
Answer. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.

11. Observe the figure A and B given below and answer the following questions

(i) The power generation by the above two methods is non-polluting. True/False
(ii) List any two applications of solar energy.
(iii) What is a photovoltaic cell?
Answer. (i) True.
(ii) (a) Electricity generation (b) Solar light
(iii) A photovoltaic cell is a semiconductor diode that converts visible light into direct current (DC).

Long Answer Type Questions
1. Write a short note on electronic waste. List the various sources of e-wastes and the problems associated with its disposal.
Answer. Discarded unusable electronic gadgets such as computers, mobile phones, circuits, television sets, etc., form electronic waste. These contain harmful toxic substances like heavy metals to which the unskilled manual workers are directly exposed.

2. What is organic farming? Discuss the benefits of organic fanning as a viable practise in the context of developing nations like India.
Answer. The use of Biofertilisers in agriculture is called organic farming. Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. The nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free- living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.

3. Water logging and soil salinity are some of the problems that have come in the wake of the Green Revolution. Discuss their causes and adverse effects to the environment.
Answer. Water logging and soil salinity are some of the problems that have come in the wake of the Green Revolution. Irrigation without proper drainage of water leads to water logging in the soil. Besides affecting the crops, water logging draws salt to the surface of the soil. The salt then is deposited as a thin crust on the land surface or starts collecting at the roots of the plants. This increased salt content is inimical to the growth of crops and is extremely damaging to agriculture.

4. What are multipurpose trees? Give the botanical and local names of any two multipurpose trees known to you and list their uses.
Answer. Multipurpose trees are that which are grown for more than one purpose or benefits. They may provide food in the form of fruit, seeds, or roots; and also provides firewood, medicines, fibres, etc.
(i) Neem (Azadirachta indicd)— Used as insect repellent, antibiotic, firewood and windbreaks.
(ii) Coconut palm (Cocos nucifera)— Used for food, purified water (juice from inside the coconut), roof thatching, firewood, shade and rope making.

5. What are the basic characteristics of a modem landfillsite. List any three and also mention the reasons for their use.
Answer. Characteristics of a modem landfill include:

1. Methods to contain leachate such as lining clay or plastic liners.
2. Compaction and covering of the waste to prevent it from being blown by wind.
3. Installation of a landfill gas extraction system to extract the gas for use in generation of power.

6. How does an electrostatic precipitator work?
Answer. Electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.

7. Observe figure and answer the followiag,questions.
(i) What ecological term is used to describe the DDT accumulation at different trophic levels?
(ii) list any one effect of DDT accumulation on birds.
(iii) Will DDT accumulation lead to eutrophication?
Does it affect the BOD?
Name disease caused by accumulation of any heavy metal.
Answer. (i) Biomagnification
(ii) High concentrations of DDT disturb, calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.
(iii) Yes.
(iv) Yes, it increases the BOD.
(v) Disease caused by eating fish found in water contaminated with industrial waste having mercury is Minamata disease. Cd pollution associated with disease is called “Itai-Itai”. Arsenic (As) poisoning causes “Black foot disease”.

NCERT Exemplar ProblemsMathsPhysicsChemistryBiology

We hope the NCERT Exemplar Class 12 Biology Chapter 16 Environmental Issues help you. If you have any query regarding NCERT Exemplar Class 12 Biology Chapter 16 Environmental Issues, drop a comment below and we will get back to you at the earliest.

NCERT Exemplar Class 12 Biology Chapter 15 Biodiversity and Conservation are part of NCERT Exemplar Class 12 Biology. Here we have given NCERT Exemplar Class 12 Biology Chapter 15 Biodiversity and Conservation. https://www.cbselabs.com/ncert-exemplar-problems-class-12-biology-biodiversity-conservation/

NCERT Exemplar Class 12 Biology Chapter 15 Biodiversity and Conservation

Multiple Choice Questions
Single Correct Answer Type

1. Which of the following countries has the highest biodiversity?
(a) Brazil (b) South Africa (c) Russia (d) India
Answer. (a) Brazil has the highest biodiversity because it is located near equator.

2. Which of the following is not a cause for loss of biodiversity?
(a) Destruction of habitat
(b) Invasion by alien species
(c) Keeping animals in zoological parks
(d) Over-exploitation of natural resources
Answer. (c) Destruction of habitat, invasion by alien species, and over-exploitation, of natural resources are cause for loss of biodiversity.

3. Which of the following is not an invasive alien species in the Indian context?
(a) Lantana (b) Cynodon (c) Parthenium (d) Eichhomia
Answer. (b) Carrot grass (Parthenium), Lantana and water hyacinth (Eichhomia crassipe) are invasive weeds that cause environment damage.

4. Where among the following will you find pitcher plant?
(a) Rain forest of North-East India
(b) Sunderbans
(c) Thar Desert
(d) Western Ghats
Answer. (a) Pitcher plants are found at rain forest’ of North-East India.

5. Which one of the following is not a characteristic feature of biodiversity hot spots?
(a) Large number of species
(b) Abundance of endemic species
(c) Mostly located in the polar regions
(d) Mostly located in the tropics
Answer. (c) Characteristic feature of biodiversity hot spots are large number of species, abundance of endemic species and mostly located in the tropics.

6. Match the animals given in column A with their location in column B.

Choose the correct match from the following:
(a) i—A, ii—C, iii—B, iv—D (b) i—D, ii—C, iii—A, iv—B
(c) i—C, ii—A, iii—B, iv—D (d) i—C, ii—A, iii—D, iv—B
Answer. (d)

7. What is common to the following plants: Nepenthes, Psilotum, Rauwoljia and Aconitum?
(a) All are ornamental plants
(b) All are phylogenic link species
(c) All are prone to over exploitation
(d) All are exclusively present in the Eastern Himalayas.
Answer. (c) Nepenthes, Psilotum, Rauwolfta md Aconitum, all are prone to over-exploitation.

8. The one-homed rhinoceros is specific to which of the following sanctuary
(a) Bhitar Kanika (b) Bandipur (c) Kaziranga (d) Corbett park
Answer.

9. Amongst the animal groups given below, which one has the highest percentage of endangered species?
(a) Insects (b) Mammals (c) Amphibians (d) Reptiles
Answer. (c) Presently, 12% all the birds species, 23% all mammals species, 31% all gymnosperms species and 32% all amphibian species in world face the threat of extinctions.

10. Which one of the following is an endangered plant species of India?
(a) Rauwolfia serpentina  (b) Santalum album (Sandal wood)
(c) Cycas beddonei (d) All of the above
Answer. (d) Endangered (ER): It is facing a high risk of extinction in the wild in the near future if conservation measures are not promptly taken.
E.g.: Red panda (AHums fulgens)

• Giant panda
• Largest lemur Idri idri of Madagascar
• Asiatic Wild Ass (Asinus hemionus khur now restricted to Rann of Kutch)-
•  Lion Tailed Macaque
• Bald Eagle
•  Asiatic lion .
• Drosera indica
• Nepenthes
•  Hombill
• Indian Aconite
•  Bentinckia nicobarica
• Snow leopard
• Rauwolfia serpentina
• Santalum album (Sandal wood)
•  Cycas beddonei

11. What is common to Lantana, Eichhomia and African catfish?
(a) All are endangered species of India.
(b) All are key stone species.
(c) All are mammals found in India.
(d) All the species are neither threatened nor indigenous species of India.
Answer. (d) Lantana, Eichhomia and African catfish, all the species are neither threatened nor indigenous species of India.

12. The extinction of passenger pigeon was due to
(a) Increased number of predatory birds
(b) Over exploitation by humans
(c) Non-availability of the food
(d) Bird flu virus infection
Answer. (b) Humans have always depended on nature for food and shelter but when ‘need’ turns to ‘greed’ it leads to over-exploitation of natural resources. In the last 500 years many species extinctions (Steller’s sea cow, passenger’s pigeon) were due to over-exploitation by human.

13. Which of the following statements is correct?
(a) Parthenium is an endemic species of our country
(b) African catfish is not a threat to indigenous catfishes.
(c) Steller’s sea cow is an extinct animal.
(d) Lantana is popularly known as carrot grass.
Answer. (c) Steller’s sea cow is an extinct animal.

14. Among the ecosystem mentioned below, where can one find maximum biodiversity?
(a) Mangroves (b) Desert
(c) Coral reefs (d) Alpine meadows
Answer. (c) Coral reefs has maximum biodiversity among above options.

15. Which of the following forests is known as the ‘lungs of the planet Earth’?
(a) Tiaga forest (b) Tundra forest
(c) Amazon rain forest (d) Rain forests of North East India
Answer. (c) Amazon rain forest is known as the ‘lungs of the planet Earth’.

16. The active chemical drug reserpine is obtained from
(a) Datura (b) Rauwolfia (c) Atropa (d) Papaver
Answer. (b) The genetic variation shown by the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of potency and concentration of the active chemical (Reserpine) obtained from roots of plants.

17. Which of the following group exhibit more species diversity?
(a) Gymnosperms (b) Algae
(c) Bryophytes (d) Fungi
Answer. (d)

18. Which of the below mentioned regions exhibit less seasonal variations?
(a) Tropics (b) Temperates
(c) Alpines (d) Both (a) and (b)
Answer. (a) Tropical regions exhibit less seasonal variations.

19. The historic convention on Biological Diversity held in Rio de Janeiro in 1992 is known as:
(a) CITES Convention (b) The Earth Summit
(c) G-16 Summit (d) MAB Programme
Answer. (b) The Earth Summit: This historical convention on biological diversity held in Rio-de-Janeiro, Brazil in 1992. Attending nations take appropriate measure for conservation of biodiversity and sustainable utilization of its benefits.

20. What is common to the techniques (i) in vitro fertilisation, (ii) Cryo preservation and (iii) tissue culture?
(a) All are in situ conservation methods.
(b) All are ex situ conservation methods.
(c) All require ultra modem equipment and large space.
(d) All are methods of conservation of extinct organisms.
Answer. (b)

Very Short Answer Type Questions
1. What characteristics make a community stable?
Answer. Characteristics that make a community stable are:
(i) A stable community should not show too much variation in productivity from year to year
(ii) It must be either resistant or resilient to occasional disturbances (natural or man-made)
(iii) It must also be resistant to invasions by alien species.

2. What could have triggered mass extinctions of species in the past?
Answer. (i) Volcanic eruption
(ii) Earthquake
(iii) Extremes of temperatures
(iv) Glaciations
(v) Continental drift

3. What accounts for the greater ecological diversity of India?
Answer. India with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows has a greater ecosystem diversity.

4. According to David Tilman, greater the diversity, greater is the primary productivity. Can you think of a very low diversity man-made ecosystem that has high productivity?
Answer. Agricultural fields like wheat field / paddy field which are also examples of monoculture practices.

5. What does ‘Red’ indicate in the IUCN Red list (2004)?
Answer. Red indicates the species that are at the verge of extinction or threatened species.

6. Explain as to how protection of biodiversity hot spots alone can reduce up to 30% of the current rate of species extinction. 
Answer. Although all the biodiversity hot spots put together cover less than 2 percent of the earth’s land area, the number of species they collectively harbour is extremely high and strict protection of these hot spots could reduce the ongoing mass extinctions by almost 30 per cent.

7. What is the difference between endemic and exotic species?
Answer. Endemic species are restricted, native to a particular geographical region. Exotic species are speeds which are introduced from other geographical regions into an area.

8. How does species diversity differ from ecological diversity?
Answer. Species diversity is the diversity at the species level while ecological diversity is at the ecosystem level diversity.

9. Why is genetic variation important in the plant Rauwolfia vomitorial ?
Answer. Genetic variation affects the production of the drug principle reserpine in the medicinal plant Rauwolfia.

10. What is Red Data Book?
Answer. The Red data book is a compilation of data on species threatened with extinction, maintained by IUCN.

11. Define gene pool.
Answer. Total genes and their alleles in a population is called gene pool.

12. What does the term ‘Frugivorous’ mean?
Answer. Frugivorous means fruit eating organisms.

13. What is the expanded form of IUCN?
Answer. International Union for Conservation of Nature and Natural Resources.

14. Define the terms (i) Bioprospecting (ii) Endemism
Answer. (i) Bioprospecting: Exploring molecular, genetic and species-level diversity for products of economic importance.
(ii) Endemism: Species confined to that region and not found anywhere else.

15. What is common to the species shown in figures A and B?

Answer. Both are invasive weed species.

16. What is common to the species shown in figures A and B?

Answer. Both are examples for Keystone species.

Short Answer Type Questions
1. How is the presently occurring species extinction different from the earlier mass extinctions?
Answer. Species extinction occurring at present is due to anthropogenic causes where as the earlier extinction was due to natural causes.

2. Of the four major causes for the loss of biodiversity (Alien species invasion, habitat loss and fragmentation, over-exploitation and co-extinctions which according to you is the major cause for the loss of biodiversity? Give reasons in support.
Answer. Habitat loss and fragmentation is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests. Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent. They are being destroyed fast. By the time you finish reading this chapter, 1000 more hectares of rain forest would have been lost. The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’) harbouring probably millions of species is being cut and cleared for cultivating soyabeans or for conversion to grasslands for raising beef cattle.

3. Discuss one example, based on your day-to-day observations, showing how loss of one species may lead to the extinction of another.
Answer. In case a species (x) becomes extinct, the plant and animal species (M, N, O, Z) associated within an obligatory way also become extinct. For example.
(i) When a fish species which is a host for a number of parasites becomes extinct the parasite species which are uniquely dependent on the host fish will also become extinct.
(ii) The insects may be polyphagous (feed on more than one plant species) or monophagous (feed on only one particular plant species) in nature. The monophagous insect species are valuable and may become extinct if the plant species upon which it feeds becomes extinct.

4. A species-area curve is drawn by plotting the number of species against the area. How is it that when a very large area is considered the slope is steeper than that for smaller areas?
Answer. Ecologists have discovered that the value of Z (slope of the line) lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region (whether it is the plants in Britain, birds in California or molluscs in New York state, the slopes of the regression line are amazingly similar). But, if you analyse the species-area relationships among very large areas like the entire continents, you will find that the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2). For example, for frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.

5. Is it possible that productivity and diversity of a natural community remain constant over a time period of, say one hundred years?
Answer. Yes, productivity and diversity of a natural climax community remain constant over a time period.

6. There is greater biodiversity in tropical /subtropical regions than in temperate region. Explain.
Answer. (a) Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification.
(b) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
(c) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.

7. Why are the conventional methods not suitable for the assessment of biodiversity of bacteria?
Answer. Many bacteria are not culturable under normal conditions in the laboratory. This becomes a problem in studying their morphological, biochemical and
other characterizations which are useful for their assessment.

8. What criteria should one use in categorizing a species as threatened?
Answer. (i) Extinction risk : Number of the individuals of the species are declining at an alarming pace.
(ii) Predation pressure
(iii) Habitat loss and fragmentation

9. What could be the possible explanation for greater vulnerability of amphibians to extinction as compared to other animal groups?
Answer. Amphibians live in terrestrial habitat but for sexual reproduction they depend on aquatic habitat. Habitat loss affects the amphibians more greatly than other animal groups because it requires both the habitat for its survival.

10. How do scientists extrapolate the total number of species on Earth?
Answer. Scientists make a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the total number of species on earth.

11. Humans benefit from diversity of life. Give two examples.
Answer. Humans derive countless direct economic benefits from nature. For example: ‘

1. Food (cereals, pulses, fruits)
2. Firewood
3. Fibre
4. Construction material .
5. Industrial products (tannins, lubricants, dyes, resins, perfumes)
6. Products of medicinal importance.

12. List any two major causes other than anthropogenic causes of the loss of biodiversity.
Answer. (i) Volcanic storms (ii) Co-extinctions

13. What is an endangered species? Give an example of an endangered plant and animal species each.
Answer. Endangered (ER): It is facing a high risk of extinction in the wild in the near future if conservation measures are not promptly taken.
E.g., Red panda (Ailurus fulgens), Drosera indica.

14. What are sacred groves and their role in biodiversity conservation?
Answer. In many cultures, tracts of forest were set aside, and all the trees and wildlife within were venerated and given total protection. Such sacred groves are found in Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra and the Sarguja. Chanda and Bastar areas of Madhya Pradesh. In Meghalaya, the sacred groves are the last refuges for a large number of rare and threatened plants.

15. Suggest a place where one can go to study coral reefs, mangrove vegetation and estuaries.
Answer. Coral reefs—Andaman and Nicobar Mangrove vegetation—West Bengal Estuaries—Kerala, Karnataka, Tamil Nadu

16. Is it true that there is more solar energy available in the tropics? Explain briefly.
Answer. As one moves from the equator to the polar regions, the length of the day decreases and the length of the night increases. The length of day and night are the same at the equator.

17. What is co-extinction? Explain with a suitable example.
Answer. When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

Long Answer Type Questions
1. Elaborate how invasion by an alien species reduces the species diversity of an area.
Answer. Some possible explanations are that the alien species may be:

1. Vigorously growing and compete with the natural plants for minerals, water etc. The less vigorous local species may be eliminated.
2. Natural pests and predators of the alien species may not be present in the introduced area-leading to proliferation in their number.
3. The introduced species may harm the local species by production of chemicals (Amensalism).
4. The alien species by proliferation may make conditions unfavourable for the growth of local native plants. (e.g.,Eichhomia)

2. How can you, as an individual, prevent the loss of biodiversity?
Answer. The loss of biodiversity can be prevented by:

1.  Practise of recycling waste paper etc.
2. Judicious exploitation of medicinal and commercial plants and animals.
3.  Generating awareness among the public on the importance of biodiversity, conversation through skits, screening of films, lectures etc.

Teaching people how to reduce green house gases emissions, through alternate eco friendly green technologies like use of solar energy, wind energy, biogas, vermicompost, organic farming etc.

3. Can you think of a scientific explanation, besides analogy used by Paul Ehrlich, for the direct relationship between diversity and stability of an ecosystem?
Answer. David Tilman’s long-term ecosystem experiments using outdoor plots provide some tentative answers. Tilman found that plots with more species showed less year-to-year variation in total biomass. He also showed that in his experiments, increased diversity contributed to higher productivity. Although, we may not understand completely how species richness contributes to the well-being of an ecosystem, we know enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet.

4. Though the conflict between humans and wildlife started with the evolution of man, the intensity of conflict has increased due to the activities of modem man. Justify your answer with suitable examples.
Answer. From a study of the history of life on earth through fossil records, we leam that large-scale loss of species like the one we are currently witnessing have also
happened earlier, even before humans appeared on the scene. During the long period (> 3 billion years) since the origin and diversification of life on earth there were five episodes of mass extinction of species. How is the ‘ Sixth Extinction’ presently in progress different from the previous episodes? The difference is in the rates; the current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times and our activities are responsible for the faster rates. Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years. The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than 2,000 species of native birds. The IUCN Red List (2004) documents the extinction of 784 species. The last twenty years alone have witnessed the disappearance of 27 species.

5. What is an ecosystem service? List any four important ecosystem services provided by the natural ecosystems. Are you in favour or against levying a charge on the service provided by the ecosystem?
Answer. The products of ecosystem processes are named as ecosystem services, for example, healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values. Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a hefty price tag. Robert Constanza and his colleagues have very recently tried to put price tags on nature’s life-support services. Researchers have put an average price tag of US $ 33 trillion a year on these fundamental ecosystems services, which are largely taken for granted because they are free. This is nearly twice the value of the global gross national product GNP which is (US $ 18 trillion).

6. Describe the consumptive use value of biodiversity as food, drugs and medicines, fuel and fiber with suitable examples.
Answer. The direct use values where the biodiversity products can be harvested and consumed directly are called consumptive use value of biodiversity, humans derive countless direct economic benefits from nature food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes ) and products of medicinal importance. More than 25 per cent of the drugs currently sold in the market worldwide are derived from plants and 25,000 species of plants contribute to the traditional medicines used by native peoples around the world.

7. Species diversity decreases as we move away from the equator towards the poles. What could be the possible reasons?
Answer. In general, species diversity decreases as we move away from the equator towards the poles. The possible reason could be as follows:

1. Temperature decreases as we move away from the equator towards the poles.
2. The intensity of sun light decreases as we move away from the equator towards the poles and hence productivity.
3. In polar regions the temperature is very low so most of the organisms cannot survive in that habitat.

8. Explain briefly the ‘rivet popper hypothesis’ of Paul Ehrlich.
Answer. Paul Ehrlich proposed Rivet popper hypothesis to show the effect of biodiversity loss on the ecosystem. An airplane (ecosystem) has thousands of rivets. Popping of rivets (causing a species to become extinct) by passenger may not affect flight safety (Proper functioning of the ecosytem) in the beginning but the plane will become dangerously weak over a period of time. Removal of a rivet of a critical part like wing (key species that derive major ecosystem functions) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or window inside the plane.

9. The relation between species richness and area for a wide variety of taxa turns out to be a rectangular hyperbola. Give a brief explanation.
Answer. During his pioneering and extensive explorations in the wilderness of South American jungles, the great German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola.

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NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem are part of NCERT Exemplar Class 12 Biology. Here we have given NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem. https://www.cbselabs.com/ncert-exemplar-problems-class-12-biology-ecosystem/

NCERT Exemplar Class 12 Biology Chapter 14 Ecosystem

Multiple Choice Questions
Single Correct Answer Type

1. Decomposers like fungi and bacteria are
i. Autotrophs ii. Heterotrophs
iii. Saprotrophs iv. Chemo-autptrophs
Choose the correct answer:
(a) i and iii (b) i and iv (c) ii and iii (d) i and ii
Answer. (c) Decomposers like fungi and bacteria are heterotrophs and saprotrophs.

2. The process of mineralisation by micro organisms helps in the release of
(a) Inorganic nutrients from humus
(b) Both organic and inorganic nutrients from detritus
(c) Organic nutrients from humus
(d) Inorganic nutrients from detritus and formation of humus.
Answer. (a)

• The process of mineralisation by microorganisms helps in the release of inorganic nutrients from humus.
• The humus is further degraded by some microbes and release of inorganic nutrients occur by the process called mineralisation.

3. Productivity is the rate of production of biomass expressed in terms of
i. (kcalm^-3 )yr^-1 ii. g^-2 y^-1 r
iii. g^-1yr^-1 iy. (kcal m^-2) yr^-1
(a) ii (b) iii (c) iiandiv (d) i and iii
Answer. (c) Productivity is the rate of production of biomass expressed in terms of g^-1yr^-1 and (heal m^-2) yr^-1.

4. An inverted pyramid of biomass can be found in which ecosystem?
(a) Forest (b) Marine (c) Grassland (d) Tundra
Answer. (b) In terrestrial ecosystem pyramid of biomass is generally upright. The pyramid of biomass in sea or lake is generally inverted because the biomass of fishes for exceeds that of phytoplankton.

5. Which of the following is not a producer?
(a) Spirogyra (b) Agaricus (c) Volvox (d) Nostoc
Answer. (b) Spirogyra, Volvox and Nostoc are producers. Agaricus is a fungus.

6. Which of the following ecosystems is most productive in terms of net primary . production?
(a) Deserts (b) Tropical rain forests
(c) Oceans (d) Estuaries
Answer. (b) Tropical rain forests ecosystems is most productive in terms of net primary production.

7. Pyramid of numbers is
(a) Always upright (b) Always inverted
(c) Ether upright or inverted (d) Neither upright nor inverted
Answer. (c) Pyramid of number in grassland or forest or pond ecosystem is upright. In parasitic food chain, the pyramid of number is inverted. In an ecosystem dominated by trees, the pyramid of number is spindle shaped/inverted.

8. Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis?
(a) Less than 1% (b) 2-10% (c) 30% (d) 50%
Answer. (b) Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis 2-10%.

9. Among the following, where do you think the process of decomposition would be the fastest?
(a) Tropical rain forest (b) Antarctic
(c) Dry arid region (d) Alpine region
Answer. (a)

• Warm and moist environment favour decomposition. Decomposition is largely an oxygen requiring process. Low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials.
• The process of decomposition would be the fastest is tropical rain forest.

10. How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?
(a) 1% (b) 10% (c) 40% (d) 90%
Answer. (b) 10% of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores.

11. During the process of ecological .succession the changes that take place in communities are
(a) Orderly and sequential
(b) Random
(c) Very quick
(d) Not influenced by the physical environment
Answer. (a) The gradual and fairly predictable change in the species composition of a given area is called ecological succession. An important characteristic of all the communities is that their composition and structure constantly change in response to the changing environmental conditions. These changes are orderly and sequential parallel with the changes in the physical environment.

12. Climax community is in a state of
(a) Non-equilibrium (b) Equilibrium
(c) Disorder (d) Constant change
Answer. (b) Climax community is in a state of equilibrium.

13. Among the following bio-geo-chemical cycles which one does not have losses due to respiration?
(a) Phosphorus (b) Nitrogen
(c) Sulphur (d) All of the above
Answer. (d) Phosphorus, nitrogen and sulphur bio-geo-chemical cycles does not have losses due to respiration.

14. The sequence of communities of primary succession in water is
(a) Phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses and trees
(b) Phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees
(c) Free-floating hydrophytes, sedges, phytoplankton, rooted hydrophytes, grasses and trees
(d) Phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees
Answer. (b) The sequence of communities of primary succession in water is phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees

15. The reservoir for the gaseous type of bio-geo chemical cycle exists in
(a) Stratosphere (b) Atmosphere (c) Ionosphere (d) Lithosphere
Answer. (b) The reservoir for the gaseous- type of bio-geo-chemical cycle exists in atmosphere.

16. Which of the following type of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 100 mm
(a) Grassland (b) Shrubby forest
(c) Desert (d) Mangrove
Answer. (c) Desert ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 100 mm.

17. The zone at the edge of a. lake or ocean which is alternatively exposed to air and immersed in water is called
(a) Pelagic zone (b) Benthic zone
(c) Lentic one (d) Littoral zone
Answer. (d) The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called littoral zone.

18. If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be
(a) Scavenger (b) Tertiary producer
(c) Tertiary consumer (d) Secondary consumer
Answer. (c)

If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be tertiary consumer.

19. Edaphic factor refers to
(a) Water (b) Soil
(c) Relative humidity (d) Altitude
Answer. (b) Edaphic factor refers to soil.

20. Which of the following is <an ecosystem service provided by a natural ecosystem?
(a) Cycling of nutrients
(b) Prevention of soil erosion
(c) Pollutant absorption and reduction of the threat of global warming
(d) All of the above
Answer. (d) Cycling of nutrients, prevention of soil erosion and pollutant absorption and reduction of the threat of global warming is an ecosystem service provided by a natural ecosystem.

Very Short Answer Type Questions
1. Name an organism found as secondary carnivore in an aquatic ecosystem.
Answer. Catfish/water snake etc.

2. What does the base tier of the ecological pyramid represent?
Answer. Producers

3. Under what conditions would a particular stage in the process of succession revert back to an earlier stage?
Answer. Natural or human induced disturbances like fire, deforestation etc.

4. Arrange the following as observed in vertical stratification of a forest: Grass, Shrubby plants, Teak, Amaranths
Answer. Grass, Amaranths, Shrubby plants, Teak

5. Name an omnivore which occurs in both grazing food chain and the decomposer food chain.
Answer. Sparrow/crow

6. Justify the pitcher plant as a producer.
Answer. It is chlorophyllous and is thus capable of photosynthesis.

7. Name any two organisms which can occupy more than one trophic level in an ecosystem.
Answer. Man and sparrow ete.

8. In the North East region of India, during the process of Jhum cultivation, forests are cleared by burning and left for regrowth after a year of cultivation. How would you explain the regrowth of forest in ecological term?
Answer. The regrowth of forest is called secondary succession.

9. Climax stage is achieved quickly in secondary succession as compared to primary succession. Why?
Answer. The rate of succession is much faster in secondary succession as the substratum (soil) is already present as compared to primary succession where the process starts from a bare area (rock).

10. Among bryophytes, lichens and fern which one is a pioneer species in a xeric succession?
Answer. Crustose lichens.

11. What is the ultimate source of energy for the ecosystems?
Answer. Sunlight (solar radiation)

12. Is the common edible mushroom an autotroph or a heterotroph?
Answer. Heterotroph (as it does not have chlorophyll)

13. Why are oceans least productive?
Answer. Oceans are least productive because they do not receive sufficient sunlight which is necessary for 1° productivity.

14. Why is the rate of assimilation of energy at the herbivore level called secondary productivity?
Answer. It is because the biomass available to the consumer for consumption is a resultant of the primary productivity from plants.

15. Why are nutrient cycles in nature called biogeochemical cycles?
Answer. Nutrient cycles in nature called biogeochemical cycles because the cycling of nutrients occurs between living organisms (bio) and non-living things-geo- (rocks, air and water, etc.)

16. Give any two examples of xerarch succession.
Answer. (a) Bare rocks (xerosere)
(b) Sandy areas (psammosere)

17. Define self sustainability.
Answer. The degree at which the system can sustain itself without external support is called self sustainability.

18. Given below is a figure of an ecosystem. Answer the following questions.

(i) What type of ecosystem is shown in the figure?
(ii) Name any plant that is characteristic of such ecosystem.
Answer. (i) Desert ecosystem
(ii) Opuntia, Cacti and Acacia

19. What is common to earthworm, mushroom, soil mites and dung beetle in an ecosystem.
Answer. They are all detritivores i.e., decomposing organisms which feed on dead remains of plants and animals.

Short Answer Type Questions
1. Organisms at a higher trophic level have less energy available. Comment.
Answer. The transfer of energy follows 10 per cent law – only 10 per cent of the
energy is transferred to each trophic level from the lower trophic level. So, higher trophic level have less energy as- compared to lower trophic level.

2. The number of trophic levels in an ecosystem are limited. Comment.
Answer. In a food chain, only 10% of the total amount of energy is passed on to the next trophic level from the previous trophic level. So, there is a decrease in the amount of energy available at the successive trophic levels. As we move higher up in the food chain the amount of energy diminishes to a level at which it cannot sustain any trophic level, thereby limiting the number of trophic levels.

3. Is an aquarium a complete ecosystem?
Answer. Aquarium has all the biotic and abiotic components of an ecosystem, so, aquarium is a complete ecosystem.

4. What could be the reason for the faster rate of decomposition in the tropics?
Answer. The rate of decomposition is regulated by climatic factors like temperature and soil moisture as they have an effect on the activities of soil microbes. The
tropics with its hot and humid.climaticcondition provides an environment which is ideal for the microbes to speed up the process of decomposition.

5. Human activities interfere with carbon cycle. List any two such activities.
Answer. Human activities have significantly influenced the carbon cycle. Rapid
deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere.

6. Flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic. Explain.
Answer. The energy from the sun reaches the food chain through the primary producers (plants). This energy is passed on through successive trophic levels in the food chain. The energy transfer in the food chain follows the 10 percent law where in only 10% of the energy is transferred from one trophic level to the next successively. So, the movement of energy is only in one direction from lower to higher trophic level.

7. Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs, what are microbes referred to as? How do the microbes fulfil their energy requirements?
Answer. Microbes are referred to as heterotrophs and saprotrophs. They fulfil their energy requirement by feeding on dead remains of plants and animals through the process of decomsposition.

8. Poaching of tiger is a burning issue in today’s world. What implication would this activity have on the functioning of the ecosystem of which the tigers are an integral part?
Answer. Poaching (hunting) of tiger disturbs the ecological balance in ecosystem. Tigers are important predator of forest. Predator keeps prey population under control. Due to hunting of tiger its population decreases, hence the population of deer (prey) increases and interspecific competition occurs between them. Due to increase in prey population (that feeds on vegetation/grass), vegetation destroyed rapidly which causes ecological disturbance.

9. In relation to energy transfer in ecosystem, explain the statement “10 kg of deer’s meat is equivalent to 1 kg of lion’s flesh”.
Answer. Transfer of energy in an ecosystem follow 10% law, i.e., only 10% energy is transferred from one trophic level to higher trophic level. So, if lion feeds on deer than 10 kg of deer’s meat will form 1 kg of lion’s flesh.

10. Primary productivity varies from ecosystem to ecosystem. Explain.
Answer. Primary productivity varies from ecosystem to ecosystem because it depends on the plant species inhabiting the area and their photosynthetic activity. It also depend on various environmental factors.

11. Sometimes due to biotic/abiotic factor the climax remain in a particular serai stage (pre climax) without reaching climax. Do you agree with this statement? If yes, give a suitable example.
Answer. It is true that any change in the. abiotie/biotic factor will arrest a particular serai stage leading to a pre-climax condition before the climax stage is achieved. This can happen in cases of forest fires, landslides, changes in soil characteristics, increase in herbivore population leading to overgrazing.

12. What is an incomplete ecosystem? Explain with the help of suitable example.
Answer. An ecosystem is a functional unit with biotic and abiotic factors interacting
with one another resulting in a physical structure. Absence of any component will make an ecosystem incomplete as it will hinder the functioning of the ecosystem. Examples of such an ecosystem can be a fish tank or deep aphotic zone of the oceans where producers are absent.

13. What are the shortcomings of ecological pyramids in the study of ecosystem?
Answer. The ecological pyramid assumes a simple food chain and does not
accommodate food webs. Thereby,’ it does not take irlto account the fact that species may belong to two or more trophic levels at a time. Also saprophytes despite their vital rolg in ecosystem are given no place in the ecological pyramids.

14. How do you distinguish between humification and mineralisation?
Answer. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients . The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.

15. Fill in the trophic levels (1, 2, 3 and 4) in the boxes provided in the figure.

Answer.

16. The rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen, pH of the soil substratum, temperature etc. Discuss.
Answer. The decomposition of detritus is due to activities of micro-organisms. The rate of growth of microbes is affected by temperature. The pH of substratum affects the composition of microbes (acidophiles / basophiles) which degrade the dead organic matter. If oxygen is present, aerobic degradation occurs. In the absence of oxygen anaerobiosis sets in and there will be incomplete degradation. Also, the degradation is due to activity of exo enzymes secreted by the microbes and the activity of enzyme is affected by factors such as temperature etc.

Long Answer Type Questions
1. A farmer harvests his crop and expresses his harvest in three different ways.
(a) I have harvested 10 quintals of wheat.
(b) I have harvested 10 quintals of wheat today in one acre of land.
(c) I have harvested 10 quintals of wheat in one acre of land, 6 months after sowing.
Do the above statements mean one and the same thing. If your answer is yes, give reasons. And if your answer is ‘no’ explain the meaning of each expression.
Answer. No, the meaning of above statements is different
(a) In this statement farmer gives information of only the quantity of the wheat but area and time period is not given.
(b) In this statement farmer gives information of primary production that is quantity and area but not the time period.
(c) In this statement farmer gives information of primary productivity that is quantity, area and time period all are given.

2. Justify the following statement in terms of ecosystem dynamics. “Nature tends to increase the gross primary productivity, while man tends to increase the net primary productivity”.
Answer. Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers).
• Nature tends to increase the gross primary productivity so that it can utilise much of the solar energy and convert it into food.
• Man tends to increase the net primary productivity so that sufficient food is provided to the growing human population.

3. Which of the following ecosystems will be more productive in terms of primary productivity? Justify your answer. A young forest, a natural old forest, a shallow polluted lake, alpine meadow.
Answer. Among these a young forest will be more productive because primary productivity depends on the plant species inhabiting a particular area. A young forest grows more rapidly than old forest hence it has more primary productivity.
A shallow polluted lake and alpine meadow has lower number of producers hence shows lower primary productivity.

4. What are. the three types of ecological pyramids? What information is conveyed by each pyramid with regard to structure, function and energy in the ecosystem?
Answer. The three ecological pyramids that are usually studied are (a) pyramid of number (b) pyramid of biortiass and (c) pyramid of energy.
• Any calculations of energy content, biomass, or numbers has to include all organisms at that trophic level. No generalisations we make will be true if we take only a few individuals at any trophic level into account. Also a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.
• In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level.

5. Write a short note on pyramid of numbers and pyramid of biomass.
Answer. Pyramid of Number
• Pyramid of number deals with number of individuals in a trophic level.

• In Grassland ecosystem only 3 top carnivores are supported in an ecosystem based on production of nearly 6 million plants.
• Pyramid of number in grassland or forest or pond ecosystem is upright.

• In parasitic food chain, the pyramid of number is inverted.
• In an ecosystem dominated by trees the pyramid of number shaped/inverted.

• Among the grassland, pond and forest ecosystem, the number of primary producers per unit area would be maximum in pond ecosystem.
Pyramid of Biomass
• Total amount of living material at various trophic level of a food chain is depicted by pyramid of biomass.

• In most of the ecosystem, the pyramids of number and biomass are upright.
• In terrestrial ecosystem pyramid of biomass is generally upright.
• The pyramid of biomass in sea or lake is generally inverted because the biomass of fishes for exceeds that of phytoplankton.

6. Given below is a list of autotrophs and heterotrophs. With your knowledge about food chain, establish various linkages between the organisms on the principle of ‘eating and being eaten’. What is this inter-linkage established known as?
Algae, Hydrilla, grasshopper, rat, squirrel, crow, maize plant, deer, rabbit, lizard, wolf, snake, peacock, phytoplankton, crustaceans, whale, tiger, lion, sparrow, duck, crane, cockroach, spider, toad, fish, leopard, elephant, goat, Nymphaea, Spirogyra.
Answer. Primary Producer’s (First trophic level): Algae, Hydrilla, maize plant, Phytoplankton, Nymphaea, Spirogyra.
Primary Consumer (Second trophic level): Crustaceans, grasshopper, deer, mouse, squirrel, rabbit, elephant, goat.
Secondly Consumer (Third trophic level): Spider, cockroach, lizard, wolf, snake, toad, fish, crane.
Top carnivore (Fourth trophic level): Lion, Tiger.

7. “The energy flow in the ecosystem follows the second law of thermodynamics.” Explain.
Answer. Ecosystems need a constant supply of energy to synthesise the molecules they require, to counteract the universal tendency toward increasing disorderliness. Hence, ecosystems are not exempt from the Second Law of thermodynamics.

8. What will happen to an ecosystem if:
(a) All producers are removed;
(b) All organisms of herbivore level are eliminated; and
(c) All top carnivore population is removed
Answer. (a) Reduction in primary productivity. No biomass available for consumption by higher trophic levels / heterotrophs
(b) Increase in primary productivity and biomass of producers.
Carnivores population will subsequently dwindle due to food shortage.
(c) Increase in number of herbivores
• Overgrazing by herbivores
• Desertification

9. Give two examples of artificial or mail made ecosystems. List the salient features by which they differ from natural ecosystems.
Answer. Crop fields and an aquarium considered as man-made ecosystems. In artificial ecosystems the biotic and abiotic components of ecosytems are maintained artificially by regular feeding and clearing of aquarium and regular irrigation and sowing of seeds in crop field ecosystem. Natural ecosystem self sustains biotic and abiotic components of an ecosystem.

10. The biodiversity increases when one moves from the pioneer to the climax stage. What could be the explanation?
Answer. In the successive serai stages there is a change in the diversity of species of organisms, increase in the number of species and organisms as well as an • increase in the total biomass. Description of ecological succession usually focuses on changes in vegetation. However, these vegetational changes in turn affect food and shelter for various types of animals. Thus, as succession proceeds, the numbers and types of animals and decomposers also change.

11. What is a biogeochemical cycle? What is the role of the reservoir in a biogeochemical cycle? Give an example of a sedimentary cycle with reservoir located in earth’s crust.
Answer. The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling. Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, water). Nutrient cycles are of two types: (a) gaseous and (b) sedimentary.
The function of the reservoir is to meet with the deficit which occurs due to imbalance in the rate of influx and efflux. For the sedimentary cycle (e.g., sulphur and phosphorus cycle), the reservoir is located in Earth’s crust.

12. What will be the P/R ratio of a climax community and a pioneer community? What explanation could you offer for the changes seen in P/R ratio of a pioneer community and the climax community?
Answer. P/R (Production/Respiration) ratio shows the relationship between gross production and respiration.
In climax community the P/R ratio will be 1. In pioneer community the P/R ratio will be more than one.

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