Archive for January 25th, 2013

Marking Scheme and Solution hints for Sample paper 2 Class XII


Sample Question Paper 2

Class XII

Biology – 2012-13

1. (i) the pollen grains are sticky. 1

2. (p+q)

2 = p2 + 2pq + q2 = 1 1

3. First exposure to the infection works as vaccination,  the immune system of the

body gets familiar with the nature of microorganisms and specific antibodies can

be produced against infection.  ½+½=1

4. Ethidium bromide (EtBr) 1

5. Centrifugation and centrifuge            ½+½=1

6. Normal Endonuclease : makes cut at random position within a DNA ½

Restriction endonuclease: makes cut only at specific position within a DNA ½

7. – Depletion of dissolved oxygen in water        ½

– Nutrient enrichment ½

8. Each trophic level has a certain mass of living material at a particular time called

as the standing crop. ½

The standing crop is measured as the mass of living organisms (biomass) or the

number in a unit area. The biomass of a species is expressed in terms of fresh or

dry weight. ½

9. Amniocentasis – A foetal sex diagnostic test based on the chromosomal pattern in

the amniotic fluid surrounding the developing embryo. 121

It is justified to ban the process for diagnosis of sex to legally check the increasing

female foeticides.




Phenotypes : 50% daughter normal (XX)

50% daughter carrier (XX)

50% son normal (XY)

50% son haemophilic (X Y) ½ ×4=2

11. Original stock of seed eating finches migrated to different habitats (of Galapagos

Islands), adapted to different feeding methods, by altered beak structure, evolved

into different types of finches. ½ ×4=2

12. Testcross , Cross purple flower plant with a (homozygous) recessive plant  with

white flowers, if all the flowers of the progeny of the above are purple , the plant

is homozygous dominant  ½ ×4=2

13. Lymphocytes are not immortal but are short lived , hence patient requires periodic

infusion of such genetically  engineered lymphocytes , however if a gene

producing ADA is isolated from marrow cells, and introduced into the cells at

early embryonic stages it could be a permanent cure. ½ ×4=2


XX X Y

14. PCR, because it is a thermostable DNA polymerase enzyme, gets isolated  from

bacteria Thermus aquaticus from hot water springs, does not get denatured at high

temperature during PCR and works as normal DNA polymerase enzyme. ½ ×4=2

15. Detrivore feeds on dead plants and animals / detritus  ½

Example : Earthworm / Nematodes  ½

Decomposer breaks down complex ( organic ) matter into simpler ( inorganic )

matter ½+½

Example : Fungus / Bacteria.

16. DDT neither excreted nor metabolized and keeps accumulating in the food chain,

interferes with Calcium metabolism, decline in bird  population / due to thinning

of egg shell / premature breaking of eggs, bio-magnification. ½ ×4=2

17. Pioneer Community (Species) – Community that invades a bare area                       1

Climax community – Last sustainable community that is in near equilibrium with

the environment                                                                                                                 1

18. a) Salmonella typhi

b) Streptococcus pneumoniae

c) Wuchereria bancrofti and Wuchereria malayi

d) Entamoeba histolytica ½×4=2


a) Acquired Immuno Deficiency Syndrome

b) Enzyme Linked Immuno Sorbent Assay                                                     1×1=2

19. (i) Regeneration of endometrium.

(ii) Uterus gets highly vascularised, ready for embryo implantation

(iii) Disintegration of the endometrium leading to menstruation  1×3=3

20. IVF – In Vitro Fertilization

ZIFT – Zygote Intra Fellopian Transfer

IUI – Intra – Uterine Insemination

MTP – Medical Termination of Pregnency   ½×4=2

21. Since there are only four bases which code for twenty aminoacids, the code should

be madeup of three bases i.e. (4 x 4 x 4) = 64 codons ; a number more than the

required.  1

If the codon consists of four letters, only (4 x 4) only  sixteen codes are possible,

which is less than the required. 1

• As the ribosome moves on mRNA the codons are read in a contiguous

fashion 1

22. DNA sequences which are repeated many a times, show a high degree of

polymorphism, and form a bulk of DNA in a genome, called as satellite DNA  1½

DNA from every tissue from an individual, shows  the same degree of

polymorphism and  is heritable,  hence very useful in DNA finger printing  1½

23. • Microbes naturally present in the sewage are employed in the secondary

treatment of the sewage.

• The effluent from the primary treatment is passed into large aeration tanks.

• This allows the rapid growth of aerobic microbes into flocs which consume the

organic matter of the sewage and reduce the BOD.

• Then the  effluent is passed into a settling tank, where the flocs are allowed to

sediment forming the activated sludge.

• Major parts of this activated sludge is pumped into anaerobic sludge digesters,

where the anaerobic bacteria digest microbes in the activated sludge.

• During this digestion bacteria produce a mixture of gases like methane,

hydrogen sulphide and carbon dioxide, which form the biogas and can be used

as a source of energy. The effluent is generally released into rivers and streams.

24. BOD – Biological Oxygen Demand, it refers to the amount of oxygen that would be

consumed if all the organic matter in one litre of water were oxidized by Bacteria.

The BOD test measures the rate of uptake of oxygen by microorganisms in a

sample of water  and thus, indirectly BOD is a measure of the organic matter

present in the water. The greater is a measure of BOD of waste water; more is its

polluting potential.

25. (i) Origin of replication / ori  site  – From here the replication starts (and any

piece of DNA when linked, can be made to replicate within the host cell)

(ii) At least two  Selectable markers – Helps in identifying and eliminating non


(iii) Unique Restriction sites – The foreign DNA links to this region of the plasmid


26. Population interaction:

Species A Species B Name of interaction

+ + Mutualism

– – Competition

+ – Predation

+ – Parasitism

+ 0 Amensalism

(i) + Beneficial- Bothe species benefit in Mutualism e.g. lichens

(ii)  – Detrimental – Both species loose in competition e.g. (detrimental)

– In Predation & Parasitism the predator and the parasite benefits but it is

detrimental to the other species (host and prey respectively)

(iii)  0 Neutral – In commensalism one species is benefits but the other is neither

harmed nor benefitted.  3

27. Plants: Ephemeral mode (complete life cycle in short period) / Deep tap roots /

Deciduous leaves / Waxy cuticle / sunken stomata / Succulence to

store water / C4 Pathway of Photosynthesis. (Any 3) 1½

Animals: No sweating / uricotelic / deposition of fat in sub epidermal

layer / burrowing nature / thick skin / body covered with

scales (Any three) 1½


Ans. (i) Particulate matter will pollute the air  1

(ii) Use of CNG / Phasing out of old vehicles / Use of unleaded  petrol /

Use of low sulphur fuel / Use of catalytic converters / Application of

stringent pollution level norms (Any four) 2

28. (a)3

(b)  Fallopian tube  1

zygote undergoes, cleavage to form, blastomeres & develop into 8-16

cell stage- the morula ½+½


(b) Egg cell – Forms zygote (2n)

Polar nuclei – Primary endosperm nucleus (3n)

Antipodals – Degenerates ½×3=1½

29. (a) DNA synthesis ½

(b) i) Semi conservative

ii) Semi discontinuous

iii) Unidirectional

(c) DNA polymerase III – adds nucleotides

DNA polymerase I – fills the gaps

RNA primase – brings primer

Helicase – breaks hydrogen bond

Toisomerase – Causes unwinding

Gyrase – relaxes supercoiling

DNA ligase – joins Okazaki fragments


Inheritance of flower colour in Pisum sativum

Pea Plant

Parent VV x vv

(violet)        (white)

Gamete V  v

F1         V v (violet) 1½

This inheritance pattern follows law of dominance, that is between the two alleles

of the flower colour (gene) the dominant allele is expressed( phenotypically), over

the recessive    1

Any 3 enzymes and their


1 x 3 = 3128

In the case of  Antirrhinum(snap dragon) the dominant flower colour is red. white

in recessive ½


Parent RR x rr

(Red)        (white)

Gamete R  r

F1                                                   R r (Pink)

This is the case of incomplete dominance, it is because the allele for red colour is

not completely dominant over its recessive allele, law of dominance not exhibited


30. (a) I will support  Aditya’s concern for the health of his family. Both

Active as well as Passive smoking is injurious to health as smoking is

associated with increased incidence of cancers of lungs, urinary

bladder, throat and oral cavity, bronchitis, emphysema / coronary

heart disease / gastric ulcer etc.          2

b) (i) By printing statutory warning on cigarette packets.

(ii) As  advertisement in mass media such as Television, Newspaper,

Internet etc.

(iii) Designating Non smoking Zones in public areas such as

Restaurants, Airports etc.         3



Class -XII Sample Paper 2 Biology

Class -XII  Sample Paper

Time : 3 hrs.                     MM.: 70

General Instructions:

i. All questions are compulsory.

ii. This question paper consists of four Sections A, B, C and D.  Section A contains 8 questions of

one mark each, Section B is of 10 questions of two marks each, Section C is of 9 questions of three

marks each and Section D is of 3 questions of five marks each.

iii. There is no overall choice.  However, an internal choice has been provided in one question of 2 marks, one question of  3  marks and  two questions of  5 marks weightage.  A student has to attempt only one of the alternatives in such questions.

iv. Wherever necessary, the diagrams drawn should be neat and properly labelled.

Section A (1×8 = 8)

1. The following statements describe the wind-pollinated plants. Which one of

these statements is incorrect?

(i)       The pollen grains are sticky.

(ii)      Stamens are well exposed.

(iii)     Flowers often have a single ovule.

2. Write the formula to calculate allele frequency in future generations according to

Hardy – Weinberg genetic equilibrium.

3. “Pranay suffered from measles at the age of 10 years. There are rare chances of his

getting infected with the same disease for the rest of his life.” Give reason for the


4. Give the name of the carcinogenic dye which is used to stain gel to make the DNA

visible under UV light.

5. Which main technique and instrument is used to isolate DNA from a plant cell?

6. How is the action of  normal endonuclease enzymes different from that of

restriction endonucleases?

7. ‘Eutrophication’ is the natural aging of a lake. Mention  another  feature which

defines this term.

8. How are standing crop and biomass related to each other?

Section B (2 × 10 = 20)

9. What do you understand by amniocentasis? Why is there a statutory ban on this?

Give reason.

10. A non-haemophilic couple was informed by their doctor that there is possibility of

a haemophilic child being born to them. Draw a checker board and find out the

percentage of possibility of such a child among the progeny.

11. How do Darwin’s finches illustrate adaptive radiation?

12. In a particular plant species, majority of the plants bear purple flowers. Very few

plants bear white flowers. No intermediate colours are observed. If you are given a

plant bearing purple flowers, how would you ascertain that it is a pure breed for

that trait? Explain.

13. Why is the introduction of genetically engineered lymphocytes  into an  ADA

deficiency patient not a permanent cure? Suggest a possible permanent cure.

14. In which technique do we use Taq polymerase enzyme and why?

15. Differentiate between a detrivore and a decomposer giving an example of each.116

16. DDT content in the water of a lake that supplies drinking water to the nearby

villages is found to be 0.004 ppm. The pelicans of that area are reported to have 2.6

ppm of DDT. Why has the concentration increased in these birds? What possible

harm will this cause to the bird population? Name the phenomenon.

17. The gradual and predictable change in the species composition of a given area is

called ecological succession. What do you understand with the pioneer and climax

community in this context?

18. Write the names of causal organisms of the following:

a) Typhoid

b) Pneumonia

c) Elephantiatis  (Filariasis)

d) Amoebiasis


Expand the following:



Section – C (3 × 9 = 27)

19.Study the graph given above  showing the levels of ovarian hormones during

menstruation  and correlate the uterine events that take place according to the

hormonal levels on:

(i)     6-15 days

(ii)    16 – 25 days

(iii)   26 – 28 days (if the ovum is not fertilized)

20. Expand the following and explain any one of them.

a) IVF                                         b) ZIFT

c) IUI                                                    d) MTP

21. What is the genetic basis for proof that codon is a triplet and is read in a

contiguous manner without punctuations?

22. What is satellite DNA in a genome? Explain their role in DNA fingerprinting.

23. “Microbes play a dual role when used for sewage treatment as they not only help

to retrieve usable water but also generate fuel”. Explain.

24. What does BOD of a water body stand for? How is it related to water pollution?

25. A vector is engineered with three features which facilitate its cloning within the

host cell. List the three features and explain each one of them.

26. Interspecific interactions of two species of any population may be beneficial,

detrimental or neutral. Explain each of them with the help of suitable examples.

27. Water is very essential for life.  List any three features that enable  plants and

animals to survive in water scarce environment.


(a) What would be the consequence of failure of the electrostatic precipitator of a

thermal plant?

(b) Mention any four methods by which vehicular air pollution can be


Section D (5 × 3 = 15)

28. (a) Draw a labelled diagram of sectional view of human ovary showing different

stages of oogenesis.

(b) Where is morula formed in humans? Explain the process of its development

from the zygote.


(a) Draw a labelled diagram of the sectional view of a typical anatropous ovule.

(b) Mention the fate of all the components of the embryo sac after fertilization?

29. (a) Write what DNA replication refers to.

(b) State the properties of DNA replication model.

(c) List any three enzymes involved in the process along with their functions.


Inheritance patterns of flower colour in garden pea plant and snap dragon

differ. Why is the difference observed? Explain the difference with the help of

crosses in their inheritance patterns.

30. Aditya participated in a group discussion in his school on “The ill effects of

Tobacco on Human Health”.  In the evening he goes with his family for dinner

and insists on sitting in the “Non-Smoking Area” to which his father (who is a

heavy smoker) objects.

(a) In this situation, who wins your support – Aditya’s concern for health &

environment or his father’s objection? Justify giving two reasons.     (2)

(b) Suggest any three effective propaganda campaigns  for anti-tobacco

awareness.  (3)

Practicals Class XII CBSE


60 Periods

A. List of Experiments

1. Study pollen germination on a slide.

2. Collect and study soil from at least two different sites and study them for texture, moisture

content, pH and water holding capacity of soil. Correlate with the kinds of plants found in


3. Collect water from two different water bodies around you and study them for pH, clarity

and presence of any living organisms.

4. Study the presence of suspended particulate matter in air at the two widely different sites.

5. Study of plant population density by quadrate method.

6. Study of plant population frequency by quadrate method.

7. Prepare a temporary mount of onion root tip to study mitosis.

8. To study the effect of the different temperatures and three different pH on the activity of

salivary amylase on starch.

Study/observation of the following (Spotting)

1. Flowers adapted to pollination by different agencies (wind, insect).

2. Pollen germination on stigma through a permanent slide.

3. Identification of stages of gamete development i.e. T.S. testis and T.S. ovary through

permanent slides (from any mammal).

1104. Meiosis in onion bud cell or grass hopper testis through permanent slides.

5. T.S. of blastula through permanent slides.

6. Mendelian inheritance using seeds of different colour/sizes of any plant.

7. Prepared pedigree charts of genetic traits such as rolling of tongue, blood groups, widow’s

peak, colour blindness.

8. Exercise on controlled pollination – Emasculation, tagging and bagging.

9. Identification of common disease causing organisms like Ascaris, Entamoeba, Plasmodium,

ringworm through permanent slides or specimens. Comment on symptoms of disease that

they cause.

10. Two plants and two animals found in xerophytic conditions. Comment upon their

morphological adaptations.

11. Plants and animals found in aquatic conditions. Comment upon their morphological