KENDRIYA VIDYALAYA SANGATHAN, CHENNAI REGION
COMMON PRE-BOARD EXAMINATION 2013 -14
CLASS – XII
BIOLOGY – SCORING KEY
1
Commensalism – Orchid is benefited by getting shelter – mango
neither harmed nor benefited
1
2
Bamboo flowers once in its lifetime. It produces a large number of
fruits and dies.
1
3
Saltation
1
4
UV – B Radiations
1
5
Which helps in identifying and eliminating non-transformants
and selectively permitting the growth of the transformants.
1
6
Lysergic acid diethyl amides
1
7
Novelty, non-obviousness & Utility
1
8
Lysozyme, Chitinase
½+½=1
9
It refers to increase in concentration of the toxicant at successive
tropic levels – DDT is an aquatic food chain. The concentration of
DDT is increased from 0.03PPM to reach 25PPM. It affects fish
eating birds and disturb calcium metabolism.
2
10
IA i x IB i = IAIB (AB),
2
11
Test tube baby program (b) ZIFT (c) GIFT (d) IUI
2
12
Standing State: The amount of nutrients such as carbon,
nitrogen, phosphorous, calcium etc. present in the soil at any
given time.
Standing Crop: Each tropic level has a certain mass of living
material at a particular time
Change of frequency of alleles in a population would then be
interpreted as resulting in evolution.
A hotspot is an area having endangered endemic species with very
high levels of species richness.
i. Number of endemic species
ii. Degree of threat which is measured in terms of habitat
loss.
1+1=2
13
14
IAi (A), IBi (B), ii (O)
2
1
+
1
Ichthyo saurs
Ramapitheaus
15

16

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i.
ii.
iii.
Breeding crops with higher levels of vitamins and
minerals of protein and fats is the most practical
means to improve public health.
Atlass 66
EcoRI – Enzyme Restriction endonuclease
R – RY13 strain
5’ GAATTC - 3’
3’ CTTAAG – 5’
(OR)
If denaturation of double stranded DNA does not take place, then
primers will not be able to annel to the template, no extension will
take place, hence no amplification will occur.
Adenosine deaminase (ADA) enzyme is crucial for the immune
system to function. The disorder is caused due to the deletion of
gene.
- Gene therapy is the collection of methods that allows
correction of a gene deflect in embryo stage.
- Due to ADA introduced into cells at early embryonic stage
Using agrobacterium vectors, nematode-specific genes were
introduced into the host plant,produced both sense and antisense RNA in the host cells, two RNAs being complementary to
each other, formed a double stranded (dsRNA),that initiated
RNAi,silenced the specifi mRNA of the nematode , the parasite
could not survive in a transgenic host, the transgenic plant
therefore got itself protected from the parasite.
Incomplete dominance- the F1 had a phenotype that did not
resemble either of the two parents
-where one allele is incompletely dominant over the other
allele.eg., dog flower(Snapdragon or Antirrhinum sp.)
-phenotypic ratio and genotypic ratio are same
Co-dominance- the alleles which are able to express themselves
independently when present together are called co-dominant
alleles and this biological phenomenon is called co-dominance.
Eg., ABO blood grouping in humans
 DNA sequences which are repeated many times, show a
high degree of polymorphism and form a bulk of DNA in a
genome called as satellite DNA.
 DNA from every tissue from an individual shows the same
degree of polymorphism and is heritable hence very useful
in DNA finger printing.
i. Habitat loss and fragmentation
ii. Over exploitation
iii. Alien species invasions
1+1 = 2
1½+½
=2
½+½+1
=2
2
1
+
½
+
½
=2
3
1½+1½
=3
1½
+
1½
=3
3
iv.
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Co-extinctions
Any 3 causes & Explanation
A. Primary productivity – The amount of biomass (or) organic
matter produced per unit area over a time period by plants
during photosynthesis.
It is expressed in terms of weight (g-2) or energy (kcal m-3)
B. GPP – An ecosystem in the rate of production of organic
matter during photosynthesis.
NPP means GPP is utilized by plants in respiration.
GPP – R = NPP
(OR)
1) Fragmentation- The process of breaking down of detritus
into smaller particles. Eg., as done by earth worm(1/2)
2) Leaching- The process by which water soluble inorganic
nutrients go down into the soil horizon and get
precipitated as unavailable salts.(1/2)
3) Catabolism- The enzyme process by which degraded
detritus is converted into simpler inorganic substances
is called catabolism. (1/2)
4) Humification- The process of accumulation of dark
coloured amorphous substance called humus and is
highly resistant to microbial action and undergoes
decomposition at an extremely slow rate.(1)
5) Mineralisation- The process by which humus is further
degraded by some microbes to release inorganic
nutrients .(1/2)
i.
Symptoms – internal bleeding, muscular pain, fever,
anemia and blockage of the intestinal passages
ii.
Ringworms
iii.
Salmonella typhi
iv.
Common Cold
v.
Fever, chills, cough and headache – the lips and the
finger nails may turn gray to bluish colour.
vi.
Wuchereria malayi (or)
Wuchereria bancrofti
A. Rich in fructose, calcium and certain enzymes.
B. Fimbriae – help in collection of the ovum after ovulation
Myometrium – Strong contraction during delivery of the
baby
A. Sporogenous tiss – The cells of sporogenous tissue undergo
meiotic division to form microspore tetrads
B. Tapetum – It nourishes the developing pollen grains
C. Middle Layer – Layers perform the function of protection
and help in dehiscence of anther to release the pollen
A. Yeast – Monascus purpureus
- Blood cholesterol lowering agent
B. Bacterium – Streptococcus – Used “clot buster” for removing
1
1
1
3
½
½
½
½
½
½
1
1
1
1
1
1
1
1
clots from the blood vessels
C. Fungus – Trichoderma polysporum – Used immuno
suppressive agent in organ transplant patients
1
28 A.
i.
i. Each primary oocyte then gets surrounded by a layer
granulosa cells
ii.
Primary follicles gets surrounded by more layers of
granulosa cells and a new theca.
iii.
Which is characterized by a fluid filled cavity called antrum.
B.
Refer the NCERT book – Fig. 3.11 – Page 52 (Diagram and
explanation)
(OR)
A – Refer the NCERT book – Pg. 26 (diagram and labeling – 3
marks)
B- Pollen tube releases the two male gametes into cytoplasm of
synergid.- one of the male gametes fuses with the egg nucleus to
form a diploid cell called zygote. This event is called syngamy .
The other male gamete fuses with polar nuclei at the centre to
produce a triploid primary endosperm nucleus. This is termed as
triple fusion. As Syngamy and triple fusion take place
simultaneously in the embryo sac, it is termed as double
fertilization. The centre cell after triple fertilization forms primary
endosperm cell (PEC) which later develops into
endosperm.Thezygote later develops into an embryo.(2 marks)
29 During cell division cycle results in the gain or loss of a
chromosome
Cell division results in an increase in a whole set of chromosomes
in an organim
A. Down Syndrome
B. Klinefelter’s Syndrome
C. Turner’s Syndrome
(OR)
A. They grew E. coli in a medium containing 15NH4Cl for many
generations.
As a result, 15N got incorporated into newly synthesized
DNA
This heavy DNA can be differentiated from normal DNA by
centrifugation in caesium chloride (CsCl) density gradient.
Then they transferred the cells into a medium with normal
15NH4Cl and took the samples at various definite time
intervals as the cells multiplied.
The extracted DNAs were centrifuged and measured to get
their densities.
The DNA extracted from culture after one generation(after
1½
3½
5
1
1
1
1
1
1½
20 minutes as E. coli divides every 20 minutes) of transfer
from the 15N medium to 14N medium showed an
intermediate hybrid density.
The DNA extracted from culture after two generations (after
40 mins) showed equal amounts of light DNA and hybrid
DNA.
By this experiment, it is proved that DNA replication is
semi-conservative.
Diagram to be drawn*
B. In bacteria, the transcription of all the three types of
RNA (mRNA, tRNA and rRNA) is catalysed by single DNAdependent enzyme called the RNA Polymerase.
In E. coli bacterium, the RNA polymerase has co-factors
β, β’, α,α’ and ω along with σ factor to catalyse the
process.
The transcription is completed in three steps: initiation,
elongation and termination – Explanation
*Diagram to be drawn*
30
i.
ii.
iii.
MOET as success rate of technique is more
Herd size is increased in short time
Genetic mother is available for another round of super
ovulation
Values:
- Critical thinking
- Problem Solving
1
1½
1
1
2
2