Biology Sample Question Paper Sheet - Class Xii, Central Board Of Secondary Education, 2010 Page 33
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3927.
An interesting property of restriction enzymes is molecular cutting and pasting. Restriction enzymes
typically recognize a symmetrical sequence of DNA.
28.
Notice that the top strand is the same as the bottom strand, but reads backward. When the enzyme
cuts the strand between G and A, it leaves overhanging chains:
A. What is this symmetrical sequence of DNA known as?
B. What is the significance of thsese overhanging chains?
C. Name the restriction enzyme that cuts the strand between G and A
3
SECTION D
th
28.
(i)
A decade back, the enormous vehicular traffic in Delhi had made Delhi rank 4
among
polluted cities of the world. Two measures taken by the Delhi Government brought marked
improvement in air quality by 2005. What were these two measures and how did they reduce
air pollution?
3
(ii)
What is the norm set by Euro II for petrol and diesel vehicles?
OR
How is the “sixth episode of extinction” of species on earth, now currently in progress, different
from the five earlier episodes? What is it due to? Explain the various causes that have brought about
this difference.
29.
(a)
Draw the embroyo sac of a flowering plant and label (i) central cell (ii) Chalazal end of the
embryo sac (iii) synergids.
(b)
Name the cell that develops into the embryo sac and explain how this cell leads to the formation
of Embryo sac . Also mention the role played by the various cells of the embryo sac.
5
OR
Show diagrammatically the stages of embryonic development from zygote upto implantation in
humans.
5
30.
Name the genes that constitute an operon. How does lac operon get switched on in the presence of
lactose?
5
OR
With the advent of rDNA technology a powerful tool is available to identify a criminal or to the real
parents. Name this technique. Write the missing steps in the procedure given below. There of three
steps are mentioned in the flow chart: Extraction of DNA from the cells - (ii)....................→(iii)
→ (iv).................→ (v)................→
DNA is cut into fragments by restriction enzymes
(vi).................→
(vii) Autoradiography.
................→ (viii).................→
5
33
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