Biology Sample Question Paper Sheet - Class Xii, Central Board Of Secondary Education, 2010 Page 13
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39•
It acts as a natural barrier by the interaction of chemical substances produced by the style.
•
Normally the pollen belonging to right mating type germinate on stigma, develop pollen tube &
bring about fertilization.
•
The pollen grains belonging to other mating type are discarded = 1 × 5 = 5
[5 Marks]
30. (a)
(i)
It is a fine powder of recycled modified plastic. This mixture is mixed with bitumen used
to lay roads = 1
Raw material - Plastic film waste = 1
(ii)
Blends of polyblend & bitumen, when used to lay roads, enhances the bitumen’s water
repellant properties and helps to increase road life by a factor of three = 1
(b)
Irreparable computers and other electronic goods are known as e-wastes = 1
Burried in landfills or incinerated = 1
[1+1+1+1+1 = 5 Marks]
OR
(a)
The gradual and fairly predictable change in the species composition of a given area = 1
During succession some species colonise an area & their populations become more numer-
ous, where as populations of other species decline and even disappear = 1 + 1 = 2
(b)
Primary Succession
Secondary Succession
It occurs in an area which has been bare
It occurs in an area which has been
from the beginning.
denuded recently.
Soil is absent at the time of beginning of
Soil is present in the area where secondary
primary succession.
succession begins.
Takes a long time for completion.
Takes less time for completion
(any two differences 1 × 2 = 2)
[ 1 + 2 + 2 = 5 Marks]
13
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