Q21 of 30 Page 1

List any four devices that develop in angiosperms to encourage cross pollination. Mention the advantage of such devices.

Devices that encourage cross pollination are known as Outbreeding devices.

There are 4 types of outbreeding devices:-


1.) Release of Pollen much before or much after the stigma is susceptible (receptiveness of stigma).


2.) Placement of anther & stigma at such positions so that the pollens do not reach the stigma of the same plant or the same flower.


3.) It is a chemical method in which the stigma inhibits the growth of its own pollen tubes into the pistil. This is known as Self Incompatibility or Self Sterility


4.) Production of flowers or plants that are UNISEXUAL i.e. the plant or flower exhibit dioecy. This is known as Dicliny.


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The collection of certain moths after industrialisation in England (1920), showed population of light winged less than that of dark winged moths, which was reverse of the observation made prior to industrialisation (1850s). Explain the observation made, with reference to Darwinian natural selection.

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Differentiate between co-dominance and incomplete dominance. Give one example of each.

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OR


(a) What does high ‘Biological Oxygen Demand’ (BOD) of a water body indicate?


(b) Explain the changes in BOD level of the primary effluent during its secondary treatment in sewage treatment tanks.