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Sexual Reproduction In Flowering Plants — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYSexual Reproduction In Flowering Plants4 Marks
Question
Write a short note on pollination by wind.
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Answer

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→ Pollination by wind is more common amongst abiotic pollinations.
→ Wind pollination also requires that the pollen grains are light and non-sticky so that they can be transported in wind currents.
→ They often possess well-exposed stamens so that the pollens are easily dispersed into wind currents, and large often-feathery stigma to easily trap air-borne pollen grains.
→ Wind pollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence.
→ A familiar example is the corn cob the - tassels you see are nothing but the stigma and style which wave in the wind to trap pollen grains.
→ Wind-pollination is quite common in grasses.

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Pollen-pistil interaction is the group of events that occur from the time of pollen deposition over the stigma to the time of pollen tube entry into ovule. It is a dynamic process which has checks at several places for promotion or inhibition of pollen growth. Pollen-pistil interaction is a safety measure to ensure that illegitimate crossings do not occur. Compatibility and incompatibility of the pollen-pistil is determined by special proteins. The compatible pollens are able to absorb water and nutrients from the surface of the stigma. They germinate and produce pollen tubes. Pollen tubes grow into the style. Their growth and path through the style are also determined by specific chemicals.

  1. Which of the following parts of gynoecium determines the compatible nature of pollen?
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  4. Thalamus.
  1. In Triforium, which type of self-incompatibility is found?
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  3.  Both GSI and SSI.
  4. None of these.
  1. Select the incorrect statement.
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  1. Given figures show the pollen-stigma interaction, where pollen wall proteins are released onto the pellicle of stigmatic papillae, where a recognition reaction occurs.

Which of the following statements drawn from given figures is incorrect?

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  2. Development of callose plug between the plasma membrane and pectocellulosic layer of stigmatic papillae results in the incompatibility reaction in Q.
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  4. Deposition of callose can be employed as a reliable bioassay to detect compatibility or incompatibility reactions of pollen and stigma.
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Restriction endonuclease was isolated for the first ti me by W. Arb er in 1962 in bacteria. Restriction endonucleases cut the DNA duplex at specific points therefore they are also called as molecular scissors or biological scissors. Three types of restriction endonucleases are Type I, Type II and Type III but only Type II restriction endonucleases are used in recombinant DNA technology. Restriction endonuclease EcoR I recognises the base sequence GAATTC in DNA duplex and cut strands between G and A.

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  1. $\ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  2. $ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  3. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \uparrow$

  4. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

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