In angiosperms, pollen grain germinates to produce two male gametes. Which one of the following functions is carried out by these gametes?
- A.Both the gametes fuse with a single egg cell
- B.Both the gametes fuse with two different egg cells
- C.One gamete fuses with the egg cell and the other one eventually degenerate
- D.One gamete fuses with the egg cell and the other one fuses with a diploid secondary nucleus
Correct answer
Explanation
The correct answer is D, one fuses with the egg cell and the other with the diploid secondary nucleus. This is double fertilisation, a feature found only in flowering plants.
The pollen tube carries the two male gametes into the embryo sac. One fuses with the egg cell (syngamy) to form the diploid zygote, which grows into the embryo. The other fuses with the secondary nucleus, formed from the two polar nuclei, in what is called triple fusion; this gives the triploid primary endosperm nucleus, which grows into the endosperm that feeds the developing embryo. Double fertilisation was discovered by S. G. Nawaschin in 1898.
A is wrong because only one male gamete fuses with the egg.
B is wrong because the embryo sac has only one egg cell.
C is wrong because the second gamete does not go to waste; it forms the endosperm.
Exam tip: syngamy gives the 2n zygote, triple fusion gives the 3n endosperm; together they make double fertilisation.
Practice Questions
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- C.tin
- D.aluminium
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- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
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1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
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- A.Only one
- B.Only two
- C.All three
- D.None
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1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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