biology : class12 Gamete Membrane Fusion : Pollen Tube, Syngamy, Triple Fusion : Fertilisation in Plants MCQ Questions and Answers
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Gamete Membrane Fusion
MCQ questions and answers.
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MCQ Questions
1. During syngamy in a flowering plant, which event most directly establishes continuity between the male and female gamete cytoplasms?
A.
Fusion of the male and female plasma membranes
B.
Fusion of the male nucleus with the egg cell wall
C.
Fusion of the pollen tube wall with the embryo sac wall
D.
Fusion of the egg nucleus with the central cell membrane
Correct Answer:
Fusion of the male and female plasma membranes
Explanation:
Syngamy begins with the fusion of the plasma membranes of the male gamete and egg. This membrane fusion permits cytoplasmic continuity, after which the two nuclei fuse to form the zygote nucleus.
2. Which sequence most accurately represents the essential cellular events during fusion of a sperm cell with the egg in an angiosperm?
A.
Nuclear fusion, cell-wall fusion, membrane rupture, cytoplasmic mixing
B.
Recognition and adhesion, plasma-membrane fusion, cytoplasmic continuity, nuclear fusion
C.
Pollen tube elongation, polar-nuclei fusion, membrane dissolution, nuclear division
D.
Egg-cell division, sperm-cell wall formation, membrane fusion, chromosome pairing
Explanation:
Gamete membrane fusion is preceded by recognition and contact. Fusion of the plasma membranes allows the gamete cytoplasms to become continuous, and karyogamy subsequently produces the diploid zygotic nucleus.
3. In triple fusion, the membrane-fusion event differs from syngamy primarily because the male gamete membrane fuses with the membrane of the
A.
Egg cell only
B.
Central cell containing the two polar nuclei
C.
Synergid containing the filiform apparatus
D.
Antipodal cell containing the haploid nucleus
Correct Answer:
Central cell containing the two polar nuclei
Explanation:
In triple fusion, the second male gamete enters the central cell and its plasma membrane fuses with the membrane of the female reproductive cell containing the two polar nuclei. Nuclear fusion then produces the triploid primary endosperm nucleus.
4. A mutation prevents the plasma membrane of a male gamete from fusing with the egg membrane but does not affect pollen-tube growth. Which immediate consequence is most likely?
A.
The sperm nucleus cannot establish cytoplasmic continuity with the egg and syngamy fails
B.
The polar nuclei fuse with the egg nucleus to restore diploidy
C.
The pollen tube automatically forms a diploid embryo without gamete fusion
D.
Triple fusion occurs with the egg nucleus instead of the polar nuclei
Correct Answer:
The sperm nucleus cannot establish cytoplasmic continuity with the egg and syngamy fails
Explanation:
Pollen-tube growth alone does not accomplish fertilisation. Fusion of the male and egg plasma membranes is required for entry and cytoplasmic continuity; without it, nuclear fusion and zygote formation cannot occur.
5. Why is membrane fusion a necessary event before karyogamy during syngamy?
A.
It converts the haploid male nucleus directly into a diploid nucleus
B.
It permits the two gamete cytoplasms to become continuous so that their nuclei can subsequently unite
C.
It causes the egg cell to undergo meiosis before nuclear fusion
D.
It ensures that the two polar nuclei are eliminated from the embryo sac
Correct Answer:
It permits the two gamete cytoplasms to become continuous so that their nuclei can subsequently unite
Explanation:
Plasma-membrane fusion brings the male and female gamete contents into a common cellular environment. Karyogamy, or fusion of their nuclei, follows this membrane-level event and produces the zygote nucleus.
6. Which comparison correctly distinguishes the products of the two membrane-fusion events involved in double fertilisation?
A.
Syngamy produces a triploid nucleus, whereas triple fusion produces a diploid nucleus
B.
Syngamy produces a diploid zygote nucleus, whereas triple fusion produces a triploid primary endosperm nucleus
C.
Both events produce diploid nuclei because each involves one male gamete
D.
Both events produce haploid nuclei because plasma membranes fuse without nuclear fusion
Correct Answer:
Syngamy produces a diploid zygote nucleus, whereas triple fusion produces a triploid primary endosperm nucleus
Explanation:
The male gamete fuses with the haploid egg during syngamy, forming a diploid zygote nucleus. The other male gamete fuses with two polar nuclei during triple fusion, forming a triploid primary endosperm nucleus.
7. If the plasma membranes of the two polar nuclei fail to participate in the fusion process involving the second male gamete, which formation is directly prevented?
Explanation:
Triple fusion requires the second male gamete to interact with the central cell containing the two polar nuclei. Failure of the relevant membrane-fusion process prevents subsequent nuclear fusion and formation of the triploid primary endosperm nucleus.
8. Which statement best explains why syngamy and triple fusion are both described as fusion events despite involving different female targets?
A.
In both, a male gamete first fuses at the membrane level with a female reproductive cell and then undergoes nuclear fusion
B.
In both, two female gametes fuse before the pollen tube releases its contents
C.
In both, the male gamete fuses only with a cell wall and never with a plasma membrane
D.
In both, the egg nucleus and polar nuclei simultaneously fuse with one male nucleus
Correct Answer:
In both, a male gamete first fuses at the membrane level with a female reproductive cell and then undergoes nuclear fusion
Explanation:
Syngamy and triple fusion share the basic pattern of male gamete–female cell membrane interaction followed by nuclear fusion. Their difference lies in the female partner: the egg in syngamy and the central cell with two polar nuclei in triple fusion.
9. A researcher observes that a male gamete has contacted the egg but its plasma membrane remains distinct from the egg membrane. Which conclusion is justified?
A.
Karyogamy has necessarily occurred because physical contact is sufficient
B.
Syngamy has not been completed because membrane fusion is required before nuclear fusion
C.
Triple fusion has occurred because the egg is part of the embryo sac
D.
The male gamete has become diploid by replicating its chromosomes
Correct Answer:
Syngamy has not been completed because membrane fusion is required before nuclear fusion
Explanation:
Contact or adhesion alone does not constitute gamete fusion. The male and egg plasma membranes must fuse to establish cytoplasmic continuity, after which their nuclei can unite during syngamy.
10. Which pairing correctly identifies the female cell involved in membrane fusion and the nuclear product formed afterward?
A.
Egg cell — triploid primary endosperm nucleus
B.
Central cell with two polar nuclei — diploid zygote nucleus
C.
Egg cell — diploid zygote nucleus
D.
Synergid — triploid primary endosperm nucleus
Correct Answer:
Egg cell — diploid zygote nucleus
Explanation:
The first male gamete fuses with the egg cell membrane and its nucleus then fuses with the egg nucleus, producing the diploid zygote nucleus. The central cell is the target of the second male gamete during triple fusion.
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