biology : class12 Embryo Sac Penetration : Pollen Tube, Syngamy, Triple Fusion : Fertilisation in Plants MCQ Questions and Answers
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Embryo Sac Penetration
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MCQ Questions
1. In a typical angiosperm embryo sac, the pollen tube most commonly enters through which route before reaching the egg apparatus?
A.
Through the chalazal end and then between the antipodals
B.
Through the micropyle and toward one of the synergids
C.
Directly through the central cell wall without entering the egg apparatus
D.
Through the integuments at the lateral surface of the ovule
Correct Answer:
Through the micropyle and toward one of the synergids
Explanation:
In the usual porogamous condition, the pollen tube enters the ovule through the micropyle and is guided toward the egg apparatus, particularly one of the synergids.
2. The filiform apparatus at the micropylar end of synergids is most directly associated with which event?
A.
Guiding and facilitating pollen-tube entry into a synergid
B.
Producing the two male gametes inside the pollen grain
C.
Preventing the pollen tube from entering the ovule
D.
Forming the cell wall of the developing embryo
Correct Answer:
Guiding and facilitating pollen-tube entry into a synergid
Explanation:
The filiform apparatus consists of wall ingrowths in synergids near the micropylar end and is involved in absorbing nutrients and guiding the pollen tube during embryo-sac penetration.
3. A pollen tube has entered the embryo sac but fails to locate a synergid. Which structural feature is most likely to be functionally compromised?
A.
The antipodal cells at the chalazal end
B.
The filiform apparatus of the synergids
C.
The polar nuclei in the central cell
D.
The outer wall of the integument
Correct Answer:
The filiform apparatus of the synergids
Explanation:
Synergids, especially their filiform apparatus, provide positional and chemical guidance for the pollen tube after it has penetrated the ovule and entered the embryo-sac region.
4. Which sequence correctly represents the usual path of a pollen tube during embryo-sac penetration in a porogamous ovule?
A.
Stigma, chalaza, nucellus, antipodal cells, egg
B.
Micropyle, integumentary opening, nucellus, synergid, egg apparatus
C.
Micropyle, antipodal cells, central cell, synergid, egg
D.
Chalaza, integument, micropyle, polar nuclei, synergid
Explanation:
The pollen tube generally passes through the micropylar opening, traverses the integumentary and nucellar region, and then enters one of the synergids in the egg apparatus.
5. In most angiosperms, the pollen tube penetrates which cell of the egg apparatus before releasing the male gametes?
A.
The egg cell
B.
A synergid
C.
An antipodal cell
D.
The central cell directly
Correct Answer:
A synergid
Explanation:
The pollen tube usually enters one synergid through its micropylar end. It commonly discharges the male gametes within or near the degenerated synergid.
6. A pollen tube enters the embryo sac through the chalazal region rather than the micropyle. This mode of ovular entry is termed:
A.
Porogamy
B.
Chalazogamy
C.
Mesogamy
D.
Autogamy
Correct Answer:
Chalazogamy
Explanation:
Chalazogamy refers to pollen-tube entry into the ovule through the chalazal region. It differs from the usual porogamy, in which the tube enters through the micropyle.
7. When a pollen tube enters an ovule through the integuments rather than through the micropyle or chalaza, the penetration is called:
A.
Mesogamy
B.
Chalazogamy
C.
Porogamy
D.
Apogamy
Correct Answer:
Mesogamy
Explanation:
Mesogamy is the condition in which the pollen tube penetrates the ovule through the integumentary region. It is an alternative route to the usual micropylar entry.
8. Which observation most strongly indicates that pollen-tube penetration of the embryo sac has occurred successfully?
A.
The pollen tube remains confined to the stigma
B.
A pollen tube is visible within a synergid near the micropylar end
C.
All antipodal cells have migrated toward the micropyle
D.
The integuments have completely disappeared before pollen arrival
Correct Answer:
A pollen tube is visible within a synergid near the micropylar end
Explanation:
Entry of the pollen tube into a synergid near the micropylar end is direct evidence that it has crossed the ovule and penetrated the embryo sac.
9. The degeneration of one synergid during pollen-tube entry is significant because it:
A.
Creates a receptive site for pollen-tube penetration and discharge
B.
Forms the micropyle in the ovule wall
C.
Converts the antipodal cells into male gametes
D.
Prevents the pollen tube from entering the embryo sac
Correct Answer:
Creates a receptive site for pollen-tube penetration and discharge
Explanation:
One synergid commonly degenerates before or during pollen-tube entry, providing a receptive pathway and site for the tube to discharge its contents near the egg apparatus.
10. A mutation eliminates the micropylar filiform apparatus but leaves the pollen tube and embryo sac otherwise normal. Which defect is most directly expected?
A.
Failure of pollen-tube guidance and entry into the synergid
B.
Failure of pollen production in the anther
C.
Failure of integument formation around the ovule
D.
Failure of antipodal cells to occupy the chalazal end
Correct Answer:
Failure of pollen-tube guidance and entry into the synergid
Explanation:
The micropylar filiform apparatus is important for attracting, guiding, and facilitating pollen-tube penetration into a synergid; its absence can disrupt embryo-sac entry even when the tube is otherwise normal.
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