biology : class12 Triploid Endosperm : Pollen Tube, Syngamy, Triple Fusion : Fertilisation in Plants MCQ Questions and Answers
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Triploid Endosperm
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MCQ Questions
1. In a diploid angiosperm with 2n = 24 chromosomes, the primary endosperm nucleus is formed by fusion of a sperm nucleus with the two polar nuclei. What will be the chromosome number of the primary endosperm nucleus?
A.
12
B.
24
C.
36
D.
48
Correct Answer:
36
Explanation:
The two polar nuclei are haploid and together contribute 24 chromosomes, while the sperm contributes 12. Thus, the primary endosperm nucleus is triploid with 24 + 12 = 36 chromosomes.
2. Which nuclear contribution most accurately represents the genomic constitution of a typical triploid endosperm in an angiosperm?
A.
One maternal haploid genome and two paternal haploid genomes
B.
Two maternal haploid genomes and one paternal haploid genome
C.
One maternal diploid genome and one paternal haploid genome
D.
Three paternal haploid genomes
Correct Answer:
Two maternal haploid genomes and one paternal haploid genome
Explanation:
The triploid endosperm originates when one male gamete fuses with two maternal polar nuclei, producing a 2 maternal : 1 paternal genomic contribution.
3. A plant species has a female gametophyte whose two polar nuclei each contain 10 chromosomes, while the sperm nucleus involved in triple fusion contains 10 chromosomes. What is the ploidy and chromosome number of the resulting primary endosperm nucleus?
A.
Diploid, 20 chromosomes
B.
Triploid, 30 chromosomes
C.
Tetraploid, 40 chromosomes
D.
Haploid, 10 chromosomes
Correct Answer:
Triploid, 30 chromosomes
Explanation:
Triple fusion combines three haploid nuclei: two polar nuclei and one sperm nucleus. Therefore, the primary endosperm nucleus is triploid and contains 10 + 10 + 10 = 30 chromosomes.
4. If the male gametophyte of a diploid species contributes a sperm nucleus with n chromosomes and the two polar nuclei remain unfused until fertilization, which event directly establishes the triploid nature of the endosperm?
A.
Fusion of the egg nucleus with one synergid nucleus
B.
Fusion of one sperm nucleus with the two polar nuclei
C.
Fusion of the two sperm nuclei with the egg nucleus
D.
Fusion of the antipodal cells with the central cell
Correct Answer:
Fusion of one sperm nucleus with the two polar nuclei
Explanation:
The primary endosperm nucleus becomes triploid when one sperm nucleus fuses with both haploid polar nuclei. This process is called triple fusion.
5. In a normally triploid endosperm, what is the expected ratio of maternal to paternal chromosome sets in the primary endosperm nucleus?
A.
1:1
B.
1:2
C.
2:1
D.
3:0
Correct Answer:
2:1
Explanation:
Two haploid polar nuclei provide two maternal chromosome sets, whereas the sperm provides one paternal chromosome set, giving a maternal-to-paternal ratio of 2:1.
6. A diploid plant has 2n = 18 chromosomes. If nondisjunction causes one of its male gametes involved in triple fusion to contain 10 chromosomes while each polar nucleus contains 9 chromosomes, what chromosome number will the primary endosperm nucleus have?
A.
27
B.
28
C.
29
D.
30
Correct Answer:
28
Explanation:
The primary endosperm nucleus receives 9 chromosomes from each polar nucleus and 10 from the abnormal sperm nucleus. Therefore, its chromosome number is 9 + 9 + 10 = 28.
7. Why is the term triploid endosperm specifically appropriate for the product of triple fusion in a typical angiosperm?
A.
It contains three complete diploid genomes formed by three zygotes
B.
It contains three haploid chromosome sets contributed by two polar nuclei and one sperm
C.
It undergoes meiosis three times before becoming endosperm
D.
It develops from three fused egg cells, each containing a haploid genome
Correct Answer:
It contains three haploid chromosome sets contributed by two polar nuclei and one sperm
Explanation:
Triploid refers to the presence of three haploid chromosome sets. In typical angiosperms, these sets arise from two polar nuclei and one sperm nucleus.
8. In a hypothetical cross, the female parent produces polar nuclei with 8 chromosomes each and the male parent produces sperm nuclei with 12 chromosomes. What will be the chromosome number of the endosperm produced by triple fusion?
A.
16
B.
20
C.
28
D.
32
Correct Answer:
28
Explanation:
The endosperm receives 8 chromosomes from each of the two polar nuclei and 12 from the sperm nucleus. Thus, its chromosome number is 8 + 8 + 12 = 28.
9. Which statement correctly distinguishes the chromosome origin of the primary endosperm nucleus from that of the zygote in a typical diploid angiosperm?
A.
Both are diploid and receive one haploid set from each parent
B.
The endosperm is triploid with two maternal sets, whereas the zygote is diploid with one maternal and one paternal set
C.
The endosperm is diploid with two paternal sets, whereas the zygote is triploid
D.
Both are triploid because each receives two polar nuclei and one sperm nucleus
Correct Answer:
The endosperm is triploid with two maternal sets, whereas the zygote is diploid with one maternal and one paternal set
Explanation:
The zygote forms by syngamy between one egg and one sperm and is diploid. The primary endosperm nucleus forms by triple fusion and is triploid, with two maternal and one paternal chromosome sets.
10. If the chromosome number of the primary endosperm nucleus in a typical angiosperm is 45, what chromosome number would be expected in each participating haploid sperm and polar nucleus, assuming all three nuclei are haploid and cytologically normal?
A.
9
B.
15
C.
22
D.
45
Correct Answer:
15
Explanation:
The primary endosperm nucleus contains three haploid chromosome sets. Therefore, each contributing haploid nucleus contains 45 ÷ 3 = 15 chromosomes.
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