Questions & Answers
Question
AnswersA typical angiosperm embryo sac at maturity is eight nucleate and
A. single-celled
B. Four celled
C. Seven celled
D. Eight celled
Answer
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Hint: The embryo sac is the gametophyte of the angiosperm. The eight nuclei of the embryo sac are not separated by proper cell walls. During sexual reproduction, only one of the eight nuclei serves as the egg. The embryo sac represents the ovule in the angiosperm.
Complete answer:
The embryo sac of angiosperms consists of seven cells. A typical angiosperm embryo at maturity is called 7 celled 8 nucleates. The cells are arranged in three sets. In the centre, there are two polar nuclei which are a part of the large central cell. The polar nuclei are present at the centre of the cell. The polar nuclei are not separated by a membrane.
There are two ends of the yolk sac. One of the ends is called the chalazal end. This end has 3 antipodal cells. The end opposite to the chalazal end bears the egg apparatus. The egg apparatus consists of the egg cell in between two synergid cells. The synergids provide nutrition to the egg cell.
The eight celled stage arises from a two-celled stage. These two cells divide continuously to give rise to a four celled stage at first, then an eight celled stage. The polar nuclei fuse with the male nucleus wrestling in a triploid cell. This forms the endosperm which will nourish the embryo (seed) after fertilization.
Hence, the correct answer is option (C).
Note: The polar nuclei may fuse before fertilization. The division of the two-celled stage takes place only for the cytoplasm. There is no nuclear division. The egg cell is the female haploid gamete which forms the zygote after fertilization.
Complete answer:
The embryo sac of angiosperms consists of seven cells. A typical angiosperm embryo at maturity is called 7 celled 8 nucleates. The cells are arranged in three sets. In the centre, there are two polar nuclei which are a part of the large central cell. The polar nuclei are present at the centre of the cell. The polar nuclei are not separated by a membrane.
There are two ends of the yolk sac. One of the ends is called the chalazal end. This end has 3 antipodal cells. The end opposite to the chalazal end bears the egg apparatus. The egg apparatus consists of the egg cell in between two synergid cells. The synergids provide nutrition to the egg cell.
The eight celled stage arises from a two-celled stage. These two cells divide continuously to give rise to a four celled stage at first, then an eight celled stage. The polar nuclei fuse with the male nucleus wrestling in a triploid cell. This forms the endosperm which will nourish the embryo (seed) after fertilization.
Hence, the correct answer is option (C).
Note: The polar nuclei may fuse before fertilization. The division of the two-celled stage takes place only for the cytoplasm. There is no nuclear division. The egg cell is the female haploid gamete which forms the zygote after fertilization.
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