IGCSE Biology Paper-2: Specimen Questions with Answers 171 - 172 of 203

Question 171

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Question

MCQ▾

What describes the nuclei in human reproduction?

Choices

Choice (4)
a.Sperm-haploid, egg-diploid, zygote-diploid
b.Sperm-diploid, egg-haploid, zygote-diploid
c.Sperm-diploid, egg-diploid, zygote-haploid
d.Sperm-haploid, egg-haploid, zygote-diploid

Answer

d.

Explanation

  • Although haploidy has not been observed in vertebrates, its natural occurrence in various eukaryotic species that had diverged from diploid ancestors suggests that there is an innate capacity for an organism to regain haploidy and that haploidy may confer evolutionary benefits.
  • Haploid embryonic stem cells have been experimentally generated from mouse, rat, monkey, and humans. Haploidy results in major differences in cell size and gene expression levels while also affecting parental imprinting, X chromosome inactivation, and mitochondrial metabolism genes. Gametes are universally haploid.
Although haploidy Although haploidy
spermeggzygote
haploidhaploiddiploid

Question 172

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Question

MCQ▾

The diagram shows a cross-section of a flower.

A cross-section of a flower

A Cross-Section of a Flower

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On which structure Pollination takes place?

Choices

Choice (4)
a.Diagram C
b.Diagram A
c.Diagram B
d.Diagram D

Answer

b.

Explanation

Gynoecium/Pistil

  • Gynoecium or pistil is the female reproductive part and carpel is the unit of gynoecium.
  • Carpel is considered modified leaf bearing ovules or megasporophylls. The folded carpel bears one or more ovules along the ventral suture.
  • Carpel is distinguished into three parts - stigma, style, and ovary.
  • In pistil, stigma is a small rounded or lobed head, which serves as a landing platform for the pollen grains. Style is slender stalk supporting the stigma and Ovary is the swollen basal part, which contains one or more chambers called locules.
  • Ovary contains one or more little rounded or oval eggs like bodies on its inner side called ovules Megasporangium ().
  • Ovules are borne on a ridge of tissue called placenta lying on the inner wall of the ovary.
  • Arrangement of ovules on the placenta is called placentation.
structure Pollination takes place

Structure Pollination Takes Place

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